Faculty Bibliography

INTRODUCTION: Rapid response teams (RRTs) have been shown to reduce cardiopulmonary arrests outside the intensive care unit (ICU). Yet the utility of RRTs remains in question, as most large studies have failed to demonstrate a significant reduction in hospital-wide mortality after RRT implementation. METHODS: A cohort design with historical controls was used to determine the effect on hospital-wide mortality of an RRT in which clinical judgment, in addition to vital-signs criteria, was widely promoted as a key trigger for activation. All nonprisoner patients admitted to a tertiary referral public teaching hospital from 2003 through 2008 were included. In total, 77, 021 admissions before RRT implementation (2003 through 2005) and 79, 013 admissions after RRT implementation (2006 through 2008) were evaluated. The a priori primary outcome was unadjusted hospital-wide mortality. A Poisson regression model was then used to adjust for hospital-wide mortality trends over time. Secondary outcomes defined a priori were unadjusted out-of-ICU mortality and out-of-ICU cardiopulmonary-arrest codes. RESULTS: In total, 855 inpatient RRTs (10.8 per 1, 000 hospital-wide discharges) were activated during the 3-year postintervention period. Forty-seven percent of RRTs were activated for reasons of clinical judgment. Hospital-wide mortality decreased from 15.50 to 13.74 deaths per 1, 000 discharges after RRT implementation (relative risk, 0.887; 95% confidence interval (CI), 0.817 to 0.963; P = 0.004). After adjusting for inpatient mortality trends over time, the reduction in hospital-wide mortality remained statistically significant (relative risk, 0.825; 95% CI, 0.694 to 0.981; P = 0.029). Out-of-ICU mortality decreased from 7.08 to 4.61 deaths per 1, 000 discharges (relative risk, 0.651; 95% CI, 0.570 to 0.743; P < 0.001). Out-of-ICU cardiopulmonary-arrest codes decreased from 3.28 to 1.62 codes per 1, 000 discharges (relative risk, 0.493; 95% CI, 0.399 to 0.610; P < 0.001). CONCLUSIONS: Implementation of an RRT in which clinical judgment, in addition to vital-signs criteria, was widely cited as a rationale for activation, was associated with a significant reduction in hospital-wide mortality, out-of-ICU mortality, and out-of-ICU cardiopulmonary-arrest codes. The frequent use of clinical judgment as a criterion for RRT activation was associated with high RRT utilization.

The phenol-soluble modulin PSM-mec is the only known staphylococcal toxin that is encoded on a mobile antibiotic resistance determinant, namely the staphylococcal cassette chromosome (SCC) element mec encoding resistance to methicillin. Here we show that the psm-mec gene is found frequently among methicillin-resistant Staphylococcus aureus (MRSA) strains of SCCmec types II, III, and VIII, and is a conserved part of the class A mec gene complex. Controlled expression of AgrA versus RNAIII in agr mutants of all 3 psm-mec-positive SCCmec types demonstrated that expression of psm-mec, which is highly variable, is controlled by AgrA in an RNAIII-independent manner. Furthermore, psm-mec isogenic deletion mutants showed only minor changes in PSMalpha peptide production and unchanged (or, as previously described, diminished) virulence compared to the corresponding wild-type strains in a mouse model of skin infection. This indicates that the recently reported regulatory impact of the psm-mec locus on MRSA virulence, which is opposite to that of the PSM-mec peptide and likely mediated by a regulatory RNA, is minor when analyzed in the original strain background. Our study gives new insight in the distribution, regulation, and role in virulence of the PSM-mec peptide and the psm-mec gene locus.

The development and spread of antibiotic resistance in bacteria is a universal threat to both humans and animals that is generally not preventable but can nevertheless be controlled, and it must be tackled in the most effective ways possible. To explore how the problem of antibiotic resistance might best be addressed, a group of 30 scientists from academia and industry gathered at the Banbury Conference Centre in Cold Spring Harbor, New York, USA, from 16 to 18 May 2011. From these discussions there emerged a priority list of steps that need to be taken to resolve this global crisis.

Staphylococcus aureus is a bacterial pathogen known to cause infections in epidemic waves. One such epidemic was caused by a clone known as phage-type 80/81, a penicillin-resistant strain that rose to world prominence in the late 1950s. The molecular underpinnings of the phage-type 80/81 outbreak have remained unknown for decades, nor is it understood why related S. aureus clones became epidemic in hospitals in the early 1990s. To better understand the molecular basis of these epidemics, we sequenced the genomes of eight S. aureus clinical isolates representative of the phage-type 80/81 clone, the Southwest Pacific clone [a community-associated methicillin-resistant S. aureus (MRSA) clone], and contemporary S. aureus clones, all of which are genetically related and belong to the same clonal complex (CC30). Genome sequence analysis revealed that there was coincident divergence of these clones from a recent common ancestor, a finding that resolves controversy about the evolutionary history of the lineage. Notably, we identified nonsynonymous SNPs in genes encoding accessory gene regulator C (agrC) and alpha-hemolysin (hla)--molecules important for S. aureus virulence--that were present in virtually all contemporary CC30 hospital isolates tested. Compared with the phage-type 80/81 and Southwest Pacific clones, contemporary CC30 hospital isolates had reduced virulence in mouse infection models, the result of SNPs in agrC and hla. We conclude that agr and hla (along with penicillin resistance) were essential for world dominance of phage-type 80/81 S. aureus, whereas key SNPs in contemporary CC30 clones restrict these pathogens to hospital settings in which the host is typically compromised.

The accessory gene regulator (agr) locus has been shown to be important for virulence in several animal models of Staphylococcus aureus infection. However, the role of agr in human infections, and specifically in antibiotic treatment, is controversial. Interestingly, agr dysfunction has been associated with reduced vancomycin responses. To systematically investigate the role of agr in virulence and treatment outcome in the context of endovascular infection, 10 well-characterized vancomycin-susceptible methicillin-resistant S. aureus (MRSA) bloodstream isolates (5 agr-I [clonal complex 45, or CC45] and 5 agr-II [CC5]) were studied for (i) agr function, (ii) RNAIII transcriptional profiles, (iii) agr locus sequences, (iv) intrinsic virulence and responses to vancomycin therapy in an experimental infective endocarditis (IE) model, and (v) in vivo RNAIII expression. Significant differences in agr function (determined by delta-hemolysin activity) correlated with the time point of RNAIII transcription (earlier RNAIII onset equals increased agr function). Unexpectedly, four MRSA strains with strong delta-hemolysin activities exhibited significant resistance to vancomycin treatment in experimental IE. In contrast, five of six MRSA strains with weak or no delta-hemolysin activity were highly susceptible to vancomycin therapy in the IE model. agr sequence analyses showed no common single-nucleotide polymorphism predictive of agr functionality. In vivo RNAIII expression in cardiac vegetations did not correlate with virulence or vancomycin treatment outcomes in the IE model. Inactivation of agr in two strains with strong delta-hemolysin activity did not affect virulence or the in vivo efficacy of vancomycin. Our findings suggest that agr dysfunction does not correlate with vancomycin treatment failures in this experimental IE model in two distinct MRSA genetic backgrounds.

OBJECTIVE: To describe the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) carriage and transmission in an ambulatory hemodialysis population. DESIGN: Prospective cohort study. SETTING: Outpatient hemodialysis facility affiliated with a large academic medical center. PARTICIPANTS: Of the 170 facility patients, 103 (61%) participated in the study. METHODS: Swab specimens of the nares, axillae, and vascular access site were collected from participants weekly for 3 weeks and then monthly for 5 months. Demographic and clinical data were collected monthly for 12 months. Molecular analysis of MRSA isolates was performed. RESULTS: The baseline MRSA carriage prevalence was 12%. Factors associated with MRSA carriage included a history of MRSA; failed renal transplantation; hospital admission within 6 months; and receipt of a first-generation cephalosporin, cefepime, or vancomycin. Six subjects acquired MRSA after enrollment (incidence, 1.2 per 100 patient-months at-risk; overall prevalence, 18%). Molecular analysis suggested that transmission occurred within the facility. The incidence of MRSA infection among carriers was 1.76 per 100 patient-months. Community-associated strains (ie, USA300) were isolated from 28% of carriers and at least 25% of infections. CONCLUSIONS: The prevalence of MRSA carriage and the incidence of infection among carriers were high among ambulatory hemodialysis patients, and community-associated MRSA was responsible for a large portion of the MRSA burden. A relatively high rate of MRSA acquisition was observed, with indirect evidence of intrafacility transmission. Additional studies are needed to confirm these findings and to identify effective and feasible methods to prevent MRSA transmission and infection among hemodialysis patients.

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 (DAP(s)/DAP(r)) 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 DAP(r) strains had point mutations in the mprF locus (with or without yyc operon mutations), while three DAP(r) strains had neither mutation. Several phenotypic parameters previously associated with DAP(r) were also examined: cell membrane order (fluidity), surface charge, and cell wall thickness profiles. Compared to the 10 DAP(s) parental strains, their respective DAP(r) 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 DAP(s) and DAP(r) strain pairs. Reduced in vitro susceptibility to two HDPs and one bacterium-derived CAP tracked closely with DAP(r) in these 10 recent MRSA clinical isolates. These results suggest that adaptive mechanisms involved in the evolution of DAP(r) also provide MRSA with enhanced survivability against HDPs. Such adaptations appear to correlate with MRSA variations in cell membrane order and cell wall structure. DAP(r) strains with or without mutations in the mprF locus demonstrated significant cross-resistance profiles to these unrelated CAPs.

On 13 June, donors to the GAVI Alliance will gather in London to affirm their commitment to fund immunizations in the developing world. At the meeting, participants will address the estimated $3.7 billion financing gap needed over the next four years to scale up childhood vaccination efforts to meet the demand forecasts for those countries that receive assistance from the Geneva-based organization. But attendees of the pledging conference will also be discussing something not on the formal agenda: the announcement last month that Seth Berkley, who founded and heads the International AIDS Vaccine Initiative (IAVI), will take over the helm of the alliance in August. Berkley will lead a unique chapter in GAVI's development as the organization narrows in on the looming deadline set by Millennium Development Goal 4, which aims to reduce child mortality by two thirds by 2015. Yet, in a sense, these efforts will be a continuation of the work Berkley has fostered at IAVI since he formally launched the New York-based nonprofit in 1996. Berkley, an epidemiologist who previously held jobs with the Rockefeller Foundation, the Carter Center and the US Centers for Disease Control and Prevention, has witnessed ups and downs in the vaccination field, from the disappointing STEP trial in 2007 to the more recent good news from the 2009 Thai study, which reported as much as 31% protection against HIV. Roxanne Khamsi spoke with Berkley about what he has learned in his quest for a preventative shot against AIDS.