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To evaluate the presence of Yersinia enterocolitica in raw chicken, 70 samples of chicken carcasses were obtained from a Buenos Aires, Argentina, processing plant. The detection of this psychotropic microorganism was carried out using the whole carcass rinse method and enrichment in phosphate-buffered saline, 0.067 M, pH 7.6, at 4 degrees C, followed by alkaline treatment and isolation on cefsulodin-irgasan-novobiocin nutrient agar. Y. enterocolitica or related species were detected in 7 of 70 samples. From them, 4.3% were identified as Y. enterocolitica, 1.4% as Yersinia intermedia, and 4.3% as Yersinia frederiksenii. The serotype and phagotype of Y. intermedia isolates were O:5(2), 5(3), and Xz and those of Y. frederiksenii were O:4.16 and Xo. All Y. enterocolitica isolates belong to the biogroup 1A, serotype O:5, phagotype Xz, which presents uncertain pathogenic potential. These findings reinforce the worldwide concern on the microbiological quality of food products. Quality assurance programs on the whole poultry process are increasingly being adopted in Argentina.

A wide variety of techniques are available for the preservation of bacteria and it may be difficult to choose a method for a particular strain, which not only assures survival, but which also makes certain that the genotype and hence the unique characteristics do not change. This paper provides a summary of the main features of various available methods with references to recent research and applications.

The conjugative enterococcal transposons Tn916 and Tn919 were introduced into Bacillus megaterium by a filtermating technique. The transfer frequencies obtained ranged from 1.3×10(-6) to 6.6×10(-7). The transposons integrated stably into the B. megaterium chromosome. Tn916 could generate auxotrophs and was transferred from B. megaterium Tn916 transconjugants to other species.

Centrifugation through sucrose gradients was adapted to separate spore-forming cells of B. megaterium deficient in poly-beta-hydroxybutyrate synthesis from wild type cells. The conditions described allowed the detection of mutant clones screening a low percentage of the mutagenized population.

Schiemann's medium was used for the isolation of Yersinia enterocolitica and Yersinia enterocolitica-like organisms. These bacteria were isolated in 90% of the samples of sewage of the city of Buenos Aires, both from direct and cold enriched samples. From a total of 19 strains, 8 were classified as Y. enterocolitica (lactose positive), 7 as Y. frederiksenii and 2 as Y. intermedia. Two strains could be included in the latter species (biotypes 4 and 5 from Brenner et al. (14] but a confirmation by DNA hybridization would be useful. All the Y. enterocolitica and Y. frederiksenii were sero and lysotyped according to the Center for Yersinia (Paris, France).

A procedure was optimized for the formation and regeneration of protoplasts in a Clostridium acetobutylicum strain isolated from cassava roots in Misiones, Argentina. The regeneration frequency was calculated as the ratio of regenerants (colony forming units on regeneration plates minus colony forming units from osmotically resistant cells) per initial cell number (colony forming units before protoplast formation). The percentage regeneration varied from 10 to 15%.