Susceptibility of Cryptococcus neoformans and Cryptococcus gattii from clinical and environment sources in Nairobi, Kenya

Abstract

Objective: To determine anti-fungal susceptibility of Cryptococcus neoformans and
Cryptococcus gattii from environmental and clinical sources in Nairobi, Kenya.
Design: Prospective study.
Setting: Kenya Medical Research Institute, Mycology laboratory, Nairobi, Kenya.
Subjects: A total of 123 isolates were tested for their susceptibility to fluconazole
(FLC), amphotericin B(AMP) and fluorocytosine (5FC). Clinical isolates were 70(66
Cryptococcus neoformans and 4 Cryptococcus gattii) while environmental isolates were
53(41 C. neoformans and 12 C. gattii). The isolates were characterised using various
phenotypic tests including microscopic morphology, physiological and biochemical
tests (API 20 Caux), pigmentation on bird seed agar and reaction on canavanineglycine-
bromthymolblue agar. European Committee on Anti-microbial Susceptibility
Standards (EUCAST) was used as the reference method for susceptibility testing.
Results: Most C. neoformans isolates; clinical (61/66; 92.4%) and environmental (38/41;
92.7%) were susceptible to FLC. The number of C. neoformans isolates inhibited at
susceptible dose dependent (SDD) range (16-32μg/ml) by FLC were clinical (4/66; 6.1%)
and environmental (2/41; 4.9%). One C. neoformans isolate each; clinical (1/66; 1.5%)
and environmental (1/41; 2.4%) was resistant to FLC. All C. gatti isolates from clinical
and environmental were fully susceptible to FLC. The percentage of C. neoformans
isolates that were susceptible (S) (MIC ≤ 1.0 μg/ml) to AMP were; clinical(52/66; 90.2%)
and environmental (37/41; 78.8%) while the rest were susceptible dose dependent
(SDD) with MIC (2-8μg/ml). Reduced susceptibilities to 5FC was displayed in all
clinical and environmental C. neoformans and C. gatii isolates; for instance resistance
to 5FC was reported in C. neoformans; clinical (8/66; 12.1%) and environmental (1/41;
2.4 %). Among the C. gattii isolates there was also decreased susceptibility to 5FC
with Minimum Inhibition Concentration (MIC) range of between 0.5-32 μg/ml. There
were no significant differences in susceptibility ranges among all the clinical and
environmental isolates.
Conclusion: This study demonstrated reduced susceptibilities among C. neoformans
and C. gattii isolates to commonly used anti-fungal drugs.