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Salmonella is the primary cause of community-acquired foodborne infections, so its resistance to antimicrobials, such as aminoglycosides, is a public health issue. Of concern, aminoglycoside resistance in Salmonella is increasing rapidly. Here, we performed a retrospective study evaluating the prevalence of Salmonella harboring armA -mediated aminoglycoside resistance in community-acquired infections and in food or environmental sources. The prevalence rates of armA -harboring Salmonella strains were 1.1/1,000 (13/12,095) and 8.7/1,000 (32/3,687) in outpatient and food/environmental isolates, respectively. All the armA -harboring Salmonella strains were resistant to multiple drugs, including fluoroquinolone and/or extended-spectrum cephalosporins, and most (34/45) belonged to serovar Indiana. The armA gene of these strains were all carried on plasmids, which spanned five replicon types with IncHI2 being the dominant plasmid type. All the armA -carrying plasmids were transferable into Escherichia coli and Acinetobacter baumannii recipients. The conjugation experiment results revealed that the armA -harboring S. Indiana strains had a relatively higher ability to acquire armA -carrying plasmids. The low similarity of their pulsed field gel electrophoresis patterns indicates that the armA -harboring Salmonella strains were unlikely to have originated from a single epidemic clone, suggesting broad armA spread. Furthermore, the genetic backgrounds of armA -harboring Salmonella strains isolated from outpatients exhibited higher similarity to those isolated from poultry than to those isolated from swine, suggesting that poultry consumption maybe an infection source. These findings highlight an urgent need to monitor the prevalence and transmission of armA -harboring Salmonella , especially S. Indiana, to better understand the potential public health threat and prevent the further spread of these strains. [ABSTRACT FROM AUTHOR]

Salmonella enterica serovar Indiana has become a widely prevalent non-typhoidal serovar in China in recent years. To improve the understanding of antimicrobial resistance and genetic bias in this emerging pathogen, a total of 214 S. Indiana isolates from foods, patients, and the environments in China from 2007 to 2016 were characterized for antimicrobial susceptibility, antimicrobial resistance-determining factors, and molecular typing. It was found that 208 (97.2%) exhibited resistance to ciprofloxacin, and 102 (47.7%) isolates to ceftriaxone. Ciprofloxacin resistance increased from 82.4% in 2007–2008 to 100.0% in 2015–2016. Ceftriaxone resistance increased from 29.4% in 2007–2008 to 47.1% in 2015–2016. In particular, the proportion of multidrug-resistant (MDR) S. Indiana isolates increased from 64.7% in 2007–2008 to 91.4% in 2015–2016. Mutations in the quinolone resistance determining region (QRDR) (gyr A and par C), plasmid-mediated quinolone resistance (PMQR) genes [ aac(6')-Ib-cr , oqx AB, qnr A, qnr S, qnr B and qep A], extended-spectrum beta-lactamase (ESBL) genes (bla OXA , bla CTX-M , bla TEM , bla CMY and bla VEB), and class I integrons were identified in these S. Indiana isolates, along with transposon units of ΔIS Ecp1 - bla CTX-M-65 -IS 903B , IS Ecp1 -IS Vsa5 - bla CTX-M-14 -IS 903B , and IS Ecp1 - bla CTX-M-55/15 -Δ orf 477. To our knowledge, the ESBL gene bla VEB was identified in Salmonella for the first time. Diverse plasmid types (IncHI2, IncN, IncA/C, IncFIB, IncI1 and IncFII) were identified in these isolates, among which IncHI2-type plasmid (49.1%) was the most common type in S. Indiana. Multilocus sequence typing (MLST) showed a single ST17 in S. Indiana. Pulsed-field gel electrophoresis (PFGE) results showed that there was a genotypic diversity, and some clones might have existed in S. Indiana between patients and foods for several years. These findings suggested that the frequent emergence of S. Indiana isolates with resistance to ciprofloxacin and ceftriaxone would pose a huge threat to food safety and public health. ∙ Ciprofloxacin and ceftriaxone co-resistant isolates were found. ∙ESBLs genes, PMQR genes with mutations in QRDR and class I integrons were observed. ∙ bla VEB was identified in Salmonella for the first time. ∙IS Ecp1 , IS Vsa5 and IS 903B was adjacent to bla CTX-M. ∙ST17 and genotypic diversity were identified in S. Indiana. [ABSTRACT FROM AUTHOR]

Salmonellosis is an important global foodborne disease, and Salmonella isolates that are resistant to a wide variety of antibiotics have become a major public health concern. The aim of this study was to investigate the distribution and transmission of mph A gene in azithromycin-resistant Salmonella isolates and characterize the plasmid bearing mph A. In this study, the azithromycin resistance was shown in 15 Salmonella enterica serovar Indiana (S. Indiana) isolates from chicken, duck and humans with concurrent resistance to ciprofloxacin and ceftriaxone, two of which were resistant to all antibiotics tested except colistin and imipenem. MLST and PFGE results suggested that these 15 isolates were closely related in phylogeny. The azithromycin resistance gene (mph A), extended-spectrum beta-lactamase (ESBL)-encoding genes (bla CTX-M-65 , bla CTX-M-14 and bla CTX-M-15) and plasmid-mediated quinolone resistance (PMQR) genes [ oqx AB, qep A, qnr A and aac(6′)-Ib-cr ] with mutations in the quinolone resistance determining region (QRDR) (gyr A and par C) were identified in these S. Indiana isolates. Plasmid conjugation and transformation were performed in these 15 isolates. The co-existence of the mph A gene with oqx AB- bla CTX-M-65 was observed on the IncHI2 plasmid with a size of~240 kbp in 7 transformants, and these 7 transformants exhibited the resistance to azithromycin (MIC from 32 μg/mL to 64 μg/mL) and ceftriaxone (MIC≥ 256 μg/mL). The complete sequence of an IncHI2 type plasmid, p13520, was determined. An approximately 80-kbp of multidrug resistance region (MRR) comprising 29 antimicrobial resistance genes (ARGs) including mph A, oqx AB, bla CTX-M-65 , fos A3 and rmt B interspersed with different insertion sequences (ISs) (IS 26 , IS Aba1 , IS 91 , IS 1006 and IS 903B) was located on the plasmid. The typical IS26- mph A- mrx - mph R-IS 6100 transposable structure was identified in the IncHI2 plasmid of nine transformants via genome sequencing and PCR mapping, which suggested that azithromycin resistance in S. Indiana was probably due to the dissemination of the IncHI2 plasmid carrying the mph A- mrx - mph R cluster. This study highlighted the emergence of S. Indiana isolates with concurrent resistance to azithromycin, ciprofloxacin and ceftriaxone in humans and retail foods in China. This is likely due to the co-existence of mph A, oqx AB and bla CTX-M-65 carried by the IncHI2 plasmid. These findings emphasized the importance of ongoing surveillance for the prevalence and transmission of the p13520-like plasmid in S. Indiana, so as to better understand the potential threat to public health. • Azithromycin, ciprofloxacin and ceftriaxone co-resistant isolates were found. • mph A, PMQR genes with mutations in QRDR and ESBLs genes were detected. • mph A co-existence with oqx AB- bla CTX-M-65 was found on ～240 kbp IncHI2 plasmid. • IS26- mph A- mrx - mph R-IS 6100 transponson was identified in the IncHI2 plasmid. [ABSTRACT FROM AUTHOR]