Evaluation of lemon grass essential oil against colistin-resistant Escherichia coli isolated from raw milk

Escherichia coli (E. coli), a member of the Enterobacteriaceae family, is a Gram-negative, flagellated, rod-shaped bacterium. This study was designed to specifically isolate and identify E. coli from raw/fresh milk collected from various local markets in Faisalabad, determine its prevalence, characterize the colistin resistance gene (mcr-1), and assess lemongrass essential oil as an alternative strategy against colistin-resistant Gram-negative bacteria. A total of 100 samples of raw milk were procured from different locations and then transferred to the Government College University, Faisalabad's Research Postgraduate Laboratory. To isolate bacteria, all milk samples were processed on MacConkey agar. After an overnight incubation at 37°C, the growth was noticed and confirmed by re-streaking on Eosin-Methylene Blue agar. Out of the 100 samples, 60 samples were subjected to bacterial growth, and of those, 32 were identified as E. coli. Biochemical characterization, including catalase, oxidase, triple sugar iron (TSI), gas production, H₂S, and indole tests, was carried out for confirmation of E. coli. Antibiotic susceptibility testing revealed that 54% of the isolates were sensitive to ciprofloxacin and 46% to gentamicin, while resistance was notably observed against amoxicillin (50%), cefixime (48%), and cefoxitin (49%). At the 100% concentration of lemongrass essential oil, the maximum inhibition zone observed was 44 mm. In conclusion, lemon grass essential oil can be used as an alternative to treat the colistin-resistant E. coli. Lemongrass essential oil demonstrated notable in vitro activity against colistin-resistant E. coli, indicating preliminary potential as a source of antibacterial compounds. These findings are limited to laboratory conditions; in vivo validation and clinical studies are required before any therapeutic application can be considered.