| Summary: | 碩士 === 國立臺灣大學 === 獸醫學研究所 === 93 === Bacteria isolated from dairy cows, dairy farm environments, and dairy workers in two geographically different areas - eastern and northern Taiwan - were evaluated for antibiotic susceptibility. The residues of antibiotics in raw milk of the same farms were also screened. There were 1346 bacteria identified, including 226 Escherichia coli (2 E. coli O157:H7), 271 Enterococcus spp., 30 Pseudomonas spp. (7 P. aeruginosa), 314 Staphylococcus spp., 195 Streptococcus spp., 51 other Gram-positives and 259 other Gram-negatives. Among them, 88% of the isolates were resistant to sulfadimethoxine. The percentages of Gram-negative bacteria resistant to oxytetracycline and streptomycin were 48% (249/515) and 78% (404/515), respectively. Gram-positive bacteria isolated from eastern Taiwan, the least polluted region of Taiwan, were found to have more antibiotic resistance than those isolated from northern Taiwan. Two E. coli O157:H7 from two different geographical areas were isolated and both showed vt2-positive but vt1-negative, and had phylogenetic similarities of 82% and 67%, respectively, to previous Taiwan isolates. This study detected 6.5% of residues oxytetracycline, penicillin, and streptomycin in raw milk samples. Oxytetracycline was detectable in the tank milk of five out of the sixteen dairy farms. Residue levels of antibiotics exceeding regulated concentrations were also observed. Information on antibiotic susceptibility of dairy farms may serve as a baseline for future studies and may also highlight the need to formulate better regulation strategies for the safe use of antibiotics on food-producing farms.
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