Temperature-dependent cultural and biochemical characteristics of rhamnose-positive Yersinia enterocolitica

Abstract

Clinical isolates of rhamnose-positive Y. enterocolitica (Y.e.rh+) were compared with typical rhamnose-negative Y. enterocolitica (Y.e.rh-) and with Y. pseudotuberculosis. The Y.e.rh+ differed from the Y.e.rh- and Y. pseudotuberculosis in their ability to ferment raffinose and lactose, utilize citrate and in their inability to grow on Hektoen enteric agar at 22 or 37.degree. C, on Salmonella-Shigella [SS] agar at 37.degree. C, and scant growth on xylose-lysine-deoxycholate agar at 37.degree. C. An extensive temperature-dependent profile of characteristics was established for the Y.e.rh+: motility, acetoin production, citrate utilization, growth on SS agar, and ampicillin resistance occurred at 22.degree. C but not 37.degree. C; fermentation of melibiose, raffinose, and cellobiose occurred within 24 h at 22.degree. C, but not before 5 days at 37.degree. C; fermentation of rhamnose and production of .beta.-galactosidase occurred within 24 h at 22.degree. C, but not before 48 h at 37.degree. C; greater resistance to ampicillin, chloramphenicol, streptomycin, kanamycin, carbenicillin and gentamicin was observed at 22 than 37.degree. C; and good growth on xylose-lysine-deoxycholate agar occurred at 22 but not 37.degree. C. For optimal recovery of Y.e.rh+ from mixed culture, e.g., stools, 2 MacConkey plates should be inoculated and incubated, 1 at 37.degree. C and 1 at 22.degree. C. Lactose-negative colonies appearing after 48 h on the 22.degree. C MacConkey agar but not the 37.degree. C MacConkey agar should be considered possible Y.e.rh+. Biochemicals should be tested in duplicate, 1 set incubated at 22.degree. C, 1 set at 37.degree. C. Antibiotic susceptibility tests of Y.e.rh+ isolates should be incubated at 37.degree. C and at a lower temperature to allow the greatest expression of resistance of these organisms to the various antibiotics.