Partial purification and characterization of bacteriocin from Yersinia kristensenii.

A raw milk bacterial isolate, identified as Yersinia kristensenii was found to produce a bacteriocin which was inhibitory to Yersinia enterocolitica but not to other selected species of Yersinia or Gram-negative bacteria. Maximum production of bacteriocin was obtained when the organism was grown in shake culture at 28 degrees C. Mitomycin C at a concentration of 0.5 micrograms ml-1 induced bacteriocin production. The bacteriocin was partially purified and characterized by ammonium sulphate fractionation and gel filtration. The bacteriocin was completely inactivated when treated with proteolytic enzymes (trypsin and chymotrypsin). Bacteriocin activity was heat-resistant and it retained some of its activity after 5 min at boiling temperature. A total of 15 bacteriocin sensitive-suspected food isolates were further identified biochemically as Yersinia enterocolitica and a non-sensitive isolate was identified as Yersinia intermedia.

Application of Yersinia kristensenii bacteriocin as a specific marker for the rapid identification of suspected isolates of Yersinia enterocolitica.

Out of 143 suspected foods and clinical isolates of the genus Yersinia, 77 isolates were bacteriocin-sensitive and 66 bacteriocin non-sensitive. Of the 77 bacteriocin-sensitive isolates, 72 (93.5%) were identified as Y. enterocolitica and 5 (6.49%) as Y. frederiksenii. Out of 66 bacteriocin non-sensitive suspected isolates, 22 (33.3%) were identified as Yersinia spp. other than Y. enterocolitica and 43 (65.1%) were other Gram-negative bacteria with the exception of one (1.5%) isolate identified as Y. enterocolitica.

Evaluation of different antimicrobial agents used as selective supplements for isolation and recovery of Yersinia enterocolitica.

Seventeen antimicrobial agents were evaluated separately or in combination for their efficiency as selective supplements in a broth medium against six different serotypes of Yersinia enterocolitica and 20 selected strains of different Gram-negative bacteria. Irgasan (DP300, 5-chloro-2-(2,4- dichlorophenoxy) phenol) at a concentration of 4 micrograms ml-1 inhibited the growth of most Gram-negative bacteria with the exceptions of Aeromonas hydrophila, Morganella morganii, Pseudomonas aeruginosa and Serratia liquefaciens. Other antimicrobial agents incorporated in the growth medium, separately or in combination with Irgasan, either inhibited some strains of Y. enterocolitica or did not inhibit the growth of Irgasan-resistant Gram-negative bacteria.

Evaluation of the ability of primary selective enrichment to resuscitate heat-injured and freeze-injured Listeria monocytogenes cells.

Resuscitation rates of injured Listeria monocytogenes on conventional selective Listeria enrichment broth and nonselective Trypticase soy broth containing 0.6% yeast extract were compared. Cells were heated to 60 degrees C for 5 min or frozen at -20 degrees C for 7 days. Inoculation of Trypticase soy broth-yeast extract with the stressed cells resulted in growth that was superior to that in Listeria enrichment broth. Injured cells were fully recovered at 6 to 8 h.

Factors affecting production and activity of phospholipase C by Yersinia enterocolitica.

The production of phospholipase C by Yersinia enterocolitica strain SG was optimum at 37 degrees C at pH 6.5. No enzyme activity could be detected when the organism was grown at extreme pH values (pH greater than 8.5 or less than 5.0). The enzyme production was maximum when the organism was grown under static conditions in TSB medium. All solvents and salts inhibited the enzyme activity, whereas loss of activity was 95% in presence of methanol (20%) and 99% in presence of sodium azide (0.2 mol/l). The enzyme activity was increased twofold in the presence of cysteine and decreased by 98% in the presence of sodium perchlorate (0.2 mol/l).

Drug resistance and lecithinase activity of Yersinia enterocolitica isolated from buffalo milk.

Two-hundred-and-seven samples of raw buffalo milk and 60 samples of pasteurized buffalo milk were screened for presence of Yersinia enterocolitica. The prevalence of Y. enterocolitica was found to be 24.1% in raw milk, however, no isolation could be made from the pasteurized milk samples. Cold enrichment in trypticase soy broth and alkali treatment methods were followed in this study. The majority of the isolates (62%) were found sensitive to all the antibiotics used and only a few (16%) were resistant to two or more than two antibiotics. The incidence of Y. enterocolitica showed seasonal variations. Incidence was much higher (25-50%) during the winter season as compared to the summer (0-17%). The incidence of lecithinase production was high (40-50%) in Yersinia isolates resistant to one or two antibiotics.

Partial purification and characterization of phospholipase C from Yersinia enterocolitica.

About 34% of the strains of Yersinia enterocolitica isolated from raw milk were found to produce lecithinase. A selected strain produced phospholipase C at 22 degrees C and 37 degrees C; production was optimum at 37 degrees C in the stationary phase (14-16 h). A decrease in phospholipase C activity at various storage temperatures (-5 degrees C, 4 degrees C, 37 degrees C) was also observed, although the enzyme was active over a wide range of temperature (5-65 degrees C) and pH (3.5-7.5). The phospholipase C was partially purified by ammonium sulphate precipitation and Sephadex column chromatography, and characterized.

Production of bacteriocin by isolates of Yersinia enterocolitica from fresh buffalo milk.

Fifty isolates of Yersinia enterocolitica from fresh buffalo milk were screened for the production of bacteriocin using isolates as indicators. Seven isolates (14%) were bacteriocin producers at 22 degrees C which had more bacteriolytic activity at 37 degrees C. Only one isolate produced bacteriocin at both temperatures.