Detection of β-Lactamase Activity in Various Clinical Bacterial Isolates by Three Different Methods And its Correlation with Drug Resistance

Background: β-lactams such as penicillins are the most widely used antibiotics, and β- lactamases are the greatest source of resistance to penicillins. Aims and Objectives: To study β-lactamase production in clinical isolates of family Enterobacteriaceae, P. aeruginosa and Staphylococci by three different methods and to correlate its potential with drug resistance; with an endeavour to evaluate convenient and economical method duly supported by relevant Minimum Inhibitory Concentration (MIC) studies. Material and Methods: Total 240 clinical isolates (Gram-negative bacilli-191, staphylo-coccia) were subjected to antimicrobial susceptibility testing by Kirby-Bauer disk diffusion method and MIC for ampicillin and penicillin was determined by agar dilution method. b-lactamase was detected by broth acidometric, iodometric cell suspension and microbiological method. Results: Multidrug resistance was observed in more than 90% isolates. One hundred and ninety Gram-negative bacilli were resistant to ampicillin and 47 staphylococcal isolates were resistant to both penicillin and ampi- cillin. Though microbiological method gave highest positive results 210 (87.5%), iodometric method could detect β-lactamase in apparently sensitive isolates as well giving satisfactory [207 (86.25%)] comparable results. Conclusion: In view of the noted bacte¬rial resistance, tests for b-lactamase should be carried out on a routine basis for an early imple¬mentation of appropriate antimicrobial therapy. Iodometric method is eminently convenient, economical and reliable method. Isolates showing MIC 0.125^g/ml for penicillin and MIC 8^g/ml for ampicillin should be checked for b-lactamase production