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PubMed1993

Classification of citrobacteria by DNA hybridization: designation of Citrobacter farmeri sp. nov., Citrobacter youngae sp. nov., Citrobacter braakii sp. nov., Citrobacter werkmanii sp. nov., Citrobacter sedlakii sp. nov., and three unnamed Citrobacter genomospecies.

DNA relatedness studies (hydroxyapatite method) were done on 112 strains of citrobacteria. By using the recommended definition of a genomospecies 11 genomospecies were identified in the genus Citrobacter. These genomospecies were separable by their biochemical profiles. Citrobacter koseri (Citrobacter diversus) and Citrobacter amalonaticus proved to be homogeneous species, as previously described. C. amalonaticus biogroup 1, as described by Farmer et al. (J. Clin. Microbiol. 21:46-76, 1985), was shown to be a separate homogeneous species, which was named Citrobacter farmeri sp. nov. The Citrobacter freundii complex was quite heterogeneous. C. freundii sensu stricto, as represented by the type strain, contained only 9 of 66 strains in this complex. The remaining 57 strains were members of seven genomospecies. Genomospecies 5, containing 21 strains, was named Citrobacter youngae sp. nov. Genomospecies 6, containing 15 strains, was named Citrobacter braakii sp. nov. Genomospecies 7 and 8, each containing six strains, were named Citrobacter werkmanii sp. nov. and Citrobacter sedlakii sp. nov., respectively. Genomospecies 9, 10, and 11, each containing three strains, were not named.

Animals↗

PubMed1999

Biochemical identification of Citrobacter species defined by DNA hybridization and description of Citrobacter gillenii sp. nov. (formerly Citrobacter genomospecies 10) and Citrobacter murliniae sp. nov. (formerly Citrobacter genomospecies 11).

Recent work describing six named species and two unnamed genomospecies within Citrobacter has enlarged the genus to 11 species. DNA relatedness and phenotypic tests were used to determine how well these species can be identified. One hundred thirty-six strains were identified to species level by DNA relatedness and then identified phenotypically in a blinded fashion. By using conventional tests, 119 of the 136 strains (88%) were correctly identified to species level. Three additional strains (2%) were identified as citrobacteria but were not identified to species level, and 14 strains (10%) were misidentified as other Citrobacter species. Carbon source utilization tests were used to identify 86 of the strains. Eighty-four strains (98%) were correctly identified, and two strains (2%) were misidentified as other Citrobacter species. Additional strains of Citrobacter genomospecies 10 and Citrobacter genomospecies 11 were identified, allowing these species to be formally named as Citrobacter gillenii sp. nov. and Citrobacter murliniae sp. nov., respectively.

Citrobacter↗

PubMed2002

Cloning and sequencing of the beta-lactamase gene and surrounding DNA sequences of Citrobacter braakii, Citrobacter murliniae, Citrobacter werkmanii, Escherichia fergusonii and Enterobacter cancerogenus.

To further identify the origins of plasmid-mediated cephalosporinases that are currently spreading worldwide, the chromosomal beta-lactamase genes of Citrobacter braakii, Citrobacter murliniae, Citrobacter werkmanii reference strains and of Escherichia fergusonii and Enterobacter cancerogenus clinical isolates were cloned and expressed into Escherichia coli and sequenced. These beta-lactamases had all a single pI value >8 and conferred a typical AmpC-type resistance pattern in E. coli recombinant strains. The cloned inserts obtained from genomic DNAs of each strain encoded Ambler class C beta-lactamases. The AmpC-type enzymes of C. murliniae, C. braakii and C. werkmanii shared 99%, 96% and 95% amino acid sequence identity, respectively, with chromosomal AmpC beta-lactamases from Citrobacter freundii. The AmpC-type enzyme of E. cancerogenus shared 85% amino acid sequence identity with the chromosomal AmpC beta-lactamase of Enterobacter cloacae OUDhyp and the AmpC-type enzyme of E. fergusonii shared 96% amino acid sequence identity with that of E. coli K12. The ampC genes, except for E. fergusonii, were associated with genes homologous to regulatory ampR genes of other chromosomal class C beta-lactamases that explain inducibility of beta-lactamase expression in these strains. This work provides further evidence of the molecular heterogeneity of class C beta-lactamases.

Amino Acid Sequence↗

PubMed1985

Bacteremias due to Citrobacter diversus and Citrobacter freundii. Incidence, risk factors, and clinical outcome.

From 1974 to 1982, 38 patients developed Citrobacter bacteremia at two adult community-teaching hospitals in the Detroit Medical Center (incidence, 1.2 cases per 10,000 discharges). Citrobacter accounted for 0.7% of all bacteremias during the study period. Of 31 cases reviewed, Citrobacter bacteremia frequently developed in elderly patients (65%) and was hospital acquired (77%). Initial sites of infection included the urinary tract (39%), gastrointestinal tract (27%), wound (10%), and unknown (13%). More bacteremias caused by Citrobacter diversus tended to arise from the urinary tract, while patients with Citrobacter freundii bacteremia had significantly more gallbladder disease. Patients with Citrobacter bacteremia were more likely than patients with Escherichia coli bacteremia to have had additional pathogens in the bloodstream, to develop bacteremia in the hospital, and to have undergone invasive procedures contributing to infection. Significant differences were not observed in demographic, host, or other epidemiologic or clinical factors examined. Of patients with Citrobacter bacteremia, 48% died.

Anti-Bacterial Agents↗

PubMed2004

Citrobacter koseri and Citrobacter amalonaticus isolates carry highly divergent beta-lactamase genes despite having high levels of biochemical similarity and 16S rRNA sequence homology.

OBJECTIVES: Isolates previously identified as Citrobacter diversus are now known as Citrobacter koseri. We measured sequence variation at the beta-lactamase structural gene among a group of clinical isolates originally identified as C. diversus by API 20E profiling. METHODS: beta-Lactamase and 16S rRNA genes were amplified by PCR and sequenced by standard methods. beta-Lactamase induction was attempted in liquid-grown cultures using cefoxitin. Nitrocefin hydrolysis assays were performed using a spectrophotometer. RESULTS: Analysis of 16S rRNA gene sequences showed that Citrobacter spp. isolates with an inducible beta-lactamase gene, cdiA, closely related to 'C. koseri ' NF85 and ULA27 are actually Citrobacter amalonaticus. C. koseri isolates, whose identities were confirmed by 16S rRNA sequencing, produce a class A beta-lactamase, Cko, constitutively at low levels. The cko and cdiA beta-lactamase genes share <45% identity. CONCLUSIONS: We have confirmed that cko is a beta-lactamase gene carried by C. koseri, and that isolates previously identified as 'C. koseri ', but carrying the cdiA beta-lactamase gene are C. amalonaticus. Thus, beta-lactamase-gene-specific PCR may provide a valuable tool to differentiate these biochemically homogeneous Citrobacter species.

Cefoxitin↗

PubMed2004

Role of Citrobacter amalonaticus and Citrobacter farmeri in dissimilatory perchlorate reduction.

The article deals with the novel physiological function of dissimilatory perchlorate reduction by strains JB101 and JB109 isolated from a laboratory-enriched mixed consortium originating from a sewage treatment facility. The biochemical and physiological data of the strains showed good correspondence with members of the family Enterobacteriaceae. The partial 16S rDNA sequence of the strains JB101 and JB109 had similarity of 99.8% to Citrobacter amalonaticus and 98% to Citrobacter farmeri, respectively. The results inferred the possibility of Citrobacter spp. to form an important group of dissimilatory perchlorate reducers among the gamma subclass of Proteobacteria, since the majority of the perchlorate reducers belong to two monophyletic groups, Dechloromonas and Dechlorosoma in beta subclass. The perchlorate-grown Citrobacter strains preferred perchlorate to nitrate as an electron acceptor unlike most of the reported dissimilatory perchlorate reducers.

Base 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↗

PubMed2001

Novel class A beta-lactamase Sed-1 from Citrobacter sedlakii: genetic diversity of beta-lactamases within the Citrobacter genus.

Citrobacter sedlakii 2596, a clinical strain resistant to aminopenicillins, carboxypenicillins, and early cephalosporins such as cephalothin, but remaining susceptible to acylureidopenicillins, carbapenems, and later cephalosporins such as cefotaxime, was isolated from the bile of a patient treated with beta-lactam and quinolone antibiotics. The isolate produced an inducible class A beta-lactamase of pI 8.6, named Sed-1, which was purified. Characterized by a molecular mass of 30 kDa, Sed-1 preferentially hydrolyzed benzylpenicillin, cephalothin, and cloxacillin. The corresponding gene, bla(Sed-1), was cloned and sequenced. Its deduced amino acid sequence shared more than 60% identity with the chromosome-encoded beta-lactamases from Citrobacter koseri (formerly C. diversus) (84%), Klebsiella oxytoca (74%), Serratia fonticola (67%), and Proteus vulgaris (63%) and 71% identity with the plasmid-mediated enzyme MEN-1. A gene coding for a LysR transcriptional regulator was found upstream from bla(Sed-1). This regulator, named SedR, displayed 90% identity with the AmpR sequence of the chromosomal beta-lactamase from C. koseri and 63 and 50% identity with the AmpR sequences of P. vulgaris and Enterobacter cloacae, respectively. By using DNA-DNA hybridization, a bla(Sed-1)-like gene was identified in two reference strains, C. sedlakii (CIP-105037) and Citrobacter rodentium (CIP-104675), but not in the 18 strains of C. koseri studied. Two DNA fragments were amplified and sequenced from the reference strains of C. sedlakii CIP-105037 and C. rodentium CIP-104675 using two primers specific for bla(Sed-1). They shared 98 and 80% identity with bla(Sed-1), respectively, confirming the diversity of the chromosomally encoded class A beta-lactamases found in Citrobacter.

Amino Acid Sequence↗

PubMed1978

[Flagellar antigens of E. coli serologically interrlelated to H40, 41 and H41, 42, 43 flagellar antigens of Citrobacter. New H-antigeny E. coli i Citrobacter].

The authors confirmed the reference of the test strains H13 (P6c) and H22 (A231a) of the international collection of E. coli to Citrobacter; their antigenic formula was established. As shown, strains P6c possessed a variety of the H-antigen which was not described in Citrobacter earlier, designated as H41a, 97. Three types of flagellar antigens characterized by the presence of an interrelationship with the partial factor H41 of the flagellar Citrobacter antigens were revealed in E. coli; the partial composition of H-antigenic components common for E. coli and Citrobacter was studied. Two of three new varieties of the E. coli H-antigen revealed was characterized by a cross correlation and a relation to the standard H19 E. coli antigen. The strain with the third variety of the H-antigen was capable of forming the H-antigenic mutants which acquired the antigenic component identical to the standard H16 E. coli antigen. E. coli strain is recommended for the replacement of the strain P6c in the International collection of E. coli.

Agglutinins↗

PubMed2000

Outbreak of nosocomial infections due to extended-spectrum beta-lactamase-producing strains of enteric group 137, a new member of the family Enterobacteriaceae closely related to Citrobacter farmeri and Citrobacter amalonaticus.

A member of the Enterobacteriaceae initially identified as Kluyvera cryocrescens by the MicroScan Gram-Negative Combo 13 panel caused an outbreak of nosocomial infections in four patients (pneumonia, n = 2; urinary tract infection, n = 1; wound infection, n = 1) and urinary tract colonization in one patient. When the strains were tested by the Enteric Reference Laboratory of the Centers for Disease Control and Prevention, biochemical results were most compatible with Yersinia intermedia, Kluyvera cryocrescens, and Citrobacter farmeri but identification scores were low and test results were discrepant. However, when the biochemical test profile was placed in the computer database as a new organism, all strains were identified as the organism with high identification scores (0. 999968 to 0.999997) and no discrepant test results. By 16S rRNA sequence analysis the organism clustered most closely with, but was distinct from, Citrobacter farmeri and Citrobacter amalonaticus. Based on its unique biochemical profile and rRNA sequence, this organism is designated Enteric Group 137. Restriction endonuclease analysis and taxonomic antibiograms of strains causing the outbreak demonstrated a single clone of Enteric Group 137, and antibiotic susceptibility testing revealed the presence of extended-spectrum beta-lactamase (ESBL) resistance. Enteric Group 137 appears to be a new opportunistic pathogen that can serve as a source of ESBL resistance in the hospital.

Aged↗

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↗

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↗

PubMed1975

Citrobacter koseri. I. An extended antigenic scheme for Citrobacter koser (syn. C. diversus, Levinea malonatica).

The names Citrobacter koseri, Levinea malonatica and Citrobacter diversus are synonymous. As a result of the study of representative strains of these organisms an antigenic scheme comprising seven O antigens has been proposed. The examination of a further 165 strains from clinical sources suggests that an additional seven antigens should be included in the scheme. The serological and biochemical reactions of the test strains for all 14 O antigens are described.

Agglutination Tests↗

PubMed1978

Citrobacter O-antigens: structure of the O-antigenic polysaccharide from Citrobacter sp. 396.

The structure of the O-specific polysaccharide moiety of the lipopolysaccharide from Citrobacter 396 was elucidated by composition, methylation, and periodate oxidation studies. The repeating unit consists of four 2-linked mannoses and one 3-linked N-acetylglucosamine. One of the mannose units is substituted at C3 with alpha-glucose, and one is substituted at C3 with alpha-(2-O-acetyl)-abequose. All the mannosyl linkages appear to have the beta-configuration; the N-acetylglucosaminyl linkage has the alpha-configuration. In bacterial agglutination and passive hemagglutination in some Salmonella antisera, Citrobacter 396 as well as its O-antigenic lipopolysaccharide expressed the serological factors 5 and 6. In corroboration of our structural studies, this showed the presence of alpha-(2-O-acetyl)-abequosyl-1,3-mannose (factor 5) and alpha-glucosyl-1,3-mannose (factor 6).

Antigens, Bacterial↗

PubMed1992

[Spondylitis due to Citrobacter diversus. Case report and review of Citrobacter diversus infections].

Citrobacter diversus (C.d.) is an unusual human pathogen. Its pathogenic potency is small or nil, and in most cases it is isolated in combination with other organisms. Most isolates are of indeterminate clinical significance. Occasionally C.d. may cause opportunistic infections, especially in subjects with primary or secondary conditions of poor host defense, immunosuppressed patients or neonates. We report a case of C.d. vertebral osteomyelitis following C.d. pneumonia. The osteomyelitis was cured by surgery and chemotherapy. This case is interesting since it involves an otherwise healthy subject with no underlying disease. C.d. was isolated in blood during the episode of pneumonia and in bone four weeks later. No other case of Citrobacter diversus vertebral osteomyelitis has hitherto been described.

Aged↗

PubMed1995

Inducible expression of the chromosomal cdiA from Citrobacter diversus NF85, encoding an ambler class A beta-lactamase, is under similar genetic control to the chromosomal ampC, encoding an ambler class C enzyme, from Citrobacter freundii OS60.

This study aimed to characterize the molecular basis of beta-lactamase induction in Citrobacter diversus. The chromosomal beta-lactamase encoding region from C. diversus, strain NF85, was cloned and expressed in Escherichia coli. The cloned region was sequenced and open-reading frames encoding a class A beta-lactamase, designated cdiA, and a putative LysR-type transcriptional regulator protein, divergently transcribed from the beta-lactamase gene and designated cdiR, were identified. The nucleotide sequence of the NF85 cdiA was identical to that of the published C. diversus ULA27 ampC sequence. A putative helix-turn-helix DNA-binding motif was located at the N-terminus of CdiR, and homology with enterobacterial AmpR proteins was noted. CdiR was demonstrated to bind to the C. diversus cdiAR intergenic region but not to the C. freundii ampCR intergenic region. A putative CdiR binding motif was identified in the cdiAR intergenic region. The cloned cdiAR region was inducible in E. coli strains SNO3 and HfrH. The inducible phenotype was dependent on the E. coli ampD and ampG gene products. We conclude that the molecular basis of inducible cdiA expression in C. diversus is similar to that of C. freundii ampC.

Amino Acid Sequence↗

PubMed1975

Citrobacter koseri. II. Serological and biochemical examination of Citrobacter koseri strains from clinical specimens.

165 strains of Citrobacter koseri isolated from clinical specimens were studied and their biochemical reactions determined. They were examined serologically by means of a scheme consisting of 14 O antigens. The sources of the clinical specimens were tabulated and the epidemiological information was summarized. The clinical significance of these findings is discussed.

Antigens, Bacterial↗

PubMed2005

Concurrent infection with an intestinal helminth parasite impairs host resistance to enteric Citrobacter rodentium and enhances Citrobacter-induced colitis in mice.

Infections with intestinal helminth and bacterial pathogens, such as enteropathogenic Escherichia coli, continue to be a major global health threat for children. To test the hypothesis that intestinal helminth infection may be a risk factor for enteric bacterial infection, a murine model was established by using the intestinal helminth Heligomosomoides polygyrus. To analyze the modulatory effect of a Th2-inducing helminth on the outcome of enteric bacterium Citrobacter rodentium infection, BALB/c and STAT 6 knockout (KO) mice were infected with H. polygyrus, C. rodentium, or both. We found that only BALB/c mice coinfected with H. polygyrus and C. rodentium displayed a marked morbidity and mortality. The enhanced susceptibility to C. rodentium and intestinal injury of coinfected BALB/c mice were shown to be associated with a significant increase in helminth-driven Th2 responses, mucosally and systemically, and correlated with a significant downregulation of protective gamma interferon and with a dramatic upregulation of the proinflammatory tumor necrosis factor alpha response. In addition, C. rodentium-associated colonic pathology in coinfected BALB/c mice was significantly enhanced, whereas bacterial burden was increased and clearance was delayed. In contrast, coinfection in STAT 6 KO mice failed to promote C. rodentium infection or to induce a more severe intestinal inflammation and tissue injury, demonstrating a mechanism by which helminth influences the development of host protective immunity and susceptibility to bacterial infections. We conclude that H. polygyrus coinfection can promote C. rodentium-associated disease and colitis through a STAT 6-mediated immune mechanism.

Animals↗