Toxicity caused by hydroxycinnamoyl-coenzyme A thioester accumulation in mutants of Acinetobacter sp. strain ADP1

Hydroxycinnamates, aromatic compounds that play diverse roles in plants, are dissimilated by enzymes encoded by the hca genes in the nutritionally versatile, naturally transformable bacterium Acinetobacter sp. strain ADP1. A key step in the hca-encoded pathway is activation of the natural substrates caffeate, p-coumarate, and ferulate by an acyl:coenzyme A (acyl:CoA) ligase encoded by hcaC. As described in this paper, Acinetobacter cells with a knockout of the next enzyme in the pathway, hydroxycinnamoyl-CoA hydratase/lyase (HcaA), are extremely sensitive to the presence of the three natural hydroxycinnamate substrates; Escherichia coli cells carrying a subclone with the hcaC gene are hydroxycinnamate sensitive as well. When the hcaA mutation was combined with a mutation in the repressor HcaR, exposure of the doubly mutated Acinetobacter cells to caffeate, p-coumarate, or ferulate at 10(-6) M totally inhibited the growth of cells. The toxicity of p-coumarate and ferulate to a DeltahcaA strain was found to be a bacteriostatic effect. Although not toxic to wild-type cells initially, the diphenolic caffeate was itself converted to a toxin over time in the absence of cells; the converted toxin was bactericidal. In an Acinetobacter strain blocked in hcaA, a secondary mutation in the ligase (HcaC) suppresses the toxic effect. Analysis of suppression due to the mutation of hcaC led to the development of a positive-selection strategy that targets mutations blocking HcaC. An hcaC mutation from one isolate was characterized and was found to result in the substitution of an amino acid that is conserved in a functionally characterized homolog of HcaC.

The application of peptide nucleic acid probes for rapid detection and enumeration of eubacteria, Staphylococcus aureus and Pseudomonas aeruginosa in recreational beaches of S. Florida

A novel chemiluminescent in situ hybridization technique using peptide nucleic acids (PNA) was adapted for the detection of bacteria in beach sand and recreational waters in South Florida. The simultaneous detection and enumeration of eubacteria and the novel indicators, Staphylococcus aureus and Pseudomonas aeruginosa, was achieved within 6-8 h of processing. Following 5 h of incubation on TSA, soybean peroxidase-labeled peptide nucleic acid probes (Boston Probes, Boston, MA) targeting species-specific 16S rRNA sequences of P. aeruginosa and S. aureus were used to hybridize microcolonies of the target species in-situ. In addition, a universal probe for 16S rRNA sequences was used to target the eubacteria. Probes were detected after a light generating reaction with a chemiluminescent substrate and their presence recorded on Polaroid film. The probes showed limited cross-reactivity with mixed indigenous bacteria extracted from seawater and sand by shaking with phosphate-buffered saline (PBS). Specificity and cross-reactivity was tested on the reference bacterial genera Pseudomonas, Staphylococcus, Vibrio, Shigella, Salmonella, Acinetobacter, Enterobacter, Escherichia and Citrobacter. These tests confirmed that the probes were specific for the microorganisms of interest and were unaffected by high salt levels. The results of the PNA chemiluminescent in situ hybridization were compared with traditional plate count methods (PCM) for total 'freshwater' eubacteria, S. aureus and P. aeruginosa. Counts of eubacteria and S. aureus were comparable with numbers obtained from traditional plate counts but levels of P. aeruginosa were higher with PNA than with PCM. It is possible that PNA is more sensitive than PCM because it can detect microcolonies on the agar surface that never fully develop with the plate count method. We conclude that the in situ hybridization technique used here represents an important potential tool for the rapid monitoring of novel indicator organisms in beaches and recreational waters.

Spread of novel aminoglycoside resistance gene aac(6')-Iad among Acinetobacter clinical isolates in Japan

A novel aminoglycoside resistance gene, aac(6')-Iad, 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')-Iad was detected in 7. Five of the producers of aminoglycoside 6'-N-acetyltransferase type Iad were identified as Acinetobacter baumannii, and two were identified as Acinetobacter genospecies 3. These results suggest that aac(6')-Iad plays a substantial role in amikacin resistance among Acinetobacter spp. in Japan.

Translocation of transposition-deficient (TndPKLH2-like) transposons in the natural environment: mechanistic insights from the study of adjacent DNA sequences

A family of plasmid-borne DNA fragments of different length, apparently inherited from an ancient plasmid, has been identified in the world population of environmental Acinetobacter strains. These fragments, named PPFs (parental plasmid DNA fragments), were >/=99.8 % identical to each other in the common regions, and contained in their central region a variant of an aberrant mercury-resistance transposon (Tn(d)PKLH2) that has lost its transposition genes. As a rule, recombinogenic elements were found at the breakpoints of identity between the different PPFs. Of these recombinogenic elements, a newly identified IS6 family element, a transposon, or a resolvase gene interrupted one end of the PPFs. At the opposite end, the breakpoint of some PPFs was mapped to the recombination point within, in each case, a different variant of a res site (RS2), whilst in other PPFs, this end was eroded by insertion of a newly identified IS6 family element. On the basis of DNA sequence data, possible mechanisms of translocation of defective Tn(d)PKLH2-like elements via recombination events implicating the nearby res (resolution) site and IS element are proposed.

Determination of epidemic clonality among multidrug-resistant strains of Acinetobacter spp. and Pseudomonas aeruginosa in the MYSTIC Programme (USA, 1999–2003)

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Programme was initiated in 1997 (1999 for the United States). This program monitors resistance in participant medical centers where carbapenems are prescribed and drug use data can be obtained. An earlier report found antimicrobial use was not a clear cause of local or aggregate changes in resistance rates. This study addresses the role of dissemination of resistant clones on susceptibility rates for nonfermentors, Acinetobacter spp. (ACB) and Pseudomonas aeruginosa (PSA). Carbapenem (CARB)-multidrug-resistant strains (MDR) from among 236 ACB and 1,111 PSA were tested by reference broth microdilution methods, automated ribotyping, and pulsed field gel electrophoresis to determine possible clonal dissemination. Each strain was also tested for metallo-beta-lactamases (MbetaL) (phenotypic and polymerase chain reaction); and then analyzed by CARB-R rate and defined daily dose (DDD)/100 days use groupings (high, moderate, and low). For the aggregate 15 sites in the MYSTIC Programme each year, the CARB-resistant rate decreased over 5 years; but other drug-resistance rates generally escalated. Changes were not related to antimicrobial use calculations. The discovered clonally spread MDR-PSA strains were more frequent in high- (1.8 clones/site) and moderate-resistance (0.6 clones/site) rate centers (21.7% to 29.5% were clonal), compared with unique strains in low-resistance hospitals. ACB clonality was extreme in one geographic area, with dissemination of 5 different clones (931.7/B, C, or D; 1090.2/A; 167.5/A) in 4 centers (02, 04, 06, and 18). Resistance rates in ACB and PSA were clearly related to clonal occurrence and spread, and one MbetaL (VIM-7) was detected. Decreased CARB resistance rates from 1999 through 2002 were directly attributed to the disappearance of resistance clones in some locations. In conclusion, ACB and PSA CARB and MDR resistance rates in MYSTIC Programme institutions have been greatly influenced by clonal dissemination and less by antimicrobial use patterns. The most serious examples of resistance were the clonality observed among ACB in New York City and the documented endemic nature of VIM-7-producing PSA (0.09% of all PSA isolates). Meropenem remained the most active antimicrobial agent tested in the program, and surveillance networks must implement epidemiologic typing to accurately assess the role of clonal spread on the study results.

Transfer of plastid DNA from tobacco to the soil bacterium Acinetobacter sp. by natural transformation

Acquisition of new genetic information by horizontal gene transfer is a major mechanism of genetic adaptation and evolution in prokaryotes. Naturally transformable cells of Acinetobacter sp. were exposed to plant DNA from leaf and root tissue of transplastomic tobacco. With the aadA gene (resistance against spectinomycin and streptomycin) as anchor sequence, the transfer of segments of the tobacco plastid DNA to Acinetobacter by homology-facilitated illegitimate recombination occurred at a frequency of 1.2 x 10(-7) per cell, which was about 0.1% of the frequency of fully homologous transfers. Without anchor sequence, transfer was not detected ( Collapse

Key Words Collapse

MESH Headings

• Acinetobacter/genetics
• Base Sequence
• DNA/genetics
• DNA/metabolism
• Drug Resistance/genetics
• Genes, Plant/genetics
• Genome, Plant
• Molecular Sequence Data
• Plastids/genetics
• Recombination, Genetic
• Soil Microbiology
• Nicotiana/genetics
• Transformation, Bacterial
• Transformation, Genetic

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Comparative activities of doripenem versus isolates, mutants, and transconjugants of Enterobacteriaceae and Acinetobacter spp. with characterized beta-lactamases

Doripenem (S-4661), a new parenteral carbapenem, was tested against over 250 clinical isolates, mutants, and transconjugants of Enterobacteriaceae and Acinetobacter spp., selected or derived for their beta-lactamase expression characteristics. Imipenem, meropenem, and ertapenem were tested as comparators, along with cephalosporins and piperacillin-tazobactam, by using National Committee for Clinical Laboratory Standards agar dilution methodology. Doripenem MICs were from 0.03 to 0.25 microg/ml for Klebsiella isolates, irrespective of the presence of extended-spectrum beta-lactamases (ESBLs) or plasmid-mediated AmpC or hyperproduced K1 beta-lactamase. Similarly, MICs of doripenem for both AmpC-inducible and -derepressed Enterobacter isolates were 0.06 to 0.5 microg/ml. ESBL production did not raise the MICs of doripenem for Escherichia coli transconjugants, and studies with known expression mutants confirmed that neither inducible nor depressed AmpC beta-lactamase expression was protective in Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, or Morganella morganii. In all of these respects, doripenem resembled meropenem and imipenem, whereas the MICs of ertapenem were raised (but still < or =1 microg/ml) for many ESBL-producing klebsiellas and AmpC-derepressed E. cloacae and C. freundii strains. Resistance to all carbapenems, including doripenem (MICs of mostly 16 to 64 microg/ml, compared with 0.25 to 1 microg/ml for typical strains), was seen in Acinetobacter isolates with metallo-beta-lactamases or OXA-carbapenemases. Isolates of Klebsiella and Serratia spp. with IMP, KPC, and SME beta-lactamases also were resistant to doripenem (MICs, 8 to >64 microg/ml) and to other carbapenems, although the continued apparent susceptibility (MICs, < or =0.5 microg/ml) of E. coli derivatives with cloned IMP-1 and NMC-A beta-lactamases suggested that carbapenem resistance might require other factors besides the enzymes.

Molecular characterization of the gene encoding a new AmpC beta-lactamase in a clinical strain of acinetobacter genomic species 3

A presumptive chromosomal cephalosporinase (pI, 9.0) from a clinical strain of Acinetobacter genomic species 3 (AG3) is reported. The nucleotide sequence of this beta-lactamase shows for the first time the gene encoding an AmpC enzyme in AG3. In addition, the biochemical properties of the novel AG3 AmpC beta-lactamase are reported

Antimicrobial susceptibility and mechanisms of resistance to quinolones and beta-lactams in Acinetobacter genospecies 3

Antimicrobial susceptibility was determined in 15 epidemiologically unrelated clinical isolates of Acinetobacter genospecies 3. Moreover, the mechanisms of resistance to some beta-lactam antibiotics may be associated with the presence of a chromosomal cephalosporinase, AmpC, and the resistance to quinolones related to mutations in the gyrA and parC genes.

Gene amplification involves site-specific short homology-independent illegitimate recombination in Acinetobacter sp. strain ADP1

A system for studying gene amplification in the bacterium Acinetobacter sp. strain ADP1 was used to isolate 105 spontaneous mutants. The method selects for the elevated expression of neighboring transcriptional units in a parent strain lacking its normal transcriptional activators. Gene amplification can compensate for the activator loss by increasing the copy number of seven weakly expressed genes. Mutant colonies arose from the parent strain at a frequency of 10(-8) within three weeks. All but one of these mutants carried tandem head-to-tail repeats of a chromosomal segment (amplicon). These amplicons varied in size from approximately 12-290 kb and ranged in copy number from 3 to more than 30. Gene amplification involved a two-step process in which duplications formed independently of recA. Illegitimate recombination fused normally distant chromosomal regions to create novel DNA duplication junctions. These junctions were isolated from amplification mutants using an assay that exploits Acinetobacter natural transformability. Sequence analysis of 72 junctions revealed little identity in the recombining regions. Furthermore, multiple independently isolated mutants contained identical junctions. Six different junctions, each found in two to six mutants, revealed that some recombination events are site-specific. Several recurring junctions were studied using PCR. In each case, the identical duplication present in the mutant was estimated to have occurred in as many as one in a million cells in populations of strains never exposed to selective conditions. These duplications appeared to form spontaneously by a novel type of short homology-independent, site-specific process. However, in the absence of recA, mutant colonies were not selected from parent cells containing these duplications. Thus, the second gene amplification step most likely depends on homologous recombination to increase amplicon copy number. These studies support the theory that gene amplification is a driving force in the evolution of functionally related gene clusters.

Integrons as tools for epidemiological studies

The integron content of Gram-negative strains implicated in three distinct episodes of suspected cross-infection among inpatients was investigated and compared with ribotyping. In the first episode, ribotyping identified a strain of Acinetobacter, isolated over a 3-month period, responsible for an outbreak associated with the use of mechanical ventilation in the intensive care unit (ICU). The second episode concerned simultaneous isolations of Pseudomonas aeruginosa and Serratia marcescens from 13 bronchoscopy patients. In these two episodes, results obtained by analysis of integron content and ribotyping were in agreement and correctly identified the epidemiologically related strains. In the third episode, isolates of Enterobacter cloacae were collected from patients in the neonatal ICU over a 3-month period. Although several isolates belonged to the same ribotype, cross-infection could not always be confirmed when the integron content was analysed. Integron detection can be considered a useful tool for studying molecular epidemiology in hospital environments, facilitating the quick detection of possible cross-infection cases, especially in critical wards such as the ICU.

Proteomic analysis of the benzoate degradation pathway in Acinetobacter sp. KS-1

The purpose of this study was to perform proteome analysis of Acinetobacter sp. KS-1, a bacterium capable of degrading benzoate as a sole carbon source. In order to understand the benzoate degradation pathway used by strain KS-1, proteomes of benzoate-cultured and succinate-cultured KS-1 were comparatively analyzed by two dimensional gel electrophoresis (2-DE). Eighteen protein spots proteins were exclusively induced from the benzoate-cultured strain KS-1. Of these 18 spots, two benzoate-degrading enzymes (catechol 1,2-dioxygenase and beta-ketoadipate succinyl-CoA transferase) were identified by MS/MS analysis by MALDI-TOF/TOF mass spectrometry, which suggests that strain KS-1 degrades benzoate by the beta-ketoadipate pathway. DEAE-chromatography suggested that strain KS-1 induced only one type of catechol 1,2-dioxygenase during benzoate degradation. The catechol 1,2-dioxygenase was purified using three steps of ammonium sulfate precipitation, DEAE-sepharose, and Mono-Q chromatography. The purified catechol 1,2-dioxygenase of strain KS-1 had strong dioxygenase activity for 4-methylcatechol as well as catechol. Sequencing analysis using N-terminal and internal amino acid sequences showed that this catechol 1,2-dioxygenase is highly homologous with catechol 1,2-dioxygenase of Acinetobacter radioresistens. These results suggest that comparative proteomic analysis of biodegrading bacteria cultured under different conditions may be a useful initial step toward the elucidation of the aromatic compound degradation pathway.

Consortium of fold-catalyzing proteins increases soluble expression of cyclohexanone monooxygenase in recombinant Escherichia coli

The cyclohexanone monooxygenase ( CHMO) gene of Acinetobacter sp. NCIMB 9871 was simultaneously expressed with the genes encoding molecular chaperones and foldases in Escherichia coli. While the expression of the CHMO gene alone resulted in the formation of inclusion bodies, coexpression of the chaperone or foldase genes remarkably increased the production of soluble CHMO enzyme in recombinant E. coli. Furthermore, it was found that molecular chaperones were more beneficial than foldases for enhancing active CHMO enzyme production. The recombinant E. coli strain simultaneously expressing the genes for CHMO, GroEL/GroES and DnaK/DnaJ/GrpE showed a specific CHMO activity of 111 units g(-1) cell protein, corresponding to a 38-fold enhancement in CHMO activity compared with the control E. coli strain expressing the CHMO gene alone.

Culturable and nonculturable bacterial symbionts in the toxic benthic dinoflagellate Ostreopsis lenticularis

The toxic benthic dinoflagellate Ostreopsis lenticularis hosts a variety of symbiont bacterial flora. Laboratory cultured Ostreopsis clones require the presence of symbiotic Pseudomonas/Alteromonas bacterial strains for growth and toxicity development. Three culturable bacterial strains associated with Ostreopsis were identified as Pseudomonas/Alteromonas strain 1, Pseudomonas/Alteromonas strain 2 and Acinetobacter. Denaturing gradient gel electrophoresis (DGGE) analyses of extracted Ostreopsis associated bacterial DNAs indicated that there were three culturable and four non-culturable associated bacterial strains. The results presented here are the first report of the presence of unculturable bacterial symbionts in a toxic benthic dinoflagellate. Ostreopsis lost toxicity when exposed to elevated temperatures in the field and laboratory culture and subsequently recovered toxicity at reduced temperatures. Ostreopsis associated culturable Pseudomonas/Alteromonas bacterial strains were significantly reduced in dinoflagellate cultures exposed to elevated temperatures. The decreased toxicity of O. lenticularis exposed to elevated temperatures and their subsequent recovery of toxicity in periods of reduced thermal stress may have resulted from the effects of elevated temperature on the spectrum of culturable and unculturable bacterial species interacting with their Ostreopsis host.

Diketone cleaving enzyme Dke1 production by Acinetobacter johnsonii--optimization of fermentation conditions

The main objective of this work was the optimization of the production of the novel dioxygenase diketone cleaving enzyme (Dke1) from Acinetobacter johnsonii. Acetylacetone was used as an inducer for enzyme production. In the first step, the growth medium was optimized by using screening designs for finding the optimal carbon and nitrogen source. In the second step, a genetic algorithm was used to optimize the concentrations of all medium components. After six generations the stopping criterion was reached and a growth medium was obtained which produced sixteen times more enzyme than the starting medium. In the next step, an addition profile for the inducer acetylacetone was developed to further increase enzyme production by using a genetic algorithm. In this case, after four generations the stopping criterion was fulfilled. By using the obtained optimal addition profile Dke1 activity was enhanced from 826 to 2584Ul(-1). In comparison to the starting conditions activity could even be increased by a factor of 50.

Histidine ligand protonation and redox potential in the rieske dioxygenases: role of a conserved aspartate in anthranilate 1,2-dioxygenase

The Rieske dioxygenase, anthranilate 1,2-dioxygenase, catalyzes the 1,2-dihydroxylation of anthranilate (2-aminobenzoate). As in all characterized Rieske dioxygenases, the catalytic conversion to the diol occurs within the dioxygenase component, AntAB, at a mononuclear iron site which accepts electrons from a proximal Rieske [2Fe-2S] center. In the related naphthalene dioxygenase (NDO), a conserved aspartate residue lies between the mononuclear and Rieske iron centers, and is hydrogen-bonded to a histidine ligand of the Rieske center. Engineered substitutions of this aspartate residue led to complete inactivation, which was proposed to arise from elimination of a productive intersite electron transfer pathway [Parales, R. E., Parales, J. V., and Gibson, D. T. (1999) J. Bacteriol. 181, 1831-1837]. Substitutions of the corresponding aspartate, D218, in AntAB with alanine, asparagine, or glutamate also resulted in enzymes that were completely inactive over a wide pH range despite retention of the hexameric quaternary structure and iron center occupancy. The Rieske center reduction potential of this variant was measured to be approximately 100 mV more negative than that for the wild-type enzyme at neutral pH. The wild-type AntAB became completely inactive at pH 9 and exhibited an altered Rieske center absorption spectrum which resembled that of the D218 variants at neutral pH. These results support a role for this aspartate in maintaining the protonated state and reduction potential of the Rieske center. Both the wild-type and D218A variant AntABs exhibited substrate-dependent rapid phases of Rieske center oxidations in stopped-flow time courses. This observation does not support a role for this aspartate in a facile intersite electron transfer pathway or in productive substrate gating of the Rieske center reduction potential. However, since the single turnovers resulted in anthranilate dihydroxylation by the wild-type enzyme but not by the D218A variant, this aspartate must also play a crucial role in substrate dihydroxylation at or near the mononuclear iron site.

Variation of 16S–23S rRNA Intergenic Spacer Regions (ISRs) in Acinetobacter baylyi (Strain B2) Isolated from Activated Sludge

To determine the variability of the 16S-23S rRNA intergenic spacer region (ISR) of the newly described Acinetobacter baylyi, 88 clones containing ISR amplicons were screened and 14 chosen for further analysis. Two different sized 16S-23S rRNA ISRs were distinguished comprising five variable and four conserved nucleotide blocks. The major regions of heterogeneity between the different sized ISRs were due to blocks of substitutions with unique secondary structures interspersed with nucleotide substitutions, rather than differences caused by presence or absence of tRNA genes, which is often the case. Recombination events causing shuffling of nucleotide blocks are considered the most likely explanation for the mosaic structure observed between the different copies of the ISR. Single base differences present in the long ISR (LISR) were then exploited in attempts to detect possible heterogeneity between rrn copies in Acinetobacter baylyi but variability was not detected by RFLP analysis of LISR-specific PCR products. These primers were shown to be highly specific for 3 Acinetobacter baylyi strains based on LISR sequence homogeneity.

Identification of four genes necessary for biosynthesis of the modified nucleoside queuosine

Queuosine (Q) is a hypermodified 7-deazaguanosine nucleoside located in the anticodon wobble position of four amino acid-specific tRNAs. In bacteria, Q is produced de novo from GTP via the 7-deazaguanosine precursor preQ1 (7-aminoethyl 7-deazaguanine) by an uncharacterized pathway. PreQ1 is subsequently transferred to its specific tRNA by a tRNA-guanine transglycosylase (TGT) and then further modified in situ to produce Q. Here we use comparative genomics to implicate four gene families (best exemplified by the B. subtilis operon ykvJKLM) as candidates in the preQ1 biosynthetic pathway. Deletions were constructed in genes for each of the four orthologs in Acinetobacter. High pressure liquid chromatography analysis showed the Q nucleoside was absent from the tRNAs of each of four deletion strains. Electrospray ionization mass spectrometry confirmed the absence of Q in each mutant strain. Finally, introduction of the Bacillus subtilis ykvJKLM operon in trans complemented the Q deficiency of the two deletion mutants that were tested. Thus, the products of these four genes (named queC, -D, -E, and -F) are essential for the Q biosynthetic pathway.

Hydroxycinnamate (hca) catabolic genes from Acinetobacter sp. strain ADP1 are repressed by HcaR and are induced by hydroxycinnamoyl-coenzyme A thioesters

Hydroxycinnamates are plant products catabolized through the diphenol protocatechuate in the naturally transformable bacterium Acinetobacter sp. strain ADP1. Genes for protocatechuate catabolism are central to the dca-pca-qui-pob-hca chromosomal island, for which gene designations corresponding to catabolic function are dca (dicarboxylic acid), pca (protocatechuate), qui (quinate), pob (p-hydroxybenzoate), and hca (hydroxycinnamate). Acinetobacter hcaC had been cloned and shown to encode a hydroxycinnamate:coenzyme A (CoA) SH ligase that acts upon caffeate, p-coumarate, and ferulate, but genes for conversion of hydroxycinnamoyl-CoA to protocatechuate had not been characterized. In this investigation, DNA from pobS to an XbaI site 5.3 kb beyond hcaC was captured in the plasmid pZR8200 by a strategy that involved in vivo integration of a cloning vector near the hca region of the chromosome. pZR8200 enabled Escherichia coli to convert p-coumarate to protocatechuate in vivo. Sequence analysis of the newly cloned DNA identified five open reading frames designated hcaA, hcaB, hcaK, hcaR, and ORF1. An Acinetobacter strain with a knockout of HcaA, a homolog of hydroxycinnamoyl-CoA hydratase/lyases, was unable to grow at the expense of hydroxycinnamates, whereas a strain mutated in HcaB, homologous to aldehyde dehydrogenases, grew poorly with ferulate and caffeate but well with p-coumarate. A chromosomal fusion of lacZ to the hcaE gene was used to monitor expression of the hcaABCDE promoter. LacZ was induced over 100-fold by growth in the presence of caffeate, p-coumarate, or ferulate. The protein deduced to be encoded by hcaR shares 28% identity with the aligned E. coli repressor, MarR. A knockout of hcaR produced a constitutive phenotype, as assessed in the hcaE::lacZ-Km(r) genetic background, revealing HcaR to be a repressor as well. Expression of hcaE::lacZ in strains with knockouts in hcaA, hcaB, or hcaC revealed unambiguously that hydroxycinnamoyl-CoA thioesters relieve repression of the hcaABCDE genes by HcaR.

Prevalence of metallo-beta-lactamase among Pseudomonas aeruginosa and Acinetobacter baumannii in a Korean university hospital and comparison of screening methods for detecting metallo-beta-lactamase

To identify the metallo-beta-lactamases (MBLs) prevalent in Korea, a total of 130 clinical isolates of Pseudomonas aeruginosa and Acinetobacter baumannii (99 P. aeruginosa and 31 A. baumannii) with a reduced susceptibility to imipenem (IPM) and/or ceftazidime (CAZ) was subjected to PCR analyses with primers specific to bla(IMP-1), bla(VIM-1), and bla(VIM-2). In addition, inhibitor-potentiated disk diffusion methods (IPD) using two kinds of substrate-inhibitor combinations (ceftazidime-2-mercaptopropionic acid (2MPA) and imipenem-EDTA) were investigated. Thirty-three isolates (29 P. aeruginosa and 4 A. baumannii) carried bla(VIM-2) and two P. aeruginosa isolates harbored bla(IMP-1). The enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) pattern revealed that many of the VIM-2-producing P. aeruginosa isolates were clonally related, whereas the A. baumannii isolates were diverse. The inhibitor-potentiated disk diffusion test using imipenem-EDTA was highly sensitive and specific for detecting the VIM-2 producer. These results suggest that VIM-2 is an important MBL in P. aeruginosa and A. baumannii in the Korean hospital of this study and that the IMP-1-producing P. aeruginosa has also emerged. Screening for MBLs and strict infection control for these isolates will contribute to prevent further spread of resistance.

Acinetobacter parvus sp. nov., a small-colony-forming species isolated from human clinical specimens

The taxonomic status of seven glucose-non-acidifying, non-proteolytic Acinetobacter strains characterized by forming small colonies on agar media was studied. With one exception, all strains were from human specimens. They could be distinguished from all described Acinetobacter (genomic) species by their ability to grow on ethanol and acetate as sole sources of carbon but not on 22 other substrates tested including DL-lactate or DL-4-aminobutyrate. DNA-DNA hybridization studies, 16S rRNA gene sequence analysis, amplified rDNA restriction analysis and DNA polymorphism analysis by AFLP showed that these strains represent a hitherto unknown species of the genus Acinetobacter, for which the name Acinetobacter parvus (type strain LMG 21765(T)=LUH 4616(T)=NIPH 384(T)=CCM 7030(T)) is proposed.