Plasmid-mediated colistin and fosfomycin resistance among clinical isolates of ESBL- and carbapenemase-producing Klebsiella pneumoniae in Northern Iran

The emergence of extensively-resistant strains of Klebsiella pneumoniae (K. pneumoniae) 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 K. pneumoniae strains producing ESBL and carbapenemases by detecting the mcr-1, mcr-2, and fosA 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 mcr-1, mcr-2 and fosA 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 fosA2 gene in four isolates and the mcr-2 genes in one isolate. However, no amplification of the fosA3 or mcr-1 genes was observed. The present study demonstrated that the frequency of K. pneumoniae isolates producing ESBL and carbapenemase, as well as mcr-1, mcr-2 and fosA 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.