-
Yukiko Watanabe,
Toshio Naito,
Ken Kikuchi,
Yu Amari,
Yuki Uehara,
Hiroshi Isonuma,
Teruhiko Hisaoka,
Terutoyo Yoshida,
Kenji Yaginuma,
Norihide Takaya,
Hiroyuki Daida,
Keiichi Hiramatsu
[show abstract]
[hide abstract]
ABSTRACT: Lactococcus garvieae is a well-recognized fish pathogen, and it is considered a rare pathogen with low virulence in human infection. We describe the 11th case of L. garvieae infective endocarditis reported in the literature, and the first reported case in Japan.
We report a case of a 55-year-old Japanese woman who had native valve endocarditis with L. garvieae. The case was complicated by renal infarction, cerebral infarction, and mycotic aneurysms. After anti-microbial treatment, she was discharged from the hospital and is now well while being monitored in the out-patient clinic.
We encountered a case of L. garvieae endocarditis that occurred in a native valve of a healthy woman. The 16S ribosomal RNA gene sequencing was useful for the identification of this pathogen. Although infective endocarditis with L. garvieae is uncommon, it is possible to treat high virulence clinically.
Journal of Medical Case Reports 08/2011; 5:356.
-
[show abstract]
[hide abstract]
ABSTRACT: Of 38 vancomycin-intermediate Staphylococcus aureus (VISA) clinical strains, 27 (71%) possessed a muta-tion(s) in rpoB encoding the -subunit of RNA polymerase. Furthermore, 95.6% of the rifampin-resistant mutants obtained from 9 methicillin-resistant S. aureus (MRSA) clinical isolates showed decreased vancomycin susceptibilities. These data indicate the involvement of an rpoB mutation in VISA phenotype expression. Staphylococcus aureus is a leading cause of hospital-acquired infections (10, 17). Vancomycin has been the therapy of choice for treating serious infections caused by multidrug-resistant S. aureus since the 1950s. However, the emergence of vancomy-cin-intermediate S. aureus (VISA), hetero-VISA (hVISA) and vancomycin-resistant S. aureus (VRSA) has threatened the rank of vancomycin as the frontline antibiotic in methicillin-resistant S. aureus (MRSA) chemotherapy (1, 8, 9). VISA and hVISA were first described in 1997. Since then the mechanism of resistance has been pursued, which is based on the accumulation of spontaneous chromosomal mutations (10, 11). Mutations identified in a couple of two-component regulatory systems, vraSR and graRS, were shown to be respon-sible for the VISA phenotype expression in the Mu3-Mu50 lineage of strains (MIC 4 g/ml) (5, 19). Howden et al. also reported the contribution of a graRS mutation to vancomycin resistance (12). Recently, however, we noticed that introduc-tion of vraS(I5N) and graR(N197S) mutations onto the chro-mosome of hVISA strain Mu3 was not sufficient to achieve the level of vancomycin resistance of VISA strain Mu50 (MIC 8 g/ml). We then found out that, besides the two regulator mutations, another mutation in rpoB, rpoB(H481Y), was addi-tionally required for the complete acquisition of the VISA phenotype expressed by Mu50 (M. Matsuo et al., submitted for publication). We also demonstrated that introduction of an-other mutation, rpoB(A621E), into a vancomycin-susceptible S. aureus (VSSA) strain conferred vancomycin and daptomycin heteroresistance onto it (6). Therefore, it is likely that the rpoB mutation is an important contributor to the VISA phenotype. Although the way that rpoB mutation affects vancomycin re-sistance is currently unknown, a thickened cell wall was noted with the strains with rpoB(H481Y) mutations, as well as those with rpoB(A621E) mutations (6; M. Matsuo et al., submitted). In any case, if an rpoB mutation were a major contributor for VISA phenotype, it would be predictable for an rpoB mutation to be frequently found in VISA clinical strains throughout the world. It is also predicted that selection of clinical S. aureus strains by rifampin should yield rifampin-resistant rpoB mu-tants with reduced susceptibilities to vancomycin. This study was performed to test these predictions. VISA strain Mu50, carrying an rpoB(H481Y) mutation, is highly rifampin resistant (MIC 128 g/ml). On the other hand, the rpoB mutation, rpoB(A621E), identified in the in vitro-derived hVISA strain, did not cause rifampin resistance (6). This indicates that there should be two groups among VISA or hVISA strains with rpoB mutations; one that is rifam-pin resistant, and another that is rifampin susceptible. With this in mind, we first generated a series of rifampin-resistant laboratory strains by selecting methicillin-resistant S. aureus (MRSA) clinical strains by using rifampin. We then evaluated the vancomycin susceptibilities of the mutants, along with those of their respective parent strains. A total of nine MRSA strains, isolated during 2005 and 2006 from bacteremia pa-tients in Juntendo University Hospital, were used. All of the strains were susceptible to vancomycin and rifampin, with MICs of 2 and 0.25 g/ml, respectively (Table 1). They belonged to the type IIA SCCmec-type II coagulase that cor-responds to the most dominant Japanese hospital-associated MRSA (HA-MRSA) clone with the ST5 genotype (20, 23). A total of 10 7 CFU of MRSA cells were inoculated on brain heart infusion (BHI) agar plates containing 10 g/ml rifampin, and rifampin-resistant colonies that appeared on the plates were picked after 24 h of incubation at 37°C. The picked colonies were cultivated in drug-free BHI medium and spread on drug-free BHI agar plates to carry out colony purification before they were established as strains. Rifampin resistance of the established mutant strains was confirmed by determining the rifampin MIC according to CLSI guidelines (2). Finally, a total of 90 rifampin-resistant mutant strains (10 from each MRSA strain) with rifampin MICs of 32 g/ml were established, and their vancomycin susceptibilities were compared to those of the respective parent strains (Table 1). The change in vanco-mycin susceptibilities of these mutant strains was first deter-mined by a vancomycin-gradient gel assay (V-GGA), which is convenient to operate and allows evaluation of a small range of susceptibility changes with a continuous value scale (7). As
Antimicrobial Agents and Chemotherapy 08/2011; 49:2680--2684. · 4.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Vancomycin-intermediate Staphylococcus aureus (VISA) is generated from vancomycin-susceptible Staphylococcus aureus by multiple spontaneous mutations. We previously reported that sequential acquisition of mutations in the two-component regulatory systems vraSR and graRS was responsible for the VISA phenotype of strain Mu50. Here we report on the identification of a novel set of regulator mutations, a deletion mutation in two-component regulatory system walRK (synonyms, vicRK and yycFG), and a truncating mutation in a proteolytic regulatory gene, clpP, responsible for the raised vancomycin resistance in a laboratory-derived VISA strain, LR5P1-V3. The contributory effect of the two mutations to vancomycin resistance was confirmed by introducing the walK and clpP mutations into the vancomycin-susceptible parent strain N315LR5P1 by a gene replacement procedure. The vancomycin MIC of N315LR5P1 was raised from 1 to 2 mg/liter by the introduction of the walK or clpP mutation, but it was raised to 4 mg/liter by the introduction of both the walK and clpP mutations. The vancomycin MIC value of the double mutant was equivalent to that of strain LR5P1-V3. Like VISA clinical strains, LR5P1-V3 and the double mutant strain LR5P1walK*clpP* exhibited a thickened cell wall, slow growth, and decreased autolytic activity. Transcriptional profiles of the mutants with gene replacements demonstrated that introduction of both the walK and clpP mutations could alter expression of dozens or hundreds of genes, including those involved in cell envelope and cellular processes, intermediary metabolism, and information pathway. A mutation prevalence study performed on 39 worldwide clinical VISA strains showed that 61.5, 7.7, 10.3, and 20.5% of VISA strains harbored mutations in walRK, clpP, graRS, and vraSR, respectively. The mutation of walRK was most frequently carried by VISA strains. Together, these results suggested that the mutations of walK and clpP identified in LR5P1-V3 constitute a new combination of genetic events causing vancomycin resistance in Staphylococcus aureus.
Antimicrobial Agents and Chemotherapy 05/2011; 55(8):3870-81. · 4.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Of 38 vancomycin-intermediate Staphylococcus aureus (VISA) clinical strains, 27 (71%) possessed a mutation(s) in rpoB encoding the β-subunit of RNA polymerase. Furthermore, 95.6% of the rifampin-resistant mutants obtained from 9 methicillin-resistant S. aureus (MRSA) clinical isolates showed decreased vancomycin susceptibilities. These data indicate the involvement of an rpoB mutation in VISA phenotype expression.
Journal of clinical microbiology 04/2011; 49(7):2680-4. · 4.16 Impact Factor
-
Longzhu Cui,
Taisuke Isii,
Minoru Fukuda,
Tomonori Ochiai,
Hui-Min Neoh,
Ilana Lopes,
Baratella Da,
Cunha Camargo, Yukiko Watanabe,
Mitsutaka Shoji,
Tomomi Hishinuma,
Keiichi Hiramatsu
[show abstract]
[hide abstract]
ABSTRACT: We have previously reported the establishment of a Staphylococcus aureus laboratory strain, 10*3d1, having reduced susceptibility to daptomycin and heterogeneous vancomycin-intermediate S. aureus (VISA) phenotype. The strain was generated in vitro by serial daptomycin selection (Camargo, I. L., H. M. Neoh, L. Cui, and K. Hiramatsu, Antimicrob. Agents Chemother. 52:4289–4299, 2008). Here we explored the genetic mechanism of resistance in the strain by whole-genome sequencing and by producing gene-replaced strains. By genome comparison between 10*3d1 and its parent methicillin-resistant Staphylococcus aureus (MRSA) strain N315IP, we identified five nonsynonymous single nucleotide polymorphisms (SNPs). One of the five muta-tions was found in the rpoB gene encoding the RNA polymerase subunit. The mutation at nucleotide position 1862 substituted the 621st alanine by glutamic acid. The replacement of the intact rpoB with the mutated rpoB, designated rpoB(A621E), conferred N315IP with the phenotypes of reduced susceptibility to daptomycin and hetero-VISA. The rpoB(A621E)-mediated resistance conversion was accompanied by a thickened cell wall and reduction of the cell surface negative charge. Being consistent with these phenotypic changes, microarray data showed that the expression of the dlt operon, which increases the cell surface positive charge, was enhanced in the rpoB(A621E) mutant. Other remarkable findings of microarray analysis of the rpoB(A621E) mutant included repression of metabolic pathways of purine, pyrimidine, arginine, the urea cycle, and the lac operon, enhancement of the biosynthetic pathway of vitamin B2, K1, and K2, and cell wall metabolism. Finally, mutations identified in rplV and rplC, encoding 50S ribosomal proteins L22 and L3, respectively, were found to be associated with the slow growth, but not with the phenotype of decreased susceptibility to vancomycin and daptomycin, of 10*3d1. Daptomycin, a semisynthetic chemical derived from Strepto-myces roseosporus, is a cyclic lipopeptide antibiotic having bac-tericidal activity against a broad range of aerobic and anaerobic Gram-positive bacteria (1, 27, 29, 48). The exact mechanism of action for daptomycin has not been fully elucidated yet. How-ever, it is generally accepted that daptomycin binds to the cytoplasmic membrane of Gram-positive bacteria via calcium-dependent binding (27). Once bound, the lipopeptide tail of the molecule is inserted into the bacterial cell membrane. This tail serves as an ion channel through which an efflux of potas-sium, and potentially other ions, can pass through, thereby causing the bacterial cell to rapidly depolarize. Depolarization results in multiple failures in the DNA, RNA, and protein synthesis of the bacteria, ultimately resulting in a rapid bacte-rial cell death (27, 47). As daptomycin has a rapid bactericidal activity, it is approved in the United States and the European Union as an alternative option for the treatment of infections caused by S. aureus (44, 49). Although daptomycin has a potent bactericidal activity against methicillin-resistant S. aureus (MRSA), it tends to have less antimicrobial activity against vancomycin-intermediate S. aureus (VISA) clinical strains (17, 43). Various groups re-ported that MRSA with reduced susceptibility to vancomycin and/or daptomycin were generated during the treatment with either vancomycin or daptomycin (21, 26, 32, 42). Recently, we reported the establishment of a laboratory MRSA strain 10*3d1 having dual heteroresistance to daptomycin and vancomycin by serial daptomycin selection (6). Despite its se-lection by daptomycin alone, this strain expressed raised resis-tance to both daptomycin and vancomycin, a thickened cell-wall, and a partially overlapped transcription profile with that of hetero-VISA (6). Here we explored the genetic mechanism for the dual heteroresistance of the strain 10*3d1. Using whole-genome sequencing and gene replacement experiments, we proved that a nonsynonymous mutation in rpoB, the gene that codes for the ß subunit of the bacterial DNA-dependent RNA polymerase, was responsible for the phenotypic conver-sion.
Antimicrobial Agents and Chemotherapy 01/2011; 54(12):5222--5233. · 4.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have previously reported the establishment of a Staphylococcus aureus laboratory strain, 10 3d1, having reduced susceptibility to daptomycin and heterogeneous vancomycin-intermediate S. aureus (VISA) phenotype. The strain was generated in vitro by serial daptomycin selection (Camargo, I. L., H. M. Neoh, L. Cui, and K. Hiramatsu, Antimicrob. Agents Chemother. 52:4289-4299, 2008). Here we explored the genetic mechanism of resistance in the strain by whole-genome sequencing and by producing gene-replaced strains. By genome comparison between 10 3d1 and its parent methicillin-resistant Staphylococcus aureus (MRSA) strain N315ΔIP, we identified five nonsynonymous single nucleotide polymorphisms (SNPs). One of the five mutations was found in the rpoB gene encoding the RNA polymerase β subunit. The mutation at nucleotide position 1862 substituted the 621st alanine by glutamic acid. The replacement of the intact rpoB with the mutated rpoB, designated rpoB(A621E), conferred N315ΔIP with the phenotypes of reduced susceptibility to daptomycin and hetero-VISA. The rpoB(A621E)-mediated resistance conversion was accompanied by a thickened cell wall and reduction of the cell surface negative charge. Being consistent with these phenotypic changes, microarray data showed that the expression of the dlt operon, which increases the cell surface positive charge, was enhanced in the rpoB(A621E) mutant. Other remarkable findings of microarray analysis of the rpoB(A621E) mutant included repression of metabolic pathways of purine, pyrimidine, arginine, the urea cycle, and the lac operon, enhancement of the biosynthetic pathway of vitamin B2, K1, and K2, and cell wall metabolism. Finally, mutations identified in rplV and rplC, encoding 50S ribosomal proteins L22 and L3, respectively, were found to be associated with the slow growth, but not with the phenotype of decreased susceptibility to vancomycin and daptomycin, of 10 3d1.
Antimicrobial Agents and Chemotherapy 12/2010; 54(12):5222-33. · 4.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Linezolid has been used for the treatment of nosocomial and community-acquired pneumonia as well as complicated skin and soft tissue infection caused by methicillin-resistant Staphylococcus aureus (MRSA) including vancomycin-intermediate S. aureus (VISA) (5, 10, 12). ...
Antimicrobial Agents and Chemotherapy 09/2008; 52(11):4207-8. · 4.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The purpose of this study was to measure the fetal subarachnoid spaces at different sites of the brain using magnetic resonance (MR) images and analyze them in relation to gestational age.
Fetal MR images were obtained from 158 fetuses between 18 and 39 weeks of gestation who later showed no neurological problems. We bilaterally measured the distance between the superoanterior gyrus and the cranium as the frontal subarachnoid space (FSS) and the distance between the cortex in the parieto-occipital sulcus and the cranium as the parietal subarachnoid space (PSS). We also measured the cisterna magna between the cerebellar vermis and the cranium. Each of these was analyzed in relation to gestational age.
The width of the FSS began to decrease significantly at 32 weeks of gestation (P < 0.05). The width of the PSS started to decrease significantly at 34 weeks of gestation (P < 0.05). There was no difference between the right and left sides (P < 0.05). The size of the cisterna magna showed a positive correlation with gestational age (P < 0.05).
Measurement of the subarachnoid space is potentially useful for evaluating fetal development.
Prenatal Diagnosis 12/2005; 25(13):1217-22. · 2.11 Impact Factor
