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Four-hour urease test for distinguishing between Klebsiella and Enterobacter.

Infections with Klebsiella and Enterobacter have increased among hospitalized patients. To study such infections, relatively simple but precise methods are needed for clinical laboratories to identify the two genera accurately. Moreover, a rapid identification is essential for assisting with the therapy of the patients. For this purpose, a new 4-hr urease test was developed so that colonies could be tested directly from blood-agar plates which have been inoculated with clinical material and allowed to incubate overnight. This 4-hr test was positive with 98.5% of 202 Klebsiella species and negative with 80 Enterobacter species. As a single criterion for distinguishing between the two major genera, the new 4-hr urease test was just as accurate as a motility test (99% of the 282 isolates were accurately identified with either). The 4-hr urease test represents a simple, rapid, and reliable technique which is ideally suited for use in clinical microbiology laboratories.

Bacteriological Techniques↗

Ten-minute test for differentiating between Klebsiella and Enterobacter isolates.

A 10-minute test, utilizing a urease paper-reagent strip (PATHO-TEC), for differentiating Klebsiella and Enterobacter species is described. By using a heavy suspension of organisms and 50 C temperature for incubation, 93% of Klebsiella strains (186/200) were positive and 95% of Enterobacter strains (190/200) were negative with this testing system. The rapid nature of the test (10 min), the facility with which it can be carried out, and the ease with which the strips can be stored and handled may make this a useful aid for the clinical microbiologist.

Agar↗

Antibiotic susceptibilities of Serratia marcescens and Enterobacter liquefaciens.

Production of 5'-nucleotides by Serratia marcescens and Enterobacter liquefaciens correlates with deoxyribonuclease production, indicating the close relationship between these two organisms. To determine further relationships, susceptibilities of 279 strains of the tribe Klebsielleae were determined by the high-potency disc method, agar-dilution method, or both, by using 14 antibiotics. Ninety-seven per cent of S. marcescens (201 of 207 strains) and 100% of E. liquefaciens (17 strains) had minimum inhibitory concentration (MIC) of 100 mug/ml or greater with colistin and polymyxin B. With these two antibiotics, 93% of other Enterobacter species (28 strains) had MIC values of less than 1.6 mug/ml, and 100% of Klebsiella (27 strains) had MIC values less than 1.6 mug/ml. Consistent patterns were not noted with the other antibiotics tested, but the results with colistin and polymyxin B provide additional evidence of the close relationship of S. marcescens and E. liquefaciens.

Anti-Bacterial Agents↗

Biological characterization of an Enterobacter cloacae outer membrane protein (OmpX).

We have described a gene coding for an Enterobacter cloacae protein, provisionally called OmpX (J. Stoorvogel, M. J. A. W. M. van Bussel, J. Tommassen, and J. A. M. van de Klundert, J. Bacteriol. 173:156-160, 1991). In the work reported here, OmpX was localized in the cell envelope by means of sucrose gradient fractionation of membrane vesicles. Overproduction of OmpX in Escherichia coli from a multicopy plasmid resulted in a reduction in the amount of OmpF. No accumulation of OmpF, of its uncleft precursor, or of its degradation products could be detected in various cell fractions by Western immunoblot analysis using monoclonal antibodies produced in response to OmpF. A decrease in the rate of synthesis of ompF mRNA was indicated by a beta-galactosidase assay in an ompF-lacZ fusion strain containing the cloned ompX gene and by Northern (RNA) blot analysis. These results indicate that the inhibition is at the level of transcription. Colony hybridization, using an internal ompX fragment as a probe, showed a widespread distribution of the ompX gene among clinical isolates of members of the family Enterobacteriaceae. To study the function of the OmpX protein and its role in the regulation of porin protein synthesis, the ompX gene was deleted from the Enterobacter cloacae chromosome and replaced by the aphA gene. The absence of the ompX gene had no apparent effect on cell growth or on the regulation of the porin proteins.

Bacterial Outer Membrane Proteins↗

Analysis of eight cases of neonatal meningitis and sepsis due to Enterobacter sakazakii.

Eight cases of neonatal meningitis due to Enterobacter sakazakii (formerly known as yellow-pigmented Enterobacter cloacae) which occurred in The Netherlands during the last 6 years were investigated retrospectively. Two patients had necrotizing enterocolitis and meningitis simultaneously. Despite treatment (in most cases with ampicillin and gentamicin), the fatality rate was 75%. Strains were much more susceptible to some of the new beta-lactam antibiotics than to ampicillin. A mode of transmission other than passage through the birth canal was likely, at least for some patients. A cluster of four patient strains in one hospital had almost identical plasmid DNA profiles. However, two strains isolated from formula at the same hospital 2 days after the onset of one case had different profiles, as did the strains from patients in other hospitals.

DNA, Bacterial↗

Typing of Enterobacter spp. by bacteriocin susceptibility and its use in epidemiological analysis.

Most clinical isolates of Enterobacter cloacae are bacteriocinogenic and susceptible to bacteriocins. Both rapidly diffusing, nonsedimentable, protease-susceptible and slowly diffusing, sedimentable, protease-resistant bacteriocins are produced. A practicable system was devised for epidemiological typing of E. cloacae isolates by their patterns of susceptibility to bacteriocins. A set of eight bacteriocin-producing strains was grown on tryptic soy agar plates for 16 h. After removal of the producer lawn, the isolates to be typed were inoculated on the agar media by a multipoint inoculator. After a second 16-h period of incubation, the strains were classified into bacteriocin types according to the patterns of growth inhibition. Typability of 134 clinical isolates was 96.3%. Only 11 (8.2%) of the isolates fell into the largest group. Repeat testing of isolates from the same patients within 2 months gave identical bacteriocin types. Other species of Enterobacter (E. agglomerans and E. aerogenes) are also typable by this method.

Bacteriocins↗

Epidemiological typing of Enterobacter aerogenes.

The applicability of Enterobacter cloacae and Klebsiella typing reagents for classifying clinical strains of Enterobacter aerogenes was evaluated. Of 75 strains, none were agglutinated by E. cloacae O antisera or were sensitive to E. cloacae bacteriophages. In contrast, 70 strains reacted with Klebsiella capsular antisera. Two-thirds of the strains were lysed by Klebsiella typing phages. A set of five E. aerogenes bacteriocin producers classified 92% of strains into 15 sensitivity types. In conclusion, E. aerogenes may be typed with Klebsiella reagents, and the simple bacteriocin test provides further discrimination between strains. The limited number of capsular antigens in the species and their apparent similarity to Klebsiella capsular antigens warrant further investigation.

Agglutination Tests↗

Enterobacter taylorae, a new opportunistic pathogen: report of four cases.

Severe nosocomial infections due to Enterobacter taylorae (formerly known as CDC Enteric Group 19) are described in four patients. Unlike most members of the Enterobacter genus, the isolates were not susceptible to penicillins or cephalosporins. Restriction endonuclease analysis of E. taylorae DNA obtained from three patients identified two distinct strains. One strain was found in two patients, suggesting a common source which we were not able to identify. We postulate that in patients harboring E. taylorae, the combination of cephalosporin therapy and instrumentation enables this organism to become an opportunistic pathogen.

Aged↗

A nosocomial outbreak due to Enterobacter cloacae strains with the E. hormaechei genotype in patients treated with fluoroquinolones.

During a 7-month period, we isolated 21 highly fluoroquinolone-resistant Enterobacter cloaecae strains in units from two hospitals in Marseille, France. Random amplification of polymorphic DNA showed clonal identity between isolates which, furthermore, presented the Enterobacter hormaechei genotype on DNA-DNA hybridization. The emergence of this clone was observed only in patients treated with fluoroquinolones.

Cross Infection↗

Dissemination of SHV-12 and characterization of new AmpC-type beta-lactamase genes among clinical isolates of enterobacter species in Korea.

To determine the prevalence and genotype of an extended-spectrum beta-lactamase and new chromosomal AmpC beta-lactamases among clinical isolates of Enterobacter species, we performed antibiotic susceptibility testing, pI determination, induction tests, transconjugation, enterobacterial repetitive consensus (ERIC) PCR, sequencing, and phylogenetic analysis. Among the 51 clinical isolates collected from a university hospital in Korea, 6 isolates have been shown to produce SHV-12 and inducible AmpC beta-lactamases. These also included three isolates producing TEM-1b and one strain carrying TEM-1b and CMY-type beta-lactamases with a pI of 8.0. The results from ERIC PCR revealed that six isolates were genetically unrelated, suggesting that dissemination of SHV-12 was responsible for the spread of resistance to extended-spectrum beta-lactams in Korea. Six genes of inducible AmpC beta-lactamases that are responsible for the resistance to cephamycins (cefoxitin and cefotetan), amoxicillin, cephalothin, and amoxicillin-clavulanic acid were cloned and characterized. A 1,165-bp DNA fragment containing the ampC genes was sequenced and found to have an open reading frame coding for a 381-amino-acid beta-lactamase. The nucleotide sequence of four ampC genes (bla(EcloK992004.1), bla(EcloK995120.1), bla(EcloK99230), and bla(EareK9911729)) shared considerable homology with that of AmpC-type class C beta-lactamase genes of gram-negative bacteria, especially that of the chromosomal ampC gene (bla(EcloMHN1)) of Enterobacter cloacae MHN1 (99.9, 99.7, 99.6, and 99.6% identity, respectively). The sequences of two ampC genes (bla(EcloK9973) and bla(EcloK9914325)) showed close similarity to the chromosomal ampC gene (bla(EcloQ908R)) of E. cloacae Q908R (99.7% identity). The results from phylogenetic analysis suggested that six ampC genes could originate from bla(EcloMHN1) or bla(EcloQ908R).

Bacterial Proteins↗

Enterobacter hormaechei subsp. oharae subsp. nov., E. hormaechei subsp. hormaechei comb. nov., and E. hormaechei subsp. steigerwaltii subsp. nov., three new subspecies of clinical importance.

Six species and six additional genovars are combined within the so-called Enterobacter cloacae complex, with one of them being the species Enterobacter hormaechei. In a recent population genetic study, two genetic clusters were found in close phylogenetic proximity to the genetic cluster of E. hormaechei. In order to prove the hypothesis that these three genetic clusters belong to the same species, we performed cross-hybridization experiments in microplates with DNAs of representatives of each genetic cluster. The close phylogenetic relationship among the clusters was reflected by their relatively low deltaT(m) values, ranging from 0.3 to 4.8, confirming the hypothesis that the clusters are parts of the same species. These clusters can be distinguished from the other species of the E. cloacae complex, which have deltaT(m) values of 5.6 to 10.3. Forty-eight E. hormaechei strains from the different genetic clusters were phenotypically characterized with 129 biochemical tests. In this way, E. hormaechei could be differentiated from the other species of the E. cloacae complex because it tests negative in the 3-hydroxy-butyrate test. The three genetic clusters of E. hormaechei could also be differentiated from each other by using phenotypic tests. Hence, we propose three new subspecies of E. hormaechei corresponding to genetic clusters VI, VII, and VIII of the E. cloacae complex. E. hormaechei subsp. hormaechei comb. nov. corresponds to the original species description, as it gives negative results for the adonitol, d-arabitol, d-sorbitol, and d-melibiose tests and a positive result for the dulcitol test. E. hormaechei subsp. oharae subsp. nov. gives negative results for the dulcitol, adonitol, and d-arabitol tests and positive results for the d-sorbitol and d-melibiose tests. E. hormaechei subsp. steigerwaltii subsp. nov. gives a negative result for the dulcitol test and positive results for the adonitol, d-arabitol, d-sorbitol, and d-melibiose tests. Among the members of the E. cloacae complex, E. hormaechei seems to be the species most frequently recovered from clinical specimens.

Bacterial Typing Techniques↗

Utility of the VITEK 2 Advanced Expert System for identification of extended-spectrum beta-lactamase production in Enterobacter spp.

Forty clinical isolates of Enterobacter spp. were identified as extended-spectrum beta-lactamase (ESBL) producers by disk diffusion. The VITEK 2 Advanced Expert System (AES) identified the ESBL phenotype in only 25 isolates (62.5%), and erroneously reported cephalosporin susceptibility in 11 isolates (28%). Refinements in the AES are required in order to improve ESBL detection in Enterobacter.

Enterobacter↗

Branchial challenge of normal subjects with the endotoxin of Enterobacter agglomerans isolated from cotton dust.

Endotoxin produced by a culture of Enterobacter agglomerans isolated from cotton dust was inhaled by 12 normal subjects. No significant airway constriction was obtained in doses equivalent to those experienced in a workshift in a dusty mill. There was a statistically significant difference between this result and the bronchoconstriction that had occurred after flax dust inhalation in the same subjects. It is suggested that Enterobacter agglomerans endotoxin is not the causative agent of the acute bronchoconstriction that follows inhalation of textile dust.

Bronchial Provocation Tests↗

Substrate specificity of glucose dehydrogenase (GDH) of Enterobacter asburiae PSI3 and rock phosphate solubilization with GDH substrates as C sources.

Enterobacter asburiae PSI3 is a rhizospheric isolate that solubilizes mineral phosphates by the action of a phosphate starvation-inducible GDH (EC 1.1.5.2). We report here that GDH activity of this isolate shows broad substrate range, being able to act on mono and disaccharides. Enterobacter asburiae PSI3 was proficient at bringing about a drop in pH and solubilization of RP with the use of 75 mmol/L of each of the GDH substrate sugars tested as the sole C source. It liberated amounts of P ranging from 450 micromol/L (on arabinose) to 890 micromol/L (on glucose). When grown on a mixture of 7 GDH substrates at concentrations of 15 mmol/L each, the bacterium solubilized RP equivalent to 46% of the value when 75 mmol glucose/L was the C source. HPLC analysis of the culture supernatant under these conditions showed that the acidification of the media is primarily due to the production of organic acids. The significance of these results on the efficacy of E. asburiae PSI3 at solubilizing phosphates under rhizospheric conditions is discussed.

Carbohydrates↗

Effect of aerosol immunization with RE 595 Salmonella minnesota on lung bactericidal activity against Serratia marcescens, Enterobacter cloacae, and Pseudomonas aeruginosa.

Intrapulmonary bactericidal activity was measured after mice were given 3 weekly aerosol exposures to acid-hydrolyzed Re 595 Salmonella minnesota. Ten days after their last immunization, mice were challenged with aerolized Serratia marcescens, Enterobacter cloacae, or Pseudomonas aeruginosa. Quantitative bacterial counts in ground lung were obtained immediately after exposure and again 4 hours later. Enhanced bactericidal activity against Serratia marcescens and Enterobacter cloacae was seen in immunized animals, whereas no difference with Pseudomonas aeruginosa was noted. In separate studies, immunization with Serratia marcescens yielded a similar enhancement of lung bactericidal activity. Mucociliary transport, as measured by disappearance of aerosolized Serratia marcescens labeled with phosphorus-32, was identical for both immunized and control animals. Using a standardized in vitro mouse alveolar macrophage phagocytic system, lung washes from animals immunized with Re 595 Salmonella minnesota had significant opsonic activity for Serratia marcescens but not for Pseudomonas aeruginosa.

Aerosols↗

Meningitis due to Enterobacter aerogenes subsequent to resection of an acoustic neuroma and abdominal fat graft to the mastoid.

Meningitis is an uncommon complication of neurosurgical procedures, with an incidence of 1.1% to 2.5%. Although unusual, the frequency of nosocomial Gram-negative meningitis appears to be increasing. Gram-negative meningitis has been documented following disruption of the dura-arachnoid barrier secondary to trauma or surgery. The association of Gram-negative bacillary meningitis with neurosurgical procedures was first reported in the 1940's. Wolff et al. described the association between Enterobacter species and post-neurosurgical infection. More recently, risk factors for nosocomial Enterobacter meningitis have been characterized by Parodi et al. Adipose graft, as an independent risk factor has not yet been reported. A patient with acoustic neuroma resection, who developed bacterial meningitis from an abdominal fat pad graft to a mastoidectomy bed is described. A brief overview was made of post-neurosurgical Gram-negative meningitis.

Adipose Tissue↗

Enterobacter cloacae ventriculitis successfully treated with cefepime and gentamicin: case report and review of the literature.

A 55-year-old woman was found unresponsive and subsequently was diagnosed with a subarachnoid hemorrhage secondary to a right posterior communicating artery aneurysm. The development of hydrocephalus and decreased mental status necessitated placement of an intraventricular catheter; 18 days later she was diagnosed with Enterobacter cloacae ventriculitis. After treatment was begun with intravenous cefepime 2 g every 8 hours and intraventricular gentamicin 5 mg every 24 hours, the catheter was replaced. Cerebrospinal fluid (CSF) and plasma cefepime concentrations and a CSF trough gentamicin concentration were obtained. Intraventricular gentamicin was administered for 6 days and cefepime for 21 days; both clinical and microbiologic resolution of the ventriculitis occurred. The literature reports limited clinical experience with cefepime for the treatment of central nervous system infections in humans. This case report provides clinical evidence to support administration of intravenous cefepime in critically ill adult patients with Enterobacter ventriculitis. Because CSF is easily obtained from patients with intraventricular catheters, strong consideration should be given to monitoring CSF cefepime concentrations in concert with the minimum inhibitory concentration of the offending pathogen to help assure the efficacy of this approach to therapy.

Cefepime↗

Traumatic late flap dehiscence and Enterobacter keratitis following LASIK.

PURPOSE: To report a case of traumatic flap dehiscence and Enterobacter keratitis 34 months after LASIK. METHODS: A 36-year-old man sustained a flap dehiscence following traumatic right eye gouging by a seagull claw. He presented the following day with uncorrected visual acuity (UCVA) in the affected eye of 3/200 and organic foreign body deposits underneath the flap. Systemic and topical antibiotics were administered and urgent surgical debridement and replacement of the LASIK flap was performed. An Enterobacter species was cultured from an intraoperative swab. RESULTS: After a prolonged postoperative course, including administration of topical ofloxacin, tobramycin, chloramphenicol, and dexamethasone, UCVA returned to 20/20. CONCLUSIONS: Good visual outcome after early debridement and appropriate antibiotics was achieved. Patients should be injury advised to seek prompt ophthalmic consultation after LASIK.

Adult↗