红霉素耐药肠球菌ermB基因与转座子Tn1545和Tn917的关系

目的研究158株儿童临床标本中分离的肠球菌对红霉素耐药性及其转座子Tn1545和Tn917介导的耐大环内酯类抗生素eFmB基因的特点。方法采用琼脂稀释法对红霉素进行最小抑菌浓度（MIC）测定，用PCR检测肠球菌ermB、，蝴基因、Tn1545和Tn917。结果158株红霉素MICC50和MIC90都为256μg／ml，红霉素耐药率为94．9％（150株／158株）。在150株红霉素耐药株中，ermB基因的总携带率为70．7％，其中粪肠球菌、屎肠球菌、坚韧肠球菌、鸟肠球菌和海氏肠球菌其ermB基因的携带率分别为：78．3％、58．1％、100％、100％、100％，粪肠球菌eFmB基因的携带率高于屎肠球菌（f=6．884，P=0．009）；粪肠球菌未检测到，啪基因，只有1株屎肠球菌检测到，卿基因。106株ermB基因阳性红霉素耐药株中，46．2％的菌株eFmB基因同时存在于转座子吼1545和Tn917：ermB基因单纯存在于转座子Tn1545的43株，占40．6％；ermB基因单纯存在于转座子Tn917的1株，占0．9％。结论儿童临床标本中分离出的肠球菌耐大环内酯类抗生素的主要耐药基因为ermB基因．并且ermB基因主要是通过转座子Tn1545来携带其对大环内酯类抗生素的耐药。     

解脲脲原体对红霉素体外耐药性与ermB基因相关性研究

目的 探讨解脲脲原体(Uu)临床株对红霉素体外耐药性与ermB耐药基因之间的关系.方法 采用微量肉汤稀释法体外测定143株临床分离的Uu对红霉素的最低抑菌浓度(MIC),以MIC≥8μg/ml为耐药判读标准;设计引物扩增ermB基因,并以多条带抗原基因为靶位设计引物对Uu进行生物学分群.结果 Uu对红霉素MIC范围为≤0.125μg/至≥128μg/ml,MIC50为16 μg/ml,MIC90≥128 μg/ml,耐药率为64.38%.ermB基凶总的阳性率为27.97%,主要分布在MIC≥8 μg/ml的菌株.两生物群之间不存在红霉素耐药性及ermB基因阳性率的差异.结论 ermB基因可能是介导Uu对红霉素耐药的基因,两生物群在对红霉素耐药性机制的差异需进一步研究.     

对氨基糖甙类高水平耐药肠球菌的检测及药敏结果分析

目的了解肠球菌对高水平庆大霉素的耐药情况及用于耐万古霉素肠球菌(VRE)治疗的氯霉素(C)、红霉素(E)、四环素(TE)、利福平(RA)的耐药情况. 方法应用纸片扩散法药敏试验检测从临床标本中分离出的40株肠球菌.分析其药敏结果. 结果庆大霉素高水平耐药株(HLGR)16株(40.0%)、氯霉素耐药株17株(42.5%)、红霉素耐药株26株(65.0%)、四环素耐药株28株(70.0%)、利福平耐药株22株(55.0%),未检出对万古霉素耐药肠球菌. 结论治疗肠球菌感染时,应根据分离株的耐药特点选择不同的治疗方案.     

22株肠球菌耐药性及8种耐药基因研究

我们收集了2003年12月至2004年5月分离自解放军98医院(湖州)的22株肠球菌，对其进行了耐药性和8内酰胺类耐药相关基因(TEM)、氨基糖苷类耐药相关基因[aac(6′／aph(2″)，aph(3′)Ⅲ，ant(6Ⅰ)]、四环素耐药相关基因(terM)、红霉素耐药相关基因(ermB)、万古霉素耐药相关基因(vanA、vanB)检测。     

对氨基糖甙类高水平耐药肠球菌的检测及药敏结果分析

目的：了解肠球菌对高水平庆大霉素的耐药情况及用于耐万古霉素肠球菌（VRE）治疗的氯霉素（C）、红霉素（E ）、四环素（TE）、利福平（RA）的耐药情况。方法：应用纸片扩散法药敏试验检测从临床标本中分离出的40株肠球菌。分析其药敏结果。结果：庆大霉素高水平耐药株（HLGR）16株（40.0%）、氯霉素耐药株17株（42.5%）、红霉素耐药株26株（65.0%）、四环素耐药株28株（70.0%）、利福平耐药株22株（55.0%），未检出对万古霉素耐药肠球菌。结论：治疗肠球菌感染时，应根据分离株的耐药特点选择不同的治疗方案。     

肺炎链球菌耐药基因ermB、mefA、tetM与转座子整合酶基因intTn的检测

目的 研究耐药基因ermB、mefA、tetM与转座子整合酶基因intTn在携带肺炎链球菌的北京儿童中分布特点。方法对185株呼吸道感染患儿鼻咽部分离的肺炎链球菌进行以下检测：E-test、琼脂稀释或纸片扩散法测定对大环内酯类、四环素、β-内酰胺类及头孢类等15种抗生素的药物敏感性。PCR检测大环内酯类耐药基因ermB和mef/A，四环素耐药基因tetM以及转座子Tn1545的整合酶基因intTn。结果185株肺炎链球菌的药敏结果显示，对红霉素、克林霉素、四环素和复方磺胺甲基异嗯唑的耐药率较高，分别为78．9％、76．2％、86．0％和78．7％，对阿莫西林，克拉维酸、头孢克洛、头孢曲松和头孢呋辛耐药率较低，分别为2．2％、15．5％、2．8％和14．1％。所有红霉素耐药株均检出ermB和／或mefA，其中79．5％为ermB阳性，17．8％为ermB和mefA同时阳性，2．7％为mefA阳性。tetM基因在分离株中的阳性率是87％，四环素耐药组的tetM基因携带率是96．9％，高于敏感组（26．9％）。四环素耐药株的红霉素耐药率（90．0％）亦高于敏感株组（11．5％）。87．6％的肺炎链球菌存在intTn基因，intTn基因阳性组的红霉素、四环素、氯霉素、复方磺胺甲基异嗯唑和环丙沙星的耐药率较intTn基因阴性组高。分离株最常见的基因组合是intTn＋terM＋ermB，占58．4％。结论北京地区呼吸道感染儿童鼻咽部肺炎链球菌耐大环内酯类抗生素的主要原因是ermB编码的23S rRNA甲基化酶致靶位改变。tetM基因编码蛋白质的核糖体保护作用，是肺炎链球菌四环素耐药的重要机制。接合性转座子Tn1545的存在与菌株的红霉素和四环素耐药关系密切，可能是肺炎链球菌多重耐药的重要机制之一。     

粪肠球菌毒力基因及耐药性分析

目的:了解临床标本与健康人群肠道来源粪肠球菌(Enterococcus faecalis,Efa)的毒力基因分布,探讨毒力基因与细菌致病性及抗生素耐药性之间关系。方法:收集89株分离临床标本和24株健康人群的粪肠球菌,采用PCR方法检测aggA、cylA、cylB、cylM、eep、efaA、enlA、esp和gelE基因,K-B法测定临床分离株对万古霉素、四环素、环丙沙星、高浓度链霉素、青霉素、替考拉宁、呋喃妥因的敏感性。结果:86.7%的粪肠球菌携带有毒力基因,以eep(76.1%)、efaA(74.3%)、esp(52.2%)和aggA(52.2%)基因为多,其他毒力基因的阳性率为31.9%～47.8%。除了毒力基因enlA以外,临床分离菌株其他毒力基因的阳性率明显高于健康人分离菌株。所有菌株中携带8种毒力基因的菌株最为多见,占总菌株的23.9%。粪肠球菌对四环素、环丙沙星和青霉素耐药率较高,对呋喃妥因耐药率低,未检出对万古霉素和替考拉宁耐药株。除了高浓度庆大霉素,携带毒力基因数的多少与抗菌药物的耐药性之间不存在关联。结论:粪肠球菌毒力因子的携带与致病性密切相关,与耐药性之间的关系需进一步研究。     

1999-2006年北京朝阳医院革兰阳性球菌耐药性分析

目的 探讨北京朝阳医院1999-2006年临床分离的革兰阳性球菌的耐药变迁,以指导临床合理使用抗菌药物.方法 采用MIC法进行抗菌药物敏感性试验,以WHONET5.3软件分析数据.结果 6192株临床分离的革兰阳性球菌中,前4位病原菌依次为凝同酶阴性葡萄球菌、金黄葡萄球菌、粪肠球菌、屎肠球菌.耐甲氧西林金黄葡萄球菌(MRSA)、耐甲氧西林凝固酶阴性葡萄球菌(MRCNS)平均检出率分别为88.4%、86.9%,金黄葡萄球菌对青霉素、氨苄西林耐药率最高,8年间始终保持在90.0%以上.未发现对万古霉素耐药或中介的金黄葡萄球菌或凝固酶阴性葡萄球菌.2003年首次分离耐万古霉素肠球菌(VRE),至2006年共发现30株VRE,其中13株为耐万古霉索粪肠球菌,均为VanB基因型;17株为耐万古霉素屎肠球菌,均为VanA基因型,耐万古霉素屎肠球菌分离率呈上升趋势.对于粪肠球菌活性最高的是万古霉素、氨苄西林、青霉素,敏感率分别为98.7%、95.7%、85.6%.但是青霉素敏感性略有下降,从94.3%降至84.6%.克林霉素的耐药率8年中始终维持在99.0%以上.屎肠球菌对红霉素、克林霉素的耐药率均达95.0%以上,对青霉素、氨苄西林、环丙沙星的耐药率均大于90.0%.屎肠球菌最为敏感的药物是万古霉素,对四环素敏感性出现上升的趋势,从27.8%升到82.6%.结论 万古霉素对临床常见的革兰阳性菌保持很高的活性,发现30株耐万古霉素的肠球菌.     

儿童社区获得性呼吸道感染的病原学研究

目的探讨儿童呼吸道感染的病原学特点,以期为临床治疗提供依据.方法采集1784名呼吸道感染患儿咽拭标本常规细菌培养和/或PCR法支原体,K-B法测定流感嗜血杆菌、肺炎链球菌耐药性,以套式-聚合酶链反应及PCR技术进行肺炎链球菌耐药基因TEM基因、ermB基因和mefA基因检测,加DAN测序分析.结果 129例细菌培养阳性,依次为流感嗜血杆菌、肺炎链球菌、肺炎克雷伯杆菌、金黄色葡萄球菌、阴沟肠杆菌、不动杆菌属;153例支原体阳性,以肺炎支原体、人型支原体为主,少数为肺炎衣原体.其中流感嗜血杆菌、肺炎链球菌对青霉素、克林霉素、红霉素、阿奇霉素、阿莫西林/克拉维酸、复方甲基异恶唑、头孢菌素及红霉素等10种常用抗生素均不同程度耐药,但对氯霉素和万古霉素均敏感;肺炎链球菌β内酰胺酶基因(TEM)、红霉素耐药基因(甲基化酶基因ermB)表达阳性,但未表达红霉素耐药基因(外排基因mefA).结论流血嗜血杆菌和肺炎链球菌本地区呼吸道感染儿童主要致病菌,对常用抗生素有不同程度耐药,肺炎支原体和人型支原体也是重要致病原;肺炎链球菌耐药可能是通过表达TEM基因和ermB基因实现的.     

血液分离肠球菌毒力基因及生物膜形成相关性分析

目的了解血液分离肠球菌毒力基因及其与生物膜形成能力的相关性。方法收集血培养分离粪肠球菌42株和屎肠球菌44株,采用纸片扩散法检测菌株对常规药物的敏感性;PCR法检测肠球菌6种毒力基因cyl、esp、asal、hyl、gelE和agg;采用结晶紫染色法测定肠球菌生物膜形成能力;统计分析肠球菌毒力基因与生物膜形成能力的关系。结果屎肠球菌对青霉素、氨苄西林、左旋氧氟沙星的耐药率高于粪肠球菌;除esp、hyl外,cyl、asal、gelE和agg基因在粪肠球菌检出率均显著高于屎肠球菌(P<0.05);血液分离肠球菌生物膜阳性率为32.6%(28/86),其中粪肠球菌和屎肠球菌生物膜阳性率分别为59.5%(25/42)和6.8%(3/44);肠球菌毒力基因的携带与其生物膜阳性率无相关性(P>0.05)。结论致血流感染的屎肠球菌其耐药率高于粪肠球菌,粪肠球菌生物膜的形成能力高于屎肠球菌,两者的毒力基因与生物膜形成不具相关性。     

Analysis of the macrolide resistance gene in penicillin-resistant Streptococcus pneumoniae

We examined the penicillin and macrolide resistance of 496 strains of Streptococcus pneumoniae (S. pneumoniae) isolated at Showa University Hospital from November 2004 to May 2005. According to the classification established by the Clinical and Laboratory Standards Institute, the ratio of penicillin susceptible S. pneumoniae (PSSP) was 25.8%, penicillin intermediate S. pneumoniae was 35.9% and penicillin resistant S. pneumoniae (PRSP) was 38.3%. The ratios of macrolide resistant S. pneumoniae were 85.3% for erythromycin and 76.2% for clarithromycin. S. pneumoniae strains were isolated mainly from pediatric patients, and the ratios of PRSP were similar between outpatients (39.8%) and inpatients (45.6%). We screened for mutations in pbp1a, pbp2b and pbp2x, and the retention rate of the macrolide resistance genes, ermB and mefA in 90 strains isolated in the same period. Seventy two strains had at least one mutation in the pbp genes. Interestingly, some of the penicillin susceptible strains had one or two pbp mutations, suggesting a progressive genetic acquirement of penicillin resistance. In screening for retention of the macrolide resistance genes, we found that 42 strains(46.7%) had ermB, 19 strains (21.1%) had mefA and 13 strains (14.4%) had both ermB and mefA. The possession of resistance genes and the minimal inhibitory concentration indicate that the resistance to erythromycin and clarithromycin were induced by ermB or mefA, and the resistance to clindamycin was induced only by ermB. Among the 72 strains with pbps mutations, 65 strains (90.3%) had ermB or mefA or both. Together, these results show that the strains with pbp mutations were being selected and, after acquiring the macrolide resistance gene, transform to multidrug resistant S. pneumoniae.     

Distribution of serotypes and antimicrobial resistance genes among Streptococcus agalactiae isolates from bovine and human hosts

To better understand the emergence and transmission of antibiotic-resistant Streptococcus agalactiae, we compared phenotypic and genotypic characteristics of 52 human and 83 bovine S. agalactiae isolates. Serotypes found among isolates from human hosts included V (48.1%), III (19.2%), Ia and Ib (13.5% each), and II (5.8%). Among isolates from bovine hosts, molecular serotypes III and II were predominant (53 and 14.5%, respectively). Four and 21 different ribotypes were found among human and bovine isolates, respectively. A combination of ribotyping and serotyping showed that two bovine isolates were indistinguishable from human isolates. Resistance to tetracycline and erythromycin was more common among human (84.6% and 26.9%, respectively) than bovine (14.5% and 3.6%, respectively) isolates. tetM was found in all tetracycline-resistant human isolates, while tetO was the predominant resistance gene among bovine isolates. tet genes were found among various ribotypes. ermB, ermTR, and mefA were detected among erythromycin-resistant human isolates, while ermB was the only erythromycin resistance determinant among isolates from bovine hosts. For isolates from human hosts, erythromycin resistance genes appeared to be associated with specific ribotypes. We conclude that (i) human and bovine S. agalactiae isolates represent distinct populations; (ii) human host-associated S. agalactiae subtypes may occasionally be transmitted to bovines; (iii) while emergence of erythromycin and tetracycline resistance appears to largely occur independently among human and bovine isolates, occasional cross-species transfer of resistant strains or transmission of resistance genes between human- and bovine-associated subtypes may occur; and (iv) dissemination of antibiotic-resistant S. agalactiae appears to include both clonal spread of resistant strains as well as horizontal gene transfer.     

Comparison and transferability of the erm (B) genes between human and farm animal streptococci

To obtain better insights into the possible exchange of resistance genes between human and animal streptococci, the sequences of the erm (B) genes of streptococcal isolates from humans, pigs, pork carcasses, chickens, and calves were compared. Identical erm (B) gene sequences were present in strains from humans, pigs, pork carcasses, and calves. During in vitro mating experiments, the erm (B) gene was exchanged between porcine Streptococcus suis and human S. pneumoniae, S. pyogenes, and S. oralis strains. The presence of different tetracycline resistance genes and the int Tn 1545 gene was determined in animal streptococci carrying the erm (B) gene. Although tet(M) and int Tn 1545 genes were detected in 24% of the porcine and pork carcass streptococcal strains, the tet(O) gene was the predominant tetracycline resistance gene in these strains (81%). The latter gene was co-transferred with the erm (B) gene from porcine S. suis strains to human streptococci in the mating experiments. These results show that, identical erm (B) gene sequences were present in animal and human streptococci and that transfer of the erm (B) gene from porcine S. suis to human streptococci and vice versa is possible, but probably occurs at a low frequency.     

Phenotypical and genotypical characteristics of invasive group B Streptococcus isolates in Western Sydney 2000-2005

AIMS: To analyse antimicrobial susceptibility and serotypes of group B streptococcus (GBS) bloodstream isolates from different patient groups. METHODS: Susceptibility to penicillin, erythromycin and clindamycin was measured for 99 bloodstream GBS isolates collected between October 2000 and July 2005. Multiplex PCR-based reverse line blot (mPCR/RLB) assays were used to identify macrolide resistance genes and capsular serotype for each isolate. Clinical correlation was obtained from chart review. RESULTS: Adult bacteraemia accounted for 84 of 99 (85%) isolates, and were usually associated with underlying diseases such as diabetes, malignancy and renal failure. Overall mortality was 10%. Known macrolide resistance genes [ermB (2), ermA/TR (3) and mefA/E (2)] were detected in seven of eight erythromycin resistance isolates. Four of these isolates expressed MLSB phenotype, two with constitutive (ermB) and two with inducible (ermA/TR) clindamycin resistance. Of four M phenotype isolates, two had mefA/E, one had ermA/TR and one had no detectable macrolide resistance genes. Serotype III was significantly more common in neonatal isolates; serotype V was more common among adult isolates and was associated with increased mortality. CONCLUSIONS: mPCR/RLB is a rapid molecular method to identify GBS serotype and macrolide resistance genes. This is the first major study correlating these characteristics with demographic data for invasive isolates.     

Characterization of ermB gene transposition by Tn1545 and Tn917 in macrolide-resistant Streptococcus pneumoniae isolates

In Streptococcus pneumoniae, the ermB gene is carried by transposons, such as Tn917 and Tn1545. This study investigated the relationship between macrolide resistance and the presence of the ermB gene on Tn917 or Tn1545 in 84 Japanese pneumococcal isolates. Macrolide-resistant strains were classified into two groups as follows. Group 1 (19 strains) showed a tendency to high resistance to erythromycin (MIC at which 50% of isolates are inhibited, 4 mg/liter; MIC at which 90% of isolates are inhibited [MIC(90)], 128 mg/liter) but susceptibility to rokitamycin (MIC(90), 1 mg/liter), with the ermB gene located on Tn1545. Group 2 (65 strains) showed a tendency to high resistance to both antibiotics (MIC(90)s for both erythromycin and rokitamycin, >128 mg/liter), with the ermB gene located on Tn917. There were no strains with constitutive macrolide resistance in either group. All of the strains in group 2 had a deletion in the promoter region of ermB and an insertion of the TAAA motif in the leader peptide. The results of pulsed-field gel electrophoresis and serogrouping showed that Tn1545 spread clonally while Tn917 spread both horizontally and clonally. In conclusion, in Japanese macrolide-resistant S. pneumoniae isolates, the ermB gene is carried and spread primarily by Tn917.     

Presence and mechanism of antimicrobial resistance among enterococci from cats and dogs

The presence and mechanism of acquired resistance to erythromycin, tylosin, lincomycin, quinupristin/dalfopristin, tetracycline, chloramphenicol, gentamicin, kanamycin, and vancomycin were determined in 97 and 104 enterococci isolated from rectal swabs of cats and dogs, respectively. Eleven feline and three canine enterococcal isolates contained the aac(6')-Ie-aph(2')-Ia gene encoding high-level resistance to gentamicin, an antibiotic often used for treating enterococcal infections in humans. The combination of erm(B) and vat(E) genes encoding resistance to streptogramins was detected in one canine quinupristin/dalfopristin-resistant Enterococcus faecium isolate. Four quinupristin/dalfopristin-resistant enterococci only contained the erm(B) gene. Cross resistance against macrolides and lincosamides (30%) and resistance against tetracyclines (55%) was found to be widely distributed among enterococci from pets. In all of the feline and in 93% of the canine macrolide and lincosamide-resistant isolates, this resistance was encoded by the erm(B) gene. tet(M) was the most prevalent tetracycline resistance gene. It was detected in 91% of the feline and 86% of the canine tetracycline- resistant enterococci. A high occurrence of the Tn916/Tn1545 transposon family was found among these tet(M)-positive isolates. Enterococci from pet animals with resistance against vancomycin were not found. This study shows that enterococci from the intestinal microbiota of cats and dogs may act as a reservoir of resistance genes for animal or human pathogens.     

Detection of the macrolide-efflux protein A gene mef(A) in Enterococcus faecalis

The mef(A) gene codes for an efflux protein that conveys resistance to 14- and 15-membered macrolides. Enterococci are emerging pathogens, as well as indicator and reservoir bacteria that are known to have a strong tendency to acquire resistance genes. A total of 485 Enterococcus faecalis strains of porcine (n = 239) and human origin (n = 246) were screened for the presence of the mef(A) gene by using polymerase chain reaction. In total, 29 E. faecalis of porcine (n = 10) and human (n = 19) origin were positive for the presence of the mef(A) gene. Most of the mef(A)-containing strains were isolated from fecal samples of healthy individuals; only one strain originated from a stool sample of a diseased pig. To our knowledge, this is the first report on the occurrence of the mef(A) gene in E. faecalis apart from mating experiments. The main clinical relevance of this study is that donor E. faecalis might transfer the mef(A) gene to recipients that are usually combated with macrolides. Hence, the role of E. faecalis as a resistance reservoir with respect to limited treatment options are a cause for concern.     

Quinupristin-dalfopristin resistance in Enterococcus faecium isolates from humans, farm animals, and grocery store meat in the United States

Three hundred sixty-one quinupristin-dalfopristin (Q-D)-resistant Enterococcus faecium (QDREF) isolates were isolated from humans, turkeys, chickens, swine, dairy and beef cattle from farms, chicken carcasses, and ground pork from grocery stores in the United States from 1995 to 2003. These isolates were evaluated by pulsed-field gel electrophoresis (PFGE) to determine possible commonality between QDREF isolates from human and animal sources. PCR was performed to detect the streptogramin resistance genes vatD, vatE, and vgbA and the macrolide resistance gene ermB to determine the genetic mechanism of resistance in these isolates. QDREF from humans did not have PFGE patterns similar to those from animal sources. vatE was found in 35%, 26%, and 2% of QDREF isolates from turkeys, chickens, and humans, respectively, and was not found in QDREF isolates from other sources. ermB was commonly found in QDREF isolates from all sources. Known streptogramin resistance genes were absent in the majority of isolates, suggesting the presence of other, as-yet-undetermined, mechanisms of Q-D resistance.     

Macrolide-resistance mechanisms in Streptococcus pneumoniae isolates from Chinese children in association with genes of tetM and integrase of conjugative transposons 1545

This study investigated macrolide-resistant Streptococcus pneumoniae carried by Beijing children presenting with respiratory tract infections. Nasopharyngeal S. pneumoniae strains were tested for sensitivity with 15 antibiotics and further analyzed for phenotypes of macrolide-resistant strains and by PCR for the macrolide-resistant genes ermB, mefA, tetM, and integrase of conjugative transposon (Tn1545) intTn. We found 185 strains of S. pneumoniae relatively highly resistant to erythromycin (78.9%), clindamycin (76.2%), tetracycline (86%), and SMZ-TMP (78.7%) but with relatively low resistance to amoxicillin (2.2%), cefaclor (15.5%), ceftriaxone (2.8%), and cefuroxime (14.1%). The 146 strains of erythromycin-resistant S. pneumoniae showed extensive cross-resistance to other macrolides like azithromycin (100%), clarithromycin (100%), acetylspiramycin (95.2%), and clindamycin (95.9%). Genes ermB and mefA were detected in all erythromycin-resistant strains, with ermB(+) 79.5%, ermB + mefA(+) 17.8%, and mefA(+) 2.7%. About 96.9% of tetracycline-resistant isolates were positive for tetM, compared to 26.9% of sensitive strains. Ninety percent of tetracycline-resistant strains were also erythromycin-resistant versus 11.5% of tetracycline-sensitive strains. The intTn gene was present in 87.6% of S. pneumoniae strains and correlated with erythromycin and tetracycline resistance. The close relationship between the conjugative transposon Tn1545 and the genes ermB and tetM is probably one of the important mechanisms explaining the multiple drug resistance of S. pneumoniae.