Staphylococcus aureus methicillin-resistance factor fmtA is regulated by the global regulator SarA

fmtA encodes a low-affinity penicillin binding protein in Staphylococcus aureus. It is part of the core cell wall stimulon and is involved in methicillin resistance in S. aureus. Here, we report that the transcription factor, SarA, a pleiotropic regulator of virulence genes in S. aureus, regulates the expression of fmtA. In vitro binding studies with purified SarA revealed that it binds to specific sites within the 541-bp promoter region of fmtA. Mutation of a key residue of the regulatory activity of SarA (Arg90) abolished binding of SarA to the fmtA promoter, suggesting that SarA binds specifically to the fmtA promoter region. In vivo analysis of the fmtA promoter using a lux operon reporter fusion show high level expression following oxacillin induction, which was abrogated in a sarA mutant strain. These data suggest that SarA is essential for the induction of fmtA expression by cell wall-specific antibiotics. Further, in vitro transcription studies show that SarA enhances fmtA transcription and suggest that regulation of fmtA could be via a SigA-dependent mechanism. Overall, our results show that SarA plays a direct role in the regulation of fmtA expression via binding to the fmtA promoter.

Comparative genotypic and phenotypic characterisation of methicillin-resistant Staphylococcus aureus ST398 isolated from animals and humans

The high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) ST398 among pigs in certain European countries and North America and its occurrence in other animal species raises a question concerning the molecular mechanisms mediating the success of this lineage. In this study a panel of S. aureus strains belonging to sequence type (ST) 5 (n = 4), ST8 (n = 5), ST15 (n = 5), ST22 (n = 8), clonal complex (CC) 30 (n = 8), CC97 (n = 8), CC130 (n = 4), CC151 (n = 4) and ST398 (n = 18) were screened by DNA microarray and PCR for the carriage of virulence and antimicrobial resistance genes. Isolates belonging to the same sequence type/clonal complex (ST/CC) were found to share similar virulence gene profiles. The ST398 lineage displayed the lowest content of virulence genes, which consisted mainly of genes detected among the majority or all of the analysed lineages. All MRSA ST398 isolates lacked accessory virulence genes that were detected in other ST/CC. In contrast to virulence genotype, the antimicrobial resistance genes profiles varied between isolates belonging to the same ST/CC and profile similarities could be observed for isolates from different lineages. MRSA ST398 isolates in particular displayed significant diversity and high content of antimicrobial resistance genes. This was comparable with certain MRSA belonging to other sequence types particularly the equine MRSA ST8. The apparent lack of significant virulence genes among MRSA ST398 strains, demonstrates that the lineage features a unique genetic background but no ST398-specific virulence markers could be identified.

Molecular characterization of Staphylococcus aureus in the United States 2004-2008 reveals the rapid expansion of USA300 among inpatients and outpatients

To assess the clonal structure of Staphylococcus aureus in the United States, we performed a molecular epidemiological study of 1,055 S. aureus isolates from a nationally representative clinical isolate collection from 2004-2008. Resistant and susceptible isolates were typed with multilocus sequence typing, tested for the presence of Panton-Valentine leukocidin (PVL), and serotyped. USA300 (multilocus sequence typing clonal complex 8, PVL positive, and methicillin-resistant) was the most frequently isolated clone, expanding from 12% of all isolates in 2004 to 38% in 2006. The USA300 clone increased significantly in frequency among both outpatients and inpatients. USA300 increased in both skin and soft-tissue and invasive infection isolates. The second most frequently observed clone was clonal complex 5, PVL-negative, and methicillin-resistant, and its frequency was stable from 2004-2008. The methicillin-susceptible S. aureus in the study was polyclonal, and decreased in frequency as it was replaced by USA300.

Rapid whole-genome sequencing for investigation of a neonatal MRSA outbreak

BACKGROUND

Isolates of methicillin-resistant Staphylococcus aureus (MRSA) belonging to a single lineage are often indistinguishable by means of current typing techniques. Whole-genome sequencing may provide improved resolution to define transmission pathways and characterize outbreaks.

METHODS

We investigated a putative MRSA outbreak in a neonatal intensive care unit. By using rapid high-throughput sequencing technology with a clinically relevant turnaround time, we retrospectively sequenced the DNA from seven isolates associated with the outbreak and another seven MRSA isolates associated with carriage of MRSA or bacteremia in the same hospital.

RESULTS

We constructed a phylogenetic tree by comparing single-nucleotide polymorphisms (SNPs) in the core genome to a reference genome (an epidemic MRSA clone, EMRSA-15 [sequence type 22]). This revealed a distinct cluster of outbreak isolates and clear separation between these and the nonoutbreak isolates. A previously missed transmission event was detected between two patients with bacteremia who were not part of the outbreak. We created an artificial "resistome" of antibiotic-resistance genes and demonstrated concordance between it and the results of phenotypic susceptibility testing; we also created a "toxome" consisting of toxin genes. One outbreak isolate had a hypermutator phenotype with a higher number of SNPs than the other outbreak isolates, highlighting the difficulty of imposing a simple threshold for the number of SNPs between isolates to decide whether they are part of a recent transmission chain.

CONCLUSIONS

Whole-genome sequencing can provide clinically relevant data within a time frame that can influence patient care. The need for automated data interpretation and the provision of clinically meaningful reports represent hurdles to clinical implementation. (Funded by the U.K. Clinical Research Collaboration Translational Infection Research Initiative and others.).

Methicillin-resistant Staphylococcus aureus (MRSA) on the skin of long-term hospitalised horses

Given the significance of methicillin-resistant Staphylococcus aureus (MRSA) infections for both horses and staff in equine veterinary hospitals, protocols are required to minimise the risk of nosocomial transmission, including the screening of the skin and nasal chambers of equine patients for evidence of infection. The objective of this study was to clarify the potential existence and extent of MRSA on the skin of horses requiring long-term hospitalisation (≥ 6 months). Thirty such horses were sampled at eight different locations on their skin and from their nasal chambers. MRSA was isolated from 12 animals (40%), with all sample sites testing positive on at least one occasion. Organisms were most frequently detected in the nasal chambers (relative sensitivity, 83.3%; 34.5% positive horses; isolation rate 33.3%). Skin presence was found in 30% of animals with the highest isolation rates found at the carpus (16.7%), neck, withers and croup (13.3% each). To achieve a relative screening sensitivity of >90%, at least one skin site was required in addition to nasal sampling. This evidence of skin as well as nasal reservoirs of MRSA in long-term hospitalised horses should facilitate the design of effective screening and containment protocols.

Longitudinal study on methicillin-resistant Staphylococcus pseudintermedius in households

Methicillin-resistant Staphylococcus pseudintermedius (MRSP) is an emerging pathogen in dogs and has been found in Europe, Asia and North America. To date most studies are one-point prevalence studies and therefore little is known about the dynamics of MRSP in dogs and their surrounding. In this longitudinal study MRSP colonization in dogs and the transmission of MRSP to humans, contact animals and the environment was investigated. Sixteen dogs with a recent clinical MRSP infection were included. The index dogs, contact animals, owners and environments were sampled once a month for six months. Samples taken from the nose, perineum and infection site (if present) of the index cases and contact animals, and the nares of the owners were cultured using pre-enrichment. Index cases were found positive for prolonged periods of time, in two cases during all six samplings. In five of the 12 households that were sampled during six months, the index case was intermittently found MRSP-positive. Contact animals and the environment were also found MRSP-positive, most often in combination with a MRSP-positive index dog. In four households positive environmental samples were found while no animals or humans were MRSP-positive, indicating survival of MRSP in the environment for prolonged periods of time. Genotyping revealed that generally similar or indistinguishable MRSP isolates were found in patients, contact animals and environmental samples within the same household. Within two households, however, genetically distinct MRSP isolates were found. These results show that veterinarians should stay alert with (former) MRSP patients, even after repeated MRSP-negative cultures or after the disappearance of the clinical infection. There is a considerable risk of transmission of MRSP to animals in close contact with MRSP patients. Humans were rarely MRSP-positive and never tested MRSP-positive more than once suggesting occasional contamination or rapid elimination of colonization of the owners.

Methicillin-resistant Staphylococcus aureus from dental school clinic surfaces and students

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) isolated from frequently touched dental school clinic surfaces were compared with MRSA isolated nasal cultures of dental students.

METHOD

Sixty-one dental students and 95 environmental surfaces from 7 clinics were sampled using SANICULT (Starplex Scientific Inc, Etobicoke, Ontario, Canada) swabs. Antimicrobial susceptibility testing was performed, and pulsed-field gel electrophoresis analysis, the mecA gene, multilocus sequence type, and SCCmec type were determined by polymerase chain reaction and sequencing.

RESULTS

Thirteen (21%) dental students and 8 (8.4%) surfaces were MRSA positive. Three MRSA strains were SCCmec type IV, whereas 3 were nontypeable isolates and Panton-Valentine leukocidin positive (PVL+), and none were USA300. One surface and 1 student isolate shared the same multilocus sequence type ST 8 and were 75% related. Two groups of students carried the same MRSA strains.

CONCLUSION

The MRSA-positive samples were from 4 of 7 dental clinics. In addition, 21% of the dental students carried MRSA, which is > 10 times higher than the general public and twice as frequent as in other university students. This is the first study to characterize MRSA from dental clinic surfaces and dental students and suggests that both may be reservoirs for MRSA. Further studies are needed to verify this premise.

[Evaluation of rapid genotype assay for the identification of gram-positive cocci from blood cultures and detection of mecA and van genes]

Rapid and accurate identification of bacterial pathogens grown in blood cultures of patients with sepsis is crucial for prompt initiation of appropriate therapy in order to decrease related morbidity and mortality rates. Although current automated blood culture systems led to a significant improvement in bacterial detection time, more rapid identification systems are still needed to optimise the establishment of treatment. Novel genotype technology which is developed for the rapid diagnosis of sepsis, is a molecular genetic assay based on DNA multiplex amplification with biotinylated primers followed by hybridization to membrane bound probes. The aim of this study was to evaluate the performance of "Genotype® BC gram-positive” test for the identification of gram-positive cocci grown in blood cultures and rapid detection of mecA and van genes. This test uses DNA.STRIP® technology which includes a panel of probes for identification of 17 gram-positive bacterial species and is able to determinate the methicillin and vancomycin resistance mediating genes (mecA and vanA, vanB, vanC1, vanC2/C3) simultaneously, in a single test run. A total of 55 positive blood cultures from BACTECTM Plus/F (Becton Dickinson, USA) aerobic and pediatric blood culture vials were included in the study. The isolates which exhibit gram-positive coccus morphology by Gram staining were identified by Genotype ® BC gram-positive test (Hain Life Science, Germany). All of the samples were also identified with the use of Phoenix PMIC/ID Panel (Becton Dickinson, USA) and antibiotic susceptibilities were determined. Of the 55 blood culture isolates, 17 were identified as Staphylococcus epidermidis [all were methicillin-resistant (MR)], 9 were S.aureus (one was MR), 18 were S.hominis (10 were MR), 4 were E.faecalis, 3 were E. faecium (one was vanconycin-resistant), 2 were S.saprophyticus (one was MR), 1 was S.warneri and 1 was S.haemolyticus, by Phoenix automated system. Genotype® BC gram-positive test results revealed consistency with Phoenix system regarding bacterial identification in 46 (83.6%) of the samples. The two bacteria identified as S.saprophyticus by the Phoenix system could not be identified by the Genotype® BC test since this species were not included in the identification panel of the system, however, mecA gene were detected in these two samples by Genotype® BC test. Genotype® BC test detected mecA gene in five samples which were not detected as methicillin resistant by the Phoenix system. Besides polymicrobial growth was determined in five samples by Genotype ® BC test, but not by the automated system. One E.faecium isolate with vanA gene was correctly identified by Genotype® BC test. In conclusion, Genotype® BC gram-positive test is a fast and reliable test for the identification of the most important gram-positive pathogens and mecA and van genes directly from positive blood culture bottles. This test was also found superior than the automated Phoenix system regarding the detection of polymicrobial growth. These data indicated that, routine use of DNA strip technology-based assay would be useful for clinical diagnosis in patients with sepsis.

Molecular epidemiology of methicillin-resistant Staphylococcus hominis (MRSHo): low clonality and reservoirs of SCCmec structural elements

Background

Methicillin resistant Staphylococcus hominis (MRSHo) are important human pathogens in immunocompromised patients. However, little is known regarding its population structure and staphylococcal chromosomal cassette mec (SCCmec) content.

Methodology/Principal Findings

To assess the population structure and the SCCmec content of S. hominis, 34 MRSHo and 11 methicillin-susceptible S. hominis (MSSHo) from neutropenic patients collected over a 3-year period were studied. The genetic backgrounds of S. hominis isolates were analyzed by pulsed-field gel electrophoresis (PFGE) and SCCmec types were determined by PCR. Cassette chromosome recombinases (ccr) were characterized by PCR and ccrB sequencing. The 34 S. hominis isolates were classified into as many as 28 types and 32 subtypes (SID = 99.82%); clonal dissemination was occasionally observed. The main SCCmec structures identified were SCCmec type VI (4B) (20%), SCCmec VIII (4A) (15%), and a new SCCmec composed of mec complex A in association with ccrAB1 (38%); 27% of the isolates harbored non-typeable SCCmec. Overall, a high prevalence of mec complex A (73.5%), ccrAB1 (50%) and ccrAB4 (44%) were found. Importantly, ccrB1 and ccrB4 from both MRSHo and MSSHo showed a high nucleotide sequence homology with those found in S. aureus SCCmec I, VI and VIII respectively (>95%).

Conclusions/Significance

The S. hominis population showed a limited clonality and a low genetic diversity in the allotypes of ccr and classes of mec complex. Moreover, our data suggest that S. hominis might have been a privileged source of mec complex A, ccrB1 and ccrB4, for the assembly of primordial SCCmec types.

Community-acquired methicillin-resistant Staphylococcus aureus--a review of literature

Recent studies suggest that the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) is changing and it is no longer only hospital-acquired but may also be community-acquired. Community-acquired Staphylococcus aureus (CA-MRSA) strains are emerging threats and are becoming important public health problem because they have been associated with high morbidity and mortality in the community. This review aims at highlighting the characteristics of these emergent strains of Staphylococcus aureus with a view to better management and control. The review, which consists of literature search of journals and chapters in books, provides an insight to the emergence of strains of methicillin-resistant Staphylococcus aureus (MRSA) in the community. It focuses on the changing epidemiology, molecular basis of resistance, pathogenesis, laboratory investigations and treatment of infections caused by these new strains. It is interesting to note that as a result of the emergence of these strains of methicillin-resistant Staphylococcus aureus (MRSA) in the community, the treatment options for MRSA is changing. This is due to the fact that these community strains have unique combinations of resistance traits and virulence factors which have enhanced their ability for colonization and pathogenesis. Their emergence in the community heralds a need for new approaches to the management of both suspected and confirmed staphylococcal infections. Since CA-MRSA constitutes a public health problem, there should be increased vigilance in the diagnosis and management of suspected and confirmed staphylococcal infections.

Diversity of SCCmec elements in methicillin-resistant coagulase-negative staphylococci clinical isolates

Background

Methicillin-resistant coagulase-negative staphylococci (MR-CoNS) are opportunistic pathogens and serve as a large reservoir of staphylococcal cassette chromosome mec (SCCmec). Characterization of SCCmec in MR-CoNS can generate useful information on the mobilization and evolution of this element.

Methodology/Principal Findings

Non-repetitive MR-CoNS clinical isolates (n = 84; 39 S. epidermidis, 19 S. haemolyticus, 9 S. hominis, 6 S. capitis, 4 S. warneri, 2 S. cohnii, 2 S. saprophyticus, 1 S. kloosii, 1 S. simulans and 1 S. massiliensis) were collected. All isolates could grow on plates with 4 mg/L cefoxitin and all had mecA as detected by PCR. Strain typing using RAPD and ERIC-PCR revealed that almost all isolates were of different strains. SCCmec typing was performed using multiplex PCR published previously. For isolates in which SCCmec could not be typed, the mec complex classes were determined by additional PCR and the ccr genes were amplified with published or newly-designed primers and then sequenced. SCCmec types were assigned for 63 isolates by multiplex PCR and were assigned for 14 other isolates by PCR targeting mec and ccr. Among 77 isolates with determined SCCmec types, 54 had a single type, including type III (n = 19), IV (n = 14), V (n = 10), II (n = 2), I (n = 1), VIII (n = 1) and five unnamed types (n = 7), while 23 isolates had two types, III+V (n = 12), II+V (n = 8), II+IV (n = 2) or IV+V (n = 1). The five unnamed types were assigned UT1 (class A mec, ccrA1/ccrB4), UT2 (class C1 mec, ccrA4/ccrB4), UT3 (class A mec, ccrA5/ccrB3), UT4 (class C2 mec, ccrA2/ccrB2 plus ccrC1) and UT5 (class A mec, ccrA1/ccrB1 plus ccrC1).

Conclusions/Significance

SCCmec types III, IV and V were prevalent in MR-CoNS and many isolates could harbor more than one type. Several new types of SCCmec were identified, highlighting the great genetic diversity and the need of developing classification schemes for SCCmec in MR-CoNS.

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.

Characterization of a new SCCmec element in Staphylococcus cohnii

Background

Many SCCmec elements of coagulase-negative staphylococci (CoNS) could not be typed using multiplex PCR. Such a ‘non-typable’ SCCmec was encountered in a Staphylococcus cohnii isolate.

Methodology/Principal Findings

The SCCmec type of methicillin-resistant S. cohnii clinical isolate WC28 could not be assigned using multiplex PCR. Newly-designed primers were used to amplify ccrA and ccrB genes. The whole SCCmec was obtained by three overlapping long-range PCR, targeting regions from left-hand inverted repeat (IRL) to ccrA/B, from ccrA/B to mecA and from mecA to orfX. The region abutting IRL was identified using inverse PCR with self-ligated enzyme-restricted WC28 fragments as the template. WC28 SCCmec had a class A mec gene complex (mecI-mecR1-mecA). The ccrA and ccrB genes were closest (89.7% identity) to ccrA_SHP of Staphylococcus haemolyticus strain H9 and to ccrB3 (90% identity) of Staphylococcus pseudintermedius strain KM241, respectively. Two new genes potentially encoding AAA-type ATPase were found in J1 region and a ψTn554 transposon was present in J2 region, while J3 region was the same as many SCCmec of Staphylococcus aureus. WC28 SCCmec abutted an incomplete SCC element with a novel allotype of ccrC, which was closest (82% identity) to ccrC1 allele 9 in Staphylococcus saprophyticus strain ATCC 15305. Only two direct target repeat sequences, one close to the 3′-end of orfX and the other abutting the left end of WC28 SCCmec, could be detected.

Conclusions/Significance

A new 35-kb SCCmec was characterized in a S. cohnii isolate, carrying a class A mec gene complex, new variants of ccrA5 and ccrB3 and two novel genes in the J1 region. This element is flanked by 8-bp perfect inverted repeats and is similar to type III SCCmec in S. aureus and a SCCmec in S. pseudintermedius but with different J1 and J3 regions. WC28 SCCmec was arranged in tandem with an additional SCC element with ccrC, SCC_WC28, but the two elements might have integrated independently rather than constituted a composite. This study adds new evidence of the diversity of SCCmec in CoNS and highlights the need for characterizing the ‘non-typable’ SCCmec to reveal the gene pool associated with mecA.

Differences between methicillin-resistant Staphylococcus aureus bacteremic isolates harboring type IV and type V staphylococcal cassette chromosome mec genes based on prior patient healthcare exposure

This observational study enrolled adult patients with bacteremia due to methicillin-resistant Staphylococcus aureus (MRSA) who were treated at the emergency department of a teaching hospital from 2001 to 2007. MRSA isolates with type IV and type V staphylococcal cassette chromosome mec (SCCmec) genes (SCC IV/V-MRSA) were included in the final analysis. Healthcare-associated SCC IV/V-MRSA (HA-SCC IV/V-MRSA) and community-acquired SCC IV/V-MRSA (CA-SCC IV/V-MRSA) were defined as the identification of an SCC IV/V-MRSA isolate from a patient with and without healthcare-associated risk factors, respectively. Thirty-four cases of CA-SCC IV/V-MRSA (20 SCCmec type IV, 14 SCCmec type V) and 81 cases of HA-SCC IV/V-MRSA (59 SCCmec type IV, 22 SCCmec type V) bacteremia were identified. Vascular device-associated infections were a significant infection source in HA-SCC IV/V-MRSA bacteremia cases. SCCmec type IV HA-SCC IV/V-MRSA isolates (3.4%) were significantly less likely to carry the Panton-Valentine leukocidin (PVL) gene than SCCmec type IV CA-SCC IV/V-MRSA isolates (35.0%, p = 0.001). The 90-day cumulative probability of survival was 76% for patients with CA-SCC IV/V-MRSA bacteremia and 66% for patients with HA-SCC IV/V-MRSA bacteremia (p = 0.247, by the Wilcoxon rank-sum test). Significant differences in antimicrobial susceptibility were observed between bacterial isolates from patients with CA-SCC IV/V-MRSA bacteremia and HA-SCC IV/V-MRSA bacteremia.

Detection of slime and methicillin resistance genes in Staphylococci isolated from nasal samples of patients with orthopaedic implants

BACKGROUND

The purposes of the present study were (1) to determine the prevalence of mecA and femA genes, (2) to investigate the presence of icaA and icaD genes responsible for slime synthesis, and (3) to search in vitro slime synthesis by staphylococcal strains isolated from the nares of patients with orthopaedic implants using the Congo red agar (CRA) plate test.

MATERIAL/METHODS

Staphylococci strains were defined by multiplex polymerase chain reaction (PCR) technique to determine intercellular adhesion genes icaA and icaD. Slime production capability was searched by the CRA plate test, phenotypically. Also, the presence of mecA and femA genes was determined by PCR in all strains.

RESULTS

The presence of icaA and icaD was detected in 101 isolates of 134 (75.4%) strains. This ratio was 74.8% (89 of 119) among the Staphylococcus epidermidis and 80% (12 of 15) among the Staphylococcus aureus isolates. A total of 63.4% of all the strains were found to be icaA and icaD positive as well as slime-forming on the CRA plate test. The percentage of icaA- and icaD-negative strains was 36.6%, and all of them were negative on the CRA plate test. Although femA presence was detected in all 15 (11.2%) S. aureus isolates, a total of 5 (3.7%) isolates carried the mecA gene.

CONCLUSIONS

The frequency of icaA and icaD genes was determined to be of high prevalence among staphylococcal isolates. The staphylococcal strains that were found in the nasal flora of patients with orthopaedic implants may be important potential sources of infection for these patients.

Methicillin resistance transfer from Staphylocccus epidermidis to methicillin-susceptible Staphylococcus aureus in a patient during antibiotic therapy

Background

The mecA gene, encoding methicillin resistance in staphylococci, is located on a mobile genetic element called Staphylococcal Cassette Chromosome mec (SCCmec). Horizontal, interspecies transfer of this element could be an important factor in the dissemination of methicillin-resistant S. aureus (MRSA). Previously, we reported the isolation of a closely related methicillin-susceptible Staphylococcus aureus (MSSA), MRSA and potential SCCmec donor Staphylococcus epidermidis isolate from the same patient. Based on fingerprint techniques we hypothesized that the S. epidermidis had transferred SCCmec to the MSSA to become MRSA. The aim of this study was to show that these isolates form an isogenic pair and that interspecies horizontal SCCmec transfer occurred.

Methodology/Results

Whole genome sequencing of both isolates was performed and for the MSSA gaps were closed by conventional sequencing. The SCCmec of the S. epidermidis was also sequenced by conventional methods. The results show no difference in nucleotide sequence between the two isolates except for the presence of SCCmec in the MRSA. The SCCmec of the S. epidermidis and the MRSA are identical except for a single nucleotide in the ccrB gene, which results in a valine to alanine substitution. The main difference with the closely related EMRSA-16 is the presence of SaPI2 encoding toxic shock syndrome toxin and exfoliative toxin A in the MSSA-MRSA pair. No transfer of SCCmec from the S. epidermidis to the MSSA could be demonstrated in vitro.

Conclusion

The MSSA and MRSA form an isogenic pair except for SCCmec. This strongly supports our hypothesis that the MRSA was derived from the MSSA by interspecies horizontal transfer of SCCmec from S. epidermidis O7.1.

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.

Distribution of Staphylococcal cassette chromosome mec Types and correlation with comorbidity and infection type in patients with MRSA bacteremia

Background

Molecular epidemiological definitions that are based on staphylococcal cassette chromosome mec (SCCmec) typing and phylogenetic analysis of methicillin-resistant Staphylococcus aureus (MRSA) isolates are considered a reliable way to distinguish between healthcare-associated MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA). However, there is little information regarding the clinical features and outcomes of bacteremia patients with MRSA carrying different SCCmec types.

Methods

From January 1 through December 31, 2006, we recorded the demographic data and outcomes of 159 consecutive adult MRSA bacteremia patients from whom isolates for SCCmec analysis were collected. All participants were patients at a tertiary care center in Taiwan.

Principal Findings

The following SCCmec types were identified in MRSA isolates: 30 SCCmec II (18.9%), 87 SCCmec III (54.7%), 22 SCCmec IV (13.8%), and 20 SCCmec V (12.6%). The time from admission to the first MRSA-positive blood culture for patients infected with isolates with the SCCmec III element (mean/median, 50.7/26 days) was significantly longer than for patients infected with isolates carrying SCCmec IV or V (mean/median, 6.7/3 days for SCCmec IV; 11.1/10.5 days for SCCmec V) (P<0.05). In univariate analysis, community onset, soft tissue infection, and deep-seated infection were predictors for SCCmec IV/V. In multivariate analysis, length of stay before index culture, diabetes mellitus, and being bedridden were independent risk factors associated with SCCmec II/III.

Conclusions

These findings are in agreement with previous studies of the genetic characteristics of CA-MRSA. MRSA bacteremia with SCCmec II/III isolates occurred more among patients with serious comorbidities and prolonged hospitalization. Community onset, skin and soft tissue infection, and deep-seated infection best predicted SCCmec IV/V MRSA bacteremia.

Evolution of methicillin-resistant Staphylococcus aureus clones in Latin America

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a prominent nosocomial bacterial pathogen, associated with significant morbidity and mortality. The global incidence is increasing, and Latin America is no exception. This article reviews MRSA clonal distribution in Latin America and implications for clinical practice.

DESIGN

A PubMed literature search (1966-2008) identified 32 articles that characterized MRSA clones in Latin America.

RESULTS

Data from these articles show that since 1990, several epidemic MRSA clones have spread in Latin America. The multidrug-resistant Brazilian clone is widespread, especially in Brazil and Argentina, but more recently clones with susceptibility to a range of antibiotics have been detected in Brazil, whereas in Argentina, as in Chile, Colombia and Paraguay, the multidrug-resistant Cordobes/Chilean clone prevails. In Mexico, the New York/Japan clone is most frequent. Data were not available from every country and, despite the increasing prevalence of community MRSA infections, most were collected from tertiary care centers.

CONCLUSIONS

A variety of epidemic MRSA clones are circulating in Latin America, some of which harbor genes that encode multidrug resistance or enhanced pathogenicity. Continued collection and reporting of epidemiological data is crucial for effective prevention and treatment.

Optical mapping reveals a large genetic inversion between two methicillin-resistant Staphylococcus aureus strains

Staphylococcus aureus is a highly versatile and evolving bacterium of great clinical importance. S. aureus can evolve by acquiring single nucleotide polymorphisms and mobile genetic elements and by recombination events. Identification and location of novel genomic elements in a bacterial genome are not straightforward, unless the whole genome is sequenced. Optical mapping is a new tool that creates a high-resolution, in situ ordered restriction map of a bacterial genome. These maps can be used to determine genomic organization and perform comparative genomics to identify genomic rearrangements, such as insertions, deletions, duplications, and inversions, compared to an in silico (virtual) restriction map of a known genome sequence. Using this technology, we report here the identification, approximate location, and characterization of a genetic inversion of approximately 500 kb of a DNA element between the NRS387 (USA800) and FPR3757 (USA300) strains. The presence of the inversion and location of its junction sites were confirmed by site-specific PCR and sequencing. At both the left and right junction sites in NRS387, an IS1181 element and a 73-bp sequence were identified as inverted repeats, which could explain the possible mechanism of the inversion event.

Recurrent community-associated methicillin-resistant Staphylococcus aureus infections among HIV-infected persons: incidence and risk factors

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are well described among the general population, but little is known regarding the incidence of and predictors for recurrent CA-MRSA infections among HIV-infected persons. We retrospectively evaluated HIV-infected patients seen at the Naval Medical Center San Diego from January 1, 2000 to June 30, 2007 for wound culture-proven MRSA infections defined as community-associated based on Centers for Disease Control and Prevention (CDC) criteria. Data on skin/soft tissue infections (SSTIs) following an initial CA-MRSA infection were collected by review of medical records and culture results. Patients with or without recurrent infections were compared for predictors of recurrence using multivariate logistic regression models. Thirty-one (6.8%) of 458 patients with HIV had wound culture-proven CA-MRSA SSTIs for an incidence rate of 12.3 infections per 1000 person-years. Those who developed a MRSA infection had a mean age of 40 years, 97% were male, 58% were Caucasian, 23% were Hispanic, 16% were African American, and 3% were other; demographics were similar to the overall study population. Fourteen (41%) HIV patients with an initial MRSA infection had recurrent SSTIs; of these, seven (21%) had culture-confirmed recurrent CA-MRSA. The median time between infection recurrences was 4 months (range, 1-20 months). Suppressed HIV-1 RNA levels of less than 1000 copies per milliliter (odds ratio [OR] 0.14, p = 0.03) was associated with a lower rate of SSTI recurrence. In summary, HIV-infected persons have a high incidence of CA-MRSA skin/soft tissue infections and a high rate of recurrence. HIV control may be associated with a reduced risk of recurrent skin/soft tissue infections.

A seasonal study of the mecA gene and Staphylococcus aureus including methicillin-resistant S. aureus in a municipal wastewater treatment plant

The spread of methicillin-resistant Staphylococcus aureus (MRSA), in which the mecA gene mediates resistance, threatens the treatment of staphylococcal diseases. The aims were to determine the effect of wastewater treatment processes on mecA gene concentrations, and the prevalence of S. aureus and MRSA over time. To achieve this a municipal wastewater treatment plant was investigated for the mecA gene, S. aureus and MRSA, using real-time PCR assays. Water samples were collected monthly for one year, at eight sites in the plant, reflecting different aspects of the treatment process. The mecA gene and S. aureus could be detected throughout the year at all sampling sites. MRSA could also be detected, but mainly in the early treatment steps. The presence of MRSA was verified through cultivation from inlet water. The concentration of the mecA gene varied between months and sampling sites, but no obvious seasonal variation could be determined. The wastewater treatment process reduced the mecA gene concentration in most months. Taken together our results show that the mecA gene, S. aureus and MRSA occur over the year at all sites investigated.

[Use of phenotypic methods to estimate species diversity for methicillin-resistant Staphylococcus epidermidis strains--comparative analysis]

Many identification and typing methods has been commonly used in microbiological laboratories. Phenotypic methods are the most frequently used. The aim of this study was to compare biochemical profiles and susceptibility patterns ofmethicillin-resistant S. epidermidis strains isolated from clinical material. 46 methicillin-resistant S. epidermidis strains were included in this study. Most of them were isolated from wound swabs (65.2%) and catheters (19.6%) from different surgical clinics (76.1%). To receive biochemical profiles ID 32 Staph tests and GPI cards of Vitek 1 were used receiving 18 and 14 profiles, respectively. 28 susceptibility patterns were obtained by disc-diffusion method and automatic system Vitek 1 using GPS-527 cards. ID 32 Staph tests and Vitek GPI cards represented the lowest discriminate power for methicillin-resistant S. epidermidis strains and they should not be recommended for typing them. Estimation of the susceptibility patterns was far more sensitive among examined phenotypic methods. Groups of strains have often the same profile received in ID 32 Staph test and Vitek GPI cards but different susceptibility.