Expression of a Serratia marcescens chitinase gene in Sinorhizobium fredii USDA191 and Sinorhizobium meliloti RCR2011 impedes soybean and alfalfa nodulation.
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A gene encoding chitinase from Serratia marcescens BJL200 was cloned into a broad-host-range vector (pRK415) and mobilized into Sinorhizobium fredii USDA191. Chitinolytic activity was detected in S. fredii USDA191 transconjugants that carried the S. marcescens chiB gene. Chitinase-producing S. fredii USDA191 formed nodules on soybean cultivar McCall. However, there was a delay in nodule formation and a marked decrease in the total number of nodules formed by the chitinase-producing S. fredii in comparison with the wild-type strain. Expression of chitinase in S. meliloti RCR2011 also impeded alfalfa nodulation. Thin-layer chromatography of 14C-labeled Nod factors from chitinase-producing S. fredii USDA191 revealed hydrolysis of lipochitooligosaccharides. (+info)
Crystal structure of prolyl aminopeptidase from Serratia marcescens.
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Prolyl aminopeptidase from Serratia marcescens specifically catalyzes the removal of N-terminal proline residues from peptides. We have solved its three-dimensional structure at 2.3 A resolution by the multiple isomorphous replacement method. The enzyme consists of two contiguous domains. The larger domain shows the general topology of the alpha/beta hydrolase fold, with a central eight-stranded beta-sheet and six helices. The smaller domain consists of six helices. The catalytic triad (Ser113, His296, and Asp268) is located near the large cavity at the interface between the two domains. Cys271, which is sensitive to SH reagents, is located near the catalytic residues, in spite of the fact that the enzyme is a serine peptidase. The specific residues which make up the hydrophobic pocket line the smaller domain, and the specificity of the exo-type enzyme originates from this smaller domain, which blocks the N-terminal of P1 proline. (+info)
Application of infrequent-restriction-site PCR to clinical isolates of Acinetobacter baumannii and Serratia marcescens.
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We applied infrequent-restriction-site PCR (IRS-PCR) to the investigation of an outbreak caused by 23 isolates of Acinetobacter baumannii in an intensive care unit from November 1996 to May 1997 and a pseudoepidemic caused by 16 isolates of Serratia marcescens in a delivery room from May to September 1996. In the epidemiologic investigation of the outbreak caused by A. baumannii, environmental sampling and screening of all health care workers revealed the same species from the Y piece of a mechanical ventilator and the hands of two health care personnel. IRS-PCR showed that all outbreak-related strains were genotypically identical and that three strains from surveillance cultures were also identical to the outbreak-related strains. In a pseudoepidemic caused by S. marcescens, IRS-PCR identified two different genotypes, and among them one genotype was predominant (15 of 16 [93.8%] isolates). Extensive surveillance failed to find any source of S. marcescens. Validation of the result of IRS-PCR by comparison with that of field inversion gel electrophoresis (FIGE) showed that they were completely concordant. These results suggest that IRS-PCR is comparable to FIGE for molecular epidemiologic studies. In addition, IRS-PCR was less laborious and less time-consuming than FIGE. To our knowledge, this is the first report of the application of IRS-PCR to A. baumannii and S. marcescens. (+info)
The third chitinase gene (chiC) of Serratia marcescens 2170 and the relationship of its product to other bacterial chitinases.
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The third chitinase gene (chiC) of Serratia marcescens 2170, specifying chitinases C1 and C2, was identified. Chitinase C1 lacks a signal sequence and consists of a catalytic domain belonging to glycoside hydrolase family 18, a fibronectin type III-like domain (Fn3 domain) and a C-terminal chitin-binding domain (ChBD). Chitinase C2 corresponds to the catalytic domain of C1 and is probably generated by proteolytic removal of the Fn3 and ChBDs. The loss of the C-terminal portion reduced the hydrolytic activity towards powdered chitin and regenerated chitin, but not towards colloidal chitin and glycol chitin, illustrating the importance of the ChBD for the efficient hydrolysis of crystalline chitin. Phylogenetic analysis showed that bacterial family 18 chitinases can be clustered in three subfamilies which have diverged at an early stage of bacterial chitinase evolution. Ser. marcescens chitinase C1 is found in one subfamily, whereas chitinases A and B of the same bacterium belong to another subfamily. Chitinase C1 is the only Ser. marcescens chitinase that has an Fn3 domain. The presence of multiple, divergent, chitinases in a single chitinolytic bacterium is perhaps necessary for efficient synergistic degradation of chitin. (+info)
Molecular epidemiology of a cluster of cases due to Klebsiella pneumoniae producing SHV-5 extended-spectrum beta-lactamase in the premature intensive care unit of a Hungarian hospital.
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Fifteen nosocomial cases of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae occurred among 132 neonates in a premature intensive care unit in Hungary in June through November 1998. Fourteen strains were indistinguishable by molecular biological typing and harbored the same single conjugative extended-spectrum beta-lactamase-encoding plasmid that was spontaneously found in a Serratia marcescens strain in the same patient. (+info)
Therapeutic experience with netilmicin.
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Netilmicin, a new aminoglycoside antibiotic, was used to treat 19 patients with urinary tract infection and 5 with systemic infection. The causal organisms were Escherichia coli (in 2), Klebsiella pneumoniae (in 4), Serratia marcescens (in 12) and Pseudomonas aeruginosa (in 7); 1 patient was infected with two of these organisms. All the isolates of causal organisms except one of Serratia were initially sensitive to netilmicin but many were resistant to other aminoglycosides. Sixteen of the urinary tract infections responded to netilmicin therapy, although relapse occurred in three patients. Two of the three patients with musculoskeletal infection responded to combined therapy with surgery and netilmicin; the other patient responded to the same regimen but with carbenicillin added. Netilmicin cured pneumonia in one patient but failed in the other patient with pneumonia, who had leukemia. Superinfection occurred in five patients with urinary tract infection. Adverse reactions to netilmicin were minor. Netilmicin may prove to be a useful agent, particularly for infections due to multiresistant Klebsiella or Serratia, or when prolonged aminoglycoside therapy is required. (+info)
Defective cellular immunity to gram-negative bacteria in cystic fibrosis patients.
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In vitro lymphocyte responses to Pseudomonas aeruginosa have been found to be impaired in cystic fibrosis patients with advanced clinical disease. The responses to Klebsiella pneumoniae, Serratia marcescens, and Proteus mirabilis were studied in a similar group of cystic fibrosis patients and normal individuals. Cystic fibrosis patients found to be unresponsive to pseudomonas were also unresponsive to klebsiella, serratia, and proteus. Responsiveness to Staphylococcus aureus was not impaired in cystic fibrosis patients. We postulate that in vitro lymphocyte responses to several gram-negative bacteria require the function of a lymphocyte subpopulation which may be impaired in some cystic fibrosis patients. (+info)
Allosteric signal transmission involves synergy between discrete structural units of the regulatory subunit of aspartate transcarbamoylase.
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Previous studies have shown that the S5' beta-strand (r93-r97) of the regulatory polypeptides of the aspartate transcarbamoylases (ATCases) from Serratia marcescens and Escherichia coli are responsible for their diverged allosteric regulatory patterns, including conversion of CTP from an inhibitor in E. coli to an activator in S. marcescens. Similarly, mutation of residues located in the interface between the allosteric and the zinc domains resulted in conversion of the ATP responses of the E. coli enzyme from activation to inhibition, suggesting that this interface not only mediates but also discriminates the allosteric responses of ATP and CTP. To further decipher the roles and the interrelationships of these regions in allosteric communication, allosteric-zinc interface mutations (Y77F and V106A) have been introduced into both the native and the S5' beta-strand chimeric backgrounds. While the significance of this interface in the allosteric regulation has been confirmed, there is no direct evidence supporting the presence of distinct pathways for the ATP and CTP signals through this interface. The analysis of the mutational effects reported here suggested that the S5' beta-strand transmits the allosteric signal by modulating the hydrophobic allosteric-zinc interface rather than disturbing the allosteric ligand binding. Intragenic suppression by substitutions in the hydrophobic interface between the allosteric and the zinc domains of the regulatory chains resulted in the partial recovery of allosteric responses in the EC:rS5'sm chimera and reduced the activation by ATP in the Sm:rS5'ec chimera. Thus, it seems that there is a synergy between these two structural units. (+info)