Occurrence of vancomycin-intermediate-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> in Japan

The Clinical and Laboratory Standards Institute (CLSI) amended the criteria for vancomycin susceptibility and resistance of Staphylococcus aureus in 2006. The earlier criteria had established that S. aureus with minimum inhibitory concentrations (MICs) of vancomycin of < or =4 microg/ml, 8 to 16 microg/ml, and > or =32 microg/ml were vancomycin-susceptible, -intermediate-resistant and -resistant, respectively. The revised recommendation states that bacteria showing vancomycin MICs of < or =2 microg/ml, 4 to 8 microg/ml, and > or =16 microg/ml are -susceptible, -intermediate-resistant, and -resistant, respectively. We examined, based on these new criteria, the vancomycin susceptibility of methicillin-resistant S. aureus (MRSA) strains isolated in Japan from 1978 through 2005 at 17 general hospitals. The results showed that, among 2446 MRSA isolates tested, 8 were classified as intermediate-vancomycin-resistant (VISA). Re-examination of vancomycin susceptibility in these 8 strains in 2006 revealed that 6 strains showed a vancomycin MIC of 4 microg/ml, as tested by the agar dilution method, broth dilution methods, and E-test; the 2 other strains had lost the vancomycin resistance. Pulsed-field gel electrophoresis (PFGE) of the chromosomal DNA of these strains exhibited five unique profiles; 2 strains isolated from the same hospital were identical. These results revealed that at least five different types of VISA strains could be identified in Japan so far according to the new CLSI criteria. All these VISA strains had type II staphylococcal cassette chromosome, mec. This study revealed, for the first time in Japan, the presence of intermediate vancomycin-resistant MRSA in this country.     

Community-associated methicillin-resistant Staphylococcus aureus, eastern Argentina

Sixty-nine community-associated methicillin-resistant Staphylococcus aureus recovered in 6 healthcare centers from northeastern and eastern Argentina were genotyped by pulsed-field gel electrophoresis. The predominant pulsotype was widely distributed harbored SCCmec type IV and Panton-Valentine leukocidin genes. Representative isolates were characterized by multilocus sequence typing and spa typing, demonstrating that this clone belonged to ST5 and spa type 311.     

Effect of arbekacin on a methicillin-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>-induced biofilm in a rat model

Biofilms are a major concern for clinicians in the treatment of infectious disease because of their resistance to a wide range of antibiotics. Arbekacin, an aminoglycoside antibiotic, is the drug of choice for the treatment of infection caused by methicillin-resistant Staphylococcus aureus (MRSA). However, it has not yet been defined whether arbekacin tends to penetrate into the biofilm structure induced by MRSA infection. In this study, we treated a biofilm mode of MRSA growth with arbekacin, using a rat air-pouch model. The model has the advantage of permitting frequent sampling of exudates for bacterial counts and antibacterial activity. A clear dose-dependent bactericidal effect was detected in rats treated with arbekacin at con-centrations between 0.3 and 10mg/kg, but 0.1mg/kg of arbekacin was ineffective against the experimental MRSA infection in rats. Morphological studies using scanning electron microscopy and histochemical staining demonstrated that an effective dosage of arbekacin induced dramatic changes in the biofilm membranous structure as well as in the inflammatory response, resulting in eradication of the biofilm structure and resolution of inflammation.     

Trends in the gentamicin and arbekacin susceptibility of methicillin-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> and the genes encoding aminoglycoside-modifying enzymes

It is generally accepted that methicillin-resistant Staphylococcus aureus (MRSA) is also resistant to aminoglycoside antibiotics. We investigated trends of gentamicin and arbekacin susceptibilities and the prevalence of the genes encoding aminoglycoside-modifying enzymes (AMEs) for a total of 218 strains of MRSA isolated from blood specimens obtained from 1978 through 2002 in one hospital. The minimum inhibitory concentrations of gentamicin at which 50% of the strains were inhibited (MIC₅₀) were ≥128 and 32 μg/ml for isolates obtained from 1978 to 1984 and from 1985 to 1989, respectively, and 0.5 μg/ml for isolates obtained from 1990 to 2002. The MIC₉₀ of gentamicin was consistently ≥128 μg/ml. Investigation of the occurrence of AME revealed that the MIC₅₀ of gentamicin was highly correlated with the presence of aac(6′)/aph(2″) encoding aminoglycoside acetyl/phosphotransferase. The MIC₅₀ of arbekacin was 2 μg/ml for strains isolated in 1978–1984 and ≤0.5 μg/ml for strains isolated from 1985 to 2002. The MIC₉₀ of arbekacin was 8 μg/ml for the strains isolated in 1978–1989 and 1 to 2 μg/ml for strains isolated in 1990–2002. Though it has been established that AAC(6′)/APH(2″) modifies arbekacin, the trend of arbekacin resistance was not necessarily consistent with the presence of this enzyme. However, the prevalence of both aac(6′)/aph(2″) and aph(3′)-III in the strains isolated from 1978 through 2002 was correlated with the MIC₉₀ values of arbekacin. Thus, it is most likely that APH(3′)-III, in addition to AAC(6′)/APH(2″), is somehow involved in arbekacin resistance in S. aureus. Our results imply that gentamicin- and arbekacin-resistant MRSAs have consistently decreased for the past 25 years and that this finding is, most likely, attributable to the declining prevalence of genes encoding for AMEs.     

Trends of β-lactam antibiotic susceptibility in blood-borne methicillin-resistant Staphylococcus aureus (MRSA) and their linkage to the staphylococcal cassette chromosome mec (SCC mec ) type

We investigated trends of beta-lactam antibiotic susceptibility in a total of 218 strains of blood-borne methicillin-resistant Staphylococcus aureus (MRSA) isolated from 1978 through 2002 at a middle-size geriatric hospital in Tokyo; the strains were classified by the MRSA marker, staphylococcal cassette chromosome mec (SCCmec). The minimum growth inhibitory concentration (MIC) of cloxacillin at which 50% of the strains were inhibited (MIC50) was 2 microg/ml in the strains isolated in 1978-1984 and 32 to 64 microg/ml in the strains isolated subsequently. Similarly, the MIC50 values of cefazolin and imipenem in the 1978-1984 isolates were 16 and 相似文献   

Changes in drug susceptibility and toxin genes in <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> isolated from blood cultures at a university hospital

We studied changes in toxin-producing genes and drug susceptibility in Staphylococcus aureus isolated from blood cultures at the University of Tokyo Hospital between 1980–1984 (six mecA gene-positive methicillin resistant S. aureus [MRSA] strains and 20 mecA gene-negative methicillin-susceptible S. aureus [MSSA] strains) and 1999 (11 MRSA and 20 MSSA strains). The prevalence of strains with toxin-producing genes increased from 66.7% to 90.9% in MRSA, and from 30.0% to 55.0% in MSSA during the interval. Among toxin-producing gene-positive S. aureus, the dominant strains shifted from those with the enterotoxin (ET) – A gene in 1980–1984 to those with both the toxic shock syndrome toxin-1 and the ET-C genes in 1999. All strains were susceptible to vancomycin and teicoplanin. Mupirocin and arbekacin inhibited all strains at concentrations of less than or equal to 0.5µg/ml and 4µg/ml, respectively. More than half of the MRSA strains in 1999 were considered to be nonsusceptible to flomoxef. Because almost all MRSA and more than half of MSSA among recently isolated strains possessed the toxin-producing genes, we should pay attention to whether toxin-related diseases caused by MRSA and MSSA are increasing.     

Superior in vitro activity of carbapenems over anti-methicillin-resistant Staphylococcus aureus (MRSA) and some related antimicrobial agents for community-acquired MRSA but not for hospital-acquired MRSA

Eighty-eight strains of Panton-Valentine leukocidin (PVL)-positive and -negative community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) and 152 strains of hospital-acquired MRSA (HA-MRSA) were examined for susceptibility to carbapenems, oxacillin, and other antimicrobial agents. CA-MRSA strains were more susceptible to carbapenems (MIC₉₀, 1–4 μg/ml) than HA-MRSA strains (MIC₉₀, 32–64 μg/ml). Among the carbapenems examined, CA-MRSA strains were most susceptible to imipenem (MIC₅₀, 0.12 μg/ml; MIC₉₀, 1 μg/ml). A similar tendency was observed with oxacillin, but less markedly (MIC₉₀: 32 μg/ml for CA-MRSA and ≥256 μg/ml for HA-MRSA). This difference was also observed between CA-MRSA and HA-MRSA in susceptibility levels to cephems, erythromycin, clindamycin, and levofloxacin, but not to ampicillin, vancomycin, teicoplanin, linezolid, and arbekacin. The data indicate that, in terms of MIC₅₀ or MIC₉₀ values, CA-MRSA is 64–256 times more susceptible to imipenem than HA-MRSA, and for CA-MRSA, some carbapenems, e.g., imipenem, show better in vitro activity than anti-MRSA or some related agents.     

Microbial substitution of <Emphasis Type="Italic">Mycobacterium avium-intracellulare</Emphasis> to <Emphasis Type="Italic">Mycobacterium abscessus</Emphasis> during clinical course

Mycobacterium avium-intracellulare (MAI) is, among acid-fast bacilli, the most common cause of nontuberculous pulmonary diseases, and MAI infections are often treated according to the guidelines of the American Thoracic Society. However, despite the use of multiple drugs, patients sometimes do not recover with the initial round of treatment. Other kinds of nontuberculous mycobacteria are sometimes found in patients' respiratory samples, even during such treatment for MAI pulmonary disease. We experienced three patients with pulmonary disease due to Mycobacterium abscessus (MA) in whom the disease was difficult to treat because of resistance to all the antituberculous agents used. MA infection had occurred in these patients after long-term treatment with multiple drugs for previous MAI pulmonary disease. We considered that the MA infection in these patients appeared to be the result of insufficient efficacy of the drugs used for MAI and insufficiently aggressive use of antituberculous agents. It thus appeared that MA infection was the result of microbial substitution, and that, if this is the case, the guidelines for the treatment of MAI may need to be modified to eliminate microbial substitution.     

Effect of linezolid against postneurosurgical meningitis caused by methicillin-resistant <Emphasis Type="Italic">Staphylococcus epidermidis</Emphasis>: case report

A 67-year-old man who had twice previously undergone operations for a tuberculum sellae meningioma was admitted to hospital for further treatment. After the third surgical intervention, the patient developed persistent low-grade fever and impaired consciousness. Computed tomography, 1 week after surgery, showed postsurgical hydrocephalus. Cerebrospinal fluid (CSF) studies revealed high intracranial pressure (above 30 cm H₂O), and increased cell count (1232/3). One week after the ventricular drainage, coagulase-negative Staphylococcus epidermidis was recovered from his CSF, and antimicrobial susceptibility results indicated that the organism was methicillin-resistant. After 14 days of intravenous vancomycin (VCM) administration failed, linezolid (LZD) was initialized intravenously, resulting in a resolution of the meningitis. After a ventriculoperitoneal shunt procedure was performed, LZD was continued orally, which resulted in a cure. CSF penetration by VCM is reported to be poor, i.e., approximately 10% of serum concentration, which may explain its lack of efficacy. In this case, the penetration of LZD into the CSF was 58.9% of the peak value and 133% of the trough value of serum concentrations. LZD must be considered one of the first-line treatments against surgical-site infection in neurosurgery caused by methicillin-resistant Staphylococci.     

Dissemination of extended-spectrum β-lactamase-producing <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> and <Emphasis Type="Italic">Escherichia coli</Emphasis> in Thai hospitals

Fifty clinical isolates of Klebsiella pneumoniae and Escherichia coli with reduced susceptibility to third-generation cephalosporins, collected from 11 hospitals in Thailand, were studied. All isolates were found to produce extended-spectrum β-lactamase (ESBL), as judged by double-disk synergy and combination disk methods. Most ESBL-producing K. pneumoniae isolates were resistant to ceftazidime (94%) and aztreonam (90%). In contrast, most ESBL-producing E. coli isolates were resistant to ceftriaxone (95%) and cefotaxime (74%). Plasmid DNA was isolated and β-lactamase genes were identified by PCR and sequencing. We found that SHV-12 and CTX-M-14 were the main ESBLs responsible for resistance in K. pneumoniae and E. coli, respectively. SHV-27, SHV-28, and CTX-M-14 were detected in three, two, and four K. pneumoniae isolates, respectively. A high genetic diversity among ESBL-producing K. pneumoniae and E. coli isolates was observed. In addition, the finding of a few isolates that produced identical restriction patterns on pulsed field gel electrophoresis (PFGE) suggests the clonal spread of resistant bacteria within the hospital.     

Molecular epidemiology of uropathogenic <Emphasis Type="Italic">Escherichia coli</Emphasis>

Escherichia coli is the most common cause of complicated as well as uncomplicated urinary tract infections (UTIs). Most of these uropathogenic E. coli (UPEC) strains exhibit certain virulence factors (VFs), including adhesins, iron uptake systems, synthesis of cytotoxins, and specific O:K:H serotypes. Molecular epidemiological studies of UPEC have contributed to the discovery of uropathogenic VFs, to an understanding of the pathogenesis of UTIs as ascending infections, and to the clarification of genetic linkages between different virulence genes such as pathogenicity islands (PAIs), which are one of the mechanisms for horizontal VF gene transfers between the same or related species. Uropathogenic VFs not only play an important role individually but also work cooperatively in a fine-tuned manner with coordinated regulation and expression.     

First isolation of <Emphasis Type="Italic">bla</Emphasis><Subscript>IMP-7</Subscript> in a <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> in Japan

We report here the first isolation in Japan of a carbapenem-resistant Pseudomonas aeruginosa strain that carries the metallo-β-lactamase gene bla _IMP-7. This isolate revealed high-level resistance to all of the tested antibiotics except for piperacillin, showing a multidrug-resistant phenotype.     

Antibacterial activity and PK/PD of ceftriaxone against penicillin-resistant <Emphasis Type="Italic">Streptococcus pneumoniae</Emphasis> and β-lactamase-negative ampicillin-resistant <Emphasis Type="Italic">Haemophilus influenzae</Emphasis> isolates from patients with community-acquired pneumonia

The suitability of ceftriaxone for penicillin-resistant Streptococcus pneumoniae (PRSP) and ampicillin-resistant Haemophilus influenzae (especially β-lactamase-negative ampicillin-resistant (BLNAR) H. influenzae) and the relationship between in vitro antimicrobial activities and pharmacokinetic parameters were evaluated. The values for percentage of time above the MIC (%T>MIC) for ceftriaxone, cefotiam, flomoxef, sulbactam/cefoperazone, sulbactam/ampicillin, and meropenem, using 400 S. pneumoniae isolates and 430 H. influenzae isolates from patients with community-acquired pneumonia (CAP) from more than 100 geographically diverse medical centers during January to July of 2005, were calculated by measuring the MIC for each isolate and by using patameters of pharmacokinetics. A broth microdilution method was used to determine the MIC, using the guidelines of the Clinical and Laboratory Standards Institute (CLSI). Meropenem showed the lowest MIC against penicillin-susceptible S. pneumoniae, followed by sulbactam/cefoperazone and ceftriaxone. Ceftriaxone had the best activity against penicillin-resistant S. pneumoniae and β-lactamase-negative and β-lactamase–producing ampicillin-resistant H. influenzae. Ceftriaxone was unique, showing a long elimination half-life and low MIC values where its serum level duration time was above the MIC for longer than other cephalosporins. Accordingly, the %T>MIC of ceftriaxone for a once-daily administration greatly exceeded the efficacy levels of those for the other antibacterial agents tested. Ceftriaxone has an excellent balance between in vitro antimicrobial activities and pharmacokinetic profiles; and therefore remains effective as a therapeutic agent against PRSP and BLNAR H. influenzae in CAP.     

Chlorpromazine has intracellular killing activity against phagocytosed <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> at clinical concentrations

Chlorpromazine (CPZ) has in vitro antimicrobial activity against Staphylococcus aureus at concentrations that greatly exceed those achieved clinically. It is concentrated by tissues that are rich in macrophages and it is active against phagocytosed mycobacteria when the concentration in the medium is compatible with that achieved clinically. In this report we show that nontoxic concentrations of CPZ below clinical levels have killing activity against S. aureus phagocytosed by human monocyte-derived macrophages that have nominal killing activity against these bacteria. Little or no resistance to the antimicrobial activity of this compound is anticipated to result because of its large number of cellular targets. Therefore, CPZ may have a role in the management of intracellular staphylococcal infections that normally require the use of antibiotics whose potential toxicity exceeds that associated with short-term management with CPZ.     

Chronic <Emphasis Type="Italic">Helicobacter pylori</Emphasis> infection is associated with peripheral arterial disease

It is reported that Helicobacter pylori infection is associated with coronary atherosclerosis both epidemiologically and pathogenetically, but no conclusions have yet been reached. Therefore, we investigated the relationship between H. pylori infection and peripheral arterial disease (PAD). Sixty-nine patients with PAD attending Harasanshin General Hospital (Fukuoka, Japan) were compared with 143 controls (age-matched asymptomatic outpatients with hyperlipidemia). H. pylori infection was diagnosed by the detection of IgG antibodies, the (13)C-urea breath test, and histological examination. Multiple logistic regression analysis was used to assess the data. The 69 PAD patients and 143 controls were aged from 50 to 92 years. According to the Fontaine classification, 43/69 PAD patients (62.3%) were grade I, 25 (36.2%) were grade II, and 1 (0.14%) was grade III. The prevalence of H. pylori infection was higher in the PAD patients than in the controls (79.7% versus 44.8%; P < 0.01). Stepwise logistic regression analysis revealed that H. pylori infection and hypertension had a significant influence on the occurrence of PAD. Our results suggest that chronic H. pylori infection may be one of the risk factors for PAD.     

Remarkably high prevalence of <Emphasis Type="Italic">fts I</Emphasis> gene mutations in <Emphasis Type="Italic">Haemophilus influenzae</Emphasis> isolates from upper respiratory tract infections in children of the Sapporo district,Japan

Recently, the frequency of isolation of beta-lactamase-negative ampicillin resistant (BLNAR) strains of Haemophilus influenzae in Japanese children has been increasing rapidly. Drug resistance in BLNAR strains is associated with mutations of the fts I gene, which encodes penicillin-binding protein 3. In the otolaryngological field, only a few reports have been available concerning fts I gene mutations in BLNAR. We investigated the prevalence of fts I gene mutations, by polymerase chain reaction (PCR) genotyping, in H. influenzae isolates from the upper respiratory tracts of children in the Sapporo district, Japan. When the isolates were classified according to PCR genotyping, 34 (44.2%) of 77 isolates were beta-lactamase-negative ampicillin-sensitive (g-BLNAS), 8 (10.4%) were g-low-BLNAR, 30 (39.0%) were g-high-BLNAR, 2 (2.6%) were beta-lactamase-positive ampicillin-resistant (g-BLPAR), and 3 (3.9%) were beta-lactamase-positive ampicillin/clavulanic acid-resistant (g-high-BLPACR). Mutations in the fts I gene were generally parallel to ampicillin susceptibility, and were frequently observed in children who were 7 years or younger. Of the beta-lactams tested, cefditoren showed the strongest inhibition of H. influenzae isolates, and it inhibited g-BLNAR and g-BLPACR. This study revealed a remarkably high prevalence of fts I gene mutations (g-BLNAR and g-BLPACR) in our district. Furthermore, a regional difference in the prevalence of fts I gene mutations was observed even at the district level.     

Comparative evaluation of a rapid MRSA detection assay based on multiplex real-time PCR versus MRSA screening cultures containing egg yolk

Although the Centers for Disease Control and Prevention (CDC) has been recommending the performance of active surveillance culture (ASC) for the prevention of methicillin-resistant Staphylococcus aureus (MRSA) infections and their control since the guideline was issued in 2006, many variant types of MRSA with various characteristics have been found recently. As this change in MRSA characteristics makes it harder to screen MRSA only by cultures, it is expected that ASC will not be sufficient for the prevention of MRSA infections or MRSA infection control. We evaluated the comparative utility of the BD GeneOhm MRSA assay (a rapid MRSA detection test based on a multiplex real-time polymerase chain reaction [PCR] assay; Becton Dickinson, Fukushima, Japan) and MRSA screening cultures containing egg yolk. The results of the BD GeneOhm MRSA assay were as follows: all MRSA strains were positive, including one strain which became positive by retest; all methicillin-resistant S. epidermidis (MRSE) strains and methicillin-sensitive S. epidermidis (MSSE) strains were negative; 11 of 12 methicillin-sensitive S. aureus (MSSA) strains were negative, while 1 strain was positive; ATCC 33591 was positive, and ATCC 29213 was negative. The sensitivity and specificity of the BD GeneOhm MRSA assay were 100% and 97.4%, respectively. Nine egg yolk reaction-negative MRSA strains were found in 50 MRSA strains, and all MRSE, MSSA, and MSSE strains were denied as MRSA on Pourmedia MRSA II (Eiken Chemical, Tokyo, Japan) after 24-h or 48-h incubation at 35°C. The sensitivity and specificity of Pourmedia MRSA II were 82% and 100%, respectively. Similar results were obtained with some other cultures containing egg yolk.     

The antagonistic effects of a combination of vancomycin and minocycline in <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> with heterogeneous resistance to vancomycin

Some methicillin-resistant Staphylococcus aureus (MRSA) strains in which combinations of vancomycin (VCM) and β-lactam antibiotics show antagonism have recently emerged, and these strains are called β-lactaminduced VCM-resistant MRSA (BIVR). We examined whether various antibiotics exhibited an antagonistic effect with VCM when used against Mu3 and Fu10 (representative BIVR strains), using a simple agar disc method. Chloramphenicol, tetracyclines, macrolides, and lincosamides showed an antagonistic effect with VCM. We attempted to elucidate the antagonistic mechanism of a combination of VCM and minocycline (MINO) in BIVR strains. We determined the rates of autolysis, autolytic activities, and the change in morphology of Mu3 treated with a combination of VCM and MINO. We observed that Mu3 grown in a combination of VCM and MINO showed increasing rates of autolysis, and lower minimal bacteriolytic enzyme dose (MBD) values compared with Mu3 grown in VCM alone, but no cell wall thickening was observed. Taken together, these results suggest that cell wall thickening may not be essential in the increased resistance of BIVR strains. Our present data therefore suggest that these combination therapies of VCM with tetracyclines should be adopted with great care in order to prevent VCM treatment failure.     

<Emphasis Type="Italic">Mycobacterium peregrinum</Emphasis>: bactericidal activity of antibiotics alone and in combination

Mycobacterium peregrinum is a rapidly growing mycobacterium that is occasionally associated with disease at different locations. At present, little information is available on antibiotic activity against this microorganism. For this reason, we have carried out a study on the in vitro activity of 15 antibiotics, alone and in combination, against M. peregrinum. Our study shows that the new fluoroquinolones with a C8-methoxy group, especially moxifloxacin, exhibit greater activity against this species. These data should be evaluated in clinical assays or animal models in order to confirm their clinical significance.     

Splenic abscess in an infant caused by <Emphasis Type="Italic">Streptococcus intermedius</Emphasis>

We report a 20-month-old girl with splenic abscess. The patient was admitted to our hospital because of persistent high fever and abdominal pain. Laboratory data showed leucocytosis and elevated C-reactive protein levels. Abdominal computed tomography showed multiple low-density lesions in the spleen. These findings were consistent with a diagnosis of splenic abscess. She was successfully treated with ultrasonographically guided percutaneous drainage for 11 days and intravenous antibiotic for 17 days. On culture, aspirated fluid from the abscess grew Streptococcus intermedius. This case illustrates that the differential diagnosis of unknown-focus infection in infants should include splenic abscess. We recommend conservative therapy (antibiotics and drainage) as first-line therapy for splenic abscess in pediatric patients, based on the importance of the immunological functions of the spleen.