Plasmid-Mediated Colistin and Fosfomycin Resistance among Clinical Isolates of ESBL- and Carbapenemase-Producing in Northern Iran.

The emergence of extensively-resistant strains of () in healthcare settings is linked to prolonged hospitalization and uncontrolled use of antibiotics. There is a paucity of data regarding the prevalence and mechanisms of colistin and fosfomycin resistance encoding genes rate and mechanisms in Iran. The objective of this study was to determine the prevalence of biofilm formation and fosfomycin and colistin resistance among strains producing ESBL and carbapenemases by detecting the , , and genes in Tehran, Iran, during the 2020-2021 period. After collecting 73 samples, the isolates were identified using biochemical tests. Antibiotic susceptibility test was performed using the disk diffusion method. The phenotypic determination of extended-spectrum beta-lactamases (ESBLs) and carbapenemase enzymes was conducted using combined disk and CARBA-NP tests, respectively. The biofilm formation was conducted using a microtiter tissue plate assay. Polymerase chain reaction (PCR) was employed to detect the , and genes,which are associated with colistin and fosfomycin resistance, respectively. The highest resistance rate was observed against ampicillin (97%), chloramphenicol (90%), and ciprofloxacin (87%), respectively.In contrast, the lowest resistance rate was noted against gentamicin (4%), amikacin (10%), and cotrimoxazole (18%). Moreover, 44 and 23 isolates were identified as ESBL and carbapenemase -producing K. pneumonia), respectively. Of the fortyeight isolates that formed strong biofilms,one was a non-biofilm producer. The PCR test revealed the amplification of the gene in four isolates and the genes in one isolate. However, no amplification of the or genes was observed. The present study demonstrated that the frequency of isolates producing ESBL and carbapenemase, as well as , and genes, was relatively low.However,given the potential for these genes to be disseminated more widely, it is imperative to implement effective isolation and control measures. Moreover, these strains demonstrated the capacity to form biofilms in vitro, which can lead to persistent infections in the hospital settings.