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Background  Beta-lactam and quinolone antimicrobials are commonly used for treatment of infections caused by non-typhoidal  Salmonella  (NTS) and other pathogens. Resistance to these classes of antimicrobials has increased significantly in the recent years. However, little is known on the genetic basis of resistance to these drugs in  Salmonella  isolates from Ethiopia.    Methods    Salmonella  isolates with reduced susceptibility to beta-lactams ( n  = 43) were tested for genes encoding for beta-lactamase enzymes, and those resistant to quinolones ( n  = 29) for mutations in the quinolone resistance determining region (QRDR) as well as plasmid mediated quinolone resistance (PMQR) genes using PCR and sequencing.    Results  Beta-lactamase genes ( bla ) were detected in 34 (79.1%) of the isolates. The dominant  bla  gene was  bla TEM, recovered from 33 (76.7%) of the isolates, majority being TEM-1 (24, 72.7%) followed by TEM-57, (10, 30.3%). The  bla OXA-10 and  bla CTX-M-15 were detected only in a single  S.  Concord human isolate. Double substitutions in  gyr A (Ser83-Phe + Asp87-Gly) as well as  par C (Thr57-Ser + Ser80-Ile) subunits of the quinolone resistance determining region (QRDR) were detected in all  S.  Kentucky isolates with high level resistance to both nalidixic acid and ciprofloxacin. Single amino acid substitutions, Ser83-Phe ( n  = 4) and Ser83-Tyr ( n  = 1) were also detected in the  gyr A gene. An isolate of  S . Miami susceptible to nalidixic acid but intermediately resistant to ciprofloxacin had Thr57-Ser and an additional novel mutation (Tyr83-Phe) in the  par C gene. Plasmid mediated quinolone resistance (PMQR) genes investigated were not detected in any of the isolates. In some isolates with decreased susceptibility to ciprofloxacin and/or nalidixic acid, no mutations in QRDR or PMQR genes were detected. Over half of the quinolone resistant isolates in the current study 17 (58.6%) were also resistant to at least one of the beta-lactam antimicrobials.    Conclusion  Acquisition of  bla TEM was the principal beta-lactamase resistance mechanism and mutations within QRDR of  gyr A and  par C were the primary mechanism for resistance to quinolones. Further study on extended spectrum beta-lactamase and quinolone resistance mechanisms in other gram negative pathogens is recommended.

antimicrobial resistance and infection control

Genetic markers associated with resistance to beta-lactam and quinolone antimicrobials in non-typhoidal Salmonella isolates from humans and animals in central Ethiopia