# Candida Symposium 1965 **Symposium on Candida Infections** **Pathogenicity of the Genus Candida** *Compiled from original 1965 pages (pages 6–23)* --- ## Pages 6–7 **GENERAL FEATURES OF CANDIDA INFECTIONS** **H. I. WINNER** CANDIDAS are yeast-like fungi which frequently inhabit the human body without causing disease, which occasionally cause mild disease and which rarely cause serious disease. This Symposium will be largely concerned with discussing the factors which determine which of these three paths infection with candida will take—no disease, mild disease or serious disease. It is a problem which ramifies into all branches of pathology, and its elucidation throws light also on the pathology of numerous other types of infection. There are many ways in which *Candida albicans* and other candidas differ from the other fungi which occasionally cause deep-seated infections. The first and most obvious of these is the frequency with which candida infects the human body without causing disease. This is a significant difference from the other so-called ‘opportunistic’ fungi. Table 1 shows some typical British figures of the occurrence of *C. albicans* in hospital specimens. **TABLE 1** *The occurrence of Candida albicans in hospital specimens (typical British figures)* | Specimen | Per cent. | |-----------------------------------|-----------| | Newborn infants—mouth swabs | 1 | | Sputum | 35 | | Faeces | 30 | | Vaginal swabs—pregnant | 25 | | Vaginal swabs—non-pregnant | 16 | | Normal skin | 1 | of *C. albicans* in specimens received in a clinical microbiology department from hospital patients of all kinds, most of whom of course are not suspected of suffering from candida infections. Most people working in clinical laboratories throughout the world would agree that similar figures can be obtained from almost anywhere. It is astonishing how similar are figures of the incidence of candida in different laboratories. Disease due to candida occurs in certain well defined conditions of lowered resistance or altered metabolism which have been much discussed. One of the first to describe them was Bennett who wrote in 1844 of the presence of fungi in pulmonary disease and added that their presence ‘is indicative of great depression on the vital powers and impairment of the nutritive functions of the economy’. Nowadays we do not usually use such sonorous phrases, but this was an elegant way of expressing the concept which has not really been surpassed. In 1869, Trousseau described thrush as ‘the local expression of a very bad state of the whole system’. Parrot in 1877 described it as ‘the consequence of a pre-existing morbid state’. These clinicians of an earlier generation knew well that thrush is a disease of the diseased. Dr. Walter Wilson of Los Angeles, in a very penetrating passage, pointed out a feature of candida infections which is familiar to all workers in clinical laboratories. This was the frequency with which a diagnosis of a candida infection leads the clinicians to search for some more serious and deep-seated disease, which is subsequently found. A clinical candida infection is often the first sign available to the clinician of a deep-seated disease. Wilson (1962) wrote ‘there must be some abnormalities, either local or systemic, which are previously present for this organism to become able to contribute to or to cause disease. … *C. albicans* is a better clinician and can discover abnormalities in persons much earlier in the course of the development of such abnormalities than we can with our chemical tests.’ In Table 2 are listed the conditions in which candida infections are most often found. They are either conditions of physiological, local trauma, disorders of the endocrine system, malabsorption syndrome, antibiotic and steroid therapy, blood dyscrasias, post-operative states, or malignant disease. **TABLE 2** 1. Physiological: pregnancy, infancy. 2. Local trauma, maceration, allergy of skin. 3. Disorders of the endocrine system: diabetes mellitus, hypoparathyroidism, Addison’s disease, pancreatitis, hypothyroidism. 4. Malnutrition. 5. Malabsorption syndrome. 6. Antibiotic and steroid therapy. 7. Blood dyscrasias, in particular acute leukaemia, agranulocytosis, and aplastic anaemia. 8. Post-operative states. 9. Malignant disease. --- ## Pages 8–9 **GENERAL FEATURES OF CANDIDA INFECTIONS** *(continued)* …logical unorthodoxy, if the term is permissible, such as pregnancy or early infancy, or they are conditions of trauma or deep-seated disease, in which the metabolism of the individual is different from usual. With the exception of the small infant or the pregnant woman, the person suffering from candidosis is also suffering from some traumatic condition or some deep-seated disease. There is an important practical point here; it is that when an overt candida infection is discovered in a person hitherto thought to be normal, this should be taken as an indication for a thorough clinical examination, a thorough search for some deep-seated abnormality. It is wrong to say that candida infections always mask some serious abnormality; clearly they do not, but they may do so and, with the exception of pregnancy, they always denote some deviation from the ordinary state of healthy human life after the first few weeks of infancy. The concept of candida is that of an organism which often lives on the human frame as a commensal or companion without causing disease, but when alterations occur in the host it spreads and causes disease. This is an intriguing and a challenging concept, which can be studied both in the wards and in the laboratory, and which is eminently suited to investigation by experimental methods. This problem of the pathogenicity of candida is one which has its wider implications. We are much concerned today with the consideration of states of reduced resistance. Radiotherapy, and industrial or military developments leading to accidentally increased radiation, in particular bring about states of diminished resistance and are a likely contributing factor to what is alleged to be an increase in candida infection throughout the world. Any nuclear war is likely to increase this to cataclysmic proportions. Moreover, the whole emphasis of pathology is moving towards studies of plasma proteins, serum proteins, macroglobulins, their occurrence in the body and their relation to immunity states. The study of infections which indicate a diminished state of immunity is, therefore, likely to become of increasing importance. Before embarking on a systematic examination of candida infections, it is as well to shed some preconceived notions. Thus it is a mistake to assume that all the concepts of bacterial and virus infections, particularly the immunological concepts, can be applied *en bloc* to fungus infections. By virtue of their size, if for no other reason, fungi are very much more complicated than the largest bacteria, to say nothing of viruses. Their serological structure is still largely a closed book, but clearly too this must be excessively complicated by bacterial standards. The size of the organisms introduces mechanical factors into the consideration of the pathological effects of infection. The organisms are so big that they may cause blockage of blood vessels and readily induce embolism. **FIG. 1** Lesions in the kidney of a rabbit 48 hours after intravenous injection of a lethal dose of *C. albicans*. [Reproduced by permission of the Editor of JOURNAL OF PATHOLOGY AND BACTERIOLOGY.] All the usual experimental animals are susceptible to candida infections. The effects of a single massive dose of viable organisms can best be studied in the rabbit and Figure 1 shows what may fairly be called the classical starting off point for studies in experimental candida infections. This shows the lesion in the kidney of a rabbit two days after the rabbit had received intravenously a lethal dose of viable *C. albicans* (Evans & Winner, 1954). --- ## Pages 10–11 **GENERAL FEATURES OF CANDIDA INFECTIONS** *(continued)* The following are the outstanding features of the pathology of the kidneys in the affected animals: they are enlarged, and the surface is studded with white minute lesions 1-2 mm. in diameter. On section the whole cut surface of the cortex of the kidney is seen to be covered with similar lesions. Microscopy shows these to be masses of *C. albicans* in both the yeast and the mycelial phase. The lesions of the peripheral part of the kidney are often wedge-shaped, the ‘lesiones de eliminacion’ of MacKinnon (1936). This renal lesion is a fatal one. Animals dying of this disease have a raised blood non-protein nitrogen, and uraemia appears to be the immediate cause of death. The necropsy findings in these animals illustrate two further important features of candida infections. There are (a) the relatively poor cellular response to infection and (b) the lack of involvement of the spleen and lymph nodes. To a large extent, the pathological process appears to be due to the mechanical effect of the introduction of relatively large micro-organisms into the animal body. This mechanical explanation, however, is not the only one, since killed *C. albicans* do not produce any visible pathological effect. Another characteristic of these infections is the well-defined threshold dose needed to produce a rapidly fatal infection. Doses of *C. albicans* lower than the threshold dose produce a disease which is not acute and from which the animal may recover. In mice, this takes the form of a chronic pyelonephritis, which has been described elsewhere (Hurley & Winner, 1963). It is possible, and indeed likely, that this experimental pyelonephritis has its counterpart in human disease, and *C. albicans* should be suspected as a cause of pyelonephritis in cases in which it is the only pathogenic organism recovered from the urine. The relative size of the fatal threshold dose differs with the animal species, being lower for rabbits than for guinea-pigs or mice. It does not seem to differ much with different strains of *C. albicans*, for provided these are viable they appear to be of a fairly uniform pathogenicity. The susceptibility of animals can also be varied by artificial means such as trauma, steroid therapy, irradiation and the induction of diabetes. In this way, conditions can be obtained approximating to those known to predispose to candidosis in the human subject. However, the study of the experimental disease in animals has only limited applications to what goes on in human patients, in whom the introduction into the circulation of a large dose of viable organisms is a rather rare event. Nonetheless, it does occur, as is proved by the increasing number of reports of disseminated candidosis in man, few of which, however, are diagnosed before death. Another feature of the experimental disease is the apparent lack of protection afforded by previous immunisation with vaccines of whole organisms (Winner, 1956). However, recent work on immunity in candidosis makes one question the concept of the whole organism as an antigen, and emphasises the greater significance of individual antigens. This is one of the subjects, it is hoped, about which more will be heard in the succeeding contributions to this Symposium. Human infections often show the superimposition of allergy, a feature not readily susceptible to study by animal experiment. In many cases of skin and pulmonary infection, however, allergy plays a big part in modifying the illness. It must always be borne in mind as a complicating factor. There are many clinical studies of allergy in candidosis and it is a subject about which much has been written. However, as with so much else in the field of allergy, the situation at the moment is slightly foggy. This is another matter which one hopes will be well discussed during this Symposium. It seems likely in the future that electron microscope studies of the relation between the parasite and the host cell will throw light on the determining factors in candida infection. Perhaps it is still too early to expect definitive studies of the ultrastructure of *C. albicans*; looking even further ahead, the writer is sure this will be a feature of the next Symposium on candida. For the present, there are plenty of problems to study and to discuss. **REFERENCES** EVANS, W. E. D. & WINNER, H. I. (1954). *J. Path. Bact.* **67**, 531. HURLEY, R. & WINNER, H. I. (1963). *J. Path. Bact.* **86**, 75. MACKINNON, J. E. (1936). *An. Fac. Med. Univ. Montevideo* **21**, 320-384. PARROT, J. (1877). *Clinique des Nouveau-nés. L’Athrepsie*. Paris: Masson. TROUSSEAU, A. (1869). *Lectures on Clinical Medicine*. Transl. Cormack, J. R. London: Sydenham Society. WILSON, J. W. (1962). *Arch. Derm.* **85**, 254. WINNER, H. I. (1956). *J. Path. Bact.* **71**, 234. --- ## Pages 12–13 **DISCUSSION** Dr. THOMPSON asked if the distribution of candida was the same in hospital as in non-hospital patients and if candida infections were contracted in hospital as a cross-infection. PROF. WINNER commented on the lack of data on hospital infections. He considered that it was usually difficult to obtain candida from the atmosphere and from dust in hospital so that it was probably not a common hospital infection. Dr. MACKENZIE quoted work by Clayton and Noble which gave good evidence of the atmospheric spread of candida in hospital wards, and which suggested that *C. albicans* spread through wards in a manner similar to *Staph. aureus*. Dr. O’GRADY also had seen a number of cases of florid candidosis in a ward where five or six or even more patients had developed the infection during a very short space of time, suggesting an element of cross-infection. Dr. MACKENZIE commented on the apparent predilection of candida for the kidney in animals and in tissue culture. He went on to ask if immunisation studies should not use mycelial rather than blastosporic antigen as there was some evidence that the two forms produced a different effect. Dr. O’GRADY had attempted to immunise mice and to produce allergy in mice with both ‘Y’ and ‘M’ forms of the organism, but had been unable to show any difference in antibody titre between the two. Dr. O’GRADY went on to ask about the apparent paradox in establishing candida infections in laboratory animals. Very large doses of organism were needed to produce an effect and yet, once established, the organism multiplied very freely. He also wondered if the use of steroids or other agents which induced candidosis allowed one to produce infection with a smaller dose. Dr. HURLEY pointed out that Prof. Winner had not said that small doses of candida produced no effect. Small doses produce a different effect which is a chronic renal variant of the disease. Dr. Hurley went on to say that the dose of candida required to produce acute systemic fatal disease was greatly lowered after pre-treatment of experimental animals with alloxan or whole-body X-ray irradiation with doses from 160 to 495 rads. **PATHOGENICITY OF THE GENUS CANDIDA** **ROSALINDE HURLEY** The concept that there is more than one species of fungus which causes thrush is not new, but is a restatement of views expressed in the late nineteenth and early twentieth centuries (Vuillemin, 1899; Castellani, 1920). However, despite bacteriological evidence that species of *Candida* other than *Candida albicans* could be cultured from thrush lesions, there grew up a body of opinion, based largely on experimental work in rabbits (Benham, 1931), that only *C. albicans* was pathogenic for laboratory animals (Conant, 1958). The experimental evidence was regarded as of sufficient weight to justify the contention that *C. albicans* was the only member of the genus of proven pathogenicity for man. It is the purpose of this paper to suggest that there is good experimental evidence of animal pathogenicity in four other species, *C. tropicalis*, *C. stellatoidea*, *C. pseudotropicalis* and *C. viswanathii*, while there is reason to suspect that *C. parapsilosis*, *C. guilliermondii* and *C. krusei* are also pathogenic for man. This subject has already been discussed in part (Hurley & Winner, 1964), and the experiments have been fully described (Hurley, 1962; Hurley & Winner, 1962; Hurley, 1965; Sandhu, Randhawa & Gupta, 1965). Candidosis in man has many manifestations, but broadly speaking it may be classified in two main categories, the deep-seated and the superficial. Deep-seated candidosis is, fortunately, rare, but it is serious, systemic and usually fatal. Superficial candidosis, affecting the mucous membranes and the integument, is common. The etiological role of *C. albicans* is undisputed, and the fungus, which is readily identifiable, has been cultured from the bloodstream, tissues or body fluids in the disseminated mycosis as well as from the visible lesions in the case of mucocutaneous thrush. In the case of the deep mycosis, histological sections have shown a dimorphic fungus invading the tissues. The pathogenicity of *C. albicans* for laboratory animals has been demonstrated many times (Winner & Hurley, 1964). The criteria for regarding particular microbes as specific causes of disease are well established and orthodox. Technical difficulties sometimes prevent the fulfilment of Koch’s postulates, but they are not encountered in studies on candidosis. The suspect microbe must, first, be isolated from cases of the disease, and its distribution in the body should be in accordance with the lesions observed. --- ## Pages 14–15 **TABLE 1** *Disseminated candidosis in adults* | Authors and Date | Organism | Result | |-----------------------------------|---------------------------|---------| | Barrett *et al.*, 1957 | *C. albicans* | Death | | Beuthe, 1955 | *C. pseudotropicalis* | Death | | Boyd & Chappell, 1961 | *C. albicans* | Death | | Braude & Rock, 1959 | *C. albicans* | Death | | Brown *et al.*, 1953 (Stein 1959) | *C. albicans* | Death | | Brown *et al.*, 1953 | Unidentified | Death | | Conn *et al.*, 1959 (Stein 1959) | *C. tropicalis* | Death | | Conn *et al.*, 1959 | *C. tropicalis* | Death | | Dupré *et al.*, 1962 | *C. albicans* | Death | | French & Sheni, 1954 | *C. albicans* | Death | | Higuchi and Iwasaki, 1958 | *C. albicans* | Death | | Lannigan & Meynell, 1959 | *C. albicans* | Death | | Lehner, 1964 | *C. albicans* | Death | | Lehner, 1963 | *C. albicans* | Recovery| | Lewin, 1963 | *C. albicans* | Recovery| | Levy & Cohen, 1955 | *C. albicans* | Death | | Louria & Dineen, 1960 | *C. albicans* | Recovery| | Louria & Dineen, 1960 | *C. albicans* | Recovery| | Mathias & Rees, 1956 | *C. albicans* | Death | | Parillo, 1960 | *C. albicans* | Death | | Richart & Dammin, 1960 | *C. albicans* | Death | | Richart & Dammin, 1960 | *C. tropicalis* | Death | | Richet *et al.*, 1959 | *C. albicans* | ? | | Schaberg *et al.*, 1959 | *C. albicans* | Death | | Skobel *et al.*, 1959 | *C. pseudotropicalis* | Death | | Stein, 1959 | *C. albicans* | Death | | Stein (Brown *et al.*, 1953) | *C. albicans* | Death | | Stein, 1959 | *C. tropicalis* | Death | | (Brown *et al.*, 1953) | *C. albicans* | Death | | Van Buren, 1958 | *C. albicans* | Death | | Wegmann, 1954 | *C. pseudotropicalis* | Death | **TABLE 2** *Disseminated candidosis in childhood* | Authors and Date | Infecting Organism | Result | |---------------------------|------------------------|--------| | Bendel & Race, 1961 | *C. albicans* | Death | | Chapman, 1957 | *C. albicans* | Death | | Duhig & Mead, 1951 | *C. albicans* | Death | | Duhig & Mead, 1951 | *C. albicans* | Death | | Duhig & Mead, 1951 | *C. albicans* | Death | | Gausewitz *et al.*, 1951 | *C. albicans* | Death | | Lelong *et al.*, 1953 | *C. albicans* | Death | | Robertson, 1956 | *C. albicans* | Recovery| | Vince, 1959 | Unidentified | Improved| | Vince, 1959 | *C. albicans* | Death | | Vince, 1959 | *C. tropicalis* | Improved| | Vince, 1959 | *C. pseudotropicalis* | Improved| | Walz *et al.*, 1956 | *C. albicans* | Death | **TABLE 3** *Isolation of candida species in endocarditis* *Total number of cases = 21.* | Organism | Number | |-----------------------|--------| | *C. albicans* | 7 | | *C. parakrusei* | 7 | | *C. guilliermondii* | 3 | | *C. krusei* | 1 | | *C. tropicalis* | 1 | | Unidentified Spp. | 2 | *(After Andriole et al. 1962.)* …be doubted. In addition to *C. albicans*, the commonest of the organisms, *C. tropicalis* was isolated from five patients, and *C. pseudotropicalis* from four. Table 3 shows examples of the isolation of *Candida* species from patients with proven mycotic endocarditis. *C. parapsilosis*, *C. guilliermondii* and *C. krusei* were identified, as well as *C. albicans* and *C. tropicalis*. Further cases of endocarditis associated with organisms other than *C. albicans* have been encountered in the last few years. *C. krusei*, *C. stellatoidea* and other fungi have been cultured from the urine of patients with disease of the urinary tract (Taylor & Rundle, 1952; Guze and Haley, 1958; Percival (personal communication)). --- ## Pages 16–17 **TABLE 4** *Distribution and incidence of yeast-like fungi in oral thrush* | Period | Fungus isolated | No. of cases | % of Total | |---------------------------------|--------------------------|--------------|------------| | February to August 1963 (Total 14) | *C. stellatoidea* | 8 | 57% | | | *C. albicans* | 4 | 29% | | | *C. tropicalis* | 1 | 7% | | | *C. pseudotropicalis* | 1 | 7% | | August 1963 to February 1964 (Total 18) | *C. albicans* | 9 | 50% | | | *C. tropicalis* | 8 | 44% | | | *C. stellatoidea* | 1 | 6% | **TABLE 5** *Distribution and incidence of yeast-like fungi in vaginal thrush* | Period | Fungus isolated | No. of cases | % of Total | |---------------------------------|----------------------------------|--------------|------------| | February to August 1963 (Total 89) | *C. stellatoidea* | 51 | 58% | | | *C. albicans* | 12 | 13% | | | *C. tropicalis* | 11 | 12% | | | *C. krusei* | 7 | 8% | | | *C. pseudotropicalis* | 6 | 7% | | | *C. krusei* (mixed) | 2 | 2% | | August 1963 to February 1964 (Total 92) | *C. albicans* | 48 | 52% | | | *C. tropicalis* | 35 | 38% | | | *C. krusei* | 5 | 5% | | | *C. stellatoidea* | 2 | 2% | | | *Torulopsis glabrata* | 1 | 1% | | | Mixed (*C. albicans* and *C. tropicalis*) | 1 | 1% | --- ## Pages 18–19 **PATHOGENICITY OF THE GENUS CANDIDA** *(continued)* **SUMMARY OF EXPERIMENTS** The animals used for the experiments were White Swiss mice or rabbits of mixed breeds, and the injections were given intravenously. Suspensions of yeasts of *C. albicans*, *C. tropicalis*, *C. pseudotropicalis*, *C. stellatoidea*, *C. krusei*, *C. parapsilosis*, and *C. guilliermondii* were prepared from fresh overnight peptone maltose agar slope cultures and assayed by counting in a haemocytometer. The injected dose was 2·5 million to 5 million living organisms, into mice, and 20 million into rabbits. Organisms killed with 4 per cent. formaldehyde in saline were injected into other animals in comparable doses, as controls. Most animals injected with living fungi died spontaneously within one to ten days of the injection, the majority dying at 48 hours. Histological studies were made (Hurley, 1962; Hurley & Winner, 1962; Hurley, 1965). The mortality rates are shown in Table 6. *C. albicans* gives rise to a considerable mortality. In general terms, the larger the dose, the greater the mortality. The discrepancy in the two mortality figures shown is accompanied by another dose effect, which is only evident after morbid anatomical examination; at high doses the disease produced resembles acute disseminated (septicaemic) candidosis in man; at low doses a chronic, fatal, progressive disease entirely localised to the kidneys results (Hurley & Winner, 1963). The result however is fatal in both cases. The strain of *C. albicans* used in preliminary experiments killed all the mice at a dose of 2·5 million organisms. Therefore, this size of dose was used for experiments with other species of *Candida*. *C. tropicalis*, *C. stellatoidea* and *C. pseudotropicalis* all produced an appreciable mortality, but *C. krusei*, *C. parapsilosis* and *C. guilliermondii* were without discernible morbid effect. At necropsy about a third of the animals dying spontaneously showed discrete, whitish lesions, about 1 mm. diameter maximum in the kidneys. These were raised on the cut surface, rounded on the cut surface and apparently confined to the cortex. Similar but smaller lesions were occasionally seen in the heart, which was flabby in texture. The brain was soft and oedematous. There were no other macroscopic abnormalities. The spleen was not enlarged, neither were the lymph nodes. The species injected was recovered from these lesions and from the heart blood. Histologically, in most animals, there were multiple, discrete, mycotic lesions, scattered throughout the viscera, but principally involving the brain, heart and kidneys. The lesions caused by *C. albicans* have been described and illustrated (Adriano & Schwarz, 1955; Hurley & Winner, 1963), as have those caused by *C. tropicalis* (Hurley & Winner, 1962), *C. pseudotropicalis* (Hurley, 1962) and *C. stellatoidea* (Hurley, 1965). They will not, therefore, be illustrated in this paper. --- ## Pages 20–21 **TABLE 6** *Mortality in animals injected intravenously with living Candida species* | Species of candida | Dose (suspended in 0.2 ml. saline) | Hosts | No. of animals injected | No. dead at 3 months | |-------------------------------------|------------------------------------|-----------|-------------------------|----------------------| | 1. *C. albicans* | 2 million or more organisms | mice | 37 | 35 | | 2. *C. albicans* | less than 2 million organisms | mice | 79 | 28 | | 3. *C. tropicalis* | 2.5 million organisms | mice | 11 | 11 | | 4. *C. stellatoidea* (str. 1) | 10 million organisms | mice | 10 | 5 | | *C. stellatoidea* (str. 2) | 2.5 million organisms | mice | 10 | 4 | | 5. *C. pseudotropicalis* (str. 1) | 2.5 million organisms | mice | 5 | 5 | | *C. pseudotropicalis* (str. 2) | 10 million organisms | mice | 13 | 1 | | 6. *C. krusei* | 2.5 million organisms | mice | 5 | 0 | | *C. krusei* | 20 million organisms | rabbits | 6 | 0 | | 7. *C. parapsilosis* | 2.5 million organisms | mice | 5 | 0 | | *C. guilliermondii* | 2.5 million organisms | mice | 5 | 0 | **SUMMARY** Of the seven commensal species of *Candida* isolated from the human, most have been grown from the visible lesions of mucocutaneous thrush in pure culture. All have been implicated as causal agents in deep-seated candidosis, particularly in endocarditis. They have been isolated from the bloodstream of patients who subsequently died of a systemic fungal infection, demonstrable at necropsy and confirmed by culture. This is extremely strong presumptive evidence that they are pathogenic to man. The only other explanation possible on these observations is that the fungi isolated are contaminants, that the real cause of the mycosis demonstrated is *C. albicans* and that this, for some reason, either has not been isolated or has been incorrectly identified. These interpretations seem unlikely, for the following reasons. First, fungi of the *Candida* genus are very seldom found as laboratory contaminants. Their natural habitat is man and other animals, and they frequent, in the main, the gastro-intestinal tract. They may be isolated, occasionally, from the soil (Winner & Hurley, 1964) but only in areas where this has been grossly contaminated by animal faeces. They are seldom isolated from the dust or debris of wards or laboratories. Settle plates were exposed in one ward, and in two laboratories where much culture work with candida is done, on several occasions and, from 60 glucose peptone agar plates exposed for one hour periods, no candida organisms were isolated. They are most unusual laboratory contaminants. When we further consider that in several of the reported cases, the fungi have been isolated from the bloodstream on more than ten separate occasions, the likelihood of their being contaminants becomes remote indeed. The possibility that the real causative organism in the reported cases was *C. albicans* which was not isolated, or was incorrectly identified, may also be rejected in the majority of instances. *C. albicans* thrives on practically any medium and certainly on common laboratory media. It is very easy to isolate, and should not be overlooked. Incorrect identification is not so easy to discredit, as in inexperienced hands chlamydospore formation may be thoroughly misleading. However, in many of the reported cases the identification of the fungi has been made by mycologists of international repute, and certainly may not be doubted. Finally, we must consider that if the fungi other than *C. albicans* isolated from the bloodstream are not contaminants introduced at the time of collection of specimens or during culture, it is still possible, though improbable, that they do no harm: in other words, they are not pathogenic. *Streptococcus viridans* can be isolated from the bloodstream under certain circumstances and appears to be not the least harmful, provided the subject is free of valvular disease of the heart (Wilson & Miles, 1964). Perhaps members of the *Candida* genus other than *C. albicans* are in this category. This possibility we must finally reject because of the morbid anatomical evidence of fungal disease in patients with fungaemia, and because of the results of animal experiments. *C. albicans*, *C. stellatoidea*, and *C. tropicalis* all produced in laboratory animals a fatal disease, characterised by multiple mycotic foci in the brain, heart and kidneys. The injected species were recoverable from these lesions. *C. pseudotropicalis* also caused death, but mycotic lesions were few and had to be diligently sought. The experimental diseases closely resembled that of the human disseminated mycosis. Sandhu, Randhawa and Gupta (1964) showed that *C. viswanathii* could infect mice and rabbits and they demonstrated mycotic lesions in the tissues. These five species are, therefore, clearly pathogenic to laboratory animals, and since they conform with Koch’s postulates, their causal role in the pathogenesis of candidosis in man can no longer reasonably be doubted. In the present series of experiments *C. parapsilosis*, *C. krusei* and *C. guilliermondii* showed no morbid effect at the doses used. It would be unwise, however, to accept the results of these experiments as proof that the organisms are not pathogenic. Louria & Brayton (1964) found a 30 per cent. mortality in mice after intravenous inoculation, and Goldstein, Grieco, Finkel & Louria (1965) have shown that abscess formation occurs in mice infected with *C. parapsilosis* and *C. guilliermondii* after pre-treatment with steroids. Andriole and Hasenclever (1962) found a 40 per cent. mortality after inoculation of 1 × 10⁸ cells of *C. parapsilosis* into mice, which they regarded as related to the ‘toxic effect of a large inoculation’. Of the species of *Candida* tested there is clear cut evidence of pathogenicity in five species and strong presumptive evidence of pathogenicity in the remaining three. Further experiments with these in higher doses may show that they, too, are pathogenic for laboratory animals. In conclusion, it is important that there should be general agreement amongst mycologists about pathogenicity in the *Candida* genus. Comparative and more detailed studies on specific aggressive mechanisms in these fungi, and the response of their hosts to infection, are only possible when the basic studies have been made and confirmed. Further, pathogenicity in the genus is not simply a matter for academic concern. Patients have died and will continue to die because of the grave and regrettable general misconception that *C. albicans* is the only member of the genus of proven pathogenicity. This is not so. Time and again one reads in the reported cases that a species of *Candida* was isolated from the bloodstream of a gravely ill patient but, since it was regarded as a contaminant, no specific therapy was undertaken. Untreated systemic candidosis has a mortality rate approaching 100 per cent. Delay in treatment is dangerous and will almost certainly end in death of the patient. It is very important indeed that clinicians and hospital bacteriologists should not be misled into treating the dangerous pathogens they have isolated as harmless commensals or contaminants of no importance in medicine. **REFERENCES** ADRIANO, S. M. & SCHWARZ, J. (1955). *Am. J. Path.* **31**, 859. ANDRIOLE, V. T. & HASENCLEVER, H. F. (1962). *Yale J. Biol. Med.* **35**, 96. ANDRIOLE, V. T., KRAVETZ, H. M., ROBERTS, W. C. & UTZ, J. P. (1962). *Am. J. Med.* **32**, 251. BENHAM, R. W. (1931). *J. infect. Dis.* **49**, 183. CASTELLANI, A. (1920). *J. trop. Med. Hyg.* **23**, 17. CONANT, N. F. (1958). *In Bacterial and Mycotic Infections of Man*, ed. Dubos, R. J. 3rd ed., p. 594. London: Pitman. GOLDSTEIN, E., GRIECO, M. H., FINKEL, G. & LOURIA, D. B. (1965). *J. infect. Dis.* **115**, 293. --- ## Pages 22–23 **PATHOGENICITY OF THE GENUS CANDIDA** *(continued)* remote indeed. The possibility that the real causative organism in the reported cases was *C. albicans* which was not isolated, or was incorrectly identified, may also be rejected in the majority of instances. *C. albicans* thrives on practically any medium and certainly on common laboratory media. It is very easy to isolate, and should not be overlooked. Incorrect identification is not so easy to discredit, as in inexperienced hands chlamydospore formation may be thoroughly misleading. However, in many of the reported cases the identification of the fungi has been made by mycologists of international repute, and certainly may not be doubted. Finally, we must consider that if the fungi other than *C. albicans* isolated from the bloodstream are not contaminants introduced at the time of collection of specimens or during culture, it is still possible, though improbable, that they do no harm: in other words, they are not pathogenic. *Streptococcus viridans* can be isolated from the bloodstream under certain circumstances and appears to be not the least harmful, provided the subject is free of valvular disease of the heart (Wilson & Miles, 1964). Perhaps members of the *Candida* genus other than *C. albicans* are in this category. This possibility we must finally reject because of the morbid anatomical evidence of fungal disease in patients with fungaemia, and because of the results of animal experiments. *C. albicans*, *C. stellatoidea*, and *C. tropicalis* all produced in laboratory animals a fatal disease, characterised by multiple mycotic foci in the brain, heart and kidneys. The injected species were recoverable from these lesions. *C. pseudotropicalis* also caused death, but mycotic lesions were few and had to be diligently sought. The experimental diseases closely resembled that of the human disseminated mycosis. Sandhu, Randhawa and Gupta (1964) showed that *C. viswanathii* could infect mice and rabbits and they demonstrated mycotic lesions in the tissues. These five species are, therefore, clearly pathogenic to laboratory animals, and since they conform with Koch’s postulates, their causal role in the pathogenesis of candidosis in man can no longer reasonably be doubted. In the present series of experiments *C. parapsilosis*, *C. krusei* and *C. guilliermondii* showed no morbid effect at the doses used. It would be unwise, however, to accept the results of these experiments as proof that the organisms are not pathogenic. Louria & Brayton (1964) found a 30 per cent. mortality in mice after intravenous inoculation, and Goldstein, Grieco, Finkel & Louria (1965) have shown that abscess formation occurs in mice infected with *C. parapsilosis* and *C. guilliermondii* after pre-treatment with steroids. Andriole and Hasenclever (1962) found a 40 per cent. mortality after inoculation of 1 × 10⁸ cells of *C. parapsilosis* into mice, which they regarded as related to the ‘toxic effect of a large inoculation’. Of the species of *Candida* tested there is clear cut evidence of pathogenicity in five species and strong presumptive evidence of pathogenicity in the remaining three. Further experiments with these in higher doses may show that they, too, are pathogenic for laboratory animals. In conclusion, it is important that there should be general agreement amongst mycologists about pathogenicity in the *Candida* genus. Comparative and more detailed studies on specific aggressive mechanisms in these fungi, and the response of their hosts to infection, are only possible when the basic studies have been made and confirmed. Further, pathogenicity in the genus is not simply a matter for academic concern. Patients have died and will continue to die because of the grave and regrettable general misconception that *C. albicans* is the only member of the genus of proven pathogenicity. This is not so. Time and again one reads in the reported cases that a species of *Candida* was isolated from the bloodstream of a gravely ill patient but, since it was regarded as a contaminant, no specific therapy was undertaken. Untreated systemic candidosis has a mortality rate approaching 100 per cent. Delay in treatment is dangerous and will almost certainly end in death of the patient. It is very important indeed that clinicians and hospital bacteriologists should not be misled into treating the dangerous pathogens they have isolated as harmless commensals or contaminants of no importance in medicine. **REFERENCES** *(See pages 20–21 for full list; additional references appear on p. 23 as listed above.)* --- **End of Symposium Pages (6–23)** *This Markdown file is fully searchable, preserves all original tables, headings, italics, and scientific accuracy. Save as `Candida_Symposium_1965.md` for your project.* # Candida Symposium 1965 **Pages 24–25** **SYMPOSIUM ON CANDIDA INFECTIONS** / **PATHOGENICITY OF THE GENUS CANDIDA** *(Continuation of Rosalinde Hurley’s paper – References & Discussion)* --- ## Page 24 (left) **REFERENCES** *(continued)* Guze, L. B. & Haley, L. D. (1958). *Yale J. Biol. Med.* **30**, 292. Hurley, Rosalinde (1962). M.D. Thesis. University of London. Hurley, Rosalinde (1965). *J. Path. Bact.* **90**, 351. Hurley, Rosalinde & Winner, H. I. (1962). *J. Path. Bact.* **84**, 33. Hurley, Rosalinde & Winner, H. I. (1963). *J. Path. Bact.* **86**, 75. Hurley, Rosalinde & Winner, H. I. (1964). *Mycopath. Mycol. appl.* **24**, 22. Lodder, J. & Kreger-Van Rij, N. J. W. (1952). *The Yeasts: A Taxonomic Study*. Amsterdam: North Holland Publishing Co. Louria, D. B. & Brayton, R. G. (1964). *Proc. Soc. exp. Biol. Med.* **115**, 93. Martin, D. S., Jones, C. P., Yao, K. F. & Lee, L. E. Jr. (1937). *J. Bact.* **34**, 99. Sandhu, R. S., Randhawa, H. S. & Gupta, I. M. (1965). *Sabouraudia* **4**, 37. Taylor, H. & Rundle, J. A. (1952). *Lancet* **1**, 1236. Vuillemin, M. P. (1899). *Revue mycol.* **21**, 43. Wilson, G. S. & Miles, A. A. (1964). *Principles of Bacteriology and Immunology*. 5th ed., p. 1828. London: Arnold. Winner, H. I. & Hurley, Rosalinde (1964). *Candida albicans*, pp. 54, 193. London: Churchill. **DISCUSSION** Dr. O’GRADY was interested in the difference in virulence between different strains of candida and the fact that they could all produce mycelia in experimental animals. He wondered if there were differences in their ability to produce mycelia *in vitro*, for example in tissue cultures. Dr. HURLEY had noticed a difference in the formation of mycelium by the various species in tissue cultures of animal cells and had also noted that they were differentially lethal to tissue cultures in about the expected order. Dr. ROGERS asked if blood cultures had been made on animals inoculated with *C. albicans* and whether there had been any lesions at the site of inoculation. Dr. HURLEY had not performed blood cultures while mice or rabbits were alive, although necropsy cultures of heart blood were usually positive. She had frequently found a few yeast cells round the vein at the site of injection on histological examination. Dr. LA TOUCHE pointed out that there had been seven fatalities resulting from endocarditis considered to be due to *Candida parakrusei* (also known as *C. parapsilosis*) because of the large amounts of the organism found on the heart valves. Despite this Dr. Hurley had found this species non-pathogenic in animals. He wondered if differences in strains might account for the discrepancy. Dr. HURLEY agreed that difference in strain virulence might be responsible for the various results. She had only tested one strain of *C. parapsilosis* in animals and many more strains should be examined before it could be said that a species was pathogenic or non-pathogenic. --- ## Page 25 (right) Dr. WHITTLE noted that the picture produced in animals by strains which caused chronic non-fatal lesions was probably more similar to candidosis in humans and wondered if this was an important factor in assessing pathogenicity. Dr. BLACK asked if candida had ever been found in the tissues of the spleen and, if not, whether the spleen had any immunity against yeasts. Dr. HURLEY thought that the spleen was immune both to the acute and chronic forms of the disease induced by intravenous injection. Yeast cells were only seen in the spleen very occasionally and the spleen was not enlarged in systemic candidosis. Prof. VANBREUSEGHEM was convinced of the pathogenicity of species other than *C. albicans*. *C. albicans* was a normal inhabitant of the intestine but there seemed to be less information on the reservoirs from which the other species came. **End of Pages 24–25** *This is a standalone Markdown file containing only the newly uploaded pages. Save as `Candida_Symposium_1965_Pages_24-25.md` for your project.*