Detection of an archaic clone of Staphylococcus aureus with low-level resistance to methicillin in a pediatric hospital in Portugal and in international samples: relics of a formerly widely disseminated strain?

ST105 Lineage of MRSA: An Emerging Implication for Bloodstream Infection in the American and European Continents

Sequence-type 5 (ST5) of methicillin-resistant Staphylococcus aureus (MRSA), harboring the staphylococcal chromosomal cassette mec type IV (SCCmecIV), was first detected in Portugal. It emerged as a significant cause of healthcare-associated (HA) infection in pediatric units and was hence named the pediatric clone. Another ST5 lineage, which carries SCCmecII, also prevailed in the USA and Japan for multiple years. More recently, another MRSA lineage, ST105-SCCmecII, part of the evolution of clonal complex 5 (CC5) MRSA, has emerged as the cause of hospital-acquired bloodstream infection outbreaks in countries including Portugal, the USA, and Brazil. This article reviews studies on the epidemiology and evolution of these newly emerging pathogens. To this end, a search of PUBMED from inception to 2024 was performed to find articles reporting the occurrence of ST105 MRSA in epidemiologic studies. A second search was performed to find studies on MRSA, CC5, ST5, and SCCmecII. A search of PUBMED from 1999 to 2024 was also performed to identify studies on the genomics and evolution of ST5, CC5, and ST105 MRSA. Further studies were identified by analyzing the references of the previously selected articles from PUBMED. Most articles on ST105 MRSA were included in this review. Only articles written in English were included. Furthermore, only studies that used a reliable genotyping method (e.g., whole genome sequencing, or MLST) to classify the CC5 lineages were selected. The quality and selection of articles were based on the consensus assessment of the three authors in independent evaluations. In conclusion, ST105-SCCmecII is an emerging MRSA in several countries, being the second/third most important CC5 lineage, with a relatively high frequency in bloodstream infections. Of concern is the increased mortality from BSI in patients older than 15 years and the higher prevalence of ST105-SCCmecII in the blood of patients older than 60 years reported in some studies.

Virulence attributes of successful methicillin-resistant Staphylococcus aureus lineages

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of severe and often fatal infections. MRSA epidemics have occurred in waves, whereby a previously successful lineage has been replaced by a more fit and better adapted lineage. Selection pressures in both hospital and community settings are not uniform across the globe, which has resulted in geographically distinct epidemiology. This review focuses on the mechanisms that trigger the establishment and maintenance of current, dominant MRSA lineages across the globe. While the important role of antibiotic resistance will be mentioned throughout, factors which influence the capacity of S. aureus to colonize and cause disease within a host will be the primary focus of this review. We show that while MRSA possesses a diverse arsenal of toxins including alpha-toxin, the success of a lineage involves more than just producing toxins that damage the host. Success is often attributed to the acquisition or loss of genetic elements involved in colonization and niche adaptation such as the arginine catabolic mobile element, as well as the activity of regulatory systems, and shift metabolism accordingly (e.g., the accessory genome regulator, agr). Understanding exactly how specific MRSA clones cause prolonged epidemics may reveal targets for therapies, whereby both core (e.g., the alpha toxin) and acquired virulence factors (e.g., the Panton-Valentine leukocidin) may be nullified using anti-virulence strategies.

Molecular characterization and antimicrobial resistance of nasal Staphylococcus aureus in the community of Kabul

OBJECTIVES

This study aimed to investigate the prevalence and molecular characteristics of community methicillin-resistant Staphylococcus aureus (MRSA) nasal carriage among students at Kabul University.

METHODS

Nasal swabs were collected from anterior nares of 150 healthy non-medical students at Kabul University. Antimicrobial susceptibility testing was performed on all S. aureus isolates, and all detected MRSA isolates were then confirmed by mecA/mecC polymerase chain reaction and characterized using DNA microarray.

RESULTS

A total of 50 S. aureus strains were isolated from the anterior nares of the 150 participants. The prevalence of S. aureus and MRSA nasal carriage among Kabul students was 33.3% and 12.7%, respectively. Seven (36.8%) MRSA isolates and 8 (25.8%) methicillin-susceptible S. aureus (MSSA) isolates were multidrug-resistant (i.e. resistant to at least three different antimicrobials tested). All MRSA isolates (n = 19) were susceptible to linezolid, rifampicin, and fusidic acid. Seven MRSA clones, belonging to four clonal complexes (CCs), were identified. The most commonly identified clone was CC22-MRSA-IV TSST-1-positive, which accounted for 63.2% (12/19) of MRSA isolates. SCCmec typing showed that most MRSA strains harboured SCCmec type IV (94.7%). Thirteen (68.4%) MRSA isolates carried the TSST-1 and 5 (26.3%) PVL genes.

CONCLUSION

Our findings revealed the relatively high prevalence of MRSA nasal carriers in the community in Kabul, with the predominance of the CC22-MRSA-IV TSST-1-positive clone and frequent multidrug resistance among these isolates.

High frequency of increased triclosan MIC among CC5 MRSA and risk of misclassification of the SCCmec into types

BACKGROUND

Typing of staphylococcal cassette chromosome mec (SCCmec) elements is commonly used for studies on the molecular epidemiology of MRSA.

OBJECTIVES

To perform an investigation centred on uncovering the reasons for misclassification of MRSA clonal complex 5 (CC5) SCCmec type II clinical isolates in our laboratory.

METHODS

MRSA isolates from CC5 were subjected to WGS and SCCmec typing.

RESULTS

This investigation led to the discovery that the classification failure was due to an insertion of IS1272 carrying the fabI gene on a transposable element (TnSha1) that confers increased MIC to the biocide triclosan. Genomic analysis revealed that fabI was present in 25% of the CC5 MRSA isolates sampled. The frequency of TnSha1 in our collection was much higher than that observed among publicly available genomes (0.8%; n = 24/3142 CC5 genomes). Phylogenetic analyses revealed that genomes in different CC5 clades carry TnSha1 inserted in different integration sites, suggesting that this transposon has entered CC5 MRSA genomes on multiple occasions. In at least two genotypes, ST5-SCCmecII-t539 and ST5-SCCmecII-t2666, TnSha1 seems to have entered prior to their divergence.

CONCLUSIONS

Our work highlights an important misclassification problem of SCCmecII in isolates harbouring TnSha1 when Boye's method is used for typing, which could have important implications for molecular epidemiology of MRSA. The importance of increased-MIC phenotype is still a matter of controversy that deserves more study given the widespread use of triclosan in many countries. Our results suggest expanding prevalence that may indicate strong selection for this phenotype.

A fusidic acid-resistant (PVL+) clone is associated with the increase in methicillin-resistant Staphylococcus aureus in New Caledonia

OBJECTIVES

Since 2014, Staphylococcus aureus methicillin resistance is rapidly increasing in New Caledonia and is associated with potential serious clinical repercussions. In the present study, we investigated the epidemiology of Methicillin-Resistant S. aureus (MRSA) in New Caledonia and the possible emergence of a particular clonal strain.

METHODS

An overview of the distribution of MRSA in New Caledonia in 2019 is presented. We collected and analysed 171 clinical MRSA isolates from New Caledonia medical laboratories during August and September 2019. Among this collection, 49 representative isolates were analyzed by the French National Reference Center for Staphylococci using StaphyType DNA microarray allowing genetic characterization of the isolates.

RESULTS

Among the 1144 S. aureus isolated over the year 2019, 442 isolates (39%) were resistant to methicillin and 62% of these isolates were resistant to fusidic acid (FA). During the inclusion period, FA resistance rate was similar (60%). Genetic characterization evidenced CC6 as the predominant clonal complex (70%) with 26 isolates (53%) identified as CC6-MRSA-[IV+fus] (PVL+).

CONCLUSIONS

These findings demonstrated a low diversity of MRSA in New Caledonia with the dominance of a clonal complex not reported previously. The frequent fusidic acid (FA) resistance in MRSA was associated with a high prevalence of fusC, suggesting that FA misuse contributed to driving the selection of this clone. Our findings suggest the recommendation to stop the topical use of FA to control the emergence of this severe MRSA clone and decrease the rate of MRSA in New Caledonia.

Exebacase Is Active In Vitro in Pulmonary Surfactant and Is Efficacious Alone and Synergistic with Daptomycin in a Mouse Model of Lethal Staphylococcus aureus Lung Infection

Exebacase (CF-301) is a novel antistaphylococcal lysin (cell wall hydrolase) in phase 3 of clinical development for the treatment of Staphylococcus aureus bacteremia, including right-sided endocarditis, used in addition to standard-of-care antibiotics. In the current study, the potential for exebacase to treat S. aureus pneumonia was explored in vitro using bovine pulmonary surfactant (Survanta) and in vivo using a lethal murine pneumonia model. Exebacase was active against a set of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains, with an MIC₉₀ of 2 μg/ml (n = 18 strains), in the presence of a surfactant concentration (7.5%) inhibitory to the antistaphylococcal antibiotic daptomycin, which is inactive in pulmonary environments due to specific inhibition by surfactant. In a rigorous test of the ability of exebacase to synergize with antistaphylococcal antibiotics, exebacase synergized with daptomycin in the presence of surfactant in vitro, resulting in daptomycin MIC reductions of up to 64-fold against 9 MRSA and 9 MSSA strains. Exebacase was also observed to facilitate the binding of daptomycin to S. aureus and the elimination of biofilm-like structures formed in the presence of surfactant. Exebacase (5 mg/kg of body weight 1 time every 24 h [q24h], administered intravenously for 3 days) was efficacious in a murine model of staphylococcal pneumonia, resulting in 50% survival, compared to 0% survival with the vehicle control; exebacase in addition to daptomycin (50 mg/kg q24h for 3 days) resulted in 70% survival, compared to 0% survival in the daptomycin-alone control group. Overall, exebacase is active in pulmonary environments and may be appropriate for development as a treatment for staphylococcal pneumonia.

Multidrug-Resistant Methicillin-Resistant Staphylococcus aureus Associated with Bacteremia and Monocyte Evasion, Rio de Janeiro, Brazil

We typed 600 methicillin-resistant Staphylococcus aureus (MRSA) isolates collected in 51 hospitals in the Rio de Janeiro, Brazil, metropolitan area during 2014-2017. We found that multiple new clonal complex (CC) 5 sequence types had replaced previously dominant MRSA lineages in hospitals. Whole-genome analysis of 208 isolates revealed an emerging sublineage of multidrug-resistant MRSA, sequence type 105, staphylococcal cassette chromosome mec II, spa t002, which we designated the Rio de Janeiro (RdJ) clone. Using molecular clock analysis, we hypothesized that this lineage began to expand in the Rio de Janeiro metropolitan area in 2009. Multivariate analysis supported an association between bloodstream infections and the CC5 lineage that includes the RdJ clone. Compared with other closely related isolates, representative isolates of the RdJ clone more effectively evaded immune function related to monocytic cells, as evidenced by decreased phagocytosis rate and increased numbers of viable unphagocytosed (free) bacteria after in vitro exposure to monocytes.

Totally implantable venous access port infection caused by Staphylococcus pseudintermedius: Possible transmission from a companion dog to a human

S. pseudintermedius, recently identified as a novel Staphylococcus, causes a rare zoonotic infection that can be transmitted from dogs to humans. A 41-year-old man with atopic dermatitis receiving central parenteral nutrition through a totally implantable venous access port (TIVAP) after surgery for pseudomyxoma peritonei visited our outpatient clinic with a 2-day history of fever. The four strains isolated from the blood cultures from the TIVAP, dog's mouth, dog's nose, and dog's skin were all identified as S. pseudintermedius by partial heat shock protein (hsp60) gene sequencing. Initially, antibiotic-lock therapy with vancomycin (5 mg/mL in normal saline) through the catheter was administered concurrently with intravenous therapy. However, 52 days after the first discharge, he came back with a recurrent TIVAP infection with S. pseudintermedius bacteremia. He was successfully treated with intravenous antibiotic therapy after port removal and had no recurrence for 6 months without contact with the dog. The isolated strains were resistant to fluoroquinolone, which was consistent with trends in veterinary medicine in Japan. This case report raises awareness on S. pseudintermedius infections transmitted from domesticated dogs to patients with any implantable device, and the emerging resistance of S. pseudintermedius to current antibiotics.

Development and Evaluation of a Sensitive Bacteriophage-Based MRSA Diagnostic Screen

Engineered luciferase reporter bacteriophages provide specific, sensitive, rapid and low-cost detection of target bacteria and address growing diagnostic needs in multiple industries. Detection of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization and antibiotic susceptibility play a critical supportive role in preventing hospital-acquired infections and facilitating antibiotic stewardship. We describe the development and evaluation of a novel phage-based MRSA diagnostic screen for nasal swab specimens. The screen utilizes two luciferase reporter phages capable of recognizing genetically-diverse Staphylococcus aureus. The beta-lactam antibiotic cefoxitin is included to differentiate between resistant (MRSA) and susceptible organisms. The screen positively identified 97.7% of 390 clinical MRSA isolates at low bacterial concentrations. At higher inoculums, 93.5% of 123 clinical non-MRSA Staphylococcus aureus yielded appropriate negative results. Although cross-reactivity of the phage cocktail was observed with other staphylococcal and bacillus species, these false positives were absent under selective conditions. MRSA remained detectable in the presence of 38 distinct competing species and was accurately identified in 100% of 40 spiked nasal specimens. Thus, this six-hour screen sensitively detected MRSA both in vitro and in human nasal matrix.

Molecular Characterization of Staphylococcus aureus Isolates Associated with Nasal Colonization and Environmental Contamination in Academic Dental Clinics

Aim: To determine the genetic makeup of methicillin-sensitive/methicillin-resistant Staphylococcus aureus (MSSA/MRSA) from nasal colonization and environmental contamination in dental clinics. Materials and Methods: Nasal swabs from students and health care workers and environmental swabs were obtained at two academic dental clinics in the United Arab Emirates. The StaphyType DNA microarray-based assay was used for molecular characterization. Results: Forty-eight S. aureus isolates were identified phenotypically (nasal: n = 43; environmental: n = 5), but 6 of these were assigned to S. argenteus by genotyping. These were CC_(argenteus)2596, CC_(arg)2250-MSSA, CC_(arg)2250-MSSA-(Panton Valentine leukocidin [PVL]+) (n = 2), and CC_(arg)2198-MSSA (n = 2). MRSA nasal colonization rate was 5.4% (n/N = 8/146) with the following strain affiliations: CC5-MRSA-[IV+fus+ccrAB], "Maltese Clone"; CC6-MRSA-IV, "WA MRSA-51"; CC22-MRSA-IV (PVL+/tst+); CC22-MRSA-[IV+fus+ccrAA/(C)]; and two each of CC5-MRSA-[VI+fus] and CC97-MRSA-[V/VT+fus]. The SCC-borne fusidic acid resistance (fusC) gene was detected in MRSA (n = 5) and MSSA (n = 1). Some MSSA strains, CC1-MSSA-[fus+ccrAB1] and ST1278-MSSA-[ccrA1], harbored recombinase genes. A CC30-MSSA harbored ACME locus/arc-genes, while ST1278-MSSA-[ccrA1] had an ACME-III element. Enterotoxin genes were commonly carried, but tst-1 gene was found in only CC22, CC30, and CC34 strains, while pvl genes were identified in CC_(arg)2250 and CC22-MRSA-IV. Of the 51 noncoagulase staphylococci (CoNS) identified, 18 were mecA positive. Conclusion: The findings demonstrate the first report of rare strains (ST1278 MSSA, CC_(arg)2198, CC_(arg)2596, and PVL+CC_(arg)2250) in our region. Detection of MSSA with recombinase genes and ACME loci alongside mecA-positive CoNS is of clinical significance as this could provide a milieu for acquisition and transfer of SCC-elements, either with different ACME types, with fusC or the mecA gene resulting in conversion of MSSA into MRSA.

Emergence of community-acquired methicillin-resistant Staphylococcus aureus EMRSA-15 clone as the predominant cause of diabetic foot ulcer infections in Portugal

Methicillin-resistant Staphylococcus aureus (MRSA) are often found in infected diabetic foot ulcers, in which the prevalence may reach 40%. These complications are one of the main causes of morbidity in diabetic patients. The objectives of this study were to investigate the prevalence and antimicrobial resistance of MRSA strains in infected diabetic foot ulcers and to characterize their genetic lineages. Samples collected from 42 type 2 diabetic patients, presenting infected foot ulcers, were seeded onto ORSAB plates with 2 mg/L of oxacillin for MRSA isolation. Susceptibility to 14 antimicrobial agents was tested by the Kirby-Bauer disk diffusion method. The presence of resistance genes, virulence factors, and the immune evasion cluster system was studied by PCR. All isolates were characterized by MLST, accessory gene regulator (agr), spa, and staphylococcal chromosomal cassette mec (SCCmec) typing. Twenty-five MRSA strains were isolated. All isolates showed resistance to penicillin and cefoxitin. Sixteen isolates showed phenotypic resistance to erythromycin being 7 co-resistant to clindamycin. Resistance to trimethoprim-sulfamethoxazole was found in 2 isolates harboring the dfrA and dfrG genes. The IEC genes were detected in 80% of isolates, 16 of which were ascribed to IEC-type B. Isolates were assigned to 12 different spa types. The MLST analysis grouped the isolates into 7 sequence types being the majority (68%) ascribed to SCCmec type IV. In this study, there was a high prevalence of the EMRSA-15 clone presenting multiple resistances in diabetic foot ulcers making these infections complicated to treat leading to a higher morbidity and mortality in diabetic patients.

Emergence of novel methicillin-resistant Staphylococcus aureus strains in a tertiary care facility in Riyadh, Saudi Arabia

PURPOSE

There is a need for continuous surveillance of methicillin-resistant Staphylococcus aureus (MRSA) to identify emergence of new strains. We hypothesize that MRSA strains are evolving with ongoing acquisition of SCCmec elements. This study was carried out to evaluate the evolution of MRSA at a tertiary care facility in Saudi Arabia.

METHODS

MRSA isolates associated with invasive clinical infection, which were identified in 2017 at the microbiology laboratory, King Khalid University Hospital (KKUH) in Riyadh, Saudi Arabia, were studied. The molecular characterization of isolates was carried out using StaphyType DNA microarray (Alere Technologies GmbH/Abbott, Jena, Germany).

RESULTS

The 125 MRSA isolates studied belonged to 18 clonal complexes (CC) which were distributed into 32 strain assignments. The predominant CC were CC5 (n=30), CC6 (n=17), CC80 (n=13), CC22 (n=12), CC361 (n=12). The findings demonstrated the first identification of CC152, CC361 and CC1153 MRSA as well as ST5-MRSA-[I+fus], "Geraldine Clone", CC6-MRSA-IV (PVL+) and CC88-MRSA-V (PVL+), WA MRSA-117 in Saudi Arabia. Four novel variants were identified: CC5-MRSA-[VI+fus+tirS], CC22-MRSA-[V/VT+fus](PVL+), CC152-MRSA-[V+fus](PVL+) and CC361-MRSA-[VT+fus]. Fifty-four isolates (n/N=54/125; 43.2%) including the novel strains carried the Q6GD50 SCCfusC gene while the Panton-Valentine leukocidin genes were present in 30.4% (n/N=38/125).

CONCLUSION

The findings demonstrate an expanding MRSA repertoire in our setting including emergence of previously unreported clonal complexes and novel strains. The high carriage of fusC gene suggests a role for fusidic acid misuse in driving the evolution of the MRSA genome and underscores the need for increased monitoring of antibiotic use.

Novel staphylococcal cassette chromosome composite island (SCC-CI) with a new subtype of SCCmecVI cassette found in ST5 methicillin-resistant Staphylococcus aureus in France

An emergent kanamycin-susceptible ST5 methicillin-resistant Staphylococcus aureus (MRSA) lineage has been identified in France. Whole-genome sequencing revealed a 40-kb staphylococcal cassette chromosome (SCC) composite island with a mosaic structure including three SCC elements: a ΨSCC_cop/ars, a SCC_Lim88A with a ccrC recombinase, and a novel subtype of SCCmec type VI (VIb). This mosaic structure suggests a high recombination rate of SCC elements from distinct staphylococci species.

Dissemination of the Methicillin-resistant Staphylococcus aureus Pediatric Clone (ST5-T002-IV-PVL+) as a Major Cause of Community-associated Staphylococcal Infections in Bedouin Children, Southern Israel

INTRODUCTION

Pediatric community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are emerging worldwide. High CA-MRSA carriage rates were previously described in healthy Bedouin children. We assessed demographic, clinical and molecular characteristics of pediatric MRSA infections in southern Israel.

METHODS

The Soroka University Medical Center laboratory serves the entire population of southern Israel, divided into 2 ethnic groups, Bedouins and Jews. All in-hospital MRSA clinical isolates from children 0 to 18 years old obtained in 2016 were included. Health care-associated and community-associated infections were defined according to the Centers for Disease Control and Prevention case definition. All isolates were evaluated for staphylococcal cassette chromosome, Panton-Valentine leukocidin, S. aureus protein A type, pulsed field gel electrophoresis and antimicrobial susceptibility testing.

RESULTS

Overall, 95 MRSA isolates (18% of all S. aureus), with 25 different MRSA strains, were identified. Twenty-eight isolates (29.5% of MRSA) belonged to the pediatric clone, rarely observed in Israel, staphylococcal cassette chromosome IV, Panton-Valentine leukocidin positive, S. aureus protein A type 002. All isolates demonstrated identical pulsed-field-gel-electrophoresis fingerprints. Eighty-two percent of infections caused by this clone were community-acquired, mainly observed in young Bedouin children, causing skin and soft-tissue infections. The new clone infection characteristics were similar to those of other CA-MRSA. All isolates of the pediatric clone were susceptible to trimethoprim/sulfamethoxazole, ciprofloxacin, gentamicin, tetracycline, rifampicin and vancomycin; 17.8% were nonsusceptible to erythromycin and clindamycin.

CONCLUSION

The pediatric CA-MRSA clone, previously described only in sporadic cases in Israel, is emerging among healthy, young Bedouin children, typically causing skin and soft-tissue infections. Isolates are susceptible to a variety of non-beta-lactam antibiotics.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Frequencies and Antimicrobial Susceptibility of Methicillin-Resistant Staphylococcus aureus (MRSA) Isolated from Horses in South Korea

Background:

Methicillin-ResistantStaphylococcus Aureus(MRSA) has become one of the most prevalent pathogens in animals and humans giving rise to various diseases. MRSA infection in horses and transmission between horses and humans have dramatically increased recently.

Objective:

This study investigated the isolation frequency and antimicrobial susceptibility of MRSA isolated from horses in South Korea.

Method:

Screening of the MRSA isolates was conducted by conventional methods and multiplex Polymerase Chain Reaction (PCR). Minimum Inhibitory Concentration (MIC) of oxacillin was determined by the broth microdilution test method. Overall antibiogram was obtained by disk diffusion susceptibility test. All antimicrobial tests were conducted in accordance with the Clinical and Laboratory Standards Institute (CLSI) guidelines.

Results:

S. aureuswas isolated from 116 (19.46%) of 596 horses tested. Of the 116S. aureusisolates, 52 (8.72%) strains were identified as MRSA by multiplex PCR. Among the 52 MRSA strains, 24 (46.15%) and 28 (53.85%) were oxacillin-resistant MRSA (OR-MRSA) and oxacillin-susceptible MRSA (OS-MRSA), respectively. OR-MRSA showed the highest susceptibility to florfenicol (100.00%), followed by doxycycline (95.83%), cefepime (91.67%), tetracycline (75.00%), and trimethoprim/sulphamethoxazole (70.83%). OS-MRSA showed the highest susceptibility to florfenicol (100.00%) and trimethoprim/sulphamethoxazole (100.00%), followed by cefoxitin (96.43%), ciprofloxacin (92.86%), enrofloxacin (92.86%), lincomycin + spectinomycin (89.29%), cefuroxime (89.29%), and cefonicid (89.29%).

Conclusion:

This study may facilitate treatment and prevention of MRSA infections and further benefit not only horses, but also people related with horse farms, horse riding clubs and animal hospitals.

Frequent MRSA nasal colonization among hospitalized children and their parents in Angola and São Tomé and Príncipe

BACKGROUND

The prevalence of nosocomial meticillin-resistant Staphylococcus aureus (MRSA) was previously estimated as 23% in a paediatric hospital in Luanda, Angola and 18% in a general hospital in São Tomé and Príncipe.

AIM

To evaluate the prevalence of S. aureus/MRSA colonization among hospitalized children and their parents at two hospitals in Angola and São Tomé and Príncipe.

METHODS

In 2017, 127 hospitalized children and 129 of their parents had nasal swabs for S. aureus/MRSA carriage in the two countries. The isolates were tested for the presence of the mecA and Panton-Valentine leukocidin (PVL) genes, and characterized by pulsed-field gel electrophoresis (PFGE), spa typing, multi-locus sequence typing and SCCmec typing.

FINDINGS

Twenty of 127 children (15.7%) and 13 of 129 parents (10.1%) were MRSA nasal carriers. Three lineages comprised 88% of the MRSA isolates: (i) PFGE A-ST5-SCCmec IVa (N=15; 45%), associated with spa type t105, recovered in Angola alone; (ii) PFGE N-ST8-IV/V (N=7; 21%), associated with spa types t008/t121, recovered in São Tomé and Príncipe alone; and (iii) PFGE B-ST88-IVa (N=7; 21%), associated with spa types t325/t786, present in both countries. Fifteen child/guardian pairs were colonized with identical MRSA (N=8) or meticillin-susceptible S. aureus (N=7) strains. PVL was detected in 25% of isolates, including two MRSA (ST30-V and ST8-IVa).

CONCLUSION

Hospitalized children and their parents are important reservoirs of MRSA. Infection control measures should focus on parents in order to minimize the spread of MRSA to the community.

Characteristics of methicillin-resistant Staphylococcus aureus in patients on admission to a teaching hospital in Rio de Janeiro, Brazil

BACKGROUND

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are associated with greater mortality and morbidity; however, risk factors for community-acquired infections caused by MRSA have not been established. Therefore, community patients who are admitted to hospitals without the necessary contact precautions and are infected with community-acquired lineages eventually cause these lineages to spread to these settings. The aim of this study was to detect community-acquired lineages of MRSA in patients on admission to a Brazilian teaching hospital.

METHODS

The antimicrobial susceptibility of the MRSA isolates from nasal swabs was evaluated as was the molecular characteristics of the staphylococcal cassette chromosome mec (SCCmec). The clonality was determined using pulsed-field gel electrophoresis and multilocus sequence type analysis.

RESULTS

A total of 702 patients were evaluated between March 2012 and March 2013; 180 (25%) of them were colonized by S aureus, and 21 (3%) were MRSA. The SCCmec IV/USA1100/sequence type (ST) 30 was the predominant MRSA lineage (42.8%), followed by SCCmec IV/USA800/ST5 (23.8%).

CONCLUSIONS

The occurrence of MRSA colonization was very low, and only 1 patient from cardiac surgery developed an infection, which was caused by an SCCmec II/USA100/ST5 isolate. Screening for MRSA colonization on admission does not seem to be productive; however, for populations submitted to specific surgeries, active surveillance should be implemented.

Bacteriophage Lysin CF-301, a Potent Antistaphylococcal Biofilm Agent

Biofilms pose a unique therapeutic challenge because of the antibiotic tolerance of constituent bacteria. Treatments for biofilm-based infections represent a major unmet medical need, requiring novel agents to eradicate mature biofilms. Our objective was to evaluate bacteriophage lysin CF-301 as a new agent to target Staphylococcus aureus biofilms. We used minimum biofilm-eradicating concentration (MBEC) assays on 95 S. aureus strains to obtain a 90% MBEC (MBEC₉₀) value of ≤0.25 μg/ml for CF-301. Mature biofilms of coagulase-negative staphylococci, Streptococcus pyogenes, and Streptococcus agalactiae were also sensitive to disruption, with MBEC₉₀ values ranging from 0.25 to 8 μg/ml. The potency of CF-301 was demonstrated against S. aureus biofilms formed on polystyrene, glass, surgical mesh, and catheters. In catheters, CF-301 removed all biofilm within 1 h and killed all released bacteria by 6 h. Mixed-species biofilms, formed by S. aureus and Staphylococcus epidermidis on several surfaces, were removed by CF-301, as were S. aureus biofilms either enriched for small-colony variants (SCVs) or grown in human synovial fluid. The antibacterial activity of CF-301 was further demonstrated against S. aureus persister cells in exponential-phase and stationary-phase populations. Finally, the antibiofilm activity of CF-301 was greatly improved in combinations with the cell wall hydrolase lysostaphin when tested against a range of S. aureus strains. In all, the data show that CF-301 is highly effective at disrupting biofilms and killing biofilm bacteria, and, as such, it may be an efficient new agent for treating staphylococcal infections with a biofilm component.

Staphylococcal chromosomal cassettes mec (SCCmec): A mobile genetic element in methicillin-resistant Staphylococcus aureus

Considered to be a potential "superbug", methicillin-resistant Staphylococcus aureus (MRSA) has been one of the major recent infectious pathogens and thus poses a challenge to hospital infection control. The mobile genetic element staphylococcal chromosomal cassette mec (SCCmec) carries both the mecA or mecC gene, encoding for a novel specific penicillin-binding protein (PBP2a), and site-specific recombinase genes ccrAB or/and ccrC. In MRSA, the acquisition of SCCmec leads to the resistance to the β-lactam antibiotics. As SCCmec plays a core role in the antimicrobial resistance characteristics, molecular epidemiology and evolution of MRSA, a thorough summary and comprehensive understanding of the prevalence and structural characteristics of SCCmec may aid in global surveillance, implementation and investigation on MRSA isolates, as well as further development of preventive and therapeutic approaches. Consequently, this review is aimed at describing the history, prevalence, types and subtypes, and current typing methods of SCCmec, with the focus on the typical structures of the SCCmec cassette.

Molecular Characterization of Methicillin-ResistantStaphylococcus aureusDisseminated in a Home Care System

Objective.

To study colonization with methicillin-resistantStaphylococcus aureusin a home care service during a 4-month period.

Design.

Prospective study.

Setting.

A home care service located in Rio de Janeiro, Brazil.

Participants.

Patients admitted to the home care service during this period, their household contacts, and health care workers (HCWs).

Methods.

Swab specimens from the anterior nares were collected from each patient in the 3 groups at admission. Screening was repeated every 7 days. MRSA was detected using a mecA probe, and the clonality of isolates was evaluated by molecular methods, primarily pulsed-field gel electrophoresis.

Results.

Of the 59 study patients, 9 (15.3%) had MRSA colonization detected; these cases of colonization were classified as imported. Only 1 (2.0%) of the 50 patients not colonized at admission became an MRSA carrier (this case of colonization was classified as autochthonous). Two (0.9%) of 224 household contacts and 16 (7.4%) of 217 HCWs had MRSA colonization. Cross-transmission from patient to HCW could be clearly demonstrated in 8 cases. The great majority of MRSA isolates belonged to the Brazilian epidemic clone.

Conclusions.

MRSA colonization was common in the home care service analyzed. The fact that the majority of MRSA isolates obtained were primarily of nosocomial origin (and belonged to the so-called Brazilian epidemic clone) substantiated our findings that all but 1 patient had already been colonized before admission to the home care service. Only cross-transmission from patients to healthcare workers could be verified. On the basis of these results, we believe that a control program built on admission screening of patients for detection of MRSA carriage could contribute to the overall quality of care.

Clonal Structure and Characterization of Staphylococcus aureus Strains from Invasive Infections in Paediatric Patients from South Poland: Association between Age, spa Types, Clonal Complexes, and Genetic Markers

The aim of current study was to examine clonal structure and genetic profile of invasive Staphylococcus aureus isolates recovered from infants and children treated at the Jagiellonian University Children’s Hospital of Krakow, Poland. The 107 invasive S. aureus isolates, collected between February 2012 and August 2014, were analysed retrospectively. Antimicrobial susceptibility testing, spa typing and DNA microarray analysis were performed to determine clonal distribution, diversity and gene content in regard to patients characteristics. In total, 107 isolates were recovered from 88 patients with clinical symptoms of invasive bacterial infection. The final set of 92 non-duplicate samples included 38 MRSA isolates. Additionally, a set of 54 S. aureus isolates collected during epidemiological screening was genotyped and analysed. There were 72 healthcare-associated (HCA) and 20 community-onset (CO) infection events caused by 33 and 5 MRSA isolates, respectively. The majority of isolates were affiliated with the major European clonal complexes CC5 (t003, spa-CC 002), CC45 (spa-CC 015), CC7 or CC15 (t084, t091, spa-CC 084). Two epidemic clones (CC5-MRSA-II or CC45-MRSA-IV) dominated among MRSA isolates, while MSSA population contained 15 different CCs. The epidemiological screening isolates belonged to similar genetic lineages as those collected from invasive infection cases. The HCA infection events, spa types t003, t2642 or CC5 were significantly associated with infections occurring in neonates and children under 5 years of age. Moreover, carriage of several genetic markers, including erm(A), sea (N315), egc-cluster, chp was significantly higher in isolates obtained from children in this age group. The spa types t091 and t008 were underrepresented among patients aged 5 years or younger, whereas spa type t008, CC8 and presence of splE was associated with infection in children aged 10 years or older. The HCA-MRSA strains were most frequently found in children under 5 years, although the majority of invasive infections was associated with MSSA strains. Moreover, an association between age group of children from the study population and a specific strain genotype (spa type, clonal complex or genetic content) was observed among the patients.

Contamination of public transports by Staphylococcus aureus and its carriage by biomedical students: point-prevalence, related risk factors and molecular characterization of methicillin-resistant strains

OBJECTIVES

To analyse the contamination of public transports by Staphylococcus aureus and assess its carriage by biomedical students, focussing on the point-prevalence, related risk factors and molecular characterization of methicillin-resistant strains.

STUDY DESIGN

Cross-sectional survey.

METHODS

Methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) isolated from handrails of buses (n = 112) and trains (n = 79) circulating in Porto and from nasal swabs of local university students (n = 475) were quantified, characterized by molecular typing methods and related to possible risk factors.

RESULTS

The MRSA prevalence in buses (16.1%) was not significantly different from trains (8.9%). There was also no identifiable association between the counts of MSSA and MRSA in buses and trains and the number of travellers in each sampling day, specific routes (including those passing by main hospitals) or other risk factors. Of the students, 37.1% carried S. aureus, and having a part-time job or smoking were found to be risk factors for carriage. EMRSA-15 (ST22-SCCmecIVh) was the prevalent MRSA clonal lineage, found not only in the buses (n = 14) and trains (n = 2) but also in the single MRSA-carrier among the students. The characteristics of the community-associated Southwest Pacific MRSA clone were found in a single ST30-IVa isolate, which may suggest a recent SCCmec acquisition by an MSSA background in the community.

CONCLUSIONS

The spread of EMRSA-15, a common hospital-associated lineage, among different public transports and as a nasal coloniser is of concern and warrants adequate public health control measures.

Staphylococcus aureus in former Portuguese colonies from Africa and the Far East: missing data to help fill the world map

The aim of the present study was to determine the prevalence and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) nasal carriage among patients and healthcare workers in Angola (ANG), São Tomé and Príncipe (STP), Cape Verde (CV) and East Timor (ET), and to characterize the antimicrobial susceptibility, virulence content and population structure of all S. aureus. Despite the importance of MRSA as a major human pathogen, data from these former Portuguese colonies in Africa and Asia are scarce. A total of 2065 nasal swabs recovered between 2010-14 were included in the study. Antimicrobial susceptibility testing and molecular characterization of S. aureus showed: (i) a very high MRSA prevalence in ANG (61.6%), moderate in STP (25.5%), low in CV (5.6%) and null in ET; (ii) a high prevalence of Panton-Valentine leukocidin in STP (36.8%), ET (29.2%) and CV (28.3%) contrasting with ANG (7.9%); (iii) ST5-SCCmecIVa, ST8-IV/V and ST5-VI were the major MRSA clones in ANG (65.2%), STP (44.8%) and CV (50%), respectively; (iv) a high resistance to trimethoprim-sulfamethoxazole in ANG (66.5%) and STP (50.9%), to rifampin in ANG (77.3%), and to tetracycline in STP (26.3%) and ET (20.8%); (v) three major methicillin-susceptible S. aureus clones (ST15, ST508, ST152) were present in all four countries. Age <18 years (OR 2.03, 95% CI 1.24-3.31), previous surgery (OR 2.45, 95% CI 1.24-4.83), no smoking (OR 4.04, 95% CI 1.05-15.50), and longer hospitalization (OR 2.53, 95% CI 1.49-4.28) were risk factors for MRSA carriage. This study provided the first comprehensive overview on MRSA in former Portuguese colonies in Africa and Asia, missing data in the world map.

Insights into alpha-hemolysin (Hla) evolution and expression among Staphylococcus aureus clones with hospital and community origin

Background

Alpha-hemolysin (Hla) is a major virulence factor in the pathogenesis of Staphylococcus aureus infection, being active against a wide range of host cells. Although hla is ubiquitous in S. aureus, its genetic diversity and variation in expression in different genetic backgrounds is not known. We evaluated nucleotide sequence variation and gene expression profiles of hla among representatives of hospital (HA) and community-associated (CA) S. aureus clones.

Methods

51 methicillin-resistant S. aureus and 22 methicillin-susceptible S. aureus were characterized by PFGE, spa typing, MLST and SCCmec typing. The internal regions of hla and the hla promoter were sequenced and gene expression was assessed by RT-PCR.

Results

Alpha-hemolysin encoding- and promoter sequences were diverse, with 12 and 23 different alleles, respectively. Based on phylogenetic analysis, we suggest that hla may have evolved together with the S. aureus genetic background, except for ST22, ST121, ST59 and ST93. Conversely, the promoter region showed lack of co-evolution with the genetic backgrounds. Four non-synonymous amino acid changes were identified close to important regions of hla activity. Amino acid changes in the RNAIII binding site were not associated to hla expression. Although expression rates of hla were in general strain-specific, we observed CA clones showed significantly higher hla expression (p = 0.003) when compared with HA clones.

Conclusion

We propose that the hla gene has evolved together with the genetic background. Overall, CA genetic backgrounds showed higher levels of hla expression than HA, and a high strain-to-strain variation of gene expression was detected in closely related strains.

Contribution of peptidoglycan amidation to beta-lactam and lysozyme resistance in different genetic lineages of Staphylococcus aureus

The enzymes responsible for peptidoglycan amidation in Staphylococcus aureus, MurT and GatD, were recently identified and shown to be required for optimal expression of resistance to beta-lactams, bacterial growth, and resistance to lysozyme. In this study, we analyzed the impact of peptidoglycan amidation in representative strains of the most widespread clones of methicillin resistant S. aureus (MRSA). The inhibition of the expression of murT-gatD operon resulted in different phenotypes of resistance to beta-lactams and lysozyme according to the different genetic backgrounds. Further, clonal lineages CC1 and CC398 (community-acquired MRSA [CA-MRSA]) showed a stronger dependency on MurT-GatD for resistance to beta-lactams, when compared to the impact of the impairment of the cell wall step catalyzed by MurF. In the remaining backgrounds similar phenotypes of beta-lactam resistance were observed upon the impairment of both cell-wall-related genes. Therefore, for CA-related backgrounds, the predominant beta-lactam resistance mechanism seems to involve genes associated with secondary modifications of peptidoglycan. On the other hand, the lack of glutamic acid amidation had a more substantial impact on lysozyme resistance for cells of CA-MRSA backgrounds, than for hospital-acquired MRSA (HA-MRSA). However, no significant differences were found in the resistance level of the respective peptidoglycan structure, suggesting that the lysozyme resistance mechanism involves other factors. Taken together, these results suggested that the different genetic lineages of MRSA were able to develop different molecular strategies to overcome the selective pressures experienced during evolution.

Redefining the role of the β-lactamase locus in methicillin-resistant Staphylococcus aureus: β-lactamase regulators disrupt the MecI-mediated strong repression on mecA and optimize the phenotypic expression of resistance in strains with constitutive mecA expression

In response to β-lactam chemotherapy, Staphylococcus aureus has acquired two resistance determinants: blaZ, coding for β-lactamase, which confers resistance to penicillins only, and mecA, coding for an extra cell wall cross-linking enzyme with reduced affinity for virtually all other β-lactams. The transcriptional control of both resistance determinants is regulated by homologous repressors (BlaI and MecI, respectively) and sensor inducers (BlaR1 and MecR1, respectively). There is a cross-talk between the two regulatory systems, and it has been demonstrated that bla regulators stabilize the mecA acquisition. In a recent study, we have unexpectedly observed that in most MRSA strains, there was no significant change in the resistance phenotype upon the overexpression in trans of a MecI repressor, whereas in those few strains negative for the bla locus, there was a massive decrease of resistance (D. C. Oliveira and H. de Lencastre, PLoS One 6:e23287, 2011). Here, we demonstrate that, contrary to what is currently accepted, the bla regulatory system efficiently disrupts the strong MecI-mediated repression on mecA, enabling the optimal expression of resistance. This effect appears to be due to the formation of MecI::BlaI heterodimers that might bind less efficiently to the mecA promoter and become nonfunctional due to the proteolytic inactivation of the BlaI monomer. In addition, we have also observed that the presence of bla regulators may enhance dramatically the expression of β-lactam resistance in MRSA strains with constitutive mecA expression, compensating for the fitness cost imposed by the large β-lactamase plasmid. These observations point to important unrecognized roles of the bla locus for the expression of the methicillin-resistant S. aureus (MRSA) phenotype.

New multilocus sequence typing of MRSA in São Paulo, Brazil

An increased incidence of nosocomial and community-acquired infections caused by methicillin-resistant Staphylococcus aureus (MRSA) has been observed worldwide. The molecular characterization of MRSA has played an important role in demonstrating the existence of internationally disseminated clones. The use of molecular biology methods in the surveillance programs has enabled the tracking of MRSA spread within and among hospitals. These data are useful to alert nosocomial infection control programs about the potential introduction of these epidemic clones in their areas. Four MRSA blood culture isolates from patients hospitalized at two hospitals in the city of São Paulo, Brazil, were analyzed; one of them was community acquired. The isolates were characterized as SCCmec, mecA and PVL by PCR, pulsed-field gel electrophoresis (PFGE) profile and molecular sequence typing (MLST) genotyping. The isolates presented type IV SCCmec, and none proved to be positive for PVL. The isolates showed a PFGE profile similar to the pediatric clone. MLST genotyping demonstrated that the isolates belonged to clonal complex 5 (CC5), showing a new yqiL allele gene, resulting in a new sequence typing (ST) (1176). Our results showed that strains of MRSA carrying a new ST are emerging in community and nosocomial infections, including bacteremia, in São Paulo, Brazil.

Evidence for a purifying selection acting on the β-lactamase locus in epidemic clones of methicillin-resistant Staphylococcus aureus

Background

The β-lactamase (bla) locus, which confers resistance to penicillins only, may control the transcription of mecA, the central element of methicillin resistance, which is embedded in a polymorphic heterelogous chromosomal cassette (the SCCmec element). In order to assess the eventual correlation between bla allotypes and genetic lineages, SCCmec types and/or β-lactam resistance phenotypes, the allelic variation on the bla locus was evaluated in a representative collection of 54 international epidemic methicillin-resistant Staphylococcus aureus (MRSA) clinical strains and, for comparative purposes, also in 24 diverse methicillin-susceptible S. aureus (MSSA) strains.

Results

Internal fragments of blaZ (the β-lactamase structural gene) were sequenced for all strains. A subset of strains, representative of blaZ allotypes, was further characterized by sequencing of internal fragments of the blaZ transcriptional regulators, blaI and blaR1. Thirteen allotypes for blaZ, nine for blaI and 12 for blaR1 were found. In a total of 121 unique single-nucleotide polymorphisms (SNP) detected, no frameshift mutations were identified and only one nonsense mutation within blaZ was found in a MRSA strain. On average, blaZ alleles were more polymorphic among MSSA than in MRSA (14.7 vs 11.4 SNP/allele). Overall, blaR1 was the most polymorphic gene with an average of 24.8 SNP/allele. No correlation could be established between bla allotypes and genetic lineages, SCCmec types and/or β-lactam resistance phenotypes. In order to estimate the selection pressure acting on the bla locus, the average dN/dS values were computed. In the three genes and in both collections dN/dS ratios were significantly below 1.

Conclusions

The data strongly suggests the existence of a purifying selection to maintain the bla locus fully functional even on MRSA strains. Although, this is in agreement with the notion that in most clinical MRSA strains mecA gene is under the control of the bla regulatory genes, these findings also suggest that the apparently redundant function of blaZ gene for the MRSA resistant phenotype is still important for these strains. In addition, the data shows that the sensor-inducer blaR1 is the primary target for the accumulation of mutations in the bla locus, presumably to modulate the response to the presence of β-lactam antibiotic.

A field guide to pandemic, epidemic and sporadic clones of methicillin-resistant Staphylococcus aureus

In recent years, methicillin-resistant Staphylococcus aureus (MRSA) have become a truly global challenge. In addition to the long-known healthcare-associated clones, novel strains have also emerged outside of the hospital settings, in the community as well as in livestock. The emergence and spread of virulent clones expressing Panton-Valentine leukocidin (PVL) is an additional cause for concern. In order to provide an overview of pandemic, epidemic and sporadic strains, more than 3,000 clinical and veterinary isolates of MRSA mainly from Germany, the United Kingdom, Ireland, France, Malta, Abu Dhabi, Hong Kong, Australia, Trinidad & Tobago as well as some reference strains from the United States have been genotyped by DNA microarray analysis. This technique allowed the assignment of the MRSA isolates to 34 distinct lineages which can be clearly defined based on non-mobile genes. The results were in accordance with data from multilocus sequence typing. More than 100 different strains were distinguished based on affiliation to these lineages, SCCmec type and the presence or absence of PVL. These strains are described here mainly with regard to clinically relevant antimicrobial resistance- and virulence-associated markers, but also in relation to epidemiology and geographic distribution. The findings of the study show a high level of biodiversity among MRSA, especially among strains harbouring SCCmec IV and V elements. The data also indicate a high rate of genetic recombination in MRSA involving SCC elements, bacteriophages or other mobile genetic elements and large-scale chromosomal replacements.

High prevalence of EMRSA-15 in Portuguese public buses: a worrisome finding

BACKGROUND

The nosocomial prevalence of methicillin resistant Staphylococcus aureus (MRSA) in Portugal remains one of the highest in Europe and is currently around 50%. Transmission of S. aureus, including MRSA, occurs principally by direct human-to-human skin contact. However, S. aureus can survive for long periods on inanimate objects, which may represent an important reservoir for dissemination as well.

METHODOLOGY/PRINCIPAL FINDINGS

Between May 2009 and February 2010, handrails of 85 public urban buses circulating in Oporto, Portugal, were screened for the occurrence of MRSA. Twenty-two (26%) buses showed MRSA contamination. The molecular characterization of a total of 55 MRSA, by pulsed-field gel electrophoresis (PFGE), staphylococcal cassette chromosome (SCC) mec typing, spa typing, and multilocus sequence typing (MLST), clustered the isolates into three clonal types. However, the overwhelming majority (n = 50; 91%) of the isolates belonged to a single clone (PFGE A, spa types t747, t032, t025 or t020, ST22, SCCmec type IVh) that exhibits the characteristics of the pandemic EMRSA-15, currently the major lineage circulating in Portuguese hospitals, namely in the Oporto region. Two additional clones were found but in much lower numbers: (i) PFGE B, ST5, spa type t002, SCCmec IVa (n = 3), and (ii) PFGE C, spa type t008, ST8, SCCmec IVa (n = 2). None of the 55 isolates was PVL positive.

CONCLUSIONS/SIGNIFICANCE

Public buses in Oporto seem to be an important reservoir of MRSA of nosocomial origin, providing evidence that the major hospital-associated MRSA clone in Portugal is escaping from the primary ecological niche of hospitals to the community environment. Infection control measures are urgently warranted to limit the spread of EMRSA-15 to the general population and future studies are required to assess the eventual increase of MRSA in the Portuguese community, which so far remains low.

Prevalent genotypes of meticillin-resistant Staphylococcus aureus: report from Pakistan

Meticillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen in Pakistan and is emerging in the community. This is one of the first reports of the prevalent genotypes of MRSA in both hospital and community settings in Pakistan. Isolates collected in 2006–2007 were characterized by PFGE, staphylococcal cassette chromosome mec (SCCmec) typing and multilocus sequence typing (MLST). PFGE identified nine pulsotypes, the majority of isolates belonging to pulsotypes A (n=70) and B (n=38), which were predominant among hospital-onset MRSA (HO-MRSA) and community-onset MRSA (CO-MRSA) isolates, respectively. Among the HO-MRSA isolates, variants of SCCmec type III were prevalent, whilst SCCmec type IV or variants were predominant in the CO-MRSA isolates. MLST identified two principal sequence types, ST8 and ST239. An association was observed between ST8, PFGE pulsotype B and SCCmec type IV in the CO-MRSA (ST8-MRSA-IV). Similarly, ST239, PFGE pulsotype A and SCCmec type III were associated with HO-MRSA (ST239-MRSA-III). Therefore, the prevalent genotypes circulating in Pakistan at the time of study were ST8-MRSA-IV and ST239-MRSA-III in the community and hospital settings, respectively. A set of HO-MRSA isolates collected in 1997 were characterized by PFGE and SCCmec typing for comparison. The isolates belonged to two PFGE pulsotypes (A, n=28; B, n=11) and contained just two SCCmec types. These results suggest that an increase in genetic diversity occurred over the period 1997–2007 as a result of either microevolution or the importation of strains from surrounding areas.

High prevalence of ST121 in community-associated methicillin-susceptible Staphylococcus aureus lineages responsible for skin and soft tissue infections in Portuguese children

In order to evaluate the incidence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Portugal, we analyzed a collection of 38 S. aureus isolates recovered from 30 children attending the pediatric emergency department of a central hospital in Lisbon due to skin and soft tissue infections. Molecular characterization identified seven clonal lineages among the 35 methicillin-susceptible S. aureus (MSSA) isolates, of which the major lineage PFGE A/t159/ST121 included 63% of the isolates. The three MRSA isolates belonged to the Pediatric clone PFGE D/t535/ST5-IV (n = 2) and to the European CA-MRSA clone PFGE G/t044/ST80-IVc (n = 1). All isolates harbored several virulence factors, namely, leukocidins. Panton-Valentine leukocidin (PVL) was produced by isolates from five MSSA lineages and by the ST80 MRSA. Of interest, this is the first reported isolation of CA-MRSA ST80 in Portugal.

Molecular typing of Staphylococcus aureus bloodstream isolates from geriatric patients attending a long-term care Spanish hospital

All Staphylococcus aureus isolates (n=31) that caused bacteraemia in a Spanish geriatric hospital during 1996-2006 were analysed by a simple, rapid and inexpensive PCR technique based on variations in the hsdS1 and hsdS2 genes encoding the sequence recognition subunits of the Sau1 restriction-modification (RM) system. An equal number of isolates collected from surgical wounds over the same time period (control group) were similarly characterized. The RM test allocated 75 % of the isolates to the six major clonal complexes (CC1, CC5, CC8, CC22, CC30 and CC45) for which it was developed. However, recognition of minor CCs and precise identification of the circulating clones required more powerful and comprehensive techniques such as spa typing and multilocus sequence typing (MLST), which are more demanding and expensive. The RM test is not intended to replace spa or MLST typing, but may be of use when time, technical and/or financial resources are limited. Overall, nine and seven CCs were detected in bloodstream and wound isolates, respectively. In both groups, CC5 was the most frequent (35.5 % each), followed by CC45 or CC8 (22.6 and 32.3 % of bloodstream and wound isolates, respectively). The frequency of meticillin resistance was lower in bloodstream (16.1 %) than in wound (51.6 %) isolates (P=0.0025). Among the former, sequence type (ST) 5-staphylococcal cassette chromosome mec (SCCmec) II, ST5-SCCmec IV, ST45-SCCmec IV and ST125-SCCmec IV (now dominant in Spanish hospitals) clones were found. Among the wound isolates, nine meticillin-resistant clones were represented, with three of them (ST125-SCCmec III, ST125-SCCmec V and ST14-SCCmec V) being newly described.

Prevalence and clonality of methicillin-resistant Staphylococcus aureus (MRSA) in the Atlantic Azores islands: predominance of SCCmec types IV, V and VI

In order to obtain insights into the methicillin-resistant Staphylococcus aureus (MRSA) population structure in the Azores archipelago, 106 MRSA isolates were collected from patients attending an Azorean central hospital between January 2007 and February 2008. Antimicrobial resistance was determined for all isolates. Molecular typing was performed by pulsed-field gel electrophoresis (PFGE), spa typing, multilocus sequence typing (MLST), staphylococcal chromosome cassette mec (SCCmec) typing and the presence of Panton–Valentine leukocidin (PVL). The majority of the isolates (87%, n = 92) belonged to the EMRSA-15 clone (ST22, SCCmec-IVh), followed by the Pediatric clone (ST5-VI/IVc) (11%, n = 12). The Berlin clone (ST45-IVa) and a new clone (spa type t1839, ST1339 and SCCmec V variant) were represented by single isolates. All of the isolates carried SCCmec types IV, V or VI and a non-multiresistant antibiotic profile, resembling the currently emerging community MRSA. Moreover, PVL was described for the first time to be associated with the Pediatric clone carrying SCCmec type VI. We provided the first description of the population structure of MRSA in the Azores islands, which seems to be shaped by genetic events occurring locally, as well as by the regular population exchange between the islands, continental Portugal, the United Kingdom and the United States.

Molecular characterization of resistance to Rifampicin in an emerging hospital-associated Methicillin-resistant Staphylococcus aureus clone ST228, Spain

Background

Methicillin-resistant S. aureus (MRSA) has been endemic in Hospital Universitari de Bellvitge, Barcelona, since 1990. During the 1990-95 period the Iberian clone (ST-247; SCCmec-I) was dominant. Isolates of clonal complex 5 (ST-125; SCCmec-IV) gradually replaced the Iberian clone from 1996 to 2003. A new multiresistant MRSA phenotype showing rifampicin resistance emerged in 2004 and rapidly increased from 25% in 2004 to 45% in 2006. The aims of this study were i) the molecular characterisation of rifampicin resistant MRSA isolates, ii) the study of the rifampicin resistance expression by disk diffusion, microdilution and E-test, and iii) the analysis of the rpoB gene mutations involved in rifampicin resistance.

Results

A sample of representative 108 rifampicin-resistant MRSA isolates belonged to a single PFGE genotype, ST-228, SCCmec type I and spa type t041. Of 108 isolates, 104 (96%) had a low-level rifampicin resistance (MICs, 2 to 4 mg/L) and 4 a high-level rifampicin resistance (MICs, 128 - ≥ 256 mg/L). Disk diffusion and E-test methods failed to identify a low-level rifampicin resistance in 20 and 12 isolates, respectively. A low-level rifampicin resistance was associated with amino acid substitution 481His/Asn in the beta-subunit of RNA polymerase. Isolates with a high-level rifampicin resistance carried additional mutations in the rpoB gene.

Conclusions

The emergence of MRSA clone ST228-SCCmecI, related to the Southern Germany clone, involved a therapeutical challenge for treating serious MRSA infections. Decreased susceptibility to rifampicin in MRSA strains of ST228-SCCmecI was associated with one or two specific mutations in the rpoB gene. One fifth of isolates with low-level rifampicin-resistance were missed by the diffusion methods.

Clonal complexes and diversity of exotoxin gene profiles in methicillin-resistant and methicillin-susceptible Staphylococcus aureus isolates from patients in a Spanish hospital

Molecular epidemiology studies have allowed the identification of the methicillin (meticillin)-resistant (MRSA) and methicillin-susceptible (MSSA) clonal complexes (CCs) and clones of Staphylococcus aureus circulating in a Spanish hospital recently. Of 81 isolates tested, 32.1% were MRSA. Most of them carried staphylococcal cassette chromosome mec (SCCmec) IVc (88.5%) and belonged to CC5 (88.5%; multilocus sequence typing types ST125 [mainly associated with spa type t067], ST5, and ST228). A higher diversity was found among MSSA isolates (67.9%). Eighty percent shared the genetic background of major MRSA lineages (CC5 [38.2%; ST125 and ST5], CC30 [25.5%; ST30], CC45 [14.5%; ST45 and ST47], and CC8 [1.8%; ST8]), but CC12, CC15, CC51, and CC59 were also detected. Many exotoxin genes were present in each of the 81 isolates, independent of whether they were involved in sepsis (11 to 22) or other types of infections (13 to 21), and they appeared in 73 combinations. The relevant data are that (i) all isolates were positive for hemolysin and leukotoxin genes (98.8% for lukED and 25.9% for lukPV); (ii) all contained an enterotoxin gene cluster (egc with or without seu), frequently with one or more genes encoding classical enterotoxins; (iii) about half were positive for tst and 95% were positive for exfoliatin-encoding genes (eta, etb, and/or etd); and (iv) the four agr groups were detected, with agrII (55.6%) and agrIII (23.5%) being the most frequent. Taken together, results of the present study suggest a frequent acquisition and/or loss of exotoxin genes, which may be mediated by efficient intralineage transfer of mobile genetic elements and exotoxin genes therein and by eventual breakage of interlineage barriers.

Comparison of different methods for detecting methicillin resistance in MRSA isolates belonging to international lineages commonly isolated in the American continent

The aim of the present paper was to compare different methods for detecting methicillin resistance in Staphylococcus aureus. Among the isolates analyzed, 52 belonged to MRSA international lineages commonly detected in the American continent and 14 to sporadic MRSA clones. Both 30 microg-cefoxitin disk and PBP2a had 100% sensibility/specificity when the low-level heterogeneous isolates were tested and, thus, are highly recommended.

Staphylococcal interspersed repeat unit typing of Staphylococcus aureus: evaluation of a new multilocus variable-number tandem-repeat analysis typing method

The present study evaluates the performance of the staphylococcal interspersed repeat unit (SIRU) method applied to a diverse collection of 104 Staphylococcus aureus isolates previously characterized by pulsed-field gel electrophoresis (PFGE), spa typing, multilocus sequence typing (MLST), and staphylococcal cassette chromosome mec typing for methicillin-resistant S. aureus. The SIRU method distributed the 104 strains into 81 SIRU profiles that could be clustered into 12 groups and 29 singletons. The discriminatory power of the method at the profile level, translated by Simpson's index of diversity (SID), was similar to that of PFGE subtyping (SID = 99.23% versus 99.85%) and slightly higher than that of spa typing (SID = 97.61%). At the group level, the SIRU SID (93.24%) was lower than that of PFGE typing (95.41%) but higher than that of MLST (SID = 91.77%). The adjusted Rand (AR) coefficient showed that SIRU typing at the group level had the highest congruence with MLST (AR = 0.5736) and with clonal complex (CC) (AR = 0.4963) but the lowest congruence with PFGE subtype (AR = 0.0242). The Wallace coefficient indicated that in the present collection, two strains with the same SIRU profile have a 100% probability of belonging to the same CC, a 90% probability of sharing the same spa type, and an 83% probability of being classified in the same sequence type. The high discriminatory power of the SIRU method, along with its apparent concordance with MLST results, makes it potentially valuable for S. aureus short-term epidemiological investigations and population dynamics as well.

Epidemiology of invasive methicillin-resistant Staphylococcus aureus clones collected in France in 2006 and 2007

We conducted a prospective multicenter study of methicillin-resistant Staphylococcus aureus (MRSA) isolates, including the first five consecutive clinical isolates, collected between September 2006 and February 2007 in 23 hospitals located throughout France (Fig. 1). The 111 isolates were tested for their antibiotic susceptibility patterns and were extensively characterized by screening for drug resistance and agr alleles, multilocus sequence typing (ST), staphylococcal cassette chromosome mec (SCCmec) typing, spa typing, and PCR profiling of 21 toxin genes. Clones were designated by their ST followed by their SCCmec type (I to VI). The Lyon clone ST8-IV or ST8-IV(variant) (n = 77; 69.4%) was widely distributed. Four minor clones were also detected, namely, the "classical" Pediatric clone ST5-IV (n = 9; 8.1%), the "new" Pediatric clone ST5-VI (n = 8; 7.2%), the clone Geraldine ST5-I(truncated) (n = 7; 6.3%), and the European clone ST80-IV (n = 4; 3.6%). The six other isolates were related to five rare clones. Relative to that of other European countries, the situation in France is marked by the predominance of a specific major clone and the worrying emergence of minor clones with enhanced virulence and new antibiotic susceptibility profiles.

Changing patterns in frequency of recovery of five methicillin-resistant Staphylococcus aureus clones in Portuguese hospitals: surveillance over a 16-year period

A total of 629 nonduplicate methicillin-resistant Staphylococcus aureus MRSA isolates were recovered between June and November 2006 from 11 hospitals located in different areas of Portugal. Selected isolates (n = 271, 43%) were typed by pulsed-field gel electrophoresis (PFGE), representatives of which were additionally characterized by spa typing, multilocus sequence typing, staphylococcal cassette chromosome mec (SCCmec) typing, and the presence of Panton-Valentine leukocidin (PVL). The 271 isolates were classified into 13 different clonal types. Three pandemic clones included the majority (n = 241, 88%) of the isolates and were observed in several hospitals: (i) EMRSA-15 (54%)-PFGE type A, ST22, spa type t022, SCCmec IV-was found in the 11 hospitals studied and was identified as the major clone in seven of them; (ii) the New York/Japan clone (17%)-PFGE B, ST5, spa type t067, SCCmec II-was identified in nine hospitals and represented the major clone in four; and (iii) the Brazilian MRSA (17%)-PFGE C, ST239, spa type t037, SCCmec IIIA-was also detected in nine hospitals but never as the main clone. All isolates tested were PVL negative. Clone EMRSA-15 is currently the predominant MRSA clonal type circulating in Portuguese hospitals, but a new wave of MRSA has emerged in the country with the recent introduction and spread of the New York/Japan clone. The Brazilian MRSA that was the leading clone in Portugal in the late 1990s is declining and being progressively replaced by the two former clones. We report the first isolate SCCmec type V (ST45) in Portugal.

Molecular diagnostics of clinically important staphylococci

Bacterial species of the genus Staphylococcus known as important human and animal pathogens are the cause of a number of severe infectious diseases. Apart from the major pathogen Staphylococcus aureus, other species until recently considered to be nonpathogenic may also be involved in serious infections. Rapid and accurate identification of the disease-causing agent is therefore prerequisite for disease control and epidemiological surveillance. Modern methods for identification and typing of bacterial species are based on genome analysis and have many advantages compared to phenotypic methods. The genotypic methods currently used in molecular diagnostics of staphylococcal species, particularly of S. aureus, are reviewed. Attention is also paid to new molecular methods with the highest discriminatory power. Efforts made to achieve interlaboratory reproducibility of diagnostic methods are presented.