Molecular Characterization and Susceptibility Testing of Extended Spectrum P- Lactamase (ESBL) Producing Enterobacteriaceae
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Extended Spectrum p-lactamases (ESBLs) are produced by Escherichia coli and Klebsiella pneumoniae. ESBLs are enzymes that bind and hydrolyze p-lactam antibiotics, rendering the enzymes ineffective. The p-lactamases identified in this study were SHV-type, TEM-type, CTX-M-1, CTX-M-2, CTX-M-9, CTX-M-25, OXA-1, OXA-2 and OXA-10. In this study, 62 ESBL presumptive isolates acquired from 2010 to 2017 from hospitals in the United States were phenotypically investigated using the Broth Microdilution Minimum Inhibitory Concentration testing (MIC) assay. Results showed that 49 of the 62 isolates indicated phenotypic conformation of ESBLs. After verifying the ESBL phenotypes, the prevalence of antibiotic resistant genes was* explored by the Polymerase Chain Reaction (PCR) and gel electrophoresis. Genotypic testing showed that twelve non-phenotypic isolates, were indeed ESBLs, marking a limitation of the phenotypic ESBL MIC assay test in correctly identifying all ESBL activity in the isolates. In order to evaluate how multiple ESBLs correlated to antibiotic resistance, further MIC testing was conducted using a panel of sixteen antibiotics used by hospitals in the United States. Results indicated that higher antibiotic resistances by enterobacteriaceae are not correlated with the number of ESBLs present, but rather by the combination of ESBLs that make up the strain. A K. pneumoniae strain that was not susceptible to any test antibiotic contained TEM, SHV, and CTX-M-1 p-lactamases. A main reason for the rapid increase of bacterial ESBLs is the overuse of antibiotics in healthcare management. Therefore, it is imperative to be able to correctly assess the p-lactamases present in Enterobacteriaceae, therefore prescribing only the antibiotics that are needed.