Coagulase-Negative Staphylococci

A Comparison of Endoscopic Culture Techniques for Chronic Rhinosinusitis

Background

Recent evidence suggests that endoscopically obtained cultures from the middle meatus give comparable results to antral puncture for acute sinusitis. The best method for obtaining middle meatal cultures remains somewhat controversial because it has been theorized that specimens obtained with a swab are contaminated easily. This study compares endoscopic culture results from two different methods: swab and aspiration. Specifically, this study sought to determine whether or not the culture contamination rate is higher using the swab versus an aspiration technique.

Methods

One hundred consecutive culture specimens from 81 chronic rhinosinusitis patients were compared. Fifty cultures were obtained using a swab technique (group I) and another 50 cultures were obtained by aspirating pathological material into a sterile suction trap (group II). The patient populations in each group were similar; there were no differences in terms of age, gender, comorbid medical conditions, or prior medical therapy. Cultures were considered contaminated if they yielded normal nasal flora or if rare or few Staphylococcus coagulase-negative colonies grew after no bacteria was identified in gram stain. Staphylococcus aureus, Staphylococcus coagulase-negative, and Pseudomonas aeruginosa were the three most common organisms in both groups.

Results

Gram-negative bacteria were noted in 21/60 (35%) positive cultures. Although the contamination rate of the suction aspiration group (14%) was less than the endoscopic swab group (10%), this did not approach statistical significance (p = 0.75).

Conclusions

Data from this study suggest that endoscopically guided aspiration of pathological material is no better than properly obtained swabs in directing antimicrobial therapy for chronic rhinosinusitis.

Molecular techniques open up new vistas for typing of coagulase-negative staphylococci

Several methods were used to type 64 clinical isolates of coagulase-negative staphylococci (CNS) derived from hospitals in Morocco. The clinical isolates originated principally from blood cultures and wound sources. These isolates provided the opportunity to substantially compare the proficiency of developing molecular techniques with conventional phenotypic tests for use in the identification of clinical staphylococci. The following molecular methods were examined: Utility ribotyping analysis (Ribotyping); PCR analysis performed with 16S-23S ribosomal-DNA intergenic spacer (ITS-PCR); PCR-based random amplified polymorphic DNA (RAPD). The results obtained by the molecular techniques were contrasted to those of conventional phenotypic tests. Conventional phenotypic tests allowed the outright recognition of the majority of isolates (50/64). These 50 isolates were subdivided into 33 novobiocin-susceptible and 17 novobiocin-resistant strains of CNS. However, 2 other novobiocin-susceptible and 12 other novobiocin-resistant isolates remained unclassified by these tests. There was a good agreement between the conventional phenotypic tests and RAPD for the 33 novobiocin-susceptible isolates. But, the RAPD technique permitted the assignment of the two unidentified novobiocin-susceptible isolates to the Staphylococcus hominis species. A complete correlation was obtained between the three molecular tools for recognition of the 12 novobiocin-resistant isolates that were not identified by phenotypic typing; these were in fact identified as 5 Staphylococcus cohnii and 4 Staphylococcus equorum. Three isolates remained unidentified by all three systems of molecular techniques.

Nasal colonization by methicillin-resistant coagulase-negative staphylococcus in community skilled nursing facility patients

BACKGROUND

Methicillin-resistant coagulase-negative staphylococci (MRCNS) are increasing nosocomial pathogens in acute care hospital patients. However, there is little information on the epidemiology of MRCNS in skilled nursing facilities (SNFs). We report a pilot survey of the prevalence of MRCNS colonization in SNF patients.

METHODS

Anterior nasal swabs were plated on oxacillin salt screening agar for selection of MRCNS. Suspected MRCNS were confirmed by coagulase and catalase tests and standard disc-diffusion antimicrobial susceptibility tests.

RESULTS

The overall prevalence of MRCNS was 40% for in-house continuing SNF patients, 49% for newly admitted patients, and 60% for SNF nursing personnel. The prevalence was 13% in a "control" group of nonmedical personnel. Forty-six percent of MRCNS were resistant to ciprofloxacin. The frequency of colonization with MRCNS increased over time. After an average 17 months of facility stay, 32% of noncarriers acquired MRCNS. High frequency of colonization was associated with greater disability.

CONCLUSION

Colonization with MRCNS is common among SNF patients, who can serve as a reservoir for transfer of such strains to acute care hospitals. Careful infection control practice, including judicious use of antibiotics with frequent handwashing, will remain critical policies for limiting spread of such strains.

An inflammatory polypeptide complex from Staphylococcus epidermidis: isolation and characterization

Staphylococcus epidermidis releases factors that activate the HIV-1 long terminal repeat, induce cytokine release, and activate nuclear factor B in cells of macrophage lineage. The active material had a mass of 34,500 daltons, was inactivated by proteases and partitioned into the phenol layer on hot aqueous phenol extraction, and thus was termed phenol-soluble modulin (PSM). High performance liquid chromatography (HPLC) of crude PSM yielded two peaks of activity designated PSM peak 1 and peak 2. MALDI-TOF (matrix-assisted laser desorption ionization-time of flight) mass spectroscopy indicated the presence of two components in peak 1, which were designated PSM and PSM. Peak 2 contained a single component, designated PSM. Separation of PSM and PSM in peak 1 could be achieved by a second HPLC procedure. The structure of each component was determined by amino acid sequence analysis and identification and sequencing of their genes. PSM, PSM, and PSM were 22-, 44-, and 25-amino acid, respectively, strongly hydrophobic polypeptides. PSM was identified as Staphylococcus epidermidis delta toxin, whereas PSM and PSM exhibited more distant homology to previously described staphylococcal toxins. They appeared to exist as a complex or aggregate with activity greater than the component parts. The properties of the S. epidermidis PSMs suggest that they may contribute to the systemic manifestations of Gram-positive sepsis.

In vitro study of the potential role of quinupristin/dalfopristin in the treatment of catheter-related staphylococcal infections

The susceptibility of clinical isolates of methicillin-susceptible and -resistant staphylococci from cancer patients with central venous catheter bacteremia to quinupristin/dalfopristin, a semisynthetic streptogramin, was determined in vitro. Susceptibility of these isolates to nine other antistaphylococcal antibiotics was also determined for comparison. A total of 197 staphylococcal strains were tested from 1983 to 1992. Quinupristin/dalfopristin was bactericidal against all isolates, independent of their resistance to methicillin. Its activity was similar to that of vancomycin but superior to that of teicoplanin. Quinupristin/dalfopristin may prove to be an important addition to our armamentarium against catheter-related staphylococcal infections.

Clinically significant coagulase-negative staphylococci: identification and resistance patterns

Coagulase-negative staphylococci (CNS) of clinical significance, isolated from 131 patients, were investigated during the period 1989-90 in northern Norway. The staphylococci were isolated from blood cultures (68; 51.9%), vascular catheters (6), osteomyelitis foci (13), postoperative and other wounds (15), and urine samples (29). The use of Gram-positive Identification Card (Vitek) and 'Staph-zym' (Rosco) both gave a primarily correct species identification in 95% of the cases. Staphylococcus epidermidis was the predominant species (72.3%). Methicillin-resistance was found in 40 of 131 (30.5%) of all CNS and in 34 of 96 (35.4%) of S. epidermidis. Methicillin-resistant (MR) S. epidermidis strains were usually resistant to gentamicin, tetracycline, chloramphenicol and trimethoprim. MR strains were, however, less resistant to sulphonamides than methicillin-sensitive strains (10 out of 34 vs. 55 out of 62). Methicillin-resistance implied resistance to all beta-lactam antibiotics, including imipenem. Among S. epidermidis, MR isolates increased from 10% in 1987 to 35.4% in 1989-90. All strains were sensitive to vancomycin and rifampicin.

The crisis in antibiotic resistance

The synthesis of large numbers of antibiotics over the past three decades has caused complacency about the threat of bacterial resistance. Bacteria have become resistant to antimicrobial agents as a result of chromosomal changes or the exchange of the exchange of genetic material via plasmids and transposons. Streptococcus pneumoniae, Streptococcus pyogenes, and staphylococci, organisms that cause respiratory and cutaneous infections, and members of the Enterobacteriaceae and Pseudomonas families, organisms that cause diarrhea, urinary infection, and sepsis, are now resistant to virtually all of the older antibiotics. The extensive use of antibiotics in the community and hospitals has fueled this crisis. Mechanisms such as antibiotic control programs, better hygiene, and synthesis of agents with improved antimicrobial activity need to be adopted in order to limit bacterial resistance.

Phage typing of coagulase-negative staphylococci

Seventy-nine staphylococcal strains isolated from blood cultures (57 coagulase-negative staphylococci (CNS) and 22 S. aureus) and 308 CNS isolated from the skin of healthy donors were phage typed. S. epidermidis and S. capitis were readily typed with 91 strains out of 124 and 24 strains out of 43 strains being successful. Species such as S. haemolyticus, S. hominis and S. simulans could be moderately phage typed. Others gave only a few strains capable of being typed, such as S. saprophyticus and S. sciuri. Under our experimental conditions the S. warneri, S. xylosus and S. cohnii could not be typed with our set of phages.

The continuing importance of staphylococci as major hospital pathogens

Rates of hospital-acquired staphylococcal infection have risen substantially in the United States over the last decade. Moreover, it has been shown that bloodstream infections caused by these organisms account for significant morbidity and mortality. It is likely that the changes in medical practice and in types of patient account for these changes, and current antibiotic therapy has helped select more resistant organisms. The increasing use of implantable and temporary medical devices and the increased use of immunosuppressive therapies correlate strongly with the rising incidence of these organisms. Likewise, more patients are predisposed to these infections because of poor immune status and factors favouring colonization. Intrinsic microbiological factors such as glycocalyx production and the presence of bacterial surface proteins allow these organisms to adhere to protein coated foreign bodies and basement membranes thus enabling them to initiate infection and cause disease. Moreover, virulence factors such as encapsulation, slime production and elaboration of extracellular enzymes aid their resistance to host defences. As a group, staphylococci are a leading cause of hospital-acquired infection, and species identification is required for both treatment and control.

Antimicrobial prophylaxis in coronary bypass surgery: a critical appraisal

The literature has been examined to assess the optimal prophylactic antimicrobial regimen for patients undergoing coronary bypass surgery. Antimicrobial surgical prophylaxis should be based on the two main potential pathogens, Staphylococcus epidermidis and S. aureus. It is unclear whether the prophylactic use of antimicrobials can or should be guided by in vitro antimicrobial susceptibility testing; data from well-performed clinical trials should be evaluated. The data fail to demonstrate consistently a significant difference within the cephalosporin class of antimicrobials with regard to prevention of infectious complications. Although it does not reach statistical difference, the trend with respect to efficacy appears to be cefuroxime, then cefamandole, and then cefazolin. The lack of significant difference among antimicrobials suggests an institution-individualized approach to the selection of the optimal antimicrobial for prophylaxis. For our facilities we recommend the following regimen: cefazolin sodium 1-2 g iv q8h for two days. There are not enough data at this time to recommend less than two days of antimicrobial prophylaxis for this type of surgery. In addition, aminoglycosides provide no added benefit when added to cephalosporins.

In vitro activity of LY264826 compared to other glycopeptides and daptomycin

LY264826 a new naturally occurring glycopeptide inhibited 90% of methicillin-susceptible and -resistant Staphylococcus aureus at 1 micrograms/ml. LY264826 had similar activity against methicillin-susceptible and -resistant coagulase-negative staphylococci. The LY264826 MIC90 for Streptococcus pyogenes was 0.25 microgram/ml, twofold more active than vancomycin and twofold less active than teicoplanin. LY264826 was eightfold more active than vancomycin and twofold more active than teicoplanin against enterococci. LY264826 inhibited Streptococcus pneumoniae at 0.25 microgram/ml and Listeria monocytogenes at 0.5 microgram/ml. Clostridium were inhibited by less than or equal to 0.25 microgram/ml of LY264826 and peptococci, peptostreptococci, and Fusobacterium were inhibited by less than 0.5 microgram/ml. Bacteroides species were LY284826 -resistant as were all Enterobacteriaceae, Flavobacterium, and Neisseria spp. Minimum bactericidal and inhibitory concentrations (MBCs and MICs) were within a dilution for S. aureus, S. pyogenes, and S. pneumoniae, but greater than or equal to 32-fold greater for enterococci.