Molecular characteristics of florfenicol-resistant Salmonella based on whole-genome sequencing

Salmonella is a significant foodborne pathogen,the increased rate of detecting rate of florfenicol-resistant Salmonella poses a serious threat to public health. This study used a combination of dry and wet experiments to conduct molecular epidemiological analysis on 11 strains of florfenicol resistant Salmonella. The results indicated that 9 out of the 11 florfenicol-resistant Salmonella strains were multidrug-resistant, with seven different serotypes and sequence types (STs) identified. Notably, HYSAL-187 represents a new ST type (ST11178), with a beta-lactamase gene combination pattern of blaOXA-1+blaCMY-2+blaTEM-1. Conjugation experiments showed that 10 strains were successfully conjugated, except for HYSAL-229. 11 strains of bacteria carry seven types of plasmids, among which IncHI2 and IncHI2A are the most common. Different strains carry significantly different numbers of antibiotic resistance genes (75-101), reflecting the diversity of Salmonella in the food chain. Interestingly, florfenicol-resistant Salmonella was detected in different stages of the food chain, demonstrating its potential for transmission. The floR gene, encoding resistance to florfenicol, primarily relied on IncHI2A plasmids for horizontal transfer between strains. Moreover, an ST34 Salmonella typhimurium monophasic variant was identified, carrying the mcr-1.1 resistance gene co-located with floR on the same plasmid.