Comparative in-vitro study of killing activities and morphological changes of Cefpirome, Cefepime, Imipenem and Meropenem alone and in combination against gram negative bacteria

Abstract

The beta-lactam antibiotics are generally regarded as the bactericidal agents. the mechanism of action is inhibiting of the enzymes in late stage of peptidoglycan synthesis namely Penicillin binding proteins (PBPs). The inhibitions of PBPs cause morphological changes lead to bacteriolysis and cell death. The relationship among PBPs, morphological changes and bactericidal activities by the beta-lactam antibiotics has been evaluated in this research. Cefpirome, Cefepime, Imipenem and Meropenem were tested against susceptible strain of P. aeruginosa, E. cloacae and E. coli by time kill method. Cefpirome and Cefepime demonstrated bactericidal properties to E. coli from 4 MIC, whereas E. cloacae showed regrowth to both drugs in concentration range from 1/4MIC-128MIC after 24 hours of exposure. For morphological changes both drugs established the filamentous cell on both Enterobacteria, which related to PBP3 binding as primary target of Cephalosporins. Interestingly, Cefepime above 32MIC manifested filamentous with bulbous cells that correlated to PBP3 and PBP2 binding with an increase of bactericidal property. Imipenem and Meropenem exerted bactericidal property to E. coli above concentration 1MIC-2MIC, whereas P. aeruginosa required concentration up to 4MIC for this propertry after 24 hours of exposure. For morphoiogical changes, both drugs established ovoidal cells that related to PBP2 binding as primary target of Carbapenems while Meropenem required concentration above 32MIC to establish the filamentous with bulbous cells that connected to PBP2 and 3 binding in E. coli. For synergy determination, the combination between Cefpirome (PBP3 attacker) and Imipenem (PBP2 attacker) at 1/4MIC and 2MIC was done in E.coli. The synergism was detected in 1/4MIC combination, whereas the regrowth was observed in both combinations after 24 hours of exposure. Thus, it can be concluded that drug's concentrations attacked to many types of essential PBPs, can increase bactericidal properties and morphological changes of the susceptible bacteria.