Effects Of Antibiotic Resistance

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1.2.2 Mechanism of antibiotic resistance
Bacteria may become resistant to various antimicrobial agents through several mechanisms. Major mechanisms of antibiotic resistance in bacteria includes : (1) modification in target site so the antibiotic cannot recognise the target; (2) enzyme production that will inactivate or modify the drug before its effect; (3) expelling or extruding the antibiotic outside the cell by one or more efflux pumps so the drug is unable to reach the target site to exert its antibacterial action; and (4) alterations in the cell membrane permeability that inhibits the access of drug into the cell (Périchon & Courvalin, 2009; Verraes et al., 2013).
Antimicrobial resistance could be intrinsic or acquired. Intrinsic resistance
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As a result, in developed countries the occurrence of antimicrobial resistance in layers is low compared to broilers (Gyles, 2008). In the USA Salmonella isolates (n=45) from eight different serovars, recovered from commercial layer farm, were characterised for antibiotic resistance profile. Thirty-five percent (16 of 45) of the Salmonella isolates were resistant to at least one antibiotic. A high percentage of the Salmonella isolates were resistant to tetracycline, ampicillin, streptomycin, and ceftiofur, whereas no resistance was detected to gentamycin, kanamycin, and nalidixic acid. Among the eight identified serotypes, S. Kentucky, untypeable, Typhimurium (var. 5- ), and Montevideo were antibiotic resistant, whereas S. Heidelberg and Senftenberg, 8, (20): Nonmotile and 8, (20):-:z6 were susceptible to all of the antibiotics tested (Li et al., 2007). Another study in the USA characterised antimicrobial resistance in Salmonella recovered from shell eggs collected from three commercial egg-processing plants. The results of this study showed that 60.1% Salmonella isolates were resistant to more than 11 antimicrobial compounds (Musgrove et al., 2006). Antibiotic resistance was predominantly found in S. Typhimurium isolates for tetracycline (63.4%), nalidixic acid (63.4%), and streptomycin (61%), whereas S. Kentucky isolates exhibited …show more content…
Poultry products are a major source of Salmonella infection in humans. In Australia, currently there are no published studies describing antimicrobial resistance pattern in Salmonella isolated from commercial egg farm or eggs. However, results from the Australian Reference Centre have shown differences in resistance pattern in Salmonella isolates recovered from egg and meat producing chickens (Australian Salmonella Reference Centre, 2009). Of the 1475 meat chicken isolates, 31, 10, 7 and 6 % were resistant to streptomycin, tetracycline, sulphonamides and ampicillin respectively. Whereas, of the 265 isolates from egg farms, 2, 4, 2 and 5% were resistant to streptomycin, tetracycline, sulphonamides and ampicillin respectively (Australian Salmonella Reference Centre, 2009). Resistance to fluoroquinolones and ceftiofur was not detected in any of the isolates tested. Multidrug resistance (resistance to 4 or more antibiotics) was observed in 3% and 0.4% of chicken meat and egg farm isolates respectively (Australian Salmonella Reference Centre, 2009; Ndi & Barton, 2011). In Australia, antimicrobial resistance in Salmonella spp isolated from poultry is low compared to other parts of the world due to the restricted use of antibiotics however, the contamination of egg and egg products remains a significant concern for the

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