**6. Antimicrobial resistance in poultry food chain**

The practice of using antimicrobials in food animals is rigorous, it may be either for growth promotion, prophylactic, therapeutic or metaphylactic reasons and this results in MDR. In poultry sector, the use of antimicrobials as growth promoters, such as bambermycin, bacitracin, chlortetracycline, penicillin, tylosin, fluoroquinolones and cephalosporins is concerning [56]. Consumption of low doses of antibiotics in poultry feed for rapid poultry growth is a general practice. Use of antibiotics not only kill majority of the gut microbiota, but, some resilient bacteria survive and become resistant. Over time, these resistant bacteria transfer antibiotic resistant genes to other susceptible microbial population. The situation is crucial in developing countries where laws to control the sale and use of antibiotics are not strict. For therapy, antimicrobials like erythromycin, fluoroquinolones, gentamycin, neomycin, penicillin, spectinomycin, tetracyclines and tylosin are commonly used in poultry [56]. The minimum time period from administering the last dose of medication to the production of meat or other animal-derived products for consumption purpose is referred to as withdrawal period. The withdrawal period for antimicrobials should be followed strictly, in order to prevent the detrimental effects of drug residues in food. There are numerous programmes to reduce the flow of foodborne pathogens from animals to humans, for instance programs for meat and poultry inspection, Hazard Analysis Critical Control Point (HACCP) system and standard operating procedures for sanitation.

The drug-resistant bacteria can be present anywhere, in various environmental samples, farms, and retail meat products. *S.* Enteritidis (88%) isolated from hatching eggs, litter, feed, drinkers, bird rinse, and ceca, were reported to be resistant to drugs, ampicillin, nalidixic acid, and tetracycline [57]. There is a frequent isolation of *Salmonella* serovars such as *S.* Enteritidis, *S.* Infantis, *S.* Typhimurium, and *S.* Heidelberg from broiler carcasses. The antibiotic-resistant *Salmonella* isolates has been found from poultry chiller water and carcasses. The isolated *Salmonella* were resistant to antibiotics including tetracycline, ampicillin, amoxicillin-clavulanic acid, ceftiofur, streptomycin, and sulfisoxazole. Broiler farms with *Salmonella* isolates resistant to multiple antibiotics, i.e. streptomycin (30.9%), gentamicin (12.6%), sulfadimethoxine (20.9%), tetracycline (13.9%), and trimethoprimsulfamethoxazole combination (8.6%) were recovered. Among these isolates, 67% of *S.* Heidelberg and 54% of *S.* Kentucky isolates showed resistance to five or more antibiotics [11]. These serovars have a high resistance towards ceftriaxone and ceftiofur antibiotics. It has been observed that conversion of conventional farms to organic farms can reduce the prevalence of antibiotic resistant *Salmonella* from 44% to 6% [58]. A comparison between the *Salmonella* isolates obtained from poultry samples of Maryland retail shop from conventional and organic farms revealed that conventional carcass samples were resistant for five to seven antimicrobials, whereas 79% of the isolates from organic carcass samples were susceptible to all 17 tested antimicrobials. Assessment of the status of poultry retail shops is necessary, as in many countries, people prefer to procure the freshly slaughtered chicken. In such retail shops, the likelihood of cross-contamination of poultry carcasses is high and MDR-*Salmonella* has been isolated from retail meat shops as well. The Food and Drug Administration (FDA) have reported the National Antimicrobial Resistance Monitoring System (NARMS), regarding retail meat interim report for *Salmonella*, which includes the antibiotic resistance profile of *Salmonella* sp. in retail poultry meat [59]. The retail meats show high resistance to the common antibiotics such as tetracycline, streptomycin, sulfamethoxazole, and ampicillin.

### **7. Diagnosis**

*Salmonella* diagnosis requires isolation of bacterium from the clinical samples and its culture in suitable culture media. The most common selective media used for *Salmonella* are SS agar, bismuth sulfite agar, Hektoen Enteric (HE) medium, Brilliant Green agar and Xylose-Lysine-Deoxycholate (XLD) agar. To further confirm diagnosis, biochemical, and serological tests are employed. The biochemical tests include sugar fermentation test, decarboxylation and dehydrogenation reactions, and hydrogen sulphide production. Serological examinations are usually carried out in outbreaks. Suffering from any other ailments makes diagnosis more cumbersome such as in cases of HIV-infected adults [60]. Hence, development of a rapid and sensitive diagnostic test is the need of the hour. A multiplex PCR has been found to be useful to identify NTS i.e. *S.* Typhimurium and variants, *S.* Enteritidis, *S.* Dublin and *S.* Stanleyville with 100% sensitivity and specificity [61]. Presence of low number of bacilli in clinical specimen is a limitation to this. So, to detect low infective loads of NTS, a microwave-accelerated metal-enhanced fluorescence (MAMEF) technique has been developed [62], which is well efficient enough to detect as little as 1 CFU/ml in less than 30 seconds. But, this still needs wider field applicability. A well defined ELISA with a definitive cut-off has not yet being commercialized for detection of NTS. But several researchers have suggested the use of lipopolysaccharide antigens from *S.* Enteritidis (serogroup D) and *S.* Typhimurium (serogroup B) for NTS detection [63].
