Detection and CRISPR subtyping of Salmonella spp. isolated from whole raw chickens in Yangzhou from China

- Report of Salmonella contamination in whole raw chickens available to consumers.
- The MPN value was used to estimate the bacterial load.
- CRISPR typing was carried out to analyze Salmonella isolates.
- CRISPR type was confirmed to show excellent correspondence with Salmonella serotype.

This study was undertaken to acquire data on Salmonella contamination of whole raw chickens, eggs, and vegetables available to consumers in Yangzhou city, China, between April 2011 and March 2012. In total, 240 chicken carcasses were tested, and the overall contamination rate for Salmonella was 33.8%. While the prevalence of Salmonella in 100 eggs and 155 vegetable samples was 7.0% and 3.2%, respectively. The 84 isolated strains were identified in 19 different serotypes with Salmonella enterica serovar Indiana (S. Indiana) (25.0%), S. Typhimurium (21.4%) and S. Enteritidis (17.9%) as the predominant serovars. Moreover, the median load of the contaminated chicken samples reached 6.4 MPN/100 g with 3.6 MPN/100 g as the 25th percentile and 15.0 MPN/100 g as the 75th percentile. Chicken carcasses collected in October had not only the highest prevalence of Salmonella (70%), but also the highest median load (33 MPN/100 g) and 75th percentile load (460 MPN/100 g), while the lowest prevalence (10%) was in April. The clustered regularly interspaced short palindromic repeats (CRISPR) subtyping method was then used to identify serotypes of Salmonella and distinguish strains from the same Salmonella serotypes. We found that 85.7% of strains were distributed in 11 serotypes speculated by CRISPR typing, which corresponded to the identified serotypes by O and H antiserum. The speculated serotypes of 7.1% of the strains by CRISPR typing are very close to the identified ones, as they belong to the same O group with a small difference in the O or H antigen. All of the above findings implied that CRISPR typing could be applied to serotyping of Salmonella. In addition, CRISPR typing method could be used to subtype different strains from the same serotype, specifically S. Hadar.