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We have described a 55-year-old man with fever, productive cough, and a right upper lobe infiltrate, which subsequently cavitated. Cultures of bronchial secretions obtained by bronchoscopic protected brush catheter technique revealed Enterobacter cloacae, a previously unreported cause of acute necrotizing pneumonia.
Gas gangrene is a life-threatening emergency. Most cases are caused by clostridial infections, but nonclostridial causes are being increasingly recognized. Nonclostridial gas gangrene is most often due to polymicrobial organisms. Early diagnosis and therapy are required, since the disease may rapidly progress to fatal toxemia. We report a case of gangrenous, atraumatic, nonclostridial myonecrosis of the arm due to Enterobacter cloacae in a nondiabetic patient with neutropenia.
STUDY DESIGN: This case report describes infection in a lumbar disc in a healthy young man with an organism of low pathogenicity. The patient was taking a prolonged course of antibiotics at the time the infection occurred. OBJECTIVE: To describe this unique case of infective spondylodiscitis. SUMMARY OF BACKGROUND DATA: To the authors' knowledge, spinal infection with Enterobacter agglomeranshas never been reported. This organism is a transient gut colonizer, and may have established itself secondary to the patient's prolonged ingestion of tetracycline for acne. METHODS: This 22-year-old farmer had spontaneous lumbar back pain. Radiologic investigations showed an abnormality in the L4-L5 disc region, and together with other investigations, were suggestive of infection. The diagnosis was confirmed by surgical aspiration. RESULTS: Antibiotic therapy was administered, and the patient made a complete recovery. Follow-up radiographs showed a complete loss of the L4-L5 disc space with only minimal bone destruction. CONCLUSION: A unique cause of infective lumbar discitis is presented. Several features of this case are unusual. The magnetic resonance findings were not readily diagnostic. The cultured organism is usually nonpathogenic. The infection may have been secondary to prolonged tetracycline therapy.
Large colonies of Enterobacter cloacae which were about 700 micrometer thick were frozen in liquid nitrogen and sectioned horizontally. The sections were disrupted and several oxidative enzymes were assayed in the crude unfractionated homogenates. In the top 120 micrometer of the colonies the specific activities of the enzymes were high and characteristic of aerobically adapted cells. Cells nearer the base of colonies had very low enzyme activities.
Esterases of 14 strains of Klebsiella pneumoniae, 14 strains of K. oxytoca, 16 strains of Enterobacter aerogenes and 16 strains of E. gergoviae were analysed by horizontal electrophoresis in polyacrylamide-agarose gel. Four principal esterase bands (designated E1 to E4) and nine minor bands differing in their activity towards synthetic substrates and in their sensitivity to heat and to di-isofluoropropyl phosphate were defined. The comparative distribution of bands showed that the four species analysed were characterized by distinct electrophoretic patterns of their esterases. Band E1 was found in all four species, bands E2 and E3 only in K. oxytoca and band E4 only in some strains of E. gergoviae. The apparent molecular weights of esterases E2 and E3, determined by electrophoresis in a 4 to 30% polyacrylamide gradient gel, were 58000 (+/- 1000) and 72000 (+/- 1800), respectively.
The effect of cyanide on the physiology of lactate- and oxygen-limited Enterobacter aerogenes NCTC 10336 was studied in chemostat culture (D = 0.1 h-1). In the absence of cyanide, the molar growth yield from oxygen (YO2) under oxygen limitation was 60% of the carbon-limited value. A similar decrease in yield was observed in a lactate-limited culture (excess oxygen) which was continuously fed low concentrations of potassium cyanide. The cultures with the lower growth yields possessed respiratory systems less sensitive to inhibition by cyanide. This was particularly marked in cultures grown in the presence of cyanide. Increased cyanide resistance was associated with an increase in the concentration of a cytochrome oxidase tentatively identified as a d-type and the appearance of additional cytochromes tentatively identified as b-type.
Induction of beta-lactamase was monitored in a strain of Enterobacter cloacae exhibiting high resistance to most beta-lactam antibiotics. Large amounts of the enzyme were induced not only in the presence of beta-lactams, but also in the presence of other bicyclic molecules such as folic acid, thiamin, tryptophan or haemin. Moreover, complex media (such as Trypticase soy broth and Schaedler's broth) and various body fluids (serum, pleural fluid and cerebrospinal fluid) also possessed considerable induction potency. Neither 'specific' induction (by beta-lactams) nor 'non-specific' induction (by other bicyclic compounds) could be augmented by addition of exogenous cAMP. These findings indicate that inducible beta-lactamases deserve more attention, above all with respect to the development of resistance against third-generation cephalosporins.
Two antibiotic-resistant mutants of Enterobacter cloacae (AZT-R and AMA-R), obtained by selection with aztreonam and carumonam, were studied. Both mutants were resistant to beta-lactam antibiotics. In addition, AMA-R was also resistant to chloramphenicol, trimethoprim and brodimoprim, whereas AZT-R was hypersensitive to these compounds. Cytoplasmic and outer membranes of these bacteria were separated by sucrose density gradient centrifugation. Analysis of the outer membranes using SDS-PAGE showed marked changes in the bands corresponding to the porins (between 35 and 40 kDa). In the two mutants, the 39 kDa band was reduced to approximately 30% of the wild-type and the 36.5 kDa band was absent. Labelling of the outer membranes with the hydrophobic photolabel 3-(trifluoomethyl)- 3-(m-[125I]iodophenyl)diazirine ([125I]TID) enabled the above bands as well as a 28.8 kDa band to be identified as integral membrane proteins, thus supporting the suggestion that they correspond to porins and OmpA protein, respectively. Whereas the changes observed in outer-membrane proteins are assumed to be responsible for resistance to beta-lactam antibiotics, the basis of hypersensitivity of AZT-R to hydrophobic antibiotics remains to be more clearly defined.
The influence of outer membrane (OM) permeability on carbapenem susceptibility was studied in strains of Enterobacter cloacae, a species in which carbapenem resistance depends upon the conjunction of overproduction of the chromosomal cephalosporinase and reduction of OM permeability. Relative trans-OM diffusion rates were measured using the liposome swelling assay. Proteoliposomes were reconstituted with OM from the members of an isogenic set of E. cloacae strains, selected in vivo or in vitro, which produced either porins F and D (wild-type), or F or D only, or neither. For all but one mutant, and compared with the wild-type strain, the respective increases in MICs and decreases in trans-OM diffusion of carbapenems were: nil and 13 to 18%; 4- to 32-fold and 33 to 50%; > or = 64-fold and > or = 90%. Our results suggest (i) that carbapenems (and other beta-lactam antibiotics) diffuse through porins F and D, but more rapidly through porin F, and (ii) that OM permeability is the critical factor in determining the level of MICs of carbapenems for cephalosporinase-overproducing strains of E. cloacae. The OM of one particular low-level carbapenem-resistant and porin F- and D-deficient mutant was at least five times more permeable to carbapenems than the similarly porin-deficient high-level resistant mutants. We infer from this observation the possible existence of an alternative carbapenem penetration pathway which could be associated with two as yet uncharacterized overproduced OM proteins of about 22 and 47 kDa.
A tryptophanase gene from Enterobacter aerogenes SM-18 was cloned and sequenced. The structural gene for tryptophanase, tnaA, consisted of 1389 bp encoding 462 amino acid residues, and its nucleotide sequence and deduced amino acid sequence showed significant homology to those of tnaA from Escherichia coli K12. A short open reading frame consisting of 31 amino acid residues was found upstream of tnaA, and it showed some similarity to the E. coli tnaC gene known to be a cis-acting regulatory element for transcription. A partial open reading frame homologous to the 5' end of E. coli tnaB was observed at the 3'-flanking region of tnaA. These genes may thus constitute an operon as in E. coli.
The Escherichia coli tsx gene encodes an integral outer-membrane protein (Tsx) that functions as a substrate-specific channel for deoxynucleosides and the antibiotic albicidin, and also serves as a receptor for bacteriophages and colicins. We cloned the structural genes of the Tsx proteins from Salmonella typhimurium, Klebsiella pneumoniae and Enterobacter aerogenes and expressed them in an E.coli tsx mutant. The heterologous Tsx proteins fully substituted the E.coli Tsx protein with respect to its function in deoxynucleoside and albicidin uptake, and as receptor for colicin K. The Tsx proteins from K. pneumoniae and Ent. aerogenes were also proficient as receptors for several Tsx-specific bacteriophages, whereas the corresponding protein from S. typhimurium did not confer sensitivity against these phages. The nucleotide sequence of the tsx genes from S. typhimurium, K. pneumoniae and Ent. aerogenes was established. Each of the Tsx proteins is initially synthesized with typical bacterial signal sequence peptides and the predicted mature forms of the Tsx proteins have a calculated M(r) of 30,567 (265 residues), 31,412 (272 residues) and 31,477 (272 residues), respectively. Multiple sequence alignments between the Tsx proteins showed a high degree of sequence identity and revealed the presence of four hypervariable regions, which are thought to constitute segments of the polypeptide chain exposed at the cell surface. Most notable was a deletion of 8 amino acids in one of these hypervariable domains in the S. typhimurium Tsx protein. When this deletion was introduced by site-directed mutagenesis into the corresponding region of the E.coli tsx gene, the mutant Tsx-515 protein lost its phage receptor function but still served as a colicin K receptor and as a substrate-specific channel, indicating that the region between residues 198 and 207 might be part of the bacteriophage receptor area. Multiple sequence alignments, structural predictions and the properties of previously characterized Tsx missense mutants were taken into account to develop a two-dimensional model for the topological organization of the Tsx protein within the outer membrane.
Continuous cultures of Enterobacter agglomerans CNCM 1210 were performed under regulated pH conditions (pH 7.0) with glycerol or glucose (20 g l-1) as carbon source. Cultures grown on glucose produced mainly acetate, ethanol and formate. In contrast, 1,3-propanediol (PPD) was the main product with glycerol. The carbon flow distribution at branching metabolic points was investigated. Higher PPD yields with increased dilution rate were correlated with an important increase in the relative ratio of glycerol dehydratase to glycerol dehydrogenase. Determination of intracellular triose-phosphate and fructose 1,6-biphosphate concentrations demonstrated that glyceraldehyde-3-phosphate dehydrogenase is the limiting step in glycerol dissimilation. At the pyruvate branching point, pyruvate dehydrogenase (PDH) activity was systematically detected. The pyruvate flow shifted to PDH is suspected to represent up to 22% of the acetyl-CoA formed. In addition, this enzyme pattern combined with the enhanced in vivo lactate dehydrogenase activity at high growth rates, was correlated with a decrease in the pyruvate formate-lyase activity. A regulation of this latter enzyme by the accumulation of triose-phosphate is suspected.
Enterobacter aerogenes is among the five most frequently isolated nosocomial pathogens in France, and this bacterium also shows increasing multidrug resistance. In this study, various E. aerogenes strains isolated from hospital units were characterized for their outer-membrane proteins, antibiotic susceptibilities (inhibition diameters and MICs) and resistance mechanisms associated with modification of envelope permeability (porin alteration and active efflux). Diminished outer-membrane permeability due to porin alterations was found in conjunction with the expression of an enzymic barrier in resistant isolates. Interestingly, changes in the functional expression of porins appeared to play a special role in susceptibility to cefepime. An active efflux to quinolones was also identified. Simultaneous changes in envelope permeability, i.e. a porin deficiency (in) and an efflux mechanism (out), were clearly evident in two clinical strains.
Seventy-six phages active against Enterobacter cloacae were isolated from sewage and other sources. They were tested at RTD on 92 selected strains of E. cloacae and their lytic reactions were used to select phages for a typing set. Numerical analysis by the Jaccard coefficient was used to assess the similarity between the phages. A computer-based test selection procedure selected sub-sets of phages to discriminate between all 92 E. cloacae strains and within the most frequent serological groups. A subjective analysis of the candidate phages based on similarity, clarity of plaque and frequency of lysis was combined with the computer selected sub-sets to produce a final set of 25 phages that gave a good theoretical discrimination of clinical isolates of E. cloacae.
A set of 25 Enterobacter cloacae typing phages was evaluated. Of 384 test strains, 93.8% were lysed by at least one phage; the mean number of reactions/strain was 7.3. Discrimination between strains was satisfactory within the most frequent O serotypes; 0.9 patterns/strain were found for strains of serotypes O3 and O8. Overall, 325 patterns were found. Phage patterns were completely reproducible when duplicates of strains were typed on the same day, but only 40% reproducible when repeated after 18 months. The combination of O serology and phage typing discriminated well between hospital isolates.
The activities of beta-lactam antibiotics were compared against Enterobacter cloacae clinical isolates and mutants which had inducible, stably-derepressed, and basal expression of a pI 8.4 subtype of the Ia chromosomal beta-lactamase. These activities were correlated with the results of studies of the beta-lactamase-lability and beta-lactamase-inducer-power of the antibiotics. Cefoxitin and ampicillin were labile, and induced beta-lactamase production strongly at concentrations below their MIC values. Consequently, beta-lactamase-inducible and beta-lactamase-stably-derepressed organisms were highly resistant (MIC greater than 256 mg/L) to these antibiotics, whereas enzyme-basal strains and mutants were much more susceptible (MIC 1-16 mg/L). Imipenem also induced beta-lactamase production strongly at concentrations below its MIC, but was more stable than ampicillin and cefoxitin. It was active against enzyme-inducible and stably-derepressed organisms at 0.25-0.5 mg/L and against beta-lactamase-basal organisms at 0.06-0.25 mg/L. Thus the beta-lactamase afforded only very low-level protection against imipenem; this appeared to be by a non-hydrolytic mechanism, with the enzyme binding to the antibiotic in a relatively stable complex. This complex, which probably was an intermediate in a hydrolytic pathway, was isolated by gelfiltration chromatography and shown to have a breakdown half-life of 47 +/- 2 min. Cefotaxime, ceftriaxone and mezlocillin were labile to the pI 8.4 beta-lactamase but induced beta-lactamase production weakly at concentrations below their MIC values. Consequently, beta-lactamase-inducible and beta-lactamase-basal organisms remained equally susceptible (MIC 0.06-4 mg/L), but stably-derepressed organisms were considerably more resistant (MIC greater than 64 mg/L) to these antibiotics.
Diabetic mice were significantly more susceptible than normal mice to bladder infection with Enterobacter cloacae or Serratia marcescens but not to intraperitoneal infection. Normal urine inhibited the growth of E. cloacae and S. marcescens, whereas urine from diabetic mice permitted multiplication. The addition of urea to urine from diabetic mice restored its antibacterial properties for E. cloacae and S. marcescens. We consider that the decreased urea content of the urine of diabetic mice was responsible for their increased susceptibility to bacterial infection of the bladder.
Susceptibilities to cefotaxime (Ctx) and ceftazidime (Caz) were examined for 90 recent clinical isolates of Enterobacter cloacae from Greek hospitals. Most (68%) of the isolates were resistant to both drugs, and all were resistant to cefoxitin. beta-Lactamase activities against cephaloridine in crude extracts from Ctx-Caz-resistant isolates were high, irrespective of whether or not the cells were grown with cefoxitin as an inducer of the chromosomal beta-lactamase, indicating stable derepression of the gene for the enzyme. On the other hand, double disk antagonism tests showed that all the Ctx-Caz-sensitive isolates possessed inducible expression of this beta-lactamase. Iso-electric focusing revealed the presence of five forms of the chromosomal beta-lactamase, randomly distributed amongst the Ctx-Caz-resistant and -sensitive isolates. Plasmid-mediated beta-lactamases of TEM and PSE types also were found in many isolates. These data indicate that the extremely high prevalence of Ctx-Caz-resistant E. cloacae isolates in Greek hospitals is attributed to the dissemination of mutants which constitutively overproduce the class-I chromosomal beta-lactamase. Over 90% of these isolates exhibited cross-resistance to aminoglycosides, suggesting the accumulation of unrelated antibiotic resistance mechanisms.