Abstract
Background:
Mastitis is a common disease that affects the dairy sector globally because it not only impacts animal welfare but can also lead to significant financial losses.

Aim:
This study examined the phenotypic and genotypic profiles of the multidrug-resistant (MDR) Escherichia coli (E. coli) strains that were isolated from mastitic cows in Egypt to detect their pattern of antibiotic resistance.

Methods:
Four-hundred native breed lactating cows were evaluated to identify clinical and subclinical mastitis. A total of 100 mastitic milk samples (64 from clinical mastitis and 36 from subclinical mastitis) were collected for phenotypic isolation and identification of coliform bacteria. E. coli isolates were identified through their morphological features, Gram staining, and biochemical tests. The identified E. coli strains were examined against various antibiotics using disk diffusion methods. All E. coli strains were analyzed for the antibiotic resistance genes aadA, blaTEM, tetA, sul1, and qnrA using PCR.

Results:
Among 400 examined dairy cows, the prevalences of clinical and subclinical mastitis were 16% and 9%, respectively. Bacteriological isolation of coliform bacteria from mastitic milk samples revealed that E. coli was the most prevalent bacterium. Among 10 isolates of biochemically verified E. coli strains, 8 (80%) were MDR across 6 distinct classes of antibiotics. All recovered E. coli strains exhibited higher resistance to Amoxicillin, Cefotaxime, Sulphamethaxzole/Trimethoprim, and Tetracycline. High susceptibility was noticed to Ciprofloxaccin, Amoxicillin+Clavulinic, Streptomycin, Gentamicin, Chloramphenicol, and Colistin. The blaTEM gene is among the most common antibiotic resistance genes found in E. coli isolates (100%). Furthermore, the genotypes encoding resistance to Tetracycline (tetA), Streptomycin (aadA), and Sulfonamides (sulI) were 50%, 40%, and 50%, respectively.

Conclusion:
MDR pathogenic E. coli strains are common in mastitic dairy cows in Egypt, and preventive actions must be implemented to avoid serious public health concerns.

Key words: Antibiogram, Coliform bacteria, Dairy cows, Mastitis, Milk, Resistance genes