International Journal of Antimicrobial Agents

2010-03-01

Characterisation of breakthrough invasive mycoses in echinocandin recipients: an evidence-based review

Hsin-Yun Sun, Nina Singh — 2009-12-28

Abstract: The echinocandins have emerged as important antifungal agents in the current era. Despite their potent antifungal activity, breakthrough invasive mycoses occur in echinocandin recipients, however their precise incidence and causative pathogens are not well delineated. This review shows that breakthrough mycoses occur in 2.4% of patients receiving echinocandins as prophylaxis and are predominantly due to non-albicans Candida spp. and less frequently to invasive aspergillosis. Candida isolates demonstrating reduced susceptibility occurred following prolonged exposure to the echinocandins, primarily in severely immunocompromised patients, and manifested as recurrent episodes of candidaemia or invasive candidiasis.

Multidrug-resistant Acinetobacter baumannii: mechanisms of virulence and resistance

Nicola C. Gordon, David W. Wareham — 2010-01-04

Abstract: Infection due to Acinetobacter baumannii has become a significant challenge to modern healthcare systems. The organism shows a formidable capacity to develop antimicrobial resistance, yet the clinical impact of A. baumannii infection remains unclear. Much is known about the processes involved in multidrug resistance, but those underlying the pathogenicity and virulence potential of the organism are only beginning to be elucidated. In this article, we provide an overview of current knowledge, focusing on mechanisms of pathogenesis, the molecular basis of resistance and options for treatment in the absence of novel therapeutic agents.

Antimicrobial resistance among clinical isolates from the Chinese Meropenem Surveillance Study (CMSS), 2003–2008

2010-01-04

Abstract: The Chinese Meropenem Surveillance Study (CMSS) programme was initiated in 2003 with the aim of monitoring the antimicrobial activity of broad-spectrum agents against nosocomial Gram-negative bacilli in China. From 2003 to 2008, a total of 3892 isolates were collected from 10 teaching hospitals. The minimum inhibitory concentrations (MICs) of 11 antimicrobial agents were determined by the agar dilution method. During the study period, a marked decrease in the susceptibility of Acinetobacter spp. to meropenem and imipenem was noticed, from 94.6% to 60.7% and from 92.5% to 62.1%, respectively. However, for Pseudomonas aeruginosa the susceptibility was relatively stable, with susceptibility rates of 86.2% to 76.0% for meropenem and 74.8% to 70.5% for imipenem. Meropenem and imipenem exhibited the highest activities against enterobacterial organisms, with ranges of MIC90 values (MIC for 90% of the organisms) from 0.064mg/L to 0.25mg/L and 0.25 to 4mg/L, respectively. Except for Acinetobacter spp., the next most active agent against the majority of isolates was amikacin, with susceptibility ranging from 78.8% to 93.3%, followed by piperacillin/tazobactam (73.7% to 98.2%), cefoperazone/sulbactam (63.9% to 99.1%), cefepime (67.0% to 95.4%) and ceftazidime (54.5% to 93.3%). The percentage of isolates positive for extended-spectrum β-lactamases among Escherichia coli, Klebsiella spp. and Proteus mirabilis ranged from 50.9% to 66.7%, 25.4% to 42.4% and 8.9% to 24.2%, respectively. These CMSS results have demonstrated increasing resistance of Acinetobacter spp. to carbapenems, resulting from the spread of highly resistant clones. Continued surveillance studies, including CMSS, as well as potent measures for controlling the spread of resistant clones are required.

Dissecting the ribosomal inhibition mechanism of a new ketolide carrying an alkyl-aryl group at C-13 of its lactone ring

2010-01-04

Abstract: Ketolides are effective not only against macrolide-sensitive bacteria but also against some macrolide-resistant strains. Here we present data regarding a new ketolide with an alkyl-aryl side chain at C-13 of its lactone ring. It behaves as a strong inhibitor of protein synthesis in a model coupled transcription/translation system, although it does not affect the accuracy of translation. In addition, detailed kinetic analysis shows that it slowly forms a very tight, slowly reversible complex with prokaryotic ribosomes, a property that could be correlated with its superior activity compared with erythromycin against Escherichia coli both in vivo and in vitro.

Antimicrobial susceptibility of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Enterobacteriaceae isolates to fosfomycin

2009-12-25

Abstract: The advancing antimicrobial drug resistance among Enterobacteriaceae renders the evaluation of potential novel therapeutic options necessary. We sought to evaluate the in vitro antimicrobial activity of fosfomycin against multidrug-resistant (MDR) Enterobacteriaceae isolates. Antimicrobial susceptibility to fosfomycin and 12 additional antibiotics of MDR Enterobacteriaceae isolates collected between November 2007 and April 2009 at the University Hospital of Heraklion, Crete, Greece, was examined using the Etest method. A total of 152 MDR Enterobacteriaceae isolates were studied, including Klebsiella pneumoniae (76.3%), Escherichia coli (17.1%), Proteus mirabilis (4.6%) and other species (2.0%). Antimicrobial susceptibility rates were highest for fosfomycin (92.8%), tigecycline (92.1%) and colistin (73.0%) followed by imipenem (35.5%), tetracycline (20.4%), gentamicin (19.7%), trimethoprim/sulfamethoxazole (12.5%) and ciprofloxacin (10.5%). Of the 152 isolates, 85 (55.9%) were extensively drug-resistant (XDR), of which 78 (91.8%) remained susceptible to fosfomycin. Susceptibility to fosfomycin of the 79 carbapenemase-producing, 34 extended-spectrum β-lactamase-producing and 24 metallo-β-lactamase-producing isolates was 94.9%, 94.1% and 83.3%, respectively. In conclusion, in this study fosfomycin exhibited good in vitro antimicrobial activity against MDR and XDR Enterobacteriaceae. We suggest further evaluation of the potential clinical utility of fosfomycin against infections caused by these pathogens.

Deletion of penicillin-binding protein 5 (PBP5) sensitises Escherichia coli cells to β-lactam agents

Sujoy K. Sarkar, Chiranjit Chowdhury, Anindya S. Ghosh — 2010-01-04

Abstract: Escherichia coli penicillin-binding protein 5 (PBP5), a dd-carboxypeptidase encoded by the dacA gene, plays a key role in the maintenance of cell shape. Although PBP5 shares one of the highest copy numbers among the PBPs, it is not essential for cell survival. To determine the effect of this redundant PBP on β-lactam antibiotic susceptibility, PBP5 was deleted from O-antigen-negative E. coli K-12 (CS109) and O8-antigen-positive E. coli 2443, thus creating strains AM15-1 and AG1O5-1, respectively. Compared with the parent strains, both mutants were four- to eight-fold more susceptible to all the β-lactam antibiotics tested. Reversion to β-lactam resistance was observed in the mutants upon complementing with cloned PBP5, indicating the involvement of PBP5 in maintaining an O-antigen-independent intrinsic β-lactam resistance in E. coli cells. To check whether other dacA homologues were able to substitute this behaviour of E. coli PBP5, AG1O5-1 was complemented with its nearest dacA homologues (Salmonella enterica serovar Typhimurium LT2, Vibrio cholerae and Haemophilus influenzae). All of the cloned homologues were capable of restoring the lost β-lactam resistance in AG1O5-1, either completely or at least partially. Therefore, apart from maintaining cell shape, involvement of PBP5 in maintaining intrinsic β-lactam resistance is an important physiological observation and we speculate that such a strategy of deleting PBP5 may be helpful to introduce β-lactam susceptibility in the laboratory.

Interaction of antimicrobial peptide s-thanatin with lipopolysaccharide in vitro and in an experimental mouse model of septic shock caused by a multidrug-resistant clinical isolate of Escherichia coli

2010-01-04

Abstract: s-thanatin, an analogue of thanatin, was synthesised by substituting the fifteenth amino acid threonine with serine and showed broad antimicrobial activity against Gram-negative and Gram-positive bacteria. To evaluate its antimicrobial activity against a multidrug-resistant (MDR) clinical isolate as well as its anti-endotoxin activity, its lipopolysaccharide (LPS)-binding and -neutralising activity in vitro and its therapeutic efficacy in an experimental model of septic shock caused by a MDR clinical isolate of Escherichia coli were studied. The ability of s-thanatin to bind or neutralise LPS from E. coli O111:B4 was determined using a quantitative assay kit. Male ICR mice were given an intraperitoneal (i.p.) administration of 2×1010 colony-forming units of E. coli E79466. Following bacterial challenge, all animals were randomised to receive i.p. administration of saline, 40mg/kg ceftazidime (CAZ), or 40mg/kg CAZ+s-thanatin (10, 20 or 40mg/kg). The results showed that s-thanatin not only completely bound to the LPS (median effective concentration of 17.5μg/mL) but also improved the survival and reduced the number of inoculated bacteria in a mouse model of septic shock. s-thanatin may be an attractive candidate to develop as an anti-MDR bacterial agent.

Purification, characterisation and identification of acidocin LCHV, an antimicrobial peptide produced by Lactobacillus acidophilus n.v. Er 317/402 strain Narine

2010-01-04

Abstract: In the last two decades, antimicrobial peptides (AMPs) have been gaining attention as antimicrobial alternatives to chemical food preservatives and commonly used antibiotics. Lactobacillus acidophilus n.v. Er 317/402 strain Narine produces a small AMP with a molecular weight of 1.1kDa, designated acidocin LCHV. In this study, the AMP was extremely heat stable (90min at 130°C), was active over a wide pH range and was found to be sensitive to proteolytic enzymes (trypsin, pepsin and proteinase K). Acidocin LCHV has a broad spectrum of activity both against Gram-positive and Gram-negative pathogens, including several that are classified as Especially Dangerous Infections by the World Health Organization as well as meticillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS) was used to determine the molecular mass and sequence of the purified peptide. Complete killing with immediate impact on cells was observed within a very short period of time (10min).

Fluoroquinolone resistance of Pseudomonas aeruginosa isolates causing nosocomial infection is correlated with levofloxacin but not ciprofloxacin use

Yuarn-Jang Lee, Hsin-Yi Liu, Yi-Chun Lin, Kuo-Lun Sun, Chi-Li Chun, Po-Ren Hsueh — 2010-01-04

Abstract: This study investigated the correlation between fluoroquinolone (ciprofloxacin or levofloxacin) use and rates of fluoroquinolone resistance in Pseudomonas aeruginosa isolates from patients with nosocomial infection at a medical centre in Taiwan. Antibiotic utilisation data were extracted on a monthly basis from the inpatient pharmacy computer system records from January 2003 to December 2008. Fluoroquinolone use was expressed as defined daily dose per 1000 patient-days and was correlated with rates of fluoroquinolone-resistant P. aeruginosa every 6 months. Regression analysis was performed to explore the relationship between ciprofloxacin and levofloxacin use (both parenteral and oral forms) and resistance of P. aeruginosa isolates. During the study period, the susceptibility of P. aeruginosa to fluoroquinolones decreased after increasing use of fluoroquinolones, and increased after decreasing use of levofloxacin. Parenteral levofloxacin use was significantly positively correlated with resistance of P. aeruginosa to ciprofloxacin (P=0.015) and fluoroquinolones (either ciprofloxacin or levofloxacin, P=0.014). Use of both parenteral and oral forms of levofloxacin was also significantly positively correlated with resistance of P. aeruginosa isolates to ciprofloxacin (P=0.029), levofloxacin (P=0.031) and fluoroquinolones (P=0.010). The total amount of ciprofloxacin (oral and parenteral) and parenteral ciprofloxacin use were negatively correlated with resistance of P. aeruginosa isolates to fluoroquinolones. However, the amounts of oral ciprofloxacin, parenteral levofloxacin, oral levofloxacin and total levofloxacin use were each positively correlated with resistance of P. aeruginosa to fluoroquinolones. Levofloxacin use was associated with increased resistance of P. aeruginosa to fluoroquinolones, whereas ciprofloxacin use did not have a significant impact on fluoroquinolone resistance rates.

In vivo selection of imipenem-resistant Klebsiella pneumoniae producing extended-spectrum β-lactamase CTX-M-15 and plasmid-encoded DHA-1 cephalosporinase

Gaelle Cuzon, Thierry Naas, Michele Guibert, Patrice Nordmann — 2009-12-25

Abstract: Four Klebsiella pneumoniae isolates (KP1–4) were recovered sequentially from an infected patient. Whilst KP1–3 were resistant to all β-lactams except carbapenems, KP4 recovered after 24 days of imipenem-containing treatment showed additional resistance to carbapenems. No carbapenem hydrolysis could be identified in KP4. Molecular characterisation revealed that KP1–4 were indistinguishable by pulsed-field gel electrophoresis, contained a 95-kb self-transferable plasmid harbouring blaCTXM-15 and blaTEM-1 genes and a 65-kb plasmid that was not transferred by conjugation into Escherichia coli, and harboured the plasmid-mediated blaDHA-1 AmpC β-lactamase gene. In addition, KP4 failed to express OmpK36 owing to a point mutation leading to a premature stop of the protein. This study demonstrates development of carbapenem resistance related to loss of OmpK36 expression in a K. pneumoniae isolate harbouring extended-spectrum β-lactamase and plasmid-mediated cephalosporinase genes following prolonged imipenem exposure.

Susceptibility patterns and molecular epidemiology of multidrug-resistant Acinetobacter baumannii strains from three military hospitals in China

2009-12-28

Abstract: To date, little has been reported on the susceptibility patterns and molecular characterisation of multidrug-resistant Acinetobacter baumannii (MDRAB) clinical isolates from different Chinese military hospitals. In this study, 49 MDRAB strains were collected from three military hospitals during 2007. The minimum inhibitory concentrations (MICs) of 13 antibiotics were determined for each strain. Genotyping and dendrogram analysis of MDRAB strains were performed using the repetitive sequence-based polymerase chain reaction (rep-PCR) DiversiLab™ Microbial Typing System. PCR screening was carried out to investigate the distribution of various genes contributing to each resistance phenotype in the main clonal types. The rates of resistance to the majority of antibiotics tested varied between 75.5% and 100%, with the exception of polymyxin B. Two DiversiLab rep-PCR clones (A and B) were widespread in three hospitals in different cities, one clone (D) existed only in two hospitals located in the same city (Beijing), and the other two clones (C and E) were present in only one hospital. In addition, this study shows a high distribution of intI1, ISAba1, blaOXA-23, blaADC, adeB, adeJ, abeM and tet(B) genes, which mediate resistance to structurally unrelated antimicrobials in MDRAB isolates. These results suggest that all isolates were resistant to at least three classes of antibiotics. In addition, clonal dissemination among the three hospitals located in two different cities in China, previously documented in many regions of Europe and Asia-Pacific nations, emphasises the epidemic potential of these MDRAB isolates.

In vitro interference of β-lactams with biofilm development by prevalent community respiratory tract isolates

2009-12-25

Abstract: Interference of cefditoren (CDN) and amoxicillin/clavulanic acid (AMC) with biofilm production was studied using 11 Streptococcus pneumoniae isolates with minimum inhibitory concentrations (MICs) ranging from 0.015μg/mL to 0.5μg/mL for CDN and from 0.06μg/mL to 2μg/mL for AMC (except for one isolate with an AMC MIC of 8μg/mL) and 5 Haemophilus influenzae isolates with MICs of 0.03–0.06μg/mL for CDN and 0.5–16μg/mL for AMC. Slime production was assessed in antibiotic-free medium and with 0.03μg/mL CDN or 1/0.5μg/mL AMC by measuring the optical density at 450nm (OD450). Significantly lower mean OD450 values were obtained for S. pneumoniae with antibiotics compared with controls (CDN, 0.088 vs. 0.118, P=0.003; and AMC, 0.095 vs. 0.112, P=0.003), with significant correlation between both antibiotics (r=0.752; P=0.008). Percent reduction in OD450 values was higher for CDN compared with AMC (24.02% vs. 15.92%; P=0.008). For H. influenzae, significantly lower mean OD450 values were obtained with CDN compared with controls (0.083 vs. 0.096; P=0.043) but not with AMC (0.086 vs. 0.095; P=0.08). Comparing percent reductions in S. pneumoniae versus H. influenzae for each antibiotic, no differences were found for AMC (15.92% vs. 9.40%; P=0.36), with a tendency for CDN (24.02% vs. 13.79%; P=0.069). Different β-lactams may have different capabilities of interfering with S. pneumoniae biofilm development when tested under the same experimental conditions.

Rifaximin-induced alteration of virulence of diarrhoea-producing Escherichia coli and Shigella sonnei

Zhi-Dong Jiang, Shi Ke, Herbert L. DuPont — 2010-01-04

Abstract: Rifaximin shortens the duration of travellers’ diarrhoea without important alteration of colonic flora. This study investigated the expression of virulence factors [heat-stable (ST) and heat-labile (LT) enterotoxins, surface adhesion factors (CS2/CS3, CS6) and matrix metalloproteinase-9 (MMP-9)] as well as the interleukin (IL)-8 induction potential of diarrhoeagenic Escherichia coli and Shigella sonnei strains exposed to rifaximin (8, 32 and 64mg/L) for 4, 8, 18 and 24h. Following exposure to rifaximin, enterotoxigenic E. coli (ETEC) isolates did not express ST/LT, CS2/CS3 or CS6, whereas enteroaggregative E. coli (EAEC) and S. sonnei isolates did not produce detectable amounts of MMP-9. Moreover, induction of IL-8 was undetectable. At subinhibitory concentrations, rifaximin alters the virulence of ETEC, EAEC and S. sonnei isolates. These findings help explain the efficacy of rifaximin despite minimal alteration of colonic flora.

Evaluation of the activity of fusidic acid tested against contemporary Gram-positive clinical isolates from the USA and Canada

Michael A. Pfaller, Mariana Castanheira, Helio S. Sader, Ronald N. Jones — 2009-12-28

Abstract: We evaluated the antimicrobial activity of fusidic acid (CEM-102) against 1140 clinical strains of Gram-positive bacteria obtained from patients with bacteraemia or skin and skin-structure infections collected in more than 30 medical centres in the USA and Canada over a 10-year period (1997–2006). Fusidic acid was very active against meticillin-susceptible Staphylococcus aureus (MSSA), meticillin-resistant S. aureus (MRSA) and coagulase-negative staphylococci (CoNS), with MIC90 values (minimum inhibitory concentration encompassing 90% of isolates tested) at 0.12μg/mL for US strains of MSSA, MRSA and CoNS and 0.25μg/mL for Canadian strains of MSSA and MRSA. A progressive increase in fusidic acid resistance was observed among Canadian strains of S. aureus (12.2% in 2005–2006) and among Canadian strains of CoNS. In contrast, no fusidic acid resistance was detected among US S. aureus strains and only 1.5% among CoNS. Fusidic acid was equally active against community-acquired MRSA and linezolid-resistant staphylococci. Fusidic acid exhibited equal or greater potency against staphylococci compared with vancomycin, daptomycin and linezolid.

Antimicrobial and immunomodulatory activities of an ovine proline/arginine-rich cathelicidin

Pak-Lam Yu, Martin L. Cross, Richard G. Haverkamp — 2009-12-25

Abstract: In in vitro co-culture experiments, the ovine-derived cathelicidin OaBac5mini showed antimicrobial activity against Escherichia coli cells and modulated production of a cytokine by a mammalian inflammatory cell type (macrophage). Using atomic force microscopy, the morphology of peptide-treated E. coli bacteria showed no cell lysis, indicating an intracellular mode of action of the peptide leading to bacterial cell inhibition. At a concentration of 50μg/mL OaBac5mini, the peptide suppressed production of the inflammatory cytokine interleukin-12 by murine J774A cells that had been stimulated with Staphylococcus aureus strain Cowan; levels of other cytokines were unaffected. Thus, certain cationic peptides can enter and disrupt invading Gram-negative pathogens and may be able to modulate inflammatory responses induced by Gram-positive bacterial products.

Inhibition of Listeria monocytogenes infection by neurological drugs

Linda A. Lieberman, Darren E. Higgins — 2009-12-25

Abstract: To gain insights into the cellular processes required for intracellular bacterial pathogenesis, we previously developed a generalisable screening approach to identify small molecule compounds that alter Listeria monocytogenes infection. In this report, a small molecule library enriched for compounds affecting neurological functions was screened and 68 compounds that disrupted L. monocytogenes infection of macrophages were identified. Many of these compounds were known antimicrobial agents, however 26 compounds were novel inhibitors of intracellular infection. Two of the compounds chosen for further study, the antipsychotic drug thioridazine and the calcium channel blocker bepridil, exhibited dose-dependent inhibition of vacuolar escape and intracellular replication of L. monocytogenes during infection of murine macrophages. These results suggest that clinically approved neurological drugs may provide a novel source of anti-infective agents that are suitable for development as therapeutics against intracellular bacterial infections.

Safety and efficacy of intravenous colistin (colistin methanesulphonate) for severe multidrug-resistant Gram-negative bacterial infections

Chien-Yu Cheng, Wang-Huei Sheng, Jann-Tay Wang, Yee-Chun Chen, Shan-Chwen Chang — 2010-01-04

Abstract: Multidrug-resistant (MDR) bacterial infections are increasing in Taiwan hospitals, prompting the common use of colistin. In this study, the safety and efficacy of intravenous (i.v.) colistin was assessed. The medical records of patients receiving colistin for treatment of MDR Gram-negative bacterial infections between January 2006 and September 2008 at a Taiwan medical centre were reviewed retrospectively. Demographics, clinical presentation, causative organism, adverse events and outcomes were recorded. Of the 115 patient records analysed, 74 patients (64%) were treated in the Intensive Care Unit. Common underlying diseases were hypertension (49%), chronic pulmonary disease (46%), chronic kidney disease (33%) and malignancy (31%). Lower respiratory tract infections were most common (71%), followed by primary bloodstream infections (12%), urinary tract infections (8.7%) and others (7.8%). Successful treatment with i.v. colistin against MDR Gram-negative bacterial infections occurred in 59 patients (51%). Multivariate analysis showed that a higher Acute Physiology and Chronic Health Evaluation (APACHE) II score (odds ratio=1.14; 95% confidence interval 1.02–1.28; P=0.02) was independently associated with a poor clinical response. Overall, 12 (14%) of 84 patients presented nephrotoxicity and 4 patients (3.5%) had neurotoxicity. In conclusion, colistin is an effective antimicrobial agent for severe infections caused by MDR Gram-negative bacteria. Clinical outcomes are associated with the severity of infection and underlying diseases. Compared with previous reports, this study showed a lower incidence of nephrotoxicity and neurotoxicity.

Meropenem monotherapy is as effective as and safer than imipenem to treat brain abscesses

2010-01-04

Abstract: The efficacy of carbapenems versus cefotaxime (8g/day)+metronidazole (1.5–2g/day) [combined standard chemotherapy (CSC)] for the treatment of brain abscess was compared. Fifty-nine adult patients with brain abscesses received either imipenem or meropenem (3–4g/day) or CSC for a mean of 5 weeks, in addition to neurosurgery in most cases. Cure was obtained in 84.7% of cases; 42/47 (89.4%) on carbapenems [18/22 (81.8%) on imipenem versus 24/25 (96.0%) on meropenem] and 8/12 (66.7%) on CSC (P=0.06). Seven patients with multiple abscesses were treated with imipenem (1 died; cure rate 85.7%), five with meropenem (all survived; cure rate 100%) and five with CSC (2 died; cure rate 60%) (P<0.4). Neurosurgery was performed in 43/59 cases (72.9%); 17 (77.3%) in the imipenem group, 21 (84.0%) in the meropenem group and 5 (41.7%) in the CSC group (P=0.02). There was no significant difference in the rate of relapse requiring re-intervention. Treatment with meropenem was associated with a lower mortality than CSC (P=0.026). Seizures were observed only with carbapenems [8/22 (36.4%) for imipenem versus 2/25 (8.0%) for meropenem; P=0.03]. Carbapenems were more effective than CSC for treatment of brain abscesses. Because meropenem induced significantly fewer seizures than imipenem with at least the same clinical efficacy, the former appears to be a better choice to treat this infection.

Inclusion of OXA-143 primers in a multiplex polymerase chain reaction (PCR) for genes encoding prevalent OXA carbapenemases in Acinetobacter spp.

Paul G. Higgins, Marlene Lehmann, Harald Seifert — 2009-12-18

We recently identified the novel OXA-143 enzyme in Acinetobacter baumannii . The gene blaOXA-143 was undetectable using the current established multiplex polymerase chain reaction (PCR) that identifies the acquired OXA enzymes blaOXA-23-like, blaOXA-40-like and blaOXA-58-like . The prevalence of OXA-143 is therefore unknown. In the present study, we have designed primers to amplify blaOXA-143 that can be used as an additional primer pair in the established multiplex PCR. Primers OXA-143-F (5′-TGGCACTTTCAGCAGTTCCT-3′) and OXA-143-R (5′-TAATCTTGAGGGGGCCAACC-3′) were used to amplify a 149bp fragment. These primers were tested by adding them to the existing multiplex PCR and using the published PCR parameters against three blaOXA-143 isolates and 10 each of previously characterised carbapenem-resistant A. baumannii isolates possessing the following: blaOXA-23-like; blaOXA-58-like; and isolates negative for an acquired OXA enzyme but with insertion sequence ISAba1 adjacent to blaOXA-51-like . blaOXA-40-like shares 88% DNA identity with blaOXA-143 and, to ensure specificity, the primers were tested against 25 blaOXA-40-like isolates. shows the results of the multiplex PCR. The new primer pair amplified blaOXA-143 and did not interfere with the other PCR products. This modified multiplex PCR can aid in monitoring the spread of carbapenem-resistant A. baumannii simply by the addition of the OXA-143-F and OXA-143-R primers.

Phenotypic characterisation of Clostridium difficile reveals lack of extracellular virulence factor production and significant differences in antibiogram profiles

Lauren M. Green, Tony Worthington, Anthony C. Hilton, Peter A. Lambert — 2009-12-25

Clostridium difficile-associated diarrhoea (CDAD) is currently the leading healthcare-associated infection in the UK . Although toxin production is well documented as the major virulence factor of C. difficile, there is evidence to support the production of extracellular enzymes; however, sample size numbers have been restricted and levels of enzyme production have been found to vary between isolates . Reporting of CDAD cases by Primary Care Trusts in England and Wales became mandatory in 2004, followed in 2005 by the introduction of the random sampling scheme. Such reporting has enabled the surveillance both of ribotype epidemiology and antibiotic resistance in C. difficile isolates, both of which have altered significantly in the past 5 years. The changes observed in the antibiotic sensitivity patterns of the three most commonly encountered ribotypes in the UK (001, 027 and 106) demonstrate the importance of antibiotic susceptibility surveillance and lend support to routine culture and susceptibility testing. The aims of this investigation were two-fold: first, to determine the antibiotic sensitivity patterns of a large panel of C. difficile isolates recovered from patients at two tertiary trusts; and second, to assess whether isolates produced virulence factors other than toxins A and B.

Variable daptomycin susceptibility in patients receiving intravenous vancomycin for meticillin-resistant Staphylococcus aureus infections

Marjorie Golden, Walid Shaib, Nancy Havill — 2009-12-25

Daptomycin is a lipopeptide antibiotic approved for the treatment of Staphylococcus aureus bloodstream infections. We report four patients with meticillin-resistant S. aureus (MRSA) isolates that appeared to be daptomycin non-susceptible by an in-house Etest [minimum inhibitory concentration (MIC)>1μg/mL]. Reference laboratory confirmatory testing with broth microdilution (BMD) did not validate these results.

Variability of polymyxin B major components in commercial formulations

2010-01-04

Polymyxin B (PB) is a lipopeptide antibiotic increasingly used as a last therapeutic option due to the emergence of multidrug-resistant (MDR) bacteria . Commercial formulations of PB for intravenous administration are chemically undefined mixtures containing multiple structurally related components. The major constituents of PB are PB1, PB2, PB3 and ile-PB1, differing only in the fatty acyl moiety . Current quality control procedures focus on overall antimicrobial activity of the mixture rather than on the quantity of each component. Therefore, variations in the composition of PB components may exist in commercial formulations. Different components may not exhibit equivalent pharmacological activity and toxic propensity , which could make comparison of studies using PB products from different manufacturers difficult. To facilitate valid and consistent comparison across different studies, we compared the relative proportions of each PB component in formulations produced by four different manufacturers. In addition, the relative in vitro potency of PB1 to the PB mixture against several clinically important bacteria was explored.

Activity of tigecycline against multidrug-resistant clinical isolates of Clostridium spp. from Europe

Stephen P. Hawser — 2010-01-04

Clostridium spp., especially Clostridium difficile, comprise the major causative pathogens of nosocomial gastrointestinal disorders and in the case of C. difficile have been associated with large outbreaks of infection, including the emergence of ‘hypervirulent’ strains . Tigecycline is approved both in Europe [European Medicines Agency (EMEA)] and the USA [US Food and Drug Administration (FDA)] for the treatment of complicated skin and skin-structure infections and complicated intra-abdominal infections and was recently approved by the FDA for the treatment of community-acquired pneumonia. The author recently reported the in vitro activity of tigecycline against clinical isolates of C. difficile and showed that all isolates were susceptible to this agent . As part of the ongoing global Tigecycline Evaluation and Surveillance Trial (TEST) program, the current study investigating the activity of tigecycline against multidrug-resistant (MDR) isolates of Clostridium spp. was designed to elaborate further on the positive in vitro activity of tigecycline against C. difficile .

Severe and refractory Clostridium difficile infection successfully treated with tigecycline and metronidazole

2010-01-04

Clostridium difficile was identified as the causative pathogen of antibiotic-associated diarrhoea and pseudomembranous colitis in 1978 . In recent years, the incidence of C. difficile infection has increased rapidly . Standard treatment for C. difficile infection includes metronidazole and vancomycin . However, the emergence of C. difficile infection with a new hypervirulent strain was noted since 2005. This strain is more frequently refractory to standard treatment and is associated with treatment failure. Tigecycline, a structural analogue of minocycline, was approved by the US Food and Drug Administration (FDA) for the treatment of complicated skin and soft-tissue infection and complicated intra-abdominal infection in 2005 and for community acquired pneumonia in 2009. A low tigecycline minimum inhibitory concentration (MIC) for C. difficile was reported in several recent studies . Here we describe a patient with severe C. difficile infection refractory to metronidazole and vancomycin treatment who was successfully treated with tigecycline and metronidazole.

Typing of vancomycin-resistant enterococci obtained from patients at Danish hospitals and detection of a genomic island specific to CC17 Enterococcus faecium

2010-01-04

Vancomycin-resistant enterococci (VRE) are emerging in hospitals in Europe. Resistance to vancomycin can be encoded by seven different genes in enterococci, of which the vanA and vanB genotypes are most prevalent among clinical isolates. Genomic studies employing multilocus sequence typing (MLST) have shown nosocomial Enterococcus faecium outbreaks and infections to be associated with a specific clonal complex (CC) referred to as CC17 . Recently, Heikens et al. have identified a genomic island specific to CC17 E. faecium. This island encodes a metabolic pathway involved in carbohydrate transport and metabolism.