Ruegg P L, Oliveira L, Jin W, Okwumabua O
Department of Dairy Science, University of Wisconsin, Madison 53706.
Department of Dairy Science, University of Wisconsin, Madison 53706.
J Dairy Sci. 2015 Jul;98(7):4521-34. doi: 10.3168/jds.2014-9137. Epub 2015 Apr 23.
In the United States, few intramammary antimicrobials exist that are approved for treatment of bovine mastitis; thus, ensuring judicious use of these products is a priority. The objectives of this study were to determine phenotypic susceptibility and presence of selected antimicrobial resistance genes from staphylococci, streptococci, and streptococcal-like organisms recovered from cases of clinical mastitis occurring in cows on large Wisconsin farms. Staphylococcus aureus (n=35 from 19 herds), coagulase-negative staphylococci (n=51 from 30 herds), Streptococcus spp. (n=78 from 36 herds), and streptococcal-like organisms (n=31 from 19 herds) were used in this study. All Staphylococcus spp. were susceptible to ceftiofur, cephalothin, and the combination of penicillin and novobiocin. Of all staphylococci, only a single Staphylococcus epidermidis exhibited phenotypic resistance to oxacillin. Phenotypic susceptibility to erythromycin was observed in only 8.6 and 15.7% of Staphylococcus aureus and coagulase-negative staphylococci, respectively. Approximately 20% of staphylococci and 13 to 22% of streptococci and streptococcal-like organisms exhibited phenotypic resistance to pirlimycin. All Streptococcus spp. exhibited phenotypic susceptibility to ceftiofur, cephalothin, and oxacillin. The proportion of isolates exhibiting phenotypic susceptibility to pirlimycin and sulfadimethoxine differed among Streptococcus dysgalactiae and Streptococcus uberis. All streptococcal-like organisms exhibited phenotypic susceptibility to ceftiofur, cephalothin, oxacillin, penicillin, and the combination of penicillin and novobiocin. Of all organisms tested, 36.9% did not carry any of the resistance genes (ermC, blaZ, tetK, or tetM), 35.4% carried 1 gene, and 27.7% carried multiple genes (usually blaZ in combination with a tet gene). Eighteen (51.4%) Staph. aureus and 12 (48.0%) Staphylococcus chromogenes carried multiple resistance genes. Six (12.2%) Strep. dysgalactiae and no Strep. uberis carried multiple resistance genes. Results indicate that most gram-positive mastitis organisms were susceptible to most antimicrobials used for intramammary administration, but some resistance to drugs used for systemic treatment of mastitis was noted. The presence of selected resistance genes was not proportional to the occurrence of phenotypic resistance.
在美国，经批准可用于治疗牛乳腺炎的乳房内用抗菌药物很少；因此，确保合理使用这些产品是当务之急。本研究的目的是确定从威斯康星州大型农场奶牛临床乳腺炎病例中分离出的葡萄球菌、链球菌及类链球菌的表型敏感性和所选抗菌药物耐药基因的存在情况。本研究使用了金黄色葡萄球菌（来自19个牛群的35株）、凝固酶阴性葡萄球菌（来自30个牛群的51株）、链球菌属（来自36个牛群的78株）和类链球菌（来自19个牛群的31株）。所有葡萄球菌属菌株对头孢噻呋、头孢噻吩以及青霉素和新生霉素的组合均敏感。在所有葡萄球菌中，仅1株表皮葡萄球菌表现出对苯唑西林的表型耐药。金黄色葡萄球菌和凝固酶阴性葡萄球菌中分别仅有8.6%和15.7%的菌株对红霉素表现出表型敏感性。约20%的葡萄球菌以及13%至22%的链球菌和类链球菌对吡利霉素表现出表型耐药。所有链球菌属菌株对头孢噻呋、头孢噻吩和苯唑西林均表现出表型敏感性。乳房炎链球菌和乳房链球菌对吡利霉素和磺胺二甲氧嘧啶表现出表型敏感性的分离株比例有所不同。所有类链球菌对头孢噻呋、头孢噻吩、苯唑西林、青霉素以及青霉素和新生霉素的组合均表现出表型敏感性。在所有检测的菌株中，36.9%未携带任何耐药基因（ermC、blaZ、tetK或tetM），35.4%携带1个基因，27.7%携带多个基因（通常是blaZ与tet基因组合）。18株（51.4%）金黄色葡萄球菌和12株（48.0%）产色葡萄球菌携带多个耐药基因。6株（12.2%）乳房炎链球菌携带多个耐药基因，乳房链球菌未携带。结果表明，大多数革兰氏阳性乳腺炎病原体对大多数用于乳房内给药的抗菌药物敏感，但也注意到对用于乳腺炎全身治疗的药物存在一些耐药情况。所选耐药基因的存在与表型耐药的发生不成比例。
