Multidrug-resistant Acinetobacter baumannii: an emerging pathogen among older adults in community hospitals and nursing homes

BACKGROUND

Drug-resistant Acinetobacter species are problematic in tertiary-care hospitals. We describe the epidemiology, resistance patterns, and outcomes of older adults with Acinetobacter infection in community hospitals.

METHODS

We queried the microbiology databases of the Oakwood Healthcare System (4 hospitals with 632, 259, 199, and 168 beds) for clinical Acinetobacter cultures obtained in 2003-2008. Patients aged 60 years who were admitted from home or nursing homes were included. We recorded the initial Acinetobacter isolate and susceptibility to 8 antibiotics. Cultures obtained 48 h after hospitalization were categorized as "nosocomial." Administrative databases provided patients' origins (home or nursing home) and discharge destinations (home, nursing home, long-term acute-care facility, another hospital, or hospice care or death).

RESULTS

During the 6-year period, 560 community-dwelling (mean age +/- standard deviation, 74 +/- 8.6 years) and 280 nursing home-dwelling (78 +/- 9.1 years) patients had Acinetobacter isolated. During this period, Acinetobacter prevalence increased 25% (P<.001, by trend test). In comparison of 2003 with 2008, Acinetobacter resistance to imipenem and ampicillin/sulbactam increased (from 1.8% to 33.1%; P<.001), as did "panresistance" (ie, resistance to all 8 antibiotics; increase from 0.0% to 13.6%; P<.001). Although resistance was stable in community-acquired isolates (resistance to approximately 4.2 antibiotics), resistance increased among nursing home-acquired and nosocomial-acquired isolates (from 4.5 to 5.7 and from 5.0 to 6.0 antibiotics, respectively; P<.01). At discharge, only 25% of community-dwelling and 50% of nursing home-dwelling patients returned to their place of origin; the remainder required higher levels of care or died. After adjustment for age, length of stay, and origin, resistance to each additional antibiotic predicted a >20% increased risk for discharge to higher levels of care or death (odds ratio, 1.23; 95% confidence interval, 1.11-1.36).

CONCLUSIONS

The prevalence and resistance of Acinetobacter species are increasing in the community. Patients with resistant isolates are selectively discharged to nursing homes and long-term acute-care facilities, introducing resistance to new facilities.

Effect of chronic treatment of ethanol on benzodiazepine and picrotoxin sites on the GABA receptor complex in regions of the brain of the rat

Ethanol has been shown to enhance gamma-aminobutyric acid (GABA)ergic transmission. In this study an examination was made of the effect of chronic treatment with ethanol and its withdrawal at 24 h on the binding of [3H]flunitrazepam and [35S]t-butylbicyclophosphorothionate (TBPS) to brain regions in rat. Rats were rendered tolerant to, and dependent on, ethanol by an intragastric intubation method. The affinity (KD) or the binding capacity (Bmax) of [3H]flunitrazepam or [35S]TBPS was not altered by chronic treatment with ethanol or during withdrawal from ethanol. Neither the enhancing effect of GABA on the binding of [3H]flunitrazepam nor its inhibitory effect on the binding of [35S]TBPS were affected by chronic treatment with ethanol or its withdrawal at 24 h. These results suggest that the sensitivity of benzodiazepine and picrotoxin sites on the oligomeric GABA receptor complex is not affected during tolerance to, or withdrawal from ethanol. It is suggested that the effects of ethanol on GABAergic transmission may be produced at the level of coupled chloride ion channels.

Enhancement of diazepam and gamma-aminobutyric acid binding by (+)etomidate and pentobarbital

(+)Etomidate and pentobarbital enhance [3H]diazepam and [3H]gamma-aminobutyric acid [( 3H]GABA) binding to cerebral cortex membranes. Both (+)etomidate and pentobarbital increase the affinity of [3H]diazepam for its binding sites. In contrast, they increase the Bmax of both the high- and low-affinity GABA receptor sites. The enhancement of [3H]diazepam and [3H]GABA by (+)etomidate and pentobarbital is blocked by GABA antagonists. These results indicate that hypnotic drugs such as (+)etomidate and pentobarbital, which are not structurally related, modulate diazepam and GABA binding sites via similar mechanisms.

The effect of in vitro and in vivo ethanol administration on [35S]t-butylbicyclophosphorothionate binding in C57 mice

Previous studies have shown that ethanol may produce some of its effects by facilitation of GABAergic transmission. One of the potential sites of drug action at the GABA receptor complex is the picrotoxin site, which can be studied with [35S]t-butylbicyclophosphorothionate (TBPS). Ethanol inhibited the binding of [35S]TBPS to C57 mice brain regions in vitro. This inhibition appears to be noncompetitive since ethanol decreased the Bmax and not the KD value of [35S]TBPS. C57 mice were chronically treated with ethanol in liquid diet to determine if the sensitivity of TBPS binding is altered following chronic treatment or during withdrawal. Chronic treatment with ethanol and during withdrawal did not alter the KD or Bmax values of [35S]TBPS binding in C57 mice brain regions. It is suggested that the sensitivity of picrotoxin site on the oligomeric GABA receptor complex is not altered during ethanol tolerance or withdrawal. The effects of ethanol on GABA system may be mediated by its interaction with the coupling mechanism(s) or a direct effect on the chloride channels.

Transport of microorganisms into cellulose nanofiber mats

Electrospun cellulose nanofiber mat “sponges” are a green platform technology that has the potential to remove detrimental microorganisms from wounds, trap bacteria within a protective military textile, or remediate contaminated water.

GABA and benzodiazepine binding sites in spontaneously hypertensive rat

The binding of GABA to its central receptor sites and of benzodiazepines to central and peripheral types of binding sites was compared in age-matched spontaneously hypertensive rat (SHR) and normotensive (WKY) rat. The KD and Bmax values of GABA agonist binding were not significantly different between SHR and WKY rat in the forebrain, cerebellum or pons-medulla. The binding of [3H]flunitrazepam to central types of binding sites was also not different in 12 week-old SHR and WKY rat. However, the binding of [3H]flunitrazepam and [3H]RO5-4864 was significantly lower in the SHR kidney, as compared to WKY rat kidney. This decrease was due to a lower Bmax in SHR kidney. In contrast, the binding of these radioligands in the hearts of the two strains was not different. These results indicate that the SHR has lower peripheral benzodiazepine binding sites in the kidney as compared to age-matched normotensive WKY rat kidney.

Increased expression of TACI on NOD B cells results in germinal centre reaction anomalies, enhanced plasma cell differentiation and immunoglobulin production

B cells have an important pathogenic role in the development of type 1 diabetes in the non-obese diabetic (NOD) mouse. We have previously reported that NOD mice display an increased percentage of TACI^high -expressing B cells compared with C57BL/6 mice and this trait is linked to chromosomes 1 and 8. In this paper the genetic association of the transmembrane activator, calcium modulator and cyclophilin ligand interactor (TACI) trait was confirmed using double congenic NOD.B6C1/Idd22 mice. TACI ligation by a proliferation-inducing ligand (APRIL) has been shown to influence plasma cell differentiation, immunoglobulin production and isotype switch. Hence, the functional consequence of the up-regulation of TACI on NOD B cells was analysed both in vitro and in vivo. NOD B cells stimulated with APRIL showed an enhanced plasma cell differentiation and class switch to IgG and IgA compared with B cells from C57BL/6 mice. Moreover, flow cytometry analyses revealed that germinal centre B cells in NOD failed to down-regulate TACI. Availability of the TACI ligand B-cell activating factor (BAFF) has been shown to be a limiting factor in the germinal centre reaction. In line with this, upon immunization with 4-hydroxy-3-nitrophenylacetyl hapten-conjugated hen egg lysozyme, NOD mice produced higher titres of low-affinity antibodies compared with C57BL/6 mice. This observation was supported by the detection of increased levels of BAFF in NOD germinal centres after immunization compared with C57BL/6 by immunofluorescence. Our results support the hypothesis that increased TACI expression on NOD B cells contributes to the pathogenesis of type 1 diabetes in the NOD mouse.

Contribution of both B-cell intrinsic alterations as well as non-hematopoietic-derived factors in the enhanced immune response of the NOD mouse

The underlying cellular and molecular mechanism for the development of Type 1 diabetes is still to be fully revealed. We have previously demonstrated that the NOD mouse, a model for Type 1 diabetes, display a prolonged and enhanced immune response to both self and non-self-antigens. The molecular explanation for this defect however, has not been determined. In this study we immunized NOD and C57BL/6 (B6) with the conventional antigen i.e. hen egg lysozyme (HEL) and analyzed B cell activation, germinal center reaction and antibody clearance. Corroborating our previous observations NOD mice responded robustly to a single immunization of HEL. Immunofluorescence analysis of the spleen revealed an increased number of germinal centers in unimmunized NOD compared to B6. However, post immunization germinal center numbers were similar in NOD and B6. NOD mice showed lower response to BCR stimulation with anti-IgM, in particular at lower concentrations of anti-IgM. Antibody clearance in vivo did not differ between the strains. To determine the cell type that is responsible for the prolonged and enhance immune response, we reconstituted NOD-RAGs with cells from primed donors in different combinations. NOD B cells were required to reproduce the phenotype; however the non-lymphoid compartment of NOD origin also played a role. Based on our results we propose that preexisting GCs in the NOD promote the robust response and alteration in the BCR signaling could promote survival of stimulated cells. Overall, this mechanism could in turn also contribute to the activation and maintenance of autoreactive B cells in the NOD mouse.

Group-selective reagent modification of the benzodiazepine-gamma-aminobutyric acid receptor-ionophore complex reveals that low-affinity gamma-aminobutyric acid receptors stimulate benzodiazepine binding

The modification of membrane proteins with diethylpyrocarbonate (DEP) and diazotized sulfanilate was investigated on the binding of three benzodiazepine radioligands in three brain regions. Both of these reagents produced a dose-dependent inactivation of [3H] diazepam, [3H]flunitrazepam, and [3H]propyl beta-carboline-3-carboxylate binding to cortex, cerebellum, and hippocampus. Both DEP and diazotized sulfanilate decrease the Bmax of the benzodiazepine binding sites without altering the KD. The ability of muscimol and pentobarbital to enhance [3H]diazepam binding was not altered by DEP pretreatment in any of the three regions. Scatchard analysis indicated that, following the inactivation of 40-50% of [3H]diazepam binding by 1 mM DEP, pentobarbital and muscimol were still able to increase the affinity of [3H]diazepam binding in cortex, cerebellum, and hippocampus. In contrast, diazotized sulfanilate pretreatment abolishes the ability of muscimol and pentobarbital to enhance [3H]diazepam binding in these three regions. The effects of these reagents on [3H] gamma-aminobutyric acid (GABA) binding revealed that sulfanilate but not DEP eliminates the low-affinity GABA receptor sites in cortex and cerebellum. Thus, while both DEP and sulfanilate inactivate benzodiazepine binding sites, only sulfanilate abolishes the low-affinity GABA binding sites and the ability of the GABA agonists to enhance [3H]diazepam binding. These results suggest that the stimulation of benzodiazepine binding appears to be mediated by the low-affinity GABA receptors.

The human bone marrow plasma cell compartment in rheumatoid arthritis - Clonal relationships and anti-citrulline autoantibody producing cells

A majority of circulating IgG is produced by plasma cells residing in the bone marrow (BM). Long-lived BM plasma cells constitute our humoral immune memory and are essential for infection-specific immunity. They may also provide a reservoir of potentially pathogenic autoantibodies, including rheumatoid arthritis (RA)-associated anti-citrullinated protein autoantibodies (ACPA). Here we investigated paired human BM plasma cell and peripheral blood (PB) B-cell repertoires in seropositive RA, four ACPA+ RA patients and one ACPA- using two different single-cell approaches, flow cytometry sorting, and transcriptomics, followed by recombinant antibody generation. Immunoglobulin (Ig) analysis of >900 paired heavy-light chains from BM plasma cells identified by either surface CD138 expression or transcriptome profiles (including gene expression of MZB1, JCHAIN and XBP1) demonstrated differences in IgG/A repertoires and N-linked glycosylation between patients. For three patients, we identified clonotypes shared between BM plasma cells and PB memory B cells. Notably, four individuals displayed plasma cells with identical heavy chains but different light chains, which may indicate receptor revision or clonal convergence. ACPA-producing BM plasma cells were identified in two ACPA+ patients. Three of 44 recombinantly expressed monoclonal antibodies from ACPA+ RA BM plasma cells were CCP2+, specifically binding to citrullinated peptides. Out of these, two clones reacted with citrullinated histone-4 and activated neutrophils. In conclusion, single-cell investigation of B-cell repertoires in RA bone marrow provided new understanding of human plasma cells clonal relationships and demonstrated pathogenically relevant disease-associated autoantibody expression in long-lived plasma cells.

Contribution of autoallergy to the pathogenesis in the NOD mice

The immunoglobulin isotype IgE is commonly associated with allergy. However, its involvement in autoimmune disease in general, and Type 1 diabetes (T1D) in particular, is still not completely clarified, nonetheless IgE has been observed in patients with T1D. In this article, we aimed to elucidate the contribution of IgE in the pathogenesis of the disease in a spontaneous model for T1D, i.e. the NOD mouse. We observed increased levels of IgE in splenic, lymph node and peripheral blood B cells in the NOD mice compared to the control C57BL/6 (B6) mice. No correlation was found between the IgE levels on B cells and those in the sera of these mice, indicating a B cell intrinsic property mediating IgE capture in NOD. Functionally, the B cells from NOD were similar to B6 in rescuing the IgE-mediated immune response via the low affinity receptor CD23 in a transgenic adoptive transfer system. However, the involvement of IgE in diabetes development was clearly demonstrated, as treatment with anti-IgE antibodies delayed the incidence of the diabetes in the NOD mice compared to the PBS treated group. Pancreas sections from a 13-week-old NOD revealed the presence of tertiary lymphoid structures with T cells, B cells, germinal centers and IgE suggesting the presence of autoantigen specific IgE. Our study provides an insight to the commonly overlooked immunoglobulin IgE and its potential role in autoimmunity.