Characterization of Two Novel AmpC Beta-Lactamases from the Emerging Opportunistic Pathogen, .

The genus (family ) causes a wide spectrum of acute infections in immunocompromised hosts, from pneumonia and bacteremia to oral ulcers and dialysis-related peritonitis. While infections are reported infrequently in the literature, documented clinical cases of this emerging opportunistic human pathogen have occurred worldwide. has clinical significance and exhibits antimicrobial drug resistance. However, little is known about the molecular basis underlying the resistance phenotypes in . We previously hypothesized that the open-reading frame in the SSMD04 genome encodes a chromosomal Ambler class C (AmpC) β-lactamase based on sequence homology. In this study, recombinant polyhistidine-tagged proteins were created by cloning the putative genes from SSMD04 and ATCC 33855 (a clinical isolate) into the pET-6xHN expression vector, overexpressing the proteins, and then purifying the recombinant AmpCs (rAmpCs) using immobilized metal affinity chromatography (Ni-NTA). The in vitro enzymatic analysis of the purified rAmpCs was performed to determine the and for various β-lactam substrates. The rAmpCs are functional class C β-lactamases when assayed using the chromogenic β-lactamase substrate, nitrocefin. The presence of functional AmpCs in both strains underscores the necessity of performing antibiotic susceptibility testing in the management of infections.