Nosocomial infection caused by vancomycin-susceptible multidrug-resistant Enterococcus faecalis over a long period in a university hospital in Japan.

Compared with other developed countries, vancomycin-resistant enterococci (VRE) are not widespread in clinical environments in Japan. There have been no VRE outbreaks and only a few VRE strains have sporadically been isolated in our university hospital in Gunma, Japan. To examine the drug susceptibility of Enterococcus faecalis and nosocomial infection caused by non-VRE strains, a retrospective surveillance was conducted in our university hospital. Molecular epidemiological analyses were performed on 1711 E. faecalis clinical isolates collected in our hospital over a 6-year period [1998-2003]. Of these isolates, 1241 (72.5%) were antibiotic resistant and 881 (51.5%) were resistant to two or more drugs. The incidence of multidrug resistant E. faecalis (MDR-Ef) isolates in the intensive care unit increased after enlargement and restructuring of the hospital. The major group of MDR-Ef strains consisted of 209 isolates (12.2%) resistant to the five drug combination tetracycline/erythromycin/kanamycin/streptomycin/gentamicin. Pulsed-field gel electrophoresis analysis of the major MDR-Ef isolates showed that nosocomial infections have been caused by MDR-Ef over a long period (more than 3 years). Multilocus sequence typing showed that these strains were mainly grouped into ST16 (CC58) or ST64 (CC8). Mating experiments suggested that the drug resistances were encoded on two conjugative transposons (integrative conjugative elements), one encoded tetracycline-resistance and the other erythromycin/kanamycin/streptomycin/gentamicin-resistance. To our knowledge, this is the first report of nosocomial infection caused by vancomycin-susceptible MDR-Ef strains over a long period in Japan.

Tuberculosis screening using a T-cell interferon-γ release assay in Japanese medical students and non-Japanese international students.

Screening of medical students and international students for tuberculosis (TB) at the time of admission is a key strategy to control and prevent the spread of infection on university campus and teaching hospitals because of the high risk of exposure to TB patients. The Mycobacterium tuberculosis antigen-specific T-cell interferon-γ release assays (IGRAs) are specific latent tuberculosis detection methods used in such groups. Currently, in Japan, there are no guidelines and no baseline data on IGRAs to evaluate the risk of TB in these high-risk groups. In order to evaluate TB risk at the time of admission in university campus and medical schools in Japan, a retrospective study was conducted. A total of 969 students (585 Japanese students and 384 international students) were screened for TB using the IGRAs at the time of admission. Eight Japanese students (0.9%) were positive for IGRAs, but none were diagnosed with active TB at the follow-up. In contrast, 30 international students (7.8%) were positive for IGRAs, including two students diagnosed with active TB during follow up. Positive ratio of IGRAs in international students was significantly higher than that of medical students at the time of admission. Here we propose a standard approach for TB screening with IGRAs at the time of admission for medical students and international students in Japan.

[Comparison between blood culture and in-situ hybridization of bacteria].

We compared blood culture and in situ hybridization method (Hybrisep) to detect bacteria in blood samples. One thousand and two hundred and sixty nine blood culture samples were tested in 2003 in our hospital. One hundred and sixty seven samples (13.1%) were positive for bacteria. Total number of detected bacteria was 178. Of 178 bacteria, 49.4% was gram positive, 32.6% was gram negative, 13.5% was Candida spp., and 4.5% was anaerobic. Twenty five samples were tested with both blood culture and Hybrisep. Three samples were positive for both methods, and 13 samples were negative for both methods. The identical results were obtained in 64% of samples. Although the microscopic determination of positive signals in Hybrisep requires trained skills, Hybrisep may be a rapid and sensitive method providing valuable information to diagnose sepsis with an automated equipment and an increased number of probes.

[Nationwide surveillance of parenteral antibiotics containing meropenem activities against clinically isolated strains in 2006].

The antibacterial activity of meropenem (MEPM) and other parenteral antibiotics against clinical isolates of 876 strains of Gram-positive bacteria, 1764 strains of Gram-negative bacteria, and 198 strains of anaerobic bacteria obtained from 30 medical institutions during 2006 was measured. The results were as follows; 1. MEPM was more active than the other carbapenem antibiotics tested against Gram-negative bacteria, especially against enterobacteriaceae and Haemophilus influenzae. MEPM was also active against most of the species tested in Gram-positive and anaerobic bacteria, except for multi-drug resistant strains including methicillin-resistant Staphylococcus aureus. 2. As for Pseudomonas aeruginosa, all of the MEPM-resistant strains were resistant to imipenem (IPM). MEPM showed low cross-resistant rate both againt IPM-resistant P. aeruginosa (41.8%) and ciprofloxacin-resistant P. aeruginosa (33.3%). 3. The proportion of extended-spectrum beta-lactamase (ESBL) strains was 4.3% (6 strains) in Escherichia coli, 1.1% (1 strain) in Citrobacter freundii, 21.7% (5 strains) in Citrobacter koseri, 3.1% (4 strains) in Klebsiella pneumoniae, 3.3% (3 strains) in Enterobacter cloacae, 0.8% (1 strain) in Serratia marcescens, and 4.9% (2 strains) in Providencia spp. The proportion of metallo-beta-lactamase strains was 3.1% (10 strains) in P. aeruginosa. 4. Of all species tested, there were no species, which MIC90 of MEPM was more than 4-fold higher than those in our previous study. Therefore, there is almost no significant decrease in susceptibility of clinical isolates to meropenem. In conclusion, the results from this surveillance study suggest that MEPM retains its potent and broad antibacterial activity and therefore is a clinically useful carbapenem at present, 11 years after available for commercial use.

[In-vitro susceptibilites to levofloxacin and various antibacterial agents of 18,639 clinical isolates obtained from 77 centers in 2004].

A total of 18,639 clinical isolates in 19 species collected from 77 centers during 2004 in Japan were tested for their susceptibility to fluoroquinolones (FQs) and other selected antibiotics. The common respiratory pathogens, Streptococcus pyogenes, Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae showed a high susceptible rate against FQs. The isolation rate of beta lactamase non-producing ampicillin-resistant H. influenzae was approximately three times as large as those of western countries. Most strains of Enterobacteriaceae were also susceptible to FQs. The resistance rate of Escherichia coli against FQs has however been rapidly increasing so far as we surveyed since 1994. The FQs-resistant rate in methicillin-resistant Staphylococcus aureus (MRSA) showed approximately 90% except for 36%. of sitafloxacin while FQs-resistant rate in methicillin-susceptible S. aureus (MSSA) was around 5%. The FQs-resistant rate of methicillin-resistant coagulase negative Staphylococci (MRCNS) was also higher than that of methicillin-susceptible coagulase negative Staphylococci (MSCNS), however, it was lower than that of MRSA. In Pseudomonas aeruginosa clinical isolates, 32-34% from UTI and 15-19% of from RTI was resistant to FQs. Acinetobacter spp. showed a high susceptibility to FQs. Although FQs-resistant Neisseria gonorrhoeae have not been increased in western countries, it is remarkably high in Japan. In this survey, isolates of approximately 85% was resistant to FQs.

Presence of Pseudomonas putida strains harboring plasmids bearing the metallo-beta-lactamase gene bla(IMP) in a hospital in Japan.

To determine the persistence and spread of antibiotic-resistant strains in Gunma University Hospital, 83 Pseudomonas putida strains (each from a different patient) were isolated from January 1997 through December 2001. Of the 83 strains isolated, 27 were resistant to carbapenems. All 27 produced metallo-beta-lactamase and were found to be PCR positive for the bla(IMP) gene. Most (22 strains) were primarily isolated from the wards (W7 [9 strains] and W4 [8 strains]). Another five bla(IMP)-positive P. putida strains from wards W7 and W4 were obtained by swabbing around the water pipes. A total of 32 bla(IMP)-positive P. putida strains were assessed by pulsed-field gel electrophoresis (PFGE) and testing of drug susceptibility to 10 chemotherapeutic agents. Both PFGE and MIC patterns revealed that there were long-term resident strains among inpatients and hospital environments. The bla(IMP) genes of 22 of 32 strains were all transferable to a recipient strain of Pseudomonas aeruginosa by conjugation or transformation and conferred resistance to carbapenems and cephems. The bla(IMP) plasmids were conjugally transmissible among P. aeruginosa strains and mediated resistance to amikacin as well as beta-lactams. Ten of the 22 plasmids mediated additional resistance to gentamicin and tobramycin. Plasmids with identical DNA and drug resistance patterns were found in P. putida strains with identical PFGE patterns and with different PFGE patterns. We presumed that P. putida was one of the resident species in inpatients and especially in hospital environments, spreading drug resistance genes via plasmids among P. putida strains and supplying them to more pathogenically important species, such as P. aeruginosa.

Detection of a variant metallo-beta-lactamase, IMP-10, from two unrelated strains of Pseudomonas aeruginosa and an alcaligenes xylosoxidans strain.

The gene bla(IMP-10) of a variant metallo-beta-lactamase, IMP-10, had a single base replacement of G by T at nucleotide 145, which led to an amino acid alteration of Val49 to Phe compared to the IMP-1 enzyme, indicating that IMP-10 was a point mutation derivative of IMP-1. Highly purified enzymes revealed that IMP-10 was different from IMP-1 in its extremely low hydrolyzing activities for penicillins, such as benzylpenicillin, ampicillin, and piperacillin.