James A. McKinnell

Carotenoid-Related Alteration of Cell Membrane Fluidity Impacts Staphylococcus aureus Susceptibility to Host Defense Peptides

ABSTRACT Carotenoid pigments of Staphylococcus aureus provide integrity to its cell membrane (CM) and limit oxidative host defense mechanisms. However, the role of carotenoids in staphylococcal resistance to nonoxidative host defenses has not been characterized. The current study examined the relationship among CM carotenoid content, membrane order, and in vitro susceptibility to daptomycin or to prototypic neutrophil-derived, platelet-derived, or bacterium-derived cationic antimicrobial peptides (human neutrophil defensin-1 [hNP-1], platelet microbicidal proteins [PMPs], or polymyxin B, respectively). A previously characterized methicillin-susceptible Staphylococcus aureus (MSSA) isogenic clinical strain set was used, including a parental isolate with an intact carotenoid biosynthetic operon (crtOPQMN) containing the crtM gene encoding early steps in staphyloxanthin biosynthesis, a crtM deletion mutant, and a crtMN multicopy plasmid-complemented variant. Compared to the parental and crtM knockout strains, the crtMN-complemented strain exhibited (i) increased carotenoid production, (ii) increased CM rigidity (P < 0.001), and (iii) uniformly reduced susceptibility to killing by the above-mentioned range of cationic peptides (statistically significant for hNP-1 [20 μg/ml]; P = 0.0037). There were no significant differences in phospholipid composition and asymmetry, fatty acid profiles, surface charge, or cell wall thickness among the strain set. Collectively, these data support the concept that carotenoid biosynthesis can contribute to the ability of S. aureus to subvert nonoxidative host defenses mediated by cationic peptides, potentially by increasing target membrane rigidity.

In Vitro Cross-Resistance to Daptomycin and Host Defense Cationic Antimicrobial Peptides in Clinical Methicillin-Resistant Staphylococcus aureus Isolates

ABSTRACT We investigated the hypothesis that methicillin-resistant Staphylococcus aureus (MRSA) isolates developing reduced susceptibilities to daptomycin (DAP; a calcium-dependent molecule acting as a cationic antimicrobial peptide [CAP]) may also coevolve reduced in vitro susceptibilities to host defense cationic antimicrobial peptides (HDPs). Ten isogenic pairs of clinical MRSA DAP-susceptible/DAP-resistant (DAPs/DAPr) strains were tested against two distinct HDPs differing in structure, mechanism of action, and origin (thrombin-induced platelet microbicidal proteins [tPMPs] and human neutrophil peptide-1 [hNP-1]) and one bacterium-derived CAP, polymyxin B (PMB). Seven of 10 DAPr strains had point mutations in the mprF locus (with or without yyc operon mutations), while three DAPr strains had neither mutation. Several phenotypic parameters previously associated with DAPr were also examined: cell membrane order (fluidity), surface charge, and cell wall thickness profiles. Compared to the 10 DAPs parental strains, their respective DAPr strains exhibited (i) significantly reduced susceptibility to killing by all three peptides (P < 0.05), (ii) increased cell membrane fluidity, and (iii) significantly thicker cell walls (P < 0.0001). There was no consistent pattern of surface charge profiles distinguishing DAPs and DAPr strain pairs. Reduced in vitro susceptibility to two HDPs and one bacterium-derived CAP tracked closely with DAPr in these 10 recent MRSA clinical isolates. These results suggest that adaptive mechanisms involved in the evolution of DAPr also provide MRSA with enhanced survivability against HDPs. Such adaptations appear to correlate with MRSA variations in cell membrane order and cell wall structure. DAPr strains with or without mutations in the mprF locus demonstrated significant cross-resistance profiles to these unrelated CAPs.

A systematic literature review and meta-analysis of factors associated with methicillin-resistant Staphylococcus aureus colonization at time of hospital or intensive care unit admission.

OBJECTIVE Screening for methicillin-resistant Staphylococcus aureus (MRSA) in high-risk patients is a legislative mandate in 9 US states and has been adopted by many hospitals. Definitions of high risk differ among hospitals and state laws. A systematic evaluation of factors associated with colonization is lacking. We performed a systematic review of the literature to assess factors associated with MRSA colonization at hospital admission. DESIGN We searched MEDLINE from 1966 to 2012 for articles comparing MRSA colonized and noncolonized patients on hospital or intensive care unit (ICU) admission. Data were extracted using a standardized instrument. Meta-analyses were performed to identify factors associated with MRSA colonization. RESULTS We reviewed 4,381 abstracts; 29 articles met inclusion criteria (n = 76,913 patients). MRSA colonization at hospital admission was associated with recent prior hospitalization (odds ratio [OR], 2.4 [95% confidence interval (CI), 1.3-4.7]; P < .01), nursing home exposure (OR, 3.8 [95% CI, 2.3-6.3]; P < .01), and history of exposure to healthcare-associated pathogens (MRSA carriage: OR, 8.0 [95% CI, 4.2-15.1]; Clostridium difficile infection: OR, 3.4 [95% CI, 2.2-5.3]; vancomycin-resistant Enterococci carriage: OR, 3.1 [95% CI, 2.5-4.0]; P < .01 for all). Select comorbidities were associated with MRSA colonization (congestive heart failure, diabetes, pulmonary disease, immunosuppression, and renal failure; P < .01 for all), while others were not (human immunodeficiency virus, cirrhosis, and malignancy). ICU admission was not associated with an increased risk of MRSA colonization (OR, 1.1 [95% CI, 0.6-1.8]; P = .87). CONCLUSIONS MRSA colonization on hospital admission was associated with healthcare contact, previous healthcare-associated pathogens, and select comorbid conditions. ICU admission was not associated with MRSA colonization, although this is commonly used in state mandates for MRSA screening. Infection prevention programs utilizing targeted MRSA screening may consider our results to define patients likely to have MRSA colonization.

Blastomycosis: New Insights into Diagnosis, Prevention, and Treatment

The basic science and clinical understanding of infection with Blastomyces dermatitidis has been a field of constant evolution and continued revision of hypotheses. This article highlights some areas in which recent progress has the potential for significant impact on the clinical care of patients. Specifically, this article examines the application of modern technology to epidemiologic studies, the development of novel vaccine candidates, emerging populations at risk for the disease, rapid diagnostic tools, and the application of novel antifungal agents in the treatment of blastomycosis.

Quantifying the Impact of Extranasal Testing of Body Sites for Methicillin-Resistant Staphylococcus aureus Colonization at the Time of Hospital or Intensive Care Unit Admission

OBJECTIVE Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of healthcare-associated infections. Recent legislative mandates require nares screening for MRSA at hospital and intensive care unit (ICU) admission in many states. However, MRSA colonization at extranasal sites is increasingly recognized. We conducted a systematic review of the literature to identify the yield of extranasal testing for MRSA. DESIGN We searched MEDLINE from January 1966 through January 2012 for articles comparing nasal and extranasal screening for MRSA colonization. Studies were categorized by population tested, specifically those admitted to ICUs and those admitted to hospitals with a high prevalence (6% or greater) or low prevalence (less than 6%) of MRSA carriers. Data were extracted using a standardized instrument. RESULTS We reviewed 4,381 abstracts and 735 articles. Twenty-three articles met the criteria for analysis ((n = 39,479 patients). Extranasal MRSA screening increased the yield by approximately one-third over nares alone. The yield was similar at ICU admission (weighted average, 33%; range, 9%-69%) and hospital admission in high-prevalence (weighted average, 37%; range, 9%-86%) and low-prevalence (weighted average, 50%; range, 0%-150%) populations. For comparisons between individual extranasal sites, testing the oropharynx increased MRSA detection by 21% over nares alone; rectum, by 20%; wounds, by 17%; and axilla, by 7%. CONCLUSIONS Extranasal MRSA screening at hospital or ICU admission in adults will increase MRSA detection by one-third compared with nares screening alone. Findings were consistent among subpopulations examined. Extranasal testing may be a valuable strategy for outbreak control or in settings of persistent disease, particularly when combined with decolonization or enhanced infection prevention protocols.

Systematic Review and Meta-Analysis of Linezolid and Daptomycin for Treatment of Vancomycin-Resistant Enterococcal Bloodstream Infections

ABSTRACT Bloodstream infections due to vancomycin-resistant enterococci (VRE-BSI) result in substantial patient mortality and cost. Daptomycin and linezolid are commonly prescribed for VRE-BSI, but there are no clinical trials to determine optimal antibiotic selection. We conducted a systematic review for investigations that compared daptomycin and linezolid for VRE-BSI. We searched Medline from 1966 through 2012 for comparisons of linezolid and daptomycin for VRE-BSI. We included searches of EMBASE, clinicaltrials.gov, and national meetings. Data were extracted using a standardized instrument. Pooled odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using a fixed-effects model. Our search yielded 4,243 publications, of which 482 contained data on VRE treatment. Most studies (452/482) did not present data on BSI or did not provide information on linezolid or daptomycin. Among the remaining 30 studies, 9 offered comparative data between the two agents. None were randomized clinical trials. There was no difference in microbiologic (n = 5 studies, 517 patients; OR, 1.0; 95% CI, 0.4 to 1.7; P = 0.95) and clinical (n = 3 studies, 357 patients; OR, 1.2; 95% CI, 0.7 to 2.0; P = 0.7) cures between the two antibiotics. There was a trend toward increased survival with linezolid compared to daptomycin treatment (n = 9 studies, 1,074 patients; OR, 1.3; 95% CI, 1.1 to 1.8; I2 = 0 [where I2 is a measure of inconsistency]), but this did not reach statistical significance (P = 0.054). There are limited data to inform clinicians on optimal antibiotic selection for VRE-BSI. Available studies are limited by small sample size, lack of patient-level data, and inconsistent outcome definitions. Additional research, including randomized clinical trials, is needed before conclusions can be drawn about treatment options for VRE therapy.

Nitrofurantoin Compares Favorably to Recommended Agents as Empirical Treatment of Uncomplicated Urinary Tract Infections in a Decision and Cost Analysis

OBJECTIVE To analyze the costs of nitrofurantoin use compared to those of other antibiotics recommended for treatment of uncomplicated urinary tract infection (UTI). PATIENTS AND METHODS We used a decision analysis model to perform cost-minimization and sensitivity analyses to determine the level of trimethoprim-sulfamethoxazole (TMP-SMX) and fluoroquinolone resistance that would favor the use of nitrofurantoin as a first-line empirical treatment of uncomplicated UTIs. The model used a program perspective to evaluate costs. RESULTS Nitrofurantoin was cost-minimizing when the prevalence of fluoroquinolone resistance exceeded 12% among uropathogens or the prevalence of TMP-SMX resistance exceeded 17%. On 2-way sensitivity analysis, variables that had a significant impact on our cost-minimization threshold included cost of antibiotics and probability of clinical cure with antibiotics. CONCLUSION From a payer perspective, nitrofurantoin appears to be a reasonable alternative to TMP-SMX and fluoroquinolones for empirical treatment of uncomplicated UTIs, especially given the current prevalence of antibiotic resistance among community uropathogens. On the basis of efficacy, cost, and low impact on promoting antimicrobial resistance, clinicians should consider nitrofurantoin as a reasonable alternative to TMP-SMX and fluoroquinolones for first-line therapy for uncomplicated UTIs.

Combinatorial Phenotypic Signatures Distinguish Persistent from Resolving Methicillin-Resistant Staphylococcus aureus Bacteremia Isolates

ABSTRACT Persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia (PB) (positive blood cultures after ≥7 days of therapy) represents a clinically challenging subset of invasive MRSA infections. In this investigation, we examined the potential correlation of specific virulence signatures with PB versus resolving MRSA bacteremia (RB) (negative blood cultures within 2 to 4 days of therapy) strains. Thirty-six MRSA isolates from patients enrolled in a recent multinational clinical trial were studied for (i) susceptibility to host defense cationic peptides (HDPs) (i.e., thrombin-induced platelet microbicidal proteins [tPMPs] and human neutrophil peptide 1 [hNP-1]); (ii) adherence to host endovascular ligands (fibronectin) and cells (endothelial cells); and (iii) biofilm formation. We found that PB isolates exhibited significantly reduced susceptibilities to tPMPs and hNP-1 (P < 0.001 and P = 0.023, respectively). There was no significant association between the PB outcome and fibronectin binding, endothelial cell binding, or biofilm formation (P = 0.25, 0.97, and 0.064 versus RB strains, respectively). However, multiple logistic regression analysis revealed that the PB outcome was significantly associated with the combination of reduced susceptibilities to HDPs and extent of biofilm formation (P < 0.0001). Similar results were obtained in a second analysis using days of bacteremia as a continuous outcome, showing that reduced HDP susceptibilities and increased biofilm formation cocontributed to predict the duration of bacteremia. Our data indicate that PB isolates have specific pathogenic signatures independent of conventional antimicrobial susceptibility. These combinatorial mosaics can be defined and used to prospectively distinguish PB from RB strains in advance and potentially to predict ultimate clinical outcomes.

Pneumocystis pneumonia in hospitalized patients: a detailed examination of symptoms, management, and outcomes in human immunodeficiency virus (HIV)-infected and HIV-uninfected persons

Pneumocystis jirovecii pneumonia (PCP) is a life‐threatening infection for immunocompromised individuals. Robust data and clear guidelines are available for prophylaxis and treatment of human immunodeficiency virus (HIV)‐related PCP (HIV‐PCP), yet few data and no guidelines are available for non‐HIV‐related PCP (NH‐PCP). We postulated that prevention and inpatient management of HIV‐PCP differed from NH‐PCP.

Observational study of the epidemiology and outcomes of vancomycin-resistant Enterococcus bacteraemia treated with newer antimicrobial agents

Vancomycin-resistant Enterococcus bloodstream infections (VRE-BSI) are a growing problem with few clinical trials to guide therapy. We conducted a retrospective study of management and predictors of mortality for VRE-BSI at a tertiary-care centre from January 2005 to August 2008. Univariate and multivariable analyses examined the relationship of patient characteristics and antibiotic therapy with 30-day all-cause mortality. Rates of VRE-BSI increased from 0·06 to 0·17 infections/1000 patient-days (P=0·03). For 235 patients, 30-day mortality was 34·9%. Patients were primarily treated with linezolid (44·2%) or daptomycin (36·5%). Factors associated with mortality were haemodialysis [odds ratio (OR) 3·2, 95% confidence interval (CI) 1·6-6·3, P=0·007], mechanical ventilation (OR 3·7, 95% CI 1·3-10·4, P=0·01), and malnutrition (OR 2·0, 95% CI 1·0-4·0, P=0·046). Use of linezolid, but not daptomycin (P=0·052) showed a trend towards an association with survival. In conclusion, VRE-BSI is a growing problem, associated with significant 30-day mortality. Multiple factors were associated with poor outcomes at our hospital.