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An antigenic scheme, based on the determination of 17 somatic and 9 flagellar antigens, is proposed for Citrobacter koseri. Seven of the flagellar antigens constituted the specific phase (a through g), and the others (1 and 2) were nonspecific. Of the 238 theoretically possible serotypes, 48 were identified among 680 cultures examined.
Investigations of nursery outbreaks of Citrobacter diversus sepsis and meningitis have been hampered by lack of adequate epidemiologic markers for the organism. We studied outer membrane protein profiles from clinical isolates of C. diversus by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to determine whether this method might be useful in the epidemiologic differentiation of strains. Paired cerebrospinal fluid isolates from each of three separate nursery outbreaks of C. diversus meningitis, paired isolates from the vagina of a postpartum woman and the cerebrospinal fluid of her newborn infant, one isolate from an infant with pneumonia and two from colonized nursery cohorts, and 30 epidemiologically unrelated clinical isolates were included. Eleven distinct profiles were differentiated by the presence or absence of five outer membrane proteins. Complete concordance of profiles was observed for epidemiologically related isolates. Unrelated epidemic strains had outer membrane protein profiles distinct from one another. Biotyping complemented determination of outer membrane protein profiles; the two markers differentiated each of the five epidemic strains from all but one of 30 unrelated nonepidemic isolates. Determination of outer membrane protein profiles is potentially useful in epidemiologic investigations of disease caused by C. diversus.
Genetic diversity and relationships among 42 strains of Citrobacter diversus recovered from the cerebrospinal fluid of human infants with meningitis and from other clinical sources in the United States were estimated on the basis of electrophoretically detectable allelic variation in 20 genes encoding metabolic enzymes. Sixteen distinctive multilocus enzyme genotypes were identified, among which the mean genetic diversity per locus was 0.244. The recovery of isolates of the same genotype in several regions of the United States and over periods as long as 20 years indicates that the population structure of C. diversus is clonal. There was little association between multilocus enzyme genotype and biotype, piliation, or presence of a 32-kilodalton outer membrane protein. The observation that the 32-kilodalton outer membrane protein, which is expressed predominantly by strains recovered from infants with meningitis, occurs in a variety of genotypically diverse clones belonging to several phylogenetic lineages supports the hypothesis that this protein confers virulence.
We describe the first case in which a diagnostic rise in titers of antibody to formalinized Legionella pneumophila serogroup 1 yolk sac antigen was shown to be caused by a cross-reaction between L. pneumophila and another organism, Citrobacter freundii.
Forty-seven strains of Citrobacter diversus were isolated during a 12-month period from clinical material obtained from patients in a general hospital in Israel. The majority of cultures (38) were recovered from urine and wound discharges. There was one case of septicemia. The biochemical reactions of all cultures were typical for this species, except one that was anaerogenic, and they could be divided into five biotypes (a through e). Thirty-nine strains were identified serologically and found to belong to one of seven O groups described by Gross and Rowe (1974). All cultures were sensitive to tetracycline and nalidixic acid. All strains were resistant to carbenicillin and ampicillin and produced beta-lactamase.
Oligonucleotide probes which match consensus sequences of the repetitive extragenic palindromic (REP) element hybridize to genomic DNA of diverse bacterial species. Primers based on the REP sequence generate complex band patterns with genomic DNA in the polymerase chain reaction (PCR), a technique named REP-PCR. We used REP-PCR with genomic DNA to fingerprint 47 isolates of Citrobacter diversus. Previously, 37 were assigned electrophoretic types (ETs) by multilocus enzyme electrophoresis and 35 were evaluated by using outer membrane protein profiles. Fingerprints were compared by visual inspection and by similarity coefficients (SimCs) based on the number of common bands versus total bands between two given isolates. DNA fingerprints were highly similar visually for patient pairs and outbreak-related sets. SimCs for these were > or = 0.952. Fingerprints of isolates with different ETs generally were distinctive. Among 21 unrelated isolates representing 15 ETs, only 6 of 210 comparisons had SimCs of > or = 0.952. REP-PCR rapidly generated DNA fingerprints which were highly similar for epidemiologically linked isolates of C. diversus and distinct for previously characterized strains within this species. The ability of this method to discriminate between C. diversus isolates with the same biotype was similar to that of multilocus enzyme electrophoresis and outer membrane protein profiles. REP-PCR may be useful in evaluation of apparent outbreaks of this or other bacterial species which possess these extragenic, repetitive elements.
A series of bacteriophages specific for Escherichia coli (E-1, E-2, E-3, and E-4), Citrobacter freundii (phi I, phi II, and phi III), Enterobacter cloacae (Ent), and Shigella spp. (Sh) have been isolated from hospital sewage. These bacteriophages, in combination with Felix Salmonella phage O-I, were used as a diagnostic phage typing set which included seven phage preparations: O-I, C (phi I and phi III), Sh, E (E-1 and E-2), CE (phi II and E-3), E-4, and Ent. After 20,280 cultures of 27 species and 9 biogroups of 15 genera of the family Enterobacteriaceae and 276 cultures of 8 species of 6 genera outside the Enterobacteriaceae were tested, it was shown that most strains of salmonellae, E. coli, C. freundii, and E. cloacae can be identified accurately. The sensitivities of identification were 83.6% for E. cloacae, 88.8% for C. freundii, 90.3% for E. coli, and 95.76% for salmonellae. The specificities were 99.78% for salmonellae, 99.84% for E. cloacae, 99.89% for E. coli, and 99.97% for C. freundii. The results of bacteriophage lytic patterns were highly correlated with Shigella serotypes. Therefore, such a phage typing set may be used routinely in public hygiene and clinical laboratories.
A biochemically typical strain of Citrobacter freundii which carries the Escherichia coli O157 antigen is described. The significance of differentiating such strains from typical E. coli O157 strains is stressed.
Citrobacter sedlakii was isolated from blood and cerebrospinal fluid cultures of a 5-day-old premature infant with sepsis, meningitis, and brain abscess. This newly described organism was difficult to identify due to discrepancies between the Vitek and API 20E identification systems. To our knowledge, this is the first report of the isolation of C. sedlakii from cerebrospinal fluid.
A case of sepsis in a pediatric patient due to the newly described Citrobacter species C. farmeri is described. Factors predisposing this child to infection included short-bowel syndrome requiring total parenteral nutrition.
A nonpathogenic strain of Citrobacter sedlakii which expresses the Escherichia coli O157 antigen is described. The discovery of this strain emphasizes the necessity of additional biochemical and/or toxigenicity testing when isolates react with E. coli O157 latex reagents.
The phylogenetic relationships of Enterobacter sakazakii strains were investigated using 16S ribosomal DNA (rDNA) and hsp60 sequencing. Each analysis distributed E. sakazakii strains among four clusters, indicating substantial taxonomic heterogeneity. The E. sakazakii type strain 16S rDNA sequence was 97.8% similar to that of Citrobacter koseri but 97.0% similar to that of Enterobacter cloacae.
Two-hundred consecutive, single patient isolates of Enterobacter spp., Serratia spp., Citrobacter spp., and Pseudomonas aeruginosa were evaluated for AmpC production using a variety of inducer-substrate antibiotic combinations in a disk approximation format. The combinations examined included cefoxitin-piperacillin, imipenem-cefotaxime, imipenem-ceftazidime, imipenem-piperacillin-tazobactam, and imipenem-cefoxitin. All isolates were also screened for the presence of extended-spectrum beta-lactamase (ESBL) activity. In total, 85.5% of isolates were shown to be inducible for the production of AmpC by one or more inducer/substrate combinations and 11% of all isolates were stably derepressed for the expression of AmpC. Of all of the combinations, imipenem/piperacillin-tazobactam provided the greatest sensitivity (97.1%). All combinations were 100% specific when a positive test was observed. Given this background among these organisms in our institution, it is reasonable to develop an antibiotic reporting strategy that favors the selection of agents for therapy of these organisms that do not serve as labile substrates of AmpC.
The resistance mechanism of extended-spectrum cephalosporins in clinical isolates of Citrobacter freundii, Enterobacter spp., and Serratia marcescens was studied. Of 152 isolates, 45 isolates (29.6%) were derepressed AmpC mutants and 39 isolates (25.7%) produced extended-spectrum beta-lactamase (ESBLs). The most prevalent ESBLs were CTX-M enzymes, followed by TEM-52 and SHV-12.
It is shown for the first time for the Enterobacteriaceae family that a gene encoding L-methionine gamma-lyase (MGL) is present in the genome of Citrobacter freundii. Homogeneous enzyme has been purified from C. freundii cells and its N-terminal sequence has been determined. The hybrid plasmid pUCmgl obtained from the C. freundii genomic library contains an EcoRI insert of about 3000 bp, which ensures the appearance of MGL activity when expressed in Escherichia coli TG1 cells. The nucleotide sequence of the EcoRI fragment contains two open reading frames. The first frame (the megL gene) encodes a protein of 398 amino acid residues that has sequence homology with MGLs from different sources. The second frame encodes a protein with sequence homology with proteins belonging to the family of permeases. To overexpress the megL gene it was cloned into pET-15b vector. Recombinant enzyme has been purified and its kinetic parameters have been determined. It is demonstrated that a presence of a hybrid plasmid pUCmgl, containing the megL gene in the E. coli K12 cells, leads to a decrease in efficiency of EcoKI-restriction. It seems likely that decomposition of L-methionine under the action of MGL leads to a decrease in the intracellular content of S-adenosylmethionine. Expression of the megL gene in the C. freundii genome occurs only upon induction by a significant amount of L-methionine.
An outbreak of meningitis due to Citrobacter koseri in a special care baby unit is described. The organism showed a high capacity for spread among the babies on the unit and although the intestinal carriage rate was high, the clinical case:carrier ratio was low.
Non-motile, Gram-negative rods, isolated from the intestinal tract and kidney of several dead animals in a gerbil colony, were identified as Citrobacter rodentium (formerly included in C. freundii species) on the basis of 31 biochemical tests. The isolates were tested against 40 antimicrobial agents and were all susceptible to ticarcillin plus clavulanate, ceftazidime and most of the quinolones studied, but were all resistant to most of the penicillins and aminoglycosides tested, and to fosfomycin, metronidazole and tiamulin. This bacterial species has been primarily associated with transmissible murine colonic hyperplasia, and this appears to be the first report of an epidemic infection in a gerbil colony with a fatal outcome in most of the animals affected.
Analysis of gases evolved when Citrobacter intermedius and a Pseudomonas species are co-cultured on an acetate or glucose - nitrate - mineral salts medium indicates that acetate is anaerobically oxidized by CO2.