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PubMed1988

Induction of chromosomal beta-lactamases by different concentrations of clavulanic acid in combination with ticarcillin.

The effect of different concentrations of clavulanic acid (CA) in combination with ticarcillin on beta-lactamase production and ticarcillin MIC was studied in four clinical isolates of Pseudomonas aeruginosa, Enterobacter cloacae, Serratia marcescens, Citrobacter freundii and indole positive Proteus strains. Ticarcillin alone showed a low inducing effect for all species tested, Ser. marcescens excepted. The increase in beta-lactamase activity after addition of CA (2-10 mg/l) was strain and species dependent. No synergy or antagonism was observed on the ticarcillin MIC for the micro-organisms producing only a chromosomally mediated beta-lactamase, though the susceptibility to ticarcillin strongly increased if the strains also produced a plasmid-mediated beta-lactamase. Addition of 50 or 100 mg/l CA resulted in all strains. C. freundii excepted, in a strong increase in beta-lactamase activity and in a strong synergistic effect on the ticarcillin MIC. However, these concentrations are unlikely to be achieved at clinical doses. Thus, irrespective of the inducing effect of ticarcillin and CA (2-10 mg/l) combinations, induction of the chromosomal beta-lactamase did not result in a decrease in ticarcillin susceptibility.

Bacteria↗
PubMed1992

Development of resistance during ceftazidime and cefepime therapy in a murine peritonitis model.

Resistance emerging after ceftazidime or cefepime therapy was investigated in a peritonitis model. Mice were given a peritoneal challenge (10(8) cfu plus talcum) and treated by either antibiotic (50 mg/kg/dose, which produced similar antibiotic concentrations in peritoneal fluid in both cases). After one or three doses, resistance never developed in Serratia marcescens or Citrobacter freundii infections. After Enterobacter cloacae and Pseudomonas aeruginosa challenge, ceftazidime selected more resistance (21/36 cases) than did cefepime (1/36 cases). In mice challenged with resistant strains selected by ceftazidime therapy, cefepime (six doses) successfully treated 7/18 E. cloacae infections but 0/18 P. aeruginosa infections; ceftazidime was never effective. Neither cefepime nor ceftazidime cured mice infected with the resistant strain selected by cefepime. MICs were poor predictors of further emergence of resistance in mice inoculated with strains classified as susceptible, but antibiotic-containing agar gradients plated with a high inoculum (10(8) cfu) allowed better prediction. In selected clinical situations, cefepime may be preferable because it may be associated with less frequent emergence of resistance.

Animals↗
PubMed1994

Production of a plasmid mediated AmpC-like beta-lactamase by a Klebsiella pneumoniae septicaemia isolate.

A septicaemia Klebsiella pneumoniae isolate from Greece (Ath1) was shown to be resistant to third generation cephalosporins, aztreonam and cefoxitin and this resistance was not decreased in the presence of clavulanic acid. The gene coding for the resistance phenotype, associated with a beta-lactamase showing cephalosporinase activity and a pI of 8.6, could be transferred into Escherichia coli K-12 by conjugation and transformation. DNA-hybridisation showed that this gene was located on two different plasmids, 7.8 and 80 kb respectively. The larger, conjugative plasmid also carried genes coding for another beta-lactamase (pI 6.6) and resistance to aminoglycosides, tetracycline, chloramphenicol and trimethoprim. Under highly stringent conditions the gene coding for the pI 8.6 beta-lactamase hybridised with chromosomal DNA from Citrobacter freundii OS60 but not from E. coli or Enterobacter cloacae. Furthermore, the restriction map of this beta-lactamase gene corresponded to that of ampC from C. freundii OS60. The regulatory ampR gene could not be detected in the plasmid DNA from the Ath1 K. pneumoniae by DNA hybridisation. The relationship between a plasmid-mediated extended spectrum beta-lactamase in a K. pneumoniae septicaemia isolate and chromosomal AmpC beta-lactamase from C. freundii was demonstrated.

Citrobacter freundii↗
PubMed2003

SHV-34: an extended-spectrum beta-lactamase encoded by an epidemic plasmid.

OBJECTIVES: To elucidate the causes for treatment failure in children given extended-spectrum cephalosporins. METHODS: During April 1998-March 2000, 18 isolates of members of the family Enterobacteriaceae, fulfilling microbiological criteria for carriage of extended-spectrum beta-lactamases (ESBLs) and carrying blaSHV, were isolated from paediatric inpatients. The collection was subjected to a retrospective molecular analysis. RESULTS: Three species were represented in the collection: Citrobacter koseri (one isolate), Escherichia coli (one isolate) and Klebsiella pneumoniae (16 isolates). A common plasmid was found in these bacteria, as judged by restriction endonuclease digestion. This was able to transfer an ESBL phenotype from donors to a laboratory strain of E. coli. Nucleotide sequence analysis revealed that this phenotype was associated with a new variant in blaSHV encoding SHV-34. CONCLUSIONS: Analysis reveals the presence of an epidemic plasmid in this collection of bacteria. This carries a gene encoding the SHV-34 ESBL, described for the first time in this report. Nucleotide sequence analysis shows that there is a mutation from A-->G affecting the codon at amino acid position 64 (GAA-->GGA), changing the glutamic acid typically seen in this position to glycine.

Amino Acid Substitution↗
PubMed2006

The presence of a conjugative Gram-positive Tn2009 in Gram-negative commensal bacteria.

OBJECTIVES: To determine whether mef(A)-msr(D) and tet(M) genes are linked in representative Gram-negative isolates and/or transferred together during conjugation. To molecularly characterize the Acinetobacter junii element and compare the structure and sequence with the non-conjugative Streptococcus pneumoniae Tn2009 element. METHODS: PCR assays, DNA-DNA hybridization and sequencing of PCR products were used. Nucleotide sequences were determined at the integration site of the mef(A) element into Tn916 and upstream and downstream flanking regions of the element. RESULTS: A total of 10 mef(A)-msr(D)- and tet(M)-positive isolates carried conjugative element(s). The A. junii Tn2009 element was indistinguishable from S. pneumoniae Tn2009. The region upstream of the A. junii Tn2009 contained an orf that was 89-91% identical to an S. pneumoniae spr1206 gene found upstream of the streptococcal Tn2009. In the A. junii, the spr1206 gene was separated by 67 bp from the end of the Tn2009, while 29 bp were found separating spr1206 from the streptococcal Tn2009. The 1201 bp downstream A. junii sequences included 913 unique sequences. CONCLUSIONS: A total of 10 different Gram-negative genera were found to carry the tet(M) genes, including the first description in three genera (Citrobacter, Proteus and Stenotrophomonas). All isolates were able to transfer the genes into > or =1 recipient with macrolide selection. Over 3000 bp were sequenced on each side of the insertion mef junction region in the A. junii and were indistinguishable from the streptococcal Tn2009. The A. junii Tn2009 element was flanked by an S. pneumoniae gene upstream and a unique sequence downstream, suggesting that the A. junii Tn2009 could be part of a larger element.

Acinetobacter↗
PubMed1975

Tryptophanase of fecal flora as a possible factor in the etiology of colon cancer.

Twenty-three strains of intestinal anaerobes obtained from two laboratories were examined for indole production from tryptophan. Among the 23 isolates tested, three of Bacteroides fragilis thetaiotaomicron and one Citrobacter sp. were indole positive. The tryptophanase of the indole-positive strains of intestinal anaerobes was inducible by tryptophan and was susceptible to glucose repression. The products of tryptophanase activity were formed in stoichiometric amounts by dialyzed, freshly prepared extracts. The tryptophan concentration and tryptophanase activity in feces from rats on an all-meat diet were significantly higher than those in feces from rats on a normal diet. The results indicated that the higher tryptophanase activity in the feces of rats fed an all-meat diet is due to the inducibility of this enzyme by tryptophan and is not due to any inhibitor in the feces of rats on a normal diet. The results also suggested that a population with a diet rich in meat has a greater chance for exposure to possible carcinogens such as indole and other tryptophan metabolites. This agrees with the hypothesis, based on epidemiologic data, that a high intake of meat may be related to the development of colon cancer in man.

Bacteroides↗
PubMed1989

Sequence motifs characteristic of DNA[cytosine-N4]methyltransferases: similarity to adenine and cytosine-C5 DNA-methylases.

The sequences coding for DNA[cytosine-N4]methyltransferases MvaI (from Micrococcus varians RFL19) and Cfr9I (from Citrobacter freundii RFL9) have been determined. The predicted methylases are proteins of 454 and 300 amino acids, respectively. Primary structure comparison of M.Cfr9I and another m4C-forming methylase, M.Pvu II, revealed extended regions of homology. The sequence comparison of the three DNA[cytosine-N4]-methylases using originally developed software revealed two conserved patterns, DPF-GSGT and TSPPY, which were found similar also to those of adenine and DNA[cytosine-C5]-methylases. These data provided a basis for global alignment and classification of DNA-methylase sequences. Structural considerations led us to suggest that the first region could be the binding site of AdoMet, while the second is thought to be directly involved in the modification of the exocyclic amino group.

Amino Acid Sequence↗
PubMed2000

DNA methylation at the CfrBI site is involved in expression control in the CfrBI restriction-modification system.

We have previously found that genes of the CFR:BI restriction-modification (R-M) system from Citrobacter freundii are oriented divergently and that their promoter regions overlap. The overlapping promoters suggest regulation of gene expression at the transcriptional level. In this study the transcription regulation of CFR:BI R-M genes was analyzed in vivo and in vitro in Escherichia coli. It was shown that in the presence of CFR:BI methyltransferase (M.CFR:BI), cell galactokinase activity decreases 10-fold when the galactokinase gene (galK) is under the control of the cfrBIM promoter and increases 20-fold when galK is under the control of the cfrBIR promoter. The CFR:BI site, proven to be unique for the entire CFR:BI R-M gene sequence, is located in the -35 cfrBIM promoter region and is in close vicinity of the -10 cfrBIR promoter region. A comparison of the cfrBIM and the cfrBIR promoter activities in the in vitro transcription system using methylated and unmethylated DNA fragments as templates demonstrated that the efficiency of CFR:BI R-M gene transcription is regulated by enzymatic modification at the N-4-position of cytosine bases of the CFR:BI site by M.CFR:BI. From the results of the in vivo and in vitro experiments we suggest a new model of gene expression regulation in type II R-M systems.

Base Sequence↗
PubMed1991

Temporal and topological clustering of diverged residues among enterobacterial dihydrofolate reductases.

The complete nucleotide and encoded amino acid sequences were determined for the dihydrofolate reductase (DHFR) from the bacteria Enterobacter aerogenes and Citrobacter freundii. These were compared with the closely related Escherichia coli DHFR sequence. The ancestral DHFR sequence common to these three species was reconstructed. Since that ancestor there have been seven, nine, and one amino acid replacements in E. coli, E. aerogenes, and C. freundii, respectively. In E. coli, five of its seven replacements were located in the beta-sheet portion of the protein, and all seven were located in a single restricted region of the protein. In E. aerogenes, all nine of its replacements were located within surface residues, with five clustered in a region topologically distinct from the E. coli cluster. The replaced side chains are sometimes in direct contact but more often are separated by an intervening side chain. It is argued that the temporal clustering of replacements is typical for the evolution of most proteins and that the associated topological clustering gives a picture of how evolutionary change is accommodated by protein structure.

Amino Acid Sequence↗
PubMed1992

Neonatal septicaemia in an African city of high altitude.

Ninety-nine cases of neonatal septicaemia prospectively seen over a 3-year period in a large cosmopolitan African city of high altitude is presented. An incidence of 6.5 per 1000 live births was noted. Though the most important pathogens were Klebsiella spp. and Staphylococcus aureus, Citrobacter difficile and Alkalegenes faecalis were the pathogens associated with a high mortality rate. Low birth weight infants were significantly more affected. The overall mortality rate was 27.3 per cent. The commonest predisposing perinatal factors were birth asphyxia and prolonged rupture of fetal membranes. On the basis of the trend of organisms isolated and their sensitivity pattern, it is suggested that the initial use of gentamicin alone is satisfactory.

Africa↗
PubMed2000

Ascending cholangitis as a cause of pyogenic liver abscesses complicated by a gastric submucosal abscess and fistula.

Ruptures of nonamebic (pyogenic) liver abscesses into the thorax and peritoneum are very uncommon; but, hepatoduodenal and hepatocolonic fistulas are ever more rare. We report a case where ascending cholangitis was associated with pyogenic liver abscess formation and a gastric fistula. Drainage into the stomach was demonstrated by gastroduodenal endoscopy for gastric bleeding. After fistula formation, we could successfully treat the inflammation caused by infection of Citrobacter freundii and Candida albicans with intravenous infusion of both antibiotic and antifungal agents.

Aged↗
PubMed1990

Cefotaxime and aminoglycoside treatment of meningitis caused by gram-negative enteric organisms.

We reviewed cases of Gram-negative enteric bacillary meningitis in infants and children treated with cefotaxime at Texas Children's Hospital from January, 1984, through June, 1989. Seventeen of 20 children had an underlying condition predisposing to the development of meningitis. The etiologic organisms in these 20 children (2 days to 12 years old; median, 12 days old) were Klebsiella sp, 9; Escherichia coli, 4; Enterobacter cloacae, 3; Citrobacter diversus, 2; other, 2. With the exception of one isolate of Acinetobacter, all isolates were susceptible to cefotaxime. In addition to cefotaxime 17 children received an aminoglycoside intravenously. Children with meningitis caused by Klebsiella sp. or non-Klebsiella organisms received cefotaxime for 31 +/- 14 and 37 +/- 17 days, respectively. Aminoglycosides were administered for 16 +/- 10 days in both groups. Five children in each group also received intraventricular doses (1 to 25) of an aminoglycoside (9) or colistimethate (1). The mean durations of positive lumbar, ventricular cerebrospinal fluid or brain abscess cultures were 5.8 +/- 4.7 and 7.2 +/- 5.0 days after start of therapy in the Klebsiella and non-Klebsiella meningitis patients, respectively. Only three children were normal at the time of discharge or follow-up. Gram-negative enteric meningitis remains difficult to treat despite the excellent in vitro activity of cefotaxime against Gram-negative enterics, in part as a result of the predisposing conditions resulting in the development of this infection.

Aminoglycosides↗
PubMed1994

Plantar cellulitis.

An unusual case of acute cellulitis of the foot in a child is reported. The child failed to respond to standard treatment even after removal of an occult foreign body. Wound cultures revealed Klebsiella oxytoca and Citrobacter freundii. This is the first documented report on Klebsiella oxytoca in cellulitis. The cellulitis resolved after being treated with the appropriate antibiotics.

Cellulitis↗
PubMed1993

Dependence of induction of enterobacterial AmpC beta-lactamase on cell-wall peptidoglycan, as demonstrated in Proteus mirabilis and its wall-less protoplast L-form.

The mobilizable plasmid pMD101 (ampR, ampC) was constructed by inserting cloned ampC, the structural gene for the chromosomal AmpC beta-lactamase of Citrobacter freundii, and the closely linked ampR encoding the transcriptional regulator essential for enzyme induction, into the broad host-range plasmid pKT231. Plasmid pMD101 was transconjugated into Proteus mirabilis VI and its isogenic, cell-wall-less protoplast L-form LVI. AmpC beta-lactamase was expressed constitutively from cloned ampR and ampC in bacteria and in some L-form protoplasts. However, induction of the enzyme by beta-lactam antibiotics occurred only in bacterial cells and not in the cell-wall- and peptidoglycan-deficient L-form. In agreement with current models, induction of AmpC beta-lactamase is thought to be initiated by an induction signal arising from the metabolic disturbance of cell-wall peptidoglycan.

Bacterial Proteins↗
PubMed2002

Mutagenesis of conserved tryptophan residues within the receptor-binding domain of intimin: influence on binding activity and virulence.

Intimate bacterial adhesion to intestinal epithelium is a pathogenic mechanism shared by several human and animal enteric pathogens, including enteropathogenic and enterohaemorrhagic Escherichia coli and Citrobacter rodentium. The proteins directly involved in this process are the outer-membrane adhesion molecule intimin and the translocated intimin receptor, Tir. The receptor-binding activity of intimin resides within the carboxy terminus 280 aa (Int280) of the polypeptide. Four tryptophan residues, W117/776, W136/795, W222/881 and W240/899, are conserved within different Int280 molecules that otherwise show considerable sequence variation. In this study the influence of site-directed mutagenesis of each of the four tryptophan residues on intimin-Tir interactions and on intimin-mediated intimate attachment was determined. The mutant intimins were also studied using a variety of in vitro and in vivo infection models. The results show that all the substitutions modulated intimin activity, although some mutations had more profound effects than others.

Adhesins, Bacterial↗
PubMed1976

Nitrogen fixation by bacteria from the hindgut of termites.

Anaerobically grown bacteria isolated from the hindgut contents of the termites Coptotermes lacteus (Froggatt), Mastotermes darwiniensis Froggatt and Nasutitermes exitiosus (Hill) were nitrogenase-positive as assayed by acetylene reduction. Nitrogen fixation, confirmed with 15N2, was highest in the isolate from M. darwiniensis. All isolates were identified as Citrobacter freundii (Braak) Werkman & Gillen.

Anaerobiosis↗
PubMed1978

Effects of cephalexin, erythromycin and clindamycin on the aerobic Gram-negative faecal flora in man.

The effects of 5-day courses of orally administered cephalexin, clindamycin and erythromycin on the Gram-negative, aerobic faecal flora of healthy adults were examined. The concentration of cephalexin reached in the intestine was high enough to cause the emergence of resistant Gram-negative bacteria; organisms belonging to the genera Enterobacter, Citrobacter and Pseudomonas increased to easily detectable levels. The faecal concentration of erythromycin was high and caused a severe reduction of the coliform flora. Clindamycin administration resulted in a considerable increase in the coliform count; the increase in the proportion of klebsiellae was especially marked.

Administration, Oral↗
PubMed1996

The detection of verocytotoxins in bacterial cultures from human diarrhoeal samples with monoclonal antibody-based ELISAs.

Bacterial cultures from 1801 human diarrhoeal faecal specimens were examined for verocytotoxins I and II by monoclonal antibody-based sandwich ELISAs. Of the 68 ELISA-positive cultures selected from initial screening, 32 were positive by ELISA on repeat or from freshly grown cultures. ELISA-positive pure cultures were obtained from 13 of these, of which seven were confirmed as verocytotoxin positive by cytotoxicity assay. These seven strains were typed as O26 (5) and O146 (2). The six false positive results were from isolates of Enterobacter sp. (1), Citrobacter Freundii (1) and Escherichia coli (4), one each of types O1, O18ac and O98 and an untypable strain. Despite the occurrence of false positive reactions, sandwich ELISA was a useful method for the rapid screening of samples, and detected verocytotoxin-positive E. coli strains, other than O157, from patients with clinical conditions in which they could be implicated.

Adult↗