Probiotic bacteria can protect immunodeficient mice from orogastric candidiasis but cause some pathology of their own. Severely immunodeficient patients may be at risk if fed viable probiotics, so this study evaluated the probiotic potential of nonviable probiotic bacteria to protect immunodeficient mice from Candida albicans infections. Heat-killed probiotic bacteria were fed to gnotobiotic bg/bg–nu/nu and bg/bg–nu/+ mice to ascertain if they could protect the mice from mucosal and systemic candidiasis. Both heat-killed Lactobacillus acidophilus (HKLA) and heat-killed Lactobacillus casei (HKLC), in comparison to control mice not fed the probiotic bacteria but challenged (oral) with C. albicans, suppressed the severity of orogastric candidiasis in bg/bg–nu/nu mice at 2 weeks after colonization with C. albicans, inhibited disseminated candidiasis in C. albicans-colonized bg/bg–nu/+ mice at 4 weeks after colonization, and suppressed the number of viable C. albicans in the alimentary tract. HKLA, but not HKLC, treatment inhibited disseminated candidiasis in bg/bg–nu/nu mice at 2 weeks after oral challenge and enhanced the proliferative responses of splenocytes from C. albicans-colonized bg/bg–nu/+ mice to C. albicans antigens. Neither HKLA nor HKLC were able to prolong the survival of gnotobiotic bg/bg–nu/nu mice after oral challenge with C. albicans. These results demonstrate that heat-killed lactobacilli can induce some (limited) protection (pro-biotic effect) against candidiasis in mice.
† Present address: National Center for Toxicological Research, Microbiology Division, 3900 NCTR Drive, Jefferson, AR 72079-9502, USA.