Structure and Functional Characterisation of a Distinctive β-Lactamase from an Environmental Strain EMB20 of Bacillus cereus

Abstract

The rampant use and misuse of antibiotics in human medicine, agriculture and veterinary have become the key contributors to global antimicrobial resistance. One of the significant resistance mechanisms that inactivates antibiotics and impedes treatment of bacterial infections is the expression of β-lactamases. Rising evidence of newer variants of β-lactamases in the environment is therefore a serious threat to the presently available antibiotic armoury. The present work describes the purification of a variant β-lactamase isolated from a soil strain EMB20 of Bacillus cereus. The lactamase was purified using three-phase partitioning and gel filtration chromatography to a 30-fold purification and 15% recovery yield. Contrary to the general trend, the lactamase was not a metalloenzyme, but its activity was enhanced in the presence of Mg²⁺ and Mn²⁺. The EMB20 lactamase exhibited improved stability against inhibitors and denaturing agents such as urea and GdmCl as compared to its commercial analogue. The improved stability of EMB20 lactamase was further validated by circular dichroism and fluorescence spectroscopy. This study reemphasizes the rising prevalence of environmental lactamase variants. Decoding the structure-function correlation of such lactamases in the presence of inhibitors will provide insights into the response of this enzyme towards inhibitors as well as its substrates.

Keywords: Antimicrobial resistance; Circular dichroism; Fluorescence; Lactamase inhibitors; Three-phase partitioning chromatography; β-Lactamases.