Determination of minimum inhibitory concentration is more informative than disc diffusion for decision making purpose: A study on the cases of urinary tract infection from a tertiary care hospital of eastern India

Abstract

Background: Urinary Tract Infection ranks second among the hospital acquired infections after respiratory tract infections in adults, a major section of which is treatable by oral antimicrobials. Objectives: Detection of prevalent uropathogens in adults and comparison of minimum inhibitory concentration of apt oral antimicrobials by disc diffusion and micro-broth dilution methods, to assess the effect on reporting and detection of antimicrobial resistance. Methods: Samples from suspected urinary tract infection cases from outdoor and indoor departments of a medical college hospital were included in this prospective observational study following exclusion and inclusion criteria. Isolates were processed as per standard conventional techniques. Antimicrobial susceptibility test (AST) and detection of minimum inhibitory concentration were done by both dilution and diffusion methods following the international and national guidelines. Data had been summarized by simple descriptive statistics with 95% Confidence Interval (CI) for selected results. The extent of agreement between different methods of susceptibility technique was assessed using Chi-square test and p-value calculation using www.vssarstat.net Result: Out of 506 culture-confirmed adult urine samples only 318 were included in the study. Escherichia coli was the commonest isolate followed by Klebsiella spp. The asynchrony of results between the two methods of AST was compared by statistical methods. For E. coli and Klebsiella spp., AST patterns were similar for nitrofurantoin, levofloxacin, cefuroxime, fosfomycin (for E. coli), where methods could not be used interchangeably. The pairs of levofloxacin-Pseudomonas aeruginosa, cefuroxime –Proteus mirabilis cannot be tested by alternative methods; whereas; those of Enterococcus faecalis and nitrofurantoin, levofloxacin and fosfomycin; as well as Staphylococcus spp. including CoNS and levofloxacin can be. However, nitrofurantoin needs to be tested separately for Staphylococci. Conclusion: Oral antibiotics for treatment of UTI needed testing by different methodology in order to obtain exact results. Validity of extrapolation of results did not hold true for all cases.

Keywords

• uropathogens
• mic
• oral antimicrobials
• broth dilution