Clinically Isolated β-Lactam-Resistant Gram-Negative Bacilli in a Philippine Tertiary Care Hospital Harbor Multi-Class β-Lactamase Genes

Abstract

In the Philippines, data are scarce on the co-occurrence of multiple β-lactamases (BLs) in clinically isolated Gram-negative bacilli. To investigate this phenomenon, we characterized BLs from various β-lactam-resistant <i>Klebsiella pneumoniae</i>, <i>Escherichia coli</i>, <i>Acinetobacter baumannii</i>, and <i>Pseudomonas aeruginosa</i> isolated from a Philippine tertiary care hospital. The selected Gram-negative bacilli (<i>n</i> = 29) were resistant to either third-generation cephalosporins (resistance category 1 (RC1)), cephalosporins and penicillin-β-lactamase inhibitors (RC2), or carbapenems (RC3). Isolates resistant to other classes of antibiotics but susceptible to early-generation β-lactams were also selected (RC4). All isolates underwent antibiotic susceptibility testing, disk-diffusion-based BL detection assays, and PCR with sequence analysis of extended-spectrum BLs (ESBLs), metallo-BLs, AmpC BLs, and oxacillinases. Among the study isolates, 26/29 harbored multi-class BLs. All RC1 isolates produced ESBLs, with <i>bla</i>_CTX-M as the dominant (19/29) gene. RC2 isolates produced ESBLs, four of which harbored <i>bla</i>_TEM plus <i>bla</i>_OXA-1 or other ESBL genes. RC3 isolates carried <i>bla</i>_NDM and <i>bla</i>_IMP<i>_,</i> particularly in three of the metallo-BL producers. RC4 <i>Enterobacteriaceae</i> carried <i>bla</i>_CTX-M, <i>bla</i>_TEM, and <i>bla</i>_OXA-24-like, while <i>A. baumannii</i> and <i>P. aeruginosa</i> in this category carried either <i>bla</i>_IMP or <i>bla</i>_OXA-24. Genotypic profiling, in complement with phenotypic characterization, revealed multi-class BLs and cryptic metallo-BLs among β-lactam-resistant Gram-negative bacilli.