Pal N, Sharma B, Sharma R, Vyas L
Department of Microbiology, SMS Medical College, Jaipur, India.
J Postgrad Med. 2010 Jul-Sep;56(3):182-5. doi: 10.4103/0022-3859.68637.
Macrolide (MLS B ) resistance is the most widespread and clinically important mechanism of resistance encountered with Gram-positive organisms. Resistance may be constitutive (cMLS B phenotype) or inducible (iMLS B phenotype). The iMLS B phenotypes are not differentiated by using standard susceptibility test methods, but can be distinguished by erythromycin-clindamycin disk approximation test (D-test) and demonstration of resistance genes by molecular methods.
To demonstrate in vitro inducible clindamycin resistance (iMLS B ) in erythromycin-resistant (ER) and clindamycin-susceptible (CLI-S) clinical isolates of Staphylococci spp., and interpretation of susceptibility tests to guide therapy.
Eight hundred and fifty-one isolates of Staphylococci spp. were recovered from various clinical specimens. All the Staphylococcal spp. were identified by conventional microbiological methods including colony morphology, Gram stain, catalase, slide coagulase and tube coagulase. Antibiotic susceptibility testing was performed by Kirby Bauer disc diffusion method. Erythromycin-resistant isolates were examined for inducible clindamycin resistance (iMLS B ) by using double disk approximation test (D-test) at 15 mm disk separation.
The Staphylococci spp. isolated were 379 S. aureus [31.60% methicillin-resistant S. aureus (MRSA), 12.92% methicillin-sensitive S. aureus (MSSA)] and 472 coagulase-negative Staphylococci (CNS) [37.60% methicillin-resistant coagulase-negative Staphylococci (MRCNS), 17.86% methicillin-sensitive coagulase-negative Staphylococci (MSCNS)]. Four hundred and thirty (50.52%) Staphylococcal spp. isolates showed erythromycin resistance. Constitutive resistance was demonstrated in 202 (46.97%), inducible clindamycin resistance (iMLS B ) in 101 (23.48%), and non-inducible (MS) in 127 (29.53%). Two distinct induction phenotypes, D (18.13%) and D + (5.34%) were observed. All iMLS B isolates were susceptible to linezolid and vancomycin while 78.78% to ciprofloxacin.
Fifty percent of Staphylococcal spp. were ER among which 23.48% were iMLS B phenotypes. Eighty-seven per cent of iMLS B phenotypes were observed to be methicillin-resistant. The high frequency of methicillin resistance isolates (87.12%) with in vitro inducible clindamycin resistance at our institute raises concern of clindamycin treatment failures with methicillin-resistant infections. So we recommend that microbiology laboratories should include the D-test for inducible resistance to clindamycin in the routine antibiotic susceptibility testing.
大环内酯（MLS B）耐药是革兰氏阳性菌中最普遍且临床上最重要的耐药机制。耐药可能是组成型（cMLS B表型）或诱导型（iMLS B表型）。使用标准药敏试验方法无法区分iMLS B表型，但可通过红霉素-克林霉素纸片扩散法（D试验）以及分子方法检测耐药基因来进行区分。
在红霉素耐药（ER）且克林霉素敏感（CLI-S）的葡萄球菌属临床分离株中证明体外诱导型克林霉素耐药（iMLS B），并解释药敏试验以指导治疗。
从各种临床标本中分离出851株葡萄球菌属菌株。所有葡萄球菌属菌株均通过常规微生物学方法进行鉴定，包括菌落形态、革兰氏染色、过氧化氢酶、玻片凝固酶和试管凝固酶试验。采用 Kirby Bauer 纸片扩散法进行抗生素药敏试验。对红霉素耐药菌株，通过在纸片间距为15 mm时使用双纸片扩散法（D试验）检测诱导型克林霉素耐药（iMLS B）。
分离出的葡萄球菌属菌株中，有379株金黄色葡萄球菌[31.60%耐甲氧西林金黄色葡萄球菌（MRSA），12.92%甲氧西林敏感金黄色葡萄球菌（MSSA）]和472株凝固酶阴性葡萄球菌（CNS）[37.60%耐甲氧西林凝固酶阴性葡萄球菌（MRCNS），17.86%甲氧西林敏感凝固酶阴性葡萄球菌（MSCNS）]。430株（50.52%）葡萄球菌属菌株表现出红霉素耐药。202株（46.97%）表现为组成型耐药，101株（23.48%）表现为诱导型克林霉素耐药（iMLS B），127株（29.53%）表现为非诱导型（MS）。观察到两种不同的诱导表型，D（18.13%）和D +（5.34%）。所有iMLS B分离株对利奈唑胺和万古霉素敏感，而对环丙沙星敏感的占78.78%。
50%的葡萄球菌属菌株为ER，其中23.48%为iMLS B表型。观察到87%的iMLS B表型为耐甲氧西林。我院耐甲氧西林分离株（87.12%）体外诱导型克林霉素耐药的高频率引发了对耐甲氧西林感染克林霉素治疗失败的担忧。因此，我们建议微生物实验室应在常规抗生素药敏试验中纳入对克林霉素诱导耐药的D试验。
