Antimicrobial resistance and virulence gene profiling of Salmonella Agona isolated from patients with diarrhea

Abstract

Objective To investigate the antimicrobial resistance, molecular phenotypes, virulence gene profiles of Salmonella Agona (S.Agona) isolated from patients with acute diarrhea, and to better understand its epidemic trend, prevention and treatment. Methods Clinical data and stool samples of patients with acute diarrhea during April to October in 2013 and 2014 from the Second Hospital of Tianjin Medical University were collected. Enrichment culture, biochemical identification and serotyping analysis were used to isolate and identify S. Agona strains. The isolated strains were further analyzed with antibiotics susceptibility test, pulsed field gel electrophoresis (PFGE), multiple locus sequence typing (MLST), Quinolone resistance determining region (QRDR). Plasmid-mediated quinolone resistance (PMQR) and β-lactamases genes (TEM, SHV, OXA, and CTX-M) were amplified by polymerase chain reaction (PCR) and sequencing. The representative genes carried by Salmonella pathogenicity islands (SPI) 1—6, 9—12 and virulence plasmids were amplified by PCR. And the clinical characteristics of S. Agona infection were analyzed. Results Among 119 non-repetitive (non-typhoidal salmonella, NTS) isolates during the two years, eight isolates (6.7%) of S. Agona were identified. The resistance rate of S. Agona strains to streptomycin was 100.0%, those to ampicillin and gentamicin were 62.5%, to levofloxacin, ciprofloxacin and nalicixic acid were 25.0%, to chloramphenicol, amoxillin/clavulanic acid and piperacillin tazobactam were 12.5%. The strains were susceptible to other drugs. All 8 isolates had the identical ST13 genotype. PFGE showed 5 clones, and 4 out of 5 isolates had the exact same patterns of PFGE and drug susceptibility. Two (fluoroquinolones, FQ) resistant strains carried gyrA mutation leading to amino acid substitutions at position 87 in GyrA, and no PMQR genes was detected, while one of which was sensitive to ciprofloxacin by K-B method. All five ampicillin-resistant isolates were positive for TEM-1b gene and one isolate of them was resistant to β-lactam/β-lactamase inhibitor complex. The representative genes carried by SPI 1—6, 9, 11, 12 (hilA, sseL, mgtC, siiE, sopB, pagN, bapA, pagC and sspH2) were 100.0% positive, while the genes carried by SPI10 (sefA) virulence plasmids (spvB, prot6E) were negative. Two patients with FQ resistant strains infection were clinically diagnosed with bacillary dysentery, and the remaining six cases with FQ susceptible strains infection were clinically diagnosed with acute gastroenteritis. Conclusions FQs-resistant and multi-drug resistant S. Agona isolates have emerged in clinical settings. These isolates carry a variety of virulence genes. Resistance to FQ of S. Agona may cause more severe illness. ST13 might be the dominant genotype of S. Agona in China, and we should try to prevent the infection outbreak of S. Agona. Key words: Salmonella Agona; Antimicrobial resistance; Multiple locus sequence typing; Pulsed field gel electrophoresis; Infection outbreak; Salmonella pathogenicity islands