Carbapenem-induced ß-lactamase-isoform expression trends in Acinetobacter baumannii.

Carbapenem-resistant Acinetobacter baumannii (CRAb) is an urgent bacterial threat to public health, with only a few treatment options and a >50% fatality rate. Although several resistance mechanisms are understood, the appearance of these mutations is generally considered stochastic. Recent reports have, however, begun to challenge this assumption. Here, we demonstrate that independent samples of Ab, exposed to different carbapenems with escalating concentrations, show concentration- and carbapenem-dependent trends in ß-lactamase-isoform expression. This result, based on the isoforms identified through label-free-quantification LC-MS/MS measurements of cell-free, gel-separated ß-lactamases, suggests that the appearance of antibiotic resistance may be somewhat non-stochastic. Specifically, several minor AmpC/ADC ß-lactamase-isoforms were found to exhibit both dose- and carbapenem-dependent expression, suggesting the possibility of non-stochastic mutations. Additionally, these also have high sequence similarity to major expressed isoforms, indicating a potential path over which resistance occurred in independent samples. Antibiotic resistance maybe somewhat antibiotic-directed by a hitherto unknown mechanism and further investigation may lead to new strategies for mitigating antibiotic resistance. Teaser: The emergence of antibiotic-resistant ß-lactamase proteins from mutations may exhibit patterns based on specific antibiotics.

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. Thirteen proteins were identified and evaluated using a 1789 sequence database of Ab ß-lactamases from UniProt, the majority of which were Class C ß-lactamases (≥ 80%). Importantly, different antibiotics, even those of the same class (e.g. penicillin and amoxicillin), induced non-equivalent responses comprising various isoforms of 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.

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.