Commensals of Mucous Surfaces Used to Control Nosocomial Diseases: Efficacy and Possible Acting Mechanisms

Background: Nosocomial infections caused by multiresistant opportunistic pathogens are more frequently observed in patients with detected immune system disorders. Commensal bacteria play a crucial role in the maintenance of the host’s mucosal immune responsiveness as determined by complex molecular mechanisms. Therefore, new knowledge of host/bacterial interaction is required to implement alternative methods to control nosocomial diseases. Methods: Identification of the selected clinical isolates was performed using VITEK2 automatic system. Their genetic congeniality and correspondingly etiological role in the registered nosocomial infections were confirmed by PCR and PFGE. The antibacterial efficacy of commensal bacteria against dominative pathogens was tested in vitro and in vivo. The level of cytokines secreted by different subsets of epithelial (mice) and dendritic (human) cells were assessed by ELISA. The level of SP-D and REG III beta/gamma genes expression in lungs and colon correspondingly was detected by qRT-PCR. Results: The following clinical isolates were referred to as the agents of nosocomial infection: MRSA, S.warnery, S.pneumoniae, E.cloaceae, K.pneumoniae, K.oxytoca, P.morganii, Acinetobacter spp., P.aeruginosa. B.subtilis 090 and L.salivarius ASF 361 demonstrated inhibitory activity against pyogenic coccus (in concentrations of 50 MIO of CFU/ml) and Gram-negative bacteria (300 MIO of CFU/ml), but not against Acinetobacter or P.aeruginosa. Schaedler’s E.coli and E.coli 058 were active against E.cloaceae, K.pneumoniae and K.oxytoca (50 MIO of CFU/ml). The B.subtilis 090 and Shaedler’s E.coli stimulated IL-10 production by human DC after 5and 10-hour-long bacterial exposure up to 70 and 45pg/ml, correspondingly. K.pneumoniae R mutant non-virulent strain differed in stimulation of TNF-alpha, but not of IL-10 and IL-6, compared with the wild virulent strain. L.salivarius stimulated expression of SP-D and REG III beta/gamma genes, and Shchaedler’s E.coli induced the highest level of the locally produced IFN-gamma. Conclusion: Our results provide a new insight into the mechanisms of probiotic and/or vaccine protection of human nosocomial diseases.