BlaTEM-positive Salmonella enterica serovars Agona and Derby are prevalent among food-producing animals in Chongqing, China

Abstract

Salmonella is one of the most important foodborne zoonotic pathogens, causing global morbidity and mortality in both humans and animals. Due to the extensive use of antimicrobials in food-producing animals, the antimicrobial resistance of Salmonella has attracted increasing attention globally. There have been many reports concerning the antimicrobial resistance of Salmonella from food-producing animals, meats and the environment. However, few studies on Salmonella from food-producing animals have been reported in Chongqing municipality, China. The aim of the present study was to determine the prevalence, serovar diversity, sequence types, and antimicrobial resistance of Salmonella isolated from livestock and poultry in Chongqing. Meanwhile, we also want to know the presence of β-lactamase genes, plasmid-mediated quinolone resistance (PMQR) genes and quinolone resistance-determining region (QRDR) mutations of Salmonella isolates. A total of 129 Salmonella strains were recovered from 2,500 fecal samples at 41 farms from pigs, goats, beef cattle, rabbits, chickens, and ducks. Fourteen serovars were identified, with S. Agona and S. Derby being the dominant serovars. The 129 isolates had high resistance to doxycycline (87.6%), ampicillin (80.6%), tetracycline (79.8%), trimethoprim (77.5%), florfenicol (76.7%) chloramphenicol (72.9%), and trimethoprim-sulfamethoxazole (71.3%), but were susceptible to cefepime. A total of 114 (88.4%) isolates showed multidrug resistant phenotypes. The prevalence of β-lactamase genes in Salmonella isolates was 89.9% (116/129), and among these isolates, 107 (82.9%) harbored blaTEM, followed by blaOXA (26, 20.2%), blaCTX-M (8, 6.2%), and blaCMY (3, 2.3%). In addition, qnrB, qnrD, qnrS, oqxA, oqxB, and aac(6′)-Ib-cr were detected in 11, 2, 34, 34, 43, and 72 PMQR-producing isolates, respectively. Moreover, QRDR mutations were very common in PMQR-positive Salmonella isolates (97.2%, 70/72) with mutation(s) in parC or combinative mutations in gyrA and parC. More significantly, 32 extended spectrum beta-lactamase (ESBL)-producing isolates were identified, and 62.5% of them were found to harbor one to four PMQR genes. Furthermore, 11 sequence types were identified from the isolates, and most of ESBL-producing isolates were attributed to ST34 (15.6%) and ST40 (62.5%). The coexistence of PMQR genes with β-lactamase genes and the extensive mutations in QRDR present in Salmonella isolates from food-producing animals suggest a potential threat to public health. Reasonable utilization and strict control strategies for antimicrobials in animal husbandry and animal treatment are necessary to reduce the emergence and dissemination of drug-resistant Salmonella isolates.

Serovar and sequence type distribution and phenotypic and genotypic antimicrobial resistance of Salmonella originating from pet animals in Chongqing, China

“…As one of the most important zoonotic pathogens, people often pay attention to Salmonella in food-producing animals or food of animal origin transmission chains ( 28 , 46 , 47 ) while less attention has been given to Salmonella originating from pets. However, Salmonella colonizing the intestines of pet animals can also be transmitted to humans, leading to the onset of illness that requires attention.…”

“…Briefly, rectal swabs in BPW pre-enrichment broth were homogenized using a vortex mixer for 30 s and incubated at 37°C for 16–24 h. A 300 µL pre-enriched suspension was added to 9.7 mL of tetrathionate broth (TTB) (HuanKai Microbial, Guangdong, China) and incubated at 37°C for 18 h. A loop of inoculum from each enrichment culture was streaked onto CHROMagar Salmonella -selective plate (Chromagar, Shanghai, China) at 37°C for 24–48 h. Typical mauve colonies on chromogenic plates were further confirmed by specific polymerase chain reaction (PCR) with Taq PCR Mix (Sangon Biotech, Shanghai, China) targeting the invA gene ( 28 ). The confirmed isolates were aliquoted and stored at −80°C in Luria–Bertani (LB) broth supplemented with 50% glycerol until further testing.…”

“…The primer sequences and corresponding PCR conditions are presented in Table S14. The amplified β-lactamase genes were bla TEM ( 71 ), bla CTX-M ( 72 ), bla SHV ( 71 ), bla OXA ( 73 ), bla CMY ( 71 ), bla PSE ( 74 ), bla PER ( 74 ), bla VEB ( 75 ), and bla GES ( 75 ), whereas the amplified PMQR genes included qnrA ( 76 ), qnrB ( 77 ), qnrC ( 28 ), qnrD ( 28 ), qnrVC ( 28 ), qnrS ( 28 ), aac(6′)-Ib-cr ( 28 ), oqxA ( 28 ), oqxB , and qepA ( 78 ). Moreover, tetracycline resistance genes were identified by PCR according to reports from Ng et al ( 79 ) ( tet (A), tet (B), tet (C), tet (D), tet (E), tet (G), tet (M), tet (S), and tet (X)), Fan et al ( 80 ) ( tet (J)), and Ji et al ( 81 ) ( tet (X1), tet (X2), tet (X3), tet (X4), and tet (X5)).…”

“…Antimicrobial resistance (AMR) of Salmonella has become a serious public health problem in recent years, especially for strains with multidrug resistance (MDR), which is defined as acquired non-susceptibility to at least one agent in three or more antimicrobial categories ( 27 ). There have been many reports of infections caused by drug-resistant Salmonella in food animals ( 6 , 7 , 11 , 28 ). Additionally, the AMR of pet-associated Salmonella has attracted increasing attention.…”