Emergence of community-associated methicillin-resistant Staphylococcus aureus USA 300 clone as a cause of health care-associated infections among patients with prosthetic joint infections

BACKGROUND: Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as an important cause of staphylococcal infections, but there have been little data on whether CA-MRSA causes health care-associated infections. METHODS: A case-control study was performed to identify risk factors for prosthetic joint infections (PJI). Antibiograms of isolates associated with PJI were reviewed. Molecular typing of available MRSA isolates was done using pulsed field gel electrophoresis (PFGE). Nares cultures of health care workers who provided care to those orthopedic patients were obtained. RESULTS: Over a 13-month period (January 2003-January 2004), 9.5% of patients with prosthetic hip (THA) or knee (TKA) joint surgery developed PJI (7 TKA and 2 THA). The mean time to development of PJI was 20 days. Five infections were caused by CA-MRSA and 3 by methicillin-susceptible S aureus; one was culture negative. All CA-MRSA isolates had identical antibiograms (resistant to beta-lactams and erythromycin; susceptible to clindamycin, trimethoprim-sulfamethoxazole, rifampin, gentamicin, levofloxacin, and vancomycin). Molecular typing of 2 available CA-MRSA isolates revealed that these were the USA300 clone; these isolates were PVL+ and carried SCCmec IV. CA-MRSA was not recovered from nares cultures from 31 health care workers. In multivariate analysis, TKA (OR, 8.1; 95% CI: 1.3-48.1) and surgery time >180 minutes (OR, 7.4; 95% CI: 1.4-39.6) were associated with PJI. CONCLUSION: We have demonstrated that the CA-MRSA USA300 clone is no longer just a cause of community-acquired infections but has also emerged as a cause of health care-associated infections, causing PJI at our institution.     

A single treatment of yttrium-90-labeled CHX-A"-C6.5 diabody inhibits the growth of established human tumor xenografts in immunodeficient mice

Antitumor diabody molecules are noncovalent single-chain Fv dimers that recapitulate the divalent binding properties of native IgG antibodies. Diabodies are capable of substantial accumulation in tumor xenografts expressing relevant antigens in immunodeficient mouse models. With a Mr of approximately 55,000, diabodies are rapidly cleared from the circulation, resulting in tumor-to-blood ratios that significantly exceed those achieved early after the administration of monoclonal antibodies. We have evaluated the therapeutic potential of the beta-emitting isotope yttrium-90 (t1/2, 64 hours) conjugated to the C6.5K-A diabody that specifically targets the HER2/neu human tumor-associated antigen. We have found that a single intravenous dose of 150 microCi (200 microg) 90Y-CHX-A"-C6.5K-A diabody substantially inhibits the growth rates of established MDA-361/DYT2 human breast tumor xenografts in athymic nude mice. In contrast, 300 microCi (300 microg) 90Y-CHX-A"-C6.5K-A diabody resulted in only a minor delay in the growth of SK-OV-3 human ovarian cancer xenografts. The maximum tolerated dose was also dependent on the tumor xenograft model used. These studies indicate that genetically engineered antitumor diabody molecules can be used as effective vehicles for radioimmunotherapy.     

Somatic loss of maternal chromosome 11 causes parent-of-origin-dependent inheritance in SDHD-linked paraganglioma and phaeochromocytoma families

Germline mutations in succinate dehydrogenase subunits B, C and D (SDHB, SDHC and SDHD), genes encoding subunits of mitochondrial complex II, cause hereditary paragangliomas and phaeochromocytomas. In SDHB (1p36)- and SDHC (1q21)-linked families, disease inheritance is autosomal dominant. In SDHD (11q23)-linked families, the disease phenotype is expressed only upon paternal transmission of the mutation, consistent with maternal imprinting. However, SDHD shows biallelic expression in brain, kidney and lymphoid tissues (Baysal et al., 2000). Moreover, consistent loss of the wild-type (wt) maternal allele in SDHD-linked tumours suggests expression of the maternal SDHD allele in normal paraganglia. Here we demonstrate exclusive loss of the entire maternal chromosome 11 in SDHD-linked paragangliomas and phaeochromocytomas, suggesting that combined loss of the wt SDHD allele and maternal 11p region is essential for tumorigenesis. We hypothesize that this is driven by selective loss of one or more imprinted genes in the 11p15 region. In paternally, but not in maternally derived SDHD mutation carriers, this can be achieved by a single event, that is, non-disjunctional loss of the maternal chromosome 11. Thus, the exclusive paternal transmission of the disease can be explained by a somatic genetic mechanism targeting both the SDHD gene on 11q23 and a paternally imprinted gene on 11p15.5, rather than imprinting of SDHD.     

Preconditioning enhances the expression of mitochondrial antioxidant thioredoxin-2 in the forebrain of rats exposed to severe hypobaric hypoxia

The impact of severe hypoxia and preconditioning on the expression of the mitochondrial antioxidant thioredoxin-2 (Trx-2) in rat hippocampus (CA1, CA2, CA3 fields, and dentate gyrus) and neocortex was studied by immunocytochemistry. The preconditioning consisted of three trials of mild hypobaric hypoxia (360 Torr, 2 hr) spaced at 24 hr. The last trial was followed by severe hypobaric hypoxia (180 Torr, 3 hr) 24 hr later. Both in hippocampus and in neocortex, severe hypobaric hypoxia resulted in enhanced Trx-2 expression at 3 hr, followed by a slight decline in Trx-2 levels, which nevertheless remained increased at 24 hr elsewhere except for the CA1 region. The preconditioning considerably augmented severe hypoxia-induced Trx-2 immunoreactivity, affecting both the number of immunoreactive cells and the intensity of immunostaining. The findings suggest a role for Trx-2 in the formation of brain hypoxic/ischemic tolerance accomplished by the preconditioning.     

Conversion to dementia among two groups with cognitive impairment. A preliminary report

OBJECTIVE: To determine the conversion rates to dementia in patients diagnosed with mild cognitive impairment (MCI) thought to be caused by incipient Alzheimer's disease (MCI-AD) or with MCI with features of vascular disease (MCI-Vas). METHODS: On the basis of patient history, neurocognitive, neurological and MRI evaluation, 99 patients were diagnosed with MCI-AD and 35 with MCI-Vas. Conversion to dementia over an average of a 2.4 +/- 1.8-year period was determined. RESULTS: Over the follow-up period, 44% converted to dementia, 51.5% remained classified as MCI, and 4.5% were reclassified as cognitively normal. The conversion rate to dementia was significantly faster at 3 years for the MCI-AD (50.5%) than for the MCI-Vas group (25.7%). The neuropsychological test found to best differentiate converters from non-converters was the Fuld-OME, a measure of learning and recall. Age, education, gender or APOE epsilon4 allele frequency did not differentiate converters from non-converters. CONCLUSIONS: MCI-AD and MCI-Vas are clinically meaningful subtypes of MCI that may convert to dementia at different rates. Prospective studies on larger subsets of MCI patients are required to confirm these findings.     

Independent inheritance of genes regulating two subpopulations of mouse clonogenic keratinocyte stem cells

Mouse keratinocyte stem cells originate from the bulge of hair follicle, and, according to definition, possess a clonogenic activity in vitro. We have investigated seven inbred (C57BL/6, C3H, DBA/2, BALB/c, FVB) and outbred (SENCAR, CD-1) mouse strains and found that three genetically distinct subsets of mouse strains differ significantly in the frequency of clonogenic activity in vitro. The analysis of keratinocyte colonies in two reciprocal backcross [C57BL/6 x (BALB/c x C57BL/6); BALB/c x (BALB/c x C57BL/6)] and intercross [(BALB/c x C57BL/ 6)F2] of BALB/c and C57BL/6 mice allowed us to identify two subpopulations of clonogenic keratinocytes able to produce small (less than 2 mm2) and large (more than 2 mm2) colonies. We conducted linkage analysis and found that small colonies associated with mouse chromosomes 1, 6, 7, 8, and 9; but large colonies--with the chromosome 4. We defined locus on the chromosome 9 that associated with small colonies as keratinocyte stem cell locus 1 (Ksc1), and locus on the mouse chromosome 4 associated with large colonies-keratinocyte stem cell locus 2 (Ksc2). Ksc1 and loci on chromosomes 6 and 7 are close if not equal to loci associated with sensitivity to skin carcinogenesis. We conclude that two subpopulations of stem cells able to produce small and large colonies regulated by different genes and genes regulating small colonies might be responsible for sensitivity to skin carcinogenesis.     

Surface modification of tricalcium phosphate for improvement of the interfacial compatibility with biodegradable polymers

The surface of tricalcium phosphate (TCP) filler particles was activated by treatment with dilute aqueous phosphoric acid. ATR-IR spectra indicated the formation of calcium hydrogen phosphate dihydrate at the surface. Oligo(lactone)s were formed by the subsequent reaction of the activated TCP with L-lactide and epsilon -caprolactone, respectively, at 150 degrees C without any additional catalysts. After extraction of the oligo(lactide), the residue of modified TCP-included calcium lactate whereas the water of crystallization of the dihydrate disappeared as shown by ATR-IR spectroscopy.Owing to the insolubility of TCP in common solvents, the analogous reaction between water-soluble disodium hydrogen phosphate dihydrate and L-lactide was used to study the kind of chemical bonds by high-resolution NMR spectroscopy. The 1H and 13C NMR spectra of the reaction product also pointed out the presence of calcium lactate. Additionally, signals were found indicating a covalent attachment of lactic acid units onto the phosphorus.For the preparation of composites, poly(L,DL-lactide) was mixed with TCP and modified TCP, respectively, in a ratio of 75/25 (w/w) and directly injection moulded into tensile test specimens at a barrel temperature of 180 degrees C. Although mechanical properties were not improved, scanning electron microscopy (SEM) indicated a better interfacial phase interaction in the composite with the modified TCP. Chemical bonds between filler and polymer matrix are assumed to be formed by transesterification reactions.     

Insulin-like growth factor-I enhances lymphoid and myeloid reconstitution after allogeneic bone marrow transplantation

BACKGROUND: Prolonged immunodeficiency after allogeneic bone marrow transplantation (allo BMT) results in significant morbidity and mortality from infection. Previous studies in murine syngeneic BMT models have demonstrated that posttransplantation insulin-like growth factor (IGF)-I administration could enhance immune reconstitution. METHODS: To analyze the effects of IGF-I on immune reconstitution and graft-versus-host disease (GVHD) after allo BMT, we used murine models for MHC-matched and -mismatched allo BMT. Young (3-month-old) recipient mice received 4 mg/kg per day of human IGF-I from days 14 to 28 by continuous subcutaneous administration. RESULTS: IGF-I administration resulted in increased thymic precursor populations (triple negative-2 and triple negative-3) as determined on day 28 but had no effect on overall thymic cellularity. In the periphery, the numbers of donor-derived splenic CD3+ T cells were increased and these cells had an improved proliferative response to mitogen stimulation. IGF-I treatment also significantly increased the numbers of pro-, pre-, and mature B cells and myeloid cell populations in the spleens of allo BMT recipients on day 28. The administration of IGF-I in combination with interleukin 7 had a remarkable additive effect on B-cell, but not on T-cell, lymphopoiesis. Finally, we tested the effects of IGF-I administration on the development of GVHD in three different MHC-matched and -mismatched models and found no changes in GVHD morbidity and mortality. CONCLUSION: IGF-I administration can enhance lymphoid and myeloid reconstitution after allo BMT without aggravating GVHD.     

Beta2-microglobulin aberrations in diffuse large B-cell lymphoma of the testis and the central nervous system

Human leukocyte antigen (HLA) class I molecules are expressed on the surface of all nucleated cells and present antigenic peptides to cytotoxic T cells, thereby playing an important role in initiating the cellular anti-tumor immune response. We previously reported that loss of HLA class I expression in diffuse large B-cell lymphoma (DLBCL) of the central nervous system (CNS) and the testis is a common event. Loss of expression and mutations of the light chain of the HLA class I molecule, beta(2)-microglobulin (beta(2)m) have been described in a variety of human tumors and cell lines. In our study, we screened 15 DLBCL cases with a combined loss of HLA class I and beta(2)m expression for mutations in the latter gene by direct sequencing. Frame shift mutations in repetitive sequences within the beta(2)m gene leading to loss of functional beta(2)m were detected in 2 cases. Loss of heterozygosity (LOH) and fluorescent in situ hybridization (FISH) analysis for chromosome 15 exhibited loss of the remaining copy of the beta(2)m gene in both cases but also hemizygous deletions and monosomies in 6 additional cases. Since similar mutations in the beta(2)m gene have been associated with microsatellite instability (MSI), we used 8 markers to study MSI involvement in DLBCL. Low MSI was more frequent (33%) as compared to nodal DLBCL (n=15) but did not correlate with the beta(2)m mutations. Our data indicate that multiple mechanisms lead to downregulation of beta(2)m and concomitant loss of HLA class I expression in DLBCL.