伤寒沙门菌主动外排多重耐药基因acrB与表达水平研究

目的调查临床分离伤寒沙门菌对常用抗生素的耐药情况与多重耐药主动外排基因acrB的检测、序列分析及其表达水平。方法根据NCCLS推荐的琼脂二倍稀释法测定7种抗生素对伤寒沙门菌的抗菌活性，以基因库序列为参考设计引物PCR扩增acrB、测序并用RT—PCR方法检测其表达水平。结果32株伤寒沙门菌对氧氟沙星、环丙沙星、头孢噻肟、哌拉西林、氯霉素、四环素、庆大霉素的耐药率分别为0、0、0、28．13％、43．75％、40．63％和12．5％，其中多重耐药菌10株。所有细菌均检测到多重耐药外排基因acrB．测序显示与参考沙门菌序列（No．AL627267）比较，有2处碱基变异。与大肠埃希菌（No．ECU00734）比较，碱基同源性为85．51％（61／421），提示其碱基序列同源性极高。对不同种类抗生素耐药及不耐药部分伤寒沙门菌共16株进行一步法RT—PCR检测acrB表达水平，结果所测伤寒沙门菌均检测到多重耐药外排基因acrB的表达，多重耐药株主动外排的表达较其它菌株明显增强。结论伤寒沙门菌对喹诺酮类、第三代头孢菌素类耐药率低，对哌拉西林、氯霉素、四环素耐药率相对较高，且有多重耐药。伤寒沙门菌中均存在acrAB主动外排系统，acrB与大肠埃希菌同源性高，对不同结构抗生素耐药的种类越多，表达水平越高。主动外排机制可能是伤寒沙门菌多重耐药的主要原因之一。     

辽宁地区沙门菌整合子与耐药相关性研究

摘要：目的 及时掌握辽宁地区沙门菌整合子的分布以及对常用抗菌药物的耐药情况,获取沙门菌整合子与耐药性的相关性,从而为临床用药及治疗提供指导。方法 本文对来源于食品以及病患的149株沙门菌,利用PCR扩增的方法,进行整合子类别的筛选,并将扩增的整合子基因盒进行基因测序,同时通过药敏板测定(耐药性实验)对沙门菌与15种临床常用抗菌药物的耐药相关性进行研究。结果 149株沙门菌中未发现第II类、第III类整合子,检出第I类整合子的菌株50株,I类整合子阳性率为33.6%。50株整合子阳性菌株中25株携带耐药基因盒,片段范围从1500~1800 bp。测序结果表明,其中22株整合子携带dfrA17-aadA5基因盒,2株携带dfrA12-aadA2基因盒,1株首次检出罕见耐药基因盒linG。根据整合子携带情况不同,对15种抗菌药物的耐药率进行对比分析,结果显示整合子阳性菌对9种抗菌药物的耐药率显著高于整合子阴性菌(P<0.01),分别为氨苄西林、四环素、氯霉素、头孢噻肟、头孢唑林、庆大霉素、复方磺胺甲恶唑、阿奇霉素和环丙沙星。辽宁地区沙门菌多重耐药率达50.3%。结论 I类整合子在沙门菌中分布广泛,抗性基因表型与耐药结果相一致,整合子的携带与沙门菌多重耐药率高度相关。沙门菌对亚胺培南和头孢西丁保持高敏感率,可以用于对常规抗菌药物耐药的沙门菌的治疗。     

耐亚胺培南铜绿假单胞菌8株基因型分析

目的检测8株耐碳青霉烯类抗菌药物铜绿假单胞菌携带的耐药基因。方法采用K-B琼脂扩散法做抗菌药物敏感实验,聚合酶链式反应技术（PCR）在所收集菌株中扩增BLAimp、BLAvim、OXA基因。结果用PCR技术在8株亚胺培南耐药的铜绿假单胞菌基因组中扩增出BLAimp基因。结论实验室检测可帮助临床合理选用抗菌药物并减少耐药性的传播,提高烧伤感染的治愈率。     

儿童非伤寒沙门菌肠道感染的流行病学特点和药敏结果分析

[摘要]目的：了解本地区儿童非伤寒沙门菌肠道感染的流行病学特点,并监测分析其对抗菌药物的敏感性,探讨阿奇霉素治疗肠道非伤寒沙门菌感染的可能性,为进一步控制非伤寒沙门菌感染提供科学依据。方法：回顾性分析2014年7月至2016年6月深圳市儿童医院确诊并住院治疗的76例肠道非伤寒沙门菌感染患儿的年龄、性别、发病季节等流行病学特点;采用纸片扩散法检测5种常用抗菌药物的敏感性,使用E-Test法和纸片扩散法检测阿奇霉素的最低抑菌浓度（MIC）,并对阿奇霉素的MIC值与其抑菌圈直径进行直线相关回归分析。结果：76株非伤寒沙门菌属于4种血清群,以鼠伤寒沙门菌血清型和肠炎沙门菌血清型为主;1岁以下小婴儿54例,占71.05%;非伤寒沙门菌对复方磺胺甲恶唑、头孢曲松、氯霉素、奈定酸、氨苄西林的敏感性分别为73.68%、63.16%、60.53%、27.63%和22.37%;检出多重耐药非伤寒沙门菌16株,占21.05%;E-TEST法检测阿奇霉素对沙门菌的MIC为2~96 μg/mL,MIC50为3 μg/mL,MIC90为4 μg/mL;纸片扩散法检测其抑菌圈直径范围为6.50 ~19.75 mm,二者显著相关（P<0.01,︱r︱=-0.836)。结论：本地区儿童肠道感染的非伤寒沙门菌血清型多样,以小婴儿为主,多重耐药菌比例较高;检出的非伤寒沙门菌对阿奇霉素的基础数据可以作为以后临床应用的参考指标。     

36例儿童非伤寒沙门菌感染的临床特点及其对抗菌药物的耐药性分析

目的:分析36例儿童非伤寒沙门菌感染的临床特点及其对抗菌药物的耐药性,为临床合理使用抗菌药物提供参考。方法:选取2013年7月—2016年6月期间收治的非伤寒沙门菌感染患儿36例资料,采用回顾性分析法分析其临床特点及其对抗菌药物的耐药性。结果:36例非伤寒沙门菌感染患儿中,主要临床类型为胃肠炎型(7~11月为发病高峰期),其最常见的病原菌类型为鼠伤寒沙门菌,且其对多种抗菌药物耐药;根据药敏试验结果选用抗菌药物对症治疗,患者的预后良好。结论:非伤寒沙门菌感染的致病机制尚未完全明确,采用脉冲场凝胶电泳(PFGE)分型可有效地检测菌株的同源性;非伤寒沙门菌的耐药情况严重,需根据药敏试验结果合理选用抗菌药物,尤其是重视院内交叉感染。     

大肠埃希菌耐喹诺酮类抗菌药的相关耐药基因检测及耐药机制分析

目的 探讨大肠埃希菌耐喹诺酮类抗菌药的相关耐药基因检测及耐药机制.方法 选取我院尿液等排泄物和分泌物标本中分离出的150株大肠埃希菌株,应用纸片扩散法进行药敏试验,采用PCR技术检测qnr以及aac(6')-Ib-cr质粒基因的表达,并对PCR产物进行DNA测序分析.结果 150株大肠埃希菌对喹诺酮类抗菌药物的耐药率均超过50％,20株菌检出阳性基因qnrB,qnrS以及aac(6')-Ib-cr的阳性率分别为12.20％、9.76％、13.41％,共有8株菌同时携带超过2种质粒基因,其对喹诺酮类药物均耐药,同时合并有其他类型抗菌药物的耐药情况,12株菌检出单个质粒基因,其中4株对喹诺酮类敏感.结论 大肠埃希菌的耐药情况十分严重,存在qnrB、qnrS、aac(6')-1b-cr流行,并存在两种及多种耐药基因共存于同一细菌中的现象,质粒介导的喹诺酮耐药基因数量与耐药种类数量呈正相关.     

婴幼儿腹泻沙门菌分型与耐药机制分析

目的对我国武汉地区0~3岁临床婴幼儿腹泻沙门菌进行了分离、鉴定、耐药性和分子分型分析。方法超广谱头孢菌素和氟喹诺酮类抗生素是临床上用于治疗侵袭性沙门菌感染的重要抗生素,对这些抗生素的耐药性传播已引起了广泛的重视,本研究从3746例儿科临床门诊病人粪便样本中共检出221(5.9%)株沙门菌,分别属于29个血清型,抗生素的耐药谱在不同血清型间存在明显差异。环丙沙星耐药株多为鼠伤寒沙门菌,且均对4种以上非喹诺酮类抗生素耐药,22株环丙沙星耐药鼠伤寒沙门菌中19株位于同一个脉冲场群中。在18株沙门菌中检出质粒介导的喹诺酮耐药机制aac-(6’)-Ib-cr,其中4株菌中还携带qnr基因。在7株菌中检出质粒介导的超广谱-内酰胺酶类CTX-M-14编码基因,其中2株菌对环丙沙星的敏感性下降。结果与结论氟喹诺酮类抗生素不适于在当地用于侵袭性鼠伤寒沙门菌感染治疗,同时应对头孢曲松耐药-氟喹诺酮敏感性下降的菌株进行积极的主动监测。     

296例腹泻患儿非伤寒沙门菌菌型分布及药敏分析

目的 了解2013至2015年广州地区腹泻患儿非伤寒沙门菌感染的流行病学特征和耐药情况.方法 对2013至2015广东省妇幼保健院门诊及住院的腹泻患儿的粪便标本进行沙门菌培养和血清学分型,采用VITEK-2 Compact进行药物敏感性试验.结果 296株非伤寒沙门菌可分为33种血清型,其中鼠伤寒沙门菌171株(占57.43％),斯坦利沙门菌29株(占9.80％),肠炎沙门菌18株(占6.08％).患儿男女性别比约为1.51∶1(178/118),＜1岁的患儿占84.45％,每年的7～ 10月为发病高峰.296株沙门菌除了对碳青霉烯类、左氧氟沙星和三代头孢耐药率较低外,对一、二代头孢、庆大霉素、妥布霉素和复方磺胺甲恶唑耐药较为严重.鼠伤寒沙门菌对三代头孢的耐药率呈现逐年上升的趋势.结论 广州地区儿童非伤寒沙门菌感染性腹泻以＜1岁的婴幼儿居多,夏秋季节高发.鼠伤寒沙门菌是本地区最主要的菌型,也是耐药最严重的血清型.临床应根据药敏试验结果合理选用抗生素.     

沙门菌血清学鉴定与耐药性的临床分析

目的分析沙门菌所致感染性腹泻及食物中毒的主要血清型及耐药性情况,掌握耐药趋势,为临床合理使用抗菌药物提供依据。方法对2011年3月至2013年11月我市某腹泻病监测点感染性腹泻病例分离出的106株沙门菌进行血清学鉴定,并对其对不同抗菌药物药敏试验结果及耐药性进行数据处理。结果 106株沙门菌鉴定出10种不同的血清型,其中肠炎沙门菌、德尔卑沙门菌和鼠伤寒沙门菌菌株最多;12种抗生素都有不同程度的耐药性,其中对环丙沙星的耐药率最低为4.72%,对氨苄西林的耐药率最高为61.32%。结论提高对医院感染的监测,及时掌握细菌耐药的最新动态,避免抗菌药物的滥用,为合理使用抗生素提供临床依据。     

2017～2020年我院非伤寒沙门菌感染患儿流行病学特点及药敏分析

摘要：目的:了解宁德市医院就诊儿童非伤寒沙门菌肠道感染的流行病学特点及耐药情况,为临床正确诊断及合理用药提供依据。方法:收集我院2017～2020年确诊为非伤寒沙门菌感染的127例患儿相关资料,统计分析年龄、性别、发病季节等流行病学特点,并进行血清分型和耐药性分析。结果:我院非伤寒沙门菌感染患儿发病时间多集中于5～10月;0～1岁和1～2岁患儿检出非伤寒沙门菌最多,分别为59株和31株。127株沙门菌分为10种血清型,最常见为鼠伤寒沙门菌（49.61%）,其次为都柏林沙门菌（10.24%）。127株非伤寒沙门菌对氨苄西林、复方磺胺甲噁唑耐药率较高,对氯霉素、环丙沙星、头孢曲松、阿奇霉素和头孢哌酮/舒巴坦耐药率相对较低;其中鼠伤寒沙门菌对上述7种药物的耐药率高于都柏林沙门菌;对美罗培南全部敏感。结论:我院患儿感染非伤寒沙门菌以夏秋季节为主,2岁以内高发;检出率最高的血清型为鼠伤寒沙门菌和都柏林沙门菌,其中鼠伤寒沙门菌耐药率较高。     

Antimicrobial resistance of Salmonella enterica group C strains isolated from humans in Turkey, 2000-2002

Fifty-three Salmonella enterica group C isolates obtained from various human samples (47 stool, 4 blood and 2 urine) in ten provinces of Turkey between 1 July 2000 and 30 June 2002 were serotyped and resistance to antimicrobials was investigated by agar dilution tests. The isolates were identified as S. Choleraesuis (11), S. Hadar (7), S. Irumu (4), S. Virchow (3), S. Tallahassee (3), S. Paratyphi C (2), S. Braenderup (2), S. Othmarschen (2), S. Menston (2), S. Concord (2), S. Infantis (2), S. Kottbus (2), S. Edinburg (1), S. Oranienburg (1), S. Muenchen (1) and S. Malmoe (1). Antimicrobial resistance rates of S. enterica groups C1 and C2 were high for ampicillin (26% and 60%, respectively), amoxicillin/clavulanic acid (11% and 40%), chloramphenicol (16% and 27%) and tetracycline (3% and 40%). The percentages of strains sensitive to all antimicrobials were 58% and 33%, respectively. Multiresistance was not observed in group C1 isolates, but the rate of multiresistant isolates was 13% in group C2. The rate of decreased ciprofloxacin susceptibility (CipL) was 61% in serogroup C1 and 20% in serogroup C2. These results indicated that S. enterica group C infections in humans were not infrequent in Turkey and that multiple antimicrobial resistance was common within these strains.     

Prevalence and antimicrobial susceptibility patterns among gastroenteritis-causing pathogens recovered in Europe and Latin America and Salmonella isolates recovered from bloodstream infections in North America and Latin America: report from the SENTRY Antimicrobial Surveillance Program (2003)

Gastroenteritis-causing pathogens are the second leading cause of morbidity and mortality worldwide. Complicating the clinical diarrhoea syndrome is the emergence of antimicrobial resistance among the responsible bacterial pathogens. The reported increases in fluoroquinolone resistance in Salmonella, Shigella and Campylobacter have been extremely worrisome considering the primary role of ciprofloxacin as a treatment. In this study, 1479 bacterial isolates from gastroenteritis infections were collected in Europe and Latin America, which included Salmonella spp. (834; 56%), Shigella spp. (311; 21%), Campylobacter spp. (182; 12%) and Aeromonas spp. (72; 5%). The fluoroquinolones displayed the greatest activity against these pathogens, with only three non-Campylobacter spp. strains being non-susceptible using current Clinical and Laboratory Standards Institute (CLSI) breakpoint criteria. Whilst ciprofloxacin resistance in European and Latin American Salmonella was only 0.2% and 0.0%, respectively, a total of 16.2% and 12.9% of isolates were resistant to nalidixic acid, indicating possible first-step gyrA mutations. Among confirmed extended-spectrum beta-lactamase-producing Salmonella strains, CTX-M genes were detected in 15 originating from Russia. Erythromycin and azithromycin were the most potent agents tested against Campylobacter spp. (values of minimum inhibitory concentration for 90% of the organisms, 0.5 mg/L and 0.12 mg/L, respectively), with erythromycin displaying the highest susceptibility (91.1%). Salmonella isolates from bloodstream infections displayed antibiograms that were nearly identical to strains causing gastroenteritis. Considering the role that antimicrobial therapy plays in the management of moderate to severe bacterial gastroenteritis, global surveillance and local/national public health programmes can provide critical data illuminating the dissemination of resistance and guidance for empirical therapy.     

Salmonella bloodstream infections: report from the SENTRY Antimicrobial Surveillance Program (1997-2001)

Salmonella spp. are significant bloodstream pathogens and are routinely monitored for antimicrobial resistance by the SENTRY Antimicrobial Surveillance Program. Six hundred and one bloodstream infection (BSI) isolates of Salmonella spp., collected over a 5-year period (1997-2001) were tested for their susceptibility against 20 antimicrobial agents, comparing year and geographical region. Salmonella enterica serotype Typhi was the most frequently identified 'species' (43% of identified strains), although 'unspeciated' strains predominated overall (54.2%). The rank order for six selected drugs tested by their MIC(90) values and percentage susceptibility was: ceftriaxone (< or =0.25 mg/l; 99.5% susceptible)>ciprofloxacin (0.12 mg/l; 99.3%)> trimethoprim/sulphamethoxazole (< or =0.5 mg/l; 92.7%)>amoxycillin/clavulanate (16 mg/l; 89.7%)>ampicillin (>16 mg/l; 81.0%)>tetracycline (>8 mg/l; 79.4%). Most isolates remained highly susceptible to all 20 agents examined, with the exception of Salmonella Typhimurium (only 35.3% susceptible to tetracycline, 41.2% to ampicillin, and 61.8% to amoxycillin/clavulanate). DT104 resistance phenotypes were noted in 3.4 and nearly 60.0% of unspeciated Salmonella and S. Typhimurium, respectively. Unexpectedly, the highest overall susceptibility rates were recorded in Latin America. Fluoroquinolone resistance was observed and nalidixic acid screening MICs (< or =8 mg/l) predicted full susceptibility to ciprofloxacin. Five-year results from the SENTRY Program show no clear trend toward greater resistances in Salmonella spp. BSIs for the commonly used antimicrobial classes. With the exception of S. Typhimurium DT104, most Salmonella spp. remain highly susceptible to the tested antimicrobials that maybe utilized for Salmonella BSI.     

Emergence of multidrug-resistant Salmonella enterica serovar Typhi associated with a class 1 integron carrying the dfrA7 gene cassette in Nepal

A total of 121 Salmonella enterica serovars Typhi and Paratyphi A isolated from enteric fever patients at a university hospital in Nepal between February 2004 and January 2006 were tested for their antimicrobial susceptibility. The occurrence and cassette content of integrons as well as the molecular mechanisms of resistance among the multidrug-resistant (MDR) S. Typhi were evaluated. Thirty-nine percent of the isolates were susceptible to all the antimicrobial agents tested. Seven of the S. Typhi strains were MDR. None of the 121 S. enterica isolates were resistant to ciprofloxacin, cefazolin, rifampicin or kanamycin. All MDR S. Typhi isolates contained a class 1 integron with a single cassette, dfrA7, conferring resistance to trimethoprim. Pulsed-field gel electrophoresis (PFGE) of XbaI-generated genomic restriction fragments yielded 12 different patterns. Five of the seven MDR isolates containing class 1 integrons had an identical PFGE pattern. Resistance to sulfamethoxazole, streptomycin, ampicillin, tetracycline and chloramphenicol was mediated by sul1, strA-strB, blaTEM-like, tetB and catA genes, respectively. To the best of our knowledge, this is the first report of integron-associated multidrug resistance as well as the first molecular characterisation of the mechanism of resistance of S. Typhi isolated from Nepal. This study indicates the spread of integron-associated multidrug resistance in S. Typhi in Nepal.     

High prevalence of plasmid-mediated quinolone resistance determinant aac(6')-Ib-cr amongst Salmonella enterica serotype Typhimurium isolates from hospitalised paediatric patients with diarrhoea in China

In this study, the antimicrobial susceptibilities and prevalence of plasmid-mediated quinolone resistance determinants amongst Salmonella enterica serotype Typhimurium isolates from hospitalised paediatric patients with diarrhoea in China were investigated. In total, 40 (64.5%) of 62 S. Typhimurium isolates were resistant to ciprofloxacin (minimum inhibitory concentration ≥0.5 μg/mL), comprising 28 isolates with low-level resistance and 12 isolates with high-level resistance. All ciprofloxacin-resistant isolates were multiresistant to other antimicrobial agents. Four pulsed-field gel electrophoresis (PFGE) clusters were found amongst the 40 ciprofloxacin-resistant isolates, amongst which PFGE clusters A, B, E and D accounted for 7, 4, 1 and 28 isolates, respectively. Two isolates with high-level ciprofloxacin resistance had two mutations in the quinolone resistance-determining regions (QRDRs) of gyrA and parC. The remaining ciprofloxacin-resistant isolates had only one mutation in the QRDR of gyrA. All 62 S. Typhimurium isolates were negative for qnr genes and qepA and 23 (37.1%) of the isolates were positive for aac(6')-Ib-cr. Nineteen isolates harbouring aac(6')-Ib-cr belonged to PFGE cluster D. A high prevalence of ciprofloxacin resistance and aac(6')-Ib-cr was found amongst S. Typhimurium isolates in China from hospitalised paediatric patients with diarrhoea not receiving quinolones. A single mutation in the QRDR of gyrA as well as production of AAC(6')-Ib-cr contributed to ciprofloxacin resistance. Clonal spread was responsible for the dissemination of aac(6')-Ib-cr amongst S. Typhimurium isolates.     

Stenotrophomonas maltophilia resistance to trimethoprim/sulfamethoxazole mediated by acquisition of sul and dfrA genes in a plasmid-mediated class 1 integron

Stenotrophomonas maltophilia is becoming a more and more common cause of infections. In this study, the minimal inhibitory concentrations of trimethoprim/sulfamethoxazole (SXT), ceftazidime, minocycline, levofloxacin, chloramphenicol and ticarcillin/clavulanic acid were determined and the distribution of integrons and sul1, sul2 and dfrA genes was investigated in 102 S. maltophilia isolates collected from patients treated in 31 hospitals in Anhui, China, in the month of September in 2006-2008. The rate of resistance to SXT was up to 30.4%, and 64.7% of isolates were class 1 integron-positive. Sequencing data revealed the following novel gene cassettes embedded in class 1 integrons: dfrA17-aadA5; dfrA12-aadA2; aacA4-catB8-aadA1; aadB-aac(6')-II-bla(CARB-8); and arr-3-aacA4. This is the first report of the gene cassettes dfrA17-aadA5 and dfrA12-aadA2 and of sul2 genes in SXT-resistant S. maltophilia isolates in China. None of the SXT-susceptible S. maltophilia isolates were positive for sul2 or dfrA gene products by polymerase chain reaction (PCR), but PCR products for sul1 were detected in 27 SXT-susceptible and 25 SXT-resistant isolates. The findings from this study indicate that the sul1 gene, in combination with dfrA17 and dfrA12 gene cassettes and sul2 genes located within a 7.3kb plasmid, lead to a high rate of SXT resistance and also confirm the need for ongoing resistance surveillance.     

致病性猪沙门菌四环素耐药基因tetB的PCR检测

目的检测临床分离猪源致病性沙门菌四环素的耐药基因,确定沙门菌四环素耐药基因类型。方法用KB法测定分离株对四环素等21种抗生素的耐药情况,用PCR方法检测四环素耐药基因tetA、tetB、tetC、tetD、tetE、tetG及tetK,并对扩增产物进行测序。结果临床分离株全部对四环素耐药,33株沙门菌中有29株扩增出tetB特异性片段,基因序列与参考菌的同源性为99%,tetB检测与药敏试验阳性符合率为87.9%。结论tetB的PCR检测对四环素耐药性具有较高的特异性,tetB基因是决定本试验中临床分离株四环素耐药的主要基因,为四环素耐药性的分子流行病学监测提供了依据。     

Recognition of mechanisms involved in bile resistance important to halting antimicrobial resistance in nontyphoidal Salmonella

Increasing antimicrobial resistance in nontyphoidal Salmonella (NTS) is a global public health problem that complicates antimicrobial therapy. As an enteric pathogen, Salmonella must endure the presence of bile in the intestinal tract during the course of infection. In this study, we sought to identify Salmonella genes necessary for bile resistance and to investigate their association with antimicrobial resistance. Four genes related to bile resistance were identified, namely rfaP, rfbK, dam and tolC. The first three genes are involved in lipopolysaccharide synthesis, and tolC is associated with an efflux pump. Antimicrobial susceptibility testing showed increased susceptibility to polymyxin B and ciprofloxacin in rfaP and tolC mutants of Salmonella, respectively. Genetic analysis of 45 clinical isolates of NTS revealed that all isolates with reduced susceptibility to fluoroquinolones (minimum inhibitory concentration ≥0.125 mg/L) were associated with point mutations in the quinolone resistance-determining regions of the gyrA and parC genes. The efflux pump also played a role, as evidenced by the reduction in fluoroquinolone resistance when the TolC efflux pump was inhibited by Phe-Arg-β-naphthylamide, a competitive efflux pump inhibitor. Based on these results, we conclude that an intact membrane structure and the efflux pump system provide mechanisms enabling NTS to resist bile. Caution should be taken when using ciprofloxacin and polymyxin B to treat Salmonella enteric infection, as resistance to these agents involves the same mechanisms. Addition of an efflux pump inhibitor to fluoroquinolones may be an effective strategy to deal with the increasing resistance in NTS.     

Antimicrobial susceptibilities and analysis of genes related to penicillin or macrolide resistance in Streptococcus pneumoniae

One hundred and seventy-seven strains of Streptococcus pneumoniae derived from respiratory specimens between 1987 and 2001 were evaluated for their antimicrobial susceptibilities and distribution of genes related to penicillin and macrolide resistance. Resistance rates tended to be higher for the 1996-2001 isolates than for the 1987-1995 isolates for all beta-lactams tested. For benzylpenicillin the MIC(90) value of the isolates derived between 1996 and 2001 was 1.56 mg/L, while that of strains isolated between 1987 and 1990 was 0.05 mg/L. Furthermore, the number of strains susceptible to macrolides also decreased, but only two strains isolated in 1993 were resistant to levofloxacin of the 177 S. pneumoniae strains tested. When of genes relating to penicillin resistance were analysed using PCR with primers specific to susceptible alleles, although more than 50% of strains from 1987 to 1990 and 1991 to 1995 revealed no mutations in the pbp 1a, 2x and 2b genes, only 30.0% of strains derived between 1996 and 2001 showed no mutations in the pbp gene. Strains having mutations in all three pbp genes (1a, 2x and 2b) by the PCR method increased from only 2.2% in the 1987-1990 derived strains to 27.5% in the 1996-2001 strains. Furthermore, 64.1 and 60.0% of the isolates from 1987 to 1990 and 1991 to 1995, respectively, did not possess either the mefA or ermB by PCR analysis. Conversely, 75.0% of isolates from 1996 to 2001 possessed mefA and/or ermB. These genetic changes may explain the increase in the number of penicillin and macrolide resistant strains. We believe that it is important to evaluate changes in MIC as well as genetic mutations in order to select the most appropriate therapy for S. pneumoniae infections.     

Antimicrobial susceptibility phenotypes, resistance determinants and DNA fingerprints of Salmonella enterica serotype Typhimurium isolated from bovine in Southern Japan

A longitudinal study was conducted in cattle to determine the antimicrobial resistance phenotypes, integron elements, resistance genes and pulsed-field gel electrophoresis fingerprints among Salmonella enterica serotype Typhimurium isolates. A total of 33 strains were isolated and categorised into Groups A, B and C during the period 1989-2004. Thirty-one strains (93.9%) showed resistance to ampicillin (A) encoded by bla(OXA-1), bla(TEM) and bla(PSE-1) genes; 84.8% showed resistance to chloramphenicol (C) encoded by floR and catA1; 97.0% were resistant both to streptomycin (S) and sulfamethoxazole (Su), the former encoded by aadA1 and aadA2; 100% were resistant to oxytetracycline (T) encoded by tetA, tetB and tetG; and 42.4% were resistant to kanamycin (Km) encoded by aphA1-Iab. Multidrug resistance types observed were ACSSuT-Km (n=13), ACSSuT (n=15), ASSuT (n=3) and SSuT (n=2). Class 1 integrons ranging from 1.0 kb to 1.9 kb were detected from 54.5% of isolates (18/33). Integrons were not detected initially (1989-1992), then during the 1993-1996 interval a high frequency of 1.0 kb and 1.2kb amplicons were detected and during 2000-2004 the amplicon size increased to 1.7 kb and 1.9 kb. We report evidence of additional integration of resistance gene cassettes as shown by integrons with increased size. Finally, group B strains showed banding patterns indistinguishable from S. Typhimurium DT104 reference strain, indicating that the DT104 lineage existed on the island since 1993.