Comparison of Therapeutic Versus Subtherapeutic Levels of Chlortetracycline in the Diet for Selection of Resistant Salmonella in Experimentally Challenged Chickens

Abstract

Sixteen broiler chicks per group were fed chlortetracycline (CTC) at 0 (control) and 55, 110, and 220 ppm (subtherapeutic levels) continuously for 44 days or 550 ppm (therapeutic level) for three 5-day periods from 1 to 19 days of age. All birds were challenged at 4 days of age with a 10:1 mixture of CTC-sensitive and resistant (CTCr) Salmonella typhimurium. Chicks were sampled periodically through postchallenge day (PCD) 41, half in each pen by cloacal swabbing and the remainder by collection of droppings. Escherichia coli was monitored at PCD 6 and 34. Salmonella recovery from cloacal swabs indicated increased (P less than .05) prevalence of CTCr salmonella-positive birds in the 550 ppm treatment at PCD 6 and 13 compared to all other treatments, and at PCD 27 compared to 0, 55, and 110 ppm CTC. Mean recovery scores followed a similar pattern. Area under the curve analysis of CTCr salmonella scores from cloacal swabs for PCD 3 to 41 confirmed increased (P less than .05) selection for CTCr salmonella by 550 ppm CTC. Isolations from droppings showed increased (P less than .05) CTCr salmonella prevalence at PCD 20 for the 100 ppm treatment group compared to control, and at PCD 34 for the 110 ppm groups compared to all other groups and for 220 and 550 ppm groups compared to 0 and 55 ppm CTC birds. The CTCr salmonella counts in droppings were higher (P less than .05) at PCD 34 for the 110, 220, and 550 ppm groups compared to the control.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of subtherapeutic vs. therapeutic administration of macrolides on antimicrobial resistance in Mannheimia haemolytica and enterococci isolated from beef cattle

“…These discrepancies may reflect species-specific (cattle vs. chicken) differences in gastrointestinal physiology and diet. Others have found that short-term therapeutic use of chlortetracycline in the diet was no less likely to select for resistant Salmonella populations than long-term subtherapeutic use (Kobland et al, 1987). In-feed and subcutaneous administration of oxytetracycline were also equally responsible for increasing the proportion of feedlot cattle excreting tetracycline resistant E. coli in faeces (Checkley et al, 2010).…”

Tetracycline Antibiotics: Mode of Action, Applications, Molecular Biology, and Epidemiology of Bacterial Resistance

“…The tet(G) (11,319), tet(H) (94), and tet(I) genes (116) have not been extensively examined for their distribution in gram-negative bacteria. It is clear that many environmental (8,52) and food and animal (14,40,46,55,60,61,101,102,133,135,141,266,276,280) isolates are tetracycline resistant. However, these bacteria have not yet been as extensively examined as those associated with human disease.…”

“…These issues have been the subject of intense and continuous debate since the 1960s, when the Swann Committee in the United Kingdom concluded that antibiotics used in human chemotherapy or those that promote cross-resistance to other therapeutically valuable agents should not be used as growth promoters in animals (288). The antibiotics used as growth promoters in animals are considered to be associated with the greatest risk for selection of resistance because of the continuous subtherapeutic levels used in growth promotion regimens compared to the higher, short-term, therapeutic levels used to treat animal infections (50,133,217). Even though there is only circumstantial evidence that resistance in humans is exacerbated by the use of antibiotics in animal feed (http://europa.eu.int/comm/dg24/health/sc/index _en.html) (50,83,109), there are increasing concerns, and growing public awareness, that use of antibiotics in animal feed could constitute a human health hazard.…”

Opinion of the Scientific Panel on biological hazards (BIOHAZ) related to the use of antimicrobials for the control of Salmonella in poultry

“…has been reported (Smith and Tucker, 1975;Gast and Stephens, 1986;Gast et al, 1988). Once resistance has emerged or been introduced, administration of antimicrobials leads to an increased shedding of bacteria (Latour and Barnum, 1981;Kobland et al, 1987;Manning et al, 1994). This may affect the degree of contamination of food products (Gast et al, 1988).…”