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Salmonellosis, caused by multidrug-resistant Salmonella species, in particular, is one of the leading notifiable foodborne diseases in Singapore and an emerging public health concern worldwide. The objectives of this study were to determine the prevalence, antibiotic resistance and the presence of gyrA and parC mutations in Salmonella isolated from retail fresh chicken meat in Singapore. A significantly higher prevalence of Salmonella was found in chicken meat from the wet markets (25%, 30/120), as compared to supermarkets (12.7%, 19/150). The top four serovars isolated in this study were S. Saintpaul (32.7%, 17/52), followed by S. Brancaster (21.2%, 11/52), S. Albany (11.5%, 6/52), and S. Stanley (9.6%, 5/52). More than 80% of Salmonella isolates exhibited resistance to at least one of eleven antibiotics tested. The most common phenotypic resistances exhibited were towards ampicillin (78.8%, 41/52), tetracycline and chloramphenicol (61.5%, 32/52), sulfamethoxazole-trimethoprim (55.8%, 29/52) and nalidixic acid (30.8%, 16/52). Of the 52 Salmonella isolates, 59.6% (31/52) were multi-drug resistant strains, resistant to 3 or more antibiotic classes. No mutation in parC gene was found in any of the isolates that expressed phenotypic resistance or reduced susceptibility towards quinolone and/or fluoroquinolone. Mutations at two different sites of gyrA gene were found in 7 isolates, which further discriminates the quinolone resistance genotype in Salmonella isolates from fresh chicken meat. Our findings provide opportunities for risk assessment and management of salmonellosis and antibiotic-resistant Salmonella species in the country and the region. [ABSTRACT FROM AUTHOR]

Background: Salmonella enterica subspecies enterica serovar Saintpaul (S. Saintpaul) is an important gut pathogen which causes salmonellosis worldwide. Although intestinal salmonellosis is usually self-limiting, it can be life-threatening in children, the elderlies and immunocompromised patients. Appropriate antibiotic treatment is therefore required for these patients. However, the efficacy of many antibiotics on S. enterica infections has been greatly compromised due to spreading of multidrug resistance (MDR) plasmids, which poses serious threats on public health and needs to be closely monitored. In this study, we sequenced and fully characterized an S. enterica MDR plasmid pSGB23 isolated from chicken. Results: Complete genome sequence analysis revealed that S. Saintpaul strain SGB23 harbored a 254 kb megaplasmid pSGB23, which carries 11 antibiotic resistance genes responsible for resistance to 9 classes of antibiotics and quaternary ammonium compounds that are commonly used to disinfect food processing facilities. Furthermore, we found that pSGB23 carries multiple conjugative systems, which allow it to spread into other Enterobacteriaceae spp. by self-conjugation. It also harbors multiple types of replicons and plasmid maintenance and addictive systems, which explains its broad host range and stable inheritance. Conclusions: We report here a novel MDR plasmid pSGB23 harboured by S. enterica. To our knowledge, it carried the greatest number of antibiotic resistance genes with the broadest range of resistance spectrum among S. enterica MDR plasmids identified so far. The isolation of pSGB23 from food sources is worrisome, while surveillance on its further spreading will be carried out based on the findings reported in this study. [ABSTRACT FROM AUTHOR]