Serovar and sequence type distribution and phenotypic and genotypic antimicrobial resistance of
Salmonella
originating from pet animals in Chongqing, China
Authors: Zhao Meiyuan , Wang Xudong , He Jiawei , Zhou Kexin , Xie Mengqi , Ding Honglei 
Published: May 2024

A total of 334
Salmonella
isolates were recovered from 6,223 pet rectal samples collected at 50 pet clinics, 42 pet shops, 7 residential areas, and 4 plazas. Forty serovars were identified that included all strains except for one isolate that did not cluster via self-agglutination, with
Salmonella
Typhimurium monophasic variant,
Salmonella
Kentucky,
Salmonella
Enteritidis,
Salmonella
Pomona, and
Salmonella
Give being the predominant serovars. Fifty-one sequence types were identified among the isolates, and ST198, ST11, ST19, ST451, ST34, and ST155 were the most common. The top four dominant antimicrobials to which isolates were resistant were sulfisoxazole, ampicillin, doxycycline, and tetracycline, and 217 isolates exhibited multidrug resistance. The prevalence of β-lactamase genes in
Salmonella
isolates was 59.6%, and among these isolates, 185 harbored
bla
TEM
, followed by
bla
CTX-M
(66) and
bla
OXA
(10). Moreover, six PMQR genes, namely, including
qnrA
(4.8%),
qnrB
(4.2%),
qnrD
(0.9%),
qnrS
(18.9%),
aac(6')-Ib-cr
(16.5%), and
oqxB
(1.5%), were detected. QRDR mutations (76.6%) were very common in
Salmonella
isolates, with the most frequent mutation in
parC
(T57S) (47.3%). Furthermore, we detected six tetracycline resistance genes in 176 isolates, namely,
tet
(A) (39.5%),
tet
(B) (8.1%),
tet
(M) (7.7%),
tet
(D) (5.4%),
tet
(J) (3.3%), and
tet
(C) (1.8%), and three sulfonamide resistance genes in 303 isolates, namely,
sul1
(84.4%),
sul2
(31.1%), and
sul3
(4.2%). Finally, we found 86 isolates simultaneously harboring four types of resistance genes that cotransferred 2–7 resistance genes to recipient bacteria. The frequent occurrence of antimicrobial resistance, particularly in dogs and cats, suggests that antibiotic misuse may be driving multidrug-resistant
Salmonella
among pets.

IMPORTANCE

Pet-associated human salmonellosis has been reported for many years, and antimicrobial resistance in pet-associated
Salmonella
has become a serious public health problem and has attracted increasing attention. There are no reports of
Salmonella
from pets and their antimicrobial resistance in Chongqing, China. In this study, we investigated the prevalence, serovar diversity, sequence types, and antimicrobial resistance of
Salmonella
strains isolated from pet fecal samples in Chongqing. In addition, β-lactamase, QRDR, PMQR, tetracycline and sulfonamide resistance genes, and mutations in QRDRs in
Salmonella
isolates were examined. Our findings demonstrated the diversity of serovars and sequence types of
Salmonella
isolates. The isolates were widely resistant to antimicrobials, notably with a high proportion of multidrug-resistant strains, which highlights the potential direct or indirect transmission of multidrug-resistant
Salmonella
from pets to humans. Furthermore, resistance genes were widely prevalent in the isolates, and most of the resistance genes were spread horizontally between strains.