Late prosthetic knee joint infection with Staphylococcus xylosus

Prosthethic Joint Infection (PJI) is a severe complication following joint replacement. Late PJI can occur years after implantation by hematogenous seeding of a microbial agent. Staphylococcus xylosus is a coagulase-negative commensal of the human skin and rarely associated with opportunistic human infections. We report the rare case of a 70-year old Patient suffering from knee pain 18 years after primary Total Knee Arthroplasty. Microbiological sampling detected S. xylosus as causative agent. The patient was successfully treated with a two-stage implant exchange and antibiotic therapy using co-amoxicillin and rifampicin/cotrimoxazol. This case illustrates the ability of S. xylosus to cause late PJI and the importance of not letting coagulase-negative Staphylococci be routinely categorized as contaminants of microbiological samples.

Bacteremia in critically ill immunocompromised patients with acute hypoxic respiratory failure: A post-hoc analysis of a prospective multicenter multinational cohort

PURPOSE

The characteristics and impact of bacteremia have not been widely investigated in immunocompromised patients with acute respiratory failure (ARF).

METHODS

We performed a secondary analysis of a prospective cohort of immunocompromised patients with ARF (EFRAIM study). After exclusion of blood cultures positive for coagulase negative Staphylococci, we compared patients with (n = 236) and without (n = 1127) bacteremia.

RESULTS

The incidence of bacteremia was 17%. Bacterial pneumonia and extra-pulmonary ARDS were the main causes of ARF in bacteremic patients. Bacteremia involved gram negative rods (48%), gram positive cocci (40%) or were polymicrobial (10%). Bacteremic patients had more hematological malignancy, higher SOFA scores and increased organ support within 7 days. Bacteremia was associated with higher crude ICU mortality (40% versus 32%, p = 0.02), but neither hospital (49% versus 44%, p = 0.17) nor 90-day mortality (60% versus 56%, p = 0.25) were different from non-bacteremic patients. After propensity score matching based on baseline characteristics, the difference in ICU mortality lost statistical significance (p = 0.06), including in a sensitivity analysis restricted to patients with pneumonia.

CONCLUSIONS

We analyzed a large population of immunocompromised patients with ARF and an incidence of bacteremia of 17%. We could not demonstrate an impact of bacteremia on mortality after adjusting for baseline characteristics.

Staphylococcus pettenkoferi-positive Blood cultures in Hospitalized Patients in a Multi-site Tertiary Center

Staphylococcus pettenkoferi (S.pettenkoferi), originally described in Germany in 2002 by Trülzsch et al, is a coagulase negative staphylococcus whose clinical relevance is yet to be determined. With about 10 case reports in the literature from several parts of the world, there is no data on S. pettenkoferi infection from the United States. This is a retrospective cohort study of 80 patients ≥ 18 years of age who had at least 1 S. pettenkoferi-positive blood culture, identified by matrix-assisted laser desorption/ionization time-of-flight at a tertiary academic center in Detroit, Michigan. We describe the features of S. pettenkoferi-positive blood cultures in order to identify cases of true bacteremia. The mean age of the cohort was 66 ± 16 years and 1 out of 3 had immunosuppressing conditions. No case of true S.pettenkoferi bacteremia was identified. More studies are needed to determine its role as a pathogen in the United States.

Incidence of coagulase-negative staphylococcal bacteremia among ICU patients: decontamination studies as a natural experiment

The epidemiology of coagulase-negative staphylococcal (CNS) bacteremia among adult ICU patients remains unclear. Decontamination studies among ICU patients provide a unique opportunity to study the impacts of different diagnostic criteria, exposure to various decontamination interventions, and various other factors, on its incidence over three decades. Decontamination studies among ICU patients reporting CNS bacteremia incidence data were obtained mostly from recent systematic reviews. The CNS bacteremia incidence within component (control and intervention) groups of decontamination studies was benchmarked versus studies without intervention (observational groups). The impacts of antibiotic versus chlorhexidine decontamination interventions, control group concurrency, publication year, and diagnostic criteria were examined in meta-regression models. Among non-intervention (observational) studies which did versus did not specify stringent (≥ 2 positive blood cultures) diagnostic criteria, the mean CNS bacteremia incidence per 100 patients (and 95% CI; n) is 1.3 (0.9–2.0; n = 23) versus 3.6 (1.8–6.9; n = 8), respectively, giving an overall benchmark of 1.8 (1.2–2.4; n = 31). Versus the benchmark incidence, the mean incidence is high among concurrent control (5.7; 3.6–9.1%) and intervention (5.2; 3.6–6.9%), but not non-concurrent control (1.0; 0.4–3.9%) groups of 21 antibiotic studies, nor among eleven component groups of chlorhexidine studies. This high incidence remained apparent (p < 0.01) in meta-regression models adjusting for group wide factors such as diagnostic criteria and publication year. The incidence of CNS bacteremia within both intervention and concurrent (but not non-concurrent) control groups of antibiotic-based decontamination studies are unusually high even accounting for variable diagnostic criteria and other factors.

Distribution of main Gram-positive pathogens causing bloodstream infections in United States and European hospitals during the SENTRY Antimicrobial Surveillance Program (2010-2016): concomitant analysis of oritavancin in vitro activity

This study updates the distribution and trends of Gram-positive organisms causing bloodstream infections (BSIs) in the United States (US) and Europe during 2010-2016. In vitro activities of oritavancin and comparators were also evaluated. Staphylococcus aureus, Enterococcus spp., and coagulase-negative staphylococci (CoNS) were the most common organisms in both regions. The proportion of methicillin-resistant S. aureus (MRSA) among all isolates declined (from 11.5% to 9.9%) in the US, a trend also noted for methicillin resistance rates within S. aureus (from 45.7% to 41.9%). MRSA rates (4.1% to 4.2%) in Europe remained stable during 2013-2016. Enterococcus faecalis (7.0-5.2%) and E. faecium (5.1-3.0%) rates declined in the US while remaining stable in Europe (4.5-5.7% and 3.3-4.7%, respectively). Rates for CoNS increased in the US; no temporal trends were noted in Europe. Oritavancin (MIC_50/90, 0.03/0.06 µg/mL) inhibited 99.7-99.8% of S. aureus from both regions at ≤0.12 µg/mL and inhibited 96.8-97.9% of E. faecalis and 99.1-99.9% of E. faecium at this concentration. Oritavancin inhibited 99.7% of streptococci at the susceptible breakpoint. This study updates the distribution of pathogens causing BSI in the US and Europe. The in vitro activity for oritavancin against BSI pathogens supports its further development for bacteraemia.

[Infective endocarditis in Morocco through the experience of a hospital department]

Infective endocarditis is a grave disease because of a high level of morbidity and mortality. We conducted a retrospective analysis of 100 patients hospitalized for infective endocarditis from January 2009 until December 2015. The mean age was 41 years with a male predominance. Infective endocarditis occurs on a native valve (77 patients), prosthetic valves (12 patients), Pacemaker (7 patients) and congenital heart disease (4 patients). The diagnostic delay was 77 days on average. The fever was present in 85 patients. Blood cultures were negative in 54 patients. Echocardiography allowed visualizing the vegetations in 95 patients. In patients with prosthetics valves, a paraprosthetic regurgitation was diagnosed in 54 % of these patients and vegetation in 18 %. The main complications are heart failure (42), neurological (19), spleen (10) and renal (23) complications. The evolution under medical treatment was marked by the clinical-laboratory improvement in 57 patients, the lack of improvement with persistent fever in 21 patients. The mortality rate of our series is 23 %. Only seven patients underwent urgent surgery for hemodynamic and infectious indications. At the end of this work, it is emphasized that the epidemiological profile of infective endocarditis does not follow the changes of Wold. Its management is difficult in our context (significant diagnostic delay, often negative blood cultures, high level of morbidity, lack of recourse to early surgery). The improvement of this disease consistes of the prevention of acute articular rhumatism and the establishment of an heart team endocarditis to adapt international recommendations to our context.

Clinical Behavior of Implant Infections Due to Staphylococcus Epidermidis

Surgical implants and other foreign material are increasingly used in modern medicine to restore or to improve the function of the human body. Infection of an implant is associated with considerable morbidity due to frequent hospitalizations, surgery and antimicrobial treatment. The underlying mechanism is the formation of a bacterial biofilm on the surface of the implanted body. The recognition and diagnosis of implant infections is essential for further therapy and, above all, the decision to remove and exchange the implant.

Methods

We compared the data of 60 patients with implant infections with those of 60 patients with transient bacteremia caused by Staphylococcus epidermidis. The pathogens isolated from blood were characterized with regard to antimicrobial susceptibility and formation of biofilms using a static microtiter plate model. Wild type skin isolates from non-hospitalized healthy volunteers served as control with regard to antimicrobial susceptibility and biofilm formation.

Results

Clinical signs and symptoms, underlying diseases and outcome were not different in either group. However, patients with implant infection had fever over a longer time (mean 12 days versus 3 days, respectively, p & 0.05) and more often positive blood cultures than patients with transient bacteremia (3.1 versus 1.2, p & 0.05). Thrombocytopenia was observed in patients with implant infections but not in patients with transient bacteremia (p & 0.05). Biofilms were formed in 86.4 % of the isolates in implant infection, in 88.8 % in transient bacteremia and in 76.9 % of the isolates from healthy volunteers (not significant). Multi-resistance to penicillin, oxacillin, erythromycin, clindamycin, ciprofloxacin and trimethoprim was more common in the hospital strains than in the wild type strains (75.6 % versus 48.7 %, p & 0.05).

Conclusions

The clinical features of implant infections are indistinguishable from those of transient bacteremia. Persisting fever and multiple blood culture yielding the growth of skin flora bacteria are strong indicators for infection of implanted material. Biofilm formation and antimicrobial multiresistance, as common in implant infection as in transient bacteremia, seem to be accessory factors in infections due to Staphylococcus epidermidis.

Simultaneous Two-site Blood Culture for Diagnosis of Neonatal Sepsis

OBJECTIVE

To evaluate efficacy of two blood cultures taken simultaneously from two different sites as compared to standard practice of single blood culture in diagnosis of neonatal sepsis.

STUDY DESIGN

Prospective cohort study.

Setting

A tertiary-care center at a public hospital.

PARTICIPANTS

475 neonates admitted to intensive care unit with suspected sepsis, from August 2014-July 2015.

INTERVENTION

Two blood cultures drawn from two different peripheral veins in patients with suspected neonatal sepsis.

MAIN OUTCOME MEASURES

Increase in culture-positivity rate with use of two blood cultures.

RESULTS

475 babies with suspected sepsis were enrolled. 185 patients had only first culture positive (38.9%). When we added second culture positivity, yield increased to 221 (46.5%). Adding on second culture increased the culture yield by 36 (7.6%; 95% CI 2.41 to 12.79; P=0.018). The most common organisms isolated were E. coli, S. aureus and Candida spp. Major morbidities and mortality were more common in blood culture positive patients Contamination was ruled out in 25 babies who grew Coagulase negative Staphylococcus (CONS) (n=10) and Candida spp. (n=15) in either of the two cultures.

CONCLUSION

Two blood cultures taken simultaneously from two different sites improve rate of pathogen detection as compared to routine practice of single blood culture.

Determining the Clinical Significance of Coagulase-Negative Staphylococci Isolated From Blood Cultures

Background and Objective:

Coagulase-negative staphylococci are both an important cause of nosocomial bloodstream infections and the most common contaminants of blood cultures. Judging the clinical significance of coagulase-negative staphylococci is vital but often difficult and can have a profound impact on an institution's bloodstream infection rates. Our objective was to develop an algorithm to assist in determining the clinical significance of coagulase-negative staphylococci.

Design:

A single experienced reviewer examined the medical records of 960 consecutive patients with positive blood cultures in a tertiary-care referral teaching hospital. Four hundred five of the cultures contained coagulase-negative staphylococci. A determination of clinical significance was made and the performances of various published algorithms that contained readily available clinical and laboratory data were compared.

Results:

Eighty-nine (22%) of the episodes were considered significant, whereas 316 were contaminants. Patients with bacteremia were significantly more likely to be neutropenic and exhibit signs of sepsis syndrome. The algorithm with the best combined sensitivity (62%) and specificity (91%) for determining the clinical significance of coagulase-negative staphylococci was defined as at least two blood cultures positive for coagulase-negative staphylococci within 5 days, or one positive blood culture plus clinical evidence of infection, which includes abnormal white blood cell count and temperature or blood pressure.

Conclusion:

Use of this algorithm could potentially reduce misclassification of nosocomial bloodstream infections and inappropriate use of vancomycin for positive blood cultures likely to represent contamination (Infect Control Hosp Epidemiol2005;26:559-566).

Nosocomial Bacteremia Clinical Significance of a Single Blood Culture Positive for Coagulase-Negative Staphylococci

Objectives:

To describe the epidemiology of nosocomial coagulase-negative staphylococci (CoNS) bacteremia and to evaluate the clinical significance of a single blood culture positive for CoNS.

Design:

A 3-year retrospective cohort study based on data prospectively collected through hospital-wide surveillance. Bacteremia was defined according to CDC criteria, except that a single blood culture growing CoNS was not systematically considered as a contaminant. All clinically significant blood cultures positive for CoNS nosocomial bacteremia were considered for analysis.

Setting:

A large university teaching hospital in Geneva, Switzerland.

Results:

A total of 2,660 positive blood cultures were identified. Of these, 1,108 (41.7%) were nosocomial; CoNS were recovered from 411 nosocomial episodes (37.1%). Two hundred thirty-four episodes of CoNS bacteremia in the presence of signs of sepsis were considered clinically relevant and analyzed. Crude mortality and associated mortality were 24.4% and 12.8%, respectively. Associated mortality was similar among patients with one positive blood culture and those with two or more (16.2% vs 10.8%, respectively;P= .3). Mortality rates after bacteremia for patients with a single positive blood culture and for those with two or more were 15.3% and 7.0%, respectively, at day 14 (RR, 2.2; CI%, 0.87-5.46) and 20.8% and 11.3%, respectively, at day 28 (RR, 1.9; CI95, 0.9-3.8). On multivariate analysis, only age and a rapidly fatal disease were independently associated with death.

Conclusion:

CoNS bacteremia harbor a significant mortality and a single positive blood culture in the presence of signs of sepsis should be considered as clinically relevant.

Understanding Bacterial Isolates in Blood Culture and Approaches Used to Define Bacteria as Contaminants: A Literature Review

BACKGROUND

Interpretation of blood culture isolates is challenging due to a lack of standard methodologies for identifying contaminants. This problem becomes more complex when the specimens are from sick young infants, as a wide range of bacteria can cause illness among this group.

METHODS

We used 43 key words to find articles published between 1970 and 2011 on blood culture isolates and possible contaminants in the PubMed database. Experts were also consulted to obtain other relevant articles. Selection of articles followed systematic methods considering opinions from more than 1 reviewer.

RESULTS

After reviewing the titles of 3869 articles extracted from the database, we found 307 relevant to our objective. Based on the abstracts, 42 articles were selected for the literature review. In addition, we included 7 more articles based on cross-references and expert advice. The most common methods for differentiating blood culture isolates were multiple blood cultures from the same subject, antibiograms and molecular testing. Streptococcus pneumoniae, Hemophilus influenzae, Neisseria meningitidis and group A and B streptococcus were always considered as pathogens, whereas Bacillus sp., Diphtheroids, Propionibacterium and Micrococcus were commonly regarded as contaminants. Coagulase-negative staphylococci were the most frequent isolates and usually reported as contaminants unless the patient had a specific condition, such as long-term hospitalization or use of invasive devices (catheters).

CONCLUSIONS

Inaccurate interpretation of blood culture may falsely guide treatment and also has long-term policy implications. The combination of clinical and microbiological knowledge, patient's clinical history and laboratory findings are essential for appropriate interpretation of blood culture.

Airborne Dispersal as a Novel Transmission Route of Coagulase-Negatwe Staphylococci Interaction Between Coagulase-Negative Staphylococci and Rhinovirus Infection

Objective:

To investigate whether rhinovirus infection leads to increased airborne dispersal of coagulase-negative staphylococci (CoNS).

Design:

Prospective nonrandomized intervention trial.

Setting:

Wake Forest University School of Medicine, Winston-Salem, North Carolina.

Participants:

Twelve nasalStaphylococcus aureus-CoNS carriers among 685 students screened forS. aureusnasal carriage.

Interventions:

Participants were studied for airborne dispersal of CoNS in a chamber under three conditions (street clothes, sterile gown with a mask, and sterile gown without a mask). After 2 days of pre-exposure measurements, volunteers were inoculated with a rhinovirus and observed for 14 days. Daily quantitative nasal and skin cultures for CoNS and nasal cultures for rhinovirus were performed. In addition, assessment of cold symptoms was performed daily, mucous samples were collected, and serum titers before and after rhinovirus inoculation were obtained. Sneezing, coughing, and talking events were recorded during chamber sessions.

Results:

All participants had at least one nasal wash positive for rhinovirus and 10 developed a symptomatic cold. Postexposure, there was a twofold increase in airborne CoNS (P= .0004), peaking at day 12. CoNS dispersal was reduced by wearing a gown (57% reduction,P< .0001), but not a mask (P= .7). Nasal and skin CoNS colonization increased after rhinovirus infection (P<.05).

Conclusions:

We believe this is the first demonstration that a viral pathogen in the upper airways can increase airborne dispersal of CoNS in nasalS. aureuscarriers. Gowns, gloves, and caps had a protective effect, whereas wearing a mask did not further reduce airborne spread.

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

Objectives.

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

Design.

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

Results.

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

Conclusions.

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

Methicillin-Resistant Staphylococcal Bacteremia in Patients with Hematologic Malignancies: Clinical and Microbiological Retrospective Comparative Analysis ofS. haemolyticus, S. epidermidisandS. aureus

Although Staphylococcus haemolyticus (SH) represents an emerging etiology of methicillin-resistant (MR) coagulase-negative staphylococcal nosocomial bacteremia, little is known of clinical significance of this infection. Thus, we performed case-control retrospective comparative analysis of MRSH bacteremias (MRSHB), methicillin-resistant S. epidermidis bacteremias (MRSEB), and methicillin-resistant S. aureus bacteremias (MRSAB) in patients with hematologic malignancies. Most patients in the three groups were neutropenic and had a central venous catheter (CVC) in place at the onset of bacteremia. However, MRSHB patients had a CVC in place prior to bacteremia for a time significantly more prolonged than MRSEB and MRSAB ones (p<0.05). Severe sepsis or septic shock were more common in patients with MRSAB as compared with MRSHB (p=0.02). Nosocomial attributable mortality rate was very low in the 3 study groups (0 to 5.4%) and only two patients developed metastatic infections. Overall, reduced susceptibility to teicoplanin was observed in 19 (47.5%) MRSH and in 4 (10%) MRSE isolates. Resistance to teicoplanin was observed in 6 isolates, all MRSH. Reduced susceptibility or resistance to vancomycin was observed in 2 isolates, both MRSH. All MRSA isolates were susceptible to the glycopeptides. Comparison between cases of bacteremia in patients with MRSH isolates with reduced susceptibility to teicoplanin and those with susceptible MRSH did not reveal significant differences in the clinical-microbiological response to teicoplanin therapy and outcome. Our results seem to suggest that MRSHB in hematologic patients is associated with low morbidity and mortality rates. MRSH frequently shows a reduced susceptibility to teicoplanin; however these in vitro data do not seem associated with an unfavorable clinical response to teicoplanin therapy for MRSHB in patients with hematologic malignancies.

Preliminary evaluation of a new clinical algorithm to interpret blood cultures growing coagulase-negative staphylococci

Evaluating the clinical significance of blood cultures positive for coagulase-negative staphylococci (CoNS) is of critical importance since these microorganisms represent both the first contaminants of blood cultures and one of the leading causes of bloodstream infection (BSI). This prospective 2-centre study aimed to compare a previously reported algorithm to a clinical algorithm based on our experience. We identified 84 patients with CoNS-positive blood cultures. Twenty-seven (32%) were considered to have BSI according to our study algorithm. Thirty-seven (44%) patients were considered to have CoNS BSI according to the previously reported algorithm. The 2 algorithms isolated patients with similar rates of recurrences and hospital mortality. Our algorithm seemed to result in less diagnoses of CoNS BSI without harmful consequences compared to the previously reported algorithm. The impact on patient outcome and the inappropriate use of antibiotics deserves further investigation.

How can the microbiologist help in diagnosing neonatal sepsis?

Neonatal sepsis can be classified into two subtypes depending upon whether the onset of symptoms is before 72 hours of life (early-onset neonatal sepsis—EONS) or later (late-onset neonatal sepsis—LONS). These definitions have contributed greatly to diagnosis and treatment by identifying which microorganisms are likely to be responsible for sepsis during these periods and the expected outcomes of infection. This paper focuses on the tools that microbiologist can offer to diagnose and eventually prevent neonatal sepsis. Here, we discuss the advantages and limitation of the blood culture, the actual gold standard for sepsis diagnosis. In addition, we examine the utility of molecular techniques in the diagnosis and management of neonatal sepsis.

Coagulase-negative staphylococcal infections in the neonatal intensive care unit

BACKGROUND

Coagulase-negative staphylococci (CoNS) are the most commonly isolated pathogens in the neonatal intensive care unit (NICU). CoNS infections are associated with increased morbidity, including neurodevelopmental impairment.

OBJECTIVE

To describe the epidemiology of CoNS infections in the NICU. To determine mortality among infants with definite, probable, or possible CoNS infections.

METHODS

We performed a retrospective cohort study of all blood, urine, and cerebrospinal fluid cultures from samples obtained from infants aged <121 postnatal days.

SETTING

A total of 248 NICUs managed by the Pediatrix Medical Group from 1997 to 2009.

RESULTS

We identified 16,629 infants with 17,624 episodes of CoNS infection: 1,734 (10%) definite, 3,093 (17%) probable, and 12,797 (73%) possible infections. Infants with a lower gestational age and birth weight had a higher incidence of CoNS infection. When controlling for gestational age, birth weight, and 5-minute Apgar score, we found that infants with definite, probable, or possible CoNS infection had lower mortality (odds ratio [OR], 0.74 [95% confidence interval {CI}: 0.61, 0.89], 0.68 [95% CI, 0.59, 0.79], and 0.69 [95% CI, 0.63, 0.76], respectively) compared with infants who had negative culture results (P = .001). No significant difference in overall mortality was found in infants who had definite CoNS infection compared with those who had probable or possible CoNS infection (OR, 0.93 [95% CI, 0.75, 1.16] and 0.85 [95% CI, 0.70, 1.03], respectively).

CONCLUSIONS

CoNS infection was strongly related to lower gestational age and birth weight. Infants with clinical sepsis and culture-positive CoNS infection had lower mortality rates than infants with clinical sepsis and negative blood culture results. No difference in mortality between infants with a diagnosis of definite, probable, or possible CoNS infection was observed.

Trends among pathogens reported as causing bacteraemia in England, 2004-2008

The Health Protection Agency in England operates a voluntary surveillance system that collects data on bacteraemias reported by over 90% of laboratories in England. Trends in causative microorganisms reported between 2004 and 2008 were analyzed using a generalized linear model with a log link function for Poisson distribution. In 2008, 101,276 episodes of bacteraemia were reported; a rate of 189 per 100,000 population. More than one-half occurred in those aged over 65 years and males. The most common organisms reported were Escherichia coli (23%), coagulase-negative staphylococci (CNS) (16.9%) and Staphylococcus aureus (11.4%). Between 2004 and 2008, E. coli bacteraemia increased by 33% (p < 0.001); the species now accounts for more than 30% of bacteraemia in those aged over 75 years. There also were significant increases in bacteraemia caused by other Gram-negative pathogens and marked seasonal variation. Bacteraemia caused by S. aureus increased until 2005, with a decline after 2006 (p < 0.001) entirely due to methicillin-resistant strains. CNS bacteraemia have declined significantly since 2007. The renewed dominance of Gram-negative pathogens as major causes of bacteraemia in England is of particular concern because they are associated with a high morbidity and increasing resistance to antibiotics. Further investigation of the underlying causes and prevention strategies is a public health priority. Recent declines in methicillin-resistant S. aureus bacteraemia have not been reflected in other pathogens, including methicillin-susceptible S. aureus.

Foreign body infections due to Staphylococcus epidermidis

Staphylococcal infections are one of the main causes of complications in patients with implanted foreign prosthetic material. Implants are associated with a significant reduction of the threshold at which contaminating Gram-positive bacteria, particularly Staphylococcus epidermidis, become infectious and develop a biofilm with phenotypic resistance to almost all antibiotics. A 1000-fold increase in minimal bactericidal levels against most antibiotics except rifampin has been repeatedly observed. Since only removal of the foreign material reverses these phenomena, the clinical challenge consists in finding approaches to cure the infection without removal of the implanted device. Rifampin combinations with other antibiotics, administration of exceedingly high antibiotic concentrations in situ, and early therapy before biofilm development are efficacious. Although these strategies have dramatically improved the outcome of foreign body infections, an improved understanding of biofilm-grown S. epidermidis is necessary to develop new antibacterial agents. Here, we review the pathogenesis, prevention, and treatment of implant infections due to S. epidermidis and highlight some new compounds with already promising in vitro results.

Low frequency of bacteremia after an endoscopic resection for large colorectal tumors in spite of extensive submucosal exposure

BACKGROUND

During an EMR or endoscopic submucosal dissection (ESD) for colorectal tumors, an injection needle catheter is passed through the contaminated endoscopic channel and may directly inoculate bacteria into the blood stream during submucosal injection. In addition, extensively exposed submucosa, especially with an ESD, directly contacts colonic luminal bacteria after the procedure, which may increase the risk of bacteremia. However, the incidence of bacteremia after an EMR or ESD for colorectal tumors has not been reported.

OBJECTIVE

To evaluate the frequency of bacteremia associated with an EMR or ESD for colon lesions.

DESIGN

A prospective study.

PATIENTS

A total of 40 patients who underwent a conventional EMR (n = 30), an EMR after circumferential pre-cutting (n = 3), or ESD (n = 7) for colorectal tumors.

INTERVENTIONS AND MAIN OUTCOME MEASUREMENTS

Blood cultures were obtained immediately before, 5 minutes after, and 30 minutes after the procedure. Patients were closely monitored for 24 hours after the procedure to detect the development of infectious complications.

RESULTS

Blood cultures at baseline and 5 minutes after the procedure were all negative. However, a blood culture at 30 minutes after the procedure showed a positive result in 1 of 40 patients (2.5%). This patient underwent a conventional EMR, and the isolated microorganism was coagulase-negative Staphylococcus, which might be regarded as a contaminant. None of the 40 patients showed any signs or symptoms associated with infection.

LIMITATION

The small sample size.

CONCLUSIONS

An EMR, or even an ESD, for colon lesions may be considered a low-risk procedure for infectious complications that does not warrant prophylactic administration of antibiotics.

Fusidic acid and heparin lock solution for the prevention of catheter-related bloodstream infections in critically ill neonates: a retrospective study and a prospective, randomized trial

OBJECTIVE

Catheter-related bloodstream infections (CRBSIs) are one of the main morbidities in critically ill neonates. The objective of the present study was to assess the efficacy of a fusidic acid-heparin lock in the prevention of CRBSIs.

DESIGN

A preliminary retrospective study showed that staphylococcal infections were largely prevalent. We planned a prospective, randomized trial to ascertain whether fusidic acid and heparin lock of central venous catheters would reduce the incidence of CRBSIs.

SETTING

Level III neonatal intensive care unit.

PATIENTS

One hundred three neonates were enrolled and randomly assigned to a treatment group (n = 50) or control group (n = 53).

INTERVENTIONS

Fusidic acid (4 mg/mL) and heparin (10 IU/mL) lock in the treatment group.

MEASUREMENTS AND MAIN RESULTS

The treatment group showed significantly lower incidence of CRBSIs (6.6 vs. 24.9 per 1000 catheter days; p < .01; relative risk 0.28; 95% confidence interval 0.13-0.60). No staphylococcal infections occurred in the treatment group, while in the control group Staphylococcus remained the main agent of CRBSI. Cost analysis comparing the present study and for the treatment of CRBSIs proved that antibiotic lock is financially favorable.

CONCLUSIONS

Fusidic acid-heparin lock solution reduced the incidence of CRBSIs in our neonatal intensive care unit. However, we recommend basing antibiotic lock on local CRBSI epidemiology. With regard to fusidic acid, further and broader studies could be useful to confirm our results.

Serum Procalcitonin for Discrimination of Blood Contamination from Bloodstream Infection due to Coagulase-Negative Staphylococci

The diagnostic value of serum procalcitonin (PCT) to distinguish blood contamination from bloodstream infection (BSI) due to coagulase-negative staphylococci was evaluated. Patients with BSI had higher PCT concentration than those with blood contamination at day -1, day 0 and day +1 with regard to blood culture collection (p < 0.05), whereas serum C-reactive protein values were significantly higher only on day +1. At a cutoff of 0.1 ng/dl, PCT had a sensitivity of 86% and 100%, and a specificity of 60% and 80% for the diagnosis of BSI on day -1 and 0, respectively. In addition to clinical and microbiological parameters, PCT may help discriminating blood contamination from BSI due coagulase-negative staphylococci.

Assessment of ica operon carriage and biofilm production in Staphylococcus epidermidis isolates causing bacteraemia in bone marrow transplant recipients

The clinical significance of coagulase-negative staphylococci isolated from blood culture is typically assessed on the basis of a combination of clinical and microbiological criteria. However, these criteria are difficult to apply to haematology patients who are highly immunosuppressed and from whom blood cultures are obtained most frequently through a central venous catheter. This study analysed 112 episodes of Staphylococcus epidermidis bacteraemia that occurred in 79 bone marrow transplant recipients. In 73 (65%) episodes, only one blood culture set was positive for S. epidermidis, while 39 (35%) episodes grew S. epidermidis from multiple blood cultures. Nine patients had two or more episodes of bacteraemia with the same strain, as determined by pulsed-field gel electrophoresis (PFGE). The PFGE method also showed that 34 (31%) isolates belonged to seven clusters, indicating the persistence of certain clones in the environment. Of the 109 isolates analysed, 59 (54%) produced biofilm and 91 (83.5%) carried the ica operon. Isolates that produced biofilm were observed to colonise central venous catheters faster than non-biofilm-producing isolates (18 vs. 37 days; p 0.03). No clinical features were associated with carriage of the ica operon, but the ica operon was carried more frequently by the isolates that formed clusters.

Routine antimicrobial susceptibility testing of coagulase-negative staphylococci isolated from blood cultures: is it necessary?

The clinical significance of discontinuing routine antibiotic susceptibility testing (AST) of coagulase-negative Staphylococcus (CNS) isolates from blood cultures was investigated. Prospectively, AST was requested primarily for patients with serious underlying illnesses. Antibiotic use did not change significantly when AST was not performed routinely. Laboratory cost savings were 75% if AST was not performed, but more specimens were submitted from these patients. Oxacillin resistance in coagulase-negative staphylococci from blood cultures has remained > 70% since implementation of this protocol, while annual vancomycin utilisation has shown only small, incremental increases. Therefore, it is suggested that routine AST of CNS isolates from blood culture is not essential.

Importance of adequate initial antimicrobial therapy

BACKGROUND

It has become an article of faith that appropriate antibiotic therapy is needed for best outcomes during a serious infection. Despite this long-held view, there is some debate about the role of appropriate outcome in serious infections, in particular with nosocomial pneumonia. Therefore, more recent data on adequacy of antibiotic therapy and outcomes were reviewed.

METHODS

The medical literature from 1997 to 2004 was surveyed for articles that directly dealt with appropriate therapy. Search terms included 'appropriate and inappropriate antibiotic therapy', 'adequate antibiotic therapy', 'resistance and antibiotic failures' and 'delayed therapy'. The data were abstracted to obtain their essential findings.

RESULTS

In bacteremia, data are most persuasive that appropriate and timely therapy significantly influences outcomes. Areas where this may not be the case are studies where coagulase-negative staphylococci are isolated in large numbers or in studies where the incidence of appropriate therapy is high. One area where data are not conclusive concerns the treatment of enteric bacteria carrying extended spectrum betalactamases, where the only cephalosporin of concern is ceftazidime. There is not enough data to compare carbapenems with specific cephalosporins to conclude that these are the most appropriate agents. The studies in regard to nosocomial pneumonias are not as conclusive as those with bacteremias. There appears to be a subset of patients that do not respond to therapy or do not survive, which confounds studies of this population; however, most studies favor a role of appropriate therapy.

CONCLUSIONS

Appropriate antibiotic therapy has several dimensions. It improves outcomes in most serious diseases. Timing of administration and appropriateness, based on susceptibility, are the most important determinants, but dosing intervals and dose probably play similarly important roles in outcomes that have not been examined exhaustively in humans. Other aspects of appropriate therapy that deserve attention include a shift to more 'resistance'-proof antibiotics in empiric therapy, which may be accompanied by better outcomes.

mecA is not involved in the sigmaB-dependent switch of the expression phenotype of methicillin resistance in Staphylococcus epidermidis

A lack of sigma(B) activity reduces methicillin resistance in heterogeneous Staphylococcus epidermidis 1057, whereas inactivation of the anti-sigma factor RsbW switched the phenotype to homogeneous expression of resistance. Oxacillin induction of mecA transcription is reduced in a sigma(B)-negative strain. However, mecA is not involved in the switch of expression phenotype.

Evaluation of the BD PHOENIX automated microbiology system for detection of methicillin resistance in coagulase-negative staphylococci

The new BD PHOENIX automated microbiology system (Becton Dickinson Diagnostic Systems, Sparks, Md.) is designed for automated rapid antimicrobial susceptibility testing and identification of clinically relevant bacteria. In our study, the accuracy and speed of the BD PHOENIX oxacillin MIC determination for detecting methicillin resistance was evaluated for 200 clinical isolates of coagulase-negative staphylococci (CoNS). Compared to mecA PCR, the BD PHOENIX system detected methicillin resistance with a sensitivity of 99.2%. According to the actual NCCLS oxacillin MIC breakpoint of > or =0.5 microg/ml, the specificity was only 64.9%, attributable to false-positive results in 26 mecA-negative strains, including 16 non-Staphylococcus epidermidis strains. Alternative oxacillin breakpoints of > or =1, > or =2, and > or =4 microg/ml resulted in increased specificities of 83.8, 94.6, and 100% and high sensitivities of 99.2, 99.2, and 96.7%, respectively. Similarly, NCCLS broth microdilution oxacillin MICs exhibited a sensitivity of 100% but a low degree of specificity. However, the previous oxacillin MIC breakpoint of > or =4 microg/ml performed with a sensitivity of 98.4% and a specificity of 98.7%. BD PHOENIX oxacillin MIC results were available after 9 h for 40.5% of the examined CoNS strains and were completed after 17 h. Our results revealed the high reliability of the BD PHOENIX system as a phenotypic method for detection of resistance to oxacillin in mecA-positive CoNS. However, for the improvement of specificity, reevaluation of the optimal oxacillin MIC breakpoint for CoNS appears to be necessary.

RsbU-dependent regulation of Staphylococcus epidermidis biofilm formation is mediated via the alternative sigma factor sigmaB by repression of the negative regulator gene icaR

Transposon mutagenesis of rsbU leads to a biofilm-negative phenotype in Staphylococcus epidermidis. However, the pathway of this regulatory mechanism was unknown. To investigate the role of RsbU in the regulation of the alternative sigma factor sigma(B) and biofilm formation, we generated different mutants of the sigma(B) operon in S. epidermidis strains 1457 and 8400. The genes rsbU, rsbV, rsbW, and sigB, as well as the regulatory cascade rsbUVW and the entire sigma(B) operon, were deleted. Transcriptional analysis of sarA and the sigma(B)-dependent gene asp23 revealed the functions of RsbU and RsbV as positive regulators and of RsbW as a negative regulator of sigma(B) activity, indicating regulation of sigma(B) activity similar to that characterized for Bacillus subtilis and Staphylococcus aureus. Phenotypic characterization of the mutants revealed that the dramatic decrease of biofilm formation in rsbU mutants is mediated via sigma(B), indicating a crucial role for sigma(B) in S. epidermidis pathogenesis. However, biofilm formation in mutants defective in sigma(B) or its function could be restored in the presence of subinhibitory ethanol concentrations. Transcriptional analysis revealed that icaR is up-regulated in mutants lacking sigma(B) function but that icaA transcription is down-regulated in these mutants, indicating a sigma(B)-dependent regulatory intermediate negatively regulating IcaR. Supplementation of growth media with ethanol decreased icaR transcription, leading to increased icaA transcription and a biofilm-positive phenotype, indicating that the ethanol-dependent induction of biofilm formation is mediated by IcaR. This icaR-dependent regulation under ethanol induction is mediated in a sigma(B)-independent manner, suggesting at least one additional regulatory intermediate in the biofilm formation of S. epidermidis.

Blood culture results during the period 1995-2002 in a Greek tertiary care hospital

Data on BacT/Alert blood cultures in a Greek hospital from 1995 to 2002 were analysed retrospectively. There was a gradual increase in the number of blood cultures (4981 in 1995 to 9054 in 2002), the true positive rate (14.4% to 16.5%) and the number of bloodstream infections/1000 hospital admissions (22.1 to 30.7). The five most common pathogens were Eschericia coli, Staphylococcus aureus, coagulase-negative staphylococci, enterococci and Klebsiella spp. The relative rates of Gram-negative and Gram-positive isolates inverted during the study period because of an increasing frequency of coagulase-negative staphylococci and enterococci.

Chronic fatigue and immune dysfunction syndrome associated with Staphylococcus spp. bacteraemia responsive to thiacetarsamide sodium in eight birds of prey

Chronic fatigue and immune dysfunction syndrome (CFIDS) is a recognized human illness with zoonotic implications that is rarely described in animals. Eight birds of prey examined between 1992 and 1995 and sharing common symptoms (asthenia, inability to fly, poor appetite and emaciation) underwent laboratory tests revealing immunodeficiency, anaemia, high creatine kinase levels and low serum magnesium levels. Diagnosis of CFIDS was based upon these features. The effectiveness of an arsenic-based medication, thiacetarsamide sodium, administered intravenously for 2-3 days at low dosages (0.1 ml/kg/day) has been demonstrated by checks carried out 10, 20 and 30 days after therapy. The symptoms and the immune and haematological dysfunctions disappeared within 2-4 weeks of treatment. In all patients, micrococcus-like organisms found adhering to the outer surface of many red blood cells, had disappeared at post-treatment controls. Two of five blood cultures were positive for Staphylococcus spp. (S. intermedius and S. xilosus). Consideration is given to the pharmacological activity of an arsenic-based drug in animal illnesses resembling CFIDS.

Genome-based analysis of virulence genes in a non-biofilm-forming Staphylococcus epidermidis strain (ATCC 12228)

Staphylococcus epidermidis strains are diverse in their pathogenicity; some are invasive and cause serious nosocomial infections, whereas others are non-pathogenic commensal organisms. To analyse the implications of different virulence factors in Staphylococcus epidermidis infections, the complete genome of Staphylococcus epidermidis strain ATCC 12228, a non-biofilm forming, non-infection associated strain used for detection of residual antibiotics in food products, was sequenced. This strain showed low virulence by mouse and rat experimental infections. The genome consists of a single 2499 279 bp chromosome and six plasmids. The chromosomal G + C content is 32.1% and 2419 protein coding sequences (CDS) are predicted, among which 230 are putative novel genes. Compared to the virulence factors in Staphylococcus aureus, aside from delta-haemolysin and beta-haemolysin, other toxin genes were not found. In contrast, the majority of adhesin genes are intact in ATCC 12228. Most strikingly, the ica operon coding for the enzymes synthesizing interbacterial cellular polysaccharide is missing in ATCC 12228 and rearrangements of adjacent genes are shown. No mec genes, IS256, IS257, were found in ATCC 12228. It is suggested that the absence of the ica operon is a genetic marker in commensal Staphylococcus epidermidis strains which are less likely to become invasive.

Prospective risk assessment of bacteremia and other infectious complications in patients undergoing EUS-guided FNA

BACKGROUND

There are few data regarding the risk of bacteremia with EUS-guided FNA. This study prospectively evaluated the frequency of bacteremia and other infectious complications after EUS-guided FNA.

METHODS

Patients referred for EUS-guided FNA of the upper GI tract lesions were considered for enrollment. Patients were excluded if there was an indication for preprocedure administration of antibiotics based on ASGE guidelines, had taken antibiotics within the prior 7 days, or if they had a pancreatic cystic lesion. Blood cultures were obtained immediately before the procedure, after routine endoscopy/radial EUS, and 15 minutes after EUS-guided FNA.

RESULTS

Fifty-two patients underwent EUS-guided FNA at 74 sites (mean 1.4 sites/patient) totaling 266 passes of the fine needle (mean 5.1 FNA/patient). Coagulase negative Staphylococcus was grown in cultures from 3 patients (5.8%; 95% CI [1%, 15%]) and was considered a contaminant. Three patients (5.8%; 95% CI [1%, 15%]) developed bacteremia: Streptococcus viridans (n = 2), unidentified gram-negative bacillus (n = 1). No signs or symptoms of infection developed in any patient.

CONCLUSION

EUS-guided FNA of solid lesions in the upper GI tract should be considered a low-risk procedure for infectious complications that does not warrant prophylactic administration of antibiotics for prevention of bacterial endocarditis.

Bacteremic sepsis in intensive care: temporal trends in incidence, organ dysfunction, and prognosis

OBJECTIVE

To determine whether changes have occurred at our center in the incidence, patterns of organ dysfunctions, prognostic factors, and case-fatality rate of bacteremic sepsis.

DESIGN

Retrospective comparative study (1984-1988 vs. 1994-1997).

SETTING

University hospital surgical intensive care unit.

PATIENTS

A total of 372 critically ill patients with sepsis and positive blood cultures.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

In the 1984-1988 study, 176 patients developed bacteremic sepsis (3.2 per 100 admissions), with a fatality rate of 35% at 28 days, whereas in the 1994-1997 study, 196 patients had bacteremic sepsis (4.3 per 100 admissions), with a 28-day fatality rate of 37%. The frequency of primary bacteremia increased from 21% to 47% (p <.001), paralleled by an increase in the proportional frequency of Gram-positive microorganisms. In 1984-1988, 69% (n = 120) of patients had at least one organ dysfunction, compared with 80% (n = 156) in 1994-1997 (p =.02). The prevalence of pulmonary and cardiac dysfunction increased. The case- fatality rate of septic shock remained high (69% vs. 68%). For both cohorts, the two strongest predictors of mortality remained the Acute Physiology and Chronic Health Evaluation II score at the onset of sepsis and the number of evolving organ dysfunctions.

CONCLUSION

The fatality rate of bacteremic sepsis remained constant over the study period, despite an increased incidence of bacteremia and associated organ dysfunction. Continued efforts need to be directed toward the prevention of bacteremic sepsis, given the magnitude and poor prognosis of this syndrome.

Rapid detection of methicillin resistance in coagulase-negative Staphylococci with the VITEK 2 system

The aim of the present study was to evaluate the accuracy of the new VITEK 2 system (bioMérieux, Marcy l' Etoile, France) for the detection of methicillin resistance in coagulase-negative staphylococci (CoNS) by using AST-P515 and AST-P523 test cards. Analyses of the VITEK 2 oxacillin MIC determination evaluated according to the actual breakpoint (>/=0.5 micro g/ml) of the National Committee for Clinical Laboratory Standards resulted in a high sensitivity of 99.2% but a moderate specificity of 80%. The newly included oxacillin resistance (OR) test of the VITEK 2 system displayed a high sensitivity and a high specificity of 97.5 and 98.7%, respectively. Concordance between the results of the mecA PCR and the VITEK 2 oxacillin MIC was observed for almost all Staphylococcus epidermidis strains, but the reduced specificity was attributable to higher oxacillin MICs for mecA-negative non-S. epidermidis strains, especially S. saprophyticus, S. lugdunensis, and S. cohnii. Evaluation of alternative oxacillin MIC breakpoints of 1, 2, or 4 micro g/ml resulted in improved degrees of specificity of 84, 90.7, and 97.3%, respectively. Only minor changes occurred in the corresponding sensitivity values, which were 98.4, 97.5, and 97.5%, respectively. Methicillin resistance in CoNS was detected after 7 and 8 h in 91.1 and 93.5% of the mecA-positive strains, respectively, by the VITEK 2 OR test and in 86.3 and 89.5% of the mecA-positive strains, respectively, by VITEK 2 oxacillin MIC determination. After 7 and 8 h the VITEK 2 OR test classified 59.2 and 78.9% of the mecA-negative strains, respectively, as susceptible to oxacillin, whereas comparable values were obtained 2 h later by VITEK 2 oxacillin MIC determination. The results of our study encourage the use of the VITEK 2 system, which proved to be a highly reliable and rapid phenotypic method for the detection of methicillin resistance in CoNS.

Catheter-related infections: diagnosis and intravascular treatment

The diagnosis of catheter-related infections relies on the presence of clinical manifestations of infection and the evidence of colonization of the catheter tip by bacteria, mycobacteria, or fungi. The reference method to confirm the latter requires the withdrawal of the catheter for culturing, which frequently turns out to be inconvenient, unnecessary and costly. New methods try to avoid these drawbacks and to assess the presence of tip colonization without withdrawal. Comparative quantitative blood cultures with a marked increase (> or = 5) in colony counts between blood obtained from the catheter lumen and from a peripheral vein simultaneously is one of those methods. It has a high sensitivity (>80%) and specificity (94-100%) but it is cumbersome and requires both an easy backflow of blood in the catheter and the existence of bacteremia. Cytocentrifugation and acridine orange staining of blood withdrawn from an infected catheter lumen has a sensitivity and a specificity of over 90% for the diagnosis of tip colonization. 'Superficial cultures' comprise the semiquantitative culture of the hub, of the skin surrounding the catheter entrance and of the first subcutaneous portion (1 cm) of the catheter after swabbing. The sensitivity of this method is >90%, specificity is >80%, and positive and negative predictive values for catheters (considering together those with and without clinical data of infection) are 66 and 97%, respectively. Endoluminal brushing has proved to be an impractical and unreliable procedure, at least in our experience. New methods based on the speed of bacterial growth to detectable levels of micro-organisms in conventional blood cultures are a new and interesting way of assessing catheter-related infections. Moreover, as the use of antimicrobial-coated catheters becomes more prevalent, the existing definitions of catheter colonization and catheter-related infection may need to be modified, because such coatings may lead to false-negative culture results. Many catheter infections, diagnosed without catheter withdrawal, can be handled nowadays with the so-called 'antibiotic lock-in technique', which consists in 'locking' the infected catheter lumen with a solution containing antibiotics. A high proportion of infected catheters, mainly those with coagulase-negative staphylococci, can be maintained in place and sterilized with this technique, including catheters in patients with therapeutic failure after receiving conventional intravenous antibiotic therapy. New diagnostic and therapeutic techniques may avoid the unnecessary withdrawal of thousands of efficient, difficult to replace and expensive intravascular lines.

Clinical and epidemiologic significance of coagulase-negative staphylococci bacteremia in a tertiary care university Israeli hospital

OBJECTIVES

To characterize the clinical significance of coagulase-negative staphylococci (CNS) bacteremia.

DESIGN

Prospective cohort study.

SETTING

A 900-bed hospital in Haifa, Israel, from November 1996 to March 1997.

RESULTS

Of 137 episodes of positive blood cultures for CNS, 41 (30%) were considered as true infection. Twenty-seven of 119 episodes associated with only 1 blood culture positive for CNS (23%) met the definition of infection as compared with 14 of 18 episodes (78%) associated with 2 or more blood cultures positive for CNS (P <.001). Methicillin resistance was significantly more frequent among Staphylococcus epidermidis isolates of episodes of true bacteremia than of episodes of contamination (15 of 22 [68%] vs. 11 of 33 [33%], respectively; P =.02). S hominis was isolated only in episodes considered as contamination (P =.01). It was estimated that CNS represents 24% of all nosocomial bloodstream pathogens. When CNS were isolated in the first 48 hours of hospitalization, an intravascular device was more frequently associated with episodes of true bacteremia than in those considered as contamination (7 of 7 [100%] vs. 10 of 57 [18%], respectively; P <.001). The mortality rate among patients with true CNS bacteremia was 16%.

CONCLUSION

Some laboratory parameters may help identify episodes of true CNS bacteremia, which appears to be more common than previously considered.

Infection control in the ICU

Nosocomial infections (NIs) now concern 5 to 15% of hospitalized patients and can lead to complications in 25 to 33% of those patients admitted to ICUs. The most common causes are pneumonia related to mechanical ventilation, intra-abdominal infections following trauma or surgery, and bacteremia derived from intravascular devices. This overview is targeted at ICU physicians to convince them that the principles of infection control in the ICU are based on simple concepts and that the application of preventive strategies should not be viewed as an administrative or constraining control of their activity but, rather, as basic measures that are easy to implement at the bedside. A detailed knowledge of the epidemiology, based on adequate surveillance methodologies, is necessary to understand the pathophysiology and the rationale of preventive strategies that have been demonstrated to be effective. The principles of general preventive measures such as the implementation of standard and isolation precautions, and the control of antibiotic use are reviewed. Specific practical measures, targeted at the practical prevention and control of ventilator-associated pneumonia, sinusitis, and bloodstream, urinary tract, and surgical site infections are detailed. Recent data strongly confirm that these strategies may only be effective over prolonged periods if they can be integrated into the behavior of all staff members who are involved in patient care. Accordingly, infection control measures are to be viewed as a priority and have to be integrated fully into the continuous process of improvement of the quality of care.

Catheter-related infections: diagnosis and intravascular treatment

The diagnosis of catheter-related infections relies on the presence of clinical manifestations of infection and the evidence of colonization of the catheter tip by bacteria, mycobacteria or fungi. The reference method to confirm the latter requires the withdrawal of the catheter for culturing, which frequently turns out to be inconvenient, unnecessary and costly. New methods try to avoid these inconveniences and to assess the presence of tip colonization without withdrawal. One of these methods uses quantitative blood cultures with a jump (> or = 5) in colony counts between blood obtained from the catheter lumen and simultaneously from a peripheral vein. It has a high sensitivity (>80%) and specificity (94%-100%) but is cumbersome and requires both an easy backflow of blood in the catheter and the existence of bacteremia. Cytocentrifugation and acridine orange staining of blood withdrawn from an infected catheter lumen has a sensitivity and a specificity of over 90% for the diagnosis of tip colonization. "Superficial cultures" consist in the semiquantitative culture of the hub, of the skin surrounding the catheter entrance and of the first (1 cm) subcutaneous portion of the catheter after swabbing. Sensitivity of this method is >90% and specificity is >80%, and positive and negative predictive values for catheters (considering together those with and without clinical data of infection) are 66% and 97%, respectively. Endoluminal brushing has turned out to be an impractical and unreliable procedure, at least in our experience. New methods based on the speed of bacterial growth to detectable levels of microorganisms in conventional blood cultures are a new and interesting way of assessing catheter-related infections. Besides, as use of antimicrobial-coated catheters becomes more prevalent, the existing definitions of catheter colonization and catheter-related infection may need to be modified, because such coatings may lead to false-negative culture results. Many catheter infections, diagnosed without catheter withdrawal, can be handled nowadays with the so-called "antibiotic lock-in technique", which consists in locking the infected catheter lumen with a solution containing antibiotics. A high proportion of infected catheters, mainly those with coagulase-negative staphylococci, can be maintained in place and sterilized with this technique, including catheters in patients with therapeutic failure after receiving conventional intravenous antibiotic therapy. New diagnostic and therapeutic techniques may avoid the unnecessary withdrawal of thousands of efficient, difficult to replace and expensive intravascular lines.

Molecular analysis of coagulase-negative Staphylococcus isolates from blood cultures: prevalence of genotypic variation and polyclonal bacteremia

Fifty-seven coagulase-negative Staphylococcus isolates from 22 inpatients who had > or =2 blood cultures that were positive for Staphylococcus within 24 hours were analyzed to determine the frequency of polyclonal bacteremia. Patients were considered to have bacteremia (14 patients) or contamination of sample (8 patients) on the basis of clinical criteria. Nine colonies were randomly selected from each blood culture and genotyped by means of SmaI digestion/pulsed-field gel electrophoresis. Relatedness was determined by calculation of the Dice coefficient of banding-pattern similarity (S(AB)). Analysis of bacteremic isolates demonstrated the presence of a single species in 35 of 41 blood cultures, 1 related variant in 5 blood cultures (87%-92% S(AB)), and an unrelated strain in 1 blood culture (79% S(AB)). Analysis of contaminated samples demonstrated the presence of a single strain in 10 of 16 blood cultures and 1-3 variants (28%-97% S(AB)) in the remainder. Genotype diversity was significantly more common in the contaminated samples (P=.036). Almost all coagulase-negative Staphylococcus bacteremias were monoclonal.

Rapid detection of methicillin resistance in coagulase-negative staphylococci by a penicillin-binding protein 2a-specific latex agglutination test

The detection of PBP 2a by the MRSA-Screen latex agglutination test with 201 clinical coagulase-negative staphylococci had an initial sensitivity of 98% and a high degree of specificity for Staphylococcus epidermidis strains compared to PCR for mecA. Determination of oxacillin MICs evaluated according to the new breakpoint (0.5 microg/ml) of the National Committee for Clinical Laboratory Standards exhibited an extremely low specificity for this population.

Biofilm formation by Staphylococcus epidermidis depends on functional RsbU, an activator of the sigB operon: differential activation mechanisms due to ethanol and salt stress

Staphylococcus epidermidis is a common pathogen in medical device-associated infections. Its major pathogenetic factor is the ability to form adherent biofilms. The polysaccharide intercellular adhesin (PIA), which is synthesized by the products of the icaADBC gene cluster, is essential for biofilm accumulation. In the present study, we characterized the gene locus inactivated by Tn917 insertions of two isogenic, icaADBC-independent, biofilm-negative mutants, M15 and M19, of the biofilm-producing bacterium S. epidermidis 1457. The insertion site was the same in both of the mutants and was located in the first gene, rsbU, of an operon highly homologous to the sigB operons of Staphylococcus aureus and Bacillus subtilis. Supplementation of Trypticase soy broth with NaCl (TSB(NaCl)) or ethanol (TSB(EtOH)), both of which are known activators of sigB, led to increased biofilm formation and PIA synthesis by S. epidermidis 1457. Insertion of Tn917 into rsbU, a positive regulator of alternative sigma factor sigma(B), led to a biofilm-negative phenotype and almost undetectable PIA production. Interestingly, in TSB(EtOH), the mutants were enabled to form a biofilm again with phenotypes similar to those of the wild type. In TSB(NaCl), the mutants still displayed a biofilm-negative phenotype. No difference in primary attachment between the mutants and the wild type was observed. Similar phenotypic changes were observed after transfer of the Tn917 insertion of mutant M15 to the independent and biofilm-producing strain S. epidermidis 8400. In 11 clinical S. epidermidis strains, a restriction fragment length polymorphism of the sigB operon was detected which was independent of the presence of the icaADBC locus and a biofilm-positive phenotype. Obviously, different mechanisms are operative in the regulation of PIA expression in stationary phase and under stress induced by salt or ethanol.

Evaluation of two commercial systems and a new identification scheme based on solid substrates for identifying coagulase-negative staphylococci from bovine mastitis

Coagulase-negative staphylococci (CNS), mainly isolated from bovine mastitis (n = 89, representing 11 different species), were used to evaluate two commercial identification systems: ID 32 Staph and Staph-Zym. The level of agreement between the ID 32 Staph and Staph-Zym systems and conventional methods was 77 and 94%, respectively. An alternative method, based on solid biochemical substrates, is also presented. This can be used for identifying novobiocin-sensitive CNS strains from bovine mastitis.

Identification of three essential regulatory gene loci governing expression of Staphylococcus epidermidis polysaccharide intercellular adhesin and biofilm formation

The formation of adherent multilayered biofilms embedded into a glycocalyx represents an essential factor in the pathogenesis of Staphylococcus epidermidis biomaterial-related infections. Using biofilm-producing S. epidermidis 1457 and transposon Tn917 carried on plasmid pTV1ts, we isolated nine isogenic biofilm-negative transposon mutants. Transduction by S. epidermidis phage 71 was used to prove the genetic linkage of transposon insertions and altered phenotypes. Mapping of the different transposon insertions by Southern hybridization and pulsed-field gel electrophoresis indicated that these were inserted in four unlinked genetic loci. According to their phenotypes, including quantitative differences in biofilm production in different growth media, in the amount of the polysaccharide intercellular adhesin (PIA) produced, in the hemagglutination titers, and in the altered colony morphology, the mutants could be separated into four phenotypic classes corresponding with the genetic classes. Synthesis of PIA was not detectable with class I and II mutants, whereas the amount of PIA produced reflected the residual degree of biofilm production of class III and IV mutants in different growth media. Chromosomal DNA flanking the transposon insertions of five class I mutants was cloned and sequenced, and the insertions were mapped to different locations of icaADBC, representing the synthetic genes for PIA. Expression of icaADBC from a xylose-dependent promoter in the different isogenic mutant classes reconstituted biofilm production in all mutants. In a Northern blot analysis no icaADBC-specific transcripts were observed in RNA isolated from mutants of classes II, III, and IV. Apparently, in addition to icaADBC, three other gene loci have a direct or indirect regulatory influence on expression of the synthetic genes for PIA on the level of transcription.