Epidemiology and Molecular Genetics of Macrolide Resistance in Staphylococcus aurous.

金黄色葡萄球菌对大环内酯类抗生素的耐药型分为A、B、C三组，A组菌株对大环内酯类抗生素(M)、林可酰胺类(L)和B型链球菌素类抗生素(S)具有结构性耐药。C群菌株对MLS有诱导耐药。B组菌株对14种大环内酯类抗生素和S类诱导耐药，我们将这种表型称为PMS。1978年至1989年期间，匈牙利共分离到413株对PMS耐药的金黄色葡萄球菌。对青霉素、四环素和氯霉素的耐药率分别为99%、79%和63%。它们大多(94%)属于52-相型络合物，表明它们来自同一来源。对43株PMS菌株的进一步检测发现，PMS表型的决定基因位于3种质粒中的一种上，这3种质粒也编码β-内酰胺酶的产生和对镉离子的抗性，但不编码对砷的抗性。四环素和氯霉素耐药由DNA大小分别为4.4kb和2.9kb的独立质粒编码。PMS质粒DNA大小分别为50kb、23.8kb和16.8kb。23.8kb和50kb的质粒也携带汞抗性基因，不亲和性包括编码A组大环内酯类抗药性的pI258。用限制性内切酶分析了PMS质粒的23.8kb和16.8kb的DNA片段图谱。PMS和pI258的DNA编码β-内酰胺酶和复制的区域相同，但两个区域的片段有很大差异。PI258非同源的10kb区域是A组MLS决定簇的位置，PMS质粒上的4kb区域是PMS决定簇的位置。16.8kb的PMS质粒不含汞抗性基因，其余区域与23.8kb的相同。

Types of macrolide resistance in Staphylococcus aureus are classified into 3 groups, A, B and C. Group A strains are constitutively resistant to macrolides (M), lincosamides (L), and streptogramin Type B antibiotics (S). Group C strains are inducibly resistant to MLS. Group B strains are inducibly resistant to 14-member macrolides and S. We referred to this phenotype as PMS.During a period from 1978 to 1989, 413 PMS-resistant S. aurous strains were isolated in Hungary. They were also resistant to penicillin (99%), tetracycline (79%) and chloramphenicol (63%). Most of them (94%) belonged to the phase type 52-complex, suggesting that they are from the same origin. 43 strains were further examined, and we found that the determinant for PMS phenotype was located on one of 3 kinds of plasmid, which also encoded beta-lactamase production and cadmium ion resistance, but not arsenate resistance. Tetracycline and chloramphenicol resistances were encoded by independent plasmids whose DNA size were 4.4kb and 2.9kb respectively. The DNA size of PMS plasmids was 50kb, 23.8kb or 16.8kb. 23.8kb and 50kb plasmids also carried genes for mercury resistance.The incompatibility of the PMS-plasmids was incl as pI258, which encodes group A macrolide resistance. 23.8kb and 16.8kb DNA of PMS plasmids were examined for their fragment pattern by restriction enzymes. The DNA areas encoding beta-lactamase and replication were the same between PMS plasmids and pI258, but fragments between the 2 areas were quite different. Non-homologous 10kb area of pI258 is known as the site of group A MLS determinants, and 4kb area on PMS plasmids is the site of PMS determinants. 16.8kb PMS plasmid lacked mercury resistance genes, but other area was the same as that of 23.8kb plasmid.