Methicillin-resistant Staphylococcus aureus typing methods: which should be the international standard?

Epidemiology of Staphylococcus aureus food isolates: Comparison of conventional methods with whole genome sequencing typing methods

A variety of methods exists for typing bacteria. However, guidelines for the application and interpretation of typing tools in epidemiologic investigations of Staphylococcus aureus are lacking. This study aimed to identify appropriate typing methods for S. aureus population studies and outbreak investigation. We compared pulsed-field gel electrophoresis (PFGE), seven loci multi-locus sequence typing (MLST), core genome MLST (cgMLST), core single nucleotide polymorphism (cSNP), and enterotoxin (se/SE) profiles on 351 S. aureus isolates. The discriminatory power, concordance, and congruence of typing results were assessed. cgMLST, cSNP, and PFGE yielded the highest discrimination value, followed by se/SE typing and MLST. The best concordance of results was found between cgMLST and cSNP, while the best congruence was observed for cgMLST and cSNP with all methods, followed by PFGE with MLST. The strengths and weaknesses of each method are highlighted. For population structure, cgMLST and cSNP performed better than PFGE and MLST in terms of resolution of clusters and in phylogenetic inference. Enterotoxin profiles matched with MLST groups, suggesting the use of se/SE typing to predict MLST results. For the retrospective analysis of 31 outbreaks, all methods performed almost equally to discriminate epidemiologically related strains and can be used to unambiguously distinguish outbreak strains.

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 MRSA epidemics have occurred in waves, whereby a previously successful lineage has been replaced by a more fit and better adapted lineage.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.

Control of Methicillin-Resistant Staphylococcus aureus Strains Associated With a Hospital Outbreak Involving Contamination From Anesthesia Equipment Using UV-C

Methicillin-resistant Staphylococcus aureus (MRSA) is considered an opportunistic pathogen in humans and is mainly associated with healthcare-associated infections (HCAIs). This bacterium colonizes the skin and mucous membranes of healthy people and causes frequent hospital outbreaks. The aim of this study was to perform molecular typing of the staphylococcal cassette chromosome mec (SCCmec) and agr loci as wells as to establish the pulsotypes and clonal complexes (CCs) for MRSA and methicillin-sensitive S. aureus (MSSA) outbreaks associated with the operating room (OR) at a pediatric hospital. Twenty-five clinical strains of S. aureus (19 MRSA and 6 MSSA strains) were recovered from the outbreak (patients, anesthesia equipment, and nasopharyngeal exudates from external service anesthesia technicians). These clinical S. aureus strains were mainly resistant to benzylpenicillin (100%) and erythromycin (84%) and were susceptible to vancomycin and nitrofurantoin. The SCCmec type II was amplified in 84% of the S. aureus strains, and the most frequent type of the agr locus was agrII, which was amplified in 72% of the strains; however, the agrI and agrIII genes were mainly detected in MSSA strains. A pulsed-field gel electrophoresis (PFGE) analysis grouped the 25 strains into 16 pulsotypes (P), the most frequent of which was P1, including 10 MRSA strains related to the anesthesia equipment, external service anesthesia technicians, and hospitalized patients. Multilocus sequence typing (MLST) identified 15 sequence types (STs) distributed in nine CCs. The most prevalent ST was ST1011, belonging to CC5, which was associated with the SCCmec type II and agrII type. We postulate that the external service anesthesia technicians were MRSA carriers and that these strains were indirectly transmitted from the contaminated anesthesia equipment that was inappropriately disinfected. Finally, the MRSA outbreak was controlled when the anesthesia equipment disinfection was improved and hand hygiene was reinforced.

Functionalized titanium implant in regulating bacteria and cell response

BACKGROUND

Biological complications are an issue of critical interest in contemporary dental and orthopedic fields. Although titanium (Ti), graphene oxide (GO) or silver (Ag) particles are suitable for biomedical implants due to their excellent cytocompatibility, bioactivity, and antibacterial properties, the exact antibacterial mechanism is not understood when the three substances are combined (Ti-GO-Ag).

MATERIALS AND METHODS

In this work, the material characterization, antibacterial property, antibacterial mechanisms, and cell behavior of Ti-GO-Ag fabricated by electroplating and ultraviolet reduction methods respectively, were investigated in detail.

RESULTS

The material char acterization of Ti-GO-Ag tested by atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, nanoindentation, nanoscratch, inductively coupled plasma mass spectrometer, and contact angle tester revealed the importance of GO concentration and Ag content in the preparation process. The antibacterial tests of Ti-GO-Ag clearly demonstrated the whole process of bacteria interacting with materials, including reactive oxygen species, endocytosis, aggregation, perforation, and leakage. In addition, the behavior of Ti-GO-Ag showed that cell area, length, width, and fluorescence intensity were affected.

CONCLUSION

Briefly, Ti-GO-Ag nanocomposite was a dual-functionalized implant biomaterial with antibacterial and biocom patible characterization.

Impact of mass migrations on the clonal variation of clinical Staphylococcus aureus strains isolated from the Western region of Saudi Arabia

OBJECTIVES

A rapid molecular typing system was used to determine the impact of mass migration on the clonal variation of Staphylococcus aureus isolates recovered from King Abdulaziz University Hospital (KAUH) Jeddah, in the western region of Saudi Arabia. This region experiences an annual influx of millions of pilgrims.

METHODS

SmaI-multiplex PCR typing (SMT) was used for the initial analysis of strains and the resulting data subsequently supported by Multi-Locus Sequence Typing (MLST).

RESULTS

A total of 89 S. aureus isolates were SMT typed and revealed a high degree of genetic variation, with 40 SMT profiles detected among the isolates. Representatives of all forty SMT types were subsequently analysed by MLST, identifying 26 sequence types. A novel sequence type (ST), named ST3303, was identified in two methicillin-sensitive S. aureus (MSSA) isolates. MSSA strains exhibited more diversity than methicillin-resistant S. aureus (MRSA) strains, with community acquired MSSA and MRSA strains reaching alarmingly high levels.

CONCLUSION

The relatively high degree of genetic diversity found among S. aureus isolates of single hospital was attributed to the fact that Jeddah is the principal gateway to Mecca, visited each year by millions of pilgrims from many countries. The observed diversity clearly reflects the impact of such mass migrations in the rapid dissemination of strains world-wide. Our findings suggest the importance of surveillance programmes in locations affected by mass migrations, both to monitor their impact on endemic strains and for the detection of pandemic strains. SMT provides a cost-effective and sensitive typing method for achieving this objective.

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.

Overview of phenotypic methods used for differentiation of Staphylococcus aureus

Choosing the appropriate method for differentiation of Staphylococcus aureus strains is important for effective diagnostics and epidemiological investigations. Despite the fact that the results of phenotypic methods are strongly dependent on environmental conditions, they can still be useful in the investigation of epidemic strains of S. aureus. In this article, the potential application of commonly used phenotypic methods in epidemiological studies of S. aureus was analysed. Advantages and disadvantages of methods such as biotyping, serotyping, phage typing, AST (Antimicrobial Susceptibility Testing), SDS-PAGE (Sodium Dodecyl Sulphate Polyacryl Gel Electrophoresis), MLEE (Multilocus Enzyme Electrophoresis) and MALDI-TOF MS (Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectroscopy) were also discussed. Finally, phenotypic techniques were compared in terms of their discriminatory potential, typeability of isolates, time of analysis, reproducibility, ease of performance and ease of results interpretation.

SDS-PAGE and Gel IEF: Tool for Differentiation of Methicillin-Resistant and Methicillin-Sensitive Strains of Staphylococcus aureus

The methicillin-resistant Staphylococcus aureus causes difficult-to-treat healthcare-associated infections in humans. For fast and effective selection of an appropriate antibiotic therapy, it is essential to have rapid and reliable methods for differentiation of methicillin-resistant S. aureus from less dangerous methicillin-sensitive S. aureus. There have been many methods for the identification of methicillin-resistant S. aureus described but none has been accepted as an international standard. The most commonly used techniques such as phenotyping and genotyping have a few disadvantages, for instance, these techniques are not reproducible and stable. In addition, they are time-consuming, expensive, and they are not capable to distinguish all S. aureus strains. In this study, the methicillin-resistant and methicillin-sensitive S. aureus isolates obtained from patients were extracted in hot water. The released proteins were characterised by sodium dodecyl sulphate polyacrylamide gel electrophoresis and gel isoelectric focusing. These two methods were able to differentiate among tested bacterial strains. The proposed methods are time saving, they are applicable in standard biochemical laboratories, and they do not require any expensive equipment.

Discriminatory Indices of Typing Methods for Epidemiologic Analysis of Contemporary Staphylococcus aureus Strains

Historically, a number of typing methods have been evaluated for Staphylococcus aureus strain characterization. The emergence of contemporary strains of community-associated S. aureus, and the ensuing epidemic with a predominant strain type (USA300), necessitates re-evaluation of the discriminatory power of these typing methods for discerning molecular epidemiology and transmission dynamics, essential to investigations of hospital and community outbreaks. We compared the discriminatory index of 5 typing methods for contemporary S. aureus strain characterization. Children presenting to St. Louis Children's Hospital and community pediatric practices in St. Louis, Missouri (MO), with community-associated S. aureus infections were enrolled. Repetitive sequence-based PCR (repPCR), pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), staphylococcal protein A (spa), and staphylococcal cassette chromosome (SCC) mec typing were performed on 200 S. aureus isolates. The discriminatory index of each method was calculated using the standard formula for this metric, where a value of 1 is highly discriminatory and a value of 0 is not discriminatory. Overall, we identified 26 distinct strain types by repPCR, 17 strain types by PFGE, 30 strain types by MLST, 68 strain types by spa typing, and 5 strain types by SCCmec typing. RepPCR had the highest discriminatory index (D) of all methods (D = 0.88), followed by spa typing (D = 0.87), MLST (D = 0.84), PFGE (D = 0.76), and SCCmec typing (D = 0.60). The method with the highest D among MRSA isolates was repPCR (D = 0.64) followed by spa typing (D = 0.45) and MLST (D = 0.44). The method with the highest D among MSSA isolates was spa typing (D = 0.98), followed by MLST (D = 0.93), repPCR (D = 0.92), and PFGE (D = 0.89). Among isolates designated USA300 by PFGE, repPCR was most discriminatory, with 10 distinct strain types identified (D = 0.63). We identified 45 MRSA isolates which were classified as identical by PFGE, MLST, spa typing, and SCCmec typing (USA300, ST8, t008, SCCmec IV, respectively); within this collection, there were 5 distinct strain types identified by repPCR. The typing methods yielded comparable discriminatory power for S. aureus characterization overall; when discriminating among USA300 isolates, repPCR retained the highest discriminatory power. This property is advantageous for investigations conducted in the era of contemporary S. aureus infections.

Bacteriophage types of methicillin-resistant Staphylococcus aureus in a tertiary care hospital

BACKGROUND

Phage typing had been utilised extensively to characterise methicillin-resistant Staphylococcus aureus (MRSA) outbreak strains in the past. It is an invaluable tool even today to monitor emergence and dissemination of MRSA strains.

AIMS

The aim of this study was to determine the prevalent phage types of MRSA in south India and the association between phage types, antibiotic resistance pattern and risk factors.

METHOD

A total of 48 non-duplicate MRSA strains recovered from various clinical samples during January to December, 2010 were tested against a panel of anti-staphylococcal antibiotics. Phage typing was carried out at the National Staphylococcal Phage Typing Centre, New Delhi. Out of 48, 32 hospitalised patients were followed up for risk factors and response to empirical and post sensitivity antibiotic therapy. The risk factors were compared with a control group of 30 patients with methicillin sensitive Staphylococcus aureus (MSSA) infection.

RESULTS

Amongst the five prevalent phage types, 42E was most common (52%), followed by a non-typable variant (22.9%), 42E/47/54/75 (16.6%), 42E/47 (6.2%) and 47 (2%). Phage type 42E was the predominant strain in all wards and OPDs except in the ICU where 42E/47/54/75 was most common. Although not statistically significant, strain 42E/47/54/75 (n=8) showed higher resistance to all drugs, except ciprofloxacin and amikacin, and were mostly D-test positive (87.5%) compared to the 42E strain (32%). Duration of hospital stay, intravenous catheterisation and breach in skin were the most significant risk factors for MRSA infection.

CONCLUSION

We found MRSA strain diversity in hospital wards with differences in their antibiotic susceptibility pattern. The findings may impact infection control and antibiotic policy significantly.

Whole genome sequencing in the prevention and control of Staphylococcus aureus infection

BACKGROUND

Staphylococcus aureus remains a leading cause of hospital-acquired infection but weaknesses inherent in currently available typing methods impede effective infection prevention and control. The high resolution offered by whole genome sequencing has the potential to revolutionise our understanding and management of S. aureus infection.

AIM

To outline the practicalities of whole genome sequencing and discuss how it might shape future infection control practice.

METHODS

We review conventional typing methods and compare these with the potential offered by whole genome sequencing.

FINDINGS

In contrast with conventional methods, whole genome sequencing discriminates down to single nucleotide differences and allows accurate characterisation of transmission events and outbreaks and additionally provides information about the genetic basis of phenotypic characteristics, including antibiotic susceptibility and virulence. However, translating its potential into routine practice will depend on affordability, acceptable turnaround times and on creating a reliable standardised bioinformatic infrastructure.

CONCLUSION

Whole genome sequencing has the potential to provide a universal test that facilitates outbreak investigation, enables the detection of emerging strains and predicts their clinical importance.

Typing of Methicillin resistant Staphylococcus aureus: a technical review

Increasing prevalence of Methicillin-resistant Staphylococcus aureus (MRSA) worldwide is a growing public health concern. MRSA typing is an essential component of an effective surveillance system to describe epidemiological trends and infection control strategies. Current challenges for MRSA typing are focused on selecting the most appropriate technique in terms of efficiency, reliability, ease of performance and cost involved. This review summarises the available information on application, potential and problems of various typing techniques in discriminating the strains and understanding the epidemiology of MRSA strains. The phenotypic methods in general are easier to perform, easier to interpret, cost effective and are widely available, however less discriminatory. The genotypic methods are expensive and technically demanding, however more discriminatory. Newer technologies involving sequencing of various genes are coming up as broadly applicable and high throughput typing systems. Still there is no consensus regarding the single best method for typing of MRSA strains. Phage typing is recommended as first line approach in epidemiological investigation of MRSA strains. PFGE remains the gold standard for characterisation of outbreak strains. DNA sequencing methods including MLST, spa typing, SCCmec typing and toxin gene profile typing are more practical methods for detecting evolutionary changes and transmission events. The choice of typing technique further depends on the purpose of the study, the facilities available and the utility of data generated to answer a desirable research question. A need for harmonisation of typing techniques by following standard protocols is emphasised to establish surveillance networks and facilitate global MRSA control.

The current role of pulsed-field gel electrophoresis in methicillin-resistant Staphylococcus aureus (MRSA) typing and the retrospective identification of outbreaks

The objective of this paper was to investigate whether retrospective pulsed-field gel electrophoresis (PFGE) of methicillin-resistant Staphylococcus aureus (MRSA) isolates at two-year intervals is suitable and sufficient to demonstrate changes in the clonal composition of MRSA isolates and to identify previously undetected local outbreaks. PFGE patterns of 400 MRSA isolates were collected between 2004 and 2008 at the University of Rostock Hospital in Germany, and were used to assess the prevalence of MRSA clones at different time points. Only minor changes were detected. The combined analysis of all isolates that were collected per year reduced the time needed to perform this laborious procedure. The retrospective identification of outbreaks may require shorter intervals. Improved infection prevention and control measures prevented further outbreaks in previously affected hospital departments. In conclusion, PGFE at two-year intervals is sufficient to detect changes in the clonal composition of local MRSA isolates. If time for identification is important during outbreak investigations, more rapid methods with a similarly high discriminatory power such as spa typing should be used.

SmaI restriction site-based multiplex PCR for typing of hospital- and community-acquired Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen, and morbidity and mortality rates associated with this pathogen have increased markedly in recent years. MRSA strains are generally resistant to several classes of antibiotics and are therefore difficult and costly to treat. A major issue is to identify the sources of MRSA infections and to monitor their epidemic spread. In this study, we report the development of a typing technique for S. aureus, based on single-nucleotide polymorphism (SNP) variations in and around SmaI-restriction sites (CCCGGG). An assessment of the SmaI restriction site-based multiplex PCR (SmaI-multiplex PCR) typing (SMT) with respect to pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) revealed a high level of concordance in the clustering of the test strains. The SmaI-multiplex PCR was found to be more discriminatory than MLST/staphylococcal cassette chromosome mec (SCCmec) typing but less discriminatory than PFGE. SMT can provide real-time information for the investigation of ongoing S. aureus hospital outbreaks. SMT meets the criteria of a practical typing method: it is simple, reproducible, and highly discriminatory and does not require expensive equipment or specialist expertise. Consequently, SmaI-multiplex PCR has the potential to be used in routine clinical microbiology laboratories.

Prevalence of staphylococcal enterotoxins, toxin genes and genetic-relatedness of foodborne Staphylococcus aureus strains isolated in the Marmara Region of Turkey

Staphylococcus aureus is a major foodborne pathogen and it has the ability to produce a number of extracellular toxins. We analyzed 1070 food samples obtained from retail markets and dairy farms in the Marmara Region of Turkey for the presence of S. aureus. Out of 147 isolates, 92 (62.6%) were enterotoxigenic. PCR was used to investigate the presence of staphylococcal enterotoxin genes (sea, seb, sec, sed, see, seg, seh, sei, sej, sek, sel, sem, sen, seo, sep, seq and seu), exfoliative toxin genes (eta and etb) and the toxic-shock syndrome toxin gene (tst). The PCR results showed that 53.3% of the isolates contained staphylococcal enterotoxin-like (SEl) toxin genes (seg, seh, sei, sej, sek, sel, sem, sen, seo, sep, seq and seu) which were more frequent than classical enterotoxin genes (sea to see). Furthermore, seo, sei, sem, seg, seu and sec were found in 37.0, 32.7, 30.4, 29.3, 29.3 and 27.2% of the isolates, respectively. The tst gene was detected and confirmed by DNA sequencing in 9 isolates. The presence of eta and etb were not found in the isolates. Enterotoxigenic capabilities of isolates with SEA-SEE were investigated by ELISA. Enterotoxigenic S. aureus isolates produced one to three enterotoxins, with the most frequently produced types being enterotoxin A and C. There was a correlation of 72.1% between production of a specific toxin and the presence of the respective genes. PFGE analysis was used to identify genetic-relatedness of enterotoxigenic S. aureus isolates and the results revealed that 13 groups of isolates from different or the same origin that contained the same genes showed 100% homology with indistinguishable band patterns. The other enterotoxigenic isolates showed related band patterns with 72-86% homology in sea-, 61-90% homology in sec-, 80-96% homology in seh-, and 69-96% homology in sep-positive isolates. To our knowledge, this is the first study to examine enterotoxins and related gene contents of S. aureus food isolates in the Marmara Region of Turkey.

Toxigenic status of Staphylococcus aureus isolated from bovine raw milk and Minas frescal cheese in Brazil

A group of 291 Staphylococcus aureus isolates from mastitic cow's milk (n = 125), bulk tank milk (n = 96), and Minas frescal cheese (n = 70) were screened for staphylococcal enterotoxin (SE) genes (sea, seb, sec, sed, see, seg, seh, sei, selj, and sell) and for the tst-1 gene encoding staphylococcal toxic shock syndrome toxin 1 by PCR assay. A total of 109 (37.5%) of the isolates were positive for at least one of these 11 genes, and 23 distinct genotypes of toxin genes were observed. Of the S. aureus isolates bearing SE genes, 17 (13.6%) were from mastitic cow's milk, 41 (41.7%) were from bulk tank milk, and 51 (72.9%) were from Minas frescal cheese. The occurrence of exclusively more recently described SE genes (seg through sell) was considerably higher (87 of 109 PCR-positive strains) than that of classical SE genes (sea through see, 15 strains). The SE genes most commonly detected were seg and sei; they were found alone or in different combinations with other toxin genes, but in 60.8% of the cases they were codetected. No strain possessed see. The tst-1 gene was found in eight isolates but none from mastitic cow's milk. Macrorestriction analysis of chromosomal DNA from 89 S. aureus isolates positive for SE gene(s) was conducted with the enzyme SmaI. Fifty-five distinct pulsed-field gel electrophoresis patterns were found, demonstrating a lack of predominance of any specific clone. A second enzyme, Apa I, used for some isolates was less discriminating than Sma I. The high genotype diversity of potential toxigenic S. aureus strains found in this study, especially from Minas frescal cheese, suggests various sources of contamination. Efforts from the entire production chain are required to improve consumer safety.

External quality assessment of the molecular diagnostics and genotyping of meticillin-resistant Staphylococcus aureus

Two multicentre external quality assessments (EQA) for the molecular detection and genotyping of meticillin-resistant Staphylococcus aureus (MRSA) were arranged. Firstly, 11 samples containing various amounts of inactivated MRSA strains, meticillin-susceptible S. aureus (MSSA), meticillin-resistant coagulase-negative staphylococci (MRCoNS) or Escherichia coli were distributed to 82 laboratories. Samples containing 10² or 10³ MRSA cells were correctly scored in only 16 and 46% of the datasets returned, respectively. Two of the used MSSA strains contained an SCCmec cassette lacking the mecA gene. There was a marked difference in the percentage of correct results for these two MSSA strains (37 and 39%) compared to the MSSA strain lacking the SCCmec cassette (88%). Secondly, a panel for MRSA genotyping, consisting of ten samples (two identical, three genetically related and five unique strains) was distributed to 19 laboratories. Seventy-three percent of the datasets recorded all samples correctly. Most pulsed-field gel electrophoresis (PFGE) protocols proved to be suboptimal, resulting in inferior resolution in the higher or lower fragment regions. The performance of molecular diagnostics for MRSA shows no significant changes since our first EQA in 2006. The first molecular typing results are encouraging. Both assessments indicate that programme expansion is required and that major performance discrepancies continue to exist.

Prevalence, genetic diversity, and antimicrobial susceptibility profiles of Staphylococcus aureus isolated from bovine mastitis in Zhejiang Province, China

This study was conducted to determine genetic diversity and antimicrobial susceptibility profiles of Staphylococcus aureus recovered from bovine mastitis in Zhejiang Province, China. Out of 3178 quarter milk samples from 846 lactating cows, among which 459 cows (54.3%) were found HMT positive, 890 quarters (28%) were found having subclinical mastitis. From 75 representative S. aureus isolates, 16 distinct types were identified by pulsed-field gel electrophoresis (PFGE). Four major PFGE types (A, B, C, and D) accounted for 82.7% of all isolates, and type A (41.3%) was observed in multiple herds across the studied areas. Each region was found to have a predominant type: Hangzhou type A (64.1%), Ningbo type C (34.5%) and type B (23.1%), Jinhua type D (53.3%), and Taizhou type C (62.5%). Results of antimicrobial susceptibility tests showed that 90.7% of the isolates were resistant to at least one antimicrobial. Resistance to penicillin and ampicillin (77.3%), tetracycline (60.0%), or erythromycin (48.0%) was observed. The bacteria resistant to multiple antibiotics such as penicillin, ampicillin, tetracycline, and erythromycin were commonly found. The information obtained from this study is useful for designing specific control programs for bovine S. aureus mastitis in this region.

Molecular Diagnostics and Comparative Genomics in Clinical Microbiology

Initially, the availability of molecular diagnostics was considered a panacea, but replacement of conventional tests for detection and identification of microorganisms by molecular procedures eventually gathered momentum. This chapter describes current state-of-the-art molecular diagnostics and comparative genomics in medical microbiology to provide an understanding of infectious disease over the coming years. Nucleic acid-based tests are being introduced with increasing speed into routine clinical microbiology laboratories. Some of the problems remaining to be solved prior to general acceptance of nucleic acid-mediated detection and identification of microbial pathogens are reviewed. Historic objections are slowly being taken apart, and an accelerated introduction of molecular diagnostics is being pursued in many cases. Clear improvement in clinical testing is achieved by introducing molecular tests. Therefore, swift introduction of such tests into clinical practice is important to be pursued. Several PCR tests show increased sensitivity, excellent specificity, and cost effectiveness highlighting the success of the novel applications in the field of bacterial infections. Finally, some of the problems remaining to be solved prior to general acceptation of nucleic acid-mediated detection and identification of microbial pathogens are also reviewed.

Rapid, automated epidemiological typing of methicillin-resistant Staphylococcus aureus

The QIAxcel is an accurate, automated DNA sizing system that can be used as an alternative to agarose gel electrophoresis for rapid, high throughput epidemiological typing of methicillin-resistant Staphylococcus aureus using staphylococcal interspersed repeating unit (SIRU) typing.

Epidemiologic genotyping of methicillin-resistant Staphylococcus aureus (MRSA) by pulsed-field gel electrophoresis (PFGE)

Staphylococcus aureus has long been recognized as one of the leading cause of hospital infections all over the world. Increased frequency of methicillin-resistant Staphylococcus aureus (MRSA) in hospitalized patients and possibility of vancomycin resistance requires rapid and reliable characterization of isolates and control of MRSA spread in hospitals. Typing of isolates helps to understand pathogenesis and route of the hospital pathogen spread. In this study, in the analysis of an outbreak of MRSA infections in one surgical ward, we used pulsed-field gel electrophoresis (PFGE) as a method of typing. PFGE revealed one epidemic strain type A in 13 out of 16 patients, and another two types (type B in two patients and type C in one patient). Discussing the typing results in the ward has changed the admission policy of patients with infected vascular ulcers who were then cured as outpatients, and admitted for surgery after that. This policy resulted with the stopping of the outbreak; during next 2.5 year there was no further MRSA outbreak in the ward. PFGE also showed subtypes which enabled the insight into dynamics of MRSA strain changes during the outbreak. PFGE could be recommended as a screening method in the MRSA outbreak analysis. Because of it's high discriminatory power still remains the gold standard for MRSA typing.

Bovine Staphylococcus aureus: association of virulence genes, genotypes and clinical outcome

Based on our clinical experience on bovine mastitis, we hypothesized that subtypes of Staphylococcus aureus (S. aureus) exist which differ in their contagious and pathogenic properties. In order to investigate this hypothesis, we analyzed strains of S. aureus isolated from spontaneous intramammary infection (IMI) with their virulence gene patterns and genotypes obtained by PCR amplification of the 16S-23S rRNA intergenic spacer (RS-PCR). The genotypes were then associated with epidemiological and clinical data including 26 herds. The results demonstrated a high association between genotypes and virulence gene patterns as well as between epidemiological and pathogenic properties of S. aureus. In particular, genotype B was related to high contagiosity and increased pathogenicity whereas the other types (C, OG) were found with infection of single cows. Because of the high clinical relevance, our results indicate the need to subtype the IMI-associated strains of S. aureus in the future.

Characterization of Staphylococcus aureus strains isolated from bovine milk in Hungary

Staphylococcus aureus is a major foodborne pathogen due to its capability to produce a wide range of heat-stable enterotoxins. The primary purpose of this research was to characterize S. aureus isolates recovered from mammary quarter milk of mastitic cows and from bulk tank milk produced on Hungarian dairy farms of different sizes. Macrorestriction analysis of chromosomal DNA from S. aureus isolates was performed using the restriction enzyme SmaI followed by pulsed-field gel electrophoresis (PFGE). The prevalence rates of nine S. aureus enterotoxin genes (sea, seb, sec, sed, see, seg, seh, sei, and sej) and of the toxic shock syndrome toxin 1 gene (tst) were determined by multiplex polymerase chain reaction (PCR). The bulk tank milks of 14 out of 20 farms were contaminated with S. aureus at levels of up to 6.0x10(3 )CFU/ml. Farm size had no significant effect (P>0.05) on the S. aureus counts in bulk milk. The prevalence rates of penicillin resistance were 88.9% and 20.0% among the S. aureus recovered from mastitic quarter milk and bulk tank milk, respectively. After phenotypic characterization, a total of 59 S. aureus isolates were selected for genotyping. PFGE analysis revealed 22 distinct pulsotypes, including 14 main types and 8 subtypes, at a similarity level of 86%. Only one or two main types were observed on each of the farms tested, indicating a lack of genetic diversity among S. aureus isolates within farms, and there were only two pulsotypes which occurred on more than one farm. The PFGE patterns showed genetic relatedness between the S. aureus strains recovered from quarter milk and bulk milk on two large farms, implying that on farms having a high number of mastitic cows, S. aureus from infected udders may contaminate bulk milk and, subsequently, raw milk products. Sixteen (27.1%) of the S. aureus isolates tested by multiplex PCR were found to be positive for enterotoxin genes, with 15 of them carrying just one gene and one strain carrying two genes (seg and sei). The most commonly detected toxin genes were seb, sea, and sec, whereas none of our isolates possessed the see, seh, sej, or tst genes. On 75% of the dairy farms surveyed, no enterotoxigenic staphylococci were recovered from either mastitic quarter milk or bulk tank milk.

Guidelines for the validation and application of typing methods for use in bacterial epidemiology

For bacterial typing to be useful, the development, validation and appropriate application of typing methods must follow unified criteria. Over a decade ago, ESGEM, the ESCMID (Europen Society for Clinical Microbiology and Infectious Diseases) Study Group on Epidemiological Markers, produced guidelines for optimal use and quality assessment of the then most frequently used typing procedures. We present here an update of these guidelines, taking into account the spectacular increase in the number and quality of typing methods made available over the past decade. Newer and older, phenotypic and genotypic methods for typing of all clinically relevant bacterial species are described according to their principles, advantages and disadvantages. Criteria for their evaluation and application and the interpretation of their results are proposed. Finally, the issues of reporting, standardisation, quality assessment and international networks are discussed. It must be emphasised that typing results can never stand alone and need to be interpreted in the context of all available epidemiological, clinical and demographical data relating to the infectious disease under investigation. A strategic effort on the part of all workers in the field is thus mandatory to combat emerging infectious diseases, as is financial support from national and international granting bodies and health authorities.

Use of variations in staphylococcal interspersed repeat units for molecular typing of methicillin-resistant Staphylococcus aureus strains

Staphylococcal interspersed repeat unit typing has previously been shown to have the ability to discriminate between epidemic methicillin-resistant Staphylococcus aureus strains in the United Kingdom. The current study illustrates its ability to distinguish between strains within an endemic setting thereby providing a rapid transportable typing method for the identification of transmission events.

Pathogen Detection in the Genomic Era

In the 21st century, one of the greatest challenges to public health and clinical microbiologists is the rapid detection and identification of emerging and reemerging pathogens. Complex factors such as genetic variation in the host and pathogen, environmental changes, population pressures, and global travel can all influence the emergence of infectious diseases. The SARS epidemic of 2003 highlighted the potential of an emerging pathogen to spread globally in a very short time frame (Peruski and Peruski, 2003). The diagnostics of such infectious diseases has been greatly affected in the past 20 years. No longer is cultivation and microscopy the only means of detecting infectious agents. With the introduction of molecular diagnostics, the ability to detect minute amounts of microbial nucleic acids in clinical specimens has revolutionized clinical microbiology. In particular, the utility of PCR allows the detection and quantitation of specific agents in a matter of hours. PCR sequencing of specific segments of nucleic acid allows for the determination of specific drug resistance that now aids in guiding viral therapies.

RAPD for the typing of coagulase-negative staphylococci implicated in catheter-related bloodstream infection

OBJECTIVES

A rapid random amplification of polymorphic DNA (RAPD) technique was developed to distinguish between strains of coagulase-negative staphylococci (CoNS) involved in central venous catheter (CVC)-related bloodstream infection. Its performance was compared with that of pulsed-field gel electrophoresis (PFGE).

METHODS

Patients at the University Hospital Birmingham NHS Foundation Trust, U.K. who underwent stem cell transplantation and were diagnosed with CVC-related bloodstream infection due to CoNS whilst on the bone marrow transplant unit were studied. Isolates of CoNS were genotyped by PFGE and RAPD, the latter employing a single primer and a simple DNA extraction method.

RESULTS

Both RAPD and PFGE were highly discriminatory (Simpson's diversity index, 0.96 and 0.99, respectively). Within the 49 isolates obtained from blood cultures of 33 patients, 20 distinct strains were identified by PFGE and 25 by RAPD. Of the 25 strains identified by RAPD, nine clusters of CoNS contained isolates from multiple patients, suggesting limited nosocomial spread. However, there was no significant association between time of inpatient stay and infection due to any particular strain.

CONCLUSION

The RAPD technique presented allows CoNS strains to be genotyped with high discrimination within 4h, facilitating real-time epidemiological investigations. In this study, no single strain of CoNS was associated with a significant number of CVC-related bloodstream infections.

Use of molecular epidemiology to monitor the nosocomial dissemination of methicillin-resistant Staphylococcus aureus in a University Hospital from 1991 to 2001

Methicillin-resistant Staphylococcus aureus (MRSA) has been the cause of major outbreaks and epidemics among hospitalized patients, with high mortality and morbidity rates. We studied the genomic diversity of MRSA strains isolated from patients with nosocomial infection in a University Hospital from 1991 to 2001. The study consisted of two periods: period I, from 1991 to 1993 and period II from 1995 to 2001. DNA was typed by pulsed-field gel electrophoresis and the similarity among the MRSA strains was determined by cluster analysis. During period I, 73 strains presented five distinctive DNA profiles: A, B, C, D, and E. Profile A was the most frequent DNA pattern and was identified in 55 (75.3%) strains; three closely related and four possibly related profiles were also identified. During period II, 80 (68.8%) of 117 strains showed the same endemic profile A identified during period I, 18 (13.7%) closely related profiles and 18 (13.7%) possibly related profiles and, only one strain presented an unrelated profile. Cluster analysis showed a 96% coefficient of similarity between profile A from period I and profile A from period II, which were considered to be from the same clone. The molecular monitoring of MRSA strains permitted the determination of the clonal dissemination and the maintenance of a dominant endemic strain during a 10-year period and the presence of closely and possibly related patterns for endemic profile A. However, further studies are necessary to improve the understanding of the dissemination of the endemic profile in this hospital.

Molecular epidemiology of clinical isolates of methicillin-resistant Staphylococcus aureus in Taiwan

During July 2000 and October 2001, a total of 595 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) were collected from six medical centers distributed in northern, central, and southern Taiwan. Specimen sources included blood (n = 279), pus (n = 173), sputum (n = 94), body fluids (n = 21), catheter tips (n = 20), and urine (n = 8). Pulsed-field gel electrophoresis (PFGE) with SmaI digestion was used to fingerprint these isolates. A total of 31 genotypes with 97 type-subtypes were identified. Subtypes could be identified in 7 genotypes. While there were 6 to 15 genotypes in each hospital, 433 isolates (73%) were shown to belong to a major type (genotype A, with 29 subtypes). This genotype was not only the type prevailing in all six hospitals but also the predominant clone in each hospital, accounting for 46 to 89% of all isolates in each hospital. Genotype C (16 subtypes) was the second dominant genotype, accounting for 9% of all isolates, and was distributed in five hospitals. Genotypes D (11 subtypes), E (5 subtypes), and B (6 subtypes) were distributed in five, four, and three hospitals, respectively. The other 26 types (30 type-subtypes) were minor. We conclude that the majority of MRSA clinical isolates shared a common PFGE pattern, indicating the presence of a single, epidemic MRSA clone prevailing in major hospitals in Taiwan.

Multilocus sequence typing and the evolution of methicillin-resistant Staphylococcus aureus

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in many countries is increasing and, in hospitals in some areas, more than half of all S. aureus disease isolates are MRSA. MRSA strains are becoming increasingly multiresistant, and have recently developed resistance to vancomycin, used successfully to treat MRSA for more than 30 years. This review summarises recent studies that have elucidated the evolutionary history of MRSA. The first MRSA isolate evolved from a sensitive, epidemic strain prevalent in Europe, and its progeny-the first MRSA clone-quickly spread to other continents. Analyses of epidemic MRSA isolates from hospitals in different countries by molecular methods, including multilocus sequence typing (MLST) and DNA microarray analysis, reveal that MRSA strains have evolved separately within five distinct epidemic, sensitive lineages. However, resistance has been transferred to S. aureus on many more than five occasions, as some lineages have acquired different structural types of the element carrying the methicillin resistance gene. The emergence of MRSA as a community pathogen has been noted in several countries, and MLST and SCCmec typing have been used to demonstrate that community-acquired MRSA strains are typically related only distantly to hospital MRSA strains, and thus represent novel acquisitions of SCCmec.

Methicillin resistant Staphylococcus aureus in the critically ill

Methicillin resistant Staphylococcus aureus (MRSA) is endemic within many hospitals worldwide. Critically ill patients on intensive care units have increased risk factors making them especially prone to nosocomially acquired infections. This review addresses the current situation regarding the evolution of MRSA and the techniques for identifying and epidemiologically typing it. It discusses specific risk factors, the morbidity and mortality associated with critically ill patients, and possibilities for future antibiotic treatments.

An epidemiologic survey of methicillin-resistant Staphylococcus aureus by combined use of mec-HVR genotyping and toxin genotyping in a university hospital in Japan

OBJECTIVE

To evaluate the usefulness of an assay using two polymerase chain reaction-based genotyping methods in the practical surveillance of methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

Nosocomial infection and colonization were surveyed monthly in a university hospital in Japan for 20 months. Genotyping with mec-HVR is based on the size of the mec-associated hypervariable region amplified by polymerase chain reaction. Toxin genotyping uses a multiplex polymerase chain reaction method to amplify eight staphylococcal toxin genes.

RESULTS

Eight hundred nine MRSA isolates were classified into 49 genotypes. We observed differing prevalences of genotypes for different hospital wards, and could rapidly demonstrate the similarity of genotype for outbreak isolates. The incidence of genotype D: SEC/TSST1 was significantly higher in isolates causing nosocomial infections (49.5%; 48 of 97) than in nasal isolates (31.4%; 54 of 172) (P = .004), suggesting that this genotype may represent the nosocomial strains.

CONCLUSION

The combined use of these two genotyping methods resulted in improved discriminatory ability and should be further investigated.

Phenotypic and genotypic properties of methicillin resistant Staphylococcus aureus strains isolated in Hungary, 1997-2000

An account is given on the activity of the National Center for Phage Typing of Staphylococci in Hungary in the period between 1997 and 2000 related to methicillin resistant Staphylococcus aureus (MRSA) strains originating mainly from hospital infections and sporadic cases. The rate of multiresistant MRSA strains has decreased gradually from 98.1% in 1997 to 74.6% in 2000, accordingly the typability by phages showed a considerable improvement by the international basic phages. Resistance pattern of MRSA strains became narrower in the period of the examinations. With the exception of erythromycin the rate of resistance decreased probably as a consequence of the increased use of erythromycin. The typing method was completed with the phenotypic and genotypic characterization of macrolide resistance. Among 73 MRSA strains type A was the most frequent macrolide resistance group, while type B, C1 and C2 occurred rarely. Type A was frequent also among the few MSSA and CNS strains. Out of the 168 examined S. aureus strains ermA genes occurred in 81.5%; in MSSA and CNS strains ermC1 genes were frequent, both genes are responsible for the target modification. The msrA gene, encoding the increased efflux, occurred only in CNS strains. Comparing the results obtained by phenotyping (phage typing) and genotyping (AP-PCR) methods it is of note that MRSA strains which proved non-typable by phage typing gave suitable results by the AP-PCR.

How many nosocomial infections are associated with cross-transmission? A prospective cohort study in a surgical intensive care unit

OBJECTIVE

To determine the percentage of cross-transmissions in an intensive care unit (ICU) with high nosocomial infection (NI) rates according to the data of the German Nosocomial Infection Surveillance System.

SETTING

A 14-bed surgical ICU of a 1,300-bed, tertiary-care teaching hospital.

METHOD

Prospective surveillance of NIs during a period of 9 months. If an NI was present, the isolates of the following indicator pathogens were stored and typed by species: Staphylococcus aureus, Enterococcus species, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacter species. Pulsed-field gel electrophoresis was performed for typing of S. aureus strains and arbitrarily primed polymerase chain reaction was applied for the other pathogens. The presence of two indistinguishable strains in two patients was considered as one episode of cross-transmission.

RESULTS

Two hundred sixty-two patients were observed during a period of 2,444 patient-days; 96 NIs were identified in 59 patients and the overall incidence density of NI was 39.3 per 1,000 patient-days. For 104 isolates, it was possible to consider typing results. Altogether, 36 cross-transmissions have lead to NIs in other patients. That means at least 37.5% of all NIs identified were due to cross-transmissions.

CONCLUSION

Because of the method of this study, the percentage of NIs due to cross-transmission identified for this ICU is an "at least number." In reality, the number of cross-transmissions, and thus the number of avoidable infections, may have been even higher. However, it is difficult to assess whether the percentage of NIs due to cross-transmission determined for this ICU may be the crucial explanation for the relatively high infection rate in comparison to other surgical ICUs.

Molecular epidemiology and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus in Taiwan

Methicillin-resistant Staphylococcus aureus (MRSA) has become an important nosocomial pathogen and has increased frequency in the past 20 years. It is highly transmissible between wards, hospitals, and cities. In most major hospitals in Taiwan, MRSA accounts for more than 60% of the S. aureus isolates. Whether there is a predominant strain, which is spread over the whole of Taiwan has not yet been studied. We collected 208 sequential clinical isolates of MRSA from 22 hospitals: seven in northern Taiwan, seven in western Taiwan, five in southern Taiwan, and three in eastern Taiwan during a three-month period in 1998. Using pulsed-field gel electrophoresis, 112 MRSA isolates were shown to belong to one major type,--type C, and this type was shown to have spread widely across all of Taiwan. Ninety-six isolates belonged to 20 other minor types. Most MRSA isolates of this major type were multi-drug resistant and only susceptible to vancomycin and rifampin. We concluded that the high prevalence of MRSA in Taiwan was partly due to the spreading of a predominant strain and most of them were multi-drug resistant. This might imply that more effort should be made to control the spread of MRSA in Taiwan.