土井 洋平

A total of 49 unique clinical isolates of multidrug-resistant (MDR) Acinetobacter baumannii identified at a tertiary medical center in Pittsburgh, Pennsylvania, between August 2006 and September 2007 were studied for the genetic basis of their MDR phenotype. Approximately half of all A. baumannii clinical isolates identified during this period qualified as MDR, defined by nonsusceptibility to three or more of the antimicrobials routinely tested in the clinical microbiology laboratory. Among the MDR isolates, 18.4% were resistant to imipenem. The frequencies of resistance to amikacin and ciprofloxacin were high at 36.7% and 95.9%, respectively. None of the isolates was resistant to colistin or tigecycline. The presence of the carbapenemase gene bla(OXA-23) and the 16S rRNA methylase gene armA predicted high-level resistance to imipenem and amikacin, respectively. bla(OXA-23) was preceded by insertion sequence ISAba1, which likely provided a potent promoter activity for the expression of the carbapenemase gene. The structure of the transposon defined by ISAba1 differed from those reported in Europe, suggesting that ISAba1-mediated acquisition of bla(OXA-23) may occur as an independent event. Typical substitutions in the quinolone resistance-determining regions of the gyrA and parC genes were observed in the ciprofloxacin-resistant isolates. Plasmid-mediated quinolone resistance genes, including the qnr genes, were not identified. Fifty-nine percent of the MDR isolates belonged to a single clonal group over the course of the study period, as demonstrated by pulsed-field gel electrophoresis.

A chromosomally encoded class D beta-lactamase, OXA-114, was characterized from Achromobacter xylosoxidans strain CIP69598. beta-Lactamase OXA-114 shared 56% amino acid identity with the naturally occurring class D beta-lactamase of Burkholderia cenocepacia and 42% identity with the acquired oxacillinases OXA-9 and OXA-18. OXA-114 has a narrow-spectrum hydrolysis profile, although it includes imipenem, at a very low level. PCR and sequencing revealed that bla(OXA114)-like genes were identified in all A. xylosoxidans strains tested (n = 5), indicating that this beta-lactamase is naturally occurring in that species. Induction experiments with imipenem and cefoxitin did not show inducibility of bla(OXA)-114 expression.

The genetic environment of the 16S rRNA methylase gene rmtD was investigated. rmtD was flanked by a novel ISCR motif located downstream of class I integron In163 in the original Pseudomonas aeruginosa strain. rmtD found in Klebsiella pneumoniae appeared to have been mobilized from P. aeruginosa by an IS26-mediated event.

An outbreak of cephalosporin-resistant Klebsiella pneumoniae occurred in a neonatal intensive care unit in Sao Paulo, Brazil. Of the 10 pulsotypes identified during the outbreak and follow-up periods, nine produced CTX-M-2 or its new variant CTX-M-59 and one produced SRV-5. bla(CTX-M-2/59) genes were located on closely related plasmids that were transferable.

Five highly amikacin-resistant Acinetobacter baumannii isolates were collected at a medical center in Pennsylvania. The aminoglycoside resistance was due to the production of the 16S rRNA methylase ArmA. Two of the isolates coproduced OXA-23 beta-lactamase and were highly resistant to carbapenems as well. The isolates were genetically closely related by pulsed-field gel electrophoresis.

Rates of metallo-beta-lactamase and 16S rRNA methylase production were investigated in 51 imipenem-resistant Pseudomonas aeruginosa clinical isolates collected from hospitals in S (a) over baro Paulo, Brazil. Of them, 57% and 75% produced SPM-1 and RmtD, respectively. Of note, 51% produced both enzymes, suggesting that their coproduction is already common in this geographic area.

Methylation of 16S ribosomal RNA ( rRNA) has recently emerged as a new mechanism of resistance against aminoglycosides among gram-negative pathogens belonging to the family Enterobacteriaceae and glucose-nonfermentative microbes, including Pseudomonas aeruginosa and Acinetobacter species. This event is mediated by a newly recognized group of 16S rRNA methylases, which share modest similarity to those produced by aminoglycoside-producing actinomycetes. Their presence confers a high level of resistance to all parenterally administered aminoglycosides that are currently in clinical use. The responsible genes are mostly located on transposons within transferable plasmids, which provides them with the potential to spread horizontally and may in part explain the already worldwide distribution of this novel resistance mechanism. Some of these organisms have been found to coproduce extended-spectrum beta-lactamases or metallo-beta-lactamases, contributing to their multidrug-resistant phenotypes. A 2-tiered approach, consisting of disk diffusion tests followed by confirmation with polymerase chain reaction, is recommended for detection of 16S rRNA methylase-mediated resistance.

Plasmid-mediated class C beta-lactamases are reported from Enterobocterioceoe with increasing frequency. They likely originate from chromosomal AmpC of certain Gram-negative bacterial. species and subsequently are mobilized onto transmissible plasmids. There are reports of unfavorable clinical outcomes in patients infected with these organisms and treated with broad-spectrum cephalosporins. However, unlike class A extended-spectrum beta-tactamases (ESBLs), no screening and confirmatory tests have been uniformly established for strains that produce class C beta-tactamases. Reduced susceptibility to cefoxitin is a sensitive but not specific indicator of class C beta-lactamase production. Simple confirmatory tests including tests using boronic acid compounds as specific class C beta-lactamase inhibitors have recently been developed. Their utilization will enable clinical microbiology laboratories to report those strains producing plasmid-mediated class C beta-lactamases as being resistant to all broad-spectrum cephalosporins, thus allowing physicians to prescribe appropriate antimicrobial therapy. (C) 2007 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.

Serious infections with Pseudomonas aeruginosa are frequently treated with the combination of a R-lactam antimicrobial and an aminoglycoside. P. aeruginosa strain PA0905 was isolated in 2005 from an inpatient in Brazil. It showed a panresistant phenotype that included resistance to beta-lactams, aminoglycosides, and fluoroquinolones. The beta-lactam resistance was conferred by the production of the metallo-beta-lactamase SPM-1. No inhibitory zone was observed when a disk diffusion test was performed with the semisynthetic aminoglycoside arbekacin, raising suspicion of 16S rRNA methylase production. A cloning experiment subsequently revealed the presence of a novel 16S rRNA methylase, RmtD, which accounted for the high-level resistance to all 4,6-disubstituted deoxystreptamine aminoglycosides, such as amikacin, tobramycin, and gentamicin. RmtD shared a moderate degree of identity with RmtA, another 16S rRNA methylase that was initially reported to occur in P. aeruginosa in Japan in 2003. This is the first identification of aminoglycoside resistance mediated by a 16S rRNA methylase in South America. This is also the first report to document coproduction of a metallo-beta-lactamase and a 16S rRNA methylase, a combination that would severely compromise therapeutic options for the infected patients.

We investigated ertapenem-susceptible and -resistant extended-spectrum P-lactamase-producing Enterobacter cloacae isolates obtained from the same patient. Gene transcription of OmpD and OmpF was diminished in the ertapenem-resistant isolate. An efflux pump inhibitor decreased the MICs of ertapenem in the resistant strain, suggesting a potential role of efflux pumps in ertapenem resistance.

Of 1,456 strains isolated from 2001 to 2003 demonstrating resistance to either oxyimino-cephalosporin, 317 strains, isolated in 57 of 132 clinical facilities, were found to harbor bla(CTX-M) genes by PCR. Fifty-seven, 161, and 99 strains harbored bla(CTX-M) genes belonging to the bla(CTX-M-1) bla(CTX-M-9), and bla(CTX-M-9) clusters, respectively.

Proteus mirabilis ARS68, which demonstrated a very high level of resistance to various aminoglycosides, was isolated in 2003 from an inpatient in Japan. The aminoglycoside resistance of this strain could not be transferred to recipient strains Escherichia coli CSH-2 and E. coli HB101 by a general conjugation experiment, but E. coli DH5 alpha was successfully transformed by electroporation with the plasmid of the parent strain, ARS68, and acquired an unusually high degree of resistance against aminoglycosides. Cloning and sequencing analyses revealed that the presence of a novel 16S rRNA methylase gene, designated rmtC, was responsible for resistance in strain ARS68 and its transformant. The G+C content of rmtC was 41.1%, and the deduced amino acid sequences of the newly identified 16S rRNA methylase, RmtC, shared a relatively low level of identity (<= 29%) to other plasmid-mediated 16S rRNA methylases, RmtA, RmtB, and ArmA, which have also been identified in pathogenic gram-negative bacilli. Also, RmtC shared a low level of identity (<= 28%) with the other 16S rRNA methylases found in aminoglycoside-producing actinomycetes. The purified histidine-tagged RmtC clearly showed methyltransferase activity against E. coli 16S rRNA in vitro. rmtC was located downstream of an ISEcp1-like element containing tnpA. Several plasmid-mediated 16S rRNA methylases have been identified in pathogenic gram-negative bacilli belonging to the family Enterobacteriaceae, and some of them are dispersing worldwide. The acceleration of aminoglycoside resistance among gram-negative bacilli by producing plasmid-mediated 16S rRNA methylases, such as RmtC, RmtB, and RmtA, may indeed become an actual clinical hazard in the near future.

Detection of the resistance mediated by class C beta-lactamases remains a challenging issue, considering that transferable plasmid-mediated class C beta-lactamases are of worldwide concern. Methods for the identification of strains that produce extended-spectrum beta-lactamases (ESBLs) or metallo-beta-lactamases (MBLs) have been developed and applied for routine use in clinical microbiology laboratories, but no practical methods for identification of plasmid-mediated class C producers have been established to date. We therefore developed three simple methods for clinical microbiology laboratories that allow identification of plasmid-mediated class C beta-lactamase-producing bacteria using a boronic acid derivative, 3-aminophenylboronic acid (APB), one of the specific inhibitors of class C beta-lactamases. Detection by the disk potentiation test was based on the enlargement of the growth-inhibitory zone diameter (by greater than or equal to 5 mm) around a Kirby-Bauer disk containing a ceftazidime (CAZ) or a cefotaxime (CTX) disk in combination with APB. In a double-disk synergy test, the discernible expansion of the growth-inhibitory zone around the CAZ or the CTX disk toward a disk containing APB was indicative of class C beta-lactamase production. A greater than or equal to eightfold decrease in the MIC of CAZ or CTX in the presence of APB was the criterion for detection in the microdilution test. By using these methods, Escherichia coli and Klebsiella pneumoniae isolates producing plasmid-mediated class C beta-lactamases, ACT-1, CMY-2, CMY-9, FOX-5, LAT-1, and MOX-1, were successfully distinguished from those producing other classes of beta-lactamases, such as ESBLs and MBLs. These methods will provide useful information needed for targeted antimicrobial therapy and better infection control.

Emergence of the newly identified 16S rRNA methylases RmtA, RmtB, and ArmA in pathogenic gram-negative bacilli has been a growing concern. ArmA, which had been identified exclusively in Europe, was also found in several gram-negative pathogenic bacilli isolated in Japan, suggesting global dissemination of hazardous multiple aminoglycoside resistance genes.

The nosocomial spread of six genetically related Klebsiella pneumoniae strains producing GES-type beta-lactamases was found in a neonatal intensive care unit, and we previously reported that one of the six strains, strain KG525, produced a new beta-lactamase, GES-3. In the present study, the molecular mechanism of cephamycin resistance observed in strain KG502, one of the six strains described above, was investigated. This strain was found to produce a variant of GES-3, namely, GES-4, which was responsible for resistance to both cephamycins (cefoxitin MIC, >128 mug/ml) and beta-lactamase inhibitors (50% inhibitory concentration of clavulanic acid, 15.2 +/- 1.7 muM). The GES-4 enzyme had a single G170S substitution in the Omega-loop region compared with the GES-3 sequence. This single amino acid substitution was closely involved with the augmented hydrolysis of cephamycins and carbapenems and the decreased affinities of beta-lactamase inhibitors to GES-4. A cloning experiment and sequencing analysis revealed that strain KG502 possesses duplicate bla(GES-4) genes mediated by two distinct class 1 integrons with similar gene cassette configurations. Moreover, the genetic environments of the bla(GES-4) genes found in strain KG502 were almost identical to that of bla(GES-3) in strain KG525. From these findings, these two phenotypically different strains were suggested to belong to a clonal lineage. The bla(GES-4) gene found in strain KG502 might well emerge from a point mutation in the bla(GES-3) gene harbored by its ancestor strains, such as strain KG525, under heavy antibiotic stress in order to acquire extended properties of resistance to cephamycins and carbapenems.

Escherichia coli HKY28, a ceftazidime-resistant strain isolated from a urine specimen in Japan, produced an inhibitor-sensitive AmpC beta-lactamase variant. The deduced amino acid sequence of the enzyme contained a number of substitutions and a tripeptide deletion (Gly286-Ser287-Asp288) compared with the sequence of native AmpC of E. coli. When the deletion was reverted by a 9-base insertion at the relevant site of ampC in the clone, the typical inhibitor-resistant phenotype of AmpC was restored, while at the same time the levels of resistance to ceftazidime, cefpirome, and cefepime were reduced eightfold or more. Molecular modeling studies indicated that a structural change took place in the H-10 helix as a result of the deletion, and this change caused an alteration of the substrate binding site, leading to a unique phenotype analogous to that of inhibitor-sensitive class A extended-spectrum beta-lactamases. The degree of inhibition was greater with sulbactam and tazobactam than with clavulanic acid. To our knowledge, this is the first report to have characterized an E. coli ampC that encodes chromosomal AmpC beta-lactamase sensitive to the available beta-lactamase inhibitors.

Nine Pseudomonas aeruginosa strains showing very high levels of resistance to various aminoglycosides have been isolated from clinical specimens in seven separate Japanese hospitals in five prefectures since 1997. These strains harbor the newly identified 16S rRNA methylase gene (rmtA). When an rmtA gene probe was hybridized with genomic DNAs of the nine strains digested with EcoRI, two distinct patterns were observed. The 11.1- and 15.8-kb regions containing the rmtA genes of strains AR-2 and AR-11, respectively, were sequenced and compared. In strain AR-2, a transposase gene-like sequence (sequence 1) and a probable tRNA ribosyltransferase gene (orfA) were located upstream of rmtA, and a Na+/H+ antiporter gene-like sequence (sequence 2) was identified downstream of rmtA. This 6.2-kbp insert (the rmtA locus) was flanked by 262-bp kappagamma elements. Part of the orfQ gene adjacent to an inverted repeat was found outside of the rmtA locus. In strain AR-11, the rmtA gene and sequence 2 were found, but the 5' end of the orfA gene was truncated and replaced with IS6100. An orfQ-orfI region was present on each side of the rmtA gene in strain AR-11. The G+C content of the rmtA gene was about 55%, and since the newly identified rmtA gene may well be mediated by some mobile genetic elements such as Tn5041, further dissemination of the rmtA gene could become an actual clinical problem in the near future.

A novel aminoglycoside resistance gene, aac(6')-lad, encoding aminoglycoside 6'-N-acetyltransferase, was identified in Acinetobacter genospecies 3 strain A-51. The gene encoded a 144-amino-acid protein, which shared modest identity (up to 36.7%) with some of the aminoglycoside 6'-N-acetyltransferases. The results of high-pressure liquid chromatography assays confirmed that the protein is a functional aminoglycoside 6'-N-acetyltransferase. The enzyme conferred resistance to amikacin, tobramycin, sisomicin, and isepamicin but not to gentamicin. The prevalence of this gene among Acinetobacter clinical isolates in Japan was then investigated. Of 264 Acinetobacter sp. strains isolated from geographically diverse areas in Japan in 2002, 16 were not susceptible to amikacin, and aac(6')-lad was detected in 7. Five of the producers of aminoglycoside 6'-N-acetyltransferase type lad were identified as Acinetobacter baumannii, and two were identified as Acinetobacter genospecies 3. These results suggest that aac(6')-lad plays a substantial role in amikacin resistance among Acinetobacter spp. in Japan.

Serratia marcescens S-95, which displayed an unusually high degree of resistance to aminoglycosides, including kanamycins and gentamicins, was isolated in 2002 from a patient in Japan. The resistance was mediated by a large plasmid which was nonconjugative but transferable to an Escherichia coli recipient by transformation. The gene responsible for the aminoglycoside resistance was cloned and sequenced. The deduced amino acid sequence of the resistance gene shared 82% identity with RmtA, which was recently identified as 16S rRNA methylase conferring high-level aminoglycoside resistance in Pseudomonas aeruginosa. Histidine-tagged recombinant protein showed methylation activity against E. coli 16S rRNA. The novel aminoglycoside resistance gene was therefore designated rmtB. The genetic environment of rmtB was further investigated. The sequence immediately upstream of rmtB contained the right end of transposon Tn3, including bla(TEM), while an open reading frame possibly encoding a transposase was identified downstream of the gene. This is the first report describing 16S rRNA methylase production in S. marcescens. The aminoglycoside resistance mechanism mediated by production of 16S rRNA methylase and subsequent ribosomal protection used to be confined to aminoglycoside-producing actinomycetes. However, it is now identified among pathogenic bacteria, including Enterobacteriaceae and P. aeruginosa in Japan. This is a cause for concern since other treatment options are often limited in patients requiring highly potent aminoglycosides such as amikacin and tobramycin.

From November 2000 to June 2001, Escherichia coli strains producing CTX-M-2 beta-lactamase were isolated from 6 (1.5%) of 396 cattle fecal samples and 2 (0.7%) of 270 surface swabs of cattle carcasses in Japan. The b/a(CTX-M-2) gene responsible for CTX-M-2 production was encoded on transferable plasmids, and the gene was transferred to E. coli CSH2 with a very high frequency (2 x 10(-4) to 6 x 10(-1) per donor cells) by conjugation. Random amplified polymorphic DNA analysis of nine isolates showed at least five different patterns. These findings suggest that CTX-M-2 producers might have originated from cattle through the use of cephalosporins such as ceftiofur and that cattle could be a reservoir of CTX-M-2-producing E. coli. Continuous and strategic surveillance of antimicrobial-resistant bacteria in livestock is essential to suppress further dissemination of these bacteria into society at large.

From January 2001 to December 2002, 587 strains of gram-negative bacterial isolates demonstrating resistance to ceftazidime and a combination of sulbactam and cefoperazone were subjected to a disk diffusion screening test using sodium mercaptoacetic acid; 431 strains (73.4%) appeared to produce metallo-beta-lactamase (MBL). Of these 431 strains, 357 were found by PCR to carry genes for IMP-1 type MBL (bla(IMP-1)), while only 7 and 67 strains carried the IMP-2 gene (bla(IMP-2)) and the VIM-2 gene (bla(VIM-2)), respectively. Neither VIM-1 nor SPM-1 type MBL genes were found among the strains tested. Of 431 strains, 427 carried the intI1 gene, and 4 strains carrying both the intI1 and intI3 genes were reidentified as Pseudomonas putida harboring bla(IMP-1). Of these four P. putida strains, three strains and one strain, respectively, were separately isolated from two hospitals located in the same prefecture, and the three strains showed very similar pulsed-field gel electrophoresis patterns. Of 357 bla(IMP-1) carriers, 116, 53, 51, 47, and 30 strains were identified as Pseudomonas aeruginosa, Alcaligenes xylosoxidans, P. putida/fluorescens, Serratia marcescens, and Acinetobacter baumannii, respectively. Four strains carrying bla(IMP-2) were reidentified as P. putida. Sixty-three P. aeruginosa strains and four P. putida strains carried bla(VIM-2). Of 427 intI1-positive strains, 180, 53, 51, 47, and 35 were identified as P. aeruginosa, A. xylosoxidans, P. putida/fluorescens, S. marcescens, and A. baumannii, respectively. In the present study, it was confirmed that strains carrying bla(IMP-1), with a class I integron are the most prevalent type in Japan, although several intI3 carriers have also been identified sporadically in this country.

Background Bacteria develop resistance to aminoglycosides by producing aminoglycoside-modifying enzymes such as acetyltransferase, phosphorylase, and adenyltransferase. These enzymes, however, cannot confer consistent resistance to various aminoglycosides because of their substrate specificity. Notwithstanding, a Pseudomonas aeruginosa strain AR-2 showing high-level resistance (minimum inhibitory concentration >1024 mg/L) to various aminoglycosides was isolated clinically. We aimed to clone and characterise the genetic determinant of this resistance. Methods We used conventional methods for DNA manipulation, susceptibility testing, and gene analyses to clone and characterise the genetic determinant of the resistance seen. PCR detection of the gene was also done on a stock of P aeruginosa strains that were isolated clinically since 1997. Findings An aminoglycoside-resistance gene, designated rmtA, was identified in P aeruginosa AR-2. The Escherichia coli transformant and transconjugant harbouring the rmtA gene showed very high-level resistance to various aminoglycosides, including amikacin, tobramycin, isepamicin, arbekacin, kanamycin, and gentamicin. The 756-bp nucleotide rmtA gene encoded a protein, RmtA. This protein showed considerable similarity to the 16S rRNA methylases of aminoglycoside-producing actinomycetes, which protect bacterial 16S rRNA from intrinsic aminoglycosides by methylation. Incorporation of radiolabelled methyl groups into the 30S ribosome was detected in the presence of RmtA. Of 1113 clinically isolated P aeruginosa strains, nine carried the rmtA gene, as shown by PCR analyses. Interpretation Our findings strongly suggest intergeneric lateral gene transfer of 16S rRNA methylase gene from some aminoglycoside-producing microorganisms to P aeruginosa. Further dissemination of the rmtA gene in nosocomial bacteria could be a matter of concern in the future.

A new plasmid-mediated TEM-derived extended-spectrum P-lactamase, TEM-91, was identified in a ceftazidime-resistant (MIC, >128 mug per ml) Escherichia coli strain isolated in 1996 in Japan. TEM-91 has three amino acid substitutions, R164C, M184T, and E240K, compared with TEM-1 penicillinase. The isoelectric point (pI), K-m, and k(cat) of TEM-91 for ceftazidime were 5.7, 179 muM, and 29.0 s(-1), respectively. The K-i of clavulanic acid for ceftazidime hydrolysis was 30.3 nM.

Helicobacter pylori infection induces apoptosis in gastric epithelial cells. Here, we report a novel apoptosis-inducing protein that functions as a leading factor in H. pylori-mediated apoptosis induction. We purified the protein from H. pylori by separating fractions that showed apoptosis-inducing activity. This protein induced apoptosis of AGS cells in a dose-dependent manner. The purified protein consisted of two protein fragments with molecular masses of about 40 and 22 kDa, which combined to constitute a single complex in their natural form. N-terminal sequencing indicated that both these protein fragments were encoded by the HP1118 gene. The purified protein exhibited gamma-glutamyl transpeptidase activity, the inhibition of which by 6-diazo-5-oxo-L-norleucine resulted in a complete loss of apoptosis-inducing activity. To the best of our knowledge, the apoptosis-inducing function is a newly identified physiological role for bacterial gamma-glutamyl transpeptidase. The apoptosis-inducing activity of the isogenic mutant gamma- glutamyl transpeptidase-deficient strain was significantly lower compared with that of the parent strain, demonstrating that gamma-glutamyl transpeptidase plays a significant role in H. pylori-mediated apoptosis. Our findings provide new insights into H. pylori pathogenicity and reveal a novel aspect of the bacterial gamma-glutamyl transpeptidase function.

An Escherichia coli strain, HKYM68, which showed resistance to broad-spectrum cephalosporins was isolated from a sputum specimen in Japan. The high-level resistance of the strain to ceftazidime, cefpirome, and moxalactam was carried by a self-transferable plasmid. The beta-lactamase gene responsible for the resistance was cloned and sequenced. The deduced amino acid sequence of this gene product, CMY-9, had a single amino acid substitution (E85D), the residue reported to be part of the recognition site for the R1 side chain of beta-lactams, compared with the amino acid sequence of CMY-8 and also had 78% identity with the amino acid sequence of CepH, a chromosomal cephalosporinase of Aeromonas hydrophila. A sul1-type class 1 integron containing an aacA1-orfG gene cassette was identified upstream of bla(CMY-9) and ended with a truncated 3' conserved segment. The following 2.1 kb was almost identical to the common region of integrons In6 and In7 and the integron of pSAL-1, except that orf513 encoding a putative transposase was identified instead of orf341 due to addition of a single nucleotide. bla(CMY-9) was closely located downstream of the end of the common region. These observations are indicative of the exogenous derivation of bla(CMY-9) from some environmental microorganisms such as aeromonads.

10年間にS.marcescensは43株が検出され,1998,99年には総検出数の約2%を占めた.ceftazidime耐性株は13株であり,内5株がIMP-1型メタロ-β-ラクタマーゼ(MBL)産生株で,1996年に始めて検出された.MBL産生株のimipenem(IPM)の最小発育阻止濃度は4〜16μg/mlであり,必ずしも高度耐性菌ではなかった.NCCLSの判定基準によりIPM感性と判定された株も存在した.MBL産生株が検出された患者の病棟別分布は,4例が高度救命救急センターからであり,基礎疾患は外傷や脳血管障害など重篤であった.1例は腎移植後の患者からであった.aztreonamが投与された2例では菌が陰性化した.MBL産生菌のAP-PCRによる遺伝子解析では,1996,97,98年分離株で同一パターン,99,2000年分離株で同一パターンが観察された.この結果は,遺伝的に同じ起源に由来する株が長期にわたって同一病棟に定着し続けていた可能性を示唆するもので,院内感染対策を講じることにより検出率を減少させることができた

An 8-year-old girl with acute leukemia had bacteremia caused by Klebsiella pneumoniae producing CTX-M-2-type broad spectrum beta-lactamase. K pneumoniae and Escherichia coli strains producing the same enzyme and harboring identical conjugative plasmids were recovered from stool culture. Patients with frequent episodes of neutropenia and prophylactic administration of beta-lactams are at risk of harboring colonizing strains that produce broad spectrum beta-lactamases.

The enhanced gastric epithelial cell apoptosis observed during infection with Helicobacter pylori has been suggested to be of significance in the etiology of gastritis, peptic ulcers, and neoplasia. To investigate the cell death signaling induced by H. pylori infection, human gastric epithelial cells were incubated with H. pylori for up to 72 h. H. pylori infection induced the activation of caspase -8, -9, and -3 and the expression of the proapoptotic Bcl-2 family proteins Bad and Bid. The peak of the activity of the caspases occurred at 24 h. At this time, the inhibition of caspase-8 or -9 almost completely suppressed H. pylori-induced apoptosis. Inhibition of caspase-8 suppressed the expression of Bad and Bid and the subsequent activation of caspase-9 and -3. These observations indicate that H. pylori induces apoptosis through a pathway involving the sequential induction of apical caspase-8 activity, the proapoptotic proteins Bad and Bid, caspase-9 activity, and effector caspase-3 activity. Activation of the pathway was independent of CagA or vacuolating toxin. A membrane fraction of H. pylori was sufficient to activate this pathway, and treatment with proteinase K eliminated the activity. Apoptotic activity of the membrane fraction was significantly increased by incubating the bacteria under serum-starved conditions for 24 h. These observations suggest that environmental conditions in the human stomach could induce H. pylori-mediated pathogenesis, leading to a variety of clinical outcomes.

Variously oxidized 12 natural abietanes, 6,7-dehydroferruginol methyl ether (3), ferruginol (5), 11-hydroxy-12-oxo-7,9(11),13-abietatriene (7), royleanone (9), demethyl cryptojaponol (12), salvinolone (14), sugiol methyl ether (16), sugiol (17), 5,6-dehydrosugiol methyl ether (19), 5,6-dehydrosugiol (20), 6β-hydroxyferruginol (23), and taxodione (25) were synthesized. Antimicrobial activities of synthesized phenolic diterpenes and their related compounds against MRSA and VRE were evaluated. Phenols (12-hydroxyabieta-8,11,13-trien-6-one 22 and 23), catechols (12 and 14) and taxodione 25 showed potent activity with 4-10 μg/mL of MIC against MRSA and 4-16 μg/mL of MIC against VRE. (-)-Ferruginol showed more potent activity than natural type (+)-ferruginol. Quinone methide 7 showed the most potent activity with 0.5-1 μg/mL of MIC against both MRSA and VRE. © 2001 Elsevier Science Ltd.

Multidrug resistance in gram-positive bacteria has become common worldwide. In Japan until recently, gram-negative bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Serratia marcescens were controlled by carbapenems, fluoroquinolones, and aminoglycosides. However, several of these microorganisms have recently developed resistance against many antimicrobial drugs.