Inhibition of Cryptococcus Neoformans by Pseudomonas Aeruginosa

Abstract

PLATES IV AND VD URING an investigation of Cryptococcus neoformans isolated from clinical specimens, we observed that growth of the fungus was considerably reduced in the vicinity of colonies of Pseudomonas aeruginosa. This phenomenon was first noted by Fisher (1954), who found that the inhibitory effect was exhibited only by living cultures of certain strains of P. aeruginosa. His efforts to isolate the inhibitor were unsuccessful and no further report on this phenomenon has since appeared. We report here a study of factors affecting the production of inhibitor by P. aeruginosa and an initial attempt to isolate and characterise the substances involved. MATERIALS AND METHODSStrains tested. Of 44 strains of P. aeruginosa tested for their inhibitory activity on C. neoformans, 11 (nos. 8, 10, 17, 26, 39, 52, l0/55, 8/39, 283, 577 and 584) were obtained from Dr M. T. Parker, Colindale, England; 13 (Gillies and Govan's type strains 1, 2, 3, 4, 5, 6, 7, 8 and A, By C, D, E) were obtained from the Public Health Laboratory, Edmonton, Canada; and 20 were freshly isolated from clinical specimens of wound and burn infections in Hong Kong. Fourteen strains of C. neoformans were tested for their sensitivity to the inhibitory effect of P. aeruginosa. These included 13 strains isolated from the cerebrospinal fluid of cryptococcal meningitis cases in Hong Kong and one strain, no. 1499.22, obtained from Dr Margarita Silva, Columbia University, NY, USA.The media used for this study were: Sabouraud Dextrose Agar (Oxoid), Tryptone Soya Agar (TSA, Oxoid), Diagnostic Sensitivity Test Agar (DST, Oxoid), and King's media A (without CuC12) and B. The latter two media were prepared according to the published formulae (King, Ward and Raney, 1954). Glucose was added to TSA, DST and the two King's media to final concentrations of 0.2, 0.5, 1.0, 2-0 and 3.0% to study its effect on the production of inhibitors.Methods for testing the inhibitory action of P. aeruginosa on the growth of C. neoformans. In preliminary studies, two methods were used to demonstrate the inhibitory effect. (1) By means of the technique described by Fisher (1954)' plates of TSA medium were initially lawned with C. neoformans, and after drying were inoculated centrally with P. aeruginosa (lower row, fig. 1). Small zones of inhibition were obtained. (2) With a method based on that described by Gillies and Govan (1966), P. aeruginosa from a 24-h broth culture was inoculated centrally in a circle of 1-cm diameter on TSA plates and incubated for 2 days. Growth was then removed, the residual cells were killed with chloroform vapour, and the surface of the plate was lawned with C. neoforrnans (top row, fig. 1). Zones of inhibition were larger, and it was apparent that inhibition did not depend on the presence of living P. aeruginosa.Media.

Pseudomonas aeruginosa Inhibits the Growth of Cryptococcus Species

“…Twenty years later, Teoh-Chan et al reported an initial attempt to isolate and characterize the inhibitory substances involved in 1974 [13]. However, the literature about the inhibitory effect of Pa on C. neoformans is equivocal [12, 13]. In this study, we revealed the mechanism used by Pa to inhibit the growth of Cryptococcus spp.…”

“…Previous reports reveal that Pa inhibits the growth of different microbes [10–13]. However, the mechanism that underlines the inhibitory effects of Pa on Cryptococcus species has not been investigated.…”

“…Interest in the inhibitory effect of several strains of Pa against C. neoformans in vitro started in 1954, when Fisher et al reported that strains of Pa produced a substance that inhibits the growth of C. neoformans in vitro, but the inhibitor has not been successfully separated [12]. Twenty years later, Teoh-Chan et al reported an initial attempt to isolate and characterize the inhibitory substances involved in 1974 [13]. However, the literature about the inhibitory effect of Pa on C. neoformans is equivocal [12, 13].…”

Growth inhibition of pathogenic yeasts by Pseudomonas aeruginosa in vitro: clinical implications in blood cultures

“…While only a few studies concerning this biological phenomenon have been done in vitro, the results suggest that interaction between Pseudomonas aeruginosa and Candida albicans could be important for an accurate laboratory diagnosis of mixed bacterial/fungal infections. Furthermore, some reports of co-isolations of micro-organisms in clinical specimens have shown an inhibitory effect of Pseudomonas aeruginosa on Candida albicans [9,10], Cryptococcus neqformans [11,12], Histoplasma capsulatum, Blastomyces dermatitidis [ 13 ], Aspergillus fomigatus [14] and Trichophyton rubrum [15]. It was thus important to investigate whether P. aeruginosa can inhibit the growth of the major yeast bloodstream pathogens in a blood culture medium.…”

Pseudomonas aeruginosa inhibits the growth of pathogenic fungi: In vitro and in vivo studies

“…Hughes and Kim (7) demonstrated that in CF patients infected with PA, only 10% of patients produced positive CA skin tests compared with 30% positivity in those free of PA, indicating that the antifungal substance produced by PA prevents Candida infections. There are also studies investigating the growth inhibition effect of PA in Cryptococcus species (12,13). However, to the best of our knowledge, there have been no studies regarding the isolation of Cryptococcus species from patients with CF.…”