Molecular epidemiology and mechanisms of tigecycline resistance in carbapenem-resistant Klebsiella pneumoniae isolates

BackgroundThe emergence and transmission of tigecycline‐ and carbapenem‐resistant Klebsiella pneumoniae (TCRKP) have become a major concern to public health globally. Here, we investigated the molecular epidemiology and mechanisms of tigecycline resistance in carbapenem‐resistant K pneumoniae (CRKP) isolates.MethodsForty‐five non‐duplicate CRKP isolates were collected from January 2017 to June 2019. We performed antimicrobial susceptibility tests, multilocus sequence typing (MLST), and pulsed‐field gel electrophoresis (PFGE). PCR and DNA sequencing were performed for the detection and mutation analysis of acrR, oqxR, ramR, rpsJ, tet(A), and tet(X) genes, which are related to tigecycline resistance. The expression levels of efflux pump genes acrB and oqxB and their regulator genes rarA, ramA, soxS, and marA were assessed by quantitative real‐time PCR.ResultsThe resistance rate to tigecycline in CRKP isolates was 37.8% (17/45). K pneumoniae ST307 was a predominant clone type (70.6%, 12/17) among the TCRKP isolates. The expression levels of acrB (P < .001) and marA (P = .009) were significantly higher in the tigecycline‐resistant group than in the tigecycline‐intermediate and tigecycline‐susceptible groups. Increased expression of acrB was associated with marA expression (r = 0.59, P = .013).ConclusionsWe found that the activated MarA‐induced overexpression of AcrAB efflux pump plays an important role in the emergence of tigecycline resistance in CRKP isolates.     

Molecular characterization of carbapenemase producing Klebsiella pneumoniae strains by multiplex PCR and PFGE methods: The first K.pneumoniae isolates co-producing OXA-48/KPC and KPC/NDM in Turkey

IntroductionCarbapenems are frequently used in the treatment of multidrug-resistant infections caused by Klebsiella pneumoniae. The aim of the study is to definition and incidence of transferable carbapenemase genes of carbapenem resistant K. pneumoniae (CRKP) and to determine clonal relatedness of these strains in tertiary care hospital in Turkey.MethodsIdentification of all 100 K. pneumoniae isolates and low sensitivity to any of the carbapenem group antibiotics were determined by Vitek-2 (BioMérieux, France). The frequency of carbapenemase genes (bla_OXA-48, bla_NDM, bla_KPC, bla_VIM, bla_IMP) and extended spectrum beta-lactamase (ESBL) genes (bla_CTX-M, bla_SHV, bla_TEM) which frequently detected in Turkey, have been investigated by multiplex polymerase chain reaction (PCR). Clonal relatedness was determined using Pulsed-field gel electrophoresis(PFGE).ResultsNinety five isolates carried at least one of the carbapenemase genes (81.05% bla_OXA-48, 38.9% bla_NDM, 9.47% bla_KPC,1.05% bla_VIM). One isolate was carried the bla_OXA-48+KPC and the two isolates were carried the bla_KPC+NDM. PFGE demonstrated the presence of 24 pulse types and 63.09% of the isolates were in four main pulse types.ConclusionsThis study demonstrated the incidence of bla_NDM is beginning to reach endemic levels, in addition to bla_OXA-48 found endemic in Turkey. To our knowledge, this is the first report of the co-production of these two genes (bla_{KPC + NDM} and bla_{OXA-48 + KPC}) in CRKP isolates.     

Carbapenem antibiotic stress increases bla KPC ‐2 gene relative copy number and bacterial resistance levels of Klebsiella pneumoniae

BackgroundThe clinical isolation rates of carbapenem‐resistant Klebsiella pneumoniae (CR‐KP) continue to increase. In China, clinical CR‐KP isolates are mainly attributed to the bla _KPC‐2 gene carried on plasmids, and the bla _KPC‐2 copy number correlates with the expression of KPC enzymes, which can cause elevated carbapenem MICs.MethodsThirty‐seven CR‐KP isolates were collected at the Second People’s Hospital of Lianyungang City between January 2020 and March 2021, with no duplicate isolates, and were screened for the bla _KPC‐2 gene with PCR. Analysis of current CRKP resistance to clinically relevant antimicrobials using the bioMérieux VITEK^® 2 bacterial identification card. The multilocus sequence types of the strains were confirmed with PCR and DNA sequencing. Recombinant plasmids pET20b‐bla _KPC‐2 and pET20b‐CpsG were constructed, and the copy numbers of the recombinant plasmids per unit volume was calculated based on the molecular weight of the plasmids. After the genomes DNA of clinical isolates of K. pneumoniae carrying the bla _KPC‐2 gene were purified, the bla _KPC‐2 gene relative copy number in individual K. pneumoniae strains was indicated by the double standard curve method. Detection of MIC values changes of K. pneumoniae under imipenem selection pressure by broth microdilution method.ResultsAmong the 37 CR‐KP strains isolated, only the bla _KPC‐2 gene was detected in 30 strains, three strains were positive for the bla _NDM‐1 gene, two strains carried both the bla _KPC‐2 and bla _NDM‐1 genes, and two strains without detectable carbapenem resistance genes. The ST11 clone was predominant among the 37 carbapenem‐resistant K. pneumoniae isolates. Drug sensitivity testing showed that except for polymyxins (100% susceptible) and tigecycline (75.7% intermediate), the 37 CR‐KP strains were resistant to almost all antimicrobial drugs. The bla _KPC‐2 relative copy number in nine ST11 clinical isolates of K. pneumoniae was 7.64 ± 2.51 when grown on LB plates but 27.67 ± 13.04 when grown on LB plates containing imipenem. Among these nine isolates, five CRKP strains exhibited elevated MICs to imipenem, while the remaining four strains showed unchanged MIC values to imipenem.ConclusionCarbapenem‐resistant Klebsiella pneumoniae isolates may have multiple pathways to achieve high levels of carbapenem resistance, and moderate carbapenem pressure can increase the copy number of KPC enzyme genes in CRKP strains and enhance the degree of carbapenem resistance in the strains.     

Ceftazidime-avibactam resistance and restoration of carbapenem susceptibility in KPC-producing Klebsiella pneumoniae infections: A case series

ObjectivesSince the introduction of the β-lactam/β-lactamase inhibitor ceftazidime-avibactam (CZA), rapid evolution of resistance has been reported in different KPC-producing Klebsiella pneumoniae isolates. In this multicenter retrospective study, we describe the emergence of CZA resistance and evaluate the mutations that might be responsible for the restoration of carbapenem susceptibility.MethodsDuring a study period of 18 months, KPC-producing K. pneumoniae isolates of five hospitalized patients were collected with phenotypic development of CZA resistance.ResultsIn vitro restoration of carbapenem susceptibility during treatment was observed in 3 isolates. Whole genome sequencing of these isolates showed a D179Y mutation in the KPC gene of 2 variants and a KPC-2 with a Δ242-GT-243 deletion (KPC-14). Two KPC-3 variants showed CZA resistance with sustained carbapenemase activity without genomic adaptations in the KPC gene.ConclusionsThis study confirms the emergence of CZA resistance in KPC K. pneumoniae. The role of carbapenems in treating patients with these variants is unclear and combination therapies warrant further investigation.     

Carbapenem resistance in Acinetobacter baumannii: laboratory challenges,mechanistic insights and therapeutic strategies

Unprecedented levels of antimicrobial resistance in bacterial isolates have prompted great concerns globally. In 2012 the WHO released a publication outlining the evolving threat of antimicrobial resistance in order to raise awareness and to stimulate coordinated international efforts. The carbapenem class of antibiotics is largely considered as an antibiotic of last-resort when treating infections. Now carbapenem resistance further limits treatment options. In this article the authors discuss carbapenem resistance in Acinetobacter baumannii, a bacterial isolate often implicated in nosocomial infections. Virulence factors, intrinsic and acquired resistance mechanisms, together with laboratory challenges in the detection and antibiotic susceptibility testing of A. baumannii make this a truly problematic isolate. Therapeutic options are exceedingly limited, relying on polymyxins in combinations with other antibiotics, with few, if any, new active agents in the pipeline.     

Salvage therapy with tigecycline for recurrent infection caused by ertapenem-resistant extended-spectrum β-lactamase-producing Klebsiella pneumoniae

Optimal antimicrobial therapy for infections due to ertapenem-resistant Enterobacteriaceae remains undetermined. In this study, a diabetic patient with recurrent pyomyositis and osteomyelitis caused by extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae developed ertapenem resistance after imipenem/cilastatin treatment, which was a currently recommended therapy. He was finally treated successfully using tigecycline. Ertapenem resistance was in part explained by the production of SHV-type ESBL and the absence of an outer membrane protein, OmpK36. Our observation suggests that tigecycline may be an alternative for invasive infections caused by ESBL-producing Enterobacteriaceae with decreased susceptibility to carbapenem.     

南昌4家教学医院碳青霉烯类耐药肺炎克雷伯菌耐药机制及同源性分析

目的探讨临床分离的碳青霉烯类耐药肺炎克雷伯菌(CRKP)的耐药机制及同源性。方法收集南昌地区4家教学医院耐碳青霉烯类抗菌药物(亚胺培南和/或美罗培南)的肺炎克雷伯菌29株,双纸片增效法检测超广谱β-内酰胺酶(ESBLs)、三维实验检测AmpC酶、改良Hodge实验和双纸片协同法检测碳青霉烯酶,PCR扩增耐药基因,并对扩增产物测序,确定其基因型。脉冲场凝胶电泳(PFGE)对其进行同源性分析。结果 29株分离菌除对阿米卡星的耐药率较低(37.9%)外,对其他13种抗菌药物的耐药率均大于69%,其中对头孢呋辛、亚胺培南的耐药率为100%,多重耐药肺炎克雷伯菌的检出率为62.1%(18/29)。29株分离菌中有19株携带碳青霉烯酶基因,占65.5%(19/29),以blaKPC-2为主(44.8%,13/29),其次为blaNDM-1、blaIMP-26及blaIMP-4,携带率分别为17.2%(5/29)、10.3%(3/29)及6.9%(2/29),另有3株同时携带blaKPC-2和blaIMP-26,1株同时携带blaKPC-2和blaIMP-4。17株除携带碳青霉烯酶基因外,还携带ESBLs基因和(或)AmpC基因,占58.6%。未检测到VIM、GES、SPM及OXA等其他碳青霉烯酶基因。29株分离菌中有27株被PFGE成功分型,分别属于20个不同克隆,其余2株分型不成功。属于同一克隆型且携带blaKPC-2基因的4株菌来自同一医院。结论 CRKP耐药及多重耐药现象严重;携带碳青霉烯酶基因是肺炎克雷伯菌耐碳青霉烯类药物的主要原因,blaKPC-2携带率高,且在局部有短暂流行。本地区已监测到携带blaNDM的肺炎克雷伯菌,值得关注。     

Dissemination of quinolone low-susceptible Haemophilus influenzae ST422 in Tokyo,Japan

IntroductionHaemophilus influenzae with a reduced susceptibility to quinolones (quinolone low-susceptible H. influenzae) has recently emerged in Japan. In addition, the regional outbreak of the quinolone low-susceptible H. influenzae ST422 clone has been reported. In this study, we isolated this clone from an acute care hospital located in a geographically different area from the previous outbreak and characterised the nature of this clone.MethodsEighty-nine H. influenzae isolated between 2017 and 2019 were tested. The antimicrobial susceptibility was determined by the broth dilution method. The genetic background was analysed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing. Growth ability and β-lactamase acquisition were evaluated by growth curve analysis and conjugative transfer experiments, respectively.ResultsQuinolone low-susceptible isolates accounted for 4.2% (1/24) in 2018 and 13.9% (5/36) in 2019. Most of the quinolone low-susceptible strains (83.3%) were classified as ST422 and had amino acid substitutions in quinolone resistance-determining regions in both GyrA and ParC. The patients’ backgrounds were highly diverse. In addition, these isolates showed the same PFGE pattern as outbreak strains. The growth of ST422 clone was relatively faster than other clones. Furthermore, ST422 clone was able to acquire β-lactamase from a β-lactamase positive strain by horizontal transfer, becoming highly resistant to β-lactams.ConclusionOur study indicated that the quinolone low-susceptible H. influenzae ST422 clone has been spreading in the community undetected. In addition, this clone has the potential to grow faster and become more resistant through exogenous gene transfer. Therefore, ST422 clone should be monitored attention throughout Japan.     

Characteristics of carbapenem-resistant Enterobacteriaceae isolates from Korea

In this study, the characteristics of carbapenem-resistant Enterobacteriaceae (CRE) isolates from Korea was investigated. A total of 22 CRE isolates were investigated, and most were identified as Klebsiella pneumoniae (16 isolates). In vitro antimicrobial susceptibility testing, multilocus sequence typing, and pulsed-field gel electrophoresis were performed. Extended-spectrum β-lactamase (ESBL) and carbapenemase genes were detected using gene amplification and sequencing. Efflux pump activity and inactivating mutations in OmpK35/36 were also investigated. Among 22 CRE isolates, only 5 produced metallo-β-lactamases (3 NDM-1, one VIM-2 and one IMP-1). Four and 2 K. pneumoniae and Serratia marcescens isolates showed resistance to polymyxins, respectively, and 2 CRE isolates (1 K. pneumoniae and C. freundii) were resistant to tigecycline. The prevalent carbapenem resistance mechanism found in K. pneumoniae might be porin defects. The most prevalent clone of carbapenem-resistant K. pneumoniae was ST11 (56.3%), which is the most frequently identified clone among ESBL-producing K. pneumoniae isolates from Korea. Three NDM-1-producing K. pneumoniae isolates belonged to a single clone (ST340) despite their different antimicrobial susceptibilities. In the present study, the clonal dissemination of carbapenem-resistant K. pneumoniae isolates (ST11) and NDM-1-producing K. pneumoniae isolates (ST340) was determined. Polymyxin- and tigecycline-resistant CRE isolates were also identified, which limits treatment options for infections causes by these organisms.     

Antimicrobial susceptibility of Gram-negative organisms isolated from patients hospitalized in intensive care units in United States and European hospitals (2009–2011)

Treatment of infections in the intensive care unit (ICU) represents a great challenge, especially those caused by Gram-negative organisms. Rapid introduction of appropriate antimicrobial therapy is crucial to reduce mortality; resistance rates in the ICU can be elevated due to antimicrobial selection pressure. We evaluated the antimicrobial susceptibility patterns of Gram-negative bacteria isolated from patients hospitalized in ICUs (ICU patients). The isolates were consecutively collected as part of the SENTRY Antimicrobial Surveillance Program from January 2009 to December 2011 and tested for susceptibility to multiple antimicrobial agents at a central laboratory by reference broth microdilution methods. Antimicrobial susceptibility results for 5989 bacterial isolates from ICU patients (3445 from the United States [USA] and 2544 from Europe [EU]) were analyzed and compared to those of 17,244 organisms from non-ICU patients (9271 from USA and 7973 from EU). Escherichia coli, Klebsiella spp., and Pseudomonas aeruginosa were the most frequently isolated organisms from ICU patients, followed by Enterobacter spp., Serratia spp., Haemophilus influenzae, Acinetobacter spp., and Proteus mirabilis. Susceptibility rates were generally lower among ICU isolates compared to non-ICU organisms. E. coli isolates from ICU patients exhibited elevated extended-spectrum β-lactamase (ESBL)-phenotype rates (13.7% in USA and 16.6% in EU); furthermore, only amikacin (90.5–94.8% susceptibility), colistin (99.8–100.0% inhibited at ≤2 μg/mL), imipenem (95.5–96.0%), meropenem (95.4–95.8%), and tigecycline (96.3–98.0%) exhibited good activity against Klebsiella spp. ESBL-phenotype rates have increased among both E. coli and Klebsiella spp. from ICU patients in the USA and in Europe, with the most noticeable increase among Klebsiella spp. from Europe (from 27.5% in 2009 to 41.8% in 2011; P = 0.015 and odds ratio = 0.89 [95% confidence interval, 1.13–3.18]). Meropenem susceptibility among Klebsiella spp. improved slightly in the USA but decreased markedly in Europe from 100.0% in 2009 to 89.7% in 2011. Only colistin (99.4% susceptible) and amikacin (97.3% in USA and 84.9% in EU) exhibited good activity against P. aeruginosa strains from ICU patients. The greatest differences in susceptibility rates between P. aeruginosa strains from ICU and non-ICU patients were observed for the anti-pseudomonal β-lactams, such as ceftazidime, meropenem, and piperacillin/tazobactam. The results of this study (101 medical centers) highlight major antimicrobial coverage problems and trends in antimicrobial resistance for USA and EU ICU patient isolates.     

Metronidazole- and Carbapenem-Resistant Bacteroides thetaiotaomicron Isolated in Rochester,Minnesota, in 2014

Emerging antimicrobial resistance in members of the Bacteroides fragilis group is a concern in clinical medicine. Although metronidazole and carbapenem resistance have been reported in Bacteroides thetaiotaomicron, a member of the B. fragilis group, they have not, to the best of our knowledge, been reported together in the same B. thetaiotaomicron isolate. Herein, we report isolation of piperacillin-tazobactam-, metronidazole-, clindamycin-, ertapenem-, and meropenem-resistant B. thetaiotaomicron from a patient with postoperative intra-abdominal abscess and empyema. Whole-genome sequencing demonstrated the presence of nimD with at least a portion of IS1169 upstream, a second putative nim gene, two β-lactamase genes (one of which has not been previously reported), two tetX genes, tetQ, ermF, two cat genes, and a number of efflux pumps. This report highlights emerging antimicrobial resistance in B. thetaiotaomicron and the importance of identification and antimicrobial susceptibility testing of selected anaerobic bacteria.     

Characteristics of ST11 KPC‐2‐producing carbapenem‐resistant hypervirulent Klebsiella pneumoniae causing nosocomial infection in a Chinese hospital

BackgroundThe purpose of our study is to analyze the microbiological and clinical characteristics of carbapenem‐resistant hypervirulent Klebsiella pneumoniae (CR‐hvKP) that causes nosocomial infection.MethodsWe collected the carbapenem‐resistant K. pneumoniae (CRKP) strains that caused nosocomial infection in a hospital in China and collected the relevant clinical data. We characterized these strains for their antimicrobial and virulence‐associated phenotype and genotype and analyzed the clonal relatedness. We screened hypervirulent strains and compared them with non‐hypervirulent strains.ResultsWe retrospectively analyzed 62 CRKP strains that caused nosocomial infection in a tertiary hospital within 1 year, of which 41 (41/62, 66.1%) CRKP were considered as CR‐hvKP. All CR‐hvKP strains were multi‐drug resistance (MDR) and the vast majority of isolates (39/41, 95.1%) were ST11 KPC‐2‐producing strains. Two hypermucoviscous isolates and 4 capsular types were found in 41 CR‐hvKP. Twenty‐nine isolates (29/41, 70.7%) showed hypervirulence in Galleria mellonella infection model. PFGE showed that ST11‐KL47 CR‐hvKP and ST11‐KL64 CR‐hvKP exhibited a high degree of clonality, while non‐hypervirulent strains were not significant. CR‐hvKP had higher positive rates of bla _KPC‐2 and bla _CTX‐M‐65 and higher levofloxacin resistance (p < 0.001, p = 0.005 and p = 0.046, respectively) when compared to the non‐hypervirulent strains. There was no significant difference between the two groups in terms of in‐hospital mortality (7/41, 17.1% vs 5/21, 23.8%, p = 0.743).ConclusionOur research finds that ST11 KPC‐2‐producing CR‐hvKP is the main type of CRKP that caused nosocomial infection, and clonal spread has occurred. We provide more information about CR‐hvKP in health care.     

大肠埃希菌质粒型碳青霉烯酶KPC-2检测和分析

目的 研究普外科病区出现的4株碳青霉烯类药物耐药大肠埃希菌的分子流行病学特征及耐药机制.方法 用K-B纸片法和琼脂稀释法进行药物敏感试验,三维酶抑制试验和EDTA-Na_2协同试验分析酶的性质,通过脉冲场琼脂糖凝胶电泳(PFGE)分析耐药株的分子流行病学特征,特异性PCR及序列分析、接合试验、碱裂解法提取质粒和质粒转化试验研究碳青霉烯耐药的分子机制.结果 4株大肠埃希菌对包括碳青霉烯在内的多种抗菌药物广泛耐药,PFGE显示4株分离株属于不同的克隆型,对碳青霉烯类药物的耐药主要由相对分子质量约56 000的质粒携带的KPC-2基因介导,转化试验显示对氨基糖苷类和喹诺酮类药物的耐药性并未携带在同一质粒上.结论 我院出现碳青霉烯耐药的大肠埃希菌,对碳青霉烯类药物的耐药主要由质粒介导的KPC-2基因引起.     

Coexistence of blaOXA-48 and aac(6')-Ib-cr genes in Klebsiella pneumoniae isolates from Istanbul, Turkey

This study evaluated the presence of carbapenem hydrolysing β-lactamase genes and plasmid-mediated quinolone resistance (PMQR) determinants in 22 Klebsiella pneumoniae isolates collected from the Istanbul Medical Faculty, Turkey, which reduced the susceptibility or resistance to carbapenem. The VITEK(?) 2 system and E-tests were used to determine the minimum inhibitory concentrations needed to inhibit bacterial growth. Genes were screened by polymerase chain reaction, and gene transferability was evaluated by transconjugation. Strain clonality was investigated by pulsed-field gel electrophoresis (PFGE). All strains were OXA-48 β-lactamase producers and three (13.6%) were also positive for the aac(6')-Ib-cr gene. Most of the strains harboured other β-lactamase (bla) genes such as bla(TEM), bla(SHV), bla(CTX-M) and bla(VEB-1). The transconjugants mostly harboured bla(OXA-48) and other β-lactamases separately. PFGE revealed eight pulsotypes among the isolates. The coexistence of bla(OXA-48) and PMQR in K. pneumoniae isolates may present a significant threat to health, especially in the nosocomial setting.     

Clonal diversity and resistance mechanisms in tetracycline-nonsusceptible Streptococcus pneumoniae isolates in Poland

The frequency of tetracycline resistance in Streptococcus pneumoniae isolates in Poland is one of the highest in Europe. The aim of this study was to analyze the clonal diversity and resistance determinants of tetracycline-nonsusceptible S. pneumoniae isolates identified in Poland and to investigate the effect of tetracycline resistance on their susceptibilities to tigecycline, doxycycline, and minocycline. We have analyzed 866 pneumococcal isolates collected from 1998 to 2003 from patients with respiratory tract diseases, and 242 of these (27.9%) were found to be resistant to tetracycline. All of the resistant isolates were characterized by testing of their susceptibilities to other antimicrobials, serotyping, pulsed-field gel electrophoresis (PFGE), and identification of tetracycline resistance genes and transposons. Selected isolates representing the main PFGE types were analyzed by multilocus sequence typing. Among the isolates investigated, 27 serotypes and 146 various PFGE patterns, grouped into 90 types, were discerned. The most common PFGE type, corresponding to serotype 19F and sequence type 423, was represented by 22.3% of all of the tetracycline-resistant isolates. The tet(M) gene was the sole resistance gene in the group of isolates studied, and in over 96% of the isolates, the Tn916 family of tet(M)-containing conjugative transposons was detected. Several isolates contained specific variants of the transposons, the Tn1545-like, Tn3872-like, or Tn2009-like element. The correlation between the MICs of tetracycline, doxycycline, and minocycline was revealed, whereas no cross-resistance to tetracycline and tigecycline was observed.     

In vitro activities of ceftobiprole, tigecycline, daptomycin, and 19 other antimicrobials against methicillin-resistant Staphylococcus aureus strains from a national survey of Belgian hospitals

The in vitro activities of 22 antimicrobial agents, including ceftobiprole, daptomycin, and tigecycline, against 511 methicillin-resistant Staphylococcus aureus (MRSA) isolates from 112 Belgian hospitals were studied by using the CLSI agar dilution method. Isolates were characterized by pulsed-field gel electrophoresis (PFGE) analysis and by PCR detection of determinants of resistance to aminoglycosides, macrolides-lincosamides-streptogramins, and tetracyclines. A representative set of isolates with different PFGE genotypes was further characterized by multilocus sequence typing, determination of staphylococcal cassette chromosome mec (SCCmec) type, and multiplex PCR for toxic shock syndrome type 1 (TSST-1) and Panton-Valentine leukocidin genes. MRSA isolates belonged to nine epidemic MRSA clones, of which sequence type 45 (ST45)-SCCmec IV and ST8-SCCmec IV were predominant, accounting for 49 and 20% of isolates, respectively. The distribution of antimicrobial resistance and TSST-1 genes was strongly linked to clonal types. Ceftobiprole, daptomycin, and tigecycline showed high activity against all isolates of these sporadic and epidemic MRSA clones, as indicated by MIC(90)s of 2 mg/liter, 0.5 mg/liter, and 0.25 mg/liter, respectively. The MIC distribution of daptomycin and tigecycline was not different in isolates with decreased susceptibility to glycopeptides or tetracyclines, respectively. Ceftobiprole MICs were not correlated with oxacillin and cefoxitin MICs. These data indicate excellent activity of the newly developed agents ceftobiprole, daptomycin, and tigecycline against MRSA isolates recently recovered from hospitalized patients in Belgium, supporting their therapeutic potential for nosocomial MRSA infections.     

Occurrence of tetracycline resistance genes among Escherichia coli isolates from the phase 3 clinical trials for tigecycline

Tigecycline, a member of the glycylcycline class of antibiotics, was designed to maintain the antibacterial spectrum of the tetracyclines while overcoming the classic mechanisms of tetracycline resistance. The current study was designed to monitor the prevalence of the tet(A), tet(B), tet(C), tet(D), tet(E), and tet(M) resistance determinants in Escherichia coli isolates collected during the worldwide tigecycline phase 3 clinical trials. A subset of strains were also screened for the tet(G), tet(K), tet(L), and tet(Y) genes. Of the 1,680 E. coli clinical isolates screened for resistance to classical tetracyclines, 405 (24%) were minocycline resistant (MIC > or = 8 microg/ml) and 248 (15%) were tetracycline resistant (MIC > or = 8 microg/ml) but susceptible to minocycline (MIC < or = 4 microg/ml). A total of 452 tetracycline-resistant, nonduplicate isolates were positive by PCR for at least one of the six tetracycline resistance determinants examined. Over half of the isolates encoding a single determinant were positive for tet(A) (26%) or tet(B) (32%) with tet(C), tet(D), tet(E), and tet(M), collectively, found in 4% of isolates. Approximately 33% of the isolates were positive for more than one resistance determinant, with the tet(B) plus tet(E) combination the most highly represented, found in 11% of isolates. The susceptibilities of the tetracycline-resistant strains to tigecycline (MIC(90), 0.5 microg/ml), regardless of the encoded tet determinant(s), were comparable to the tigecycline susceptibility of tetracycline-susceptible strains (MIC(90), 0.5 microg/ml). The results provide a current (2002 to 2006) picture of the distribution of common tetracycline resistance determinants encoded in a globally sourced collection of clinical E. coli strains.     

肠杆菌科细菌中质粒介导的KPC-2型碳青霉烯酶的检测

目的 研究重症监护病房(ICU)出现的碳青霉烯耐药的黏质沙雷菌、肺炎克雷伯菌和大肠埃希菌等肠杆菌科细菌的分子流行病学及耐药机制.方法 2006年4月-2007年2月,从我院2个ICU病房分离到对碳青霉烯耐药或敏感性降低的21株黏质沙雷菌、10株肺炎克雷伯菌和1株大肠埃希菌.用脉冲场凝胶电泳(PFGE)和肠杆菌基因间重复性一致序列-PCR(ERIC-PCR)分析这些菌株的分子流行病学.用接合试验、质粒消除试验、质粒图谱分析、等电聚焦电泳(IEF)、特异性PCR扩增和序列分析以及外膜蛋白分析等技术研究细菌对碳青霉烯耐药的分子机制.结果 21株黏质沙雷菌为同一克隆株;10株肺炎克雷伯菌亲缘关系相近.亚胺培南和美罗培南对黏质沙雷菌、肺炎克雷伯菌和大肠埃希菌的MIC为2～8μg/ml,肺炎克雷伯菌K10为128和256μg/ml.所有菌株接合试验均获得成功,亚胺培南和美罗培南对接合子的MIC由原来的≤0.125μg/ml上升到1～2μg/ml.IEF、PCR扩增和序列分析证实黏质沙雷菌产KPC-2型碳青霉烯酶[等电点(p1)为6.7]和pI为6.5的β内酰胺酶;肺炎克雷伯菌产TEM-1(pI5.4)、KPC-2、CTX-M-14(p17.9)和pI为7.3的β内酰胺酶;大肠埃希菌产KPC-2、CTX-M-15(pI 9.0)和pI为7.3的B内酰胺酶;所有接合子均只产KPc-2一种β内酰胺酶.所有接合子质粒DNA的EcoR Ⅰ、Hind Ⅲ和Bcu Ⅰ限制性酶切图谱完全相同.外膜蛋白的十二烷基磺酸钠一聚丙烯酰胺电泳和基因序列分析发现肺炎克雷伯菌KIO由于OmpK36基因中存在插入序列ISEcp1而导致OmpK36膜孔蛋白的缺失.结论我院ICU病房出现大量碳青霉烯耐药的黏质沙雷菌、肺炎克雷伯菌和大肠埃希菌;KPC-2是引起这些细菌对碳青霉烯耐药或敏感性降低的主要原因;KPC-2合并膜孔蛋白缺失可导致肺炎克雷伯菌对碳青霉烯高水平耐药;同一种编码blaKPC-2的质粒在3种不同属的细菌之间传播.