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The purpose of this study was to determine the effect of sublethal concentrations of nitrofurantoin, ciprofloxacin, and trimethoprim on biofilm formation in 57 uropathogenic Escherichia coli strains (UPEC). The minimum inhibitory concentration of nitrofurantoin, ciprofloxacin, and trimethoprim was determined and the biofilm formation for each isolate with and without sub-lethal concentrations of each antibiotic was then quantified. The statistical significance of changes in biofilm formation was ascertained by way of a Dunnett's test. A total of 22.8% of strains were induced to form stronger biofilms by nitrofurantoin, 12% by ciprofloxacin, and 19% by trimethoprim; conversely 36.8% of strains had inhibited biofilm formation with nitrofurantoin, 52.6% with ciprofloxacin, and 38.5% with trimethoprim. A key finding was that even in cases where the isolate was resistant to an antibiotic as defined by EUCAST, many were induced to form a stronger biofilm when grown with sub-MIC concentrations of antibiotics, especially trimethoprim, where six of the 22 trimethoprim resistant strains were induced to form stronger biofilms. These findings suggest that the use of empirical treatment with trimethoprim without first establishing susceptibility may in fact potentiate infection in cases where a patient who is suffering from a urinary tract infection (UTI) caused by trimethoprim resistant UPEC is administered trimethoprim. This emphasizes the need for laboratory-guided treatment of UTI. [ABSTRACT FROM AUTHOR]

Objectives: This study considers susceptibility test results obtained over a 6 month period for Enterobacteriaceae that caused urinary tract infections (UTIs) in the Cork region of Ireland and uses these results to examine the suitability of Irish empirical treatment guidelines.Patients and methods: UTI-causing Enterobacteriaceae isolates were analysed using EUCAST guidelines to determine resistance to a set of commonly prescribed antimicrobial agents, i.e. ampicillin, amoxicillin/clavulanate, cefalexin, ciprofloxacin, nitrofurantoin and trimethoprim. Patients were categorized by age and patient type, based on origin (hospital inpatients, patients in long-term care facilities and all other non-hospitalized patients). In total, 8999 test results were analysed using the IBM Cognos Analytics Series 7 interrogation tool and Microsoft Office Excel.Results: A variety of resistance patterns were observed. Only one antimicrobial agent, nitrofurantoin, demonstrated a resistance rate of less than 20% for all patient categories considered.Conclusions: Previous studies determined that a resistance rate of >20% renders an antimicrobial agent unsuitable for use as an empirical treatment option. This study demonstrated that this resistance rate is exceeded in many cases, potentially rendering some antimicrobial agents unsuitable for use as empirical treatment. We suggest that the focus on susceptibility when producing surveillance data to create empirical treatment guidelines may inadvertently camouflage resistance rates. The findings of this study highlight the need for laboratory-guided treatment of UTIs and ideally a pre-emptive sample should be obtained for laboratory investigation prior to commencement of antimicrobial therapy. [ABSTRACT FROM AUTHOR]