Background Candida species are important nosocomial pathogens in the neonatal intensive care unit (NICU), resulting in a relatively high rate of morbidity and mortality. While Candida albicans is the most frequently isolated species and considered most pathogenic, Candida parapsilosis accounts for approximately 25% of nosocomially acquired candidiasis on the NICU—a situation unique to the neonate. Unlike C. albicans, the epidemiology and virulence of C. parapsilosis have not been systematically evaluated.
Objective To compare the virulence of C. parapsilosis and C. albicans, as well as to evaluate the pattern of organ involvement, following systemic infection in the mouse.
Design/Methods Separate groups of mice were inoculated intravenously (IV) with 108 C. parapsilosis, 108 C. albicans, or 105 C. albicans and monitored for mortality and morbidity. Mortality was determined by observation for 14 days following inoculation (n = 12/treatment, in each of two experiments). To determine morbidity, a separate series of mice were sacrificed on days 1, 7, and 14 following intravenous inoculation, with liver and kidneys cultured for viable microbes. (n = 4-5 mice/treatment/day, in each of three experiments).
Results Mortality was highest following IV inoculation with 108 C. albicans (> 50% by day 14). Significantly fewer mice died following injection with 108 C. parapsilosis and 105 C. albicans (≈8% by day 14, p < .05). The inoculated Candida species was recovered from the liver in ≈65% of each treatment group on day 1, with clearance of the yeast by day 14 in the surviving mice (p < .01). On day 1 following inoculation, respective organisms were recovered from the kidneys of ≈65% of mice inoculated with 108 C. parapsilosis or 108 C. albicans and 43% of mice inoculated with 105 C. albicans. Approximately 40% of surviving mice inoculated with 108 C. parapsilosis or 105 C. albicans showed persistence of the yeast in the kidney by day 14 (104.4-4.9/g tissue). Surviving mice inoculated with 108 C. albicans showed persistence of the organism in the kidneys to day 7 (105 /g tissue); however, no mice survived to sacrifice on day 14 following this inoculation.
Conclusions C. albicans is more virulent than C. parapsilosis when the outcome variable is death. However, the two organisms are equally virulent with respect to the ability to cause persistent infection in the kidney following IV inoculation.
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