Prevalence of 16S rRNA Methylation Enzyme Gene armA in Salmonella From Outpatients and Food

Abstract

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.

Keywords: Salmonella; armA; multi-drug resistant; poultry; swine.

FIGURE 1

Generated dendrograms showing the cluster analysis of XbaI-digested PFGE patterns of the armA-harboring Salmonella strains isolated in this study.

FIGURE 2

Conjugation rates of the armA-harboring plasmids isolated in this study. All 45 detected armA-harboring Salmonella strains were used as the donors, and either E. coli J53 or A. baumannii was used as the recipient. Black circles show the 1/abs (log₁₀ transformation of the transfer frequency) data.

FIGURE 3

The ability of the different Salmonella serotype strains to obtain an armA-carrying plasmid. Three S. Derby strains, five S. Enteritidis strains, four S. Typhimurium strains, four naturally armA-negative S. Indiana strains, and three S. Indiana strains in which the armA-carrying plasmid was artificially eliminated were used as recipients, and three E. coli J53 strains with different lengths of armA-carrying plasmid (∼140 kb: green triangles, ∼220 kb: red circles, and ∼300 kb: blue squares) were used as donors.