Intetsu Kobayashi

Dissemination in Japanese hospitals of strains of Staphylococcus aureus heterogeneously resistant to vancomycin

BACKGROUND Since the discovery of the vancomycin-resistant Staphylococcus aureus (VRSA) strain Mu50 (minimum inhibitory concentration [MIC] 8 mg/L), there has been concern about the potential spread of such strains throughout Japanese hospitals. Two important questions need to be answered: (1) what is the prevalence of VRSA, and (2) by what mechanism does vancomycin resistance occur. METHODS The vancomycin susceptibilities of three methicillin-resistant S aureus (MRSA) strains (Mu50, Mu3, and H1) and the methicillin-susceptible S aureus type strain FDA209P were compared by MIC determinations and population analysis. Mu3 (MIC 3 mg/L) was isolated from the sputum of a patient with pneumonia after surgery who had failed vancomycin therapy. H1 (MIC 2 mg/L), which is a representative vancomycin-susceptible MRSA strain, was isolated from a patient with pneumonia who responded favourably to vancomycin therapy. Subclones of Mu3 with increased resistance against vancomycin were selected with serial concentrations of vancomycin and their MICs were determined. The prevalence of VRSA and Mu3-like strains in Japanese hospitals was estimated by population analysis from 1149 clinical MRSA isolates obtained from 203 hospitals throughout Japan. The genetic traits of the Mu3 and Mu50 strains were compared with clonotypes of MRSA from around the world. FINDINGS Mu3 and Mu50 had an identical pulsed-field gel electrophoresis banding pattern. When grown in a drug-free medium, Mu3 produced subpopulation of cells with varying degrees of vancomycin resistance, thus demonstrating natural heterogeneity, or variability, in susceptibility to vancomycin. In the presence of vancomycin, Mu3 produced subclones with resistance roughly proportional to the concentrations of vancomycin used. Selection of Mu3 with 8 mg/L or more of vancomycin gave rise to subclones with vancomycin resistance equal to that of Mu50 (MIC 8 mg/L) at a frequency of 1/1,000,000. During screening of Japanese MRSA strains, no strain of VRSA additional to Mu50 was found. The prevalence of MRSA isolates heterogeneously resistant to vancomycin was 20% in Juntendo University Hospital, 9.3% in the other seven university hospitals, and 1.3% in non-university hospitals or clinics. INTERPRETATION Heterogeneously resistant VRSA is a preliminary stage that allows development into VRSA upon exposure to vancomycin. Heterogeneously resistant VRSA was found in hospitals throughout Japan. This finding could explain, at least partly, the frequent therapeutic failure of MRSA infection with vancomycin in Japan.

Detection of Multidrug Resistance in Mycobacterium tuberculosis

ABSTRACT We developed a DNA sequencing-based method to detect mutations in the genome of drug-resistant Mycobacterium tuberculosis. Drug resistance in M. tuberculosis is caused by mutations in restricted regions of the genome. Eight genome regions associated with drug resistance, including rpoB for rifampin (RIF), katG and the mabA (fabG1)-inhA promoter for isoniazid (INH), embB for ethambutol (EMB), pncA for pyrazinamide (PZA), rpsL and rrs for streptomycin (STR), and gyrA for levofloxacin, were amplified simultaneously by PCR, and the DNA sequences were determined. It took 6.5 h to complete all procedures. Among the 138 clinical isolates tested, 55 were resistant to at least one drug. Thirty-four of 38 INH-resistant isolates (89.5%), 28 of 28 RIF-resistant isolates (100%), 15 of 18 EMB-resistant isolates (83.3%), 18 of 30 STR-resistant isolates (60%), and 17 of 17 PZA-resistant isolates (100%) had mutations related to specific drug resistance. Eighteen of these mutations had not been reported previously. These novel mutations include one in rpoB, eight in katG, one in the mabA-inhA regulatory region, two in embB, five in pncA, and one in rrs. Escherichia coli isolates expressing individually five of the eight katG mutations showed loss of catalase and INH oxidation activities, and isolates carrying any of the five pncA mutations showed no pyrazinamidase activity, indicating that these mutations are associated with INH and PZA resistance, respectively. Our sequencing-based method was also useful for testing sputa from tuberculosis patients and for screening of mutations in Mycobacterium bovis. In conclusion, our new method is useful for rapid detection of multiple-drug-resistant M. tuberculosis and for identifying novel mutations in drug-resistant M. tuberculosis.

Changing Antimicrobial Susceptibility Epidemiology of Helicobacter pylori Strains in Japan between 2002 and 2005

ABSTRACT Surveillance of Helicobacter pylori antimicrobial susceptibility reflecting the general population in Japan is limited. The antimicrobial susceptibilities of 3,707 H. pylori strains isolated from gastric mucosa samples of previously untreated patients diagnosed with gastroduodenal diseases at 36 medical facilities located throughout Japan between October 2002 and September 2005 were evaluated. Using an agar dilution method for antimicrobial susceptibility testing of H. pylori, the MIC distributions and trends during the study period for clarithromycin, amoxicillin, and metronidazole were studied. While the MIC50 and MIC90 for clarithromycin did not change during the 3-year period, the MIC80 showed a 128-fold increase. Furthermore, the rate of resistance increased yearly from 18.9% (2002 to 2003) to 21.1% (2003 to 2004) and 27.7% (2004 to 2005). With a resistance rate of 19.2% among males compared to 27.0% among females, a significant gender difference was observed (P < 0.0001). Our study shows that in Japan, there is an evolving trend towards increased resistance to clarithromycin with geographical and gender differences as well as between clinical disease conditions. No significant changes in resistance were observed for amoxicillin and metronidazole during the period. While the benefit of H. pylori antimicrobial susceptibility testing has been debated in Japan, current empirical regimens are not based on susceptibility data representative of the general population. The development of an effective H. pylori eradication regimen in Japan will require continued resistance surveillance as well as a better understanding of the epidemiology of resistance.

Multidrug-resistant Pseudomonas aeruginosa strain that caused an outbreak in a neurosurgery ward and its aac(6')-Iae gene cassette encoding a novel aminoglycoside acetyltransferase.

ABSTRACT We characterized multidrug-resistant Pseudomonas aeruginosa strains isolated from patients involved in an outbreak of catheter-associated urinary tract infections that occurred in a neurosurgery ward of a hospital in Sendai, Japan. Pulsed-field gel electrophoresis of SpeI-, XbaI-, or HpaI-digested genomic DNAs from the isolates revealed that clonal expansion of a P. aeruginosa strain designated IMCJ2.S1 had occurred in the ward. This strain possessed broad-spectrum resistance to aminoglycosides, β-lactams, fluoroquinolones, tetracyclines, sulfonamides, and chlorhexidine. Strain IMCJ2.S1 showed a level of resistance to some kinds of disinfectants similar to that of a control strain of P. aeruginosa, ATCC 27853. IMCJ2.S1 contained a novel class 1 integron, In113, in the chromosome but not on a plasmid. In113 contains an array of three gene cassettes of blaIMP-1, a novel aminoglycoside resistance gene, and the aadA1 gene. The aminoglycoside resistance gene, designated aac(6′)-Iae, encoded a 183-amino-acid protein that shared 57.1% identity with AAC(6′)-Iq. Recombinant AAC(6′)-Iae protein showed aminoglycoside 6′-N-acetyltransferase activity by thin-layer chromatography. Escherichia coli expressing exogenous aac(6′)-Iae showed resistance to amikacin, dibekacin, isepamicin, kanamycin, netilmicin, sisomicin, and tobramycin but not to arbekacin, gentamicins, or streptomycin. Alterations of gyrA and parC at the amino acid sequence level were detected in IMCJ2.S1, suggesting that such mutations confer the resistance to fluoroquinolones observed for this strain. These results indicate that P. aeruginosa IMCJ2.S1 has developed multidrug resistance by acquiring resistance determinants, including a novel member of the aac(6′)-I family and mutations in drug resistance genes.

Helicobacter pylori invades the gastric mucosa and translocates to the gastric lymph nodes.

Helicobacter pylori has been considered to be non-invasive and to rarely infiltrate the gastric mucosa, even though there is an active Th1 immune response in the lamina propria of the H. pylori-infected stomach. To elucidate whether H. pylori invades the lamina propria and translocates to the gastric lymph nodes, we examined H. pylori in formalin-fixed and paraffin-embedded tissue sections of stomach and gastric lymph nodes obtained from 51 cancer patients using real-time PCR and immunohistochemistry (IHC) with a novel anti-H. pylori monoclonal antibody that recognizes lipopolysaccharides. Fresh gastric lymph nodes were used to culture for H. pylori. In 46 patients with H. pylori in the stomach, the bacterium was found in the lymph nodes from 21 patients by culture, 37 patients by PCR, and 29 patients by IHC. H. pylori captured by macrophages was found in the lamina propria of 39 patients. In the lymph nodes, the bacterium was found in many macrophages and a few interdigitating dendritic cells at the paracortical areas. H. pylori was also found in the intracellular canaliculi of parietal cells in 21 patients, but intracytoplasmic invasion into gastric epithelial cells was not identified. When compared to the commercially available anti-H. pylori antibodies, the novel antibody showed the highest sensitivity to detect H. pylori-positive macrophages, whereas no difference was found for H. pylori in the mucous layer. The H. pylori-positive macrophages in the lamina propria correlated with chronic gastritis as well as translocation of such cells to the lymph nodes. These results suggest that H. pylori-induced gastric epithelial damage allows the bacteria to invade the lamina propria and translocate to the gastric lymph nodes, which may chronically stimulate the immune system. The bacteria captured by macrophages, whether remaining alive or not, may contribute to the induction and development of H. pylori-induced chronic gastritis.

Zyvox® Annual Appraisal of Potency and Spectrum program: linezolid surveillance program results for 2008☆

The seventh year of the Zyvox Annual Appraisal of Potency and Spectrum Program (2008) continues to monitor the in vitro activities of linezolid and comparator agents tested against Gram-positive pathogens in Latin America, Europe, Canada, and the Asia-Pacific region. Linezolid is an oxazolidinone approved for the treatment of vancomycin-resistant Enterococcus faecium infections, complicated skin and soft tissue infections, and nosocomial pneumonia caused by various Gram-positive species including methicillin-resistant Staphylococcus aureus (MRSA). Surveillance isolates were submitted from 64 medical centers (24 countries) for a total of 6121 strains. Each country was requested to send 200 consecutive isolates in 6 targeted pathogen categories to a central processing laboratory, except the United Kingdom, Japan, and China where more strains were processed (400, 400, and 800, respectively). Reference broth microdilution susceptibility testing methods were used to test the following organism groups: S. aureus (3240), coagulase-negative staphylococci (CoNS) (748), enterococci (864), Streptococcus pneumoniae (655), viridans group (297), and beta-hemolytic streptococci (317). Eight linezolid-resistant (LZD-R) isolates were detected in 7 countries (Italy [2], France, China, Brazil, Sweden, Germany, and United Kingdom) among the enterococci (Enterococcus faecalis [3] and E. faecium [2]) and CoNS (3 Staphylococcus epidermidis). Five LZD-R isolates contained 23S rRNA mutations (G2576T or G2447T), and 2 strains had undeterminable resistance mechanisms. One CoNS (Italy) contained the mobile cfr gene. Vancomycin-resistant enterococci rates ranged from 0.0% in several countries to 59.4% in Taiwan. All streptococci were linezolid susceptible (MIC(90), 1 microg/mL). In conclusion, the activity of linezolid remained uniform and stable across the sampled geographic regions studied when compared to the 2006 to 2007 results. Documented LZD-R remains rare (only 0.13% overall but highest for CoNS [0.41%] and enterococci [0.69%]) among the 24 countries sampled for the 6 different pathogen groups. Rates of clindamycin resistance and the frequency of MRSA varied by geographic region and between nations; therefore, like oxazolidinones, it requires continued surveillance for changing resistance patterns.

High prevalence of Neisseria gonorrhoeae strains with reduced susceptibility to fluoroquinolones in Japan.

OBJECTIVE--To study the antibiotic susceptibility of Neisseria gonorrhoeae strains isolated in Japan and, in particular, to examine the possibility of emerging fluoroquinolone resistance. MATERIALS AND METHODS--Sixty-nine strains of Neisseria gonorrhoeae isolated in 1992 were tested for susceptibility to 15 antibiotics including fluoroquinolones and were seroclassified. Twenty-seven strains isolated from 1981 to 1984 were also evaluated as controls. RESULTS--The MIC90 values of norfloxacin, ofloxacin, and ciprofloxacin against the isolates from 1992 were 2.0, 1.0, and 0.5 microgram/ml, respectively. The MIC90 values of norfloxacin, ofloxacin, and ciprofloxacin against the isolates from 1981-84 (controls) were 0.25, 0.125, and 0.063 microgram/ml, respectively. These results indicate that the MIC90 values of norfloxacin, ofloxacin, and ciprofloxacin against the strains from 1992 were 8-fold higher than those against the strains from 1981-84. However, there were no significant differences in susceptibility to beta-lactams, tetracyclines, macrolides, and spectinomycin between the isolates from 1992 and those from 1981-84. The majority of the isolates belonged to the WII/WIII serogroup. There was no relationship between fluoroquinolone resistance and serogroup. CONCLUSIONS--Fluoroquinolones have been used frequently as first-line therapy and have provided excellent clinical efficacy for gonococcal infections for the last several years in Japan. However, our data indicate that a rapid decrease in the susceptibility of Neisseria gonorrhoeae to fluoroquinolones is occurring in our country.

Development and Evaluation of a Line Probe Assay for Rapid Identification of pncA Mutations in Pyrazinamide-Resistant Mycobacterium tuberculosis Strains

ABSTRACT Resistance of Mycobacterium tuberculosis to pyrazinamide (PZA) derives mainly from mutations in the pncA gene. We developed a reverse hybridization-based line probe assay with oligonucleotide probes designed to detect mutations in pncA. The detection of PZA resistance was evaluated in 258 clinical isolates of M. tuberculosis. The sensitivity and specificity of PZA resistance obtained by this new assay were both 100%, consistent with the results of conventional PZA susceptibility testing. This assay can be used with sputa from tuberculosis patients. It appears to be reliable and widely applicable and, given its simplicity and rapid performance, will be a valuable tool for diagnostic use.

Gatifloxacin Resistance and Mutations in gyrA after Unsuccessful Helicobacter pylori Eradication in Japan

ABSTRACT A high resistance rate (47.9%) to gatifloxacin (GAT; 8-methoxy fluoroquinolone) in Helicobacter pylori (H. pylori) strains from 48 Japanese patients is observed after unsuccessful H. pylori eradication. A significant association between MICs for GAT equal to or above 1 μg/ml and mutations of the gyrA gene of H. pylori was demonstrated.

Analysis of quinolone resistance mechanisms in Neisseria gonorrhoeae isolates in vitro

BACKGROUND AND OBJECTIVES: Gonococcal fluoroquinolone resistance is now a significant problem in Japan. We generated gonococcal mutants resistant to norfloxacin in vitro from norfloxacin sensitive isolates and analysed the contribution of three known mechanisms of quinolone resistance in Neisseria gonorrhoeae. MATERIALS AND METHODS: Three clinical isolates of N gonorrhoeae susceptible to norfloxacin were exposed to increasing concentrations of norfloxacin. To identify mutations in the gyrA and parC genes of the gonococcal mutants, the quinolone resistance determining regions of the gyrA and parC genes were polymerase chain reaction (PCR) amplified and the PCR products were directly sequenced. Norfloxacin accumulation in the gonococcal cells was also measured. RESULTS: The MICs of norfloxacin for three variants containing a single GyrA mutation were 16-fold higher than that for their parent isolates. A variant showing reduced norfloxacin accumulation in the cells, without mutations in the GyrA or ParC proteins, was also less sensitive to norfloxacin, with a 16-fold increase in the MIC, compared with the parent strain. The MIC of norfloxacin for a variant which contained a single GyrA mutation with reduced norfloxacin accumulation in the cells was 128-fold higher than for the parent strain. A variant containing mutations in both GyrA and ParC proteins with reduced accumulation of norfloxacin in the cells showed a 256-fold increase in the norfloxacin MIC compared with the parent strain. There was no variant containing a ParC mutation without the simultaneous presence of a GyrA mutation. CONCLUSIONS: The results from this study suggest that not only a mutation in the gyrA gene but also reduced drug accumulation in cells contributes to the development of fluoroquinolone a mutation in the gyrA gene contributes to a high level of fluoroquinolone resistance in gonococci with decreases in accumulation in cells having an additional but lesser effect.