Shizuo Kayama

Emergence in Japan of an imipenem-susceptible, meropenem-resistant Klebsiella pneumoniae carrying blaIMP-6.

We identified 5 Klebsiella pneumoniae isolates showing high resistance to β-lactams except imipenem and designated them ISMRK (imipenem-susceptible but meropenem-resistant Klebsiella). They carried the bla(IMP-6) and bla(CTX-M-2) on a self-transmissible plasmid. ISMRK may be falsely categorized as susceptible to carbapenems if imipenem is used to screen carbapenem resistance.

Complete Nucleotide Sequence of the IncN Plasmid Encoding IMP-6 and CTX-M-2 from Emerging Carbapenem-Resistant Enterobacteriaceae in Japan

ABSTRACT We have determined the DNA sequence of Klebsiella pneumoniae multidrug resistance plasmid pKPI-6, which is a self-transmissible IncN-type plasmid. pKPI-6 harboring blaIMP-6 and blaCTX-M-2 confers a stealth-type carbapenem resistance phenotype on members of the family Enterobacteriaceae that is not detectable with imipenem. pKPI-6 is already epidemic in Japan, favoring the dissemination of IMP-6 and CTX-M-2 in members of the family Enterobacteriaceae.

Identification and Characterization of a Novel aac(6′)-Iag Associated with the blaIMP-1–Integron in a Multidrug-Resistant Pseudomonas aeruginosa

In a continuing study from Dec 2006 to Apr 2008, we characterized nine multi-drug resistant Pseudomonas aeruginosa strains isolated from four patients in a ward at the Hiroshima University Hospital, Japan. Pulsed-field gel electrophoresis of SpeI-digested genomic DNAs from the isolates suggested the clonal expansion of a single strain; however, only one strain, NK0009, was found to produce metallo-β-lactamase. PCR and subsequent sequencing analysis indicated NK0009 possessed a novel class 1 integron, designated as In124, that carries an array of four gene cassettes: a novel aminoglycoside (AG) resistance gene, aac(6′)-Iag, bla IMP-1, a truncated form of bla IMP-1, and a truncated form of aac(6′)-Iag. The aac(6′)-Iag encoded a 167-amino-acid protein that shows 40% identity with AAC(6′)-Iz. Recombinant AAC(6′)-Iag protein showed aminoglycoside 6′-N-acetyltransferase activity using thin-layer chromatography (TLC) and MS spectrometric analysis. Escherichia coli carrying aac(6′)-Iag showed resistance to amikacin, arbekacin, dibekacin, isepamicin, kanamycin, sisomicin, and tobramycin; but not to gentamicin. A conjugation experiment and subsequent Southern hybridization with the gene probes for bla IMP-1 and aac(6′)-Ig strongly suggested In124 is on a conjugal plasmid. Transconjugants acquired resistance to gentamicin and were resistant to virtually all AGs, suggesting that the In124 conjugal plasmid also possesses a gene conferring resistance to gentamicin.

Emergence of Staphylococcus aureus Carrying Multiple Drug Resistance Genes on a Plasmid Encoding Exfoliative Toxin B

ABSTRACT We report the complete nucleotide sequence and analysis of pETBTY825, a Staphylococcus aureus TY825 plasmid encoding exfoliative toxin B (ETB). S. aureus TY825 is a clinical isolate obtained from an impetigo patient in 2002. The size of pETBTY825, 60.6 kbp, was unexpectedly larger than that of the archetype pETBTY4 (∼30 kbp). Genomic comparison of the plasmids shows that pETBTY825 has the archetype pETBTY4 as the backbone and has a single large extra DNA region of 22.4 kbp. The extra DNA region contains genes for resistance to aminoglycoside [aac(6′)/aph(2″)], macrolide (msrA), and penicillin (blaZ). A plasmid deletion experiment indicated that these three resistance elements were functionally active. We retrospectively examined the resistance profile of the clinical ETB-producing S. aureus strains isolated in 1977 to 2007 using a MIC determination with gentamicin (GM), arbekacin (ABK), and erythromycin (EM) and by PCR analyses for aac(6′)/aph(2″) and msrA using purified plasmid preparations. The ETB-producing S. aureus strains began to display high resistance to GM, which was parallel with the detection of aac(6′)/aph(2″) and mecA, after 1990. Conversely, there was no significant change in the ABK MIC during the testing period, although it had a tendency to slightly increase. After 2001, isolates resistant to EM significantly increased; however, msrA was hardly detected in ETB-producing S. aureus strains, and only five isolates were positive for both aac(6′)/aph(2″) and msrA. In this study, we report the emergence of a fusion plasmid carrying the toxin gene etb and drug resistance genes. Prevalence of the pETBTY825 carrier may further increase the clinical threat, since ETB-producing S. aureus is closely related to more severe impetigo or staphylococcal scalded-skin syndrome (SSSS), which requires a general antimicrobial treatment.

A novel metallo-β-lactamase, IMP-34, in Klebsiella isolates with decreased resistance to imipenem

We investigated 5 metallo-β-lactamase (MBL)-positive Klebsiella isolates from Japan showing intermediate resistance to imipenem. Sequencing of the MBL gene identified a novel variant of IMP-1 with a single amino acid substitution, Glu87Gly. This variant is designated as IMP-34 where blaIMP-34 is located on a transmissible plasmid.

Imipenem-Susceptible, Meropenem-Resistant Klebsiella pneumoniae Producing OXA-181 in Japan

The incidence of infections by Enterobacteriaceae carrying the carbapenemase gene showing a paradoxical phenotype of resistance to virtually all s-lactams, including meropenem but not including imipenem, is increasing ([1][1], [2][2], [3][3]). Here we report the first isolation of Klebsiella

Meropenem Resistance in Imipenem-Susceptible Meropenem-Resistant Klebsiella pneumoniae Isolates Not Detected by Rapid Automated Testing Systems

ABSTRACT Klebsiella pneumoniae showing high resistance to all β-lactams except imipenem, designated as ISMRK (imipenem-susceptible meropenem-resistant Klebsiella) is emerging in Japan. The carbapenem resistance of ISMRK cannot be screened by the Vitek and the RAISUS rapid automated susceptibility test systems, which may lead to inappropriate antimicrobial therapy, resulting in compromised patient outcomes.

Sporadic isolations of a multi-drug resistant Pseudomonas aeruginosa clone during a 14-month epidemic in a general hospital in Hiroshima

BackgroundDuring 2005–2007, we experienced sporadic isolations of multidrug-resistant (MDRP) Pseudomonas aeruginosa from wards in a general hospital in Hiroshima. The objective of this study was to analyze epidemiology relationships and the mode of spread of the strains.MethodsClonality was assessed using pulsed-field gel electrophoresis (PFGE) and serotyping. MICs were determined using the microdilution broth method. Investigations of the affected patients’ movements and environmental sampling from the affected wards were conducted.ResultsAn abrupt increase in MDRP isolations began at the end of 2005 and ended in February 2007. A total of 25 MDRP strains were sporadically isolated from nine wards. Fourteen strains were genotypically and serologically identical. Analysis of the patients’ movements identified that six of the 14 MDRP-positive patients became positive for MDRP when they were in the intensive care unit (ICU), and two became positive after the patients moved from the ICU to another nursing unit. Four MDRP strains were isolated from patients who did not stay in the ICU and were in ward E6, which had the second highest number of isolations. In July 2006, environmental sampling of the hospital identified a toilet brush in ward E6 that was contaminated with MDRP that was genotypically and serologically identical to the clinical isolates.ConclusionsOur study suggests that the sporadic increase in MDRP isolates during 2005–2007 in the general hospital in Hiroshima was due to an epidemic of an MDRP clone. Continuity and spread of infection was probably due to cross infection and contamination in the hospital with the MDRP strain.

Tripoli metallo-β-lactamase-1 (TMB-1)-producing Acinetobacter spp. with decreased resistance to imipenem in Japan

We recently reported Klebsiella pneumoniae carrying bla IMP-type metallo-β-lactamase gene variants showing a paradoxical resistance phenotype: resistance to virtually all β-lactams except imipenem ([1][1], [2][2]). Here we report the isolation of Acinetobacter spp. showing a similar resistance

Rapid detection of blaIMP-6 by amplification refractory mutation system.

Klebsiella pneumoniae resistant to almost all ß-lactams except imipenem designated as ISMRK (imipenem-susceptible meropenem-resistant Klebsiella) is emerging in Japan. All ISMRK carries bla(IMP-6) which differs from bla(IMP-1) by only a single nucleotide at position 640. We devised a rapid detection system of bla(IMP-6) by using ARMS PCR.