Abstract
Streptomycin is used in arboriculture to control fire blight. Using sheep as a model, multidrug-resistant bacteria in mammals were found to be selected after the intentional release of streptomycin into the environment. Escherichia coli and Staphylococcus spp. were isolated from the faeces and nasal cavities, respectively, of sheep grazing on a field sprayed with streptomycin at concentrations used in orchards (test group) and on a field without streptomycin (control group). Before the application of streptomycin, the percentage of streptomycin-resistant E. coli isolates in faeces was 15.8% in the control group and 14.7% in the test group. After the application of streptomycin, the overall number of streptomycin-resistant E. coli isolates was significantly higher in the test group (39.9%) than in the control group (22.3%). Streptomycin-resistant Staphylococcus isolates were only detected after the application of streptomycin. Streptomycin resistance was frequently associated with resistance to sulfamethoxazole, ampicillin, tetracycline and chloramphenicol and less frequently to cefotaxime in E. coli, and to tetracycline, fusidic acid and tiamulin in Staphylococcus spp. This study shows that the application of low concentrations of streptomycin on grass, as occurs during the spraying of orchards, selects for multidrug-resistant nasal and enteric bacterial flora, including extended-spectrum beta-lactamase-producing E. coli.
Highlights
The number of multi-resistant bacterial strains has been increasing at an alarming rate and represents a majorReceived 12 June, 2012; revised 5 October, 2012; accepted 12 October, 2012. *For correspondence
To determine the impact of streptomycin use in orchards on the nasal and intestinal flora of grazing animals, we studied the evolution of antibiotic resistance in Escherichia coli and Staphylococcus spp. from sheep that have grazed on grass sprayed with streptomycin at concentrations used against fire blight in orchards
A total of 455 E. coli isolates (213 from the test group and 242 from the control group) from the faeces of sheep and 184 Staphylococcus spp. (86 from the test group and 98 from the control group) from nasal cavities were isolated during the 3 month period of monitoring
Summary
The number of multi-resistant bacterial strains has been increasing at an alarming rate and represents a majorReceived 12 June, 2012; revised 5 October, 2012; accepted 12 October, 2012. *For correspondence. The sharp increase in antibiotic resistance is caused by the extensive use of antibiotics in human and animal medicine and in agriculture (Neu, 1992; McManus et al, 2002; English and Gaur, 2010; Gootz, 2010; Wright, 2010). Preventive measures to reduce the generation of antibiotic-resistant bacteria have been implemented and include banning the use of all antibiotics as growth promoters in animal breeding in Switzerland in 1999 and in the European Union in 2006 (Perreten, 2003; Cogliani et al, 2011). The impact of the agricultural use of streptomycin for plant protection on the selection of antibiotic-resistant bacteria in mammals has not been fully considered
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