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PubMed1985

Characterization of restriction-modification enzymes Cfr13 I from Citrobacter freundii RFL13.

This communicatiopn describes some properties of RCfr13 I and MCfr13 I, isolated from Citrobacter freundii RFL13. RCFfr13 I restriction enzyme recognizes the 5'-G GNCC sequence and cleaves, as indicated by the arrow. MCfr13 I methylase modifies the internal cytosine producing m5C (5'-GGNm5CC). RCfr13 I is sensitive not only to this type of substrate modification but also to hemimethylation in overlapping sites by MCfr10 I (internal cytosine of RCfr13 I recognition is methylated) and MHpa II (external cytosine is methylated). From these results the sensitivity of RCfr13 I to methylation by dcm methylase of E.coli in overlapping sites is deduced.

Bacteriophage lambda↗
PubMed1987

Structure determination of the O-specific polysaccharides from Citrobacter O4- and O27-lipopolysaccharides by methylation analysis and one- and two-dimensional 1H-NMR spectroscopy.

Using sugar and methylation analyses, and one- and two-dimensional 1H-NMR spectroscopy at 500 MHz it was established that poly-beta-1,2-4-deoxy-D-arabinohexopyranose occurs as O-specific chains of lipopolysaccharides in Citrobacter serotypes O4, O27 and O36. Strong serological cross-reactivity between these serotypes is in full agreement with the chemical identity of their O-specific polysaccharides.

Chemical Phenomena↗
PubMed1990

Substitution of aspartic acid-217 of Citrobacter freundii cephalosporinase and properties of the mutant enzymes.

On the assumption that Asp-217 of a Citrobacter freundii cephalosporinase forms a salt-bridge with the conserved Lys-67, Asp-217 was changed to glutamic acid, threonine or lysine. The mutant enzymes retained about the same level of activity as that of the wild-type enzyme, and the participation of Asp-217 in the salt-bridge was ruled out. However, the mutations resulted in an increase in hydrolytic activity toward oxyimino-cephalosporins such as cefuroxime, cefmenoxime and ceftazidime, suggesting a possible mechanism of the bacterial resistance to the novel beta-lactams by a single mutation in cephalosporinases.

Aspartic Acid↗
PubMed1990

Function of the conserved triad residues in the class C beta-lactamase from Citrobacter freundii GN346.

The conserved KTG triad in the class C beta-lactamase from Citrobacter freundii GN346 was examined as to its function by means of site-directed mutagenesis. The following conversions were performed; Lys-315 to arginine, alanine or glutamic acid, Thr-316 to valine, and Gly-317 to alanine, proline or isoleucine. The resultant mutant enzymes revealed that a basic amino acid at position 315 and a small uncharged residue at position 317 are essential for the enzyme activity, but a hydroxyl group at residue 316 is not required for the enzymatic catalysis. The kinetic properties of the purified Arg-315 and Val-316 enzymes provided information on the function of these residues.

Amino Acids↗
PubMed1993

Assessment of macroporous polystyrene-based polymers for the immobilization of Citrobacter freundii.

POLYHIPE polymers represent a novel immobilization support possessing many desirable characteristics. These materials have been used to immobilize Citrobacter freundii in order to develop a continuous bioconversion system for the anaerobic production of trimethylene glycol from glycerol. Several immobilization methods were employed, of which the most successful involved culturing the organism with POLYHIPE in shake-flasks, transferring the contents into a column, and growing the cells in situ within the column. Cell activity was determined by the amount of TMG produced from a buffered glycerol solution. The latter was passed through the columns by either a recirculation system or the superior single-pass method. The optimal system was scaled up and showed potential for further large-scale investigations. Cell lifetime in the column could be improved by supplying the cells with diluted growth medium in place of the buffer.

Bacteriological Techniques↗
PubMed1988

A conductance medium to distinguish between Salmonella and Citrobacter spp.

Published methods for detecting Salmonella by conductance methods yield some Citrobacter spp. as false positives. A medium is described which, when used in conjunction with selenite-cystine/trimethylamine oxide/mannitol (SC/T/M) resolves this difficulty. It is based on the ability of Salmonella to decarboxylate lysine in the presence of selenite (4 g/l), after pre-enrichment in buffered peptone water supplemented with glucose and lysine for 7-17 h. Salmonella produced a conductance change of 250-400 microS in 24 h with a maximum rate of conductance change of 10-15 microS/10 min. 299 samples were tested and the only false positives were due to Hafnia alvei which gave no conductance response in the SC/T/M medium. Using both media in a two tube system would lead to a rapid clearance of Salmonella negative samples.

Animals↗
PubMed1988

Prior antimicrobial therapy and resistance of Enterobacter Citrobacter and Serratia to third generation cephalosporins.

During a 6-month period all inpatients from whom Enterobacter, Citrobacter or Serratia. had been isolated were reviewed and information on selected variables recorded. Two groups, one including 19 patients with organisms resistant to third generation cephalosporins and the other 111 patients with susceptible organisms were compared. In the initial analysis, the mean number of antimicrobials received in the prior 2 months was the variable most strongly associated with isolation of resistant organisms (2.6 +/- 1.5 vs 1.5 +/- 1.6; P = 0.002). When patients who had received no antimicrobials were omitted from the analysis, the mean number of antimicrobials was similar (2.6 +/- 1.5 vs 2.3 +/- 1.5; P = 0.19). Comparisons of antimicrobials received in the prior 2 months showed only cefoxitin (9/70 vs 7/19; P = 0.016) and cefotaxime (4/70 vs 5/19; P = 0.008) to be associated with isolation of resistant organisms. These data suggest that, at our institution, antimicrobial therapy with an extended spectrum cephalosporin is an important risk factor for subsequent acquisition of an organism resistant to third generation cephalosporins.

Cephalosporins↗
PubMed1990

Conjugational cotransfer of IncFI and IncI conjugative plasmids forming aggregate in a pathogenic Citrobacter freundii strain.

Two plasmids, pEM4 (IncFI) determining virulence and pEM6 (IncI) determining colicine I production and resistance to tetracycline, have been found in a pathogenic strain of Citrobacter freundii. Even though pEM4 and pEM6 plasmids are conjugative and transfer themselves very efficiently during conjugation, a high cotransfer of both plasmids is observed--an unusually high fraction of transconjugants acquiring pEM6 acquires pEM4 and vice versa. The observed cotransfer of these plasmids is connected with their ability to complement their conjugational functions. An insertion mutant of pEM4 with decreased frequency of conjugational transfer has been isolated. This mutant (pEM44) lost its ability to mobilize nonconjugative plasmids. Its transfer is stimulated by pEM6 and it is transferred from (pEM44, pEM6) donors almost exclusively with pEM6 plasmid. The role of cotransfer and stimulation phenomena in spreading of plasmid aggregates in bacterial population is discussed.

Bacteriocin Plasmids↗
PubMed1991

Cloning and nucleotide sequencing of the gene encoding the beta-lactamase from Citrobacter diversus.

The gene coding for the class A beta-lactamase of Citrobacter diversus has been cloned and sequenced. It contains the information for a 294-amino-acid precursor protein, including a 27-residue N-terminal signal peptide. The deduced sequence of the N-terminal portion of the mature protein is in excellent agreement with that determined by microsequencing of the protein and readily explains the pI differences observed between the naturally occurring forms I and II of the enzyme. The sequence of the mature protein exhibits a very high degree of similarity with that of the Klebsiella oxytoca class A beta-lactamase.

Amino Acid Sequence↗
PubMed1992

Characterization of the Citrobacter freundii phoE gene and development of C. freundii-specific oligonucleotides.

The phoE gene of Citrobacter freundii, encoding a pore-forming outer membrane protein, was cloned and its nucleotide sequence was determined. The homologies in terms of identical amino acids between the C. freundii PhoE protein and those of Escherichia coli, E. cloacae and Klebsiella pneumoniae were 90%, 86% and 84%, respectively. Two synthetic oligonucleotides, corresponding to hypervariable, cell surface-exposed regions of the protein, were tested for their specificity in polymerase chain reactions. They were specific for the species C. freundii, i.e., no reaction was detected with 35 non-C. freundii strains tested, including 17 Salmonella, two C. amalonaticus and three C. diversus strains, whereas all five C. freundii strains tested were correctly recognized.

Amino Acid Sequence↗
PubMed1987

The araC gene of Citrobacter freundii.

The araC gene of Citrobacter freundii was cloned into plasmid pBR322 and expressed in Escherichia coli and Salmonella typhimurium. The nucleotide sequence and the predicted translational product were determined and compared to those of E. coli, S. typhimurium and Erwinia carotovora. The predicted translational product is 281 amino acids (aa) long, identical in size to that of S. typhimurium, and is 11 and 29 aa shorter than that of E. coli and E. carotovora, respectively. The nucleotide sequence of the araC gene of C. freundii is 83% homologous to the araC genes of both E. coli and S. typhimurium, but only 60% homologous to that of E. carotovora with respect to the regions they share. The predicted amino acid sequence is highly conserved and shows 96% and 94% homology to S. typhimurium and E. coli, respectively. E. carotovora shows only a 58% aa homology. The activator and autoregulatory activities of each plasmid encoded AraC protein in a S. typhimurium araC::lacZ protein fusion strain were examined.

Amino Acid Sequence↗
PubMed1988

Transcriptional regulation and gene arrangement of Escherichia coli, Citrobacter freundii and Salmonella typhimurium biotin operons.

The bio operons of Citrobacter freundii and Escherichia coli K-12 (strain C600) were isolated by screening lambda banks for complementation of E. coli bio mutants. These were compared with the previously isolated bio operon of Salmonella typhimurium and previous data on E. coli K-12. The restriction maps of the operon are very different in the three species, but no difference in gene order was found. Operator-promoter DNA, identified by repressible titration and by biotin-repressible transcription in E. coli, was sequenced and compared to the published E. coli K-12 sequence. In the segment previously identified as operator/bioB promoter, C. freundii and S. typhimurium DNA are identical and differ from E. coli only by 2 bp. The DNA to the right of this segment (indicated by previous data to be the bioA promoter of E. coli) has diverged in all three species, and only E. coli has a sequence resembling a consensus promoter.

Bacteriophage lambda↗
PubMed1993

Cloning and sequences of the genes encoding the CfrBI restriction-modification system from Citrobacter freundii.

The genes encoding the CfrBI restriction and modification (R-M) systems from Citrobacter freundii and recognizing the sequence 5'-CCWWGG-3' (W = A or T) were cloned in Escherichia coli McrBC- cells. The nucleotide (nt) sequences of the genes were determined. Two large open reading frames were found. Deletion analysis showed that one of them [1128 nt coding for 376 amino acids (aa)] corresponds to a methyltransferase (MTase)-encoding gene and the other (1065 nt coding for 355 aa) to a restriction endonuclease-encoding gene. The genes are oriented divergently and separated by 76 bp. A CfrBI site (5'-m4CCATGG) was found in the intergenic region of the cfrBIRM genes. Analysis of the deduced aa sequence of M.CfrBI made it possible to determine the typical features of a m4C-specific MTase. Limited homology between the M.CfrBI and R.CfrBI proteins was also found.

Amino Acid Sequence↗
PubMedDate not supplied

[Demonstration of glycocalyx formation in vitro in Citrobacter freundii, Proteus mirabilis and Planococcus sp.: the effect of polyosidases].

Three bacterial species of different origin, Citrobacter freundii, Proteus mirabilis and Planococcus sp., formed glycocalyx in vitro and thereby showed that the phenomena does not only occur in vivo contrary to the opinion of many authors. The glycocalyx was produced in the attachment processes used or both extra- and intercellular attachment. The aggregates formed caused large errors in bacterial counts and led to questioning of the very principle of the counting procedures. The glycocalyx was not destroyed by the polyosidases utilized nor by ultrasound treatment. The glycocalyx structure differed only according to the bacterial species of origin and was unchanged by culture media or nutrient deprivation.

Bacterial Adhesion↗
PubMedDate not supplied

Citrobacter diversus and neonatal brain abscess.

A 23-day-old infant presented with apnea and was found to have Citrobacter diversus meningitis and brain abscess. The organism persisted in brain abscess fluid for over 4 weeks despite adequate antibiotic therapy. Cranial computed tomography demonstrated persistent radiolucencies in both frontal lobes, and midline shift, long after completion of antibiotic therapy. Effective therapy of C. diversus meningitis and brain abscess may require use of an antibiotic active within phagocytes, and judicious surgical drainage. A high prevalence of brain abscess mandates cranial computed tomography for any infant with C. diversus meningitis.

Bacteriological Techniques↗
PubMed2004

Structure of the O-polysaccharide of Citrobacter youngae O1 containing an alpha-D-ribofuranosyl group.

The lipopolysaccharide of Citrobacter youngae O1, strain PCM 1492 was degraded with acid or alkali under mild conditions, and the resultant polysaccharide was isolated by GPC and studied by sugar and methylation analyses and 1H and 13C NMR spectroscopies, including 2D COSY, TOCSY, NOESY and 1H, 13C HSQC experiments. The following structure of the branched tetrasaccharide repeating unit of the O-polysaccharide was established: [structure: see text] where substitution with the alpha-D-Ribf group is nonstoichiometric. This group occurs rarely in bacterial polysaccharides and is easily cleaved under mild acidic conditions. Studies with polyclonal rabbit antisera against whole cells of C. youngae PCM 1492 and PCM 1506 showed the serological identity of the lipopolysaccharides of C. youngae PCM 1492, PCM 1493 and PCM 1506, which are classified in serogroup O1.

Carbohydrate Sequence↗
PubMed2004

Structures of two O-polysaccharides of the lipopolysaccharide of Citrobacter youngae PCM 1538 (serogroup O9).

Mild acid degradation of the lipopolysaccharide of Citrobacter youngae O9, strain PCM 1538 released a homopolysaccharide of 4-acetamido-4,6-dideoxy-D-mannose (D-Rha4NAc, N-acetyl-D-perosamine). Studies by methylation analysis and (1)H and (13)C NMR spectroscopy, using two-dimensional (1)H,(1)H COSY, TOCSY, NOESY and H-detected (1)H,(13)C HSQC experiments showed the presence of two structurally different polysaccharides consisting of the following units: -->)-alpha-D-Rhap4NAc-(1 --> and --> 3)-alpha-D-Rhap4NAc-(1 --> 3)-beta-D-Rhap4NAc-(1 -->.

Carbohydrate Sequence↗
PubMed2005

Occurrence of extended-spectrum beta-lactamases among chromosomal AmpC-producing Enterobacter cloacae, Citrobacter freundii, and Serratia marcescens in Korea and investigation of screening criteria.

We assessed the occurrence and screening criterion for extended-spectrum beta-lactamases (ESBLs) among AmpC-producing Enterobacter cloacae, Citrobacter freundii, and Serratia marcescens. The 413 isolates (158 E. cloacae, 126 C. freundii, and 129 S. marcescens) isolated from 11 clinical laboratories in Korea were investigated. ESBL production was confirmed by double-disk synergy test and inhibitor-potentiated diffusion test using ceftazidime (CAZ), cefotaxime (CTX), aztreonam (AZT), and cefepime (FEP) with or without clavulanic acid. One hundred seven isolates (25.9%) were as ESBL producers. Of them, resistance was transferred by conjugation in 82 isolates. In transconjugants, structural genes for CTX-M (53.7%), TEM (46.3%), SHV (29.3%) were found. To evaluate the ESBL screening minimum inhibitory concentration (MIC) criteria, MICs for cefuroxime, CAZ, CTX, AZT, and FEP were determined and cutoff value was selected using receiver operator characteristic curve. The FEP MIC > or = 1 microg/mL had the highest sensitivity (95.3%), specificity (82.7%), and positive (65.8%) and negative predictive values (98.3%).

Anti-Bacterial Agents↗