A novel strategy to characterize the pattern of ß-lactam antibiotic-induced drug resistance in Acinetobacter baumannii.

Carbapenem-resistant Acinetobacter baumannii (CRAb) is an urgent public health threat, according to the CDC. This pathogen has few treatment options and causes severe nosocomial infections with > 50% fatality rate. Although previous studies have examined the proteome of CRAb, there have been no focused analyses of dynamic changes to ß-lactamase expression that may occur due to drug exposure. Here, we present our initial proteomic study of variation in ß-lactamase expression that occurs in CRAb with different ß-lactam antibiotics. Briefly, drug resistance to Ab (ATCC 19606) was induced by the administration of various classes of ß-lactam antibiotics, and the cell-free supernatant was isolated, concentrated, separated by SDS-PAGE, digested with trypsin, and identified by label-free LC-MS-based quantitative proteomics. Peptides were identified and evaluated using a 1789 sequence database of Ab ß-lactamases from UniProt. Importantly, we observed that different antibiotics, even those of the same class ( e.g. penicillin and amoxicillin), induce non-equivalent responses comprising various Class C and D serine-ß-lactamases, resulting in unique resistomes. These results open the door to a new approach of analyzing and studying the problem of multi-drug resistance in bacteria that rely strongly on ß-lactamase expression.