Molecular diversity and high virulence of Legionella pneumophila strains isolated from biofilms developed within a warm spring of a thermal spa.

BACKGROUND: Several cases of legionellosis have been diagnosed in the same French thermal spa in 1986, 1994 and 1997. L. pneumophila serogroup 1 (Lp1) strains have been isolated from several patients, but the source of contamination was not identified despite the presence of different Lp1 in water samples of the three natural springs feeding the spa at this period. RESULTS: Our strategy was to investigate L. pneumophila (Lp) strains from natural biofilms developed in a sulphur-rich warm spring of this contaminated site. Biofilm analysis revealed the presence of three Lp serogroups (Lp1, Lp10 and Lp12). Surprisingly, Lp10 and Lp12 were not reported in the previous described studies from water samples. Besides, the new seven Lp1 we isolated exhibit a high molecular diversity and have been differentiated in five classes according to their DNA genome patterns obtained by PFGE and mip sequences. It must be noted that these DNA patterns are original and unknown in databases. Interestingly, the 27 Lp environmental strains we isolated display a higher cytotoxicity and virulence towards the amoeba Acanthamoeba castellanii than those of known Lp1 epidemic strains. CONCLUSION: The characteristics of Legionella pneumophila Lp1 strains isolated from the warm spring are in agreement with their presence in biofilms and their probable long-term persistence in this ecosystem.

Contribution of hydrogen peroxide to the inhibition of Staphylococcus aureus by Lactococcus garvieae in interaction with raw milk microbial community.

The response of Staphylococcus aureus growth inhibition by Lactococcus garvieae to catalase and milk lactoperoxidase, and its efficiency in raw milk cheese were evaluated. S. aureus and L. garvieae were co-cultivated in broth buffered at pH 6.8, and in raw, pasteurized and microfiltered milk, in presence and absence of catalase. Although H2O2 production by L. garvieae was detected only in agitated broth, the inhibition of S. aureus by L. garvieae was reduced by catalase both in static and shaking cultures by 2.7 log, pasteurized milk (approximately 0.7 log), microfiltered milk (approximately 0.6 log) and raw milk (approximately 0.2 log). The growth of S. aureus alone in microfiltered milk was delayed compared with that in pasteurized milk and inhibition of S. aureus by L. garvieae was stronger in microfiltered milk. The inhibition of coagulase-positive staphylococci (CPS) by L. garvieae in raw milk cheese was similar to that in raw milk (approximately 0.8 log), but weaker than that in pasteurized and microfiltered milks. L. garvieae also had an early antagonistic effect on the growth of several other microbial groups, which lastingly affected populations levels and balance during cheese ripening.