Fulminant endocarditis and disseminated infection caused by carbapenem-resistant Acinetobacter baumannii in a renal-pancreas transplant recipient

Acinetobacter baumannii is an important cause of healthcare-associated infections, and is particularly problematic among patients who undergo organ transplantation. We describe a case of fulminant sepsis caused by carbapenem-resistant A. baumannii harboring the blaOXA-23 carbapenemase gene and belonging to international clone II. This isolate led to the death of a patient 6 days after simultaneous kidney-pancreas transplantation. Autopsy findings revealed acute mitral valve endocarditis, myocarditis, splenic and renal emboli, peritonitis, and pneumonia. This case highlights the severe nature of certain A. baumannii infections and the vulnerability of transplanted patients to the increasingly intractable "high-risk" clones of multidrug-resistant organisms.

Penicillin-binding protein 5 and expression of ampicillin resistance in Enterococcus faecium

We report a structural and transcriptional analysis of the pbp5 region of Enterococcus faecium C68. pbp5 exists within a larger operon that includes upstream open reading frames (ORFs) corresponding to previously reported psr (penicillin-binding protein synthesis repressor) and ftsW (whose product is a transmembrane protein that interacts with PBP3 in Escherichia coli septum formation) genes. Hybridization of mRNA from C68, CV133, and four ampicillin-resistant CV133 mutants revealed four distinct transcripts from this region, consisting of (i) E. faecium ftsW (ftsW(Efm)) alone; (ii) psr and pbp5; (iii) pbp5 alone; and (iv) ftsW(Efm), psr, and pbp5. Quantities of the different transcripts varied between strains and did not always correlate with quantities of PBP5 or levels of ampicillin resistance. Since the psr of C68 is presumably nonfunctional due to an insertion of an extra nucleotide in the codon for the 44th amino acid, the region extending from the ftsW(Efm) promoter through the pbp5 gene of C68 was cloned in E. coli to facilitate mutagenesis. The psr ORF was regenerated using site-directed mutagenesis and introduced into E. faecium D344-SRF on conjugative shuttle vector pTCV-lac (pCWR558 [psr ORF interrupted]; pCWR583 [psr ORF intact]). Ampicillin MICs for both D344-SRF(pCWR558) and D344-SRF(pCWR583) were 64 microg/ml. Quantities of pbp5 transcript and protein were similar in strains containing either construct regardless of whether they were grown in the presence or absence of ampicillin, arguing against a role for PSR as a repressor of pbp5 transcription. However, quantities of psr transcript were increased in D344-SRF(pCWR583) compared to D344-SRF(pCWR558), especially after growth in ampicillin; suggesting that PSR acts in some manner to activate its own transcription.

Genetic linkage and cotransfer of a novel, vanB-containing transposon (Tn5382) and a low-affinity penicillin-binding protein 5 gene in a clinical vancomycin-resistant Enterococcus faecium isolate

Mechanisms for the intercellular transfer of VanB-type vancomycin resistance determinants and for the almost universal association of these determinants with those for high-level ampicillin resistance remain poorly defined. We report the discovery of Tn5382, a ca. 27-kb putative transposon encoding VanB-type glycopeptide resistance in Enterococcus faecium. Open reading frames internal to the right end of Tn5382 and downstream of the vanXB dipeptidase gene exhibit significant homology to genes encoding the excisase and integrase of conjugative transposon Tn916. The ends of Tn5382 are also homologous to the ends of Tn916, especially in regions bound by the integrase enzyme. PCR amplification experiments indicate that Tn5382 excises to form a circular intermediate in E. faecium. Integration of Tn5382 in the chromosome of E. faecium C68 has occurred 113 bp downstream of the stop codon for the pbp5 gene, which encodes high-level ampicillin resistance in this clinical isolate. Transfer of vancomycin, ampicillin, and tetracycline resistance from C68 to an E. faecium recipient strain occurs at low frequency in vitro and is associated with acquisition of a 130- to 160-kb segment of DNA that contains Tn5382, the pbp5 gene, and its putative repressor gene, psr. The interenterococcal transfer of this large chromosomal element appears to be the primary mechanism for vanB operon spread in northeast Ohio. These results expand the known family of Tn916-related transposons, suggest a mechanism for vanB operon entry into and dissemination among enterococci, and provide an explanation for the nearly universal association of vancomycin and high-level ampicillin resistance in clinical E. faecium strains.

Kinetic analysis of an inhibitor-resistant variant of the OHIO-1 beta-lactamase, an SHV-family class A enzyme

The Met69-->Ile mutant of the OHIO-1 beta-lactamase, an SHV-family enzyme, is resistant to inactivation by beta-lactamase inhibitors. Analysis of purified Met69-->Ile enzyme reveals that its isoelectric point (pI 7.0) and CD spectrum are identical with those of the OHIO-1 enzyme. Levels of beta-lactamase expression in Escherichia coli as determined by immunoblotting are similar for OHIO-1 and Met69-->Ile beta-lactamase. The kinetic constants of the Met69-->Ile enzyme compared with OHIO-1 are smaller for benzylpenicillin (Km = 6 microM compared with 17 microM; kcat = 234 s-1 compared with 345 s-1 respectively) and carbenicillin (Km = 3 microM compared with 17 microM; kcat = 131 s-1 compared with 320 s-1 respectively). For the cephalosporins cephaloridine and 7-(thienyl- 2-acetamido)-3-[2-(4-N,N- dimethylaminophenylazo)pyridinium-methyl]-3-cephem-4-carboxylic acid (PADAC), a similar pattern is also seen (Km=38 microM compared with 96 microM and 6 microM compared with 75 microM respectively; kcat = 235 s-1 compared with 1023 s-1 and 9 s-1 compared with 50 s-1 respectively). Consistent with minimum inhibitory concentrations that show resistance to beta-lactam beta-lactamase inhibitors, the apparent Ki values, turnover numbers and partition ratios (kcat/kinact) for the mechanism-based inactivators clavulanate, sulbactam and tazobactam are increased. The inactivation rate constants (kinact) are decreased. The difference in activation energy, a measurement of altered affinity for the wild-type and mutant enzymes leading to acylation of the active site, reveals small energy differences of less than 8.4 kJ/mol. In total, these results suggest that the Met-->Ile substitution at position 69 in the OHIO-1 beta-lactamase alters the active site, primarily affecting the interactions with beta-lactamase inhibitors.

Transferable, plasmid-mediated vanB-type glycopeptide resistance in Enterococcus faecium

An approximately 60-kb transferable, vanB-carrying plasmid has been identified in a clinical Enterococcus faecium strain. A similar plasmid has been observed in an unrelated E. faecium strain, suggesting that plasmid transfer of vanB operons occurs in nature and plays a role in the dissemination of VanB-type resistance among strains of E. faecium.

Construction and characterization of an OHIO-1 beta-lactamase bearing Met69Ile and Gly238Ser mutations

Amino acid changes that influence activity and resistance to beta-lactams and beta-lactamase inhibitors were explored by constructing the Gly238Ser and Met69Ile-Gly238Ser mutants of the OHIO-1 beta-lactamase, a class A enzyme of the SHV family. The Km values of cefotaxime and ceftazidime for OHIO-1 and Met69Ile beta-lactamases were > or = 500 microM. The Km of cefotaxime for the Gly238Ser beta-lactamase was 26 microM, and that of ceftazidime was 105 microM. The Km of cefotaxime for the Met69Ile-Gly238Ser beta-lactamase was 292 microM, and that of ceftazidime was 392 microM. For the beta-lactamase inhibitors clavulanate and sulbactam, the apparent Ki values for the Met69Ile-Gly238Ser enzyme were 0.03 and 0.15 microM, respectively. Relative Vmax values indicate that the Met69Ile-Gly238Ser mutant of the OHIO-1 beta-lactamase possesses cephalosporinase activity similar to that of the Gly238Ser mutant but diminished penicillinase activity. In an Escherichia coli DH5alpha strain that possesses a Met69Ile beta-lactamase of the OHIO-1 family, the added Gly238Ser mutation resulted in a phenotype with qualities that confer resistance to expanded-spectrum cephalosporins and, to a lesser extent, beta-lactamase inhibitors.

OHIO-1 beta-lactamase mutants: Asp179Gly mutation confers resistance to ceftazidime

The Asp179Gly mutant of the OHIO-1 beta-lactamase, an SHV enzyme, was constructed to investigate the effect of disruption of the omega loop on beta-lactamase activity in this class A enzyme. In Escherichia coli DH5 alpha the strain possessing the Asp179Gly mutation of the OHIO-1 beta-lactamase demonstrated increased susceptibility to all beta-lactams except ceftazidime and ceftriaxone. The minimum inhibitory concentrations for ceftazidime and ceftriaxone increased from 0.25 and 0.015 microgram/ml to 4.0 and .25 micrograms/ ml respectively. For ceftazidime, a substrate not hydrolyzed by the wild-type enzyme (K(m) > or = 500 microM), the K(m) of the Asp179Gly mutant beta-lactamase was measured to be 7 microM and the Vmax was 0.13 microM/min. The minimum inhibitory concentrations, K(m), and Vmax for all other beta-lactams decreased. Our analysis of this OHIO-1 beta-lactamase mutant suggests that disruption of the salt bridge in the omega loop by substitution of a glycine at position 179 markedly decreases the catalytic efficiency of the enzyme.

Gene therapy of murine teratocarcinoma: separate functions for insulin-like growth factors I and II in immunogenicity and differentiation

Teratocarcinoma is a germ-line carcinoma giving rise to an embryoid tumor with structures derived from the three embryonic layers: mesoderm, endoderm, and ectoderm. Teratocarcinoma is widely used as an in vitro model system to study regulation of cell determination and differentiation during mammalian embryogenesis. Murine embryonic carcinoma (EC) PCC3 cells express insulin-like growth factor I(IGF-I) and its receptor, while all derivative tumor structures express IGF-I and IGF-II and their receptors. Therefore the system lends itself to dissect the role of these two growth factors during EC differentiation. With an episomal antisense strategy, we define a role for IGF-I in tumorigenicity and evasion of immune surveillance. Antisense IGF-I EC transfectants are shown to elicit a curative anti-tumor immune response with tumor regression at distal sites. In contrast, IGF-II is shown to drive determination and differentiation in EC cells. Since IGF-I and IGF-II bind to type I receptor and antisense sequence used for IGF-II cannot form duplex with endogenous IGF-I transcripts, it follows that this receptor is not involved in determination and differentiation.

Treatment and prevention of rat glioblastoma by immunogenic C6 cells expressing antisense insulin-like growth factor I RNA

Rat C6 glioma cells express insulin-like growth factor I (IGF-I) and form rapidly growing tumors in syngeneic animals. When transfected with an episome-based vector encoding antisense IGF-I complementary DNA, these cells lost tumorigenicity. Subcutaneous injection of IGF-I antisense-transfected C6 cells into rats prevented formation of both subcutaneous tumors and brain tumors induced by nontransfected C6 cells. The antisense-transfected cells also caused regression of established brain glioblastomas when injected at a point distal to the tumor. These antitumor effects result from a glioma-specific immune response involving CD8+ lymphocytes. Antisense blocking of IGF-I expression may reverse a phenotype that allows C6 glioma cells to evade the immune system.

Loss of tumorigenicity of rat glioblastoma directed by episome-based antisense cDNA transcription of insulin-like growth factor I

Malignant glioma is the most common brain tumor. The molecular basis of glioma tumorigenicity has not been defined. Cultured glioma cells accumulate high levels of insulin-like growth factor I (IGF-I) transcripts. We asked whether IGF-I expression is coupled to tumorigenicity, using a combined in vivo/in vitro system employing antisense RNA for IGF-I. An antisense IGF-I expression construct in an expression vector that incorporates Epstein-Barr virus replicative signals and the ZnSO4-inducible metallothionein I transcriptional promoter was assembled. Stable glioma transfectants were derived from C6 glioma cells, which constitutively express IGF-I. B-104 neuroblastoma cells, derived originally from the same tumor but not expressing IGF-I, were also transfected as controls. In the absence of ZnSO4, the C6 transfectants expressed high levels of IGF-I mRNA and protein as detected by in situ hybridization and immunocytochemistry, respectively. Addition of ZnSO4 in the culture medium resulted in high levels of antisense transcript accumulation and dramatically decreased levels of endogenous IGF-I mRNA and IGF-I protein. Subcutaneous injection of either nontransfected C6 parental cells or C6 cells transfected with vector without IGF-I sequences into rats resulted in large tumors after 2 weeks, as did transfected and nontransfected B-104 cells. However, the rats injected with transfected C6 cells yielded no tumors after 40 weeks of observation. Two weeks after injection of the transfected C6 cells a small cyst was apparent in six rats. Histologic sections revealed a few glioma cells infiltrated by a large number of mononuclear cells. No infiltration of mononuclear cells was apparent in the glioma tumors resulting from injection of parental (nontransfected) cells, suggesting that the parental cells, but not the antisense IGF-I transfectants, escape the host immune response.

Effects of actinomycin D and cycloheximide on transcript levels of IGF-I, actin, and albumin in hepatocyte primary cultures treated with growth hormone and insulin

The stability of several RNA transcripts in cultured hepatocytes is known to increase when serum is omitted from the culture medium. In order to investigate possible mechanisms for this phenomenon, we examined the effects of actinomycin D and cycloheximide on the levels of actin, albumin, and insulin-like growth factor I transcripts in primary cultures incubated in serum-free medium. The levels of IGF-I and albumin transcripts per culture increased for the first 4 hours following addition of actinomycin D and then declined. The levels of actin transcripts and total RNA per culture declined immediately following actinomycin D addition in a manner consistent with exponential decay. IGF-I and albumin transcript levels were relatively unaffected by cycloheximide, while actin transcript levels increased 7-fold over 7 hours. The half-lives of actin transcripts and total RNA were calculated to be 4.6 to 7.7 hours and 11 to 19 hours, respectively, with no statistically significant correlation with hormone treatment. The data suggest that the stability of albumin and IGF-I transcripts, but not actin transcripts, is controlled in part by an actinomycin D-sensitive process.

Newly synthesized RNA: simultaneous measurement in intact cells of transcription rates and RNA stability of insulin-like growth factor I, actin, and albumin in growth hormone-stimulated hepatocytes

The levels of several RNA transcripts in cultured hepatocytes are regulated by transcriptional and post-transcriptional mechanisms and are affected by growth hormone and insulin. We assessed the effects of these hormones on transcription rates and the stability of insulin-like growth factor I, actin, and albumin transcripts in intact cells of primary cultures of rat hepatocytes by analyzing thiol-labeled, newly synthesized RNA isolated by mercurated agarose affinity chromatography. The application of this concept to the measurement of transcript stability is presented in detail. The data indicate that growth hormone stimulates the transcription rates of insulin-like growth factor I, actin, and albumin genes. The stability of all three transcripts, particularly albumin, appears to be lower in growth hormone-containing medium than it is in insulin-containing medium. The experiments indicate that the rates of transcription and/or degradation of albumin mRNA are influenced by hormonal treatment. However, the cells maintain roughly constant albumin transcript levels independent of hormone treatment by compensatory changes in the rates of transcription and degradation.

Transverse myelopathy: influence of body position as a cause

A 37-year-old man developed an acute onset of paraplegia after traveling about 4 1/2 hr in the cab of a moving truck, sitting "crouched over, Indian style," with trunk flexed forward and the lower extremities in flexion, abduction, and external rotation. A diagnosis of transverse myelitis with probable spinal cord infarct was made. The sudden onset in this case supports a vascular origin, with body position as an important factor leading to vascular compromise of the spinal cord.