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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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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