Genomic characterization of oxacillin-resistant Staphylococcus epidermidis and Staphylococcus haemolyticus isolated from Brazilian medical centres

Coagulase-Negative Staphylococci Clones Are Widely Distributed in the Hospital and Community

Coagulase-negative staphylococci (CoNS) may be considered contaminants when isolated from clinical specimens but may also be a cause of true infection. This study aimed to compare the clonality and SCCmec type of a collection of CoNS isolated from blood cultures of inpatients, nasal swabs of healthy individuals, and patients with chronic wounds, all from the same community, using SCCmec typing, pulsed-field gel electrophoresis (PFGE), and MLST. Staphylococcus epidermidis, exhibited high clonal diversity, but hospital and community clusters were observed. Nosocomial S. epidermidis clones belonged to sequence types ST2, ST6, and ST23. Some Staphylococcus haemolyticus clones were found to circulate in the hospital and community, while Staphylococcus saprophyticus exhibited very high clonal diversity. Staphylococcus lugdunensis, Staphylococcus warneri, and Staphylococcus capitis revealed several isolates belonging to the same clone in the hospital and community. The detection of different SCCmec types within the same cluster indicated high diversity. S. epidermidis was associated with SCCmec I and III, S. haemolyticus with I and II, S. capitis with type V, Staphylococcus hominis with mec complex type A and ccr1, and S. warneri and S. saprophyticus with SCCmec I. The generation of elements and new combinations of cassette genes were highly associated with CoNS isolates, suggesting that SCCmec may not be a good marker of clonality in these bacteria.

Characterization of biofilms and antimicrobial resistance of coagulase-negative Staphylococcus species involved with subclinical mastitis

Biofilm formation is a central feature to guarantee staphylococcal persistence in hosts and is associated with several diseases that are difficult to treat. In this research paper, biofilm formation and antimicrobial susceptibility were investigated in staphylococcal strains belonging to several species. These strains were isolated from the milk of cows with subclinical mastitis and most of them were coagulase-negative, with the prevalence of Staphylococcus chromogenes. High genetic diversity was observed among the strains by pulsed field gel electrophoresis. Antimicrobial resistance was assessed by disk diffusion and more than 50% of the strains were resistant to ampicillin and penicillin G, with multi-resistance profiles (13.6%) also being observed. Most strains (65.9%) formed biofilms when cultivated in BHI supplemented with 1% glucose. Most strains (72.7%) carried the intercellular adhesion gene (icaA), while less than half (36.3%) carried the biofilm-associated protein gene (bap). Concentrations of up to 10xMIC of erythromycin and tetracycline were not sufficient to suppress cell viability in preformed biofilms. Our results revealed that a genetically diverse group of biofilm-forming Staphylococcus species can be involved in subclinical mastitis. Since high antimicrobial concentrations cannot eradicate biofilm cells in vitro, their use in dairy animals may be ineffective in controlling infections, while supporting selection of resistant microorganisms. These data reinforce the need for alternative therapies aiming at disrupting biofilms for effective disease control.

Comparative characterisation of human and ovine non-aureus staphylococci isolated in Sardinia (Italy) for antimicrobial susceptibility profiles and resistance genes

We present the comparative characterisation of 195 non-aureus staphylococci (NAS) isolates obtained from sheep (n = 125) and humans (n = 70) in Sardinia, Italy, identified at the species level by gap gene polymerase chain reaction (PCR) followed by restriction fragment length polymorphism analysis with AluI. Isolates were tested phenotypically with a disc diffusion method and genotypically by PCR, for resistance to 11 antimicrobial agents including cationic antiseptic agents. Among the ovine isolates, Staphylococcus epidermidis (n = 57), S. chromogenes (n = 29), S. haemolyticus (n = 17), S. simulans (n = 8) and S. caprae (n = 6) were the most prevalent species, while among human isolates, S. haemolyticus (n = 28) and S. epidermidis (n = 26) were predominant, followed by S. lugdunensis and S. hominis (n = 4). Of the 125 ovine isolates, 79 (63.2%) did not carry any of the resistance genes tested, while the remainder carried resistance genes for at least one antibiotic. The highest resistance rates among ovine isolates were recorded against tetracycline (20.8%), and penicillin (15.2%); none was resistant to methicillin and two exhibited multidrug resistance (MDR); one of which was positive for the antiseptic resistance smr gene. By contrast, most human isolates (59/70, 84.3%) were resistant to ⩾1 antimicrobials, and 41 (58.6%) were MDR. All 52 (74.3%) penicillin-resistant isolates possessed the blaZ gene, and 33 of 70 (47.1%) harboured the mec gene; of these, seven were characterised by the Staphylococcal Chromosomal Cassette (SCCmec) type IV, 6 the type V, 5 of type III and one representative each of type I and type II. The majority (57.1%) was erythromycin-resistant and 17 isolates carried only the efflux msrA gene, 11 the methylase ermC gene and an equal number harboured both of the latter genes. Moreover, 23 (32.8%) were tetracycline-resistant and all but one possessed only the efflux tetK gene. qacA/B and smr genes were detected in 27 (38.6%) and 18 (25.7%) human NAS, respectively. These results underline a marked difference in species distribution and antimicrobial resistance between ovine and human-derived NAS.

Prevalence of methicillin-resistant Staphylococcus aureus colonization among healthcare workers at a tertiary care hospital in northeastern Brazil

BACKGROUND

Staphylococcus aureus is a human pathogen of clinical importance related to a variety of infections.

AIM

The objective of this study was to analyze the molecular and epidemiological characteristics of S. aureus obtained from healthcare professionals (HCP) of a hospital in southwestern Bahia, Brazil.

METHODS

Samples were collected from hands, nasal cavity, and laboratory coats of 80 HCP. The bacterial isolates recovered from 240 samples were identified as S. aureus, and then analyzed for their antimicrobial resistance profile, genotypic characterization, and pathogenicity.

FINDINGS

178 isolates were identified as S. aureus, being mostly isolated from the nasal cavity. Thirty isolates (16.8%) were characterized as MRSA. The virulence gene frequency varied according to isolate source. All virulence genes were identified in at least one hand isolate. Isolates from laboratory coats did not show seb and pvl. Isolates from the nasal cavity did not exhibit pvl. The SCCmec type I was identified in 56.7% of MRSA isolates. Among MRSA isolates, 14 PFGE pulsotypes were characterized, with profile A being predominant (nine isolates). Clonal complexes CC5, CC45, and CC398 were found. MRSA isolates induced cytokine gene expression in macrophages, with IL-10 and IL-17 being expressed more often.

CONCLUSION

We found a high colonization rate for S. aureus among HCP. Moreover, we observed that MRSA strains presented different virulence factors and could induce cytokine gene expression, indicating an urgent need to control colonization rates of HCP by MRSA isolates in order to protect hospital patients and the general public.

Influence of antibiotics on biofilm formation by different clones of nosocomial Staphylococcus haemolyticus

Staphylococcus haemolyticus is the most common organism among clinical isolatesof methicillin-resistant staphylococci. Aim: This study evaluated the ability to produce biofilm with the presence of the antibiotics (1/4 minimum inhibitory concentrations) of S. haemolyticus strains isolated from blood culture. Methods: Clonal distribution was assessed in pulsed-field gel electrophoresis. PCR assays were performed to detect mecA, icaA, aap, atlE, atl, fbp genes. S. haemolyticus strains grown in the presence of the antibiotics were investigated for biofilm formation on glass, polystyrene and catheter surfaces. Results: Biofilm formation was independent of the presence of the icaA and mecA genes, pulsed-field gel electrophoresis type. Vancomycin, oxacillin, moxifloxacin, rifampicin, teicoplanin, tigecycline and linezolid did not inhibit biofilm formation on abiotic surfaces. Conclusion: This study demonstrated that the biofilm formation process is complex and may not be related to ica gene carriage. Furthermore, in this study the biofilm formation was increased in the presence of antimicrobial agents.

Short communication: Diversity of species and transmission of antimicrobial resistance among Staphylococcus spp. isolated from goat milk

The increasing production of goat milk and its derivatives is affected by the occurrence of intramammary infections, which are highly associated with the presence of Staphylococcus species, including some with zoonotic potential. Staphylococci in general can exchange mobile genetic elements, a process that may be facilitated by the isolate's capacity of forming biofilms. In this study we identified, to the species level, Staphylococcus isolated from goat milk samples by MALDI-TOF and confirmed the identification by sequencing housekeeping genes (rrs and tuf). Eight species were identified, more than half being either Staphylococcus epidermidis or Staphylococcus lugdunensis. The isolates were shown by pulsed-field gel electrophoresis to be genetically diverse between the studied herds. Resistance to ampicillin and penicillin was widespread, and 2 Staph. epidermidis isolates contained the methicillin-resistance gene mecA. Most of the isolates that were resistant to at least 1 of the 13 antimicrobials tested harbored plasmids, one of which was demonstrated to be conjugative, being transferred from a Staph. epidermidis to a Staphylococcus aureus strain. Biofilm formation was observed in almost every isolate, which may contribute to their capacity of exchanging antimicrobial resistance genes in addition to acting as a physical barrier to the access of drugs. Our results showed that antimicrobial resistance among goat staphylococci may be emerging in a process facilitated by the exchange of mobile genetic elements between the bacteria and the establishment of biofilms, which calls for careful monitoring and more effective control therapies.

Characterization of Staphylococcus spp. strains in milk from buffaloes with mastitis in Brazil: the need to identify to species level to avoid misidentification

ABSTRACT Mastitis is an inflammation of the mammary gland that affects dairy cattle worldwide causing economic losses. Coagulase-negative staphylococci (CNS) are the predominant cause of this type of infection. We have recently showed that coagulase-positive staphylococci could be misidentified. So, the aim of this study was to characterize the Staphylococcus spp. strains initially classified as coagulase-negative Staphylococci, isolated from buffalo with subclinical mastitis. Milk of buffaloes with mastitis in herds was collected and 9 strains were identified as CNS by phenotypic tests. Molecular methodologies latter identified the strains as coagulase-negative Staphylococcus chromogenes (5), coagulase-positive Staphylococcus hyicus (2) and coagulase-positive Staphylococcus aureus (2). Our results strongly support the need to identify the isolates to a species level in order to avoid misidentification and to be aware of the classification using the coagulase test alone.

Diversity of staphylococcal cassette chromosome mec elements in nosocomial multiresistant Staphylococcus haemolyticus isolates

Staphylococcus haemolyticus is the second, most frequently isolated coagulase-negative staphyloccus (CoNS) from patients with hospital-acquired infections, and it is usually resistant to methicillin and other semisynthetic penicillins. The purpose of this study was to characterize staphylococcal cassette chromosome mec (SCCmec) elements and assess the in-vitro activity of antibiotics against 60 S. haemolyticus strains recovered from hospitalized patients. All these strains expressed methicillin resistance and carried a mecA gene. Moreover, all strains possessed a multiresistant phenotype, i.e., exhibited resistance to more than three classes of antibiotics. Eleven strains (18 %) harbored the SCCmec type V, containing ccrC and mec complex C. Three isolates harboring the ccrC gene did not contain a known mec complex. One strain positive for mec complex C was not typeable for ccr. This suggests that ccrC and mec complex C may exist autonomously. Only four strains carried mec complex B, whereas none of the S. haemolyticus harboured mec complex A. A new combination, which is mec complex B-ccrAB ship, was found in S. haemolitycus. The ccrAB ship was also identified in two strains of S. haemolitycus in which the mec gene complex was not identified. The results of the present study indicate that in S. haemolyticus the mec gene complex and the ccr genes are highly divergent. However, ccr sequence analysis does not allow the identification of a new allotype, based on a cut-off value of 85 % identity. The ccr genes in the S. haemolitycus strain showed ≥96 % sequence identity to the ccrAB2 genes.

Transfer of mupirocin resistance from Staphylococcus haemolyticus clinical strains to Staphylococcus aureus through conjugative and mobilizable plasmids

Coagulase-negative staphylococci are thought to act as reservoirs of antibiotic resistance genes that can be transferred to Staphylococcus aureus, thus hindering the combat of this bacterium. In this work, we analyzed the presence of plasmids conferring resistance to the antibiotic mupirocin-widely used to treat and prevent S. aureus infections in hospital environments-in nosocomial S. haemolyticus strains. About 12% of the 75 strains tested were resistant to mupirocin, and this phenotype was correlated with the presence of plasmids. These plasmids were shown to be diverse, being either conjugative or mobilizable, and capable of transferring mupirocin resistance to S. aureus Our findings reinforce that S. haemolyticus, historically and mistakenly considered as a less important pathogen, is a reservoir of resistance genes which can be transferred to other bacteria, such as S. aureus, emphasizing the necessity of more effective strategies to detect and combat this emergent opportunistic pathogen.

Staphylococcus chromogenes, a Coagulase-Negative Staphylococcus Species That Can Clot Plasma

Staphylococcus chromogenes is one of the main coagulase-negative staphylococci isolated from mastitis of dairy cows. We describe S. chromogenes isolates that can clot plasma. Since the main pathogen causing mastitis is coagulase-positive Staphylococcus aureus, the coagulase-positive phenotype of S. chromogenes described here can easily lead to misidentification.

Prevalence of methicillin-resistant Staphylococcus haemolyticus in companion animals: a cross-sectional study

Background

Among coagulase-negative staphylococci, Staphylococcus haemolyticus is the second most frequently isolated species from human blood cultures and has the highest level of antimicrobial resistance. This species has zoonotic character and is prevalent both in humans and animals. Recent studies have indicated that methicillin-resistant S. haemolyticus (MRSH) is one of the most frequent isolated Staphylococcus species among neonates in intensive care units. The aim of this study was to determine the presence of MRSH in different groups of companion animals and to characterize isolates according their antimicrobial resistance.

Methods

Samples (n = 754) were collected from healthy and diseased dogs and cats, female dogs in pure-breed kennels, healthy horses, and kennel owners. Classical microbiological tests along with molecular testing including PCR and 16S rRNA sequencing were performed to identify MRSH. Clonality of the isolates was assessed by Pulsed Field Gel Electrophoresis using the SmaI restriction enzyme. Antimicrobial susceptibility testing was performed using the broth micro-dilution method. Detection of genes encoding antimicrobial resistance was performed by PCR. Statistical analysis was performed using the R Project of Statistical Computing, “R 1.8.1” package.

Results

From a total of 754 samples tested, 12 MRSH isolates were obtained. No MRSH were found in horses and cats. Eleven isolates were obtained from dogs and one from a kennel owner. Ten of the dog isolates were detected in pure-breed kennels. The isolates demonstrated the same clonality only within separate kennels.

The most frequent resistances of MRSH isolates was demonstrated to benzylpenicillin (91.7%), erythromycin (91.7%), gentamicin (75.0%), tetracycline (66.7%), fluoroquinolones (41.7%) and co-trimoxazole (41.7%). One isolate was resistant to streptogramins. All isolates were susceptible to daptomycin, rifampin, linezolid and vancomycin. The clone isolated from the kennel owner and one of the dogs was resistant to beta-lactams, macrolides, gentamicin and tetracycline.

Conclusions

Pure-breed kennels keeping 6 or more females were determined to be a risk factor for the presence of MRSH strains. MRSH isolated from companion animals were frequently resistant to some classes of critically important antimicrobials, although they remain susceptible to antibiotics used exclusively in human medicine.

Genotypic study documents divergence in the pathogenesis of bloodstream infection related central venous catheters in neonates

Objective

To investigate the pathogenesis of bloodstream infection by Staphylococcus epidermidis, using the molecular epidemiology, in high-risk neonates.

Methods

We conducted a prospective study of a cohort of neonates with bloodstream infection using central venous catheters for more than 24 h. “National Healthcare Safety Network” surveillance was conducted. Genotyping was performed by DNA fingerprinting and mecA genes and icaAD were detected by multiplex-PCR.

Results

From April 2006 to April 2008, the incidence of bloodstream infection and central venous catheter-associated bloodstream infection was 15.1 and 13.0/1000 catheter days, respectively, with S. epidermidis accounting for 42.9% of episodes. Molecular analysis was used to document the similarity among six isolates of bloodstream infection by S. epidermidis from cases with positive blood and central venous catheter tip cultures. Fifty percent of neonates had bloodstream infection not identified as definite or probable central venous catheter-related bloodstream infection. Only one case was considered as definite central venous catheter-related bloodstream infection and was extraluminally acquired; the remaining were considered probable central venous catheter-related bloodstream infections, with one probable extraluminally and another probable intraluminally acquired bloodstream infection. Additionally, among mecA+ and icaAD+ samples, one clone (A) was predominant (80%). A polyclonal profile was found among sensitive samples that were not carriers of the icaAD gene.

Conclusions

The majority of infections caused by S. epidermidis in neonates had an unknown origin, although 33.3% appeared to have been acquired intraluminally and extraluminally. We observed a polyclonal profile between sensitive samples and a prevalent clone (A) between resistant samples.

Molecular analysis of Staphylococcus epidermidis strains isolated from community and hospital environments in China

Background

Staphylococcus epidermidis is a common cause of nosocomial infections worldwide. This study analyzed the differences in genetic endowment and clonal lineages with pathogenesis and resistance traits of S. epidermidis isolates collected from community and hospital environments (patients and healthcare staff) of the same ecological niche, time period, and geographical location in China.

Methodology/Principal Findings

Molecular epidemiology and population analysis showed that nasal colonization rates of S. epidermidis in the community of Shanghai area of China and in healthcare personnel were 44.8% (methicillin-resistant S. epidermidis, MRSE: 17.2%) and 61.3% (MRSE: 30.0%), respectively. 86.7% of clinical isolates were MRSE. Among the strains studied, 44 sequence types (STs) were identified with 91.7% belonging to clonal complex 2 (CC2). Only 40.8% isolates from patients were also found in healthy individuals. MRSE-ST2-SCCmecIII was the predominant clone in clinical isolates, almost resistant to all antibiotics tested. Biofilm-related genes IS256 and icaA were detected in majority of the predominant clinical MRSE-ST2 clone with a 40.5% biofilm-positive rate. No ST2 isolate was found in community setting. We found a high prevalence of arginine catabolic mobile element (ACME) (74.1%). The prevalence of ACME-arc and ACME-opp3 clusters was 71.6% and 32.4%, respectively. Methicillin-sensitive S. epidermidis (MSSE) isolates harbored more ACME (83.3%) than MRSE isolates (67.7%), and there was no association between ACME and SCCmec types. An association was found between low-level ACME presence and invasive infections.

Conclusions/Significance

We observed a high level of diversity within S. epidermidis in this study, with CC2 as the dominant clonal complex in both community and hospital settings. Only 40.8% of the isolates from patients were also found in healthy individuals. Contrary to that biofilm formation and multiple antibiotic resistance were associated closely with pathogenicity of S. epidermidis, ACME was more likely to be an indicator for colonization rather than a virulence factor.

Comparative epidemiology of Staphylococcus epidermidis isolates from patients with catheter-related bacteremia and from healthy volunteers

Staphylococcus epidermidis is a major cause of catheter-related bloodstream infections (CRBSIs). Recent studies suggested the existence of well-adapted, highly resistant, hospital-associated S. epidermidis clones. The molecular epidemiology of S. epidermidis in Belgian hospitals and the Belgian community has not been explored yet. We compared a set of 33 S. epidermidis isolates causing CRBSI in hospitalized patients with a set of 33 commensal S. epidermidis isolates. The factors analyzed included resistance to antibiotics and genetic diversity as determined by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and SCCmec typing. Additionally, the presence of virulence-associated mobile genetic elements, the ica operon and the arginine catabolic mobile element (ACME), was assessed and compared against clinical data. CRBSI S. epidermidis isolates were significantly resistant to more antibiotics than commensal S. epidermidis isolates. The two populations studied were very diverse and genetically distinct as only 23% of the 37 PFGE types observed were harbored by both CRBSI and commensal isolates. ACME was found in 76% of S. epidermidis strains, regardless of their origin, while the ica operon was significantly more prevalent in CRBSI isolates than in commensal isolates (P < 0.05). Nine patients presented a clinically severe CRBSI, eight cases of which were due to an ica-positive multiresistant isolate belonging to sequence type 2 (ST2) or ST54. S. epidermidis isolates causing CRBSI were more resistant and more often ica positive than commensal S. epidermidis isolates, which were genetically heterogeneous and susceptible to the majority of antibiotics tested. Clinically severe CRBSIs were due to isolates belonging to two closely related MLST types, ST2 and ST54.

Contamination of X-ray cassettes with methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus haemolyticus in a radiology department

Background

We performed surveillance cultures of the surfaces of X-ray cassettes to assess contamination with methicillin-resistant Staphylococcus aureus (MRSA).

Methods

The surfaces of 37 X-ray cassettes stored in a radiology department were cultured using mannitol salt agar containing 6 µg/mL oxacillin. Suspected methicillin-resistant staphylococcal colonies were isolated and identified by biochemical testing. Pulsed-field gel electrophoresis (PFGE) analysis was performed to determine the clonal relationships of the contaminants.

Results

Six X-ray cassettes (16.2%) were contaminated with MRSA. During the isolation procedure, we also detected 19 X-ray cassettes (51.4%) contaminated with methicillin-resistant Staphylococcus haemolyticus (MRSH), identified as yellow colonies resembling MRSA on mannitol salt agar. PFGE analysis of the MRSA and MRSH isolates revealed that most isolates of each organism were identical or closely related to each other, suggesting a common source of contamination.

Conclusions

X-ray cassettes, which are commonly in direct contact with patients, were contaminated with MRSA and MRSH. In hospital environments, contaminated X-ray cassettes may serve as fomites for methicillin-resistant staphylococci.

Characteristics related to antimicrobial resistance and biofilm formation of widespread methicillin-resistant Staphylococcus epidermidis ST2 and ST23 lineages in Rio de Janeiro hospitals, Brazil

Staphylococcus epidermidis is a leading cause of hospital-acquired infections, mostly associated with the use of medical devices in seriously ill or immunocompromised patients. Currently, the characteristics of methicillin-resistant S. epidermidis (MRSE) isolates from Rio de Janeiro hospitals are unknown. In this study, staphylococcal chromosomal cassette mec (SCCmec) types, antimicrobial susceptibility profiles, biofilm formation genes, and multilocus sequence types (MLST) were investigated in 35 MRSE clinical isolates. The collection of isolates was previously well characterized by pulsed-field gel electrophoresis (PFGE) into 2 main genotypes (A and B, 22 isolates) and 10 sporadic genotypes (13 isolates). MLST revealed a total of 8 different sequence types (STs), but ST2 and ST23, which were icaAB-positive, represented the majority (71.4%) of MRSE isolates tested. Almost all isolates (91.4%) belonged to clonal complex 2. SCCmec types III and IV were identified among 71.4% of the isolates, while the remaining was nontypeable. The predominant MRSE genotypes were defined as SCCmec type III/ST2 (PFGE type A) and SCCmec type IV/ST23 (PFGE type B) isolates, which were both associated with high antimicrobial resistance and presence of biofilm-related genes.

Genotypic Characterization of Coagulase-negative Staphylococci Isolated from Sheep Milk in Slovakia

Hitherto very few reports are available presenting identification and molecular characterization of the coagulase negative staphylococci (CNS) from sheep milk in the subclinical stage of mastitis. Furthermore, very scanty data are available on the epidemiological status of CNS in different Slovak provinces. Milk samples from 54 sheep farms located in eastern Slovak region were screened. A total 240 CNS were identified with series of biochemical testes (STAPH-API) and subjected further for genotyping with the help of pulse field gel electrophoresis (PFGE). The most frequently occurring CNS species according the biochemical characterization were:S. epidermidis(36.3 %),S. caprae(21.3 %),S. hominis(6.6 %),S. chromogenes(6.3 %),S. xylosus(5.8 %),S. warneri(5.0 %) andS. capitis(4.6 %). Further PFGE-based characterization of these isolates revealed six pulsotypes of theS. epidermidis, two ofS. caprae, three ofS. chromogenes, nine ofS. hominis, five ofS. capitisand seven ofS. xylosus. These results contribute to knowledge of the epidemiological situation of the CNS from the subclinical form of mastitis in Slovakia.

Hospital strain colonization by Staphylococcus epidermidis

The skin and mucous membranes of healthy subjects are colonized by strains of Staphylococcus epidermidis showing a high diversity of genomic DNA polymorphisms. Prolonged hospitalization and the use of invasive procedures promote changes in the microbiota with subsequent colonization by hospital strains. We report here a patient with prolonged hospitalization due to chronic pancreatitis who was treated with multiple antibiotics, invasive procedures and abdominal surgery. We studied the dynamics of skin colonization by S. epidermidis leading to the development of catheter-related infections and compared the genotypic profile of clinical and microbiota strains by pulsed field gel electrophoresis. During hospitalization, the normal S. epidermidis skin microbiota exhibiting a polymorphic genomic DNA profile was replaced with a hospital-acquired biofilm-producer S. epidermidis strain that subsequently caused repetitive catheter-related infections.

Partial atlE sequencing of Staphylococcus epidermidis strains from prosthetic joint infections

Partial atlE sequencing (atlE nucleotides 2782 to 3114 [atlE(2782-3114)]) was performed in 41 Staphylococcus epidermidis isolates from prosthetic joint infections (PJIs) and 44 isolates from skin as controls. The atlE(2782-3114) allele 1 (type strain sequence) was significantly more frequent in PJI strains (38/41 versus 29/44 in controls; P = 0.0023). Most PJI strains were positive for mecA, icaA/icaD, and IS256, and most belonged to the sequence type 27 subgroup, suggesting the involvement of few related clones.

Multiplex PCR assay to identify methicillin-resistant Staphylococcus haemolyticus

Staphylococcus haemolyticus is the most frequently coagulase-negative Staphylococcus species associated with antimicrobial resistance isolated from nosocomial infections. We developed an accurate and simple multiplex PCR assay to identify methicillin-resistant S. haemolyticus (MRSH) isolates. We designed species-specific primers of the mvaA gene that encodes a 3-hydroxy-3-methylglutaryl coenzyme A involved in the mevalonate pathway of the microorganism. Simultaneously, mecA gene primers of methicillin resistance were also used. The PCR assay was established using 16 strains of different reference Staphylococcus species and validated with a collection of 147 clinical staphylococcal isolates that were also phenotypically characterized. Reliable results for the detection of MRSH isolates were obtained for 100% of the strains evaluated, showing that this PCR assay can be used for the routine microbiology laboratories. This is the first report using species-specific multiplex PCR to detect a single segment of S. haemolyticus associated with a segment of mecA gene.

Typing of Staphylococcus epidermidis clinical strains by a selected panel of Brazilian killer yeasts

Discrimination of multi-resistant microorganisms in small clinical microbiology laboratories is frequently based on the biologic profile (biotype) of phenotypic markers, such as antimicrobial susceptibility patterns (antibiograms) and serologic or enzymatic typing, but few use indicative microorganisms. The purpose of this study was to evaluate the power of a panel of selected killer yeasts for differentiating and discriminating clinical isolates of Staphylococcus epidermidis from two care hospitals and clinical microbiology laboratories from the South of Brazil. The short panel of eleven killer yeasts was capable of discriminating 100% of the sensitive strains of S. epidermidis using quantitative data matrix (QDM) and differentiating them from strains of coagulase-positive Staphylococcus. Therefore, this phenotypic methodology proved to be valid as a discriminatory tool when applied to these clinical bacteria strains, besides being simple and feasible for routine use even in microbiological laboratories with minimal resources.

Comparison of molecular typing methods for characterization of Staphylococcus epidermidis: proposal for clone definition

In the present study we give some direction on the selection of the most appropriate typing method(s) to be used for the characterization of Staphylococcus epidermidis, in view of the most recent findings on the evolution, population structure, and epidemiology of this species. In order to achieve this aim, quantitative assessment of the correlation of the results of three typing methods--pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and staphylococcal chromosomal cassette mec (SCCmec) typing, which target different regions of the chromosome that evolve at different rates--was performed. In order to evaluate the discriminatory ability and the strength and direction of the correlation of the different typing methods, Simpson's index of diversity (SID), the adjusted Rand coefficient (AR), and the Wallace coefficient (W) were calculated. PFGE was the most discriminatory method (SID = 99%), followed by MLST (SID = 90%) and SCCmec typing (SID = 75%). The values of AR and W (0.10 < AR < 0.30; 0.50 < W < 0.75) indicated that the partition of the same isolate collection by PFGE, MLST, and SCCmec typing provided results that had only a poor correlation with each other. However, the information provided by the combination of PFGE and SCCmec enabled the prediction of the results obtained by MLST at the level of the clonal complex with a high degree of precision (W > 0.90). We propose that clones of S. epidermidis be defined by the combination of the PFGE type followed by the SCCmec type, which provides reliable information on the short-term epidemiology and the ability to predict with consistency long-term clonal evolution.

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.

Bacteriocins as alternative agents for control of multiresistant staphylococcal strains

AIMS

To investigate the activity of seven staphylococcins, bacteriocins produced by staphylococci, against multiresistant Staphylococcus aureus and coagulase-negative staphylococci (CNS) involved in human infections.

METHODS AND RESULTS

Four bacteriocins produced by Staph. epidermidis (Pep5, epidermin, epilancin K7 and epicidin 280) and three produced by Staph. aureus (aureocins A70, A53 and 215FN) were tested. Sixteen Staph. aureus strains, including a representative strain of the endemic Brazilian methicillin-resistant clone (MRSA), and 57 CNS strains were used as indicators. Among the staphylococcins used, Pep5 was able to inhibit 77.2% of the CNS strains and 87.5% of the Staph. aureus strains tested, including the Brazilian MRSA endemic clone, responsible for a large number of hospital-acquired infections in Brazil. On the other hand, aureocin A53 and epidermin presented a high antagonistic activity only against the Staph. aureus strains, being able to inhibit, respectively, 87.5% and 81.3% of them, including also the Brazilian MRSA endemic clone. The remaining bacteriocins inhibited only a low percentage of the nosocomial staphylococcal strains tested.

CONCLUSIONS

Aureocin A53 and epidermin have potential applications against MRSA, whereas Pep5 seems to be an attractive agent against both MRSA and CNS, including mupirocin-resistant strains and the Brazilian endemic clone of MRSA, which is also found disseminated in other countries.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacteriocins may represent alternative agents to control important nosocomial pathogens.

Tabebuia avellanedae naphthoquinones: activity against methicillin-resistant staphylococcal strains, cytotoxic activity and in vivo dermal irritability analysis

Background

Methicillin-resistant Staphylococcus aureus (MRSA) and coagulase-negative staphylococcus infections are a worldwide concern. Currently, these isolates have also shown resistance to vancomycin, the last therapy used in these cases. It has been observed that quinones and other related compounds exhibit antibacterial activity. This study evaluated the antibacterial activity, toxicity and in vivo dermal irritability of lapachol extracted from Tabebuia avellanedae and derivatives against methicillin-resistant staphylococcal isolates. In addition, its mechanism of action was also analyzed.

Methods

The compounds β-lapachone, 3-hydroxy β N lapachone and α-lapachone were tested to determine the MIC values against methicillin-resistant S. aureus, S. epidermidis and S. haemolyticus strains, being the two last ones hetero-resistant to vancomycin. Experiments of protein synthesis analysis to investigate the naphthoquinones action were assessed. In vitro toxicity to eukaryotic BSC-40 African Green Monkey Kidney cell cultures and in vivo primary dermal irritability in healthy rabbits were also performed.

Results

The compounds tested showed antibacterial activity (MICs of 8, 4/8 and 64/128 μg/mL to β-lapachone, 3-hydroxy β N lapachone and α-lapachone, respectively), but no bactericidal activity was observed (MBC > 512 μg/mL for all compounds). Although it has been observed toxic effect in eukaryotic cells, the compounds were shown to be atoxic when applied as topic preparations in healthy rabbits. No inhibition of proteins synthesis was observed.

Conclusion

Our results suggest that quinones could be used in topic preparations against wound infections caused by staphylococci, after major investigation of the pharmacological properties of the compounds. Studies about the use of these compounds on tumoral cells could be carried on, due to their effect in eukaryotic cells metabolism.

Genetic Diversity among Methicillin-ResistantStaphylococcus epidermidis(MRSE)

We selected 106 methicillin-resistant Staphylococcus epidermidis (MRSE) and 22 methicillin-susceptible S. epidermidis (MSSE) hospital isolates--each with a different PFGE pattern--for more detailed documentation of genetic diversity. The 106 MRSE isolates showed extensive variation in the SmaI DNA fragments hybridizing with the DNA probe for mecA, the molecular size of which varied from as low as 20 kb up to over 500 kb. Parallel variation was also observed in the size of DNA fragments hybridizing with the chromosomal genes orfX and gyrA, and this was also observed in MSSE isolates. In contrast, SmaI fragments associated with the housekeeping genes murE and aroE, both located distantly from orfX, showed little size variation. Typing for the mec complex and ccr identified 10 different SCCmec structures and a large number of strains (21 isolates) that were non-typeable. The majority of strains studied (36%) carried a SCCmec type IV-like structure, including strains with non-related PFGE profiles. On the other hand, closely related strains often carried different types of SCCmec. The findings indicate that the acquisition and/or loss of mobile genetic elements, including various structural types of SCCmec, may occur frequently in the vicinity of the orfX gene on the S. epidermidis chromosome.