Serovar distribution, antimicrobial resistance profiles, and PFGE typing of Salmonella enterica strains isolated from 2007-2012 in Guangdong, China

Background: Salmonella enterica includes the major serovars associated with human salmonellosis. In this study, 1764 clinical Salmonella enterica isolates from diarrhea outpatients were collected from fifteen cities in Guangdong province, China, between 2007 and 2012. These isolates represent all of the Salmonella isolates collected from the province during that period. Methods: The isolates were characterized by serovar determination, antimicrobial susceptibility tests and PFGE fingerprint typing. Results: The serovar distribution results demonstrated that Salmonella Typhimurium (n = 523, 29.65%) and Salmonella 4,5,12:i: (n = 244, 13.83%) are the most common serovars causing infant salmonellosis, whereas Salmonella Enteritidis (n = 257, 14.57%) mainly causes human salmonellosis in adults. The serovar shift from Salmonella Enteritidis to Salmonella Typhimurium occurred in 2008. Antimicrobial susceptibility data showed a high burden of multidrug resistance (MDR) (n = 1128, 56.58%), and a 20%-30% increase in the number of isolates resistant to ciprofloxacin (n = 142, 8.05%) and third-generation cephalosporins (n = 88, 4.99%) from 2007-2012. Only 9.97% of isolates (n = 176) were fully susceptible to all agents tested. A high burden of MDR was observed in Salmonella Typhimurium and Salmonella 4,5,12: i:- for all age groups, and a reduced susceptibility to third-generation cephalosporins and quinolones occurred particularly in infants (= 6 years). The dominant PFGE patterns were JPXX01. GD0004, JEGX01. GD0006-7 and JNGX01. GD0006-7. ACSSuT was the predominant MDR profile in the Salmonella Typhimurium & 4,5,12: i:-complexes, while ASSuT-Nal and ASSu-Nal were the major MDR profiles in Salmonella Enteritidis. The predominant PFGE patterns of the Salmonella Typhimurium & 4,5,12: i:-complexes and Salmonella Stanley were most prevalent in infants (<= 6 years). However, no obvious relationship was observed between these PFGE profiles and geographic location. Conclusions: These data reveal the serovar distribution of isolates recovered from diarrhea patients, the characteristics of resistant strains and fingerprint typing in Guangdong from 2007 to 2012. These results highlight a serovar shift and a worrying percentage of MDR strains with increasing resistance to quinolones and third-generation cephalosporins. Thus, continued surveillance of Salmonella and their MDR profiles using combined molecular tools and efforts to control the rapid increase in antimicrobial resistance among Salmonella in Guangdong are needed.