Fosfomycin susceptibility in multidrug resistant uropathogens: A retrospective study in the era of antimicrobial resistance.

Background: Urinary tract Infection is one of the most prevalent clinical entities affecting people worldwide. The accelerating rate of antimicrobial resistance due to the unimpeded and rampant use of antimicrobials with over the counter availability of drugs has limited the therapeutic options for the treatment of UTI. Fosfomycin, an old broad spectrum antimicrobial with good pharmacokinetics have regained the importance for the treatment of multidrug resistant (MDR) isolates. The purpose of this study was to determine the in vitro Fosfomycin susceptibility of common uropathogens and to study the resistance pattern of these organisms against commonly prescribed antimicrobial agents.

Material and methods: A retrospective cross-sectional study was conducted in the Bacteriology section of the Microbiology laboratory at Adesh Institute of Medical Sciences and Research, Bathinda, Punjab, for duration of 6 months from Dec 2022 to May 2023 from urine samples received from all clinically suspected cases of UTI. Samples were processed immediately as per standard microbiological techniques, followed by culture by a semi-quantitative method. Kass criteria were followed for interpretation of significant bacteriuria according to which significant growth was considered if colony count was more than equal to 10⁵ colony forming unit (CFU)/mL. Culture positives were analysed by gram staining and on the basis of colony characteristics, gram staining, final identification, and antimicrobial susceptibility were done via Vitek 2 compact system.

Results: A total of 2292 urine samples received in the Microbiology laboratory were processed and cultured during the study period, which yielded 509 significant bacterial isolates, i.e. 509/2292 (22.2%) culture positivity. Among 509 culture positive samples, Escherichia coli 235/509 (46.1%) was the most common uropathogen isolated followed by Klebsiella pneumoniae 107/509 (21.1%), Enterococcus species 40/509 (7.8%). Fosfomycin depicted good in vitro susceptibility of minimum 94% in both gram negative and gram positive uropathogens as compared to nitrofurantoin that showed sensitivity of 74% and 85%, respectively. Maximum resistance was observed towards cephalosporins, i.e., ceftriaxone in Escherichia coli (60%) and Klebsiella pneumoniae (64%) respectively followed by 50% in Acinetobacter baumannii. Maximum resistance to ciprofloxacin (62%) was seen in case of Acinetobacter baumannii. 172/405 (42.4%) isolates of Enterobacteriaceae family were extended spectrum β lactamase (ESBL) producers with an average Fosfomycin susceptibility of 95.9%. Among the total isolated uropathogens, 135/509 (26.5%) were multidrug resistant, out of which 116/135 (85.9%) depicted Fosfomycin susceptibility. Metallobetalactamase (MBL) production was seen in 14.3% of the isolated gram negative uropathogens. 63/73 (86.3%) of the MBL producers were found susceptible to Fosfomycin.

Interpretation and conclusion: Fosfomycin has emerged as an effective alternative for the treatment of common uropathogens including the MDR's, ESBL producers and the MBL's in the era of increasing antimicrobial resistance. It has the potential to act as a promising oral agent for the treatment of UTI in both community and healthcare setups.