Comparison of MRSASelect Agar,CHROMagar Methicillin-Resistant Staphylococcus aureus (MRSA) Medium,and Xpert MRSA PCR for Detection of MRSA in Nares: Diagnostic Accuracy for Surveillance Samples with Various Bacterial Densities

Rapid laboratory methods provide optimal support for active surveillance efforts to screen for methicillin-resistant Staphylococcus aureus (MRSA). Most laboratories struggle to determine the optimal use of resources, considering options to balance cost, speed, and diagnostic accuracy. To assess the performance of common methods, the first comparison of MRSASelect agar (MS) and CHROMagar MRSA (CA), with and without broth enrichment followed by a 24-h subculture to MS, was performed. Results were compared to those of the Xpert MRSA assay. For direct culture methods, the agreement between MS and CA was 98.8%. At 18 h, direct MS identified 93% of all positive samples from direct culture and 84% of those identified by the Xpert MRSA. For Trypticase soy broth-enriched MS culture, incubated overnight and then subcultured for an additional 24 h, the agreement with Xpert MRSA was 96%. The agreement between direct MS and Xpert MRSA was 100% when semiquantitative culture revealed a bacterial density of 2+ or greater; however, discrepancies between culture and Xpert MRSA arose for MRSA bacterial densities of 1+ or less, indicating low density as a common cause of false-negative culture results. Since 1+ or less was established as the most common MRSA carrier state, broth enrichment or PCR may be critical for the identification of all MRSA carriers who may be reservoirs for transmission. In this active-surveillance convenience sample, the use of broth enrichment followed by subculture to MS offered a low-cost but sensitive method for MRSA screening, with performance similar to that of Xpert MRSA PCR.The spread of methicillin-resistant Staphylococcus aureus (MRSA) is a major concern in healthcare settings because human “carriers” can spread MRSA to others, resulting in increased morbidity, mortality, and costs (13, 14, 17). One strategy to help prevent and control MRSA infections is the use of active surveillance cultures to screen patients for nasal carriage of MRSA, a practice coupled with appropriate barrier precautions for colonized or infected patients. Active surveillance programs are growing in number in the United States (10, 20, 23, 24), despite differences in opinions about the practice and reported gaps in the literature (19). Therefore, clinical microbiology laboratories must respond to provide support for active surveillance screening methods.There is continued debate about the practicality and cost benefit of different MRSA detection methods. Typically, agar culture or PCR methods are used (4); however, additional workload and costs cause laboratories to struggle with resource allocation issues, which often depend on the interplay between assay accuracy, turnaround time, cost per test, and workforce availability. While PCR results can be available in as little as 2 h and are known to provide excellent sensitivity and specificity for MRSA screening (4, 25, 28), PCR methods are more costly than culture methods (6). Alternately, selective and differential chromogenic agars have gained popularity because of lower cost and mid-range speed. Because of their resistance to antimicrobials in the agar, MRSA colonies grow and subsequently produce distinct color changes caused by the cleavage of a chromogenic substrate by a specific enzyme of S. aureus. Results can be achieved in as little as 18 to 24 h of incubation, depending on the agar used (1, 4, 5, 15, 27; BBL CHROMagar MRSA package insert no. 8012632, 2006 [Becton Dickinson and Company]; MRSASelect package insert nos. 63747 and 63749, 2007 [Bio-Rad Laboratories]). Although less costly, direct agar cultures are relatively insensitive in comparison to PCR and broth enrichment cultures. Broth enrichment cultures can improve sensitivity in comparison to that of nonenriched (direct) cultures (2, 9, 16, 21); however, enrichment delays results and adds to workload and costs. Thus, a discussion of the advantages and limitations of each methodological approach become critical. Decisions about the type of screening method used must be made based on the performance of the methods and resources available for each health care system. Clearly, the most sensitive screening system is desirable; however, at times, financial realities may affect our clinical practices.Because of the critical balance between speed, accuracy, cost, and hands-on time associated with each screening method, we designed and evaluated a broth enrichment algorithm that relies on the use of chromogenic agar as the subculture medium for broth enrichment in order to maximize both the speed and sensitivity of agar-based approaches. We compared the method''s performance to that of a PCR reference method, the Cepheid Xpert MRSA assay.To our knowledge, the study is the first clinical assessment of Bio-Rad''s MRSASelect agar (MS) and Becton Dickinson''s BBL CHROMagar MRSA (CA) combined with broth enrichment and compared to the Xpert MRSA assay. It is also the first study to describe the performance of the methods relative to the various bacterial densities of MRSA which are found in active surveillance samples from hospitalized patients. The study goal was to validate an off-label use of MS as a subculture medium, in combination with tryptic soy broth (TSB) enrichment, to improve the recovery of MRSA bacteria with minimum impact to workload and cost.(This information was presented, in part, at the 108th General Meeting of the American Society for Microbiology, Boston, MA, 1 to 5 June 2008 [18].)     

Pathogen Profiling: Rapid Molecular Characterization of Staphylococcus aureus by PCR/Electrospray Ionization-Mass Spectrometry and Correlation with Phenotype

There are few diagnostic methods that readily distinguish among community-acquired methicillin (meticillin)-resistant Staphylococcus aureus strains, now frequently transmitted within hospitals. We describe a rapid and high-throughput method for bacterial profiling of staphylococcal isolates. The method couples PCR to electrospray ionization-mass spectrometry (ESI-MS) and is performed on a platform suitable for use in a diagnostic laboratory. This profiling technology produces a high-resolution genetic signature indicative of the presence of specific genetic elements that represent distinctive phenotypic features. The PCR/ESI-MS signature accurately identified genotypic determinants consistent with phenotypic traits in well-characterized reference and clinical isolates of S. aureus. Molecular identification of the antibiotic resistance genes correlated strongly with phenotypic in vitro resistance. The identification of toxin genes correlated with independent PCR analyses for the toxin genes. Finally, isolates were correctly classified into genotypic groups that correlated with genetic clonal complexes, repetitive-element-based PCR patterns, or pulsed-field gel electrophoresis types. The high-throughput PCR/ESI-MS assay should improve clinical management of staphylococcal infections.Invasive infections caused by methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) are among the most common complications of health care in the United States. Klevens et al. estimate that 94,360 invasive MRSA infections occur in the United States each year, with associated deaths in 18,650 cases (26). Infections are subcategorized as health care-associated MRSA (HA-MRSA) infections or as community-associated MRSA (CA-MRSA) infections; the latter occur in otherwise healthy people who have not experienced a hospital stay within the past 12 months (24, 35). CA-MRSA infections have largely been attributable to a few strains, designated pulsed-field types (PFTs) USA300 and USA400 (26, 29). Once introduced into a health care environment, CA-MRSA strains can be readily transmitted, blending with or replacing entrenched HA-MRSA strains (25, 35).Microbial genotyping analysis allows investigation into the clonality of an outbreak and risk factors associated with infection (5). Methods such as pulsed-field gel electrophoresis (PFGE) (39), repetitive-element-based PCR (rep-PCR) (42), and multilocus sequence typing (MLST) (10, 11) are used for microbial genotyping but are costly and labor-intensive and do not enable specific characterization of acquired genetic elements encoding virulence factors or toxins or of genes that mediate antibiotic resistance (40). A rapid technique for determining the MRSA strain genotype and its broader complement of genetic elements would enable a more comprehensive understanding of transmission dynamics and could lead to more effective actionable decisions related to bed management, prioritization of infection control resources, and treatment.Here, we describe the use of a rapid and high-throughput method to simultaneously genotype and characterize S. aureus specimens with respect to acquired genes encoding virulence factors, toxins, and antibiotic resistance determinants. The method is based on PCR coupled to electrospray ionization-mass spectrometry (ESI-MS) (8, 22, 37).The PCR/ESI-MS assay uses several novel strategies. First, broad-range primers, targeting sites that are highly conserved in all members of a microbe family, are used to amplify PCR products from groupings of microbes rather than single species. These primers are coupled with species- or strain-specific primers for the identification of specific pathogens or antibiotic targets. Second, PCR conditions are, by design, permissive and thus tolerant of mismatches, so that even sequences from novel strains can be amplified. Third, inosine and other “wild-card” nucleotides are used in primers to facilitate PCR analysis of mispaired sequences. Fourth, because MS simply measures the mass-to-charge ratio (m/z), the sequence of the amplicon need not be known in order to detect it. The technology offers advantages over routine single-target and multiplex PCR in that it is a full bioinformatics sequence analysis system.After amplification, MS is used to rapidly determine the precise mass-to-charge ratio for the amplified nucleic acid fragments present, and the A, C, T, and G contents (i.e., the base composition) of each amplicon are determined using proprietary software that creates a signature to allow organism identification and genotyping. This novel MS technology enables the rapid, sensitive, cost-effective, and simultaneous detection of a wide range of typical pathogenic organisms.We used the PCR/ESI-MS assay to analyze a well-characterized set of S. aureus strains from the CDC and geographically distinct clinical isolates from Maryland and Arizona. The PCR/ESI-MS technology effectively combines genotyping and characterization on a single high-throughput platform suitable for surveillance, infection control interventions, and patient management.     

The Th17 cytokine IL‐22 induces IL‐20 production in keratinocytes: A novel immunological cascade with potential relevance in psoriasis

Psoriasis is a common chronic skin disease. Recent studies demonstrated that IL‐20 and IL‐22, cytokines produced by keratinocytes and T cells, respectively, both inhibit keratinocyte terminal differentiation and induce psoriasis‐like epidermis alterations. Here, we investigated the relationship between these mediators. Although IL‐20 was not able to regulate IL‐22 production, IL‐22 induced IL‐20 mRNA and protein in human keratinocytes. However, IL‐22 had only a minimal effect, if any, on IL‐19 and IL‐26. Cutaneous IL‐20 was also elevated in mice following IL‐22 application. Accordingly, some of IL‐22's effects on differentiation‐regulating genes were partially mediated by an endogenous, secreted protein and attenuated by anti‐IL‐20 Ab. Like IL‐22, IL‐17A and TNF‐α induced IL‐20 in keratinocytes, whereas IFN‐γ and IL‐20 itself did not. Furthermore, IL‐17A and TNF‐α individually strengthened the IL‐22‐induced IL‐20 production. In lesional skin of psoriasis patients, highly elevated IL‐20 levels strongly correlated with IL‐22, and to a lesser extent, with IL‐17A and TNF‐α. As previously shown for IL‐22, IL‐20 blood levels correlated with the disease severity, although with a lower significance. This study demonstrates that a T‐cell mediator induces a tissue cell mediator with similar effects to its own and therefore suggests the existence of a novel type of pathogenetic cascade.     

Body mass index and risk of non-Hodgkin's and Hodgkin's lymphoma: a meta-analysis of prospective studies

We conducted a meta-analysis of prospective studies to summarise the epidemiologic evidence regarding the association of body mass index (BMI) with non-Hodgkin's lymphoma (NHL) and Hodgkin's lymphoma (HL) incidence and NHL mortality. Pertinent studies were identified by searching PubMed (1966-May 2011) and the reference lists of retrieved articles. For each study, we estimated a relative risk (RR) for a 5 kg/m(2) increase in BMI. A random-effects model was used to combine the RR estimates from individual studies. The summary RRs for a 5 kg/m(2) increase in BMI were 1.07 (95% confidence intervals (CI), 1.04-1.10) for NHL incidence (16 studies, n=17,291 cases) and 1.14 (95% CI, 1.04-1.26) for NHL mortality (five studies, n=3407 cases). BMI was significantly positively associated with risk of diffuse large B-cell lymphoma (RR, 1.13; 95% CI, 1.02-1.26), but not other NHL subtypes. The difference in risk estimates for subtypes was not statistically significant (P=0.10). There was evidence of a nonlinear association between BMI and HL (P for nonlinearity=0.01) (five studies, n=1557 cases). The summary RRs of HL were 0.97 (95% CI, 0.85-1.12) for overweight and 1.41 (95% CI, 1.14-1.75) for obesity. These results indicate that BMI is positively associated with risk of NHL and HL as well as with NHL mortality.     

Recollection and familiarity in amnestic mild cognitive impairment: a global decline in recognition memory

Despite memory failures being a central feature of amnestic mild cognitive impairment (a-MCI), there is limited research into the nature of the memory impairment associated with this condition. A further understanding could lead to refinement of criteria needed to qualify for this designation and aid in prediction of who will progress to development of clinical Alzheimer's disease. Dual process models posit that recognition memory is supported by the dissociable processes of recollection and familiarity. The present study sought to evaluate recognition memory in a-MCI in the framework of the dual process model. Patients with a-MCI and age- and education-matched controls were tested on three memory paradigms. Two paradigms were modifications of the process-dissociation procedure in which recollection required either memory of word-pair associations (associative) or the font color of words at study (featural). A final paradigm utilized the task-dissociation methodology comparing performance for item and visual spatial source memory. All three tasks revealed that familiarity was impaired to at least the same extent as recollection. As familiarity is thought to be spared in normal aging, its measurement may provide a relatively specific marker for the early pathological changes of Alzheimer's disease.     

Compensatory neural activity distinguishes different patterns of normal cognitive aging

Most cognitive neuroscientific research exploring the nature of age-associated compensatory mechanisms has compared old adults (high vs. average performers) to young adults (not split by performance), leaving ambiguous whether findings are truly age-related or reflect differences between high and average performers throughout the life span. Here, we examined differences in neural activity (as measured by ERPs) that were generated by high vs. average performing old, middle-age, and young adults while processing novel and target events to investigate the following three questions: (1) Are differences between cognitively high and average performing subjects in the allocation of processing resources (as indexed by P3 amplitude) specific to old subjects, or found throughout the adult life span? (2) Are differences between cognitively high and average performing subjects in speed of processing (as indexed by target P3 latency) of similar magnitude throughout the adult life span? (3) Where along the information processing stream does the compensatory neural activity attributed to cognitively high performing old subjects begin to take place? Our results suggest that high performing old adults successfully manage the task by a compensatory neural mechanism associated with the modulation of controlled processing and the allocation of more resources, whereas high performing younger subjects execute the task more efficiently with fewer resources. Differences between cognitively high and average performers in processing speed increase with age. Middle-age seems to be a critical stage in which substantial differences in neural activity between high and average performers emerge. These findings provide strong evidence for different patterns of age-related changes in the processing of salient environmental stimuli, with cognitive status serving as a key mediating variable.     

Body mass index and pancreatic cancer risk: A meta-analysis of prospective studies

A number of studies have examined the association between body mass index (BMI) and risk of pancreatic cancer, but uncertainty about the relationship remains. We performed a meta-analysis to summarize the evidence from prospective studies investigating this association. We searched MEDLINE for studies published in any language from 1966 to November 2006. Prospective studies were included if they reported relative risks (RRs) with 95% confidence intervals (CIs) for the association between BMI and pancreatic cancer incidence or mortality. Study-specific RR estimates were combined by use of a random-effects model. A total of 21 independent prospective studies, involving 3,495,981 individuals and 8,062 pancreatic cancer cases, met the inclusion criteria. The estimated summary RR of pancreatic cancer per 5 kg/m(2) increase in BMI was 1.12 (95% CI, 1.06-1.17; p-heterogeneity = 0.13) in men and women combined, 1.16 (95% CI, 1.05-1.28; p-heterogeneity = 0.001) in men, and 1.10 (95% CI, 1.02-1.19; p-heterogeneity = 0.12) in women. There was no evidence of publication bias (p = 0.58). Findings from this meta-analysis of prospective studies support a positive association between BMI and risk of pancreatic cancer in men and women.     

Lipid profile and socioeconomic status in healthy middle aged women in Sweden.

STUDY OBJECTIVE: To examine the relationship between socioeconomic status (SES) and full lipid profile in middle aged healthy women. PARTICIPANTS: These comprised 300 healthy Swedish women between 30 and 65 years who constitute the control group of the Stockholm female coronary risk study, a population based, case-control study of women with coronary heart disease (CHD). The age matched control group, drawn from the census register of greater Stockholm, was representative of healthy Swedish women aged 30-65 years. Five measures of SES were used; educational level, occupation, decision latitude at work, annual income, and size of house or apartment. MAIN RESULTS: Swedish women with low decision latitude at work, low income, low educational level, blue collar jobs, and who were living in small houses or apartments had an unhealthy lipid profile, suggesting an increased risk of CHD. Part of this social gradient in lipids was explained by an unhealthy lifestyle, but the lipid gradients associated with decision latitude at work and annual income were independent of these factors. Decision latitude, educational level, and annual income had the strongest associations with lipid profile. These associations were independent of age, menopausal status, smoking, sedentary lifestyle, alcohol consumption, obesity, excess abdominal fat, and unhealthy dietary habits. Of the lipid variables, low high density lipoprotein cholesterol (HDL) levels were most consistently associated with low SES. CONCLUSIONS: Decision latitude at work was the strongest SES predictor of HDL levels in healthy middle aged Swedish women, after simultaneous adjustment for other SES measures, age, and all lifestyle factors in the multivariable regression model.