Susceptibility of Clostridium difficile isolates from a Phase 2 clinical trial of cadazolid and vancomycin in C. difficile infection.

OBJECTIVES: The aim of this study was to evaluate the susceptibilities of Clostridium difficile isolates to cadazolid, a novel antibiotic for the treatment of C. difficile infection. METHODS: Ribotyping and susceptibilities were determined for C. difficile isolates from a multicentre, double-blind, Phase 2 study of oral cadazolid in patients with C. difficile infection (NCT01222702, ClinicalTrials.gov; EudraCT 2010-020941-29, European Clinical Trials Database). Patients were randomized to receive 250, 500 or 1000 mg of cadazolid twice daily or 125 mg of vancomycin four times daily, for 10 days. MICs of cadazolid, vancomycin, fidaxomicin, linezolid and moxifloxacin were determined at baseline for all patients and post-baseline for patients with clinical failure or recurrence, using the agar dilution method. RESULTS: Seventy-eight of 84 patients had an evaluable toxigenic C. difficile isolate at baseline. The most frequent PCR ribotype was 027 (15.4%). Cadazolid MICs for baseline isolates (including epidemic strain 027) ranged from 0.06 to 0.25 mg/L. Baseline cadazolid MICs were similar to those of fidaxomicin and lower than those of vancomycin, linezolid and moxifloxacin. For each clinical outcome group (clinical cure, clinical failure, sustained clinical response and clinical failure or recurrence), the baseline cadazolid MIC range was 0.06-0.25 mg/L. Mean (min-max) cadazolid faecal concentration (µg/g) on day 5 was 884 (101-2710), 1706 (204-4230) and 3226 (1481-12 600) for the doses 250, 500 and 1000 mg, respectively. CONCLUSIONS: For all cadazolid doses, the faecal concentration was in excess of several thousand-fold the MIC90 for C. difficile. The MIC of cadazolid for all C. difficile isolates, including epidemic strains, was low and in the same narrow range regardless of treatment outcome.

Cellulose and PapG are important for Escherichia coli causing recurrent urinary tract infection in women.

PURPOSE: To identify Escherichia coli factors associated with bacterial persistence in the human urogenital tract using well-defined clinical isolates from women with cystitis. METHODS: E. coli were isolated from women suffering from recurrent cystitis. For comparison, isolates from sporadically infected patients and healthy volunteers were included in the analysis. Samples were taken on three occasions from the urine, periurethra, and vagina. Isolates were typed by pulsed-field gel electrophoresis, and virulence factors were detected by PCR and morphotypic analysis. RESULTS: In all patients, the original E. coli strain was isolated repeatedly and from different regions. The presence of papG coding for a P fimbriae subtype linked to pyelonephritis was associated with strains isolated from patients with recurrent cystitis, including both among urinary and vaginal isolates. The biofilm component cellulose was detected at a higher frequency in urinary isolates from recurrent versus sporadic cystitis. CONCLUSION: The hypothesis of a periurethral/vaginal E. coli reservoir is supported by the results of this study. Our results also indicate an impact of cellulose on E. coli persistence in the human urogenital tract.

Genetic diversity of community-associated methicillin-resistant Staphylococcus aureus in southern Stockholm, 2000-2005.

This study investigated the molecular epidemiology of 104 community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) isolates from southern Stockholm during the period 2000-2005. The isolates were analysed by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, staphylococcal chromosomal cassette (SCC) mec typing and detection of genes encoding Panton-Valentine leukocidin (PVL). Overall, 28 distinct PFGE patterns and 13 sequence types (STs) were identified. ST80, ST8, ST88 and ST150 were the major CA-MRSA clones in the area, and these accounted for 75% (78/104) of all CA-MRSA isolates. ST150 isolates, which have, to date, been found only in Sweden, were isolated exclusively from a group of homeless individuals. Eighty-six (83%) of the 104 isolates in the study possessed SCCmecIV, found in ten different STs, while 16 isolates possessed SCCmecV. The PVL genes were detected in 56% (58/104) of the isolates. Strain ST80-MRSA-IV carrying PVL genes predominated over the 6-year period and accounted for 38% of all isolates. However, a polyclonal tendency was observed among the CA-MRSA isolates recovered in recent years.

European surveillance study on antimicrobial susceptibility of Gram-positive anaerobic cocci.

Gram-positive anaerobic cocci (GPAC) are a heterogeneous group of microorganisms frequently isolated from local and systemic infections. In this study, the antimicrobial susceptibilities of clinical strains isolated in 10 European countries were investigated. After identification of 299 GPAC to species level, the minimum inhibitory concentrations of penicillin, imipenem, clindamycin, metronidazole, vancomycin and linezolid were determined by the agar dilution method according to the Clinical and Laboratory Standards Institute. The majority of isolates were identified as Finegoldia magna and Parvimonas micra (formerly Peptostreptococcus micros), isolated from skin and soft tissue infections. All isolates were susceptible to imipenem, metronidazole, vancomycin and linezolid. Twenty-one isolates (7%) were resistant to penicillin (n=13) and/or to clindamycin (n=12). Four isolates were resistant to both agents. The majority of resistant isolates were identified as F. magna and originated from blood, abscesses and soft tissue infections.

Emergence of VanD-type vancomycin-resistant Enterococcus faecium in Stockholm, Sweden.

A vancomycin-resistant Enterococcus faecium isolate from the urine of a liver transplant patient in Stockholm was found to contain a vanD gene. The sequence of the vanD PCR product shared 100% identity with the vanD5 allele. The isolate was resistant to a relatively high level of vancomycin (128 mg/L) and a low level of teicoplanin (4 mg/L). This is the first VanD-type vancomycin-resistant E. faecium isolate reported in Sweden. The emergence of this strain reinforces the necessity of infection control efforts to interrupt the spread of these organisms.

Examination of cfiA-mediated carbapenem resistance in Bacteroides fragilis strains from a European antibiotic susceptibility survey.

Of 1284 Bacteroides strains collected in Europe in 2000 for antibiotic susceptibility surveillance, 65 isolates displayed imipenem minimum inhibitory concentrations (MICs) > or =1 mg/L and were chosen for a thorough analysis of their resistance mechanism. Twenty-five of the isolates were positive for the cfiA carbapenem resistance gene. The resistance rates were 0.8% and 1.3% for imipenem and meropenem, respectively. In six of the strains, insertion sequence (IS) elements (IS613, IS614B, IS1186 and IS1187) activated the cfiA gene. However, other strains displayed at least elevated carbapenem MICs or were carbapenem resistant and produced measurable carbapenemase activities but did not harbour IS elements in the region upstream of the cfiA gene. The major determinant of carbapenem resistance in Bacteroides fragilis is production of CfiA metallo-beta-lactamase via activation of the cfiA gene by IS elements (higher level resistance) or by activation of its putative own promoter.

European surveillance study on the antibiotic susceptibility of Propionibacterium acnes.

Propionibacterium acnes strains are recovered from infections linked to surgical procedures, foreign bodies and septicaemia. This study investigated the antibiotic susceptibility patterns of P. acnes isolates from different systemic infections and determined the genomic diversity among resistant P. acnes isolates with low-frequency restriction analysis of chromosomal DNA by pulsed-field gel electrophoresis (PFGE). In total, 304 P. acnes isolates from 13 laboratories in 13 European countries were tested against six antimicrobial agents by the NCCLS reference agar dilution method and the breakpoints recommended by the European Committee on Antimicrobial Susceptibility Testing. Blood isolates were encountered most frequently, followed by those from skin and soft tissue infections, and abdominal infections. Of the isolates examined, 2.6% were resistant to tetracycline, 15.1% to clindamycin, and 17.1% to erythromycin. No resistance was observed to linezolid, benzylpenicillin or vancomycin. There was considerable variation between countries in the proportion of resistant strains, ranging from 83% in Croatia and 60% in Italy to 0% in The Netherlands. Isolates from blood were predominant among the resistant isolates. Seventeen clones and 78 banding patterns were identified among the resistant isolates. It was concluded that antimicrobial resistance has now emerged among P. acnes isolates from systemic infections.

Analysis of effects of MCB3681, the antibacterially active substance of prodrug MCB3837, on human resident microflora as proof of principle.

The water-soluble prodrug MCB3837 is rapidly converted to MCB3681, active against Gram-positive bacterial species, after intravenous infusion. The aim of this study was to prove the principle that MCB3681 is efficacious in vivo by demonstrating its effect on the resident microflora or colonizers of the human skin, nose, oropharynx and intestine. MCB3837 was infused at a daily dose of 6 mg/kg for 5 days. MCB3681 was active against clostridia, bifidobacteria, lactobacilli, enterococci and Staphylococcus aureus, thus proving the principle that MCB3681 is antibacterially efficacious in vivo without affecting the Gram-negative microflora.

Effect of antimicrobial agents on the ecological balance of human microflora.

The normal microflora acts as a barrier against colonisation of potentially pathogenic microorganisms and against overgrowth of already present opportunistic microorganisms. Control of growth of opportunistic microorganisms is termed colonisation resistance. Administration of antimicrobial agents, therapeutically or as prophylaxis, causes disturbances in the ecological balance between the host and the normal microflora. Most studies on the impact of antimicrobial agents on normal microflora have been carried out on the intestinal flora. Less is known on the effects on oropharyngeal, skin, and vaginal microflora. Disturbances in the microflora depend on the properties of the agents as well as of the absorption, route of elimination, and possible enzymatic inactivation and/or binding to faecal material of the agents. The clinically most common disturbances in the intestinal microflora are diarrhoea and fungal infections that usually cease after the end of treatment. A well-balanced microflora prevents establishment of resistant microbial strains. By using antimicrobial agents that do not disturb colonisation resistance, the risk of emergence and spread of resistant strains between patients and dissemination of resistant determinants between microorganisms is reduced. In this article, the potential ecological effects of administration of antimicrobial agents on the intestinal, oropharyngeal, and vaginal microflora are summarised. The review is based on clinical studies published during the past 10 years.

Enzyme-linked immunosorbent assay (ELISA) for antibodies to Clostridium difficile toxins in patients with pseudomembranous colitis and antibiotic-associated diarrhoea.

Enzyme-linked immunosorbent assay (ELISA) was established with purified toxins from Clostridium difficile as antigen to measure antibody response in patients with pseudomembranous colitis (PMC) and prolonged antibiotic-associated diarrhoea (AAD). Positive ELISA titres were defined in a control population. Antibodies of IgG class against toxin B were demonstrated in 6/88 (7%) control sera and in 31/61 (51%) sera from 11/19 (58%) patients. Antibodies of IgA class were found in one patient while antibodies of IgM class were not demonstrated. ELISA antibodies against toxin A were not demonstrated. For comparison a neutralization test was performed and neutralizing antibodies to toxin B but not to toxin A were demonstrated in 10/61 (16%) sera from 4/19 (21%) patients and in none of the controls. ELISA was found to be a more sensitive assay than neutralization. ELISA antibodies were detected from the third week of the disease while neutralizing antibodies appeared after 5 weeks. Lack of an antibody response in ELISA seemed to correlate to a more severe colitis.

Impact of antimicrobial agents on the gastrointestinal microflora and the risk of infections.

The most common and significant cause of disturbances in the normal gastrointestinal microflora is the administration of antimicrobial agents. The microflora can be influenced by antimicrobial agents because of incomplete absorption of any orally administered antimicrobial agent, secretion of an antimicrobial agent by the salivary glands and in the bile, or secretion from the intestinal mucosa. In most cases the influence is not beneficial to the patient because suppression of the indigenous microorganisms often permits potential pathogens to overgrow and cause septic conditions, diarrhea, or colitis. Antimicrobial agents that influence the normal microflora also promote the emergence of antimicrobial-resistant strains. The authors' experience on the impact of different beta-lactams, erythromycin, clindamycin, tetracycline, and nitroimidazoles on the gastrointestinal microflora and the risk of infections when these agents are used is reviewed.

Effect of quinolones on the human intestinal microflora.

The quinolones exhibit a selective suppressive effect on the intestinal microflora. The aerobic Gram-negative bacteria are strongly suppressed, while the aerobic Gram-positive bacteria are less affected, with ciprofloxacin and ofloxacin having the greatest effect. The anaerobic microflora is not affected by administration of norfloxacin, but is suppressed slightly by ciprofloxacin and ofloxacin, and moderately by sparfloxacin and temafloxacin. Very high concentrations of the quinolones are obtained in faeces, far exceeding the minimum inhibitory concentration for most aerobic and anaerobic bacteria. The discrepancy between in vivo and in vitro outcome is explained by the binding of the quinolones to faeces, and by inoculum effects. These ecological properties of the quinolones on the intestinal microflora make them suitable for treatment of bacterial enteric infections, selective decontamination and prophylaxis against travellers' diarrhoea.

Effect of quinolones on intestinal ecology.

Quinolones have a selective effect on the normal human intestinal microflora. Published data on 13 different quinolone agents [ciprofloxacin, enoxacin, norfloxacin, ofloxacin, pefloxacin, lomefloxacin, levofloxacin, sparfloxacin, rufloxacin, sitafloxacin (DU-6859a), gatifloxacin, trovafloxacin and moxifloxacin] show that gram-negative aerobic bacteria, especially Enterobacteriaceae, are strongly suppressed or eliminated during therapy. Gram-positive aerobic cocci are affected strongly by administration of sitafloxacin and moxifloxacin and to minor degrees by the other quinolones. Three new quinolones--gatifloxacin, trovafloxacin and moxifloxacin--are very active against anaerobic bacteria in vitro but have minor effects on the anaerobic intestinal human microflora. Similar findings have been reported for the other 10 quinolones. Thus, the quinolone antibacterials have an ecological impact on the human intestinal microflora, mainly on the enterobacteria, that should be taken into account when these agents are used for prophylaxis or treatment of gastrointestinal bacterial infections.

The treatment of severe intra-abdominal infections: the role of piperacillin/tazobactam.

Intra-abdominal infections require treatment effective against both aerobic and anaerobic bacteria. Piperacillin/tazobactam, a beta-lactam/beta-lactamase-inhibitor combination, has a spectrum that includes Gram-positive and Gram-negative aerobic and anaerobic organisms. In one comparative study of piperacillin/tazobactam and gentamicin/clindamycin, 88% of patients treated with piperacillin/tazobactam had a favorable clinical outcome at endpoint compared to 74% of patients treated with gentamicin plus clindamycin. Bacteriological response at endpoint was 87% in the piperacillin/tazobactam group and 74% in the gentamicin plus clindamycin group. In a comparative trial of piperacillin/tazobactam versus imipenem/cilastatin, the clinical cure rate was 91% in the piperacillin/tazobactam group and 69% in the imipenem/cilastatin group (p = 0.005). Among microbiologically evaluable patients, the infecting organism was eradicated in 93% of piperacillin/tazobactam-treated patients compared to 76% eradication among imipenem/cilastatin-treated patients (p = 0.029). Results of these clinical trials and others have shown that piperacillin/tazobactam is a safe and effective alternative to either combination or monotherapy for intra-abdominal infections.

Impact of ketolides on resistance selection and ecologic effects during treatment for respiratory tract infections.

Ketolides are a new class of antibacterials that have been specifically developed for the treatment of community-acquired respiratory tract infections in an era of increasing resistance among major etiologic pathogens. These agents possess several unique structural features, including a 3-keto function and a large aromatic side chain, that confer not only a mode of action that differentiates them from the macrolide class but also a reduced potential to induce--or select for--resistant strains. Studies also suggest that ketolides such as telithromycin have a lower ecologic impact on the body's microflora than agents such as clarithromycin and amoxicillin-clavulanate, potentially reducing the risk of emergence of resistant strains and the spread of such resistance to pathogenic species. Therefore, available evidence suggests that ketolides may not only provide important new treatment options in an era of increasing resistance but may also contribute to reducing the pressure for development of further resistance. Clearly, further studies are required to confirm this low resistance potential once the ketolide agents become more widely used in routine practice.

Adverse effects of monobactams and carbapenems.

Monobactams and carbapenems are 2 classes of beta-lactam antibiotics that were introduced in the 1980s. This review considers the monobactam aztreonam and the carbapenems imipenem and meropenem. Imipenem is administered together with cilastatin, which inhibits the enzymatic breakdown of imipenem in the kidney. The antibacterial activities of these drugs are quite different from older beta-lactams. Aztreonam is directed towards aerobic Gram-negative bacteria, especially Pseudomonas aeruginosa, while imipenem and meropenem are active against both aerobic and anaerobic Gram-positive and Gram-negative bacteria. Thus, these drugs should be reserved for patients who have a special need for them. They are also structurally different from older beta-lactams and possess different adverse drug reaction profiles. It was initially suggested that aztreonam would be less immunogenic than previous beta-lactams because reactive breakdown products acting as haptens are less likely to be formed. Clinical reports now support this assumption, and, in particular, cross hypersensitivity between aztreonam and other beta-lactams seems to be rare which makes the drug a useful therapeutic alternative. However, hypersensitivity to aztreonam does occur. The predominant concern in terms of adverse reactions to imipenem/cilastatin is the increased tendency to cause seizures compared with other beta-lactams. The risk of producing a seizure is highly associated with inadequate dose adjustment in relation to kidney function. If appropriate care is taken, seizures occur in less than 1% of patients treated. However, it is possible that concomitant administration of other drugs with neurotoxic profiles (e.g. theophylline and cyclosporin) given in overdose, may increase the risk of seizures.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunochemical fingerprinting of Clostridium difficile strains isolated from an outbreak of antibiotic-associated colitis and diarrhoea.

Twenty eight strains of Clostridium difficile , isolated from an outbreak of antibiotic-associated colitis and diarrhoea in an orthopaedic ward and from sporadic cases throughout Sweden, were sent to Edinburgh for immunochemical fingerprinting without information about their origin. EDTA extracts of the organisms were examined by crossed immunoelectrophoresis (CIE), polyacrylamide gel electrophoresis (PAGE) and electroblot transfer. Two patterns were revealed by CIE: group A (18 strains) and group B (10 strains). PAGE and electroblot transfer revealed one major group of 10 strains (group 1), six small groups of two or three strains and six strains which were unlike any other strain. The CIE group B and PAGE- electroblot group 1 were identical. Nine of the 10 strains in this group were from patients in the outbreak. These findings indicate that a single strain spread in the orthopaedic ward as a nosocomial infection and that this strain differed from most other strains investigated. The PAGE- electroblot technique should, therefore, greatly aid investigations into the epidemiology of C. difficile infections.

Incidence and significance of intraperitoneal aerobic and anaerobic bacteria.

Intra-abdominal infections frequently occur after trauma, surgical resections, or intrinsic diseases of the gastrointestinal tract. These infections, which can be generalized or localized in intraperitoneal or extraperitoneal locations as well as in organs, are often difficult to diagnose and treat. They are usually polymicrobial, involving both aerobic and anaerobic bacteria. The average number of bacterial strains recovered is between two and five, with anaerobes dominating. The aerobic microorganisms most commonly recovered are Enterobacteriaceae (mainly Escherichia coli) and enterococci (mainly Enterococcus faecalis). Among the anaerobic microorganisms, Bacteroides fragilis, anaerobic cocci, and clostridia are usually isolated. Adequate surgical drainage and antimicrobial therapy improve the clinical course of intra-abdominal infections and reduce the risk of local complications and septicemia. The choice of antimicrobial agents should be based on the type of infection, the microorganisms most likely to be encountered, and the microbial sensitivity pattern of the clinic. The side-effect profile of the antimicrobial therapy should also be taken into consideration.

Antimicrobial susceptibility of Bacteroides fragilis group isolates in Europe.

OBJECTIVE: To evaluate the activity of old and newer antianaerobic drugs against clinical isolates of Bacteroides fragilis group strains from different parts of Europe. METHODS: Bacteroides fragilis group isolates from 37 laboratories in 19 countries were biochemically characterized. The MICs of seven antimicrobial agents were determined by the agar dilution method as recommended by the NCCLS. Production of beta-lactamase was detected by nitrocefin. RESULTS: There were 1284 B. fragilis group isolates included in the study. Abdominal infections and wounds were the most common sources of isolation and B. fragilis was the dominating species. Ninety-nine percent of the strains were resistant to ampicillin (breakpoint 2 mg/L), 6% to cefoxitin (64 mg/L), 15% to clindamycin (8 mg/L) and 9% to moxifloxacin (8 mg/L). Less than 1% were resistant to imipenem (16 mg/L), piperacillin-tazobactam (128 mg/L) and metronidazole (32 mg/L). Ninety-six percent of the isolates were beta-lactamase producers. CONCLUSIONS: Antimicrobial resistance among the B. fragilis group is increasing.