Antimicrobial susceptibility of E. coli isolated from dairy cow milk in Egypt and antibacterial activity of selected nanomaterials against MDR strains.

Escherichia coli (E. coli) is a significant livestock and foodborne pathogen. This study was designed to isolate E. coli from raw cow milk, evaluate its antimicrobial susceptibility, and investigate the antimicrobial activity of silver nanoparticles (nAg), zinc oxide nanoparticles (nZnO), and Moringa nano-emulsion (MNE) against multidrug resistant (MDR) strains. A total of 146 individual milk samples were obtained from dairy cows in Egypt. E. coli were isolated by standard culture methods and pathotyped using molecular techniques. The antibiotic resistance of the isolates was determined, and the antimicrobial activity of the selected nanomaterials was evaluated using the broth microdilution method on the identified MDR strains. E. coli was detected in 54.8% (80/146) of the samples; 42 out of 80 (52.5%) were virulent strains, including STEC (15/42; 35.7%), ETEC (12/42; 28.57%), EPEC (12/42; 28.57%), and AE-STEC (3/42; 7.1%). The isolated strains showed the highest resistance rate to sulfa-trimethoprim (52.5%), tetracycline (45%), and ampicillin (42.5%); and the lowest against marbofloxacin (8.75%) and ceftiofur (27.5%). Overall, 42.5% of the E. coli strains exhibited MDR, including virulent and non-virulent strains at 45.2% (19/42) and 39.47% (15/38), respectively. The minimum inhibitory concentration (MIC) values against MDR E. coli isolates were lowest for nAg (1.56-12.5 µg/mL), followed by nZnO (12.5-50 µg/mL). In contrast, Moringa nano-emulsion (MNE) requires much higher concentrations (125-250 µg/mL) for growth inhibition. Raw cow milk is a potential source of pathogenic and MDR E. coli, emphasizing continuous surveillance and prudent antimicrobial use. Although selected nanomaterials showed consistent in vitro efficacy, further studies are required before considering practical veterinary applications.