Comparative in-Vitro Study of Killing Activities and Morphological Changes of Cefpirome, Cefepime, Imipenem and Meropenem Alone and in Combination Against Gram Negative Bacteria

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Phisit Khemawoot
Siriporn Fungwitthaya
Nalinee Aswapokee
Surapee Tiengrim

Abstract

The β-lactam antibiotics are generally regarded as the bactericidal agents. The

mechanism of action is inhibiting of the enzymes in the late stage of peptidoglycan

synthesis namely Penicillin binding proteins (PBPs ). The inhibitions of PBPs cause

morphological changes leads to bacteriolysis and cell death. The relationship among

PBPs, morphological changes and bactericidal activities by the β -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 have demonstrated bactericidal properties in

E. coli above concentration 4MIC, whereas E. cloacae have shown regrowth to both

drugs concentration range from 1/4MIC-128MIC after 24 hours of exposure. For

morphological changes, both drugs have established filamentous cells in both

Enterobacteriaceae, which related to PBP3 binding as primary target of

cephalosporins. Interestingly, Cefepime above 32MIC has established filamentous

with bulge cells that correlated to PBP2 and 3 binding with an increase of bactericidal

property. Imipenem and Meropenem have manifested bactericidal properties in E. coli

above concentration 1MIC, whereas P. aeruginosa required concentration up to 4MIC

for this property after 24 hours of exposure. For morphological changes, both drugs

have established ovoid cells that related to PBP2 binding as primary target of

carbapenems while Meropenem required concentration above 4MIC to established the

filamentous with bulge cells that correlated to PBP2 and 3 binding in E. coli. For

synergy testing, the combination between Cefpirome (PBP3 attacker) and Imipenem

(PBP2 attacker) at 1/4MIC and 2 MIC was done in E. coli. The synergism has been

detected in 1/4MIC combination, whereas the regrowth was observed in both

combinations after 24 hours of exposure. Conclusion, drugs/concentrations that attack

to many types of essential PBPs can increase bactericidal properties and

morphological changes of the susceptible bacteria, which may be the useful data to

eradicate bacteria for clinical application.

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Section
2002 Annual Meeting Abstracts/Lectures