In-vitro Susceptibility of Fosfomycin Against XDR ndash; Klebsiella pneumoniae Isolated from Urine

Background: Managing infections caused by extensively drug-resistant (XDR) or multidrug-resistant (MDR) Klebsiella pneumoniae poses a significant challenge in hospitals and medical centers. Objectives: The present study investigated the efficacy of common and older antibiotics, including fosfomycin and colistin, among clinical isolates of K. pneumoniae. Methods: In this cross-sectional study, 43 XDR K. pneumoniae isolates were obtained from 215 urine samples collected at Milad Hospital, Tehran, Iran, between September 2023 and November 2024. Antimicrobial susceptibility testing against fosfomycin and other antibiotics was performed using the disk agar diffusion test in accordance with CLSI recommendations. Susceptibility to colistin was determined using colistin broth disk elution and chromogenic agar. The presence of mgrB, bla VIM, bla NDM, bla KPC, bla OXA-48, and bla IMP genes was identified using polymerase chain reaction (PCR). Results: The incidence rates of imipenem (IMP) and meropenem (MEM) resistance in K. pneumoniae isolates were 90.7% and 93%, respectively. The prevalence of bla IMP, bla VIM, bla KPC, and mgrB was 25.6%, 8%, 69.8%, and 93%, respectively. No bla NDM or bla OXA-48 genes were detected. The rates of sensitivity to fosfomycin and colistin were 39.5% and 7.1%, respectively. Additionally, 32.6% of K. pneumoniae isolates were intermediate to fosfomycin. Conclusions: The high rate of resistance to colistin and most other antimicrobial agents among our K. pneumoniae isolates must be considered due to the potential for antibiotic treatment failure and increased mortality and morbidity in elderly patients in healthcare settings. The relatively low rate of susceptibility to fosfomycin suggests the need for using another appropriate antibiotic in combination with fosfomycin for effective treatment of urinary infections.