The consequences of a sudden demographic change on the seroprevalence pattern, virulence genes, identification and characterisation of integron-mediated antibiotic resistance in the Salmonella enterica isolated from clinically diarrhoeic humans in Egypt

The present study was undertaken to identify and characterise integrons and integrated resistance gene cassettes among eight multidrug-resistant (MDR) Salmonella serovars isolated from humans in Egypt. Virulotyping by polymerase chain reaction (PCR) was used for the detection of the presence of virulence genes. Integron PCR was used to detect the presence of class 1 in the MDR strains. The associated individual resistance gene cassettes were identified using specific PCRs. The isolated serovars were Salmonella Grampian (C1; 2/5), Larose (C1; 1/5), Hato (B; 1/5) and Texas (B; 1/5). Among the Salmonella serovars, five Salmonella isolates showed the highest resistance to amoxicillin, ampicillin, chloramphenicol, lincomycin, gentamicin, nalidixic acid, streptomycin and trimethoprim (100 %), followed by neomycin, norfloxacin and tetracycline (80 %), while the lowest resistance was recorded to colistin sulphate and ciprofloxacin in percentages of 20 and 40 %, respectively. The inv A, avr A, ssa Q, mgt C, sii D and sop B genes were detected in all isolates (100 %), while the spv C and gip A genes were totally (100 %) absent from all isolates. The remaining three virulence genes were diversely distributed as follows: the bcf C gene was detected in all isolates except Salmonella Hato (80 %); the sod C1 gene was detected only in Salmonella Grampian and Salmonella Texas (60 %); and the sop E1 gene was detected only in Salmonella Grampian, Hato and Texas (60 %). Class 1 integrons were detected in 90 % of the MDR isolates, comprising serovars Muenster, Florian, Noya, Grampian, Larose, Hato and Texas. Of the class 1 integron-positive isolates, 45 % harboured Salmonella genomic island 1 (SGI1) either right junction or right and left junction having an A-C-S-T phenotype. Of the class 1 integron-positive isolates, 44 % harboured integron gene cassette aad A2, while 11 % harboured the flo R gene present in multidrug resistance flanked by two integrons of SGI1. The results of the present study indicate that class 1 integrons carrying gene cassettes conferring resistance mainly to aminoglycosides are widespread among the MDR Salmonella serovars isolated from humans in Egypt, indicating the important role of these genetic elements in the dissemination of multidrug resistance.