Survey of infections due to Staphylococcus species: frequency of occurrence and antimicrobial susceptibility of isolates collected in the United States, Canada, Latin America, Europe, and the Western Pacific region for the SENTRY Antimicrobial Surveillance Program, 1997-1999

New epidemiology of Staphylococcus aureus infection in Asia

Not only is Asia the most populous region in the world, but inappropriate therapy, including self-medication with over-the-counter antimicrobial agents, is a common response to infectious diseases. The high antibiotic selective pressure among the overcrowded inhabitants creates an environment that is suitable for the rapid development and efficient spread of numerous multidrug-resistant pathogens. Indeed, Asia is among the regions with the highest prevalence rates of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) and community-associated methicillin-resistant S. aureus (CA-MRSA) in the world. Most hospitals in Asia are endemic for multidrug-resistant methicillin-resistant S. aureus (MRSA), with an estimated proportion from 28% (in Hong Kong and Indonesia) to >70% (in Korea) among all clinical S. aureus isolates in the early 2010s. Isolates with reduced susceptibility or a high level of resistance to glycopeptides have also been increasingly identified in the past few years. In contrast, the proportion of MRSA among community-associated S. aureus infections in Asian countries varies markedly, from <5% to >35%. Two pandemic HA-MRSA clones, namely multilocus sequence type (ST) 239 and ST5, are disseminated internationally in Asia, whereas the molecular epidemiology of CA-MRSA in Asia is characterized by clonal heterogeneity, similar to that in Europe. In this review, the epidemiology of S. aureus in both healthcare facilities and communities in Asia is addressed, with an emphasis on the prevalence, clonal structure and antibiotic resistant profiles of the MRSA strains. The novel MRSA strains from livestock animals have been considered to constitute a public health threat in western countries. The emerging livestock-associated MRSA strains in Asia are also included in this review.

Optimizing antibiotic therapy of bacteremia and endocarditis due to staphylococci and enterococci: new insights and evidence from the literature

Gram-positive cocci are a well-recognised major cause of nosocomial infection worldwide. Bloodstream infections due to methicillin-resistant Staphylococcus aureus, methicillin-resistant coagulase-negative staphylococci, and multi-drug resistant enterococci are a cause of concern for physicians due to their related morbidity and mortality rates. Aim of this article is to review the current state of knowledge regarding the management of BSI caused by staphylococci and enterococci, including infective endocarditis, and to identify those factors that may help physicians to manage these infections appropriately. Moreover, we discuss the importance of an appropriate use of antimicrobial drugs, taking in consideration the in vitro activity, clinical efficacy data, pharmacokinetic/pharmacodynamic parameters, and potential side effects.

Antimicrobial resistance, virulence factors and genetic lineages of hospital-onset methicillin-resistant Staphylococcus aureus isolates detected in a hospital in Zaragoza

INTRODUCTION

MRSA population dynamics is undergoing significant changes, and for this reason it is important to know which clones are circulating in our nosocomial environment.

MATERIALS AND METHODS

A total of 118 MRSA isolates were collected from clinical samples from patients with previous hospital or healthcare contact (named as hospital-onset MRSA (HO-MRSA)) during a one year period. Susceptibility testing was performed by disk diffusion and microdilution. The presence of resistance genes and virulence factors were tested by PCR. All isolates were typed by SCCmec, spa and agr typing. PFGE and MLST were applied to a selection of them.

RESULTS

Eighty-three HO-MRSA isolates (70.3%) were resistant to any antibiotic included in the macrolide-lincosamide-streptogramin B group. Among these isolates, the M phenotype was the most frequent (73.5%). One hundred and seven of HO-MRSA isolates (90.7%) showed aminoglycoside resistance. The combination aac(6')-Ie-aph(2″)-Ia+ant(4')-Ia genes was the most frequent (22.4%). Tetracycline resistance rates in HO-MRSA isolates were low (3.4%), although a high level of mupirocin resistance was observed (25.4%). Most of the HO-MRSA isolates (approximately 90%) showed SCCmec type IVc and agr type II. Fifteen unrelated pulsotypes were identified. CC5 was the most prevalent (88.1%), followed by CC8 (5.9%), CC22 (2.5%), CC398 (2.5%) and CC1 (0.8%).

CONCLUSION

CC5/ST125/t067 lineage was the most frequent. This lineage was related to aminoglycoside resistance, and to a lesser extent, with macrolide resistance. The presence of international clones as EMRSA-15 (CC22/ST22), European clones as CC5/ST228, community clones related to CC1 or CC8 and livestock associated clones, as CC398, were observed in a low percentage.

The membrane protein PrsS mimics σS in protecting Staphylococcus aureus against cell wall-targeting antibiotics and DNA-damaging agents

Staphylococcus aureus possesses a lone extracytoplasmic function (ECF) sigma factor, σ(S). In Bacillus subtilis, the ECF sigma factor, σ(W), is activated through a proteolytic cascade that begins with cleavage of the RsiW anti-sigma factor by a site-1 protease (S1P), PrsW. We have identified a PrsW homologue in S. aureus (termed PrsS) and explored its role in σ(S) regulation. Herein, we demonstrate that although a cognate σ(S) anti-sigma factor currently remains elusive, prsS phenocopies sigS in a wealth of regards. Specifically, prsS expression mimics the upregulation observed for sigS in response to DNA-damaging agents, cell wall-targeting antibiotics and during ex vivo growth in human serum and murine macrophages. prsS mutants also display the same sensitivities of sigS mutants to the DNA-damaging agents methyl methane sulfonate (MMS) and hydrogen peroxide, and the cell wall-targeting antibiotics ampicillin, bacitracin and penicillin-G. These phenotypes appear to be explained by alterations in abundance of proteins involved in drug resistance (Pbp2a, FemB, HmrA) and the response to DNA damage (BmrA, Hpt, Tag). Our findings seem to be mediated by putative proteolytic activity of PrsS, as site-directed mutagenesis of predicted catalytic residues fails to rescue the sensitivity of the mutant to H2O2 and MMS. Finally, a role for PrsS in S. aureus virulence was identified using human and murine models of infection. Collectively, our data indicate that PrsS and σ(S) function in a similar manner, and perhaps mediate virulence and resistance to DNA damage and cell wall-targeting antibiotics, via a common pathway.

Strict infection control leads to low incidence of methicillin-resistant Staphylococcus aureus bloodstream infection over 20 years

OBJECTIVE

Methicillin-resistant Staphylococcus aureus (MRSA) is a worldwide issue associated with significant morbidity and mortality. Multiple infection control (IC) approaches have been tested to control its spread; however, the success of the majority of trials has been short-lived and many efforts have failed. We report the long-term success of MRSA control from a prospective observational study over 20 years.

SETTING

University Hospital Basel is a large tertiary care center with a median bed capacity of 855 and 5 intensive care units (ICUs); currently, the facility has >32,000 admissions per year.

METHODS

The IC program at the University Hospital Basel was created in 1993, after 2 MRSA outbreaks. The program has included strict contact precautions with single rooms for MRSA-colonized or -infected patients, targeted admission screening of high-risk patients and healthcare workers at risk for carriage, molecular typing of all MRSA strains and routine decolonization of MRSA carriers including healthcare workers. We used the incidence of MRSA bloodstream infections (BSIs) to assess the effectiveness of this program. All MRSA cases were prospectively classified using a standardized case report form in nosocomial and nonnosocomial cases, based on CDC definitions.

RESULTS

Between 1993 and 2012, 540,669 blood samples were cultured. The number of blood cultures increased from 865 per 10,000 patient days in 1993 to 1,568 per 10,000 patient days in 2012 (P<.001). We identified 1,268 episodes of S. aureus BSI from 1,204 patients. MRSA accounted for 34 episodes (2.7%) and 24 of these (1.9%) were nosocomial. MRSA BSI incidence varied between 0 and 0.27 per 10,000 patient days and remained stable with no significant variation throughout the study period (P=.882).

CONCLUSIONS

Long-term control of MRSA is feasible when a bundle of IC precautions is strictly enforced over time.

Impact of prior healthcare-associated exposure on clinical and molecular characterization of methicillin-susceptible Staphylococcus aureus bacteremia: results from a retrospective cohort study

By virtue of medical advances and an aging society, people have increased opportunities for healthcare exposure. Little is known about the impact of healthcare exposure on the clinical features and molecular typing of methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. We classified the onset of MSSA bacteremia into 3 mutually exclusive categories according to the Centers for Disease Control definition, and conducted a retrospective cohort study to investigate the differences among patients with community-associated (CA), healthcare-associated community onset (HACO), and hospital onset (HO) MSSA bacteremia at a medical center from January 1, 2002 through December 31, 2011. Antibiotic susceptibilities and multilocus sequence typing of MSSA isolates were also determined. A total of 290 patients with MSSA bacteremia, including of 165 (56.9%), 91 (31.4%), and 34 (11.7%) of HACO, HO, and CA, respectively, were studied. ST188 (29.3%) was the most common sequence type regardless of classification. Patients with HACO bacteremia were significantly older, had more solid tumors, higher Charlson scores, and more catheter-related bloodstream infections than those with CA bacteremia. The proportions of osteoarticular infections among patients with both HACO and CA bacteremia were higher than that of patients with HO bacteremia. By univariate analysis, patients with HO bacteremia had significantly higher in-hospital mortality compared to those with CA or HACO bacteremia (31.9% vs 18.8% and 20.4%). Multivariate analysis showed that Charlson score (odds ratio [OR], 1.29; 95% confidence interval [CI], 1.10-1.52), septic shock (OR, 5.28; 95% CI, 2.37-11.78), liver cirrhosis (OR, 3.57; 95% CI, 1.14-11.24), receipt of β-lactams other than oxacillin and cefazolin as definitive therapy (OR, 9.27; 95% CI, 4.25-20.23), and higher oxacillin minimum inhibitory concentration (MIC) (≥0.5 mg/L) (OR, 2.35; 95% CI, 1.05-5.25) of the causative pathogen were independently associated with in-hospital mortality. In conclusion, patients with HACO bacteremia had different host factors compared with those with CA bacteremia. Infection foci varied with different onset settings. Overall, ST188 was the most predominant sequence type. Onset settings were not independently associated with outcomes.

Transfer of plasmid DNA to clinical coagulase-negative staphylococcal pathogens by using a unique bacteriophage

Genetic manipulation of emerging bacterial pathogens, such as coagulase-negative staphylococci (CoNS), is a major hurdle in clinical and basic microbiological research. Strong genetic barriers, such as restriction modification systems or clustered regularly interspaced short palindromic repeats (CRISPR), usually interfere with available techniques for DNA transformation and therefore complicate manipulation of CoNS or render it impossible. Thus, current knowledge of pathogenicity and virulence determinants of CoNS is very limited. Here, a rapid, efficient, and highly reliable technique is presented to transfer plasmid DNA essential for genetic engineering to important CoNS pathogens from a unique Staphylococcus aureus strain via a specific S. aureus bacteriophage, Φ187. Even strains refractory to electroporation can be transduced by this technique once donor and recipient strains share similar Φ187 receptor properties. As a proof of principle, this technique was used to delete the alternative transcription factor sigma B (SigB) via allelic replacement in nasal and clinical Staphylococcus epidermidis isolates at high efficiencies. The described approach will allow the genetic manipulation of a wide range of CoNS pathogens and might inspire research activities to manipulate other important pathogens in a similar fashion.

Compatibility of Pulsed-Field Gel Electrophoresis Findings and Clinical Criteria Commonly Used to Distinguish Between True Coagulase-Negative Staphylococcal Bacteremia and Contamination

Objectives.

To evaluate the specificity and sensitivity of the clinical criteria widely used to differentiate true coagulase-negative staphylococcal (CoNS) bacteremia from contamination, using pulsed-field gel electrophoresis (PFGE) as the reference test.

Design.

The study sample consisted of 79 CoNS isolates recovered from cultures of blood from 38 patients. Medical charts of the patients were reviewed for demographic and clinical information. The relatedness of CoNS strains recovered from 2 or more successive blood cultures was analyzed by PFGE. Patients from whom similar strains were recovered were assumed to have true bacteremia, whereas patients from whom different strains were recovered were considered to have contaminated blood cultures. The clinical criteria comprised Centers for Disease Control and Prevention (CDC) surveillance definitions for bloodstream infection (BSI), as well as an alternative criterion based on the presence of fever, the presence of leukocytosis, the absence of another recognized infection, and the recovery of CoNS from 2 or more successive blood cultures.

Results.

Nineteen (50%) of the 38 patients had bacteremia due to similar strains; the remaining patients had bacteremia due to different strains. Criterion 2a of the CDC definition for BSI had a sensitivity of 100% and a specificity of 31.6% for distinguishing between true bacteremia and contamination. CDC criterion 2b had a sensitivity of 78.9% and a specificity of 52.6%.

Conclusions.

Molecular typing correlated poorly with the clinical criteria for true bacteremia. In view of the limited applicability of clinical criteria, more studies are needed to improve them. Periodic cross-sectional studies based on PFGE findings might be useful to estimate local contamination rates in an institution, which in turn can be used to improve the accuracy of the clinical diagnosis of bacteremia.

Methicillin-Resistant Staphylococcus aureus: A 5-Year Review of Surveillance Data in a Tertiary Care Hospital in Saudi Arabia

Background.

Staphylococcus aureus is an important pathogen that leads to serious infections in the community and in hospitals. Evidence has shown that the prevalence of infection and colonization with drug-resistant S. aureus, such as methicillin-resistant S. aureus (MRSA) and glycopeptide intermediately susceptible S. aureus, is increasing. Authorities must be aware of the prevalence of MRSA infection and colonization in their country in order to implement and monitor infection control policies that help curtail further emergence of this pathogen.

Objectives.

To examine the trend of hospital-acquired MRSA infection and colonization in a tertiary care institution in Saudi Arabia during a 5-year period in order to identify specific areas at high risk for MRSA transmission, and to review our MRSA decolonization procedure and outcomes.

Methods.

Surveillance data prospectively collected from January 1, 2000, through December 31, 2004, on hospital-acquired (HA) MRSA were analyzed, with an emphasis on the trend of HA-MRSA infection and colonization, areas of high transmission, risk factors, and effectiveness of the implemented decolonization policy.

Results.

During the study period, 442 cases of HA-MRSA infection and colonization were identified. Of these, 51.2% were infections, and 48.8% were colonizations. An increasing trend in the incidence rates of infection and colonization was noticed during the study period, and most cases were identified on the surgical ward (33.3%) and medical ward (32.1%). Of the 34 infected patients who underwent systematic decolonization, 35.3% were successfully decolonized, and of the 11 who underwent topical decolonization, 63.6% were successfully decolonized.

Conclusion.

The increasing trend of HA-MRSA infections has been a noticeable global problem. We identified a gradual increase in the rates of MRSA colonization and infection in a tertiary care center Saudi Arabia and recognize the importance of abiding by strict infection control policies, including hand hygiene and proper isolation practices. Continued surveillance for MRSA and other emerging multidrug-resistant pathogens is also needed.

Current bacterial speciation and antibiotic resistance in deep infections after operative fixation of fractures

OBJECTIVES

Infection after fracture fixation is a major source of morbidity. Information regarding bacterial speciation and antibiotic resistance is lacking. We attempted to determine the speciation and drug resistance profiles associated with fracture fixation infections.

DESIGN

Retrospective study.

SETTING

Level I trauma center.

PATIENTS

Two hundred eleven patients with 214 infections underwent surgery for postoperative infection from December 2006 to December 2010. Deep postoperative infections within 12 months of fixation were included.

INTERVENTION

None.

MAIN OUTCOME MEASUREMENTS

Incidence of each bacterial species and rate of clinically relevant resistance in Staphylococcus aureus, gram-negative rod (GNR), and Enterococcus species. The effect of timing of infection presentation and location of fracture on bacterial speciation was also investigated.

RESULTS

Fifty-six percent of infections had S. aureus present, with 58% of those (32% of all infections) being methicillin-resistant S. aureus. Thirty-two percent of infections had at least one GNR present, with only 4% of those being multidrug resistant. We found a marked increase in the rate of GNR infections of the pelvis, acetabulum, and proximal femur (63%) compared with other locations (27%), which was statistically significant (P = 0.0002).

CONCLUSIONS

At our center, S. aureus and GNR are most often found in deep postoperative infections after fixation. Methicillin-resistant S. aureus is common in this population. Our GNR rate is high, but resistance in this group was low. The proportion of GNR infections in the pelvis, acetabulum, and proximal femur was high even in closed fractures. These data provide a modern snapshot of orthopaedic infections after fracture fixation and might be useful in designing future studies and protocols for antibiotic prophylactic treatment. We are considering the use of aminoglycosides in the treatment of closed fractures of the pelvis, acetabulum, and proximal femur.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Radiosynthesis and biological evaluation of a novel enoyl-ACP reductase inhibitor for Staphylococcus aureus

The pharmacokinetics (PK) and pharmacodynamics (PD) of PT119, a potent Staphylococcus aureus enoyl-ACP reductase (saFabI) inhibitor with a Ki value of 0.01 nM and a residence time of 750 min on the enzyme target, has been evaluated in mice. PT119 was found to have promising antibacterial activity in two different S. aureus infection models: it caused a 3 log reduction in the CFU's in a mouse thigh muscle infection model and increased the survival rate from 0% to 50% in a mouse systemic infection model. PT119 was then radiolabeled with carbon-11 to evaluate its biodistribution and PK in both healthy and S. aureus infected mice using positron emission tomography (PET). The biodistribution of [11C]PT119 and/or its labeled metabolites did not differ significantly between the healthy group and the infected group, and PT119 was found to distribute equally between serum and tissue during the ∼1 h of analysis permitted by the carbon-11 half life. This approach provides important data for PK/PD modeling and is the first step in identifying radiotracers that can non-invasively image bacterial infection in vivo.

Low prevalence of methicillin resistant Staphylococcus aureus as determined by an automated identification system in two private hospitals in Nairobi, Kenya: a cross sectional study

Background

Staphylococcus aureus (S.aureus) is a major cause of both healthcare and community acquired infections. In developing countries, manual phenotypic tests are the mainstay for the identification of staphylococci with the tube and slide coagulase tests being relied upon as confirmatory tests for S. aureus. The subjectivity associated with interpretation of these tests may result in misidentification of coagulase negative staphylococci as S.aureus. Given that antibiotic resistance is more prevalent in CONS, this may result in over estimation of methicillin resistant S.aureus (MRSA) prevalence.

Methods

A review of susceptibility data from all non-duplicate S.aureus isolates generated between March 2011 and May 2013 by the Vitek-2 (bioMérieux) automated system was performed by the authors. The data was generated routinely from processed clinical specimens submitted to the microbiology laboratories for culture and sensitivity at the Aga Khan University Hospital and Gertrude’s children’s hospital both situated in Nairobi.

Results

Antimicrobial susceptibility data from a total of 731 non-duplicate S.aureus isolates was reviewed. Majority (79.2%) of the isolates were from pus swabs. Only 24 isolates were both cefoxitin and oxacillin resistant while 3 were resistant to oxacillin but susceptible to cefoxitin giving an overall MRSA prevalence of 3.7% (27/731). None of the isolates were resistant to mupirocin, linezolid, tigecycline, teicoplanin or vancomycin.

Conclusion

The prevalence of MRSA in this study is much lower than what has been reported in most African countries. The significant change in antibiotic susceptibility compared to what has previously been reported in our hospital is most likely a consequence of the transition to an automated platform rather than a trend towards lower resistance rates.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0669-y) contains supplementary material, which is available to authorized users.

Therapeutic strategies to combat antibiotic resistance

With multidrug resistant bacteria on the rise, new antibiotic approaches are required. Although a number of new small molecule antibiotics are currently in the development pipeline with many more in preclinical development, the clinical options and practices for infection control must be expanded. Biologics and non-antibiotic adjuvants offer this opportunity for expansion. Nevertheless, to avoid known mechanisms of resistance, intelligent combination approaches for multiple simultaneous and complimentary therapies must be designed. Combination approaches should extend beyond biologically active molecules to include smart controlled delivery strategies. Infection control must integrate antimicrobial stewardship, new antibiotic molecules, biologics, and delivery strategies into effective combination therapies designed to 1) fight the infection, 2) avoid resistance, and 3) protect the natural microbiome. This review explores these developing strategies in the context of circumventing current mechanisms of resistance.

Coagulase-negative Staphylococcus culture in chronic rhinosinusitis

BACKGROUND

Coagulase-negative Staphylococcus (CoNS) is commonly isolated from patients with chronic rhinosinusitis (CRS). However, the role of CoNS in CRS remains controversial. We aimed to determine the association between positive CoNS culture at functional endoscopic sinus surgery (FESS) and CRS severity.

METHODS

Adult CRS patients who underwent FESS between October 1, 2007 to December 31, 2011 were recruited. Patient demographics, disease characteristics, medication use, Lund-Mackay computed tomography (CT) scores, and 22-item Sino-Nasal Outcome Test (SNOT-22) scores were collected at baseline before FESS. Intraoperative cultures were obtained in a standard manner. Patients were placed into 2 groups based on culture findings: patients with CoNS as the sole positive culture result and patients with all other positive culture results, including CoNS, as part of a polymicrobial culture.

RESULTS

A total of 376 CRS patients met the criteria; 106 patients (28%) had CoNS as their only isolate, 260 (69%) had other positive cultures, and 10 (3%) had no bacterial growth. Compared to patients with other positive cultures, patients with the sole result of CoNS were significantly less likely to have a history of FESS (52% vs 65%, p = 0.019), nasal polyps (50% vs 65%, p = 0.006), and had a better Lund-Mackay CT score (11.95 vs 14.18, p = 0.020). After adjusting for all factors in the multiple logistic regression model, CoNS as the sole positive culture result was independently associated with having no history of FESS (odds ratio [OR] = 0.45; 95% confidence interval [CI], 0.22 to 0.94; p = 0.034).

CONCLUSION

Positive intraoperative CoNS cultures alone do not result in increased CRS disease burden by objective or subjective measures as compared to patients with other bacterial or polymicrobial culture isolates.

Reduced susceptibility to vancomycin and biofilm formation in methicillin-resistant Staphylococcus epidermidis isolated from blood cultures

This study aimed to correlate the presence of ica genes, biofilm formation and antimicrobial resistance in 107 strains of Staphylococcus epidermidis isolated from blood cultures. The isolates were analysed to determine their methicillin resistance, staphylococcal cassette chromosome mec (SCCmec) type, ica genes and biofilm formation and the vancomycin minimum inhibitory concentration (MIC) was measured for isolates and subpopulations growing on vancomycin screen agar. The mecA gene was detected in 81.3% of the S. epidermidis isolated and 48.2% carried SCCmec type III. The complete icaADBC operon was observed in 38.3% of the isolates; of these, 58.5% produced a biofilm. Furthermore, 47.7% of the isolates grew on vancomycin screen agar, with an increase in the MIC in 75.9% of the isolates. Determination of the MIC of subpopulations revealed that 64.7% had an MIC ≥ 4 μg mL^-1, including 15.7% with an MIC of 8 μg mL^-1 and 2% with an MIC of 16 μg mL^-1. The presence of the icaADBC operon, biofilm production and reduced susceptibility to vancomycin were associated with methicillin resistance. This study reveals a high level of methicillin resistance, biofilm formation and reduced susceptibility to vancomycin in subpopulations of S. epidermidis. These findings may explain the selection of multidrug-resistant isolates in hospital settings and the consequent failure of antimicrobial treatment.

Structure-based functional characterization of repressor of toxin (Rot), a central regulator of Staphylococcus aureus virulence

Staphylococcus aureus is responsible for a large number of diverse infections worldwide. In order to support its pathogenic lifestyle, S. aureus has to regulate the expression of virulence factors in a coordinated fashion. One of the central regulators of the S. aureus virulence regulatory networks is the transcription factor repressor of toxin (Rot). Rot plays a key role in regulating S. aureus virulence through activation or repression of promoters that control expression of a large number of critical virulence factors. However, the mechanism by which Rot mediates gene regulation has remained elusive. Here, we have determined the crystal structure of Rot and used this information to probe the contribution made by specific residues to Rot function. Rot was found to form a dimer, with each monomer harboring a winged helix-turn-helix (WHTH) DNA-binding motif. Despite an overall acidic pI, the asymmetric electrostatic charge profile suggests that Rot can orient the WHTH domain to bind DNA. Structure-based site-directed mutagenesis studies demonstrated that R(91), at the tip of the wing, plays an important role in DNA binding, likely through interaction with the minor groove. We also found that Y(66), predicted to bind within the major groove, contributes to Rot interaction with target promoters. Evaluation of Rot binding to different activated and repressed promoters revealed that certain mutations on Rot exhibit promoter-specific effects, suggesting for the first time that Rot differentially interacts with target promoters. This work provides insight into a precise mechanism by which Rot controls virulence factor regulation in S. aureus.

Socio-economic profile of patients with community-acquired skin and soft tissue infections in Delhi

AIM

To study the socio-demographic and clinical profile of patients with community-acquired skin and soft tissue infections (CA-SSTIs).

METHODS

This study was a cross sectional, observational study. Patients with CA-SSTIs (ICD-10 L00-L08) were enrolled from February to August 2013. Clinical and microbiological data of all patients were recorded. Socioeconomic status (SES) of each patient was calculated using the Modified Kuppuswamy Scale.

RESULTS

Seventy-three patients were studied, of whom 45 had SSTIs caused by Staphylococcus aureus. Of the 45, 11 (24%) were methicillin-resistant S. aureus (MRSA) and 34 (76%) were methicillin-sensitive S. aureus (MSSA). Patients with MRSA infections had significantly lower monthly income and lower educational status than those with MSSA infections. However, SES was not significantly different in the two groups.

CONCLUSION

S. aureus was the most common cause of CA-SSTIs, of which, MRSA was isolated in 24% of the cases. Patients with MRSA SSTIs had significantly lesser family income and lower education levels compared to patients with MSSA SSTIs.

Absence of patient-to-patient intrahospital transmission of Staphylococcus aureus as determined by whole-genome sequencing

Nosocomial transmission of pathogens is a major health care challenge. The increasing spread of antibiotic-resistant strains represents an ongoing threat to public health. Previous Staphylococcus aureus transmission studies have focused on transmission of S. aureus between asymptomatic carriers or used low-resolution typing methods such as multilocus sequence typing (MLST) or spa typing. To identify patient-to-patient intrahospital transmission using high-resolution genetic analysis, we sequenced the genomes of a consecutive set of 398 S. aureus isolates from sterile-site infections. The S. aureus strains were collected from four hospitals in the Houston Methodist Hospital System over a 6-month period. Importantly, we discovered no evidence of transmission of S. aureus between patients with sterile-site infections. The lack of intrahospital transmission may reflect a fundamental difference between day-to-day transmission events in the hospital setting and the more frequently studied outbreak scenarios.

Previous studies have suggested that nosocomial transmission of S. aureus is common. Our data revealed an unexpected lack of evidence for intrahospital transmission of S. aureus between patients with invasive infections. This finding has important implications for hospital infection control and public health efforts. In addition, our data demonstrate that highly related pools of S. aureus strains exist in the community which may complicate outbreak investigations.

Quercetin 3-O-rutinoside mediated inhibition of PBP2a: computational and experimental evidence to its anti-MRSA activity

The PBP2a is a cell wall synthesizing protein, which causes resistivity in methicillin resistant Staphylococcus aureus (MRSA) from β-lactam antibiotics but it is susceptible to 5th generation cephalosporin, ceftobiprole. Ceftobiprole inhibits the growth of MRSA by targeting the PBP2a-mediated cell wall synthesis, but it is reported to have adverse side effects. Due to this, there is a constant need to develop natural alternatives, which are generally free from adverse side effects. Hence in this study, in silico based docking analysis was performed with 37 quercetin derivatives towards PBP2a inhibition and their efficiencies were compared with β-lactam antibiotic, ceftobiprole. The docking studies suggested that quercetin 3-O-rutinoside (ZINC5280805) interacted efficiently with PBP2a, attaining the highest LibDock score (187.32) compared to other quercetin derivatives. The structural stability and dynamics of the identified lead with PBP2a were validated through molecular dynamics simulation. Simulation results such as RMSD, RMSF, and Rg values indicated that the stability of quercetin 3-O-rutinoside with PBP2a was better, with respect to the un-ligated PBP2a. Furthermore, the quercetin 3-O-rutinoside was subjected to an antibacterial susceptibility test and found to have antibacterial activity at 500, 700, and 900 μM concentration. Also, morphological changes in the bacterial colony and bacterial surface were observed using a scanning electron microscope, when MRSA was treated with 900 μM concentration of quercetin 3-O-rutinoside. Collectively, results from this study suggest that the quercetin 3-O-rutinoside has the capability to inhibit PBP2a and hence could be used as an alternative or in combination with other drugs in treating MRSA infection.

Risk factors for mortality among patients with Staphylococcus aureus bacteremia: a single-centre retrospective cohort study

INTRODUCTION

Staphylococcus aureus bacteremia is associated with significant morbidity and mortality. Given the paucity of recent Canadian data, we estimated the mortality rate associated with S. aureus bacteremia in a tertiary care hospital and identified risk factors associated with mortality.

METHODS

We retrospectively reviewed the records of adults with S. aureus bacteremia admitted to a tertiary care centre in southwestern Ontario between 2008 and 2012. Cox regression analysis was used to evaluate associations between predictor variables and all-cause, in-hospital, and 90-day postdischarge mortality.

RESULTS

Of the 925 patients involved in the study, 196 (21.2%) died in hospital and 62 (6.7%) died within 90 days after discharge. Risk factors associated with in-hospital and all-cause mortality included age, sepsis (adjusted hazard ratio [adjusted HR] 1.49, 95% confidence interval [CI] 1.08-2.06, p = 0.02), admission to the intensive care unit (adjusted HR 3.78, 95% CI 2.85-5.02, p < 0.0001), hepatic failure (adjusted HR 3.36, 95% CI 1.91-5.90, p < 0.0001) and metastatic cancer (adjusted HR 2.58, 95% CI 1.77-3.75, p < 0.0001). Methicillin resistance, hepatic failure, cerebrovascular disease, chronic obstructive pulmonary disease and metastatic cancer were associated with postdischarge mortality.

INTERPRETATION

The all-cause mortality rate in our cohort was 27.9%. Identification of predictors of mortality may guide empiric therapy and provide prognostic clarity for patients with S. aureus bacteremia.

Clinical characteristics of Staphylococcus epidermidis: a systematic review

Staphylococci are known as clustering Gram-positive cocci, nonmotile, non-spore forming facultatively anaerobic that classified in two main groups, coagulase-positive and coagulase-negative. Staphylococcus epidermidis with the highest percentage has the prominent role among coagulase-negative Staphylococci that is the most important reason of clinical infections. Due to various virulence factors and unique features, this microorganism is respected as a common cause of nosocomial infections. Because of potential ability in biofilm formation and colonization in different surfaces, also using of medical implant devices in immunocompromised and hospitalized patients the related infections have been increased. In recent decades the clinical importance and the emergence of methicillin-resistant Staphylococcus epidermidis strains have created many challenges in the treatment process.

Discovery and structure-activity relationship studies of irreversible benzisothiazolinone-based inhibitors against Staphylococcus aureus sortase A transpeptidase

Gram-positive bacteria, in general, and staphylococci, in particular, are the widespread cause of nosocomial and community-acquired infections. The rapid evolvement of strains resistant to antibiotics currently in use is a serious challenge. Novel antimicrobial compounds have to be developed to fight these resistant bacteria, and sortase A, a bacterial cell wall enzyme, is a promising target for novel therapies. As a transpeptidase that covalently attaches various virulence factors to the cell surface, this enzyme plays a crucial role in the ability of bacteria to invade the host's tissues and to escape the immune response. In this study we have screened a small molecule library against recombinant Staphylococcus aureus sortase A using an in vitro FRET-based assay. The selected hits were validated by NMR methods in order to exclude false positives and to analyze the reversibility of inhibition. Further structural and functional analysis of the best hit allowed the identification of a novel class of benzisothiazolinone-based compounds as potent and promising sortase inhibitors.

Zinc oxide therapy increases prevalence and persistence of methicillin-resistant Staphylococcus aureus in pigs: a randomized controlled trial

There is concern that therapeutic use of zinc oxide (ZnO) in swine production may select for methicillin-resistant Staphylococcus aureus (MRSA) due to co-location of the zinc resistance gene (czrC) and methicillin resistance gene (mecA) within the staphylococcal cassette chromosome mec (SCCmec). The objective of this investigation was to determine whether MRSA carriage in pigs is influenced by exposure to therapeutic doses of in-feed ZnO (3000 mg/kg) when compared to the recommended dietary levels (100 mg/kg). A randomized controlled trial was completed using 110 pigs that were naturally colonized with czrC-positive MRSA. The pigs were followed from birth to weaning (21 d), at which point they were randomized into 8 pens and exposed to either a control feed (100 mg ZnO/kg feed; n = 49 pigs) or a treatment feed (3000 mg ZnO/kg feed; n = 50 pigs); neither feed contained additional antimicrobials. MRSA carriage was monitored weekly in each group for 4 weeks post-weaning. The prevalence of MRSA was significantly higher in the treatment group at 1-week (OR = 18.1; P < 0.01) and 2 weeks (OR = 3.01; P = 0.01) post-weaning when compared to the control group, but there was no difference later in the nursery phase. Persistent MRSA carriage (testing positive ≥2 times post-weaning) was observed in 2% (1/49) of control pigs and 22% (11/50) of treated pigs (P < 0.01). All MRSA isolates (spa types t034 and t3075) carried czrC and showed uniform resistance to zinc. These findings demonstrate that the prevalence and persistence of MRSA in nursery pigs can be affected by high levels of in-feed ZnO in the absence of antibiotics.

Does universal active MRSA surveillance influence anti-MRSA antibiotic use? A retrospective analysis of the treatment of patients admitted with suspicion of infection at Veterans Affairs Medical Centers between 2005 and 2010

OBJECTIVES

After the implementation of an active surveillance programme for MRSA in US Veterans Affairs (VA) Medical Centers, there was an increase in vancomycin use. We investigated whether positive MRSA admission surveillance tests were associated with MRSA-positive clinical admission cultures and whether the availability of surveillance tests influenced prescribers' ability to match initial anti-MRSA antibiotic use with anticipated MRSA results from clinical admission cultures.

METHODS

Analyses were based on barcode medication administration data, microbiology data and laboratory data from 129 hospitals between January 2005 and September 2010. Hospitalized patient admissions were included if clinical cultures were obtained and antibiotics started within 2 days of admission. Mixed-effects logistic regression was used to examine associations between positive MRSA admission cultures and (i) admission MRSA surveillance test results and (ii) initial anti-MRSA therapy.

RESULTS

Among 569,815 included admissions, positive MRSA surveillance tests were strong predictors of MRSA-positive admission cultures (OR 8.5; 95% CI 8.2-8.8). The negative predictive value of MRSA surveillance tests was 97.6% (95% CI 97.5%-97.6%). The diagnostic OR between initial anti-MRSA antibiotics and MRSA-positive admission cultures was 3.2 (95% CI 3.1-3.4) for patients without surveillance tests and was not significantly different for admissions with surveillance tests.

CONCLUSIONS

The availability of nasal MRSA surveillance tests in VA hospitals did not seem to improve the ability of prescribers to predict the necessity of initial anti-MRSA treatment despite the high negative predictive value of MRSA surveillance tests. Prospective trials are needed to establish the safety and effectiveness of using MRSA surveillance tests to guide antibiotic therapy.

Preparation and identification of transfer factor specific to Staphylococcus aureus in vitro

The objective of the study was to explore the methods for preparing transfer factor specific to Staphylococcus aureus (SA-STF) in vitro. Under the optimum conditions, the spleen cells of rabbits were immunized with SA in vitro to prepare SA-STF, and the immune activities were identified with the phagocytosis and sterilization, skin delayed-type hypersensitivity, and immune protection tests. The concentration of polypeptide was 2.26 ± 0.27 mg/mL, and ribose was 0.684 ± 0.094 mg/mL. The phagocytosis and sterilization rates of the STF group were 70.9 ± 12.4% and 62.1 ± 12.2%, respectively, and compared with the non-specific transfer factor (NTF) group, there were no significant differences (P = 0.074 and 0.069, respectively). The skin was inflamed and marked nodules formed at the injection site in the mice of the STF group rather than the NTF and control groups. The survival rate of the STF-1 group was significantly higher than the survival rates of the STF-2 (P = 0.024) and NTF groups (P = 0.016). SA-STF was prepared and characterized successfully in vitro, and it probably is a biological candidate for therapy or adjuvant therapy for diseases caused by Staphylococcus aureus.

Mutations in mmpL and in the cell wall stress stimulon contribute to resistance to oxadiazole antibiotics in methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is a leading cause of hospital- and community-acquired infections, which exhibit broad resistance to various antibiotics. We recently disclosed the discovery of the oxadiazole class of antibiotics, which has in vitro and in vivo activities against methicillin-resistant S. aureus (MRSA). We report herein that MmpL, a putative member of the resistance, nodulation, and cell division (RND) family of proteins, contributes to oxadiazole resistance in the S. aureus strain COL. Through serial passages, we generated two S. aureus COL variants that showed diminished susceptibilities to an oxadiazole antibiotic. The MICs for the oxadiazole against one strain (designated S. aureus COL(I)) increased reproducibly 2-fold (to 4 μg/ml), while against the other strain (S. aureus COL(R)), they increased >4-fold (to >8 μg/ml, the limit of solubility). The COL(R) strain was derived from the COL(I) strain. Whole-genome sequencing revealed 31 mutations in S. aureus COL(R), of which 29 were shared with COL(I). Consistent with our previous finding that oxadiazole antibiotics inhibit cell wall biosynthesis, we found 13 mutations that occurred either in structural genes or in promoters of the genes of the cell wall stress stimulon. Two unique mutations in S. aureus COL(R) were substitutions in two genes that encode the putative thioredoxin (SACOL1794) and MmpL (SACOL2566). A role for mmpL in resistance to oxadiazoles was discerned from gene deletion and complementation experiments. To our knowledge, this is the first report that a cell wall-acting antibiotic selects for mutations in the cell wall stress stimulon and the first to implicate MmpL in resistance to antibiotics in S. aureus.

Single- and multiple-dose pharmacokinetics and absolute bioavailability of tedizolid

Objectives

Tedizolid phosphate is a novel antibacterial under investigation for the treatment of gram-positive infections. This study was conducted to assess the pharmacokinetics, safety, and tolerability of intravenous tedizolid phosphate as well as the oral bioavailability of tedizolid phosphate.

Design

Double-blind, single-ascending dose, multiple-dose pharmacokinetics study, as well as tolerability and open-label crossover studies.

Setting

Single center in the United States (Covance Clinical Research Unit, Madison, WI) between September 2009 and January 2010.

Participants

Ninety healthy volunteers.

Intervention

Single intravenous (IV) doses of tedizolid phosphate 50 mg (lead-in) and 100–400 mg. Single oral and IV dose of tedizolid phosphate 200 mg in crossover fashion. Multiple IV doses of tedizolid phosphate 200 and 300 mg for up to 7 days.

Measurements and Main Results

A dose-dependent increase was observed in the maximum plasma concentration (1.2–5.1 μg/ml) and the area under the concentration-time curve (17.4–58.7 μg × hr/ml) of tedizolid (the microbiologically active moiety of tedizolid phosphate) after single IV doses of tedizolid phosphate 100–400 mg. Administration of IV tedizolid phosphate 200 mg once/day for 7 days resulted in minimal (28%) tedizolid accumulation. The absolute oral bioavailability of tedizolid after a single 200-mg dose of tedizolid phosphate was 91%; pharmacokinetic parameters of tedizolid were similar with oral and IV administration. Treatment-related adverse events occurred in 41% of subjects. Most adverse events were related to infusion site and became more frequent with multiple dosing. In an additional 3-day tolerability study, IV tedizolid phosphate 200 mg and placebo were similarly tolerated, based on visual infusion phlebitis scores.

Conclusion

These results from a population of healthy volunteers support once/day dosing of tedizolid phosphate 200 mg with both the oral and IV formulations, without the need for dose adjustment when switching administration routes.

Long-term molecular epidemiology of Staphylococcus epidermidis blood culture isolates from patients with hematological malignancies

Staphylococcus epidermidis is an important cause of bloodstream infections in patients with hematological malignancies. Knowledge of the long-term epidemiology of these infections is limited. We surveyed all S. epidermidis blood culture isolates from patients treated for hematological malignancies at the University Hospital of Örebro, Sweden from 1980 to 2009. A total of 373 S. epidermidis isolates were identified and multilocus sequence typing, staphylococcal chromosome cassette mec (SCCmec) typing and standard antibiotic susceptibility testing were employed to characterize these isolates. The majority of the isolates 361/373 (97%) belonged to clonal complex 2, and the 373 isolates were divided into 45 sequence types (STs); Simpson's Diversity Index was 0.56. The most prevalent STs were ST2 (243/373, 65%) and ST215 (28/373, 8%). Ninety three percent (226/243) of the ST2 isolates displayed either SCCmec type III or IV. ST2 and 215 were isolated during the entire study period, and together these STs caused temporal peaks in the number of positive blood cultures of S. epidermidis. Methicillin resistance was detected in 213/273 (78%) of all isolates. In the two predominating STs, ST2 and ST215, methicillin resistance was detected in 256/271 isolates (95%), compared with 34/100 (34%) in other STs (p<0.001). In conclusion, in this long-term study of patients with hematological malignancies, we demonstrate a predominance of methicillin-resistant ST2 among S. epidermidis blood culture isolates.

Colonization and infection of the skin by S. aureus: immune system evasion and the response to cationic antimicrobial peptides

Staphylococcus aureus (S. aureus) is a widespread cutaneous pathogen responsible for the great majority of bacterial skin infections in humans. The incidence of skin infections by S. aureus reflects in part the competition between host cutaneous immune defenses and S. aureus virulence factors. As part of the innate immune system in the skin, cationic antimicrobial peptides (CAMPs) such as the β-defensins and cathelicidin contribute to host cutaneous defense, which prevents harmful microorganisms, like S. aureus, from crossing epithelial barriers. Conversely, S. aureus utilizes evasive mechanisms against host defenses to promote its colonization and infection of the skin. In this review, we focus on host-pathogen interactions during colonization and infection of the skin by S. aureus and methicillin-resistant Staphylococcus aureus (MRSA). We will discuss the peptides (defensins, cathelicidins, RNase7, dermcidin) and other mediators (toll-like receptor, IL-1 and IL-17) that comprise the host defense against S. aureus skin infection, as well as the various mechanisms by which S. aureus evades host defenses. It is anticipated that greater understanding of these mechanisms will enable development of more sustainable antimicrobial compounds and new therapeutic approaches to the treatment of S. aureus skin infection and colonization.

Virulence, Speciation and Antibiotic Susceptibility of Ocular Coagualase Negative Staphylococci (CoNS)

BACKGROUND

Coagulase negative Staphylococci (CoNS) are common inhabitants of human skin and mucous membranes. With the emergence of these organisms as prominent pathogens in patients with ocular infections, investigation has intensified in an effort to identify important virulence factors and to inform new approaches to treatment and prevention.

AIM

To isolate CoNS from ocular specimens; to study the possible virulence factors; speciation of coagulase negative staphylococci (CoNS) which were isolated from ocular complications; antibiotic susceptibility testing of ocular CoNS.

MATERIALS AND METHODS

The specimens were collected from the target patients who attended the Microbiology Laboratory of a tertiary care eye hospital in Coimbatore, Tamilnadu state, India. The isolates were subjected to tube and slide coagulase tests for the identification of CoNS. All the isolates were subjected to screening for lipase and protease activities. Screening for other virulence factors viz., slime production on Congo red agar medium and haemagglutination assay with use of 96-well microtitre plates. These isolates were identified upto species level by performing biochemical tests such as phosphatase test, arginine test, maltose and trehalose fermentation tests and novobiocin sensitivity test. The isolates were subjected to antibiotic susceptibility studies, based on the revised standards of Clinical and Laboratory Standards Institutes (CLSI).

RESULTS

During the one year of study, among the total 260 individuals who were screened, 100 isolates of CoNS were obtained. Lipolytic activity was seen in all the isolates, whereas 38 isolates showed a positive result for protease. A total of 63 isolates showed slime production. Of 100 isolates, 30 isolates were analyzed for haemagglutination, where 4 isolates showed the capacity to agglutinate the erythrocytes. The results of the biochemical analysis revealed that of the 100 isolates of CoNS, 43% were Staphylococcus epidermidis. The other isolates were identified as S. xylosus (n=8), S. captis (n=16), S. haemolyticus (n=10), S. saccharolyticus (n=2), S. hominis (n=5), S. saprophyticus (n=6) and S. intermedius (n=1). On the other hand, 9 isolates were not identified. In the antibiotic susceptibility analysis, it was found that most of the isolates were sensitive to vancomycin, amikacin and linczolid and resistant to cefatoxime, oxacillin, bacitracin and nalidixic acid.

CONCLUSION

S. epidermidis was found to be predominant in causing the ocular complications. Slime production, heamagglutination, protease and lipase activities could be the putative virulence factors of CoNS. Antibiotic susceptibility patterns of CoNS against antibacterial agents revealed maximum resistance to beta lactam groups, and the resistance was found to be higher to oxacillin, and lowest to vancomycin.

Causative organisms in revision total hip & knee arthroplasty for infection: Increasing multi-antibiotic resistance in coagulase-negative Staphylococcus and the implications for antibiotic prophylaxis

BACKGROUND AND PURPOSE

Increasing resistance among post-operative Coagulase-negative Staphylococci (CNS) infections have been reported. We present our experience changing resistance patterns.

METHODS

We examined microbiological results from hip and knee revisions from 2001 to 2010 and compared resistance to all Staphylococcus aureus (SA) and CNS cultured from regional pan-speciality sources, in order to examine the patterns of antibiotic resistance.

MAIN FINDINGS

72 revisions in 67 patients were included. The most common organisms were SA (36%) and CNS (35%). Resistance to methicillin was 72% for CNS versus 20% for SA and resistance to gentamicin was 40% for CNS versus 4% for SA. Among all regional (background pan-speciality) cultures SA resistance to methicillin fell from 32% to 16% from 2006 to 10 with no change in gentamicin resistance at 3%. During the same period resistance of CNS to methicillin and gentamicin increased from 63% to 70% and 32%-47% respectively.

CONCLUSIONS

Resistance of CNS to both methicillin and gentamicin is higher than with SA and appears to be increasing. At least 32% of CNS and 4% of SA from infected TKRs/THRs were resistant to our current prophylaxis regime. These changing patterns of resistance may have implications for future antibiotic prophylaxis regimes.

An exhaustive yet simple virtual screening campaign against Sortase A from multiple drug resistant Staphylococcus aureus

Methicillin resistant Staphylococcus aureus (MRSA) is one of the challenging bacterial pathogen due to its acquired resistance to the β lactam antibiotics. The Sortase A is an enzyme of Gram-positive bacteria including S. aureus to anchor surface proteins to the cell wall. Sortase A is well studied enzyme and considered as the drug target against MRSA. Sortase A plays active role in anchoring the virulence proteins on the cell wall of the Gram-positive bacteria. The inhibition of Sortase A activity results in the separation of S. aureus from the host cells and ultimately alleviation of the infection. Here, we adapted a structure-based virtual screening protocol which helped in identification of novel potential inhibitors of Sortase A. The protocol involved the docking of a chemical library of druglike compounds with the Sortase A binding site represented by multiple crystal structures. The compounds were ranked by multiple scoring functions and shortlisted for future experimental screening. The method resulted in shortlisting of three compounds as potential novel inhibitors of Sortase A out of a large chemical library. The high rankings of shortlisted compounds estimated by multiple scoring functions showed their binding potential with Sortase A. The results are proved to be a simple yet efficient choice of structure-based virtual screening. The identified compounds are druglike and show high rankings among all set protocols of the virtual screening. We hope that the study would eventually help to expedite the discovery of novel drug candidates against MRSA.

Differentiation between Staphylococcus aureus and coagulase-negative Staphylococcus species by real-time PCR including detection of methicillin resistants in comparison to conventional microbiology testing

BACKGROUND

Staphylococcus aureus has long been recognized as a major pathogen. Methicillin-resistant strains of S. aureus (MRSA) and methicillin-resistant strains of S. epidermidis (MRSE) are among the most prevalent multiresistant pathogens worldwide, frequently causing nosocomial and community-acquired infections.

METHODS

In the present pilot study, we tested a polymerase chain reaction (PCR) method to quickly differentiate Staphylococci and identify the mecA gene in a clinical setting.

RESULTS

Compared to the conventional microbiology testing the real-time PCR assay had a higher detection rate for both S. aureus and coagulase-negative Staphylococci (CoNS; 55 vs. 32 for S. aureus and 63 vs. 24 for CoNS). Hands-on time preparing DNA, carrying out the PCR, and evaluating results was less than 5 h.

CONCLUSIONS

The assay is largely automated, easy to adapt, and has been shown to be rapid and reliable. Fast detection and differentiation of S. aureus, CoNS, and the mecA gene by means of this real-time PCR protocol may help expedite therapeutic decision-making and enable earlier adequate antibiotic treatment.

[Infections of central venous catheters in home parenteral nutrition: a retrospective monocentric study over 2 years]

BACKGROUND AND STUDY AIMS

Infection of the central venous catheter (CVC) is the main aggravating factor of parenteral nutrition. The aim of this study was to determine the ecology of these infections in our home parenteral nutrition center and to evaluate our care protocol.

PATIENTS AND METHODS

The present study was monocentric and retrospective, and was conducted in the parenteral nutrition service of the Marseille University Hospital between 1 January 2011 and 31 May 2012. During this period, all the children who presented fever and a positive hemoculture in a medical emergency were taken into account, and the characteristics of the infection were analyzed.

RESULTS

After 17 months, 17 children had been subject to an infection in their central catheter: 47 bacteremia were identified, which is equivalent to 5.4 infections for 1000 days of CVC. An average 2.8 hemocultures were performed during this time. The most common bacterium was Staphylococcus hominis. The children affected by a digestive stoma or by a gastrostomy were not subject to more infections and their ecology was not different. All the children were referred to the hospital and treated with an intravenous antibiotic through the CVC.

DISCUSSION

As expected during the time of the study, the infection rate was very high. This finding led us to reassess our prevention protocol. It is also very likely that the number of infections was overestimated due to the protocol for sampling in the hemocultures and their subsequent analysis. Lastly, some children relapsed easily, although no predisposing factor was found in the present study. The therapy chosen was in agreement with the best practices and the ecology recovered.

CONCLUSION

The high number of infections observed during the study encourages a prospective evaluation of current practices.

Identification of the immunodominant regions of Staphylococcus aureus fibronectin-binding protein A

Staphylococcus aureus is an opportunistic bacterial pathogen responsible for a diverse spectrum of human diseases and a leading cause of nosocomial and community-acquired infections. Development of a vaccine against this pathogen is an important goal. The fibronectin binding protein A (FnBPA) of S. aureus is one of multifunctional ‘microbial surface components recognizing adhesive matrix molecules' (MSCRAMMs). It is one of the most important adhesin molecules involved in the initial adhesion steps of S. aureus infection. It has been studied as potential vaccine candidates. However, FnBPA is a high-molecular-weight protein of 106 kDa and difficulties in achieving its high-level expression in vitro limit its vaccine application in S. aureus infection diseases control. Therefore, mapping the immunodominant regions of FnBPA is important for developing polyvalent subunit fusion vaccines against S. aureus infections. In the present study, we cloned and expressed the N-terminal and C-terminal of FnBPA. We evaluated the immunogenicity of the two sections of FnBPA and the protective efficacy of the two truncated fragments vaccines in a murine model of systemic S. aureus infection. The results showed recombinant truncated fragment F1_30-500 had a strong immunogenicity property and survival rates significantly increased in the group of mice immunized with F1_30-500 than the control group. We futher identified the immunodominant regions of FnBPA. The mouse antisera reactions suggest that the region covering residues 110 to 263 (F1B_110-263) is highly immunogenic and is the immunodominant regions of FnBPA. Moreover, vaccination with F1B_110-263 can generate partial protection against lethal challenge with two different S. aureus strains and reduced bacterial burdens against non-lethal challenge as well as that immunization with F1_30-500. This information will be important for further developing anti- S. aureus polyvalent subunit fusion vaccines.

TCA cycle activity in Staphylococcus aureus is essential for iron-regulated synthesis of staphyloferrin A, but not staphyloferrin B: the benefit of a second citrate synthase

Staphylococcus aureus elaborates two citrate-containing siderophores, staphyloferrin A (SA) and staphyloferrin B (SB), that enhance growth under iron-restriction, yet, paradoxically, expression of the TCA cycle citrate synthase, CitZ, is downregulated during iron starvation. Iron starvation does, however, result in expression of SbnG, recently identified as a novel citrate synthase that is encoded from within the iron-regulated SB biosynthetic locus, suggesting an important role for SbnG in staphyloferrin production. We demonstrate that during growth of S. aureus in iron-restricted media containing glucose, SB is produced but, in contrast, SA production is severely repressed; accordingly, SB-deficient mutants grow poorly in these media. Hypothesizing that reduced TCA cycle activity hinders SA production, we show that a citZ mutant is capable of SB synthesis, but not SA synthesis, providing evidence that SbnG does not generate citrate for incorporation into SA. A citZ sbnG mutant synthesizes neither staphyloferrin, is severely compromised for growth in iron-restricted media, and is significantly more impaired for virulence than either of the single-deletion mutants. We propose that SB is the more important of the two siderophores for S. aureus insofar as it is synthesized, and supports iron-restricted growth, without need of TCA cycle activity.

Inhibition and biochemical characterization of methicillin-resistant Staphylococcus aureus shikimate dehydrogenase: an in silico and kinetic study

Methicillin-resistant Staphylococcus auerus (MRSA) strains are having a major impact worldwide, and due to their resistance to all β-lactams, an urgent need for new drugs is emerging. In this regard, the shikimate pathway is considered to be one of the metabolic features of bacteria and is absent in humans. Therefore enzymes involved in this route, such as shikimate dehydrogenase (SDH), are considered excellent targets for discovery of novel antibacterial drugs. In this study, the SDH from MRSA (SaSDH) was characterized. The results showed that the enzyme is a monomer with a molecular weight of 29 kDa, an optimum temperature of 65 °C, and a maximal pH range of 9–11 for its activity. Kinetic studies revealed that SDH showed Michaelis-Menten kinetics toward both substrates (shikimate and NADP⁺). Initial velocity analysis suggested that SaSDH catalysis followed a sequential random mechanism. Additionally, a tridimensional model of SaSDH was obtained by homology modeling and validated. Through virtual screening three inhibitors of SaSDH were found (compounds 238, 766 and 894) and their inhibition constants and mechanism were obtained. Flexible docking studies revealed that these molecules make interactions with catalytic residues. The data of this study could serve as starting point in the search of new chemotherapeutic agents against MRSA.

Phagocytosis and killing of Staphylococcus aureus by human neutrophils

Neutrophils are essential for host defense against Staphylococcus aureus infections. Although significant progress has been made, our understanding of neutrophil interactions with S. aureus remains incomplete. To provide a more comprehensive view of this process, we investigated phagocytosis and killing of S. aureus by human neutrophils using varied assay conditions in vitro. A greater percentage of bacteria were internalized by adherent neutrophils compared to those in suspension, and, unexpectedly, uptake of S. aureus by adherent neutrophils occurred efficiently in the absence of opsonins. An antibody specific for S. aureus promoted uptake of unopsonized bacteria in suspension, but had little or no capacity to enhance phagocytosis of S. aureus opsonized with normal human serum or by adherent neutrophils. Collectively, these results indicate that assay conditions can have a significant influence on the phagocytosis and killing of S. aureus by neutrophils. More importantly, the results suggest a vaccine approach directed to enhance opsonophagocytosis alone is not sufficient to promote increased killing of S. aureus by human neutrophils. With the emergence and reemergence of antibiotic-resistant microorganisms, establishing parameters that are optimal for studying neutrophil-S. aureus interactions will pave the way towards developing immune-directed strategies for anti-staphylococcal therapies.

Prosthetic joint infection

Prosthetic joint infection (PJI) is a tremendous burden for individual patients as well as the global health care industry. While a small minority of joint arthroplasties will become infected, appropriate recognition and management are critical to preserve or restore adequate function and prevent excess morbidity. In this review, we describe the reported risk factors for and clinical manifestations of PJI. We discuss the pathogenesis of PJI and the numerous microorganisms that can cause this devastating infection. The recently proposed consensus definitions of PJI and approaches to accurate diagnosis are reviewed in detail. An overview of the treatment and prevention of this challenging condition is provided.

Seasonal evaluation of bioaerosols from indoor air of residential apartments within the metropolitan area in South Korea

The aims of the present study were to determine the levels of bioaerosols including airborne culturable bacteria (total suspended bacteria, Gram-positive bacteria, Staphylococcus, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and Gram-negative bacteria), fungi, endotoxin, and viruses (influenza A, influenza B, respiratory syncytial virus types A/B, parainfluenza virus types 1/2/3, metapnemovirus, and adenovirus) and their seasonal variations in indoor air of residential apartments. Of the total suspended bacteria cultured in an indoor environment, Staphylococcus was dominant and occupied 49.0 to 61.3% of indoor air. Among Staphylococcus, S. aureus were detected in 100% of households' indoor air ranging from 4 to 140 CFU/m(3), and 66% of households were positive for MRSA ranging from 2 to 80 CFU/m(3). Staphylococcus and S. aureus concentrations correlated with indoor temperature (adjusted β: 0.4440 and 0.403, p < 0.0001). Among respiratory viruses, adenovirus was detected in 14 (14%) samples and influenza A virus was detected in 3 (3%) samples regarding the indoor air of apartments. Adenovirus concentrations were generally higher in winter (mean concentration was 2,106 copies/m(3)) than in spring (mean concentration was 173 copies/m(3)), with concentrations ranging between 12 and 560 copies/m(3). Also, a strong negative correlation between adenovirus concentrations and relative humidity in indoor air was observed (r = -0.808, p < 0.01). Furthermore, temperature also negatively correlated with adenovirus concentrations (r = -0.559, p < 0.05).