Characteristics and molecular subtyping of multidrug resistant Salmonella in Hangzhou

Abstract:

[Background] Salmonella is one of the most important food-borne pathogens. Its multidrug resistance has attracted more and more attention. [Objective] To analyze the antimicrobial-resistant characteristics and molecular subtyping of multidrug resistant (MDR) Salmonella from clinical sources in Hangzhou, the present study was performed. [Methods] A total of 339 Salmonella isolates from clinical sources were subjected to antimicrobial susceptibility testing and the minimum inhibitory concentration (MIC) was determined. The MDR isolates, which show reduced susceptibility to at least 3 of the 14 antimicrobial categories tested, were analyzed the drug-resistant characteristics, serotype distribution, and the molecular subtyping by pulsed field gel electrophoresis (PFGE). [Results] Among the 339 Salmonella isolates, 234 MDR isolates were found and the MDR rate reached 69.03%. No significant difference was observed in the MDR rate from 2017 to 2019 (χ2=0.117, P=0.943). Isolates resistant to 4?8 antimicrobial categories were most common, accounting for 56.93% (193/339) of the total number of Salmonella isolates. Most of the MDR isolates (199/234, 85.04%) showed resistance to 5?13 antimicrobial agents. The resistance patterns of the MDR isolates were quite diverse, and the relatively dominant patterns were AMP-AMS-NAL-STR-SUL (10, 4.27%) and AMP-STR-TET-MIN-DOX-SUL (7, 2.99%). The level of MDR in Salmonella Derby and monophasic Salmonella Typhimurium was prominent, which MDR rate was 100% (11/11) and 97.06% (66/68), respectively. The 234 MDR Salmonella isolates were subtyped into 162 molecular types by PFGE, with the similarity of 44.2%–100%. The PFGE profiles of the MDR isolates showed high polymorphism and no predominant PFGE profile was found, except for serotype Enteritidis and Typhimurium. For the isolates with identical PFGE profiles, their MDR patterns were either identical or different. For those with different PFGE profiles, the MDR patterns may also be identical. [Conclusion] High level of MDR was observed in Salmonella from clinical sources in Hangzhou, with the MDR patterns being quite diverse, and the PFGE profiles showed high polymorphism. The results showed that the infection of MDR Salmonella in Hangzhou was mainly sporadic. However, the genomic characteristics and the main food origin of MDR Salmonella in Hangzhou need to be further studied.