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

Carriage of community-associated methicillin-resistant Staphylococcus aureus in a cohort of infants in southern Israel: risk factors and molecular features

There are few data about the epidemiology of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) among children in Israel. This study was intended to identify risk factors for CA-MRSA colonization in healthy infants, to characterize the molecular features of colonizing organisms, and to determine whether they are responsible for health care-associated (HA) infections. Nasal cultures and demographic details were collected from a cohort of healthy infants at 5 visits between the ages of 2 and 12 months. Clinical characteristics of pediatric MRSA bloodstream infections (2001 to 2006) and wound cultures collected over 6 months were also studied. Clonal structure was evaluated by multilocus sequence typing. Isolates were studied for the staphylococcal cassette chromosome mec (SCCmec) type and for the presence of Panton-Valentine leukocidin (PVL) genes. MRSA was cultured at least once from 45 of 659 infants (346 Jewish and 313 Bedouin infants). Forty of 45 (89%) isolates were from Bedouin infants. Twenty-nine of 45 (64.4%) belonged to a new clonal complex, designated CC913, that carries SCCmec IV but not the PVL genes. CC913 was also isolated from 9/14 blood cultures and 7/8 wounds. All CC913 infections occurred in Bedouin children, and all but two were HA. In conclusion, Bedouin origin was the main risk factor for carriage of CA-MRSA. CC913 was dominant both in healthy carriers and as a cause of pediatric HA-MRSA bloodstream infections.

Staphylococcal cassette chromosomemec(SCCmec) in methicillin-resistant coagulase-negative staphylococci. A review and the experience in a tertiary-care setting

Coagulase-negative staphylococci (CNS) are increasingly recognized to cause clinically significant infections, withS. epidermidisoften cited as the third most common cause of nosocomial sepsis. Among CNS, there is a high prevalence of methicillin resistance associated with staphylococcal cassette chromosome (SCCmec) elements. Although identical SCCmectypes can exist inS. aureusand CNS, some novel classes of SCCmecmay be unique to CNS. Differences in the accuracy of identification of CNS species and use of non-standardized methods for the detection of methicillin resistance have led to confusing data in the literature. In addition to the review of SCCmecin CNS, in this paper we report a 2-year surveillance of methicillin-resistant CNS in a tertiary-care hospital in Guadalajara, Mexico.

MRSA and diabetic foot wounds: contaminating or infecting organisms?

Although infection is a well-recognized barrier to healing, evidence has emerged that wound colonization with methicillin-resistant Staphylococcus aureus (MRSA) has the same effect, which has been quantified as increasing the time to healing twofold. MRSA is a concern for those with diabetic foot ulcers based on evidence of impaired healing when it is present in the wound. However, many studies have found the bacterial content of diabetic foot ulcers to be polymicrobial, which necessitates MRSA being placed in this environmental context. Multiple variables contribute to the development of infection, including the host response, tissue perfusion, ulcer depth, ulcer location, and an adequate source of nutrition. In view of these factors, it is difficult to attribute infection to one bacterial species.

Reemergence of antibiotic-resistant Staphylococcus aureus in the genomics era

Staphylococcus aureus is the leading cause of bacterial infections in developed countries and produces a wide spectrum of diseases, ranging from minor skin infections to fatal necrotizing pneumonia. Although S. aureus infections were historically treatable with common antibiotics, emergence of drug-resistant organisms is now a major concern. Methicillin-resistant S. aureus (MRSA) was endemic in hospitals by the late 1960s, but it appeared rapidly and unexpectedly in communities in the 1990s and is now prevalent worldwide. This Review focuses on progress made toward understanding the success of community-associated MRSA as a human pathogen, with an emphasis on genome-wide approaches and virulence determinants.

Endogenous endophthalmitis caused by methicillin-resistant Staphylococcus aureus (MRSA)

PURPOSE

To report clinical features, diagnostic features, and outcome in three patients presenting with fulminant endogenous endophthalmitis caused by methicillin-resistant Staphylococcus aureus.

METHODS

Retrospective review of clinical data and microbiological findings in three cases.

RESULTS

All three patients had predisposing conditions for endogenous endophthalmitis (B-cell lymphoma, diabetes mellitus, steroid therapy, or gastrointestinal symptoms, such as vomiting and diarrhea). Two patients were colonized by methicillin-resistant Staphylococcus aureus in typical sites (nose, groin, throat, and conjunctiva), whereas one patient who developed phlebitis at the infusion puncture site followed by bacteremia presented no typical colonization. Despite adequate therapy, two patients lost visual function in the infected eye, one of which had to be enucleated. The other patient's eye regained adequate function.

CONCLUSION

Endogenous endophthalmitis by methicillin-resistant Staphylococcus aureus is a rare but serious condition. Early and specific therapy based on reliable detection of the underlying microorganism may help in preventing loss of visual function.

Staphylococcus epidermidis--the 'accidental' pathogen

Although nosocomial infections by Staphylococcus epidermidis have gained much attention, this skin-colonizing bacterium has apparently evolved not to cause disease, but to maintain the commonly benign relationship with its host. Accordingly, S. epidermidis does not produce aggressive virulence determinants. Rather, factors that normally sustain the commensal lifestyle of S. epidermidis seem to give rise to additional benefits during infection. Furthermore, we are beginning to comprehend the roles of S. epidermidis in balancing the epithelial microflora and serving as a reservoir of resistance genes. In this Review, I discuss the molecular basis of the commensal and infectious lifestyles of S. epidermidis.

Quantitative reverse transcription-PCR assay for the rapid detection of methicillin-resistant Staphylococcus aureus

AIM

To evaluate a new quantitative reverse transcription-PCR (qRT-PCR) assay for the rapid detection of methicillin-resistant Staphylococcus aureus (MRSA).

METHODS AND RESULTS

Primers for Staphylococcus-specific regions of 16S rRNA gene, spa gene and mecA gene were newly designed. RNAs extracted from broth-cultured strains were tested by qRT-PCR targeting each primer, and the bacterial counts obtained correlated well with those counted by the plating method with detection limits of 10(0), 10(1) and 10(2) CFU. The qRT-PCR assay targeting the 16S rRNA was 6430-fold or more sensitive than qPCR assay. All Staph. aureus strains tested were detected and none of the other Staphylococcus species and genus strains tested cross-reacted with the assay targeting the spa gene. All MRSAs tested were detected by the assay targeting the mecA gene. Clinical samples, faecal material and bronchial washout solutions were tested by our assay, and MRSAs were detected with a high sensitivity within 6 h.

CONCLUSION

Our qRT-PCR assay targeting three new primers to the target genes is a rapid and sensitive tool for the detection of MRSA directly from clinical samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

Because of its sensitivity and rapidity, our qRT-PCR assay is considered to be a valuable tool for clinical management.

Community-acquired methicillin-resistant Staphylococcus aureus carrying Panton-Valentine leukocidin genes: A lethal cause of pneumonia in an adult immunocompetent patient

Necrotizing pneumonia and fatal septic shock were caused by Panton-Valentine leukocidin-positive, community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) in a previously healthy, 61-y-old female. This patient did not belong to any high-risk group (e.g. homosexuals, military recruits, sports team members, etc.). CA-MRSA infection should be suspected in any adult with severe pneumonia/sepsis.

ICU stay promotes enrichment and dissemination of multiresistant coagulase-negative staphylococcal strains

Patients in the intensive care unit (ICU) are prone to be colonized and infected by multi-resistant bacteria. It is previously known that nosocomial infections are often preceded by cross-transmission events. The aim of the present investigation was to study the impact of the patient's length of ICU stay on the resistance patterns, diversity and dissemination of coagulase-negative staphylococci (CoNS) within and between patients. Two groups of patients were studied, including 20 consecutive patients sampled within 2 h from admission (short-stayers, SS), and all patients treated for at least 5 d in the ICU (long-stayers, LS), available for sampling every second week (n = 15). Sampling was performed from 5 sites: oropharynx, nares, neck, axilla and perineum. A total of 868 CoNS isolates deriving from LS patients and 403 isolates from SS patients were analysed for antimicrobial susceptibility, clonal diversity and dissemination within and between patients. The highest resistance rates were seen for oxacillin and ciprofloxacin, being 92% and 83%, respectively. Long-stayers were at significantly higher risk of being colonized with CoNS isolates resistant against oxacillin, clindamycin, ciprofloxacin, gentamicin as well as with multiresistant strains. By genotyping 22 phenotypes that were shared among at least 2 patients, 32 PFGE types of which 16 colonized more than 1 individual were identified. One of the clones was isolated from 10 individuals, including 2 SS patients, indicating an epidemic strain. Prolonged ICU stay was significantly correlated to decreased clonal diversity, increased endogenous dissemination of resistant strains and cross-transmission. The results emphasize the importance of good infection control practice, especially in this vulnerable group of patients.

Successful Treatment of Disseminated Cerebritis Complicating Methicillin-resistant Staphylococcus aureus Endocarditis Unresponsive to Vancomycin Therapy with Linezolid

A unique case of community acquired methicillin resistant Staphylococcus aureus (MRSA) sepsis, with endocardial and cerebral metastatic seeding, caused by a strain representative of the Italian clone, is described. The patient was a 47-y-old man without apparent risk factors for endocarditis and for MRSA infection who developed coma with multiple cerebritis lesions under vancomycin plus amikacin therapy. He was eventually cured with the addition of linezolid to the initial antimicrobial regimen. This observation seems to confirm previous reports of the efficacy of linezolid for the treatment of central nervous system infections caused by multidrug resistant Gram-positive bacteria. To our knowledge, this is the first report of MRSA disseminated cerebritis, a nearly always fatal disease, cured with this oxazolidinone drug. The increase in community acquired MRSA may have some impact on empirical treatment of serious infections caused by this organism.

Susceptibility of staphylococci and enterococci to antimicrobial agents at different ward levels in four north European countries

A multicentre susceptibility study was performed on staphylococci and enterococci isolated from patients at 3 different ward levels: primary care centres (PCCs), general hospital wards (GHWs) and intensive care units (ICUs), in Denmark, Finland, Norway and Sweden. There was a markedly higher incidence of resistance among CoNS in ICUs compared to GHWs and PCCs. Resistance rates were low among S. aureus isolates and no differences were found between the ward levels. Oxacillin resistance was found among 1.6% of S. aureus and 47% of CoNS isolates. 14% of CoNS and 0.9% of S. aureus isolates were glycopeptide intermediate. The prevalence of E. faecium isolates in this study differed significantly between the ward levels with the lowest prevalence found at PCCs. High level gentamicin resistant (HLGR) enterococci occurred in 11-25% of E. faecium and 6-20% of E. faecalis isolates. The HLGR rate was significantly higher among E. faecalis from hospitalized patients (GHWs and ICUs) compared to patients at PCCs. For enterococcal isolates, no other significant differences in antimicrobial resistance were found between the ward levels. All enterococci were teicoplanin susceptible, but decreased susceptibility to vancomycin was found among 2.0% and 0.6% of the E. faecium and E. faecalis isolates, respectively.

Staphylococcal cysteine protease staphopain B (SspB) induces rapid engulfment of human neutrophils and monocytes by macrophages

Abstract Circulating neutrophils and monocytes constitute the first line of antibacterial defence, which is responsible for the phagocytosis and killing of microorganisms. Previously, we have described that the staphylococcal cysteine proteinase staphopain B (SspB) cleaves CD11b on peripheral blood phagocytes, inducing the rapid development of features of atypical cell death in protease-treated cells. Here, we report that exposure of phagocytes to SspB critically impairs their antibacterial functions. Specifically, SspB blocks phagocytosis of Staphylococcus aureus by both neutrophils and monocytes, represses their chemotactic activity and induces extensive, nonphlogistic clearance of SspB-treated cells by macrophages. The proteinase also cleaves CD31, a major repulsion ('do not-eat-me') signal, on the surface of neutrophils. We suggest that both proteolytic degradation of repulsion signals and induction of 'eat-me' signals on the surface of leukocytes are responsible for the observed intensive phagocytosis of SspB-treated neutrophils by human monocyte-derived macrophages. Collectively, this may lead to the depletion of functional neutrophils at the site of infection, thus facilitating staphylococcal colonisation and spreading.

Are there differences in hospital cost between patients with nosocomial methicillin-resistant Staphylococcus aureus bloodstream infection and those with methicillin-susceptible S. aureus bloodstream infection?

OBJECTIVE

To examine the impact of methicillin resistance on in-hospital mortality, length of stay, and hospital cost after the onset of nosocomial Staphylococcus aureus bloodstream infection (BSI).

DESIGN

A retrospective cohort study.

SETTING

A tertiary care hospital in Rhode Island.

PATIENTS

A cohort of 182 consecutive patients who developed nosocomial BSI due to methicillin-susceptible and methicillin-resistant S. aureus (MSSA and MRSA, respectively)

RESULTS

Patients with MRSA BSI had a significantly longer total length of hospital and intensive care unit (ICU) stay before the onset of BSI and a higher average daily cost. Compared with ICU patients with MSSA BSI, those with MRSA BSI had a higher median total hospital cost ($42,137 vs $113,852), higher hospital cost after infection ($17,603 vs $51,492), and greater length of stay after infection (10.5 vs 20.5 days). After multivariable adjustment, ICU patients with MRSA BSI had significantly increased total hospital cost, hospital cost after infection, and length of stay after infection. However, using a propensity score approach, we found that, among ICU patients, the difference in cost after infection and the difference in length of stay after infection for MRSA, compared with MSSA BSI, were not significant. The differences among non-ICU patients who developed MRSA or MSSA BSI were not significant after multivariable adjustment or by propensity score.

CONCLUSIONS

On the basis of propensity score, we found that methicillin resistance did not independently increase hospital cost or length of stay after onset of S. aureus BSI. We believe that use of a propensity score on a comparable subset of patients may be a better method than multivariable adjustment for assessing the impact of methicillin resistance in cohort studies.

Serious infections due to methicillin-resistant Staphylococcus aureus: an evolving challenge for physicians

Methicillin-resistant Staphylococcus aureus (MRSA) is a well-recognized major cause of nosocomial infection worldwide. During the past decade, however, the epidemiology of staphylococcal infections has partially changed, with an increase in the number of patients who acquire infections in the community. The changing epidemiology is a cause for concern among physicians, leading to an increase in the number of patients with infections due to MRSA diagnosed at hospital admission and in the emergency department. The aims of this article are to review the current state of knowledge regarding MRSA infections, to identify those factors which may help physicians to recognize the patients at high risk, and to manage these infections appropriately.

Selection and characterization of murine monoclonal antibodies to Staphylococcus aureus iron-regulated surface determinant B with functional activity in vitro and in vivo

In an effort to characterize important epitopes of Staphylococcus aureus iron-regulated surface determinant B (IsdB), murine IsdB-specific monoclonal antibodies (MAbs) were isolated and characterized. A panel of 12 MAbs was isolated. All 12 MAbs recognized IsdB in enzyme-linked immunosorbent assays and Western blots; 10 recognized native IsdB expressed by S. aureus. The antigen epitope binding of eight of the MAbs was examined further. Three methods were used to assess binding diversity: MAb binding to IsdB muteins, pairwise binding to recombinant IsdB, and pairwise binding to IsdB-expressing bacteria. Data from these analyses indicated that MAbs could be grouped based on distinct or nonoverlapping epitope recognition. Also, MAb binding to recombinant IsdB required a significant portion of intact antigen, implying conformational epitope recognition. Four MAbs with nonoverlapping epitopes were evaluated for in vitro opsonophagocytic killing (OPK) activity and efficacy in murine challenge models. These were isotype switched from immunoglobulin G1 (IgG1) to IgG2b to potentially enhance activity; however, this isotype switch did not appear to enhance functional activity. MAb 2H2 exhibited OPK activity (> or =50% killing in the in vitro OPK assay) and was protective in two lethal challenge models and a sublethal indwelling catheter model. MAb 13C7 did not exhibit OPK (<50% killing in the in vitro assay) and was protective in one lethal challenge model. Neither MAb 13G11 nor MAb 1G3 exhibited OPK activity in vitro or was active in a lethal challenge model. The data suggest that several nonoverlapping epitopes are recognized by the IsdB-specific MAbs, but not all of these epitopes induce protective antibodies.

Nationwide epidemiological study revealed the dissemination of meticillin-resistant Staphylococcus aureus carrying a specific set of virulence-associated genes in Japanese hospitals

To study comprehensive toxin profiles and the chromosomal diversity of current Japanese hospital-associated meticillin-resistant Staphylococcus aureus (HA-MRSA) strains, we conducted PCR-based identification of 28 toxin genes, and staphylococcal cassette chromosome mec (SCCmec) typing and PFGE analysis of 208 MRSA strains isolated from 100 hospitals throughout Japan. Of the tested HA-MRSA strains, 80.3 % were tst-positive. The most frequent toxin gene profile was characterized by the carriage of 13 genes, tst, sec, seg, sei, sel, sem, sen, seo, lukED, hla, hlb, hld and hlg-2. Ninety of the 208 strains had this profile, which was named pattern A. Among the 118 non-pattern A strains, 100 had similar toxin gene profiles, the concordance rates to pattern A of which were more than 80 %. Consequently, 91.3 % of the examined HA-MRSA strains carried similar toxin profiles, although PFGE patterns showed a wide variation. These strains belonged to SCCmec type II, agr II and coagulase type II. We concluded that, unlike MRSA from many other countries, most of the Japanese HA-MRSA strains belonged to, or were related to, a specific group carrying the set of 13 toxin genes, irrespective of chromosomal diversity. In addition, among the 13 toxin genes, the coexistence rates of tst, sec and sel, and those of seg, sei, sem, sen and seo, were higher than for the other toxin genes. High coexistence rates of tst, sec and sel genes suggested the presence of the pathogenicity island SaPIn1 in these strains.

Characterization of coagulase-negative staphylococcal isolates from blood with reduced susceptibility to glycopeptides and therapeutic options

Background

Coagulase-negative staphylococci (CoNS) are a major cause of nosocomial blood stream infection, especially in critically ill and haematology patients. CoNS are usually multidrug-resistant and glycopeptide antibiotics have been to date considered the drugs of choice for treatment. The aim of this study was to characterize CoNS with reduced susceptibility to glycopeptides causing blood stream infection (BSI) in critically ill and haematology patients at the University Hospital Tor Vergata, Rome, Italy, in 2007.

Methods

Hospital microbiology records for transplant haematology and ICU were reviewed to identify CoNS with elevated MICs for glycopeptides, and isolates were matched to clinical records to determine whether the isolates caused a BSI. The isolates were tested for susceptibility to new drugs daptomicin and tigecycline and the genetic relationship was assessed using f-AFLP.

Results

Of a total of 17,418 blood cultures, 1,609 were positive for CoNS and of these, 87 (5.4%) displayed reduced susceptibility to glycopeptides. Clinical review revealed that in 13 cases (7 in haematology and 6 in ICU), CoNS with reduced susceptibility to glycopeptides were responsible for a BSI. Staphylococcus epidermidis was the causative organism in 11 instances and Staphylococcus haemolyticus in 2. The incidence of oxacillin resistance was high (77%), although all isolates remained susceptible to linezolid, daptomycin and tigecycline. Fingerprinting of CoNS identified one clonal relationship between two isolates.

Conclusion

Multi-resistant CoNS with reduced susceptibility to glycopeptides, although still relatively infrequent in our hospital, are emerging pathogens of clinical concern. Surveillance by antibiotyping with attention to multi-resistant profile, and warning to clinicians, is necessary.

A pentaplex PCR assay for the rapid detection of methicillin-resistant Staphylococcus aureus and Panton-Valentine Leucocidin

Background

Staphylococcus aureus is a major human pathogen, especially methicillin-resistant S. aureus (MRSA), which causes a wide range of hospital and community-acquired infections worldwide. Conventional testing for detection of MRSA takes 2–5 days to yield complete information of the organism and its antibiotic sensitivity pattern.

Results

The present study focused on the development of a pentaplex PCR assay for the rapid detection of MRSA. The assay simultaneously detected five genes, namely 16S rRNA of the Staphylococcus genus, femA of S. aureus, mecA that encodes methicillin resistance, lukS that encodes production of Panton-Valentine leukocidin (PVL), a necrotizing cytotoxin, and one internal control. Specific primer pairs were successfully designed and simultaneously amplified the targeted genes. The analytical sensitivity and specificity of the pentaplex PCR assay was evaluated by comparing it with the conventional method. The analytical sensitivity of the pentaplex PCR at the DNA level was found to be 10 ng DNA. The analytical specificity was evaluated with 34 reference staphylococci and non-staphylococcal strains and was found to be 100%. The diagnostic evaluation of MRSA carried out using 230 clinical isolates, showed 97.6% of sensitivity, 99.3% of specificity, 98.8% of positive predictive value and 98.6% of negative predictive value compared to the conventional method. The presence of an internal control in the pentaplex PCR assay is important to exclude false-negative cases.

Conclusion

The pentaplex PCR assay developed was rapid and gave results within 4 h, which is essential for the identification of Staphylococcus spp., virulence and their resistance to methicillin. Our PCR assay may be used as an effective surveillance tool to survey the prevalence of MRSA and PVL-producing strains in hospitals and the community.

Evaluation of toxic side effects of clinically used skin antiseptics in vitro

BACKGROUND

Skin antiseptics are widely used in health-care worldwide. However, there is a need to determine cytotoxicity of these medications on wounds. The aim of this study was to evaluate cytotoxic effects of five clinically used antiseptics on human skin cells.

MATERIAL AND METHODS

Five clinically used skin antiseptics (Prontosan, Lavasept, Braunol, Octenisept, and Betaisodona) were tested. The minimal inhibitory concentration was determined against Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, and Escherichia coli). The cytotoxic effects on primary keratinocytes, fibroblasts, and a HaCaT cell line were determined (MTT-assay and BrdU-ELISA) at a wide range of concentrations.

RESULTS

The agents tested showed effective antibacterial properties (Octenisept, Lavasept, and Prontosan showed higher efficacy than Braunol and Betaisodona) and different degrees of cytotoxicity. Lavasept and Prontosan demonstrated less toxicity on primary human fibroblasts and keratinocytes, whereas Octenisept, Betaisodona, and Braunol showed a significant (P<0.05) decrease in cell viability to 0% on keratinocytes at concentrations of 4%, 7.5%, and 12.5%, and on fibroblasts at 7.5% and 10%, respectively.

CONCLUSION

Due to the cytotoxic effect of some antiseptics on human skin cells, it is advised that health care professionals balance the cytotoxicity of the medication, their antiseptic properties, and the severity of colonization when selecting a wound care antiseptic. In this study, Lavasept and Prontosan showed best result regarding antibacterial efficacy and cell toxicity.

Human beta-defensin-3 promotes wound healing in infected diabetic wounds

BACKGROUND

Infected wounds present a major complication in patients with diabetes. Staphylococcus aureus is the most common single isolate in diabetic wounds. Human beta-defensin (hBD)-3 is antimicrobial active and appears to play a key role in the immune response. The present study aimed to analyse the effect of hBD-3 expression in a model of infected diabetic wounds.

METHODS

Excisional wounds were created on the backs of Yorkshire pigs and Ad5-CMV-hBD-3 vectors were microseeded. Wounds were inoculated with S. aureus, covered with a polyurethane chamber and analysed for transgene expression, bacterial infection, re-epithelialization, wound contraction, wound fluid production and blood vessel formation.

RESULTS

hBD-3-treated wounds showed a total bacterial load of 2.1 x 10(8) colony-forming units (CFU)/g tissue, versus 1.3 x 10(9) CFU/g tissue for controls (p < 0.001) at day 4. At day 12, no statistical difference could be detected. Re-epithelialization showed 75 +/- 15% wound closure for hBD-3 expressing wounds and 50 +/- 16% for controls (p < 0.01). hBD-3 expression was in the range 15-20 ng/ml of wound fluid during day 1-4. The lower dose of 2 x 10(9) Ad5-CMV-hBD-3 showed no effect, suggesting a dose dependency for hBD-3.

CONCLUSIONS

In the present study, we show that hBD-3 expression significantly promotes wound closure in S. aureus infected diabetic wounds in a preclinical large-animal model. Furthermore, a ten-fold reduction of bacterial growth on day 4 was detected. These findings indicate that beta-defensin-3 may play a major role in diabetic wound healing and wound infections.

Antimicrobial activity of tigecycline and comparative agents against clinical isolates of staphylococci and enterococci from ICUs and general hospital wards at three Swedish university hospitals

The activities of tigecycline and comparative agents on staphylococci and enterococci isolated from patients at general hospital wards (GHWs) and intensive care units (ICUs) at 3 university hospitals in Sweden were investigated. Oxacillin disc diffusion and minimal inhibitory concentration with E-test were used. The presence of mecA, vanA or vanB genes was determined with PCR. Statistically significant higher incidence of clindamycin, fusidic acid, rifampicin and multidrug-resistant CoNS was found at ICUs compared to GHWs. Resistance rates were low among S. aureus. Tigecycline, linezolid and vancomycin were the only agents with high activity against methicillin-resistant S. aureus and multidrug-resistant CoNS. Resistance rates were low among E. faecalis, except for high-level gentamicin-resistant (HLGR) E. faecalis. E. faecium showed high resistance rates to ampicillin, piperacillin/tazobactam and imipenem. The HLGR rates among E. faecium were lower than the rates for E. faecalis. Tigecycline and linezolid were the only drugs with high activity against all enterococci including vancomycin-resistant enterococci. No statistically significant differences in susceptibility rates were found between the ward levels for S. aureus and enterococcal isolates and no statistically significant differences were found between the hospitals.

MRSA genotypes in Turkey: persistence over 10 years of a single clone of ST239

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of life-threatening human infections. The clinical impact of MRSA is mounting, not only due to the ever-increasing prevalence but also due to the occurrence of new, community-acquired MRSA strains. The aim of this prospective, multi-centre study was to determine the prevalence and genetic relatedness of clinically relevant MRSA isolates, in Turkey.

METHODS

During a 1-year period, data from 20 successive patients with invasive S. aureus infections were collected from eight university hospitals, geographically distributed over the six main regions of Turkey. Among these S. aureus isolates, the genetic association of MRSA isolates was investigated by pulsed-field gel electrophoresis (PFGE) and spa typing. A selected number of isolates were also analyzed by multilocus sequence typing (MLST). Furthermore, Panton Valentine leucocidin (PVL) genes were examined.

RESULTS

In this study, the rate of methicillin resistance in S. aureus in patients with apparent infections (sepsis, meningitis, lung abscess or septic arthritis) ranged from 12 to 75% within the seven participating centres. Typing by pulsed-field gel electrophoresis and spa typing revealed the presence of 22 closely related genotypes. According to the PFGE and spa typing results, 53 out of 54 MRSA isolates were closely related. These isolates were of spa type t030 or a related spa type, contain an SCC mec type III element and belong to sequence type ST239. None of the isolates contained the PVL genes.

CONCLUSIONS

Despite the broad surface area of Turkey, a single predominant clone of ST239 circulates in hospitals in different regions and only few new types of MRSA were introduced over the past years. These results place Turkey in the epicenter of ST239 prevalence.

Methicillin resistance of airborne coagulase-negative staphylococci in homes of persons having contact with a hospital environment

BACKGROUND

The persons having contact with a hospital environment (hospital personnel workers and discharged patients) are highly exposed to colonization with multidrug-resistant bacteria. The aim of this study was to evaluate the airborne Staphylococcus genus features in homes in which inhabitants have had contact with the hospital environment.

METHODS

Airborne bacteria were collected using a 6-stage Anderson impactor. The Staphylococcus species composition and resistance to methicillin, and other antimicrobial agents among 3 coagulase-negative staphylococci (CNS) species (S cohnii spp cohnii, S epidermidis, S hominis), were determined. Antibiotic resistance of isolates was tested using the agar screen method with methicillin, the polymerase chain reaction technique to detect the mecA gene, and the disk diffusion method.

RESULTS

A higher prevalence of methicillin-resistant (MR) strains among the species isolated (40% of S epidermidis, 40% of S hominis, and 60% of S cohnii spp cohnii) was found in homes of persons who had contact with a hospital environment compared with the reference homes (only 12% of S hominis). The mecA gene was revealed in all MR S epidermidis strains and in some MR S hominis (50%) and S cohnii spp cohnii (33%) strains. All isolated MR CNS strains were susceptible to vancomycin, rifampicin, and linezolid.

CONCLUSION

High numbers of airborne multidrug-resistant MR CNS in the homes of persons having contact with a hospital environment indicates that such inhabitants pose a risk of intrafamilial spreading of MR strains via air.

Antimicrobial Activity and Chemical Composition of Senecio Sandrasicus on Antibiotic Resistant Staphylococci

The antimicrobial activity of hexane, chloroform, ethyl acetate and ethanol extracts of the aerial parts of S. sandrasicus P.H. Davis ( Asteraceae), endemic to Sandras mountain (Turkey), were determined. The antimicrobial activity of the extracts on microorganisms including multi-resistant staphylococci were evaluated using the disc diffusion method. The strains of multi-resistant staphylococci and the other standart bacteria were inhibited by some extracts. The volatile organic compouds of S. sandrasicus was determined by Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS). The major compounds of hexane extract were aromadendrene oxide 2 (13.3%), spathulenol (12.5%) and β-caryophylene (11.8%), respectively.

Cost-effectiveness of linezolid vs vancomycin in suspected methicillin-resistant Staphylococcus aureus nosocomial pneumonia in Germany

BACKGROUND

The oxazolidinone antibiotic linezolid has demonstrated efficacy in treating infections caused by methicillin-resistant Staphylococcus aureus (MRSA). In a retrospective analysis of two prospective randomized clinical trials in patients with nosocomial pneumonia (NP), initial therapy with linezolid produced significantly better clinical cure and survival rates than vancomycin in the subset of patients with documented MRSA infection. This study was designed to evaluate the economic impact of these clinical outcomes from the perspective of the German health care system to determine the use of these regimens in the light of limited resources and rising costs.

METHODS

A decision-analytic model using clinical trial data was developed to examine the costs and outcomes of treatment with linezolid or vancomycin in hospitalized patients with NP caused by suspected MRSA. The model followed an average patient from initiation of empiric treatment until treatment success, death, or second-line treatment failure. Local treatment patterns and resource use were obtained from a Delphi panel. Costs were taken from published sources. Outcomes included total cost per patient, cost per additional cure, cost per death avoided, and cost per life-year gained.

RESULTS

The model calculated that linezolid was associated with an 8.7% higher cure rate compared with vancomycin (73.6% vs 64.9%, respectively). Average total costs per episode for linezolid- and vancomycin-treated patients were 12,829 and 12,409, respectively. Death rates were 13.2% lower with linezolid than with vancomycin (20.7% vs 33.9%), resulting in an average of 2.3 life-years gained per linezolid-treated patient in a 65-year-old cohort (14.0 life-years vs 11.7 life-years). With linezolid, incremental costs per death avoided and per patient cured were 3,171 and 4,813, respectively. The base case estimated a similar mean length of stay for both drugs (11.2 vs 10.8 days). One-way sensitivity analyses did not change the overall results.

CONCLUSION

The model estimated a higher clinical cure (+8.7%) and survival (+13.2%) for linezolid compared with vancomycin at an incremental cost of 420 per treatment episode. The cost-benefit profile suggests that linezolid could be considered a cost-effective alternative to vancomycin in the treatment of patients with NP caused by suspected MRSA in Germany.

Staphylococcal infections: a historical perspective

Staphylococcus aureus is an unusually successful and adaptive human pathogen that can cause epidemics of invasive disease despite its frequent carriage as a commensal. Over the past 100 years and more, S aureus has caused cycles of outbreaks in hospitals and the community and has developed resistance to every antibiotic used against it, yet the exact mechanisms leading to epidemics of virulent disease are not fully understood. Approaches such as bacterial interference have been effective in interrupting outbreaks, but to better prevent staphylococcal disease, we will need to be vigilant about environmental factors that facilitate its spread. Even more importantly, we need to understand more about the mechanisms that lead to its virulence and transmission. With such information, it may be possible to develop a vaccine that will prevent endemic and epidemic staphylococcal disease.

Staphylococcus aureus disease and drug resistance in resource-limited countries in south and east Asia

By contrast with high-income countries, Staphylococcus aureus disease ranks low on the public-health agenda in low-income countries. We undertook a literature review of S aureus disease in resource-limited countries in south and east Asia, and found that its neglected status as a developing world pathogen does not equate with low rates of disease. The incidence of the disease seems to be highest in neonates, its range of clinical manifestations is as broad as that seen in other settings, and the mortality rate associated with serious S aureus infection, such as bacteraemia, is as high as 50%. The prevalence of meticillin-resistant S aureus (MRSA) infection across much of resource-limited Asia is largely unknown. Antibiotic drugs are readily and widely available from pharmacists in most parts of Asia, where ease of purchase and frequent self-medication are likely to be major drivers in the emergence of drug resistance. In our global culture, the epidemiology of important drug-resistant pathogens in resource-limited countries is inextricably linked with the health of both developing and developed communities. An initiative is needed to raise the profile of S aureus disease in developing countries, and to define a programme of research to find practical solutions to the health-care challenges posed by this important global pathogen.

Prevalence of nasal carriage of methicillin-resistant Staphylococcus aureus and its antibiotic susceptibility pattern in healthcare workers at Namazi Hospital, Shiraz, Iran

OBJECTIVE

The aim of this study was to determine the prevalence of nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) among healthcare workers (HCWs) at Namazi Hospital, Shiraz, Iran.

METHODS

This cross-sectional study was conducted from July to November 2006. Nasal swabs were taken from 600 randomly selected HCWs. The isolates were identified as S. aureus based on morphology, Gram stain, catalase test, coagulase test, and mannitol salt agar fermentation. To analyze sensitivity patterns of MRSA strains more precisely, minimum inhibitory concentrations (MICs) of antibiotics were determined by the E-test method. All methicillin-resistant isolates were examined for the existence of the mecA gene by total DNA extraction and PCR.

RESULTS

The prevalence of nasal carriage of methicillin-sensitive S. aureus (MSSA) was 25.7% and of MRSA was 5.3%, with the highest nasal carriage of MRSA in surgical wards and the emergency department. There was no significant difference between the sexes (p=0.247), age (p=0.817), and years of healthcare service (p=0.15) with regard to the nasal carriage of MRSA and MSSA. In the univariate analysis, a statistically significant difference was only found for occupation (p=0.032) between the carriage of MSSA and MRSA. In the multivariate analysis, the occupation 'nurse' was independently associated with MRSA carriage (p=0.012, odds ratio 3.6, 95% confidence interval 1.3-9.7). The highest resistance rate for both gentamicin and clindamycin (69%) was noted among the MRSA strains. None of the MRSA strains were resistant to mupirocin, linezolid, fusidic acid, or vancomycin. The existence of the mecA gene in all 32 methicillin-resistant isolates was observed by PCR.

CONCLUSIONS

This study revealed the prevalence of nasal carriage of S. aureus strains among HCWs to be lower than that found in other studies from Iran. The antibiotic susceptibility patterns also differed, perhaps as a result of the excessive use of antibiotics at our hospital. Only the occupation of nurse was an independent risk factor for MRSA carriage.

Staphylococcus aureus isolated from pork and chicken carcasses in Taiwan: prevalence and antimicrobial susceptibility

Staphylococcus aureus is a cause of many diseases in both humans and animals. This pathogen is also a major target in the screening of slaughterhouse carcasses to monitor hygienic conditions during slaughter. During 2004 to 2006, S. aureus was recovered from 8.8% (38 of 430), 11.3% (77 of 680), and 4.3% (13 of 300) of pork carcass samples, respectively, collected at 53 slaughterhouses in Taiwan. During 2003 to 2005, it was recovered from 0.3% (1 of 305), 0.4% (1 of 260), and 7.8% (31 of 395) of rinse fluids from chicken carcasses, respectively, collected at 17 meat processing plants. The minimum dilution method was used to determine antimicrobial susceptibility (MICs) of these strains (n = 103) as well as those collected from pork and chicken carcasses (n = 104) in a previous study beginning in 2000. All 207 strains were sensitive to nitrofurantoin and vancomycin. Over 50% were resistant to clindamycin (MIC that inhibited 90% of strains [MIC90] = 32 microg/ml) and tetracycline (MIC90 = 64 microg/ml). The percentages resistant to methicillin (oxacillin), chloramphenicol, erythromycin, and tylosin were 19.4% (40 of 207), 18.8% (39 of 207), 23.2% (48 of 207), and 20.8% (43 of 207) with MIC90s of 8, 64, > or = 64, and > or = 128 microg/ml, respectively. The methicillin-resistant S. aureus (MRSA) strains exhibited resistance to more antibiotics than did the methicillin-susceptible strains, and 87.5% (35 of 40) of the MRSA strains carried the mecA gene sequence. Since MRSA infections have become a public health concern in both communities and hospitals, testing for the presence of MRSA in animal carcasses during slaughtering operations is warranted.

Host defense and pathogenesis in Staphylococcus aureus infections

Staphylococcus aureus is the most abundant cause of bacterial infections in the United States. As such, the pathogen has devised means to circumvent destruction by the innate immune system. Neutrophils are a critical component of innate immunity and the primary cellular defense against S aureus infections. This article reviews human neutrophil function in the context of S aureus virulence mechanisms and provides an overview of community-associated methicillin-resistant S aureus pathogenicity.

Structure-based mechanism of lipoteichoic acid synthesis by Staphylococcus aureus LtaS

Staphylococcus aureus synthesizes polyglycerol-phosphate lipoteichoic acid (LTA) from phosphatidylglycerol. LtaS, a predicted membrane protein with 5 N-terminal transmembrane helices followed by a large extracellular part (eLtaS), is required for staphylococcal growth and LTA synthesis. Here, we report the first crystal structure of the eLtaS domain at 1.2-A resolution and show that it assumes a sulfatase-like fold with an alpha/beta core and a C-terminal part composed of 4 anti-parallel beta-strands and a long alpha-helix. Overlaying eLtaS with sulfatase structures identified active site residues, which were confirmed by alanine substitution mutagenesis and in vivo enzyme function assays. The cocrystal structure with glycerol-phosphate and the coordination of a Mn(2+) cation allowed us to propose a reaction mechanism, whereby the active site threonine of LtaS functions as nucleophile for phosphatidylglycerol hydrolysis and formation of a covalent threonine-glycerolphosphate intermediate. These results will aid in the development of LtaS-specific inhibitors for S. aureus and many other Gram-positive pathogens.

No relationship exists between PBP 2a amounts expressed in different MRSA strains obtained clinically and their beta-lactam MIC values

After establishing a linear relationship between the amount of penicillin-binding protein (PBP) 2a and membrane proteins of methicillin-resistant Staphylococcus aureus (MRSA) COL by dot-blot analysis using an antibody against PBP 2a, we determined the PBP 2a quantities in membrane fractions prepared from 14 different MRSA cells. Methicillin-sensitive S. aureus ATCC 6538P was used as a quality control strain. The amounts of PBP 2a diverged among the strains, and no relationship to beta-lactam MIC values were observed in the corresponding strains.

Methicillin-resistant Staphylococcus aureus (MRSA) among dental patients: a problem for infection control in dentistry?

We assessed the frequency of carriers of methicillin-resistant Staphylococcus aureus (MRSA) among 500 dental patients of a university clinic. From each participant, two specimens were taken from the anterior nares and the pharynx and analysed by culture. The participants completed a questionnaire on possible risk factors of MRSA infection. Two hundred ten individuals carried S. aureus, 90 in the nares only, 51 in the throat only and 69 in nares and throat. Isolates of 208 patients were methicillin-sensitive; two isolates were methicillin-resistant, both carried in the throat exclusively. In conclusion, the frequency of nasal and/or throat carriers of MRSA among dental patients was low and suggests few opportunities of exposure in the dental clinic assessed.

A new pathway of staphylococcal pathogenesis: apoptosis-like death induced by Staphopain B in human neutrophils and monocytes

Circulating neutrophils and monocytes form the first line of cellular defense against invading bacteria. Here, we describe a novel and specific mechanism of disabling and eliminating phagocytes by Staphylococcus aureus. Staphopain B (SspB) selectively cleaved CD11b on phagocytes, which rapidly acquired features of cell death. SspB-treated phagocytes expressed phosphatidylserine as well as annexin I and became permeable to propidium iodide, thus demonstrating distinctive features of both apoptosis and necrosis, respectively. The cell death observed was caspase and Syk tyrosine kinase independent, whilst cytochalasin D efficiently inhibited the staphopain-induced neutrophil killing. Neutrophil and monocyte cell death was not affected by integrin clustering ligands (ICAM-1 or fibrin) and was prevented, and even reversed, by IgG. This protective effect was dependent on the Fc fragment, collectively suggesting cooperation of the CD16 receptor and integrin Mac-1 (CD11b/CD18). We conclude that SspB, particularly in the presence of staphylococcal protein A, may reduce the number of functional phagocytes at infection sites, thus facilitating colonization and dissemination of S. aureus.

Diversity of staphylococcal cassette chromosome mec structures in methicillin-resistant Staphylococcus epidermidis and Staphylococcus haemolyticus strains among outpatients from four countries

In staphylococci, methicillin (meticillin) resistance (MR) is mediated by the acquisition of the mecA gene, which is carried on the size and composition variable staphylococcal cassette chromosome mec (SCCmec). MR has been extensively studied in Staphylococcus aureus, but little is known about MR coagulase-negative staphylococci (MR-CoNS). Here, we describe the diversity of SCCmec structures in MR-CoNS from outpatients living in countries with contrasting environments: Algeria, Mali, Moldova, and Cambodia. Their MR-CoNS nasal carriage rates were 29, 17, 11, and 31%, respectively. Ninety-six MR-CoNS strains, comprising 75 (78%) Staphylococcus epidermidis strains, 19 (20%) Staphylococcus haemolyticus strains, 1 (1%) Staphylococcus hominis strain, and 1 (1%) Staphylococcus cohnii strain, were analyzed. Eighteen different SCCmec types were observed, with 28 identified as type IV (29%), 25 as type V (26%), and 1 as type III (1%). Fifteen strains (44%) were untypeable for their SCCmec. Thirty-four percent of MR-CoNS strains contained multiple ccr copies. Type IV and V SCCmec were preferentially associated with S. epidermidis and S. haemolyticus, respectively. MR-CoNS constitute a widespread and highly diversified MR reservoir in the community.