Relationship between Phenotypic and Genotypic Antimicrobial Resistance of Escherichia coli Isolates from Mastitic Milk

Abstract

Abstract | Bovine mastitis is the predominant problem in dairy farms worldwide which caused mainly by Escherichia coli (E. coli) as one of the main causes of what is called "environmental mastitis". A total of 68 E. coli isolates from 205 raw milk samples of Holstein cows with mastitis in different dairy farms from different governorates by bacteriological isolation and 63 by PCR were investigated for the E. coli 16S rRNA and rfbEO157 encoding gene as Shiga toxin-producing E. coli (STEC). The occurrence of E. coli O157 in mastitic cows was 3% within E. coli isolates. Molecular investigation of extended-spectrum β-lactamases (ESBLs) and plasmid-mediated AmpC β-lactamases (PABLs) encoding genes reported in all of the isolates (100%) encoded TEM-type ESBLs, none of which (0%) encoded OXAtype ESBLs, on the other hand, CTX-M-type ESBLs and SHV-type β-lactamases were encoded in 34/63 (53.9%) and 3/63 (4.7%) of the ESBL isolates, respectively and 27% exhibited CMY..-type PABLs. Plasmid-mediated colistin resistance encoding gene (mcr-1) was expressed in 1.6% of E. coli isolates. All E. coli isolates exhibited antibiotic multiresistances with higher resistance to tetracycline and Trimethoprim-Sulfamethoxazole (45.7% and 37.3%, respectively), while the lowest resistance was observed for Amoxicillin/clavulanate (10.1%). Phenotypic resistance to extendedspectrum cephalosporins (ESCs) revealed that 42.3% of these strains were resistant to (cefotaxime and cefquinome), 15% resistant to Cefoxitin, while 32.2% were resistant to ceftazidime. Conclusively, E. coli was found to be the major cause of bovine mastitis treatment failure due to the multidrug resistance to most newly developed cephalosporins (third and fourth generations).