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PubMed2001

Characterization of an extended-spectrum class C beta-lactamase of Citrobacter freundii.

Citrobacter freundii GC3 is a clinical isolate which showed moderate resistance to oxyimino beta-lactams such as ceftazidime and aztreonam. This drug resistance was due to an extended-spectrum class C beta-lactamase encoded by chromosomal gene(s). The GC3 beta-lactamase showed high amino acid sequence homology to a known C. freundii beta-lactamase, i.e., 346 of 361 amino acids were identical with those of C. freundii GN346 beta-lactamase (Tsukamoto, K. et al, Eur. J. Biochem. 188, 15-22, 1990). Asp198 was the only dissimilar amino acid found in the omega loop region, known as the hot spot for extended-spectrum resistance in class C beta-lactamases (Haruta, S. et al, Microbiol. Immunol. 42, 165-169, 1998). However, Asp198 was eliminated as a cause of the extended-spectrum resistance by the substitution of Asn for Asp198. Subsequent investigation suggested that the moderate resistance to oxyimino beta-lactams is attributable to the replacement of amino acids on the enzyme's surface area, far from the active-site. Some or all of the replacements are assumed to delicately modify the active-site configuration. The GC3 beta-lactamase is the first example of an extended-spectrum class C beta-lactamase in which mutations are independent of the omega loop.

Amino Acid Sequence↗

PubMedDate not supplied

[Cytochrome composition and content of Citrobacter freundii].

Citrobacter freundii, strain 62, produces considerable amounts of cytochromes c and b when it grows in media with different carbon compounds under both aerobic anc anaerobic conditions. The content of cytochromes c increases under anaerobic conditions, particularly in the presence of formate or DMSO, and under aerobic conditions if formate is added. In contrast, the amount of cytochromes b decreased when the culture is grown in media with formate under anaerobic conditions. Cytochrome o is principal terminal oxidase in C. freundii. Under certain growth conditions, the microorganism, just as E. coli, produced also cytochromes a and d.

Aerobiosis↗

PubMedDate not supplied

[Enzyme activity of the formate hydrogenlyase complex in Citrobacter freundii].

Citrobacter freundii 62 can grow in the absence of oxygen in media containing glucose, peptone, fumarate or malate. When the medium contained fumarate or malate, the culture could grow under anaerobic conditions only in the presence of molecular hydrogen, formate or nitrate. The highest activity of formatehydrogenlyase and hydrogenase was found when C. freundii grew in a medium with glucose and formate. The activity was lower in media with other organic substrates, particularly, in the absence of formate or H2. The activity of hydrogenase was very low in cells grown under aerobic conditions or in the presence of nitrates while the activity of formatehydrogenlyase was not found at all for all practical purposes. The activity of formate dehydrogenase assessed in the presence of methylene blue was rather high irrespective of the conditions under which the culture was grown. However, when the activity of formate dehydrogenase was determined in the presence of benzyl viologen, it was high only in cells grown in the medium with glucose and formate.

Aerobiosis↗

PubMed1981

Plasmid specification of resistance to antibacterial compounds in environmental Citrobacter freundii.

Citrobacter freundii from an environmental source displayed resistance to a wide variety of antibacterials. Some of these resistances could be transferred by conjugation with frequencies as high as 10(-2). The complexity of plasmid involvement in the antibacterial resistance of this species was demonstrated by isolation of plasmid DNA from two isolates. In one strain, resistance to beta-lactam antibiotics was specified by a 55 x 10(6) molecular weight plasmid, whereas kanamycin and neomycin resistance was specified by a 7 x 10(6) molecular weight plasmid. Resistance to chloramphenicol and tetracycline was not plasmid mediated. The other strain contained plasmids of molecular weight 113 x 10(6) and 80 x 10(6), which specified resistance to chloramphenicol, neomycin, kanamycin, tetracycline, and mercury.

Anti-Bacterial Agents↗

PubMed2000

Resolution of high-molecular-weight components in lipopolysaccharides of Escherichia coli, Morganella morganii, Citrobacter freundii and Citrobacter diversus strains with sodium dodecyl sulfate polyacrylamide gels.

The use of 0.5% sodium dodecyl sulfate in polyacrylamide separation gels allowed the resolution in several bands of high-molecular-mass components in smooth lipopolysaccharide of bacterial outer membrane from Escherichia coli, Morganella morganii, Citrobacter freundii and Citrobacter diversus. With or without 0.1% SDS, however, such a result was not possible.

Citrobacter↗

PubMed1974

Sensitivity of Citrobacter freundii and Citrobacter koseri to cephalosporins and penicillins.

An examination of 99 field and reference strains of Citrobacter freundii showed 79% of them to be resistant to cephaloridine and sensitive to carbenicillin, while 96% of 45 field and reference strains of Citrobacter koseri examined were sensitive to cephaloridine and resistant to carbenicillin. Susceptibility tests with these two antibiotics are therefore useful in separating the two species of Citrobacter.

Ampicillin↗

PubMed1993

Structure and antigenic properties of Citrobacter freundii lipopolysaccharides.

Citrobacter freundii strain E69366 was detected in a colony immunoassay with a rabbit antiserum prepared to a strain of Escherichia coli belonging to serogroup O157. Lipopolysaccharide (LPS) was shown to contain the epitope(s) involved in antibody binding. LPS prepared from strain E69366, with hot phenol contained core-LPS that migrated to the water-phase and long-chain LPS that separated into the phenol-phase. A total of 36 strains of Cit. freundii were analysed for their LPS profiles by SDS-PAGE. Sixteen could be allocated into five groups (A(3), B(7), C(2), D(2) and E(2)) based on similarities in LPS profile. The remaining strains either expressed unique SDS-PAGE profiles (18) or did not express long-chain LPS (2). All strains with a profile 'A' reacted with the antiserum prepared to E. coli O157, whereas those with other profiles did not. The two strains of Cit. freundii expressing LPS profiles designated 'E' reacted with an antiserum prepared in rabbits to E. coli O45.

Adult↗

PubMed1990

Role of lysine-67 in the active site of class C beta-lactamase from Citrobacter freundii GN346.

Citrobacter freundii GN346 produces a class C beta-lactamase exhibiting the substrate profile of a typical cephalosporinase. The structural and promoter regions of the cephalosporinase gene, comprising 1408 nucleotides, were completely sequenced. The amino acid sequence of the mature enzyme, comprising 361 amino acids, and its molecular mass, 39,878 Da, were determined. The active site was confirmed to be Ser-64. The amino acid sequence of the enzyme differs from that of the cephalosporinase of C. freundii OS60 by nine residues. The nucleotide sequence of the promoter region suggests a possible attenuator structure. Lys-67, one of the most conserved residues found in class A and C beta-lactamases and penicillin-binding proteins, was converted into arginine, threonine or glutamic acid through site-directed mutagenesis. The Glu-67 enzyme had lost the catalytic activity and the Thr-67 enzyme only showed a trace of activity. The Arg-67 enzyme, which retained a significant amount of the activity, was purified. The Km values of the Arg-67 enzyme for cephalothin, cephaloridine and benzylpenicillin are 13-19 times those of the wild-type enzyme; the kcat values for the three substrates are 37%, 3%, and 36% those of the wild-type enzyme, respectively.

Amino Acid Sequence↗

PubMed1986

Occurrence and clinical significance of tyrosine clearing positive Citrobacter freundii in human faecal specimens.

59 tyrosine clearing positive Citrobacter strains were isolated from a total of 2062 human faecal specimens, specifically from 1167 healthy people and from 895 patients suffering from different gastrointestinal syndromes. All strains were identified biochemically as Citrobacter freundii. Citrobacter diversus 100% positive for tyrosine clearing could not be isolated in any case. Citrobacter freundii was found twice as frequently in stools of healthy human beings than of patients. There is a statistical significance of p less than 0.05 for the occurrence of tyrosine clearing Citrobacter freundii in healthy persons.

Citrobacter↗

PubMedDate not supplied

[Enzymatic synthesis of 3,4-dihydroxyphenyl-L-alanine by free and immobilized Citrobacter freundii cells].

The Citrobacter freundii 62 cells immobilized in PAAG and possessing the tyrosine-phenol-lyase (TPL) activity catalyse the synthesis of 3,4-dihydroxyphenyl-L-alanine (DOPA) from pyrocatechol and ammonium pyruvate. The synthesis of DOPA was studied using both free and immobilized bacterial cells. When the concentration of pyrocatechol is over 0.1 M the TPL activity of the cells is inhibited. The concentration of pyrocatechol can be increased up to 0.3 M by using an equimolar mixture of pyrocatechol and boric acid. The addition of ascorbic acid as an antioxidant results in a lower TPL activity of both free and immobilized bacterial cells.

Acrylic Resins↗

PubMed1987

Basic studies of hydrogen evolution by Escherichia coli containing a cloned Citrobacter freundii hydrogenase gene.

Citrobacter freundii genes that complemented Escherichia coli hyd-(hydrogenase activity) mutation were cloned in plasmids pCBH4 (6.2 kb) and pCBH6(5.7 kb). Hydrogen evolution by the transformant E. coli HK-8(pCBH4 or pCBH6) was investigated. The optimum culture temperature of recombinant E. coli cells for hydrogen evolution from glucose was in the neighborhood of 18 degrees C. The recombinant E. coli cells cultured at this condition showed a several-fold increase of hydrogen evolution, as compared with that of the wild-type cells. The plasmid-retention stability of this recombinant E. coli was extremely high, especially plasmid pCBH4, which was completely retained during 2 wk without any restriction. Hydrogen production by immobilized recombinant E. coli was then investigated using cells cultured at 18 degrees C. The hydrogen evolution rate from glucose and Lennox-broth were about twofold higher than that of E. coli C600, and this high hydrogen evolution rate was maintained for more than 1 mo.

Citrobacter↗

PubMed2000

Prediction of two- and three-amino-acid sequences of Citrobacter Freundii beta-lactamase from its amino acid composition.

The repeated amino-acid sequences in Citrobacter Freundii beta-lactamase may be indispensable for its function, because such repetitions cannot be simply attributed to a chance. In order to fully explore the functional units in Citrobacter Freundii beta-lactamase, it may need to analyse all the amino acid pairs, triplets, etc. along Citrobacter Freundii beta-lactamase from one terminal to the other terminal, to count their frequencies and calculate their probabilities. The amino-acid sequence of Citrobacter Freundii beta-lactamase was counted according to two-, three- and four-amino-acid sequences. The counted frequency and probability were compared with the predicted frequency and probability. The amino acid sequences, which appear in Citrobacter Freundii beta-lactamase and can be predicted from its amino acid composition according to a purely random mechanism, should not be deliberately evolved and conserved. By contrast, the amino acid sequences, which appear in Citrobacter Freundii beta-lactamase but cannot be predicted from its amino acid composition according to a purely random mechanism, should be deliberately evolved and conversed. Accordingly 99 (26.053%) and 33 (8.684%) of 380 two-amino-acid sequences can be predicted by the frequency and probability according to a purely random mechanism. Some kinds of amino acid sequences, which absent in Citrobacter Freundii beta-lactamase and can be predicted from its amino acid composition according to a purely random mechanism, should not be deliberately excluded from Citrobacter Freundii beta-lactamase. By contrast, some kinds of amino acid sequences, which absent in Citrobacter Freundii beta-lactamase and cannot be predicted from its amino acid composition according to a purely random mechanism, should be deliberately excluded from Citrobacter Freundii beta-lactamase. Accordingly 89 (48.370%) and 41 (22.283%) of 184 kinds of absent two-amino-acid sequences can be predicted by the frequency and probability according to a purely random mechanism, and 7236 (99.848%) of 7247 kinds of absent three-amino-acid sequences can be predicted by the frequency according to a purely random mechanism. The amino acids, whose probabilities in following certain preceding amino acids can be predicted from Citrobacter Freundii beta-lactamase amino acid composition according to a purely random mechanism, should not be deliberately evolved and conversed, accordingly 2 (0.526%) of 380 counted first order Markov transition probabilities for the second amino acid in two-amino-acid sequences match the predicted conditional probabilities.

Citrobacter↗

PubMed1999

[Citrobacter freundii endocarditis].

Infection by Citrobacter appears in man only in certain circumstances, since it usually acts as contaminant or colonizer. Bacteraemia by this bacillus can affect immunodeficient people, elderly people or those patients who have undergone invasive hospital processes. Although incidence of bacteraemia is low (0.3-0.9%), the death rate is very high, about 48%. This bacillus is seldom the cause of endocarditis. That is why we describe a case of endocarditis by Citrobacter freundii, in an aged person with previous valvulopathy.

Aged↗

PubMed1999

Adult Citrobacter freundii meningitis: case report.

Citrobacter is a distinct group of Gram-negative bacilli belonging to the Enterobacteriaceae family. Central nervous system (CNS) infections due to Citrobacter are uncommon, though they occur more frequently in neonates and young children. In adults, Citrobacter meningitis is extremely unusual with only 6 cases reported in the literature before 1998. This rare CNS infection has been seen in patients with head trauma, following neurosurgical procedures, and in those who are immunocompromised. Of the patients in the 6 reported cases, only one developed multi-antibiotic resistant Citrobacter CNS infection. Adding to this small number of reported cases, we report an adult case of post-neurosurgical meningitis and subdural empyema caused by multi-antibiotic resistant Citrobacter freundii and also review the literature related to this infection. Antimicrobial therapy with imipenem and third-generation cephalosporins failed to result in cerebrospinal fluid sterilization in our patient. Because of the use of broad-spectrum antibiotics, multi-antibiotic resistant Citrobacter species have developed in this nosocomial CNS infection and now present a therapeutic challenge. Therefore, further clinical studies are needed to determine updated therapeutic modalities for treating this life-threatening infection.

Adult↗

PubMed2001

A cryptic melibiose transporter gene possessing a frameshift from Citrobacter freundii.

Wild-type Citrobacter freundii cannot grow on melibiose as a sole source of carbon. The melibiose transporter gene melB was cloned from a C. freundii mutant M4 that could utilize melibiose as a sole carbon source. Although the cloned melB gene is closely similar to the melB genes of other bacteria, it is cryptic because of a frameshift mutation. Site-directed mutagenesis was used to construct a functional melB gene by deleting one nucleotide, resulting in the production of an active melibiose transporter. The active MelB transporter could utilize Na(+) and H(+) as coupling cations to melibiose transport. The amino acid sequence of the C. freundii MelB was found to be most similar to those of Salmonella typhimurium and Escherichia coli MelB. These facts are consistent with the phylogenetic relationship of bacteria and the cation coupling properties of the melibiose transporters.

Amino Acid Sequence↗

PubMed1995

Phosphatase production and activity in Citrobacter freundii and a naturally occurring, heavy-metal-accumulating Citrobacter sp.

The ability of a naturally occurring Citrobacter sp. to accumulate cadmium has been attributed to cellular precipitation of CdHPO4, utilizing HPO4(2-) liberated via the activity of an overproduced, Cd-resistant acid-type phosphatase. Phosphatase production and heavy metal accumulation by batch cultures of this strain (N14) and a phosphatase-deficient mutant were compared with two reference strains of Citrobacter freundii. Only strain N14 expressed a high level of acid phosphatase and accumulated lanthanum and uranyl ion enzymically. Acid phosphatase is regulated via carbon-starvation; although the C. freundii strains overexpressed phosphatase activity in carbon-limiting continuous culture, this was approximately 20-fold less than the activity of strain N14 grown similarly. Citrobacter strain N14 was originally isolated from a metal-contaminated soil environment; phosphatase overproduction and metal accumulation were postulated as a detoxification mechanism. However, application of Cd-stress, and enrichment for Cd-resistant C. freundii ('training'), reduced the phosphatase activity of this organism by about 50% as compared to Cd-unstressed cultures. The acid phosphatase of C. freundii and Citrobacter N14 had a similar pattern of resistance to some diagnostic reagents. The enzyme of the latter is similar to the PhoN acid phosphatase of Salmonella typhimurium described by other workers; the results are discussed with respect to the known phosphatases of the enterobacteria.

Acid Phosphatase↗

PubMed1977

Genetics of colicin E susceptibility in citrobacter freundii.

The insensitivity of Citrobacter freundii to the E colicins is based on tolerance to colicin E1 and resistance to colicins E2 and E3. Spontaneous colicin A resistant mutants of C. freundii also lost their colicin E1 receptor function. Sensitivity to colicin E1 can be induced by F'gal+tol+ plasmids, the tol A+ gene product of which is responsible for this effect. Receptor function for colicins E2 and E3 is induced by the E. coli F'14 bfe+ plasmid, which is also able to enhance notably the receptor capacity for colicin E1. The bfe+ gene product of E. coli, which is responsible for these phenomena, also restores the receptor function for colicin A and E1 in colicin A resistant mutants of C. freundii. All results show that there is a remarkable difference between the E. coli bfe+ gene product and the bfe+ gene product of C. freundii and also between the tol A+ gene products of these strains. The sensitivity to phage BF23 parallels the sensitivity to colicins E2 and E3 and is also induced by the F'14 bfe+ plasmid.

Citrobacter↗

PubMedDate not supplied

[Conditions for the formation of molecular hydrogen by Citrobacter freundii].

Cell suspensions of Citrobacter freundii grown under anaerobic and aerobic conditions are capable of evolving molecular hydrogen. Hydrogen evolution is more active by the cells of anaerobic cultures in the exponential growth phase in the presence of reduced methylviologen or formate. The optimal temperature for hydrogen evolution from formate is about 40 degrees C, the optimal pH is 6.2 to 6.4. The presence of O2 in the gaseous phase inhibits hydrogen evolution by the cells; however the inhibition is incomplete and reversible. Nitrate also inhibits H2 formation from formate while fumarate does not inhibit the process.

Aerobiosis↗