Occurrence, antimicrobial resistance, and molecular characterization of Salmonella enterica from chicken products and human in Wasit Governorate of Iraq

Abstract

Background: Salmonella infections are considered the most common foodborne pathogens responsible for zoonotic infections and food poisoning in humans and animal species such as birds. Antimicrobial resistance is considered a global anxiety because it causes human public health repercussions, as well as leads to an increase in animal morbidity and death.

Aim: The aims of this study are the isolation and identification of Salmonella enterica, as well as to investigate the antimicrobial susceptibility test (AST) and the molecular characteristics using polymerase chain reaction (PCR) and sequences for isolates from chicken products (eggs, livers, and minced meat) and human in the Wasit Governorate of Iraq.

Methods: A total of 300 samples (150 chicken product samples including eggs, livers, and minced meat, and 150 human fecal samples) were collected from the Wasit governorate of Iraq from January to December 2022. The bacterial isolation was done according to recommendations of ISO 6579 standard and the Global Foodborne Infections Network laboratory protocol. Serotyping test and AST were done by using 19 antibiotic agents according to the recommendations of the Clinical and Laboratory Standards Institute, 2022 by using disc diffusion susceptibility test and Vitik 2 test. Finally, the suspected isolates were confirmed using the conventional PCR method and sequencing for a unique rRNA gene.

Results: The results showed that the isolation percentage of S. enterica in chicken products was 8.66% (12% eggs, 6% livers, and 8% minced meat), while in humans it was 4.6%. Also, showed 100% of Salmonella typhi in humans. While, in chicken eggs S. typhi, Salmonella typhimurium, and Salmonella enteritidis were 50%, 33.33%, and 16.66%, respectively. Also, showed 100% of S. typhimurium in both livers and minced meat. The AST in human isolates showed resistance to Ampicillin, Cefotaxime, Ceftazidime, Cefepime, Amikacin, Gentamicin, Ciprofloxacin, Norfloxacin, and Ceftriaxone, while no resistance to Amoxicillin, Pipracillin, Ertapenem, Imipenem, Meropenem, Fosfomycin, Nitrofurantoin, Trimethoprim, Azithromycin, and Tetracycline. In chicken products, isolates were resistant with different percentages to Amikacin, Gentamicin, Tetracycline, Ciprofloxacin, Norfloxacin, Nitrofurantoin, Ampicillin, Cefotaxime, Ceftazidime, Cefepime, and Trimethoprim; while no resistance to Amoxicillin, Pipracillin, Ertapenem, Imipenem, Meropenem, Fosfomycin, Azithromycin, and Ceftriaxone. Sequencing by using rRNA gene was done for four PCR products.

Conclusion: This study showed the presence of genetic mutations for S. enterica which led to variations in the molecular characteristics, and antimicrobial drug resistance of S. enterica isolated from chicken products and humans.

Keywords: Antimicrobial susceptibility test; Chicken eggs; Molecular characterization; PCR; Salmonella enterica.

Fig. 1.. Percentages of S. enterica serotypes isolated from human and chicken products.

Fig. 2.. Gel electrophoresis (2% agarose) of the rRNA gene (865 bp and 624 bp). *Lane M: DNA ladder. *Lane N: negative control. *Lanes (1-7): DNA bands of rRNA gene of S. enterica isolated from human. *Lanes (8-20): DNA bands of rRNA gene of S. enterica isolated from chicken products.

Fig. 3.. Phylogenetic tree of sense flanking the rRNA gene of two isolates (OQ259883 and OQ259884) of S. enterica (S. typhi) isolated from Iraq during 2022, compared with the related strains documented in the Genbank. Phylogenetic analysis was conducted using MEGA 11 program.

Fig. 4.. Phylogenetic tree of sense flanking the rRNA gene of S. enterica (S. typhimurium) (OQ259885) isolated from Iraq during 2022, compared with the related strains documented in the Genbank. Phylogenetic analysis was conducted using MEGA 11 program.

Fig. 5.. Phylogenetic tree of sense flanking the rRNA gene of S. enterica (S. enteritidis) (OQ259886) isolated from Iraq during 2022, compared with the related strains documented in the Genbank. Phylogenetic analysis was conducted using MEGA 11 program.

Fig. 6.. The phylogenetic tree of sense flanking the rRNA gene of four diagnostic isolates (OQ259883, OQ259884, OQ259885, and OQ259886) with three S. enterica serovars (S. typhi, S. typhimurium, and S. enteritidis) that isolated from Iraq during 2022, and compared with the related all strains documented in the Genbank using MEGA 11 program.

Fig. 7.. Results of antibiotic susceptibility test for S. enterica isolated from chicken products.

Fig. 8.. Results of antibiotic susceptibility test for S. enterica isolated from human.