Junichi Matsuda

Clinical and bacteriological characteristics of IMP-type metallo-β-lactamase-producing Pseudomonas aeruginosa

IMP-type metallo-beta-lactamase-producing bacteria have recently emerged worldwide. We conducted a case-control study in which 69 inpatients harboring bla(IMP)-positive Pseudomonas aeruginosa and 247 control subjects with bla(IMP)-negative pathogens were investigated. Prolonged hospitalization, antineoplastic chemotherapy, corticosteroid therapy (P=.001), and indwelling urinary catheters (P=.04) were risk factors for isolation of bla(IMP)-positive pathogens. The predominant source was urine (P=.001). The duration of antibiotic treatment and the total dose (including of carbapenems) were significantly greater among case patients than among control subjects (P<.01). bla(IMP)-positive P. aeruginosa isolates were more frequently resistant to multiple drugs (P=.001) and caused more infections (P=.001) than bla(IMP)-negative pathogens. There were no significant differences in bacteriological outcome (P=.94); however, infection-related death was more frequent among case patients than among control subjects (P=.023). These results suggest that precautionary measures against the spread of bla(IMP)-positive isolates are needed, because, for most of such pathogens, no antibiotic is potent enough to be used as a single agent in treatment of infection.

Influence of antimicrobial regimen on decreased in-hospital mortality of patients with MRSA bacteremia

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important causes of bacteremia. Recently, several epidemiological and microbiological changes have become evident in MRSA infections. The purposes of this study were to assess clinical characteristics of patients with MRSA bacteremia and microbiological changes in MRSA. We conducted a retrospective observational study on patients with MRSA bacteremia who were hospitalized between 2008 and 2011. We used univariate and multivariate analysis to evaluate the predictors associated with 30-day mortality. The 7-day and 30-day mortality rates were 12.0% and 25.3%, respectively. According to multivariate analysis, the independent predictors that associated with 30-day mortality were leukopenia, low serum albumin, high sequential organ failure assessment (SOFA) score, and quinolone use within 30 days. Compared to previous data (2003-2007), the SOFA score of the new data set remained unchanged, but in-hospital mortality decreased significantly. In particular, the mortality associated with use of vancomycin (VCM) was significantly lower. Although the minimum inhibitory concentration of VCM required to inhibit the growth of 90% of organisms (MIC90) had not changed, the trough value of VCM changed significantly; a VCM trough value of 10 or greater was significantly higher compared to previous data. Of the staphylococcal cassette chromosome mec (SCCmec) types, SCCmec II values decreased significantly, and SCCmec I and IV values increased significantly. Our results indicate that changes in VCM usage might contribute to decreased in-hospital mortality.

In vitro susceptibility studies and detection of vancomycin resistance genes in clinical isolates of enterococci in Nagasaki, Japan.

Glycopeptide resistance in enterococci is now a cause of clinical concern in the United States and Europe. However, details of vancomycin resistance in enterococci in Japan have been unknown. We measured minimum inhibitory concentrations (MICs) of various antimicrobial agents for a total of 218 clinical strains of enterococci isolated in our hospital in 1995-6 in addition to 15 strains with known genotypic markers of resistance. We also screened vancomycin resistance genes using a single step multiplex-PCR. In clinical isolates, only two strains of Enterococcus gallinarum were of intermediate resistance to vancomycin (MIC, 8 micrograms/ml), while the others were all susceptible. Glycopeptides (vancomycin and teicoplanin) and streptogramins (RP 58500 and RPR 106972) showed potent antimicrobial effects for the isolates. In addition, ampicillin was also potent for Enterococcus faecalis, while ampicillin, minocycline and gentamicin were potent for Enterococcus avium. No vanA or vanB genes were detected, while vanC1 and vanC23 genes were detected from two and four strains, respectively. Our results suggest that incidence of VRE in Japan may be estimated as still very low at this time.

Analysis of Genetic Relationships and Antimicrobial Susceptibility of Verotoxin-Producing Escherichia coli Strains Isolated in Nagasaki Prefecture, Japan in 1996

A total of 19 Escherichia coli O157 isolates were obtained in Nagasaki Prefecture, in the southwestern part of Japan, between 1990 and 1996. Pulsed‐field gel electrophoresis (PFGE) and computer‐assisted analysis were applied to determine genetic relationships among these strains. Fragment patterns of the isolates in Nagasaki, as determined by PFGE, were compared with those of isolates in other areas where large outbreaks and sporadic cases of E. coli O157 infection occurred. Similarity values of all the strains isolated in Nagasaki Prefecture were over 0.65 except for E. coli O26. Some strains were identical to the strains isolated from the areas where large outbreaks occurred. All strains were susceptible to ampicillin, fosfomycin, minocycline, amikacin, ofloxacin and sulfamethoxazole‐trimethoprim.

Quantitative detection of metallo-β-lactamase of blaIMP-cluster–producing Pseudomonas aeruginosa by real-time polymerase chain reaction with melting curve analysis for rapid diagnosis and treatment of nosocomial infection

In this study, we established the rapid quantitative detection of metallo-beta-lactamase-producing Pseudomonas aeruginosa in clinical isolates and samples using real-time polymerase chain reaction (PCR) targeting gyrB (identification of P. aeruginosa) and blaIMP. The relative sensitivities and specificities of this real-time PCR assay were as follows: 100.0% and 100.0% for clinical isolates, and 100.0% and 98.4% for clinical specimens, respectively. The relative sensitivities and specificities of blaIMP-PCR were 100.0% in both clinical isolates and clinical specimens. The present PCR assay was easily and quickly performed, and it accurately detected P. aeruginosa and metallo-beta-lactamase.

Antimicrobial susceptibility and molecular characteristics of methicillin-resistant Staphylococcus aureus in a Japanese secondary care facility

Methicillin-resistant Staphylococcus aureus (MRSA) is prevalent in Japan, and the Staphylococcus cassette chromosome mec (SCCmec) type II is common among hospital-acquired MRSA isolates. Information pertaining to MRSA characteristics is limited, including SCCmec types, in primary or secondary care facilities. A total of 128 MRSA isolates (90 skin and soft tissue isolates and 38 blood isolates) were collected at a secondary care facility, Kawatana Medical Center, from 2005 to 2011. Antimicrobial susceptibility testing for anti-MRSA antibiotics and molecular testing for SCCmec and virulence genes (tst, sec, etb, lukS/F-PV) were performed. Strains positive for lukS/F-PV were analyzed by multilocus sequence typing and phage open-reading frame typing. SCCmec typing in skin and soft tissue isolates revealed that 65.6% had type IV, 22.2% had type II, 8.9% had type I, and 3.3% had type III. In blood isolates, 50.0% had type IV, 47.4% had type II, and 2.6% had type III. Minimum inhibitory concentrations, MIC(50)/MIC(90), against vancomycin, teicoplanin, linezolid, and arbekacin increased slightly in SCCmec II isolates from skin and soft tissue. MICs against daptomycin were similar between sites of isolation. SCCmec type II isolates possess tst and sec genes at a greater frequently than SCCmec type IV isolates. Four lukS/F-PV-positive isolates were divided into two clonal patterns and USA300 was not included. In conclusion, SCCmec type IV was dominant in blood, skin, and soft tissue isolates in a secondary care facility in Japan. Because antimicrobial susceptibility varies with the SCCmec type, SCCmec typing of clinical isolates should be monitored in primary or secondary care facilities.

Infections caused by multiple strains of methicillin-resistant Staphylococcus aureus —a pressing epidemiological issue

The genotype of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from several foci in the same patient was studied to identify the rate of infections caused by multiple MRSA strains during hospitalization. Twenty-one patients with MRSA bacteraemia and other specimens diagnosed between 1990-1994 were studied. Clinical data were retrospectively collected from the medical records. Genotyping of 113 MRSA isolates was performed by pulsed-field gel electrophoresis (PFGE), using the Gene Navigator System. More than one type of MRSA was detected from different foci in eight of 21 (38%) patients, and three types were identified in a single patient. Our results indicate that epidemiological investigations must be conducted carefully, especially in immunocompromised hosts with MRSA bacteraemia, as the probability of infection with multiple strains among these patients is relatively high.

Fluoroquinolone resistance in extended-spectrum β-lactamase-producing Klebsiella pneumoniae in a Japanese tertiary hospital: silent shifting to CTX-M-15-producing K. pneumoniae

Purpose. Fluoroquinolone resistance (FQ‐r) in extended‐spectrum β‐lactamase (ESBL) producers is an urgent health concern in countries where ESBL‐producing K. pneumoniae (ESBL‐Kpn) is prevalent. We investigated FQ‐r in Japan where ESBL‐Kpn is less prevalent. Methodology. Clinical ESBL‐Kpn isolates from 2011 to 2013 were collected in Nagasaki University Hospital. The ESBL genotypes included CTX‐M‐15, and the mechanisms of FQ‐r through plasmid‐mediated quinolone resistance (PMQR) and mutations in quinolone resistance‐determining regions (QRDRs) were examined. Clonality was analysed by enterobacterial repetitive intergenic consensus (ERIC)‐PCR and multi‐locus sequence typing was performed on selected isolates. Results/Key findings. Thirty ESBL‐Kpn isolates, including seven levofloxacin‐resistant isolates, were obtained from different patients. An increase in CTX‐M‐15‐producing strains was observed during the study period (0/11 in 2011, 3/8 in 2012, and 5/11 in 2013). PMQR was detected in 53.3% of the isolates and aac‐(6′)‐Ib‐cr was the most common (36.7 %). ST15 was observed in 60.0% of the isolates, and for the most predominant ERIC‐PCR profiles, 62.5% of the isolates possessed the CTX‐M‐15 genotype and 71.4% were levofloxacin‐resistant. Levofloxacin‐resistance was significantly more common in CTX‐M‐15 isolates (62.5 %) compared to non‐CTX‐M‐15 isolates (9.1 %). Three QRDR mutations and aac(6′)‐Ib‐cr, but not qnrB and qnrS, were significantly enriched in the CTX‐M‐15 isolates (100.0 %) compared to the non‐CTX‐M‐15 isolates (13.6 %). Conclusion. Cumulatively, these results indicate that the epidemic strain, the CTX‐M‐15‐producing K. pneumoniae ST15, is covertly spreading even when ESBL producers are not prevalent. Monitoring these epidemic strains and ESBLs in general is important for quickly identifying health crises and minimizing future risks from FQ‐r ESBL‐Kpn.

Performance evaluation of BD Phoenix™, an automated microbiology system, for the screening of IMP-producing Enterobacteriaceae

BD Phoenix™ is an automated bacterial identification and susceptibility testing system. Here, its performance in screening IMP-producing Enterobacteriaceae was evaluated. The system identified 97.8% of IMP producers as being nonsusceptible to imipenem or meropenem, which was higher than that identified by the broth microdilution method (91.3%, imipenem; 41.3%, meropenem).

The Rapid Induction of Carbapenem-Resistance in an Aeromonas dhakensis Blood Isolate

Meropenem-susceptible and -resistant Aeromonas dhakensis isolates from blood cultures of a fatal case of septicemia were analyzed. The two isolates were homologous and gene expression of metallo-β-lactamase in the resistant strain was upregulated. Physicians should be aware of the possibility of the induction of carbapenem-resistance, following the use of carbapenems in the treatment of Aeromonas infection.