Proteomic response of β-lactamases-producing Enterobacter cloacae complex strain to cefotaxime-induced stress

Bacteria of the Enterobacter cloacae complex are among the ten most common pathogens causing nosocomial infections in the USA. Consequently, increased resistance to beta-lactam antibiotics, particularly expanded-spectrum cephalosporins like cefotaxime (CTX), poses a serious threat. Differential In-Gel Electrophoresis (DIGE), followed by LC-MS/MS analysis and bioinformatics tools, was employed to investigate the survival mechanisms of a multidrug-resistant E. hormaechei subsp. steigerwaltii 51 carrying several beta-lactamase-encoding genes, including the 'pandemic' bla(CTX-M-15). After exposing the strain with sub-minimal inhibitory concentration (MIC) of CTX, a total of 1072 spots from the whole-cell proteome were detected, out of which 35 were differentially expressed (P <= 0.05, fold change >= 1.5). Almost 50% of these proteins were involved in cell metabolism and energy production, and then cell wall organization/virulence, stress response and transport. This is the first study investigating the whole-cell proteomic response related to the survival of beta-lactamases-producing strain, belonging to the E. cloacae complex when exposed to beta-lactam antibiotic. Our data support the theory of a multifactorial synergistic effect of diverse proteomic changes occurring in bacterial cells during antibiotic exposure, depicting the complexity of beta-lactam resistance and giving us an insight in the key pathways mediating the antibiotic resistance in this emerging opportunistic pathogen.