Myocarditis in sibling boxer puppies associated with Citrobacter koseri infection.
(1/23)
Two sibling Boxer puppies presented with severe suppurative myocarditis in the absence of additional disseminated suppurative foci. The identification of gram-negative bacteria within areas of myocarditis in both puppies and the pure growth of large numbers of Citrobacter koseri from the myocardial lesions in one of the dogs were consistent with a bacterial etiology. The fact that C. koseri is an opportunist pathogen suggested intercurrent immunosuppression. The finding of a concomitant bacterial myocarditis in two canine siblings is novel. The case is also unusual in that syncope could be related to the myocardial injury. (+info)
Citrobacter koseri brain abscess in the neonatal rat: survival and replication within human and rat macrophages.
(2/23)
A unique feature of Citrobacter koseri is the extremely high propensity to initiate brain abscesses during neonatal meningitis. Previous clinical reports and studies on infant rats have documented many Citrobacter-filled macrophages within the ventricles and brain abscesses. It has been hypothesized that intracellular survival and replication within macrophages may be a mechanism by which C. koseri subverts the host response and elicits chronic infection, resulting in brain abscess formation. In this study, we showed that C. koseri causes meningitis and brain abscesses in the neonatal rat model, and we utilized histology and magnetic resonance imaging technology to visualize brain abscess formation. Histology and electron microscopy (EM) revealed that macrophages (and not fibroblasts, astrocytes, oligodendrocytes, or neurons) were the primary target for long-term C. koseri infection. To better understand C. koseri pathogenesis, we have characterized the interactions of C. koseri with human macrophages. We found that C. koseri survives and replicates within macrophages in vitro and that uptake of C. koseri increases in the presence of human pooled serum in a dose-dependent manner. EM studies lend support to the hypothesis that C. koseri uses morphologically different methods of uptake to enter macrophages. FcgammaRI blocking experiments show that this receptor primarily facilitates the entry of opsonized C. koseri into macrophages. Further, confocal fluorescence microscopy demonstrates that C. koseri survives phagolysosomal fusion and that more than 90% of intracellular C. koseri organisms are colocalized within phagolysosomes. The ability of C. koseri to survive phagolysosome fusion and replicate within macrophages may contribute to the establishment of chronic central nervous system infection including brain abscesses. (+info)
SHV-34: an extended-spectrum beta-lactamase encoded by an epidemic plasmid.
(3/23)
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. (+info)
Citrobacter koseri and Citrobacter amalonaticus isolates carry highly divergent beta-lactamase genes despite having high levels of biochemical similarity and 16S rRNA sequence homology.
(4/23)
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. (+info)
Novel TEM-type extended-spectrum beta-lactamase, TEM-134, in a Citrobacter koseri clinical isolate.
(5/23)
A new natural TEM derivative with extended-spectrum beta-lactamase activity, TEM-134, was identified in a ceftazidime-resistant clinical isolate of Citrobacter koseri. Compared to TEM-1, TEM-134 contains the following mutations: Q39K, E104K, R164H, and G238S. The bla(TEM-134) gene was not transferable by conjugation and, apparently, was chromosomally encoded. Expression studies with Escherichia coli revealed efficient cefotaximase and ceftazidimase activity for TEM-134. (+info)
Diffuse pneumocephalus in neonatal Citrobacter meningitis.
(6/23)
Pneumocephalus, intracranial air or gas collection, associated with neonatal meningitis is extremely rare. We report the first case in the United States and the second case in the world of intracranial gas accumulation in a neonate with Citrobacter koseri meningitis. The clinical presentation was acute with pneumocephalus demonstrated by cranial sonography and computed tomography. The clinical course was fatal despite the prompt administration of antibiotics. (+info)
fliP influences Citrobacter koseri macrophage uptake, cytokine expression and brain abscess formation in the neonatal rat.
(7/23)
Citrobacter koseri causes neonatal meningitis frequently complicated with multiple brain abscesses. During C. koseri central nervous system infection in the neonatal rat model, previous studies have documented many bacteria-filled macrophages within the neonatal rat brain and abscesses. Previous studies have also shown that C. koseri is taken up by, survives phagolysosomal fusion and replicates in macrophages in vitro and in vivo. In this study, in order to elucidate genetic and cellular factors contributing to C. koseri persistence, a combinatory technique of differential fluorescence induction and transposon mutagenesis was employed to isolate C. koseri genes induced while inside macrophages. Several banks of mutants were subjected to a series of enrichments to select for gfp : : transposon fusion into genes that are turned off in vitro but expressed when intracellular within macrophages. Further screening identified several mutants attenuated in their recovery from macrophages compared with the wild-type. A mutation within an Escherichia coli fliP homologue caused significant attenuation in uptake and hypervirulence in vivo, resulting in death within 24 h. Furthermore, analysis of the immunoregulatory interleukin (IL)-10/IL-12 cytokine response during infection suggested that C. koseri fliP expression may alter this response. A better understanding of the bacteria-macrophage interaction at the molecular level and its contribution to brain abscess formation will assist in developing preventative and therapeutic strategies. (+info)
Biochemical analysis of TEM-134, a new TEM-type extended-spectrum beta-lactamase variant produced in a Citrobacter koseri clinical isolate from an Italian hospital.
(8/23)
OBJECTIVES: Kinetic characterization of TEM-134, a new TEM-type extended-spectrum beta-lactamase variant isolated from Citrobacter koseri during an Italian nationwide survey. TEM-134 is a natural derivative of TEM-2 with the following substitutions: E104K, R164H and G238S. METHODS: Recombinant TEM-134 was purified from Escherichia coli HB101 (pMGP-134) by three chromatographic steps (cation-exchange chromatography, gel permeation and fast chromatofocusing). Steady-state kinetic parameters (K(m) and k(cat)) were determined by measuring substrate hydrolysis under initial rate conditions using the Hanes linearization of the Michaelis-Menten equation. Modelling was carried out using the software Modeller (version 9.1). RESULTS: TEM-134 hydrolysed with variable efficiency (k(cat)/K(m) ranging from 5 x 10(3) to 8.0 x 10(5) M(-1) . s(-1)) penicillins, narrow-spectrum cephalosporins, cefepime, cefotaxime, ceftazidime and aztreonam, which appeared to be the best substrate. Molecular modelling of the enzyme indicated that the R164H substitution may result in a compromised omega loop in TEM-134 and this may be responsible for its narrower spectrum of activity. CONCLUSIONS: Kinetic data and molecular modelling suggested that R164H has a mild detrimental effect on the global activity of the enzyme. (+info)