THE EFFECT OF COMBINATION OF LEVOFLOXACIN AND MEROPENEM ON ESCHERICHIA COLI BA ATCC 254389

This study assessed the antimicrobial activity of Meropenem and Levofloxacin, individually and in combination, against Escherichia coli BA ATCC 254389 and evaluated biochemical variations between wild-type and mutant strains. E. coli is a major Gram-negative pathogen associated with urinary tract infections, pneumonia, sepsis, and gastrointestinal diseases, and rising antibiotic resistance has made treatment increasingly difficult. The organism was confirmed through cultural, morphological, and biochemical tests. Minimum inhibitory concentrations (MICs) for Meropenem and Levofloxacin were determined, and their interaction was assessed using the fractional inhibitory concentration index (FICI). Results showed MICs of 64.0 µg/ml for Meropenem and 8.0 µg/ml for Levofloxacin, indicating greater susceptibility to Levofloxacin. When combined, Meropenem (32.0 µg/ml) and Levofloxacin (16.0 µg/ml) produced a FICI of 4.0, demonstrating antagonism and reduced effectiveness compared to individual activity. Biochemical comparison revealed that the mutant strain lost lysine decarboxylase, urease, and arabinose activity, but gained phenylalanine deaminase, Voges–Proskauer positivity, and the ability to ferment mannitol, sucrose, and raffinose. The findings showed that Levofloxacin was more effective than Meropenem against E. coli, while their combination resulted in antagonism. Antibiotic exposure produced significant biochemical shifts in the mutant strain, highlighting the adaptive potential of E. coli and the importance of careful evaluation of antibiotic combinations to prevent reduced therapeutic efficacy and resistance development.