β-Lactamase diversity in Acinetobacter baumannii

Acinetobacter baumannii is a clinically important, Gram-negative pathogen responsible for a wide variety of nosocomial and community-acquired infections. Antibiotic resistance is a serious concern, as the organism has a wide variety of intrinsic resistance mechanisms, including chromosomal class C (bla_ADC) and D (bla_OXA-51 family) β-lactamases, and the ability to readily acquire additional β-lactamases. Surveillance studies can reveal the diversity and distribution of β-lactamase alleles, but are difficult and expensive to conduct. Herein, we describe an approach using publicly available data derived from whole genome sequences, to explore the diversity and distribution of β-lactamase alleles across 28,330 isolates. The most common intrinsic alleles at the time of writing were bla_ADC-73, bla_ADC-30, bla_ADC-222, bla_ADC-33, and bla_OXA-66, and the most common acquired allele was bla_OXA-23. Interestingly, only 63.0% of assigned bla_ADC alleles were encountered and the 10 most common bla_ADC and intrinsic bla_OXA alleles represented approximately 75% of their respective gene totals while dozens were extremely infrequent. Differences were observed over time and geography. Surprisingly, more distinct unassigned (i.e., lacking a bla_ADC or bla_OXA number) alleles were encountered than distinct, assigned alleles. Understanding the diversity and distribution of β-lactamase alleles helps to prioritize variants for further research, selects targets for drug development, and may aid in selecting therapies for a given infection.