Characterisation of the β-lactam resistance enzyme in Acanthamoeba castellanii

Abstract

β-Lactams are well known as the best antibiotics for inhibiting the cross-linking between adjacent polysaccharide chains and peptides in the peptidoglycan layer of bacterial cell walls, causing bacterial cell lysis. There are no reports on the action of and resistance mechanisms to β-lactams in protozoa. Acanthamoeba castellanii is a free-living protozoan pathogen capable of causing blinding keratitis and fatal granulomatous encephalitis. When Acanthamoeba is exposed to harsh conditions, it differentiates into the cyst stage to avoid environmental stresses, such as drug treatment. In this study, it was shown that the mature encystation rate of A. castellanii is decreased by treatment with cefotaxime (CTX) and clavulanic acid (CLA); however, the drugs do not kill the amoeba. We hypothesise that β-lactam antibiotics may disturb synthesis of the double cell wall during the encystation process of Acanthamoeba. Interestingly, CTX is considered a powerful β-lactam, whereas CLA is considered a weak β-lactam but an efficient β-lactamase inhibitor. It was demonstrated that Acanthamoeba expresses β-lactamases to prevent inhibition of the encystation process by β-lactams. To reveal the functions of Acanthamoeba β-lactamases, a recombinant Acanthamoeba β-lactamase was produced in Escherichia coli that conferred resistance to β-lactams such as CTX, cefuroxime, penicillin and meropenem. Consequently, we suggest that Acanthamoeba produces enzymes similar to β-lactamases to avoid interference from the environment. Here we provide a new point of view on an important gene responsible for drug resistance and advocate for the development of more efficient treatment against Acanthamoeba infection.