Yersinia CIN Agar ISO

The characteristic appearance of Yersinia spp. colonies after an incubation of 18-24 hours at 30 °C or 48 hours at 22 °C on CIN Agar in air is: round, pink, about 2 mm in diameter with a dark pink centre and surrounded with a precipitation zone. Confirmatory tests are required. Typical colonies of Yersinia enterocolitica will develop as a red bull's-eye surrounded by a transparent border, but will vary considerably among serotypes in colony size, smoothness and the ratio of the border to centre diameter. Most other organisms that are capable of growing on this medium produce larger colonies (> 2 mm in diameter) with diffuse pinkish centres and opaque outer zones. Some strains of Serratia, Citrobacter and Enterobacter in CIN Agar may give a colonial morphology resembling Yersinia enterocolitica. These organisms can be differentiated by biochemical tests.

At present no single isolation procedure is available for the recovery of all pathogenic strains of Yersinia enterocolitica. Selection of the proper isolation procedure will depend on the bio/serogroups of Yersinia spp. sought and on the type of sample to be examined. The ISO method for the detection of presumptive pathogenic Yersinia enterocolitica includes parallel use of the following two isolation procedures:

1. Enrichment in Peptone, Sorbitol and Bile Salts (PSB) Broth for 2-3 days at 22-25 °C with agitation or 5 days without agitation; plating on CIN Agar directly and after alkaline treatment and incubation for 24 hours at 30 °C.
2. Enrichment in ITC (Irgasan-Ticarcillin-Chlorate) Broth for 2 days at 24 °C; plating on SSDC (Salmonella-Shigella-Deoxycholate-Calcium Chloride) Agar and incubation for 2 days at 30 °C.

Physical/chemical control

Microbiological control

Spiral spreading: practical range 100 ± 20 CFU; min. 50 CFU (productivity) / 10⁴-10⁶ CFU (selectivity).

Aerobiosis. Incubation at 30 ± 2 °C. Reading at 48 h.

Sterility control

Incubation 48 hours at 30-35 °C and 48 hours at 20-25 °C: NO GROWTH.

Check at 7 days after incubation in same conditions.

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