Tikofsky Linda L, Barlow John W, Santisteban Carlos, Schukken Ynte H
Quality Milk Production Services, Department of Population Medicine and Diagnostic Services, Cornell University, Ithaca, NY 14850, USA.
Microb Drug Resist. 2003;9 Suppl 1:S39-45. doi: 10.1089/107662903322541883.
Selective pressure from antimicrobial use, mutations, or acquisition of foreign resistance determinants mediate antimicrobial resistance. If antimicrobial use is the major selective pressure encouraging the development of resistance, then reduced use should result in decreased resistance. We compared antimicrobial susceptibility patterns of Staphylococcus aureus isolates obtained from milk samples from 22 organic (nonantibiotic using) dairy herds to isolates from 16 conventional dairy herds. Susceptibility testing was performed by disk diffusion, and zone diameters were recorded in millimeters for 144 isolates from organic farms and 117 isolates from conventional farms and were also classified as susceptible or not-susceptible (intermediate and resistant categories combined). Strength of association between high or low use and proportion susceptible was evaluated by Chi-square analysis and differences in mean zone diameter for isolates from organic farms versus isolates from conventional farms were compared by analysis of variance. Analysis was done for each antimicrobial and deemed significant at p < or = 0.05. Differences in antimicrobial susceptibility were observed between S. aureus isolates from organic and conventional herds for seven of the nine antibiotics studied. Herds that were certified organic had S. aureus isolates that were more susceptible to antimicrobials. Overall, S. aureus isolates from both organic and conventional herds showed good susceptibility to most commonly used bovine mastitis antimicrobials; however, isolates from organic herds were significantly more susceptible. Longitudinal studies of herds undergoing the transition to organic farming would help elucidate the dynamics of antimicrobial resistance and the potential return of antimicrobial susceptibility.
抗菌药物使用、突变或获得外来耐药决定因素所产生的选择压力介导了抗菌药物耐药性。如果抗菌药物使用是促使耐药性产生的主要选择压力，那么减少使用应会导致耐药性降低。我们比较了从22个有机（不使用抗生素）奶牛场的牛奶样本中分离出的金黄色葡萄球菌菌株与从16个传统奶牛场分离出的菌株的抗菌药物敏感性模式。通过纸片扩散法进行药敏试验，记录了来自有机农场的144株菌株和来自传统农场的117株菌株的抑菌圈直径（以毫米为单位），并将其分为敏感或不敏感（中间和耐药类别合并）。通过卡方分析评估高使用量或低使用量与敏感比例之间的关联强度，并通过方差分析比较有机农场分离株与传统农场分离株的平均抑菌圈直径差异。对每种抗菌药物进行分析，p≤0.05时认为具有显著性。在所研究的9种抗生素中，有7种在来自有机和传统奶牛场的金黄色葡萄球菌分离株之间观察到了抗菌药物敏感性差异。获得有机认证的奶牛场的金黄色葡萄球菌分离株对抗菌药物更敏感。总体而言，来自有机和传统奶牛场的金黄色葡萄球菌分离株对最常用的牛乳腺炎抗菌药物均表现出良好的敏感性；然而，来自有机奶牛场的分离株明显更敏感。对正在向有机养殖转型的奶牛场进行纵向研究，将有助于阐明抗菌药物耐药性的动态变化以及抗菌药物敏感性的潜在恢复情况。
