摘要
Objective: To determine if ionophore-resistant ruminal bacteria are cross-resistant to other classes of antibiotics. Clostridiumaminophilum was used as a model organism because this Gram-positive ruminal bacterium can adapt to ionophores (monensin and lasalocid). Non-adapted cultures lagged for at least 12 h with 1 μM monensin or lasalocid, but initiated no growth if the concentration was 10 μM. Adapted cultures did not lag with 1 μM monensin or lasalocid, grew well even if the ionophore concentration was 10 μM and contained cells at least 100 000-fold more resistant than those in non-adapted cultures.
Methods: Ionophore-adapted and non-adapted cultures were assayed for their susceptibility to other classes of antibiotics (penicillin G, ampicillin, cephalosporin C, vancomycin, carbenicillin, tetracycline, chloramphenicol, erythromycin, streptomycin, linocomycin, rifampicin, trimethoprim, novobiocin, polymyxin B and bacitracin) using a broth microdilution method.
Results: Adapted cultures retained their resistance phenotype for at least 28 generations even if ionophore was no longer present. Monensin-adapted cultures were as resistant to lasalocid as those adapted to lasalocid, but lasalocid-adapted cultures lagged with 1 μM monensin. Monensin- and lasalocid-resistant C. aminophilum F cultures were as susceptible to most antibiotics as non-adapted cultures. The only antibiotic that seemed to have a common mechanism of resistance was bacitracin, and the ionophore-adapted cultures had a 32-fold greater MIC.
Conclusion: The use of ionophores in cattle feed and the selection of ionophore-resistant ruminal bacteria does not necessarily lead to other types of antibiotic resistance.
摘要译文
目的：确定离子载体抗性瘤胃细菌是否对其他类抗生素产生交叉耐药性。Clostridiumaminophilum被用作模型生物，因为这种革兰氏阳性瘤胃细菌可以适应离子载体（莫能菌素和拉沙里菌素）。非适应性培养物用1μM莫能菌素或lasalocid滞后至少12h，但如果浓度为10μM则不启动生长。适应的培养物没有滞后于1μM莫能菌素或拉沙里菌素，即使离子载体浓度为10μM也能很好地生长，并且细胞的耐受性比非适应培养物的耐受性高至少10万倍。方法：测定离子载体适应性和非适应性培养物对其他类抗生素（青霉素G，氨苄青霉素，头孢菌素C，万古霉素，羧苄青霉素，四环素，氯霉素，红霉素，链霉素，林可霉素，利福平，甲氧苄啶，新生霉素，多粘菌素B和杆菌肽）。结果：即使离子载体不再存在，适应的培养物仍保留至少28代的抗性表型。莫能菌素适应的培养物对拉沙里菌素的适应性与那些适应于拉沙里菌素的培养物相当，但拉沙里菌素适应的培养物滞后于1μM莫能菌素。莫能菌素和拉沙洛塞耐药C.嗜酸乳杆菌F培养物与大多数抗生素一样易受非适应性培养物的影响。似乎具有共同抗性机制的唯一抗生素是杆菌肽，离子载体适应的培养物具有32倍的MIC。结论：在牛饲料中使用离子载体和选择抗离子载体的瘤胃细菌并不一定会导致其他类型的抗生素耐药性。
Adam J. Houlihan;James B. Russell. The susceptibility of ionophore-resistant Clostridium aminophilum F to other antibiotics[J]. Journal of Antimicrobial Chemotherapy, 2003,52(4): 623–628