Molecular epidemiology and drug susceptibility of Salmonella Montevideo in Shanghai

Objective To study the molecular epidemiological characteristics and antibiotic susceptibility of Salmonella enterica serovar Montevideo (S. Montevideo). Methods The analysis was conducted by using the surveillance data in Shanghai Collect and analyze Salmonella surveillance database in Shanghai. Results S. Montevideo ranked 24th (32 isolates) among all Salmonella serotypes from human and 32nd(13 isolates) from food source in Shanghai, respectively. Twenty eight foodborne infections of S. Montevideo were laboratory confirmed among diarrheal cases. Children under 5 years old and male adults aged 20-60 years were more susceptible, and the incidence in suburb area was high. Antibiotic susceptibility test showed that both foodborne and human isolates were resistant to the third-generation cephalosporin (Ceftazidime). Moreover, multi drug resistant (MDR) foodborne isolates increased significantly in recent five years, and 28.1% of human sourced S. Montevideo isolates were intermediate to ciprofloxacin. However, the isolates from foreign animal products were mostly sensitive to antibiotics. PFGE indicated that prevalent clones of S. Montevideo strains existed in Shanghai, including MDR-ACSSuT which caused two of three outbreaks in adults. MDR-ACSSuT isolates from human and turtles shared high homology, but quite different from foreign isolates. Phylogenetic relationship existed between the two different clone clusters. Conclusion S. Montevideo is not predominant in Shanghai, but it has been transmitted to China through trade and gradually colonized in coastal turtle cultivation and food chain. The MDR clones and non-MDR strains might cause sporadic outbreaks, which are difficult to detect.