Subtyping of methicillin-resistant Staphylococcus aureus isolates from the North-West of England: a comparison of standardised pulsed-field gel electrophoresis with bacteriophage typing including an inter-laboratory reproducibility study

Characterisation of antibiotic resistance, virulence, clonality and mortality in MRSA and MSSA bloodstream infections at a tertiary-level hospital in Hungary: a 6-year retrospective study

BACKGROUND

Staphylococcus aureus bloodstream infections (BSI) cause significant morbidity and mortality due to the frequent antibiotic resistance, toxin and adhesin production of the bacterium. These characteristics differ significantly in methicillin resistant (MRSA) and methicillin sensitive S. aureus (MSSA) and also among isolates of different MRSA clones, contributing to the outcome of S. aureus bacteraemia.

METHODS

In this study, all MRSA BSI isolates from Semmelweis University, Budapest, Hungary, isolated between 2011-2016 and the same number of matched MSSA (overall 306 isolates) were characterised in terms of antibiotic susceptibility, virulence genes, clonality and their association with all-cause 30-day mortality. Effect of patient related variables, such as age, gender and comorbidities were also investigated.

RESULTS

ST22-MRSA-IV and ST5-MRSA-II were the most prevalent clones in our study. SCCmec I isolates showed the highest resistance rates and SCCmec II carried most virulence genes. Infections caused by SCCmec IV isolates were associated with the highest mortality rate (42.2%), despite the similar comorbidity rates of the different patient groups. All-cause 30-day mortality was 39.9% in the MRSA and 30.7% in the MSSA group. Increased teicoplanin MIC was associated with high mortality rate. Resistance to ciprofloxacin, erythromycin and clindamycin was common in MRSA, whereas MSSA isolates were more sensitive to all antibiotics with the exception of doxycycline. All MRSA isolates were sensitive to glycopeptides and linezolid; resistance to rifampicin and sulfamethoxazole-trimethoprim was low. MRSA isolates carried more adhesion genes, superantigens were more frequent in MSSA. Panton-Valentine leukocidin was found in 2.3% of the isolates.

CONCLUSION

This study provides insight into the clonal composition and associated mortality of BSI S. aureus isolates in Hungary. The results suggest that the outcome of the infection is determined by the antibiotic resistance, genotype of the bacterium, and patient-related factors; rather than the virulence factors carried by the bacteria.

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.

Application of molecular techniques to the study of hospital infection

Nosocomial infections are an important source of morbidity and mortality in hospital settings, afflicting an estimated 2 million patients in United States each year. This number represents up to 5% of hospitalized patients and results in an estimated 88,000 deaths and 4.5 billion dollars in excess health care costs. Increasingly, hospital-acquired infections with multidrug-resistant pathogens represent a major problem in patients. Understanding pathogen relatedness is essential for determining the epidemiology of nosocomial infections and aiding in the design of rational pathogen control methods. The role of pathogen typing is to determine whether epidemiologically related isolates are also genetically related. To determine molecular relatedness of isolates for epidemiologic investigation, new technologies based on DNA, or molecular analysis, are methods of choice. These DNA-based molecular methodologies include pulsed-field gel electrophoresis (PFGE), PCR-based typing methods, and multilocus sequence analysis. Establishing clonality of pathogens can aid in the identification of the source (environmental or personnel) of organisms, distinguish infectious from noninfectious strains, and distinguish relapse from reinfection. The integration of molecular typing with conventional hospital epidemiologic surveillance has been proven to be cost-effective due to the associated reduction in the number of nosocomial infections. Cost-effectiveness is maximized through the collaboration of the laboratory, through epidemiologic typing, and the infection control department during epidemiologic investigations.

Guidelines for the prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections in the UK

These evidence-based guidelines have been produced after a literature review of the treatment and prophylaxis of methicillin-resistant Staphylococcus aureus (MRSA) infection. The guidelines were further informed by antibiotic susceptibility data on MRSA from the UK. Recommendations are given for the treatment of common infections caused by MRSA, elimination of MRSA from carriage sites and prophylaxis of surgical site infection. There are several antibiotics currently available that are suitable for use in the management of this problem and potentially useful new agents are continuing to emerge.

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.

Comparison of Staphylococcus aureus isolates from bovine and human skin, milking equipment, and bovine milk by phage typing, pulsed-field gel electrophoresis, and binary typing

Staphylococcus aureus isolates (n = 225) from bovine teat skin, human skin, milking equipment, and bovine milk were fingerprinted by pulsed-field gel electrophoresis (PFGE). Strains were compared to assess the role of skin and milking equipment as sources of S. aureus mastitis. PFGE of SmaI-digested genomic DNA identified 24 main types and 17 subtypes among isolates from 43 herds and discriminated between isolates from bovine teat skin and milk. Earlier, phage typing (L. K. Fox, M. Gershmann, D. D. Hancock, and C. T. Hutton, Cornell Vet. 81:183-193, 1991) had failed to discriminate between isolates from skin and milk. Skin isolates from humans belonged to the same pulsotypes as skin isolates from cows. Milking equipment harbored strains from skin as well as strains from milk. We conclude that S. aureus strains from skin and from milk can both be transmitted via the milking machine, but that skin strains are not an important source of intramammary S. aureus infections in dairy cows. A subset of 142 isolates was characterized by binary typing with DNA probes developed for typing of human S. aureus. Typeability and overall concordance with epidemiological data were lower for binary typing than for PFGE while discriminatory powers were similar. Within several PFGE types, binary typing discriminated between main types and subtypes and between isolates from different herds or sources. Thus, binary typing is not suitable as replacement for PFGE but may be useful in combination with PFGE to refine strain differentiation.

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.

Intact cell mass spectrometry (ICMS) used to type methicillin-resistant Staphylococcus aureus: media effects and inter-laboratory reproducibility

Intact cell mass spectrometry (ICMS) rapidly analyses the surface composition of microorganisms providing rapid, discriminatory fingerprints for identification and subtyping of important nosocomial pathogens such as methicillin resistant Staphylocccus aureus (MRSA). In this study, ICMS using matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI TOF/MS) was assessed for the identification and subtyping of MRSA. An intra- and inter-laboratory reproducibility study was carried out and the effects of culture media (an important source of variation for ICMS) were also studied. Several media used for the cultural identification of MRSA were examined using a panel of well-characterised staphylococcal isolates (n=26). Six MRSA isolates were analysed over a 1-month period for intra-laboratory reproducibility on the same instrument and three different culture media. Spectra were consistent for each isolate between the four experiments on the same culture medium. Individual isolates produced different spectral profiles on different culture media. Spectra from organisms grown on Columbia blood agar contained more peaks (approximately 120) compared to Columbia agar (approximately 50) and methicillin mannitol salt agar (approximately 25). All 26 staphylococcal isolates were subjected to an inter-laboratory study on two MALDI instruments. For each isolate, the overall spectral profile was the same for each of the two instruments but the baseline threshold values was adjusted due to instrument differences in detector sensitivities. Differences between certain regions of the spectra reproducibly identified isolates belonging to the two major MRSA strains (EMRSA phage group 15 and 16). These results demonstrate ICMS with appropriate media selection is a rapid and reproducible technique for identification and discrimination of MRSA.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus strains: state of affairs and tomorrow' s possibilities

Methicillin-resistant strains of Staphylococcus aureus (MRSA) have posed a clinical threat for nearly 40 years. During these years, an array of additional technologies suited for identification of MRSA below the species level has become available. The technologies, whether they assess phenotype or genotype, provide data that can be used for elucidation of the routes of dissemination of individual MRSA types. This review summarizes the current state of affairs with respect to the quality of the various laboratory techniques and includes descriptions of novel strategies such as binary typing and multilocus sequence typing (MLST). Drawbacks of procedures will be compared, and the value of molecular typing in the elucidation of complex biological phenomena, such as epidemicity, carriage, and reduced vancomycin susceptibility, will be indicated. Means for integrated assessment of bacterial biology, epidemiology, and population structure will be discussed.

A hospital-acquired outbreak of methicillin-resistant Staphylococcus aureus infection initiated by a surgeon carrier

Methicillin-resistant Staphylococcus aureus (MRSA) has become an important hospital-acquired pathogen, infection with which often leads to major morbidity and mortality. The principal mode of transmission for MRSA is transfer of the organism from a carrier or infected patient to uninfected patients by the hands or clothing of staff. From January 16 1997 to April 2 1997, five patients who had undergone open-heart surgery in a hospital located in northern Taiwan, developed surgical wound infections and mediastinitis caused by MRSA. All patients were hospitalized in two adjacent surgical intensive care units (ICUs) following their respective operations. Consequently, the hospital's infection control team commenced investigation of the outbreak. Pulsed-field gel electrophoresis (PFGE) has been shown to be a good technique for epidemiological typing. By analysing cultures taken from staff by PFGE, it was demonstrated that this outbreak was most likely to be initiated by a surgeon with MRSA carriage. After elimination of the carrier state using topical mupirocin treatment, the outbreak was controlled without further incident.