Abstract
The objectives of this study were to evaluate the prevalence of extended spectrum β-lactamase (ESBL) genes, AmpC-type β-lactamase (ACBL) genes, and plasmid mediated quinolone resistance (PMQR) genes in Salmonella isolated at a Veterinary Medical Teaching Hospital microbiology laboratory, examine trends in presence of these resistance genes, and to explore the correlation between phenotypic resistance and presence of specific genes. The presence of ESBL, ACBL, and PMQR genes were detected using a single, novel multiplex qPCR. Only the genes blaCMY–2 and blaTEM were detected in the 110 Salmonella isolates tested. PMQR genes were not detected in isolates screened. Of 94 third-generation cephalosporin resistant isolates, representing eight serotypes, 48% (n = 45) were positive for blaCMY–2 only and 50% (n = 47) were simultaneously positive for blaCMY–2 and blaTEM. Two third-generation cephalosporin resistant isolates were tested negative for all β-lactamase genes in our qPCR assay and likely house ESBL genes not screened for by our qPCR assay. A logistic regression model revealed that for serotype Dublin isolates (n = 38) the odds ratio for testing positive for blaTEM when compared to all other serotypes was 51.6 (95% CI: 4.01–664.03, p = 0.0029). For serotype Typhimurium (n = 9) the odds ratio for testing positive for blaTEM when compared to all other serotypes was 43.3 (95% CI: 1.76–1000, p = 0.0216). Overall, our results suggest that the prevalence of resistance to cephalosporins and fluoroquinolones due to ESBLs, ACBLs, and PMQR genes present in bovine nontyphoidal Salmonella enterica isolates has remained relatively constant in the isolates screened over a 14-year period.
Highlights
In 2017, around 91 million cases of human gastrointestinal illness and diarrhea were believed to be caused by nontyphoidal Salmonella enterica (NTS) (Stanaway et al, 2019)
The goal of this study was to identify trends in resistance of fecal Salmonella isolates to cephalosporins and fluoroquinolones due to the presence of ESBL, ACBL, and plasmid mediated quinolone resistance (PMQR) genes from Salmonella isolates obtained from cattle fecal samples isolated and tested in the University of California, Davis William R
Of the 242 NTS isolates tested, 39% of isolates (n = 94) were phenotypically resistant to a 3GC and 98% (n = 92) and 50% (n = 47) of these resistant isolates were polymerase chain reaction (PCR)-positive for blaCMY−2 and blaTEM, respectively (Table 3)
Summary
In 2017, around 91 million cases of human gastrointestinal illness and diarrhea were believed to be caused by nontyphoidal Salmonella enterica (NTS) (Stanaway et al, 2019). Severe infections caused by Salmonella usually require treatment with specific recommended antimicrobials, including ciprofloxacin, azithromycin, and ceftriaxone (Centers for Disease Control and Prevention, 2019). Extended spectrum β-lactamase (ESBL) genes encode for enzymes which are able to cleave the β-lactam ring of a wide range of β-lactam antimicrobials (e.g., penicillins and cephalosporins) (Dhillon and Clark, 2012). They confer β-lactam resistance to the bacteria that produce them, primarily Klebsiella pneumoniae and Escherichia coli. AmpC-type β-lactamase (ACBL) genes encode for enzymes capable of degrading β-lactam antibiotics, including: extended spectrum cephalosporins (excluding cefepime and cefpirome), cephamycins, and ceftriaxone (Jacoby, 2009; Polsfuss et al, 2011). AmpC-type β-lactamase (ACBL) genes encode for enzymes capable of degrading β-lactam antibiotics, including: extended spectrum cephalosporins (excluding cefepime and cefpirome), cephamycins, and ceftriaxone (Jacoby, 2009; Polsfuss et al, 2011). blaCMY−2 is the most common plasmid mediated ACBL gene globally (Jacoby, 2009)
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