AUTHOR=Zhao Liyuan , Liu Gang , Tang Wenli , Song Xiangbin , Zhao Xiaoyu , Wang Chu , Li Youzhi , Zou Ming 

TITLE=Antimicrobial resistance and genomic characteristics of Salmonella from broilers in Shandong Province

JOURNAL=Frontiers in Veterinary Science

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2023.1292401

DOI=10.3389/fvets.2023.1292401

ISSN=2297-1769

ABSTRACT=<sec><title>Introduction</title><p>The emergence of multidrug-resistant (MDR) strains of <italic>Salmonella,</italic> which is a genus of important zoonotic pathogens, has aroused great public health concern worldwide.</p></sec><sec><title>Methods</title><p>In this study, 167 strains of <italic>Salmonella</italic> were isolated from 947 samples from broiler farms, slaughterhouses, and markets in Shandong Province. Antibiotic sensitivity testing was performed, and 70 strains of <italic>Salmonella</italic> were screened out by whole-genome sequencing (WGS) to evaluate serotypes, antimicrobial resistance genes (ARGs), the prevalence of class 1 integrons, the plasmid carriage rate, and phylogenetic characteristics and for multilocus sequence typing (MLST).</p></sec><sec><title>Results</title><p>The results showed that the 167 isolates showed the highest resistance to ampicillin (AMP, 87.4%), sulfamethoxazole (SF, 87.4%), compound sulfamethoxazole (SXT, 81.4%), nalidixic acid (NAL, 80.2%), and amoxicillin/clavulanic acid (A/C, 77.8%). All the strains were sensitive to meropenem (MEM), and 91.0% of the isolates were MDR strains. We screened a total of 45 ARGs, with the highest detection rate observed for the tetracycline (TET) resistance gene <italic>tet</italic> (A) (81.4%). A total of 21 types of plasmid replicons were detected in <italic>Salmonella</italic>, of which IncX1 was the most common (74.3%), and 62.9% of the isolates carried a class 1 integron. In addition, a total of 11 different serotypes were detected, with <italic>S. enteritidis</italic> as the predominant serovar., followed by <italic>S. infantis</italic> and <italic>S.</italic> Newport. Twelve different sequence types (STs) were detected, among which ST11 was the main type. There was a strong correspondence between serotypes and STs. We also found that <italic>S. Indiana</italic> and <italic>S.</italic> Kentucky had extremely high rates of resistance to ciprofloxacin (CIP) and third-generation cephalosporins. System-wide genome analysis showed the occurrence of long-distance transmission across fields.</p></sec><sec><title>Conclusion</title><p>In conclusion, the detection of multidrug resistance and isolates carrying multidrug resistance genes is the main problem, and emergency strategies should be implemented to address this issue.</p></sec>