Aim: The aim of this study was to determine the relationship between phenotypic resistance and genotypic resistance of isolated serotyped pathogenic Escherichia coli isolates from the clinically diseased broiler.

Materials and Methods: A total of 160 samples (heart, liver, kidney, and lung) were collected from 18 to 34 days old clinically diseased broiler from 40 broiler farms (3-5 birds/farm) reared in Giza and Kaluobaia Governorates for the isolation of pathogenic E. coli. Various E. coli isolates were tested for the pathogenicity based on Congo red (CR) dye binding assay. The obtained CR-positive E. coli isolates were subjected to serological identification using slide agglutination test. Disc diffusion test was used to study the sensitivity pattern of E. coli isolates to available 12 antibiotics. Polymerase chain reaction was performed for the detection of antimicrobial resistance genes in the studied pathogenic E. coli isolates.

Results: The results revealed that 56 samples (35 %) were positive for E. coli. The results of the CR assay indicates that 20 isolates of 56 (35.7%) were positive and 36 isolates (64.3%) were negative. Identified E. coli serotypes of CR-positive isolates were 1 (O24), 2 (O44), 2 (O55), 5 (O78), 2 (O86), 1 (124), 3 (O127), 1 (O158), and 3 untyped. Resistance rate in disc diffusion test was 85% to oxytetracycline and kanamycin; 80% to ampicillin (AMP), clindamycin, and streptomycin (S); 75% to enrofloxacin; 65% to chloramphenicol; 55% to cefotaxime and gentamicin (CN); 45% to trimethoprim+sulfamethoxazole; 35% to erythromycin (ERI); and 30% to oxacillin. All strains are multidrug-resistant (MDR). Antibacterial resistance genes CITM, ere, aac (3)-(IV), tet(A), tet(B), dfr(A1), and aad(A1) were detected in 14 (70%), 12 (60%), 12 (60%), 8 (40%), 11 (55%), 8 (40%), and 9 (45%) of tested 20 isolates, respectively. Multidrug resistance was detected in the form of resistance to 42%-83.3% of tested 12 antibiotics. Three isolates (15%) of 20 tested isolates showed a relationship between phenotype and genotype and 17 (85%) showed irregular relation. Strains are sensitive and show resistant gene (P-G+) presented in three isolates for AMP (beta-lactam), one for ERI (Macrolide), as well as five isolates for trimethoprim (pyrimidine inhibitor). E. coli isolates had resistance and lacked gene (P+ G-) reported meanly in one isolate for CN (aminoglycoside), two isolates for tetracycline, four isolates for ERI, seven isolates for trimethoprim, and eight isolates for S (aminoglycoside).

Conclusions: The study demonstrates that E. coli is still a major pathogen responsible for disease conditions in broiler. E. coli isolates are pathogenic and MDR. Responsible gene was detected for six antibiotics in most of the isolates, but some do not show gene expression, this may be due to few numbers of resistance genes tested or other resistance factors not included in this study.

Keywords: antibiotic resistance genes, broiler, Escherichia coli, isolation.

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