Halling Shirley M, Jensen Allen E
Bacterial Diseases of Livestock Research Unit, National Animal Disease Center, Agricultural Research Service, United States Department of Agriculture, 2300 Dayton Avenue, Ames, IA 50010, USA.
BMC Microbiol. 2006 Oct 2;6:84. doi: 10.1186/1471-2180-6-84.
Brucella spp. are highly similar, having identical 16S RNA. However, they have important phenotypic differences such as differential susceptibility to antibiotics binding the ribosome. Neither the differential susceptibility nor its basis has been rigorously studied. Differences found among other conserved ribosomal loci could further define the relationships among the classical Brucella spp.
Minimum inhibitory concentration (MIC) values of Brucella reference strains and three marine isolates to antibiotics binding the ribosome ranged from 0.032 to >256 microg/ml for the macrolides erythromycin, clarithromycin, and azithromycin and 2 to >256 microg/ml for the lincosamide, clindamycin. Though sequence polymorphisms were identified among ribosome associated loci 23S rrn, rplV, tuf-1 and tuf-2 but not rplD, they did not correlate with antibiotic resistance phenotypes. When spontaneous erythromycin resistant (eryR) mutants were examined, mutation of the peptidyl transferase center (A2058G Ec) correlated with increased resistance to both erythromycin and clindamycin. Brucella efflux was examined as an alternative antibiotic resistance mechanism by use of the inhibitor L-phenylalanine-L-arginine beta-naphthylamide (PAbetaN). Erythromycin MIC values of reference and all eryR strains, except the B. suis eryR mutants, were lowered variably by PAbetaN. A phylogenetic tree based on concatenated ribosomal associated loci supported separate evolutionary paths for B. abortus, B. melitensis, and B. suis/B. canis, clustering marine Brucella and B. neotomae with B. melitensis. Though Brucella ovis was clustered with B. abortus, the bootstrap value was low.
Polymorphisms among ribosomal loci from the reference Brucella do not correlate with their highly differential susceptibility to erythromycin. Efflux plays an important role in Brucella sensitivity to erythromycin. Polymorphisms identified among ribosome associated loci construct a robust phylogenetic tree supporting classical Brucella spp. designations.
布鲁氏菌属高度相似，具有相同的16S RNA。然而，它们存在重要的表型差异，如对结合核糖体的抗生素的敏感性不同。这种敏感性差异及其基础尚未得到严格研究。在其他保守核糖体基因座中发现的差异可能进一步明确经典布鲁氏菌属之间的关系。
布鲁氏菌参考菌株和三株海洋分离株对结合核糖体的抗生素的最低抑菌浓度（MIC）值，对于大环内酯类抗生素红霉素、克拉霉素和阿奇霉素，范围为0.032至>256微克/毫升，对于林可酰胺类抗生素克林霉素，范围为2至>256微克/毫升。虽然在核糖体相关基因座23S rrn、rplV、tuf-1和tuf-2中鉴定出序列多态性，但rplD中未鉴定出，这些多态性与抗生素抗性表型无关。当检测自发的红霉素抗性（eryR）突变体时，肽基转移酶中心（A2058G Ec）的突变与对红霉素和克林霉素的抗性增加相关。通过使用抑制剂L-苯丙氨酸-L-精氨酸β-萘酰胺（PAbetaN）检测布鲁氏菌外排作为一种替代的抗生素抗性机制。除猪布鲁氏菌eryR突变体外，参考菌株和所有eryR菌株的红霉素MIC值均因PAbetaN而不同程度降低。基于串联核糖体相关基因座构建的系统发育树支持流产布鲁氏菌、羊布鲁氏菌和猪布鲁氏菌/犬布鲁氏菌的独立进化路径，将海洋布鲁氏菌和新墨西哥布鲁氏菌与羊布鲁氏菌聚类。虽然绵羊布鲁氏菌与流产布鲁氏菌聚类，但自展值较低。
参考布鲁氏菌核糖体基因座之间的多态性与其对红霉素的高度敏感性差异无关。外排在布鲁氏菌对红霉素的敏感性中起重要作用。在核糖体相关基因座中鉴定出的多态性构建了一个强大的系统发育树，支持经典布鲁氏菌属的分类。
