Molecular characterization of IncFII plasmid carrying
bla
NDM-5
in a
Salmonella enterica
serovar Typhimurium ST34 clinical isolate in China
Authors: Zeng Shihan , Huang Yulan , Zhang Xiwei , Fu Liang , Sun Zhaohui , Li Xiaoyan 
Published: November 2023

The detection rate of carbapenem-resistant nontyphoidal
Salmonella
(NTS) is relatively low. However, carbapenem-sensitive and carbapenem-resistant
Salmonella enterica
serovar Typhimurium (
S. enterica
serovar Typhimurium) were isolated from a clinical outpatient within a span of 10 days, named 1104–65 and 1104–75. We aimed to reveal the mechanism of carbapenem resistance in
S. enterica
serovar Typhimurium isolates in this case. The resistance phenotype of
S. enterica
serovar Typhimurium was analyzed by the VITEK-2 Compact equipment and Kirby-Bauer disc diffusion method. Whole-genome sequencing was used to analyze the serotype, ST type, genetic relationship, resistance genes, plasmid replicon, the genetic environment of
bla
NDM-5
, and the characteristics of IncFII plasmid carrying
bla
NDM-5
in
S. enterica
serovar Typhimurium. The transferability of the IncFII plasmid carrying
bla
NDM-5
was verified by the conjugation assay and PCR. The serotypes of both NTS are
S. enterica
serovar Typhimurium, belonging to ST34. Single nucleotide polymorphisms analysis showed that they were the same clone. A conjugative IncFII plasmid pIncFII-NDM5 with transferability was detected in isolate 1104–75, which harboring the
bla
NDM-5
gene was the primary mechanism responsible for mediating carbapenem resistance in
S. enterica
serovar Typhimurium. The genetic environment of
bla
NDM-5
on pIncFII-NDM5 is “IS
26
-ΔIS
3000
-IS
5
-ΔIS
Aba125-bla
NDM-5
-
ble
MBL
-
trpF-dsbC -cutA
-IS
26
”, which was confirmed as a novel structure not previously reported in the NCBI database. Although the mechanism is rarely reported in NTS, the prevalence of IncFII plasmid pIncFII-NDM5 will pose a great threat to the clinical treatment of
S. enterica
serovar Typhimurium. Meanwhile, the coexistence of
bla
CTX-M-55
,
qnrS1
,
bla
NDM-5
, and
mph(A
) in
S. enterica
serovar Typhimurium ST34 warrants additional attention.

IMPORTANCE

In this study, an IncFII plasmid pIncFII-NDM5 carrying
bla
NDM-5
was found in carbapenem-resistant
Salmonella enterica
serovar Typhimurium (
S. enterica
serovar Typhimurium), which has conjugative transferability and carried
bla
NDM-5
,
ble
MBL
,
mph(A
), and
bla
TEM-1
four resistance genes that can mediate resistance to multiple antibiotics including cephalosporins, beta-lactamase inhibitor combinations, carbapenems, and macrolides. Phylogenetic analysis showed that 1104–65 and 1104–75 were closely related to other
S. enterica
serovar Typhimurium in this area. The above-mentioned
S. enterica
serovar Typhimurium chromosome carries
bla
CTX-M-55
,
qnrS1
, and
tet(A
) genes, so the antibiotic resistance of isolates will be further enhanced after obtaining the pIncFII_NDM5-like plasmid. Meanwhile, we discovered a novel genetic structure of
bla
NDM-5
mediated by the IS
26
composite transposon, which will expand our understanding of the emergence and spread of carbapenem-resistance genes. Altogether, the presence of the IncFII plasmid pIncFII-NDM5 further underscores the need for vigilant surveillance and appropriate infection control measures to mitigate the impact of carbapenem-resistant
S. enterica
serovar Typhimurium in clinical settings.