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ABSTRACT
Colistin, a "last-resort" antibiotic for multidrug-resistant Gram-negative bacterial infections, has seen increasing use, leading to the emergence of colistin-resistant strains. The primary aim of this study was to investigate the prevalence of colistin-resistant Enterobacterales in composted manure samples collected from different farms in Benin City, Nigeria. This study was carried out in some selected poultry farms within Benin City, Nigeria. A cross-sectional study which involved collecting composted manure samples from each selected site using sterile containers. Samples were homogenized in buffered peptone water within 24 hours post collection from the farm. The composted manure were cultured on Mac-Conkey agar plate and incubated at 370 c for 18-24 hours. Isolates were identified based on colonial morphology, motility, lactose fermentation, Gram staining reaction and biochemical tests (indole, citrate, oxidase and urease tests) The antimicrobial susceptibility testing was performed using kirby-Bauer disc diffusion method. Broth macrodilution was used to determine minimum inhibitory concentration (MIC) of colistin in calcium enhanced muellerHinton broth (MIC ≤ 2). A total of 11 enterobacterales were isolated from 272 compost manure samples, consisting of 5 isolate of Escherichia coli, 3 isolates of klebsiella species, 2 isolate of proteus species and 1 isolate of providencia spp. Of the 5 E. coli samples isolated, 1(20%) showed collistin resistance. Of the 3 Klebsiella spp isolated none showed resistance to colistin. 2 Proteus samples were isolated, all of which showed resistance to colistin. Only one isolate of Providencia was found and showed resistance to colistin in the single isolate found. The total prevalence of colistin resistance in isolated enterobacterales was 4/11(36.4%). This study revealed a concerning prevalence of colistin resistance among Enterobacterales isolated from composted manure in Benin City, Nigeria, with resistance observed in key pathogens including E. coli, Proteus spp and Providencia spp. These findings highlight the critical role of environmental reservoirs in the spread of antibiotic resistance and underscore the potential public health implications, particularly in the context of last-resort treatments for multidrug-resistant infections.
