الفهرس 
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Abstract
Continuous emergence of resistant bacteria become a significant global health issue. It poses a threat for treatment of infectious diseases in animals and humans. The present study investigated the occurrence of Salmonella resistant to extended-spectrum cephalosporins (ESCR) and to carbapenems (CR) in farmed chickens as well as in retailed chicken giblets and the surrounding environments. Furthermore, this study examined two important questions. First, whether, resistance to ESCR in Salmonella is mediated by extended-spectrum β-lactamases (ESBL), cephalosporinase (AmpC), and/or carbapenemases. Second, whether, resistance to ESC and carbapenems in Salmonella is associated with presence of the outer membrane protein A- (ompA) and absence of the outer membrane porin F- (ompF) encoding genes. Cloacal swabs (n = 301) were collected from chickens raised in poultry farms located in Cairo, Giza, and Al Qalyubia governorates. These were cultured for Salmonella, serotyped, and examined for susceptibility to ESC and carbapenems. Salmonella were isolated from 20 chickens, which belong to serotypes with public health significance like Typhimurium, Kentucky, and Infantis. The 20 isolates were ESCR, among them 16 were ESBL-producing, 3 were non-ESBL-producing, 1 was not tested for ESBL production as it shows resistance only to cefpodoxime. The 16 ESCR ESBL-producing isolates carry predominantly the ESBL ”blaTEM and blaSHV”; whereas, the 3 ESCR non-ESBL-producing isolates carry the AmpC blaCMY-2. Interestingly, the ESCR isolate not confirmed to be ESBL-producing, harbors blaCMY-2. The 20 isolates were carbapenem-susceptible and did not carry any of the tested carbapenemase (blaKPC, blaNDM, blaOXA48). All the 20 isolates carried the virulence genes invA, stn, and svpC. Partial stn sequencing of the ESCR ESBL-producing isolates revealed high genetic relatedness to Salmonella strains from patients in Egypt and Asia. This raised the question to whether ESCR and CR Salmonella strains can occur in retailed chicken products and poultry shops. Samples were obtained from chicken giblets (n=129), water used for cleaning the chicken carcasses (n=7), and workers at poultry shops (n=16) located in Giza governorate. Salmonella was isolated from 13 giblets, the isolates belong to different serotypes and were all ESCR. Of them, 4 were ESBL-producing CR; 1 ESBL-producing carbapenem-susceptible; 6 non-ESBL CR; 2 non-ESBL producing carbapenem-susceptible. All the 5 ESCR ESBL-producing isolates carried blaCMY-2 and ESBL genes, but did not carry carbapenemases. The 6 ESCR non-ESBL CR strains harbored ESBL genes, with 5 of them carried also blaCMY-2 and blaKPC. However, the 2 non-ESBL-producing carbapenem-susceptible carried ESBL-genes and blaCMY-2. Regarding the examined water, Salmonella was isolated from 2 samples. Both samples were ESCR non-ESBL-producing CR harbored ESBL genes and blaKPC; while only one isolate carried blaCMY-2. Interestingly, Salmonella were isolated from two workers and the isolates showed similar resistance phenotype and genotype as the isolates from water. All the Salmonella strains isolated from the tested chicken farms and the retailed poultry shops carried ompF, with predominant presence of ompA. In conclusion, isolation of virulent ESCR ESBL-producing Salmonella from farmed chickens. They carry ESBL genes as well as chromosomal and plasmid virulent genes. Those isolates genetically relate to human strains and belong to serotypes incriminated in food outbreaks. Occurrence of ESCR- and CR- Salmonella in retailed poultry shops, pose a risk of wide dissemination of such strains in the food chain and the surrounding environment. The presence of ompA might play a role in the resistance of Salmonella to β-lactam antibiotics. In contrast to studies in E. coli and Acinetobacter baumanni, the current study could not confirm a role of ompF in susceptibility of Salmonella to β-lactam antibiotics.