Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks

Nasal Carriage of Staphylococcus aureus As a Risk Factor for Skin and Soft Tissue Infections

Nasal carriage of Staphylococcus aureus is a major risk factor for the development of S. aureus infection, including skin and soft tissue infections and foreign body infections, such as catheter-associated bacteremia and peritonitis. In this article, we review the recent literature on S. aureus nasal carriage, including the emergence of methicillin- resistant S. aureus in the community, the pathophysiology of nasal carriage, and the epidemiology and prevention of S. aureus infections associated with nasal carriage.

Nosocomial infections among HIV-positive and HIV-negative patients in a Brazilian infectious diseases unit

BACKGROUND

Some researchers observed that HIV-infected patients have a higher risk of acquiring nosocomial infections (NI). This study compared the incidence of NI among HIV-positive and HIV-negative inpatients.

METHODS

Patients from an infectious diseases ward who were classified as positive and negative regarding their HIV status were followed-up for 21 months in a prospective cohort study. Daily surveillance was made with use of Centers for Disease Prevention and Control criteria for NI.

RESULTS

NI per 1000 patients-day were 8.16 for HIV-positive patients and 3.94 for HIV-negative patients (P =.01). Central venous catheter (CVC) and urinary catheter utilization was significantly higher among HIV-positive patients than among HIV-negative patients (P <.001). Bloodstream infections (BSI) caused most of the NI, followed by urinary tract infections, vascular infections, and pneumonia. Overall, HIV-positive patients were more likely to have a BSI than were HIV-negative patients (P =.005). When only BSI was analyzed in patients with a CVC, there was no difference in the incidence of BSI between the 2 groups of patients (P =.24). HIV-positive patients were more likely to have an NI caused by Staphylococcus aureus than were HIV-negative patients (P =.04). Other important NI agents in both groups were Acinetobacter baumanii, Klebsiella pneumoniae, Pseudomonas aeruginosa, and coagulase-negative Staphylococcus.

CONCLUSIONS

In this study the HIV-positive patients were more likely to have NI than were the HIV-negative patients. Overall, HIV-positive patients are at increased risk for an NI caused either by S aureus or a BSI. Although HIV-positive patients had more CVC-days, there was no difference in the number of BSI among both groups, suggesting that the BSI incidence in the HIV-positive group is not exclusively related to the CVC.

Staphylococcal and enterococcal infections in the neonatal intensive care unit

Along with the successes in improving the survival of preterm neonates have come changes in the epidemiology of pathogens that cause healthcare-associated infections. Although gram-negative bacilli and group B streptococci predominated in past years, gram-positive organisms such as staphylococci and enterococci have since taken on greater roles. This shift has been accompanied by difficulties in defining optimal treatments for these pathogens because of emerging resistance patterns.

New methods to investigate infectious disease transmission and pathogenesis--Staphylococcus aureus disease in drug users

Staphylococcus aureus is the single most important bacterial pathogen in infections among drug users. It is responsible for several diseases, ranging from superficial cutaneous abscesses to life-threatening intravascular infections. Although the nature of these infections is well described in published work, there is limited understanding of their epidemiology and pathogenesis. This limitation is in part due to the difficulty of studying disease transmission among drug users in the community, and the limitations of the investigative tools that have so far been used. We review the current understanding of the pathogenesis of staphylococcal disease in drug users and argue for the integration of molecular epidemiological techniques and social network methodology to increase our understanding of the basis for the persistence, distribution, and transmission dynamics of S aureus among drug users. Finally, we propose a framework for investigating the transmission of pathogens in community-based settings.

Prevalence of methicillin-resistant Staphylococcus aureus nasal carriage in the community pediatric population

BACKGROUND

Reports from various geographic regions indicate that the prevalence of community-acquired methicillin-resistant (MRSA) infection is increasing. The primary reservoir is the anterior nares; nasal carriage is a risk factor for infection in a variety of populations. Little is known about MRSA nasal carriage rates among children in Nashville, TN and the associated likelihood of community MRSA transmission.

METHODS

Nasal swabs were collected from 500 children at well-child visits at either a university hospital pediatric clinic or a private pediatric office. Cultures were plated onto selective staphylococcal media, with or without oxacillin. isolates were confirmed by coagulase tube testing. Antibiotic susceptibilities were determined for suspected methicillin-resistant isolates by standard broth microdilution methods (National Committee for Clinical Laboratory Standards). Pulsed field gel electrophoresis was used to evaluate epidemiologic relatedness. PCR testing was done to assess for the gene. A parent questionnaire was administered regarding MRSA risk factors.

RESULTS

Four patients had oxacillin-resistant isolates (MIC >or= 4 microg/ml), and two had borderline resistant isolates (MICs = 1 and 2 microg/ml). One of the borderline-resistant isolates and one of the MRSA isolates had pulsed field gel electrophoresis typing results indicating close relatedness. The gene was present in all resistant isolates and one of the borderline-resistant isolates. Only having a household member employed in a hospital was associated with a greater risk of MRSA nasal carriage (odds ratio, 9.6; P= 0.008).

CONCLUSIONS

MRSA nasal colonization is present within Nashville's healthy pediatric population. Children with household contacts employed in a hospital are significantly more likely to be colonized.

Strains of Staphylococcus aureus obtained from drug-use networks are closely linked

Drug users have a higher incidence of colonization with Staphylococcus aureus than does the general population, and, as a result, they are at increased risk of infection with their colonizing strain. The purpose of this study was to examine the role of drug-use risk networks in S. aureus transmission, the similarity of S. aureus isolates within these networks, and the possible role of inhalation drug use paraphernalia in the transmission of S. aureus. Strains of S. aureus are shared among colonized inhalation drug users within drug-use risk networks. It suggests that patterns of drug use and the geographic location where drug sharing occurs are major contributors to the transfer of staphylococci and, as a result, to the high prevalence of staphylococcal colonization and perhaps disease in this population.

Surgical site infections in orthopedic surgery: the effect of mupirocin nasal ointment in a double-blind, randomized, placebo-controlled study

The objective of this study was to determine whether use of mupirocin nasal ointment for perioperative eradication of Staphylococcus aureus nasal carriage is effective in preventing the development of surgical site infections (SSIs). A randomized, double-blind, placebo-controlled design was used. Either mupirocin or placebo nasal ointment was applied twice daily to 614 assessable patients from the day of admission to the hospital until the day of surgery. A total of 315 and 299 patients were randomized to receive mupirocin and placebo, respectively. Eradication of nasal carriage was significantly more effective in the mupirocin group (eradication rate, 83.5% versus 27.8%). In the mupirocin group, the rate of endogenous S. aureus infections was 5 times lower than in the placebo group (0.3% and 1.7%, respectively; relative risk, 0.19; 95% confidence interval, 0.02-1.62). Mupirocin nasal ointment did not reduce the SSI rate (by S. aureus) or the duration of hospital stay.

Nosocomial spontaneous bacterial peritonitis and bacteremia in cirrhotic patients: impact of isolate type on prognosis and characteristics of infection

The characteristics of and prognosis for nosocomial spontaneous bacterial peritonitis (SBP) and bacteremia were examined in a prospective study that included data from 194 consecutive episodes of SBP and 119 episodes of bacteremia, 93.3% of which were nosocomial, in 200 hospitalized cirrhotic patients. Gram-positive pathogens were predominant (70% of the total) among isolates from nosocomial infections; the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) was 24.8%. Nosocomial and staphylococcal infections were associated with a higher mortality rate than were community-acquired infections (P=.0255) and nonstaphylococcal infections (P<.001), respectively. In comparison with non-MRSA infections, MRSA infections were more likely to recur and occurred in a greater number of sites other than ascitic fluid and blood (P=.0004). Older age (P=.0048), higher Child-Pugh score (P=.0011), and infection with staphylococci (P=.0031) were independently associated with a higher mortality rate. The emergence of MRSA is important because of the recurrence and poor outcome associated with infection with such organisms.

Differences between Staphylococcus aureus isolates from medical and nonmedical hospital personnel

It is unclear whether the levels of Staphylococcus aureus colonization of hospital personnel with patient exposure are increased or whether personnel become colonized with more antibiotic-resistant strains. Differences in nasal and hand carriage of S. aureus between medical and nonmedical hospital personnel were examined. No differences in nasal carriage between the two groups were found; however, there was a trend that suggested differences in the rates of hand carriage of S. aureus (18% of nonmedical personnel and 10% of medical personnel). Medical personnel were colonized with more antibiotic-resistant isolates than nonmedical personnel (mean, 2.8 versus 2.1 isolates [P < 0.03]), and the strain profiles indicated that they tended to be more clonal in origin, suggesting that exposure to hospital isolates alters the colonization profile.

7: Soft tissue, bone and joint infections

Soft tissue infections are common and usually respond rapidly to oral antibiotics; if empirical therapy fails then exposure to unusual organisms should be considered. Septic arthritis requires early recognition, identification of the infecting pathogen and urgent joint washout to prevent irreversible cartilage and bone destruction. Prosthetic joint infection is uncommon but has high morbidity; the best outcomes are achieved with removal of the prosthesis and replacement after at least six weeks of antibiotic therapy. Osteomyelitis often complicates diabetic foot infection with ulceration and is rarely cured by antibiotics alone; early surgical intervention achieves the best outcome.

Intranasal mupirocin to prevent postoperative Staphylococcus aureus infections

BACKGROUND

Patients with nasal carriage of Staphylococcus aureus have an increased risk of surgical-site infections caused by that organism. Treatment with mupirocin ointment can reduce the rate of nasal carriage and may prevent postoperative S. aureus infections.

METHODS

We conducted a randomized, double-blind, placebo-controlled trial to determine whether intranasal treatment with mupirocin reduces the rate of S. aureus infections at surgical sites and prevents other nosocomial infections.

RESULTS

Of 4030 enrolled patients who underwent general, gynecologic, neurologic, or cardiothoracic surgery, 3864 were included in the intention-to-treat analysis. Overall, 2.3 percent of mupirocin recipients and 2.4 percent of placebo recipients had S. aureus infections at surgical sites. Of the 891 patients (23.1 percent of the 3864 who completed the study) who had S. aureus in their anterior nares, 444 received mupirocin and 447 received placebo. Among the patients with nasal carriage of S. aureus, 4.0 percent of those who received mupirocin had nosocomial S. aureus infections, as compared with 7.7 percent of those who received placebo (odds ratio for infection, 0.49; 95 percent confidence interval, 0.25 to 0.92; P=0.02).

CONCLUSIONS

Prophylactic intranasal application of mupirocin did not significantly reduce the rate of S. aureus surgical-site infections overall, but it did significantly decrease the rate of all nosocomial S. aureus infections among the patients who were S. aureus carriers.

Low prevalence of methicillin-resistant strains among Staphylococcus aureus colonizing young and healthy members of the community in Portugal

Recent reports suggest that methicillin-resistant Staphylococcus aureus (MRSA) may be emerging as a community pathogen. In Portuguese hospitals, the incidence of MRSA among disease causing isolates is extremely high (48-50%). To determine the prevalence of MRSA in the Portuguese community, nasal samples were obtained from 823 draftees, 484 nonmedical university students, and 107 high-school students. In addition, throat samples were obtained from the 823 draftees and S. aureus isolates were also recovered from 283 (13%) nasopharyngeal samples obtained from 2,111 children attending day-care centers. The rate of nasal colonization of S. aureus was 34%, 25%, and 46% for draftees, nonmedical university students, and high-school students, respectively. The rate of pharyngeal colonization of the draftees was 33%. Of the 1,001 S. aureus isolates obtained, seven were MRSA and eight were borderline oxacillin-resistant S. aureus (BORSA). By molecular typing techniques, five of the seven MRSA were identified as belonging to one of three highly epidemic clones, the Brazilian, Iberian, and Pediatric clones of MRSA, which were identified as endemic in Portuguese hospitals. The eight BORSA were all members of clones previously identified in international samples. In spite of the extremely high prevalence of MRSA in Portuguese hospitals, the carriage rate of MRSA in healthy and young individuals remains low.

Prevalence of methicillin-resistant Staphylococcus aureus colonization in surgical patients, on admission to a Welsh hospital

Nosocomial infection with methicillin-resistant Staphylococcus aureus (MRSA) is on the increase and expensive to treat. Because surgical wound infection is one of the most frequent MRSA-induced infections with often disastrous consequences, it was decided to estimate the incidence and risk factors of MRSA colonization in surgical patients. All patients admitted to general surgical and orthopaedic wards were studied prospectively. At the time of admission, a detailed questionnaire was completed, nasal swabs and swabs of any pre-existing wound sites in each patient were sent for culture. Of 430 patients studied, 23 patients were positive for MRSA on admission. The prevalence of MRSA colonization in this study was 5.3% of whom 15 (65%) were nasal carriers and eight (35%) had MRSA colonization elsewhere. All nasal MRSA carriers had at least one documented hospital admission in the preceding year. Among the MRSA-positive patients, 10 (43%) either were admitted directly from, or had been previously admitted to, a nursing home. MRSA remains mainly a hospital-acquired infection although a significant proportion is acquired in the community. The risk factors identified were previous hospital admission, patients from nursing homes, male and aged over 70.

A STRATEGY FOR RAPID IDENTIFICATION OF METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS NASAL CARRIER STATUS

Methicillin Resistant Staphylococcus aureus (MRSA) is a multi drug resistant organism responsible for severe outbreaks of life threatening infections in hospitals which are difficult to treat They are spread by nasal carriage among the hospitalised patients, staff and visitors. Mannitol cloxacillin salt agar (MCSA) is a single tube method to identify MRSA. However, tubes showing growth and change in colour on biochemical characterisation often do not prove to be MRSA. In this study we have combined two strategies for the rapid identification and isolation of MRSA by culture in MCSA and multiplex PCR for mecA and femB genes. Anterior nasal swabs obtained from nursing staff and patients admitted to a large referral hospital, were inoculated into MCSA. Of the 100 tubes inoculated, 8 tubes showed change in colour and growth. On conventional testing 4 were MRSA, 3 were methicillin sensitive S aureus (MSSA) and 1 was Methicillin Sensitive Coagulase Negative S aureus (MSCNS). Genotyping by multiplex PCR revealed 5 MRSA, 2 MSSA and 1 MRCNS. The Multiplex PCR technique to rapidly identify presence of mecA and femB genes showed presence of both mecA and femB bands in all MRSA. The methicillin sensitive organisms showed absence of mecA gene while coagulase negative organisms showed absence of the fern B gene. Combining MSCA with multiplex PCR for mec A and fem B genes made the test both rapid and specific. Use of this strategy would enable rapid screening of nasal carriers and early implementation of hospital infection control measures.

Identification of a novel methicillin-resistant Staphylococcus aureus epidemic clone in Córdoba, Argentina, involved in nosocomial infections

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are increasingly a main health concern worldwide for hospitalized patients. In addition, the prevalence of community-acquired infection has risen continuously during the last few years. Some MRSA clones spread easier than others within the hospital environment and therefore are frequently implicated in outbreaks. Thus, the spread of a unique epidemic multiresistant clone, the so-called South American clone, is the main cause of nosocomial infections produced by this bacterium in Brazil and in some regions of Argentina, Chile, and Uruguay. In the present work we describe the identification of a novel clone of MRSA that is involved in nosocomial infections and that shows a prevalence as high as that for the South American clone. A total of 53 consecutive single-patient MRSA isolates were recovered during a 3-month period (May to July 1999) from six different hospitals (955 beds) in Córdoba. The isolates were initially typed according the antibiotic resistance and phage susceptibility patterns, followed by genotyping using pulsed-field gel electrophoresis (PFGE). PFGE analysis of the 53 MRSA isolates revealed six major types (A to F) and 25 subtypes. The B-type DNA pattern was indistinguishable from that of the South American epidemic clone observed in 34% of the isolates. A novel highly prevalent clone, showing the A-type DNA pattern and representing 38% of the isolates, was also identified. Moreover, the most frequent subtype of the A clonal family triggered an outbreak in a hospital 2 months later, further confirming its epidemic feature.

Nosocomial bloodstream infections among human immunodeficiency virus-infected patients: incidence and risk factors

To assess the incidence of nosocomial bloodstream infections (NBSIs) in human immunodeficiency virus (HIV)-infected patients, and to analyze the main associated risk factors, we performed a 1-year multicenter prospective study of patients with advanced HIV infection who were consecutively admitted to 17 Italian infectious diseases wards. As of May 1999, a total of 65 NBSIs (4.7%) occurred in 1379 admissions, for an incidence of 2.45 NBSIs per 1000 patient-days. Twenty-nine NBSIs were catheter-related bloodstream infections, with a rate of 9.6 central venous catheter-associated infections per 1000 device-days. Multivariate analysis indicated that variables independently associated with NBSIs included active injection drug use, a Karnofsky Performance Status score of <40, presence of a central venous catheter, and length of hospital stay. Mortality rates were 24.6% and 7.2% among patients with and without NBSIs, respectively (P<.00001). In the era of highly active antiretroviral therapy, NBSIs continue to occur frequently and remain severe and life-threatening manifestations.

An outbreak of Staphylococcus aureus in a pediatric cardiothoracic surgery unit

OBJECTIVE

To investigate an outbreak of Staphylococcus aureus surgical-site infections.

DESIGN

Case-control study.

SETTING

Pediatric cardiothoracic surgery service of a tertiary-care university medical center.

METHOD

Molecular typing was used to identify healthcare workers who carried the epidemic strain.

RESULTS

Three children acquired surgical-site infections caused by a single strain of S. aureus. Fourteen (25%) of the staff members in the operating room and 17 (11%) on nursing units carried the epidemic strain (P = .01). A case-control study identified 4 healthcare workers who were associated statistically with the outbreak, 2 of whom (a cardiothoracic surgeon and a perfusionist) carried the epidemic strain in their nares. The surgeon also carried the epidemic strain on his hands. Each staff member who carried the epidemic strain was treated with mupirocin; those carrying the strain on their hands were required to wash their hands with chlorhexidine. The surgeon was not allowed to perform surgery until 2 of his hand cultures did not grow S. aureus.

CONCLUSIONS

Only three children were infected with the epidemic strain, but it was disseminated widely among staff who cared for children who underwent cardiothoracic surgery. No additional cases were identified after staff members who carried the epidemic strain were decolonized. Both classic epidemiologic methods and molecular typing techniques were necessary to identify the source and extent of this outbreak.

Staphylococcus aureus infections and antibiotic resistance in older adults

The prevalence of infection with Staphylococcus aureus among older adults is unknown, but clinical syndromes caused by this organism are common. Bacteremia, pneumonia, endocarditis, and bone and joint infections are encountered with relative frequency in this population, and the clinical presentation may be atypical. Underlying disease and functional debility, rather than age itself, predispose the older adult to staphylococcal carriage and infection. Infections with methicillin-resistant strains of S. aureus are acquired primarily in hospital, rather than in nursing homes or in the community. Lack of clinical suspicion for S. aureus infection and delays in appropriate therapy can be fatal. Staphylococcal infection should be considered for an older adult with risk factors for staphylococcal carriage, comorbid illness, debility, and history of recent hospitalization or nursing home stay. Choices regarding empirical therapy should be made on the basis of knowledge of local antibiotic susceptibility patterns.

Spread of Staphylococcus aureus in hospitals: causes and prevention

Methicillin-resistant Staphylococcus aureus (MRSA) has become a major nosocomial pathogen in many hospitals worldwide. Even more alarming, MRSA strains that are vancomycin intermediate-susceptible are isolated with increasing frequency, making therapy for staphylococcal infections even more difficult and prevention more important than ever. Spread of S. aureus in hospitals and infection control measures are reviewed. The major sources of S. aureus in hospitals are septic lesions and carriage sites of patients and personnel. Carriage often precedes infection. The anterior nares are the most consistent carriage site, followed by the perineal area. Skin contamination and aerial dissemination vary markedly between carriers and are most pronounced for combined nasal and perineal carriers. The principal mode of transmission is via transiently contaminated hands of hospital personnel. Airborne transmission seems important in the acquisition of nasal carriage. Infection control strategies include screening and isolation of newly admitted patients suspected of carrying MRSA or S. aureus with intermediáte resistance to vancomycin, implementation of an infection control program to prevent transmission of resistant strains between patients and hospital personnel, and institution of a proper antibiotic policy to minimize antibiotic resistance development. MRSA carriers should be treated with intranasal antibiotics, e.g. mupirocin, and skin disinfectants to eliminate carriage. Education of hospital personnel is essential. Improved knowledge about the best ways to ensure favourable infection control practices is needed. Active intervention against the spread of MRSA is important.

Nasal carriage of Staphylococcus aureus among patients receiving allergen-injection immunotherapy: associated factors and quantitative nasal cultures

OBJECTIVE

To compare the prevalence of nasal Staphylococcus aureus carriage among outpatients receiving allergen-injection immunotherapy with the prevalence among healthy controls and to determine predictors of nasal S. aureus carriage.

DESIGN

Survey.

SETTING

Allergy clinic of a university hospital.

PARTICIPANTS

A volunteer sample consisting of 45 outpatients undergoing desensitization therapy and 84 first- and second-year medical students.

RESULTS

The nasal S. aureus carriage rate was significantly higher among patients (46.7%) than among students (26.2%; P=.019). In a multivariate model adjusted for age and gender, the presence of atopic dermatitis or eczema was the only independent predictor of nasal S. aureus carriage (odds ratio [OR], 4.4; 95% confidence interval [CI95], 1.2-16.0; P=.02). The only other participant characteristic associated with nasal S. aureus carriage was immunotherapy with allergen injections (OR, 1.98; CI95, 0.7-6.0), but this association did not reach statistical significance (P=.23). The probability of nasal S. aureus carriage was 88.9% for patients receiving allergen injections and having atopic dermatitis or eczema, and 36.1% for patients receiving allergen injections without atopic dermatitis or eczema.

CONCLUSIONS

Patients undergoing desensitization have a higher nasal carriage rate of S. aureus. However, factors other than the regular use of needles, and in particular abnormalities related to the atopic constitution of these patients, may predispose this population for S. aureus carriage.

Determinants of Staphylococcus aureus nasal carriage

Nasal carriage of Staphylococcus aureus has been identified as a risk factor for community-acquired and nosocomial infections. We screened 230 donors of diverse ethnic and socioeconomic backgrounds and identified 62 (27%) whose nasal secretions were colonized by S. aureus. In 18 donors in whom the various regions of the nasal luminal surface were separately sampled, the predominant region of S. aureus colonization was the moist squamous epithelium on the septum adjacent to the nasal ostium. Nasal fluid from carriers was defective in killing endogenous S. aureus and nasal carrier isolates of S. aureus but not a laboratory S. aureus strain. Transmission electron microscopy revealed that S. aureus isolates incubated in nasal fluid from carriers for 2 h at 37 degrees C were less damaged than those incubated in noncarrier fluid and were coated with an electron-dense layer. Compared with that from healthy donors and patients with acute rhinitis, nasal fluid from carriers contained elevated concentrations of the neutrophil-derived defensins human neutrophil peptides 1 to 3 (47- and 4-fold increases, respectively), indicative of a neutrophil-mediated inflammatory host response to S. aureus colonization. The concentration of the inducible epithelial antimicrobial peptide human beta-defensin 2 was also highly elevated compared to that in healthy donors, in whom the level was below the detection limit, or patients with acute rhinitis (sixfold increase). Thus, nasal carriage of S. aureus takes hold in nasal fluid that is permissive for colonization and induces a local inflammatory response that fails to clear the colonizing bacteria.

The many faces of Staphylococcus aureus infection. Recognizing and managing its life-threatening manifestations

Serious infections caused by S aureus, particularly those associated with bloodstream infection, are rapidly increasing in frequency, likely as a result of the proliferation of invasive procedures, the increasing severity of illness of hospitalized patients, suboptimal adherence to infection control practices, selection of resistant strains by antibiotic use, high rates of injecting drug use, and diabetes mellitus. In many cases, being aware of the clinical manifestations and treatment of S aureus can help to decrease the incidence of these infections and promote better care for patients who have been--or could be--exposed to the pathogen.

Staphylococcal resistance to antimicrobial peptides of mammalian and bacterial origin

Antimicrobial host defense peptides, such as defensins, protegrins, and platelet microbicidal proteins are deployed by mammalian skin, epithelia, phagocytes, and platelets in response to Staphylococcus aureus infection. In addition, staphylococcal products with similar structures and activities, called bacteriocins, inhibit competing microorganisms. Staphylococci have developed resistance mechanisms, which are either highly specific for certain host defense peptides or bacteriocins or which broadly protect against a range of cationic antimicrobial peptides. Experimental infection models can be used to study the molecular mechanisms of antimicrobial peptides, the peptide resistance strategies of S. aureus, and the therapeutic potential of peptides in staphylococcal diseases.

Structure-function relationships in the tryptophan-rich, antimicrobial peptide indolicidin

Indolicidin is a cationic 13 amino acid peptide amide produced in the granules of bovine neutrophils with the sequence H-ILPWKWPWWPWRR-NH2. Indolicidin is both antimicrobial and, to a lesser extent, haemolytic. In order to systematically investigate structure-function relationships, the solid-phase synthesis of indolicidin and 48 distinct analogues are reported, as well as the characterization of their respective biological properties. Peptides synthesized and characterized include analogues with modified terminal functions, truncations from either terminus, an alanine scan to determine the role of each individual amino acid, specific amino acid exchanges of aromatic, charged and structural residues and several retro-, inverso- and retroinverso-analogues. Together, characterization of these analogues identifies specific residues involved in antimicrobial or haemolytic activity and suggests a core structure that may form a scaffold for the further development of peptidomimetic analogues of indolicidin.

The significance of nasal carriage of Staphylococcus aureus as risk factor for human skin infections

The present study was designed to investigate the significance and the relationship between nasal carriage of Staphylococcus aureus and staphylococcal skin infections. Thirty-one S. aureus strains, isolated from 12 patients with chronic and recurrent skin infections, one patient with septicemia and one patient with otitis externa were studied. The staphylococcal strains were isolated from the site of infection and from the anterior nares of each patient. The identity of both strains of each pair could be demonstrated by determination of phenotypic properties and by genotyping of the isolates. The phenotypic properties included hemolytic activities, antibiotic resistance data, and the production of enterotoxins. The identity was additionally confirmed by phage-typing, by determination of the size and the number of repeats of the X region of spa gene, by determination of gene polymorphisms of coa gene and by macrorestriction analysis of the chromosomal DNA of the isolates by pulsed-field gel electrophoresis. The present results showed an identity of the S. aureus obtained from anterior nares and from skin infection of each patient indicating the importance of nasal carriage of these bacteria for development of human skin infection.

Infections associated with uremia and dialysis

Patients with chronic renal failure are predisposed to infections. Infections in end-stage renal disease patients are caused by immunosuppressive effects of uremia. Patients with renal failure on dialysis have impaired host defenses and may develop infections related to vascular access. This article reviews the infectious complications related to chronic renal failure in dialysis.

Staphylococcus aureus resistance to human defensins and evasion of neutrophil killing via the novel virulence factor MprF is based on modification of membrane lipids with l-lysine

Defensins, antimicrobial peptides of the innate immune system, protect human mucosal epithelia and skin against microbial infections and are produced in large amounts by neutrophils. The bacterial pathogen Staphylococcus aureus is insensitive to defensins by virtue of an unknown resistance mechanism. We describe a novel staphylococcal gene, mprF, which determines resistance to several host defense peptides such as defensins and protegrins. An mprF mutant strain was killed considerably faster by human neutrophils and exhibited attenuated virulence in mice, indicating a key role for defensin resistance in the pathogenicity of S. aureus. Analysis of membrane lipids demonstrated that the mprF mutant no longer modifies phosphatidylglycerol with l-lysine. As this unusual modification leads to a reduced negative charge of the membrane surface, MprF-mediated peptide resistance is most likely based on repulsion of the cationic peptides. Accordingly, inactivation of mprF led to increased binding of antimicrobial peptides by the bacteria. MprF has no similarity with genes of known function, but related genes were identified in the genomes of several pathogens including Mycobacterium tuberculosis, Pseudomonas aeruginosa, and Enterococcus faecalis. MprF thus constitutes a novel virulence factor, which may be of general relevance for bacterial pathogens and represents a new target for attacking multidrug resistant bacteria.

Activities of bismuth thiols against staphylococci and staphylococcal biofilms

Indwelling medical devices are associated with infectious complications. Incorporating antimicrobials into indwelling materials may reduce bacterial colonization. Bismuth thiols are antibiofilm agents with up to 1,000-fold-greater antibacterial activity than other bismuth salts. Staphylococci are particularly sensitive, as determined by agar diffusion and broth dilution susceptibility testing. Bismuth-ethanedithiol inhibited 10 methicillin-resistant Staphylococcus epidermidis strains at 0.9 to 1.8, Staphylococcus aureus ATCC 25923 at 2.4, and S. epidermidis ATCC 12228 at 0.1 microM Bi(3+). Antiseptic-resistant S. aureus was sensitive to bismuth-2-3-dimercaptopropanol (BisBAL) at < or = 7 microM Bi(3+). Hydrogel-coated polyurethane rods soaked in BisBAL inhibited S. epidermidis for 39 days (inhibitory zone diameter in agar, > or = 30 mm for > 25 days). Slime from 16 slime-producing S. epidermidis strains was inhibited significantly by bismuth-3,4-dimercaptotoluene (BisTOL), but not by AgNO3, at subinhibitory concentrations. In conclusion, bismuth-thiols are bacteriostatic and bactericidal against staphylococci, including resistant organisms, but are also inhibitors of slime at subinhibitory concentrations. At subinhibitory concentrations, BisTOL may be useful in preventing the colonization and infection of indwelling intravascular lines, since staphylococci are important pathogens in this setting.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus strains: state of affairs and tomorrow' s possibilities

Methicillin-resistant strains of Staphylococcus aureus (MRSA) have posed a clinical threat for nearly 40 years. During these years, an array of additional technologies suited for identification of MRSA below the species level has become available. The technologies, whether they assess phenotype or genotype, provide data that can be used for elucidation of the routes of dissemination of individual MRSA types. This review summarizes the current state of affairs with respect to the quality of the various laboratory techniques and includes descriptions of novel strategies such as binary typing and multilocus sequence typing (MLST). Drawbacks of procedures will be compared, and the value of molecular typing in the elucidation of complex biological phenomena, such as epidemicity, carriage, and reduced vancomycin susceptibility, will be indicated. Means for integrated assessment of bacterial biology, epidemiology, and population structure will be discussed.

Epidemiological study of staphylococcal colonization and cross-infection in two West African Hospitals

Surveillance in two medium-size (250-300 beds) hospitals located in the most populated islands of Cape Verde was undertaken in July 1997 in order to obtain data concerning nasal carriage of staphylococci. Nasal swabs (172) taken from inpatients and health care workers (HCW) from different internment services yielded 68 Staphylococcus aureus and 105 coagulase-negative staphylococcal (CNS) isolates, demonstrating extensive colonization of both inpatients and HCW by S. aureus (carriage rate 41%) and CNS (carriage rate 65%). The most frequent CNS species were S. epidermidis and S. haemolyticus. Three species--S. aureus, S. epidermidis, and S. sciuri-were recovered from wound swabs. The antibiotic susceptibility profiles of S. aureus and CNS differed sharply: all 68 S. aureus were resistant to penicillin but were fully susceptible to oxacillin as well as the other antimicrobial agents tested-gentamicin; erythromycin, except for three strains; ciprofloxacin; sulfamethoxazole-trimethoprim, except for two strains; vancomycin; and amoxicillin/clavulanate. In contrast, most (91/105) of CNS were resistant to both penicillin and oxacillin, and a variable but substantial proportion of CNS isolates also carried multiresistant traits to gentamicin, erythromycin, sulfamethoxazole-trimethoprim, and amoxicillin/clavulanate. The analysis by PFGE of the methicillin-susceptible S. aureus (MSSA) and the methicillin-resistant S. epidermidis (MRSE) strains provided evidence for extensive cross-infection and cross-colonization from HCW to patients.

Characteristics of a new epidemic MRSA in Germany ancestral to United Kingdom EMRSA 15

In 1996 a new epidemic MRSA emerged in three hospitals North of Berlin. This strain, Barnim epidemic MRSA, was isolated in 15 hospitals in Northern Germany in 1997 and 29 hospitals throughout Germany in 1998. Isolates of this clone are non-typeable by phages, its resistance phenotype is PEN, OXA, ERY, CLI, CIP (genotype: mecA, ermC, mutations in grlA and gyrA). The Sma I macrorestriction pattern corresponds to particular phage group II strains which is confirmed by the 16S-23S rRNA gene spacer pattern. Isolates of this clone differ by less than three Sma I macrorestriction fragments from isolates of the EMRSA15 clone from the United Kingdom, the most common epidemic MRSA isolates in the United Kingdom in recent years. Both epidemic strains produce enterotoxin C and possess the sec determinant for this toxin, the configuration of the mec regulon is mecI-, mecRB+, mecRC+. Both share the same Alu I pattern of PCR amplimers of the 3' end region of the coagulase gene. EMRSA 15 and Barnim EMRSA share a common multilocus sequence type indicating a recent, shared evolutionary origin.

Isolation and characterization of methicillin-resistant Staphylococcus aureus strains from nares of nurses and their gowns

The isolation and characterization of methicillin-resistant Staphylococcus aures (MRSA) strains from the bilateral nares of nurses and their gowns are described. MRSA strains could be isolated from eigth of fifty bilateral nares of nurses and two of their gowns. Ten MRSA strains were typed using coagulase typing, and divided into two types, coagulase II and III. In this study, we found a new group (producing toxic shock syndrome toxin -1, coagulase III and staphylococcal enterotoxin C) in Japanese MRSA. Furthermore, we confirmed that MRSA strains originating from bilateral nares of three nurses were identical and two strains isolated from the left naris of one nurse and her gown were also identical by pulsed-field gel electrophoresis.

Epidemic spread of a single clone of methicillin-resistant Staphylococcus aureus among injection drug users in Zurich, Switzerland

We describe an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) among injection drug users (IDUs). From August 1994 through December 1999, we registered 31 IDUs with MRSA infections (12 with soft-tissue infection, 7 with pneumonia [fatal in 1], 7 with endocarditis [fatal in 1], 2 with osteomyelitis, 2 with septic arthritis, and 1 with ulcerative tonsillitis), with a marked increase in the number of IDUs registered during 1998 and 1999. Of 31 patients, 15 (48%) were infected with human immunodeficiency virus. A point-prevalence study among IDUs who frequented outpatient facilities in Zurich revealed an MRSA carriage rate of 10.3% (range, 0%-28.6%) in various facilities. In all but 1 case, pulsed-field gel electrophoresis banding patterns of isolates obtained from these patients were indistinguishable from isolates of the initial 31 IDUs registered. Risk factors for MRSA carriage were disability and prior hospitalization in a hospice. In summary, MRSA became endemic in IDUs in Zurich as a result of the spread of a single clone. This clone caused major morbidity and was responsible for a lethal outcome in 2 cases.

Clonal associations among Staphylococcus aureus isolates from various sites of infection

A molecular epidemiological analysis was undertaken to identify lineages of Staphylococcus aureus that may be disproportionately associated with infection. Pulsed-field gel electrophoresis analysis of 405 S. aureus clinical isolates collected from various infection types and geographic locations was performed. Five distinct S. aureus lineages (SALs 1, 2, 4, 5, and 6) were identified, which accounted for 19.01, 9.14, 22.72, 10.12, and 4.69% of isolates, respectively. In addition, 85 lineages which occurred with frequencies of <2.5% were identified and were termed "sporadic." The most prevalent lineage was methicillin-resistant S. aureus (SAL 4). The second most prevalent lineage, SAL 1, was also isolated at a high frequency from the anterior nares of healthy volunteers, suggesting that its prevalence among clinical isolates may be a consequence of high carriage rates in humans. Gene-specific PCR was carried out to detect genes for a number of staphylococcal virulence traits. tst and cna were found to be significantly associated with prevalent lineages compared to sporadic lineages. When specific infection sites were examined, SAL 4 was significantly associated with respiratory tract infection, while SAL 2 was enriched among blood isolates. SAL 1 and SAL 5 were clonally related to SALs shown by others to be widespread in the clinical isolate population. We conclude from this study that at least five phylogenetic lineages of S. aureus are highly prevalent and widely distributed among clinical isolates. The traits that confer on these lineages a propensity to infect may suggest novel approaches to antistaphylococcal therapy.

MRSA carriage: the relationship between community and healthcare setting. A study in an Italian hospital

From May 1997 to June 1998, all patients admitted to the study institution were screened at entry for MRSA carriage (both colonization and infection). Eighty-six MRSA carriers were identified; of these, 85 were nasal carriers. Risk factors were compared to those of 86 controls. Although the vast majority of both carriers and controls had at least one previous hospital stay, carriers were less likely than controls to be referred from a community setting, and had resided within the community for a shorter time before the current admission. The number of underlying conditions was comparable in the two groups, but those infected were more likely to have cancer than the controls. While community-acquired MRSA carriage is rare, exposure to a health care setting (particularly if repeated) within six months from the current admission, is a risk factor for MRSA carriage and introduction of the organism into an institution.

Should we routinely use mupirocin to prevent staphylococcal infections?

Routine use of mupirocin to prevent staphylococcal infections is controversial. We assessed attitudes and practices of healthcare professionals attending the Fourth Decennial International Conference on Nosocomial and Healthcare-Associated Infections regarding mupirocin prophylaxis. Eighty percent of participants did not use mupirocin routinely. At the end of the session, 58% indicated they would consider increased use of mupirocin.

An epidemiological study on the occurrence of Staphylococcus aureus in superficial abscesses of patients presenting for surgery in a teaching hospital in Khartoum, Sudan

A group of patients (n=86) suffering from superficial abscesses was recruited in the Khartoum Teaching Hospital, Sudan. Detailed clinical and socio-economic data were collected. It appeared that 83% of all patients were younger than 40. Labourers were most prevalent (28%), followed by students (23%) and housewives (16%). The head and neck were most often affected (22%), with hands being second (19%). In 92% of all pus cultures a microbial agents was identified, the large majority being Staphylococcus aureus (69%). Among patients, 47% were nasal carriers of S. aureus, similar to the carriage rate measured among controls, suggesting that nasal carriage is no risk factor for abscess development. Multivariate logistic regression analysis revealed that a history of abscess, recent traditional medical treatment, poor hygiene and low socio-economic status were significantly and independently associated with the occurrence of superficial abscesses.

Cutaneous microenvironment of human immunodeficiency virus (HIV)-seropositive and HIV-seronegative individuals, with special reference to Staphylococcus aureus colonization

A cross-sectional quantitative study of cutaneous bacterial and yeast flora at seven body sites in 99 human immunodeficiency virus-seropositive and 50 seronegative military personnel was performed. Statistically significant differences in carriage rates were only observed for Staphylococcus aureus on the foreheads of seropositive individuals. Seronegative individuals demonstrated staphylococcal carriage rates 1.3 to 2 times as great as those of historical controls (defined as healthy individuals not receiving any medications) at five of six body sites. We conclude that seropositive military personnel do not exhibit statistically significant elevations in densities and carriage rates of the microorganisms examined (except Staphylococcus aureus), relative to seronegative individuals. Seropositive individuals may be predisposed to staphylococcal carriage. The elevated staphylococcal carriage rates of military personnel undergoing basic training warrants a formal evaluation of the impact of training exercises on cutaneous flora. The information gained may serve to limit the spread of infection during training exercises and battlefield conditions.

Nasal carriage and antibiotic resistance of Staphylococcus aureus isolates from hospital and non-hospital personnel in Abha, Saudi Arabia

The prevalence of nasal carriage of Staphylococcus aureus, antibiograms and prevalence of methicillin-resistant S. aureus (MRSA) were studied in 1999 among healthy hospital and non-hospital personnel in Abha, Saudi Arabia. S. aureus was isolated from 26.1% of 299 adults in the community and 25.4% of 279 hospital personnel. No isolate was resistant to vancomycin. Antibiotic resistance rates, for all other antibiotics tested except cephalothin, were significantly higher for strains from hospital personnel (P values < 0.001-0.04) compared to non-hospital adults. The antibiograms were also compared with those of 140 clinical isolates. The rates of resistance of the inpatient strains to all the antibiotics tested were significantly higher than those of hospital nasal carrier strains (P < 0.001-0.05). MRSA was isolated, respectively, from 5.1% and 18.3% of non-hospital and hospital carriers; MRSA carriage rates were 1.3% and 4.7%, respectively, for non-hospital and hospital carriers, and 61% of S. aureus isolates from infected patients were MRSA. Only 8% of non-hospital but 44% of hospital carrier strains were multiply resistant (P < 0.001). Multiple resistance among inpatient strains (89%) was significantly higher than that among hospital nasal strains (44%) (P < 0.001). Such rates of multiple resistance and endemic MRSA prevalence among healthy carriers (11%) at a much higher rate than those reported in the literature should raise concern in a region with unrestricted availability of antibiotics.

Colonization with superantigen-producing Staphylococcus aureus is associated with increased severity of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disease associated with colonization of the skin with Staphylococcus aureus known to produce toxins with superantigen (SAg) activity. Besides T-cell activation these toxins induce T-cell skin homing in vitro. This may contribute to the observed induction or enhancement of skin inflammation.

OBJECTIVE

The aim of this study was to determine whether colonization with SAg-producing S. aureus isolates modulates the intensity of AD. If so, it was of interest whether this may be primarily due to the toxins' effects as SAgs or as allergens.

METHODS

In AD patients, healthy controls, and atopic controls SAg production by S. aureus isolated from skin or mucous membranes was investigated and correlated to the severity of the disease. Total IgE, SAg-specific IgE, and T-cell activation and recirculation markers were analysed and correlated with SAg production.

RESULTS

Fifty-seven percent of S. aureus strains isolated from AD patients produced SAgs. This frequency was higher compared to healthy controls (33%). SAg production by S. aureus was correlated with a significantly higher scoring of AD (SCORAD index, 58 +/- 19 in SAg-producing vs 41 +/- 7 in non-SAg-producing germs; P < 0.05). However, the severity of the disease was not associated with sensitization against the SAgs staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin B (SEB). Furthermore, SAg production by S. aureus was inversely correlated with total IgE concentration (P < 0.05) and positively correlated with T-cell activation (as measured by HLA-DR and CD69 expression) and the expression of the T-cell skin homing phenotype cutaneous lymphocyte-associated antigen.

CONCLUSION

SAg production by S. aureus is suggested to be associated with an increased severity of atopic dermatitis. Since SAg production was found neither exclusively in AD patients nor in all patients, other pathogenic factors may be additionally effective.

Nasal carriage of Staphylococcus aureus is a major risk factor for surgical-site infections in orthopedic surgery

OBJECTIVE

To determine the relative importance of different risk factors for the development of surgical-site infections (SSIs) in orthopedic surgery with prosthetic implants.

DESIGN

In a cohort of 272 patients, the following possible risk factors were studied: age, gender, method of hair removal, duration of operation, surgeon, underlying illness, and nasal carriage of Staphylococcus aureus. Infections were recorded following the Centers for Disease Control criteria. The relation between risk factors and SSI was tested in univariate and multiple logistic regression analysis.

SETTING

Community hospital in Breda, The Netherlands.

RESULTS

18 (6.6%) of 272 patients experienced SSI: 11 superficial and 7 deep SSI. These infections led in three cases to removal of the prosthesis and caused 286 extra days in hospital. The main causative pathogen was S aureus. In multiple logistic regression analysis, the following factors were independent risk factors for the development of SSI: high-level nasal carriage of S aureus (P=.04), male gender (P=.005), and surgeon 1 (P=.006). The only independent risk factor for SSI with S aureus was high-level nasal carriage of S aureus (P=.002).

CONCLUSION

High-level nasal carriage of S aureus was the most important and only significant independent risk factor for developing SSI with S aureus.

[Colonization by methicillin-resistant Staphylococcus aureus is a predictive factor for the resistance phenotype of an infectious strain of S. aureus]

OBJECTIVE

To assess the predictive value of a previous colonization with methicillin-resistant Staphylococcus aureus for the resistance pattern of a bacteriological specimen significantly positive to S. aureus.

STUDY DESIGN

Retrospective study of patients' files.

PATIENTS

Patients admitted for at least 48 hours in a surgical intensive care unit from April 1, 1996 to December 31, 1997.

METHODS

Collection of patients' characteristics and chronology of positive microbiological specimens with methicillin-susceptible (MSSA) or -resistant (MRSA) S. aureus from medical and laboratory records. During the study period, screening for nasal or perineal colonization with MRSA was systematically performed on admission and weekly thereafter.

RESULTS

The files of 540 patients were reviewed. MSSA and MRSA infections occurred in 7% (39/540) and 4% (20/540) of the patients respectively. By opposition with MSSA infections, MRSA infections occurred more frequently in patients previously colonized with MRSA (13 infections in 63 colonized patients [21%] versus 7 infections in 477 non-colonized patients [2%], odds ratio = 18, confidence interval: 6-51, P < 0.0001). The median delay between colonization and infection was 5 days. The positive and negative predictive values for previous colonization with MRSA to predict infection with MRSA in presence of a bacteriological specimen significantly positive with S. aureus were 81 and 84%, respectively.

CONCLUSION

The probabilistic use of a glycopeptide in presence of a bacteriological specimen significantly positive with S. aureus should be limited to patients already colonized with MRSA, in order to decrease the abusive administration of these antibiotics.

Relationship of nasal carriage of Staphylococcus aureus to pathogenesis of perennial allergic rhinitis

BACKGROUND

Several studies have previously shown some factors that modify the pathogenesis of perennial allergic rhinitis (PAR). However, the association between bacterial colonization and PAR has not been well understood.

OBJECTIVE

We sought to study the association between superantigen-producing Staphylococcus aureus and PAR.

METHODS

S aureus colonization in the nasal cavity and its superantigen production were studied in 65 patients with PAR and 45 nonallergic control subjects. The nasal symptom scores of the patients were evaluated. Furthermore, we examined the response to staphylococcal enterotoxin B or toxic shock syndrome toxin 1 of peripheral blood lymphocytes from both patients and control subjects by measuring proliferative responses and production of cytokines (IFN-gamma, IL-4, and IL-5).

RESULTS

The rate of nasal carriage of S aureus in the patients (44%) was significantly higher than that of the control subjects (20%, P <.01). Moreover, the rate of nasal carriage of superantigen-producing S aureus in the patients (22%) was significantly higher than that of the control subjects (6.7%, P <.05). The nasal symptom scores of the S aureus -positive patients were significantly higher than those of the S aureus -negative patients (P <.05), although there was no significant association between symptom scores and superantigen production. Peripheral blood lymphocytes from the patients showed significantly higher proliferative responses and were more likely to produce T(H2 )type cytokines in response to superantigens (P <.01), but the responses were not different among the patients with S aureus carriage and superantigen production.

CONCLUSION

This study suggests that PAR leads to a higher carriage rate of S aureus, and nasal carriage of S aureus may aggravate PAR.

Frequency of nasal and wound isolates of Staphylococcus aureus associated with TSST-1 production in Jordanian population

A total of 110 Staphylococcus aureus isolates were obtained from nasal carriers and wound infections of Jordanian population. The isolates were identified by cultural and biochemical methods. The nasal carrier rate of S. aureus among individuals was 22.7%. In comparison with the nasal S. aureus isolates the wound isolates did not produce significantly more virulence factors except DNase. Toxic shock syndrome toxin-1 production was higher among the S. aureus nasal isolates (40%) as compared with the wound isolates (26%) detected by an ELISA method which proved to be uniformly more sensitive than the immunodiffusion optimal sensitivity plate (OSP) method.