Yersinia ssp. in surface water in San Luis, Argentina.

Yersinia spp. was examined in three rivers and two lakes located in the Province of San Luis, Argentina, over a 1-year period. Water samples were concentrated either by Moore's gauze technique or by filtering through diatomaceous earth. Five enrichment media: yeast extract--Bengal rose broth (YER) with bile-oxalate-sorbose broth (BOS); 67 mmol/L phosphate-buffered saline (pH 7.6; PBS); PBS enriched with a 1% mannitol and 1% peptone (PBSMP); PBS with lyzed 0.5% sheep blood (PBSB); Wauters broth (W); and five plating media: Mac Conkey agar (MC); Salmonella--Shigella agar (SS); 5% sheep blood agar (BA); lactose-sucrose-urea agar (LSU) and irgasan-novobiocin agar (IN) were used. The following strains were isolated: Y. intermedia B1 O:4,32-4,33 Lis Xz (four strains), Y. intermedia B1 O:57 Lis Xo (one strain), Y. intermedia B2 O:57 Lis Xo (one strain), Y. enterocolitica B1 O:10-34 Lis Xz (one strain), and Y. frederiksenii undetermined biovar, O:16-16,29 Lis Xz (two strains). The incidence of isolation of Yersinia spp. was 7.14%. YER-BOS proved to be the best enrichment method since it allowed the highest recovering Yersinia spp. strains. Among plating media, the best results were obtained with MC. Apparently, the isolation of Yersinia spp. can be related to environmental variables such as temperature differences between cold and warm seasons. Negative results obtained during virulence assays suggest that isolated strains lack the pathogenic potential against man.