Tasara T, Cernela N, Stephan R
Institute for Food Safety and Hygiene, University of Zurich, Switzerland.
Schweiz Arch Tierheilkd. 2013 Jun;155(6):359-63. doi: 10.1024/0036-7281/a000471.
Molecular based approaches have gained increasing importance in routine mastitis diagnostics for typing and antibiotic resistance testing of Staphylococcus aureus. Out of 78 S. aureus strains isolated from bovine mastitis milk 10 of them harbored blaZ, blaI and blaR genes. Although 5 strains were phenotypically resistant to penicillin, the other 5 (all belonging the clonal complex 8) were penicillin susceptible. PCR amplification confirmed the presence of the blaZ, blaR and blaI genes in all 5 strains. Sequencing of these genes uncovered a 29 base deletion within the blaZ gene in all these strains that causes a translational frame shift, which is predicted to induce abrogation of BlaZ expression. Additionally single nucleotide insertions and deletions were detected in blaR of 3 strains. These insertions cause translation reading frame shifts and premature stop codons that are predicted to induce expression of truncated BlaR proteins. Using the genetically altered blaZ genes detected as targets, a real-time PCR system for detecting CC8 associated blaZ positive S. aureus strains that still remain susceptible to penicillin was developed. Such strains are part of detection challenges that must be considered in routine application of genotypic resistance testing of bovine mastitis S. aureus.
基于分子的方法在金黄色葡萄球菌的分型和抗生素耐药性检测的常规乳腺炎诊断中越来越重要。从牛乳腺炎乳汁中分离出的78株金黄色葡萄球菌中，有10株携带blaZ、blaI和blaR基因。虽然有5株在表型上对青霉素耐药，但另外5株（均属于克隆复合体8）对青霉素敏感。PCR扩增证实所有5株中均存在blaZ、blaR和blaI基因。对这些基因进行测序发现，所有这些菌株的blaZ基因内有一个29个碱基的缺失，导致翻译移码，预计会导致BlaZ表达缺失。此外，在3株菌株的blaR中检测到单核苷酸插入和缺失。这些插入导致翻译阅读框移位和过早的终止密码子，预计会诱导截短的BlaR蛋白表达。以检测到的基因改变的blaZ基因为靶标，开发了一种实时PCR系统，用于检测仍对青霉素敏感的CC8相关blaZ阳性金黄色葡萄球菌菌株。这类菌株是牛乳腺炎金黄色葡萄球菌基因型耐药性检测常规应用中必须考虑的检测挑战的一部分。
