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Fluorescent amplified fragment length polymorphism (FAFLP) genotyping demonstrates the role of biofilm-producing methicillin-resistant periocular Staphylococcus epidermidis strains in postoperative endophthalmitis.

BACKGROUND: An observational case series was used to study the virulence characteristics and genotypes of paired Staphylococcus epidermidis isolates cultured from intraocular samples and from periocular environment of patients with postcataract surgery endophthalmitis. METHODS: Eight S. epidermidis isolates were obtained from three patients (2 from patients #1 and 2 and 4 from patient #3) whose vitreous and/or anterior chamber (AC) specimens and preoperative lid/conjunctiva samples were culture positive. Cultures were identified by API-Staph phenotypic identification system and genotypically characterized by Fluorescent Amplified Fragment Length Polymorphism (FAFLP) and checked for their antimicrobial susceptibility. The isolates were tested for biofilm-production and methicillin-resistance (MR) by PCR amplification of icaAB and mecA gene respectively. RESULTS: Four out of eight S. epidermidis strains showed multiple drug resistance (MDR). All the eight strains were PCR positive for mecA gene whereas seven out of eight strains were positive for icaAB genes. In all three patients FAFLP typing established vitreous isolates of S. epidermidis strains to be indistinguishable from the strains isolated from the patient's conjunctival swabs. However, from patient number three there was one isolate (1030b from lid swab), which appeared to be nonpathogenic and ancestral having minor but significant differences from other three strains from the same patient. This strain also lacked icaAB gene. In silico analysis indicated possible evolution of other strains from this strain in the patient. CONCLUSION: Methicillin-resistant biofilm positive S. epidermidis strains colonizing the conjunctiva and eyelid were responsible for postoperative endophthalmitis (POE).

Adult↗

Mixed species biofilms of Candida albicans and Staphylococcus epidermidis.

A simple catheter disk model system was used to study the development in vitro of mixed species biofilms of Candida albicans and Staphylococcus epidermidis, two organisms commonly found in catheter-associated infections. Two strains of S. epidermidis were used: a slime-producing wild type (strain RP62A) and a slime-negative mutant (strain M7). In mixed fungal-bacterial biofilms, both staphylococcal strains showed extensive interactions with C. albicans. The susceptibility of 48-h biofilms to fluconazole, vancomycin and mixtures of the drugs was determined colorimetrically. The results indicated that the extracellular polymer produced by S. epidermidis RP62A could inhibit fluconazole penetration in mixed fungal-bacterial biofilms. Conversely, the presence of C. albicans in a biofilm appeared to protect the slime-negative staphylococcus against vancomycin. Overall, the findings suggest that fungal cells can modulate the action of antibiotics, and that bacteria can affect antifungal activity in mixed fungal-bacterial biofilms.

Anti-Bacterial Agents↗

Disruption of the transmembrane pH gradient--a possible mechanism for the antibacterial action of azelaic acid in Propionibacterium acnes and Staphylococcus epidermidis.

The effect of the topical acne treatment azelaic acid on the transmembrane proton gradient (delta pH) of Propionibacterium acnes and Staphylococcus epidermidis was studied in vitro at external pH values found on human skin (pH 4.0-6.0). Bacteria were grown in defined media using continuous culture and delta pH was estimated by measuring the accumulation of [14C] benzoic by the cells using flow dialysis. In both P. acnes and S. epidermidis the addition of 30 mM azelaic acid and the membrane active inhibitors nigericin (150 microM) and CCCP (150 microM) resulted in a rapid release of [14C] label into the dialysate indicating the dissipation of delta pH between external pH values of 4.0-6.0. The addition of 60 mM NaCl as an iso-osmotic control and 150 microM valinomycin did not induce the release of [14C] label. The addition of 30 mM azelaic acid reduced the delta pH of P. acnes by 44% at external pH 4.0 and 28% at external pH 6.0. In S. epidermidis 30 mM azelaic acid reduced delta pH by 88% at external pH 5.0 and 20% at external pH 6.0. Rapid loss of viability occurred in suspensions of P. acnes and S. epidermidis containing 30 mM azelaic acid at pH 4.0 with no viable cells recovered after 60 min incubation. At pH 6.0 little change in viable numbers of P. acnes and S. epidermidis were observed over a 2 h incubation period. The results indicate that the antibacterial activity of azelaic acid is associated with the perturbation of intracellular pH.

Anti-Bacterial Agents↗

Staphylococcus epidermidis sepsis in the intensive care nursery: a characterization of risk associations in infants < 1,000 g.

We undertook to determine Staphylococcus epidermidis colonization patterns and risks of sepsis in a cohort of 82 consecutive intensive care nursery admissions (birth weight 1,285 +/- 57 g), with 24 infants weighing < 1,000 g at birth. Colonization was determined by skin and stool cultures collected at three time points. Multiple neonatal variables were classified into three intervals preceding the time of sample collection including the occurrence of S. epidermidis sepsis. 16 infants (20%) developed S. epidermidis sepsis. 81% of these episodes occurred in infants < 1,000 g. Skin colonization was nearly universal at all sampling points. Rectal colonization was 63.6% initially (10 +/- 0.4 days), then declined to 32% by the third sample (37 +/- 0.4 days). Neither prevalence of skin nor rectal colonization influenced the incidence of sepsis significantly. Statistically significant risk associations for sepsis for the entire intensive care nursery population included: low birth weight, gestational age, presence of a central line, and delayed feeding. For infants < 1,000 g the occurrence of sepsis during the second study time period (54% of the episodes) was associated with preceding steroid exposure. During the third study time period, birth weight and delayed attainment of full enteral feeds showed a statistically significant association with sepsis. We conclude that infants < 1,000 g are at an increased risk of S. epidermidis sepsis. Extreme immaturity, steroid therapy, and prolonged hyperalimentation are all significant risk associations.

Bacteremia↗

The pathogenic role of Staphylococcus epidermidis capsular polysaccharide/adhesin in a low-inoculum rabbit model of prosthetic valve endocarditis.

BACKGROUND: The capsular polysaccharide/adhesin (PS/A) antigen of Staphylococcus epidermidis was required to produce endocarditis in a rabbit model in which infection resulted from hematogenous spread of bacteria from a contaminated catheter in the jugular vein. However, many prosthetic valve endocarditis (PVE) infections probably result from direct contamination of the valve with small numbers of bacteria during surgery. The role of PS/A in this situation was evaluated by modifying a rabbit model of endocarditis to partially mimic PVE. METHODS AND RESULTS: A Teflon catheter was contaminated with graded inocula of either PS/A-positive S epidermidis strain M187sp11 or the PS/A-negative, isogenic strain M187sn3 and inserted into the left ventricle through the aortic valve. The PS/A-positive strain had a 50% infectious dose of 1.1 x 10(2) cfu (95% CI, 3.3 to 3.7 x 10(3)) compared with 8.5 x 10(4) cfu of the PS/A-negative strain (95% CI, 8.6 x 10(3) to 8.5 x 10(5)). The odds for developing endocarditis were estimated to be 42 times higher for any given inoculum level of the PS/A-positive strain (P = .1). When the PS/A-positive strain was adherent to a catheter surface it survived in rabbit blood, whereas under the same conditions the PS/A-negative strain was killed approximately 90% in 1 hour. CONCLUSIONS: Direct contamination of an intraventricular foreign body by low levels of PS/A-positive S epidermidis results in endocarditis in rabbits, but at suitably high doses PS/A-negative strains have sufficient virulence to infect cardiac vegetations. PS/A enhances but is not absolutely required for bacterial virulence in a rabbit model of PVE.

Animals↗

Inferring a population structure for Staphylococcus epidermidis from multilocus sequence typing data.

Despite its importance as a human pathogen, information on population structure and global epidemiology of Staphylococcus epidermidis is scarce and the relative importance of the mechanisms contributing to clonal diversification is unknown. In this study, we addressed these issues by analyzing a representative collection of S. epidermidis isolates from diverse geographic and clinical origins using multilocus sequence typing (MLST). Additionally, we characterized the mobile element (SCCmec) carrying the genetic determinant of methicillin resistance. The 217 S. epidermidis isolates from our collection were split by MLST into 74 types, suggesting a high level of genetic diversity. Analysis of MLST data using the eBURST algorithm revealed the existence of nine epidemic clonal lineages that were disseminated worldwide. One single clonal lineage (clonal complex 2) comprised 74% of the isolates, whereas the remaining isolates were clustered into 8 minor clonal lineages and 13 singletons. According to our evolutionary model, SCCmec was acquired at least 56 times by S. epidermidis. Although geographic dissemination of S. epidermidis strains and the value of the index of association between the alleles, 0.2898 (P < 0.05), support the clonality of S. epidermidis species, examination of the sequence changes at MLST loci during clonal diversification showed that recombination gives rise to new alleles approximately twice as frequently as point mutations. We suggest that S. epidermidis has a population with an epidemic structure, in which nine clones have emerged upon a recombining background and evolved quickly through frequent transfer of genetic mobile elements, including SCCmec.

Algorithms↗

Antibiotic therapy of experimental Staphylococcus epidermidis endocarditis.

Endocarditis was produced in rabbits with a methicillin-resistant Staphylococcus epidermidis isolate. Subpopulations resistant to other semisynthetic penicillins and cephalosporins were detected in the isolate. Their presence was probably responsible for the increase in minimum bactericidal concentrations and minimum inhibitory concentrations when tests with high inocula, rather than low inocula were pursued. Rabbits were treated for either 2 or 7 days with nafcillin, cephalothin, cefamandole, vancomycin, rifampin, or gentamicin. Spontaneous death was uncommon in either controls (84% survival) or treated animals (80 to 94% survival). There was no significant difference in the number of bacteria in vegetations of rabbits treated for 7 days with cephalothin, cefamandole, nafcillin, or no antibiotic (control). There was a significant reduction in total bacteria in vegetations of rabbits given vancomycin, gentamicin, or rifampin for 7 days as compared with cephalothin, cefamandole, nafcillin or control. Gentamicin or rifampin sterilized significantly more vegetations after 7 days than cephalothin, cefamandole, nafcillin, or control; rifampin was more effective in sterilizing vegetations than either gentamycin or vancomycin after 2 days. Mutants resistant to 10 mug of rifampin per ml comprised the total bacterial population cultured from vegetations of 2 of 17 rabbits treated with this antibiotic for 7 days; there was no change in the susceptibility of vegetation isolates to other antibiotics. Rifampin, vancomycin, or gentamicin may prove to be more effective in humans than cephalosporins or semisynthetic penicillins in the treatment of methicillin-resistant S. epidermidis endocarditis.

Animals↗

Inhibition of virulence factor expression in Staphylococcus aureus by the Staphylococcus epidermidis agr pheromone and derivatives.

The agr quorum-sensing system in Staphylococci controls the production of surface proteins and exoproteins. In the pathogenic species Staphylococcus aureus, these proteins include many virulence factors. The extracellular signal of the quorum-sensing system is a thiolactone-containing peptide pheromone, whose sequence varies among the different staphylococcal strains. We demonstrate that a synthetic Staphylococcus epidermidis pheromone is a competent inhibitor of the Staphylococcus aureus agr system. Derivatives of the pheromone, in which the N-terminus or the cyclic bond structure was changed, were synthesized and their biological activity was determined. The presence of a correct N-terminus and a thiolactone were absolute prerequisites for an agr-activating effect in S. epidermidis, whereas inhibition of the S. aureus agr system was less dependent on the original structure. Our results show that effective quorum-sensing blockers that suppress the expression of virulence factors in S. aureus can be designed based on the S. epidermidis pheromone.

Bacterial Proteins↗

Analysis of the Staphylococcus epidermidis genes epiF, -E, and -G involved in epidermin immunity.

The lantibiotic epidermin is produced by Staphylococcus epidermidis Tü3298. The known genes involved in epidermin biosynthesis and regulation are organized as operons (epiABCD and epiQP) that are encoded on the 54-kb plasmid pTü32. Here we describe the characterization of a DNA region that mediates immunity and increased epidermin production, located upstream of the structural gene epiA. The sequence of a 2.6-kb DNA fragment revealed three open reading frames, epiF, -E, and -G, which may form an operon. In the cloning host Staphylococcus carnosus, the three genes mediated an increased tolerance to epidermin, and the highest level of immunity (sevenfold) was achieved with S. carnosus carrying epiFEG and epiQ. The promoter of the first gene, epiF, responded to the activator protein EpiQ and contained a palindromic sequence similar to the EpiQ binding site of the epiA promoter, which is also activated by EpiQ. Inactivation of epiF, -E, or -G resulted in the complete loss of the immunity phenotype. An epidermin-sensitive S. epidermidis Tü3298 mutant was complemented by a DNA fragment containing all three genes. When the epiFEG genes were cloned together with plasmid pTepi14, containing the biosynthetic genes epiABCDQP, the level of epidermin production was approximately fivefold higher. The proteins EpiF, -E, and -G are similar in deduced sequence and proposed structure to the components of various ABC transporter systems. EpiF is a hydrophilic protein with conserved ATP-binding sites, while EpiE and -G have six alternating hydrophobic regions and very likely constitute the integral membrane domains. When EpiF was overproduced in S. carnosus, it was at least partially associated with the cytoplasmic membrane. A potential mechanism for how EpiFEG mediates immunity is discussed.

ATP-Binding Cassette Transporters↗

Treatment of experimental Staphylococcus epidermidis endophthalmitis with oral trovafloxacin.

PURPOSE: To investigate the ocular pharmacokinetics and efficacy of oral trovafloxacin, a novel fluoroquinolone antibiotic, in Staphylococcus epidermidis endophthalmitis. METHODS: Albino rabbits (n = 20) were infected with an intravitreal inoculum of S epidermidis (1.0 x 10(8) colony-forming units [CFU/0.1 ml) and 24 hours later received a single oral dose of trovafloxacin (250 mg/kg). Serum and intraocular samples from infected and control (noninfected) eyes were obtained up to 24 hours after antibiotic administration for measurement of trovafloxacin levels. A second group of rabbits (n = 72) was infected intraocularly and randomized 24 hours later to oral trovafloxacin (250 mg/kg twice a day) for 6 days or no treatment (control). Treatment efficacy was assessed by vitreous culture, clinical examination, and histopathology. RESULTS: Following a single dose of trovafloxacin, maximal vitreous levels were achieved at 8 hours in infected eyes, with a penetration ratio of 36%. Vitreous levels were greater than 15 times the minimum inhibitory concentration of the strain employed. In animals with established endophthalmitis, treated eyes were sterilized after 5 days (P = .0495) compared with control eyes, which autosterilized at 14 days. Clinical and histologic examination revealed significant amelioration of anterior segment inflammation in treated eyes, although severe destruction of posterior segment structures occurred in both groups after 6 days of therapy. CONCLUSIONS: These data support trovafloxacin as a potential oral agent for treatment or prophylaxis of S epidermidis endophthalmitis, although retinal alterations that occur over the period required for vitreous sterilization suggest that it will not replace intravitreal therapy in established endophthalmitis.

Administration, Oral↗

Polyclonal Staphylococcus epidermidis intravascular catheter-related infections.

During a 4-month period we prospectively investigated the frequency of polyclonal catheter infections with Staphylococcus epidermidis. Of each catheter with pure growth of S. epidermidis, six colonies were genotypically analyzed with pulsed-field gel electrophoresis. Two out of 12 patients with catheter infection had a polyclonal infection. Both clones of each catheter had a clearly different antibiotic susceptibility. This study shows that polyclonal catheter infections are not exceptional. Further studies are needed to define the clinical consequences of polyclonal catheter infection.

Adult↗

Polymorphism of the cell wall-anchoring domain of the autolysin-adhesin AtlE and its relationship to sequence type, as revealed by multilocus sequence typing of invasive and commensal Staphylococcus epidermidis strains.

We sequenced the adhesin-cell wall-anchoring domain of the atlE gene of 49 invasive and commensal Staphylococcus epidermidis strains. We identified 22 alleles, which could be separated into two main groups: group 1 (alleles 1 and 6 to 16, 32/49 strains) and group 2 (alleles 2 to 5 and 17 to 22, 17/49 strains). Allele 1 (the type strain sequence) was by far the most prevalent (21 of 49 strains). Multilocus sequence typing showed a clear relationship between the atlE allele and the sequence type (ST), with the "nosocomial" ST27 clone and closely related STs expressing group 1 alleles.

Adhesins, Bacterial↗

Lack of mecA transcription in slime-negative phase variants of methicillin-resistant Staphylococcus epidermidis.

Five phase variants (PV1 to PV5) of the well-characterized, slime-producing, methicillin-resistant, pathogenic strain of Staphylococcus epidermidis sensu strictu RP62A (ATCC 35984) were isolated by the Congo red agar method. In comparison with the parent strain, the phase variants showed a different colonial morphology on Congo red agar, a strongly reduced adherence capacity, and decreased levels of resistance to methicillin, oxacillin, and penicillin. All phase variants yielded biochemical reaction patterns and profiles in pulsed-field gel electrophoresis identical to those of parent strain RP62A, indicating a common origin. All phase variants proved to have the capacity to shift back to the original phenotype of parent strain RP62A. A search for the resistance mechanisms of strain RP62A revealed beta-lactamase production and the presence of mecA in PV1 to PV5 as well as parent strain RP62A. In Northern blots of total staphylococcal RNA, the phase variants showed no detectable mecA-specific transcription product, whereas parent strain RP62A revealed a strong signal, indicating that mecA transcription is not the mechanism responsible for the decreased methicillin resistance phenotype of phase variants PV1 to PV5.

Anti-Bacterial Agents↗

A comparison of the effects of two antiseptic agents on Staphylococcus epidermidis colony forming units at the peritoneal dialysis catheter exit site.

Peritonitis is the most common complication of peritoneal dialysis (PD). Staphylococcus epidermidis (S. epi), a common skin organism, is the microorganism that is identified is the majority of episodes of peritonitis. The PD catheter breaks the natural skin barrier and allows a periluminal migration of bacteria from the skin surface into the sterile peritoneal cavity. Exit site care is routinely performed to decrease the colony counts of microorganisms on the skin surrounding the PD catheter. Research data is limited to support any of the currently used protocols for exit site care. This study compared the effect of two antiseptic agents, povidone-iodine (P-I) and chlorhexidine gluconate (CG), on S. epi colony forming units (cfu) at the PD catheter exit site over a 24 hour period. Because the distribution of the research data was markedly non-normal, a descriptive approach was used to interpret the data. Results showed that there was no difference between P-I and CG immediately after exit site care. All patients had zero growth at Time I. One trend that emerged was that at 24 hours after exit site care with P-I, more patients (54%) had S. epi cfu than did patients (15%) cleaned with CG.

Adult↗

Dynamics of experimentally induced Staphylococcus epidermidis mastitis in East Friesian milk ewes.

The responses of five lactating East Friesian milk ewes to experimental mammary infection with Staphylococcus epidermidis and of five control ewes were examined over a period of 10 weeks. Infection caused an influx of neutrophils into milk, the numbers of which started to rise 4 h post infection and peaked 24 h after infection. The initial response was accompanied by mild fever and mild leucopaenia in blood (8 h after infection). No other signs of systemic infection were observed. Milk appeared normal at all times, although the milk yield of infected ewes tended to decline. Staphylococci were absent in milk from four ewes at 2 d and at 3 d after infection, but re-emerged intermittently in four of five ewes at subsequent samplings. Cytokines in milk were measured by ELISA. IL-8 was elevated in infected glands at 2 h and peaked at 8 h. In the four ewes intermittently shedding bacteria, IL-8 remained elevated until the final sampling at 10 weeks. IL-1beta was transiently elevated at 1 d and 2 d and showed a pronounced peak in one sheep. Milk samples from this ewe were bacteriologically negative, somatic cell count (SCC) was within the normal range and the concentrations of IL-1beta, as well as IL-8, were similiar to the control group (n=5) from 1 week after infection until the final sampling. Histological examination revealed leucocytic infiltrates in the four glands remaining infected at the end of the experiment, and a high level of CD5+ lymphocytes in three ewes. The results suggest that the relationship between the initial neutrophil influx and the proinflammatory cytokines may be responsible for determining the course of infection. Subclinical mastitis due to coagulase-negative staphylococci leads to minor changes in milk yield and milk constituents.

Animals↗

Dispersal of methicillin-resistant Staphylococcus epidermidis by staff in an operating suite for thoracic and cardiovascular surgery: relation to skin carriage and clothing.

Methicillin-resistant Staphylococcus epidermidis (MRSE) is a common cause of deep sternal infections. The aim of the present investigation was to evaluate staff in an operating suite for thoracic and cardiovascular surgery as a possible source of MRSE and the possibility of reducing the amount of MRSE shed into the air by wearing tightly woven scrub suits. A second aim was to compare the results of dispersal obtained in a test chamber with those from an operating room. We studied carriage of MRSE in the nose and on different skin sites and made an experimental study of dispersal of MRSE during exercise in a test chamber and during operations, using two different types of scrub suits. Dispersal of MRSE [defined as > 1% of the total count of colony forming units (CFU) shed into the air] occurred in 25% of women and 43% of men. Nasal carriage was found among 28% in women and 33% in men. Among five skin-sampling sites, carriage of MRSE was most frequent on the cheek (50%) and in the axilla (24%) and least frequent in the perineum (5%). Dispersal of MRSE was however more strongly associated with carriage in the perineum (P = 0.097) than on the cheek (P = 0.5) and in the axilla (P = 0.21). With regard to shedding of bacteria into the air, there was a significant difference in favour of the tightly woven clothes regarding total counts of CFU both in the test chamber (P = 0.02) and the operating theatre (P = 0.002). Regarding MRSE, no such difference was found. We found there were too many dispersers of MRSE among operating department staff to exclude them from work. Although tightly woven scrub suits significantly reduced the amount of bacteria shed into the air, the amount of MRSE was not significantly reduced. Full-scale experiments in operating rooms are not needed when evaluating the protective capacity of different scrub suits as results from a test chamber give conclusive information.

Air Microbiology↗

Teicoplanin compared with vancomycin for treatment of experimental endocarditis due to methicillin-resistant Staphylococcus epidermidis.

This study compared teicoplanin with vancomycin without and with gentamicin and/or rifampin for treatment of experimental endocarditis due to methicillin-resistant Staphylococcus epidermidis. In rabbits treated for three days and killed 12 hr after the last doses of antimicrobial agents, no significant difference in reducing bacterial titers of vegetations was detected between vancomycin and teicoplanin without and with gentamicin and/or rifampin. Addition of gentamicin and/or rifampin to vancomycin or teicoplanin significantly reduced bacterial titers of vegetations compared with vancomycin or teicoplanin alone. Addition of rifampin alone or gentamicin plus rifampin was significantly more effective than addition of gentamicin alone. In rabbits treated for three days and killed seven days after the last doses of antimicrobial agents, no significant difference in sterilizing vegetations was detected between vancomycin and teicoplanin with gentamicin and/or rifampin. However, there was a trend (probably due to the longer elimination half-life of teicoplanin in serum) that clearly favored teicoplanin over vancomycin. Teicoplanin plus rifampin without or with gentamicin is at least as effective as vancomycin plus rifampin without or with gentamicin for treatment of experimental endocarditis due to methicillin-resistant S. epidermidis.

Animals↗

Multiple antibiotic resistance in Staphylococcus aureus and Staphylococcus epidermidis: plasmids in strains associated with nosocomial infection.

The plasmid DNA profiles were compared to phenotypically-similar, antibiotic-resistant strains of Staphylococcus aureus and Staphylococcus epidermidis associated with nosocomial infections in a Melbourne hospital. Whereas resistance to gentamicin, tobramycin and kanamycin was encoded by one of 3 plasmids [pSK1, 18 megadalton (Md); pSK4, 22 Md; pSK9, 17 Md] in S. aureus, no similar plasmids were detected in S. epidermidis. Mediated exclusively by the chromosome in S. aureus, tetracycline resistance was encoded either by the chromosome or by a 2.8 Md plasmid in strains of S. epidermidis. The inability to detect common resistance plasmids in strains of S. aureus and S. epidermidis recovered from this outbreak is in contrast to recent observations with staphylococci from other geographic areas; nevertheless, on the basis of restriction endonuclease analyses of 3 Md chloramphenicol resistance plasmids, it is suggested that a common gene pool does exist within isolates of S. aureus and S. epidermidis from Melbourne hospitals.

Aminoglycosides↗