Udo E E, Jacob L E, Mathew B
Department of Microbiology, Faculty of Medicine, Kuwait University, Kuwait.
J Med Microbiol. 2001 Oct;50(10):909-915. doi: 10.1099/0022-1317-50-10-909.
Clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) expressing high- and low-level mupirocin resistance were studied to determine the genetic location of mupirocin and other resistance determinants. Mupirocin resistance was confirmed by MIC determination with E-test strips. Curing and transfer experiments were used to establish the genetic location of the resistance determinants and the PCR with mupA-specific primers was used to detect the presence of mupA genes. High-level mupirocin-resistant isolates had MICs >1024 mg/L, whereas the low-level resistant isolates had MICs of 32-128 mg/L. The isolates carried plasmids ranging from 2.8 to 38 kb in size. All of them carried 26- and 3.0-kb plasmids, but only the high-level mupirocin-resistant isolates carried a 38-kb plasmid. Curing and transfer experiments revealed that the 26-kb plasmid encoded resistance to cadmium, mercuric chloride, propamidine isethionate and ethidium bromide and the 38-kb plasmid was a conjugative plasmid encoding high-level mupirocin resistance. One isolate, IBN287, carried both plasmid-borne high-level and chromosomal low-level mupirocin resistance. The mupA gene was detected on the 38-kb plasmid DNA but not in the genomic DNA of the low-level mupirocin-resistant isolates. The genomic DNA of strain IBN287 cured of the 38-kb mupirocin resistance plasmid did not contain mupA. The results suggest that different genes encoded low- and high-level mupirocin resistance in these isolates.
对表达高水平和低水平莫匹罗星耐药性的耐甲氧西林金黄色葡萄球菌（MRSA）临床菌株进行了研究，以确定莫匹罗星和其他耐药决定因素的基因定位。通过使用E-test试纸条测定最低抑菌浓度（MIC）来确认莫匹罗星耐药性。采用消除和转移实验来确定耐药决定因素的基因定位，并使用mupA特异性引物进行聚合酶链反应（PCR）来检测mupA基因的存在。高水平莫匹罗星耐药菌株的MIC>1024mg/L，而低水平耐药菌株的MIC为32-128mg/L。这些分离株携带大小从2.8kb到38kb不等的质粒。它们都携带26kb和3.0kb的质粒，但只有高水平莫匹罗星耐药分离株携带38kb的质粒。消除和转移实验表明，26kb的质粒编码对镉、氯化汞、乙磺半脒和溴化乙锭的耐药性，38kb的质粒是一种接合质粒，编码高水平莫匹罗星耐药性。一个分离株IBN287同时携带质粒介导的高水平和染色体介导的低水平莫匹罗星耐药性。在38kb的质粒DNA上检测到mupA基因，但在低水平莫匹罗星耐药分离株的基因组DNA中未检测到。消除了38kb莫匹罗星耐药质粒的IBN287菌株的基因组DNA不含有mupA。结果表明这些分离株中低水平和高水平莫匹罗星耐药性由不同基因编码。
