Effect of non-β-lactams on stable variants of inhibitor-resistant TEM β-lactamase in uropathogenic Escherichia coli: implication for alternative therapy.

AIMS: β-lactamase inhibitor resistance (BLIR) among the uropathogenic Escherichia coli (UPEC) minimizes treatment options. This study aimed to identify inhibitor-resistant TEM (IRT) β-lactamase that impart BLIR phenotype and explore non-β-lactams as alternative therapeutics.

METHODS AND

RESULTS

Thirty BLIR UPEC isolates were detected by Kirby-Bauer disc diffusion technique using β-lactam-β-lactamase inhibitor combination. Conjugal transfer of BLIR was successful from 17 isolates. PCR and sequencing of the TEM β-lactamases from the transconjugants indicated 14 TEM-84 (IRT) and three novel IRT variants (pUE184TEM, pUE203TEM, pUE210TEM). Three-dimensional models of the latter were predicted and validated. Molecular docking of selected non-β-lactams (morin, catechin, naringenin triacetate) with the variants using AutoDock 4.2 showed comparable docking scores with significant hydrogen bond and hydrophobic interactions. Molecular dynamics simulation study confirmed stability of the non-β-lactams inside the catalytic pocket of the enzymes. Moreover, all three non-β-lactams were found to inhibit the purified TEM β-lactamase variants in vitro. Microbroth dilution method indicated naringenin triacetate 64 μg ml-1 in combination with ceftazidime (CAZ) 30 μg ml-1 to be most effective against the BLIR transconjugants.

CONCLUSIONS

BLIR phenotypes were primarily attributed to the production of IRT β-lactamases. Administration of the non-β-lactams with CAZ demonstrated an alternative therapeutic strategy against the IRT β-lactamase producers.

SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates high risk of transmission of IRT β-lactamases and suggests β-lactam-non-β-lactam combination therapy to combat BLIR.