Staphylococcus aureus has long been recognized as an important pathogen in human disease. Due to an increasing number of infections caused by methicillin-resistant S. aureus (MRSA) strains, therapy has become problematic. Therefore, prevention of staphylococcal infections has become more important. Carriage of S. aureus appears to play a key role in the epidemiology and pathogenesis of infection. The ecological niches of S. aureus are the anterior nares. In healthy subjects, over time, three patterns of carriage can be distinguished: about 20% of people are persistent carriers, 60% are intermittent carriers, and approximately 20% almost never carry S. aureus. The molecular basis of the carrier state remains to be elucidated. In patients who repeatedly puncture the skin (e.g., hemodialysis or continuous ambulatory peritoneal dialysis [CAPD] patients and intravenous drug addicts) and patients with human immunodeficiency virus (HIV) infection, increased carriage rates are found. Carriage has been identified as an important risk factor for infection in patients undergoing surgery, those on hemodialysis or CAPD, those with HIV infection and AIDS, those with intravascular devices, and those colonized with MRSA. Elimination of carriage has been found to reduce the infection rates in surgical patients and those on hemodialysis and CAPD. Elimination of carriage appears to be an attractive preventive strategy in patients at risk. Further studies are needed to optimize this strategy and to define the groups at risk.

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Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks.

The spa gene of Staphylococcus aureus encodes protein A and is used for typing of methicillin-resistant Staphylococcus aureus (MRSA) We used sequence typing of the spa gene repeat region to study the epidemiology of MRSA at a German university hospital One hundred seven and 84 strains were studied during two periods of 10 and 4 months, respectively Repeats and spa types were determined by Ridom StaphType, a novel software tool allowing rapid repeat determination, data management and retrieval, and Internet-based assignment of new spa types following automatic quality control of DNA sequence chromatograms Isolates representative of the most abundant spa types were subjected to multilocus sequence typing and pulsed-field gel electrophoresis One of two predominant spa types was replaced by a clonally related variant in the second study period Ten unique spa types, which were equally distributed in both study periods, were recovered The data show a rapid dynamics of clone circulation in a university hospital setting spa typing was valuable for tracking of epidemic isolates The data show that disproval of epidemiologically suggested transmissions of MRSA is one of the main objectives of spa typing in departments with a high incidence of MRSA

https://jcm.asm.org/content/jcm/41/12/5442.full.pdf

Typing of methicillin-resistant Staphylococcus aureus in a university hospital setting by using novel software for spa repeat determination and database management

Three hundred and twenty isolates of Staphylococcus aureus were typed by DNA sequence analysis of the X region of the protein A gene (spa). spa typing was compared to both phenotypic and molecular techniques for the ability to differentiate and categorize S. aureus strains into groups that correlate with epidemiological information. Two previously characterized study populations were examined. A collection of 59 isolates (F. C. Tenover, R. Arbeit, G. Archer, J. Biddle, S. Byrne, R. Goering, G. Hancock, G. A. Hebert, B. Hill, R. Hollis, W. R. Jarvis, B. Kreiswirth, W. Eisner, J. Maslow, L. K. McDougal, J. M. Miller, M. Mulligan, and M. A. Pfaller, J. Clin. Microbiol. 32:407-415, 1994) from the Centers for Disease Control and Prevention (CDC) was used to test for the ability to discriminate outbreak from epidemiologically unrelated strains. A separate collection of 261 isolates form a multicenter study (R. B. Roberts, A. de Lencastre, W. Eisner, E. P. Severina, B. Shopsin, B. N. Kreiswirth, and A. Tomasz, J. Infect. Dis. 178:164-171, 1998) of methicillin-resistant S. aureus in New York City (NYC) was used to compare the ability of spa typing to group strains along clonal lines to that of the combination of pulsed-field gel electrophoresis and Southern hybridization. In the 320 isolates studied, spa typing identified 24 distinct repeat types and 33 different strain types. spa typing distinguished 27 of 29 related strains and did not provide a unique fingerprint for 4 unrelated strains from the four outbreaks of the CDC collection. In the NYC collection, spa typing provided a clonal assignment for 185 of 195 strains within the five major groups previously described. spa sequencing appears to be a highly effective rapid typing tool for S. aureus that, despite some expense of specificity, has significant advantages in terms of speed, ease of use, ease of interpretation, and standardization among laboratories.

Evaluation of Protein A Gene Polymorphic Region DNA Sequencing for Typing of Staphylococcus aureus Strains

A rapid increase in the incidence of infection and colonization with vancomycin-resistant enterococci (VRE) has been reported from U.S. hospitals in the last 5 years. This increase poses several problems, including: a) the lack of available antimicrobials for therapy of infections due to VRE, since most VRE are also resistant to multiple other drugs, e.g., aminoglycosides and ampicillin, previously used for the treatment of infections due to these organisms, and b) the possibility that the vancomycin resistance genes present in VRE may be transferred to other gram-positive microorganisms such as Staphylococcus aureus. An increased risk of VRE infection and colonization has been associated with previous vancomycin and/or multiantimicrobial therapy, severe underlying disease or immunosuppression, and intra-abdominal surgery. Because enterococci can be found in the normal gastrointestinal or female genital tract, most enterococcal infections have been attributed to endogenous sources within the individual patient. However, recent reports of outbreaks and endemic infections due to enterococci, including VRE, have shown that patient-to-patient transmission of the microorganisms can occur either via direct contact or indirectly via hands of personnel or contaminated patient-care equipment or environmental surfaces. Prevention and control of the spread of vancomycin resistance will require coordinated, concerted effort from various departments of the hospital, and can only be achieved if each of the following elements is addressed: 1) prudent vancomycin use by clinicians, 2) education of hospital staff regarding the problem of vancomycin resistance, 3) early detection and prompt reporting of vancomycin resistance in enterococci and other gram-positive microorganisms by the hospital microbiology laboratory, and 4) immediate implementation of appropriate infection-control measures to prevent person-to-person transmission of VRE.

Recommendations for preventing the spread of vancomycin resistance

Recommendations for preventing the spread of vancomycin resistance: Recommendations of the Hospital Infection Control Practices Advisory Committee (HICPAC)

The polymorphic X-region of the protein A gene (spa) was used for molecular typing of methicillin-resistant Staphylococcus aureus (MRSA) strains. The X-region is characterized by a variable number (between 3 and 15) of small repeats. DNA sequencing of MRSA strains revealed 25 distinct repeats. Analysis of MRSA strains grown in vitro and in vivo revealed that the X-region was sufficiently stable for epidemiologic typing of MRSA strains. Spa typing of MRSA strains was compared to phage typing and, in general, concordance was found between the two methods. However, spa typing was more sensitive, allowing differentiation of strains within a particular phage type. Results obtained with spa typing suggest that hospital outbreaks may be caused by two or more MRSA strains. Spa typing may be an important tool in unravelling the spread of MRSA strains within and between hospitals.

Molecular typing of methicillin-resistant Staphylococcus aureus on the basis of protein A gene polymorphism

The X region of the protein A gene of Staphylococcus aureus contains a highly polymorphic sequence which is composed of repeats of 24 bp. We used amplification by PCR to investigate whether this region could be used to discriminate between epidemic and nonepidemic methicillin-resistant S. aureus (MRSA) strains. Most epidemic MRSA strains (24 of 33) harbored more than seven repeats, while most nonepidemic MRSA strains (10 of 14) contained seven or fewer repeats. It is conceivable that a longer X region results in a better exposition of the Fc-binding region of protein A, thereby facilitating colonization of host surfaces and contributing to the epidemic phenotype.

Discrimination of epidemic and nonepidemic methicillin-resistant Staphylococcus aureus strains on the basis of protein A gene polymorphism.

Seventy-eight Salmonella typhi strains isolated in 1994 and 1995 from patients living in Dhaka, Bangladesh, were subjected to phage typing, ribotyping, IS200 fingerprinting, and PCR fingerprinting. The collection displayed a high degree of genetic homogeneity, because restricted numbers of phage types and DNA fingerprints were observed. A significant number of the S. typhi strains (67%) were demonstrated to be multiple drug resistant (MDR). The vast majority of the MDR strains were resistant to chloramphenicol, ampicillin, trimethoprim, streptomycin, sulfamethoxazole, and tetracycline (R type CATmSSuT), a resistance phenotype that has also frequently been observed in India. Only two strains displayed a distinct MDR phenotype, R type AT-mSSuT. Pulsed-field gel electrophoresis demonstrated the presence of large plasmids exclusively in the MDR strains of both R types. The plasmids present in the S. typhi strains of R type CATmSSuT could be conjugated to Escherichia coli and resulted in the complete transfer of the MDR phenotype. PCR fingerprinting allowed discrimination of MDR and susceptible strains. The DNA fragments enabling discrimination of MDR and susceptible S. typhi strains by PCR were useful genetic markers for identifying MDR encoded by large plasmids of the H1 incompatibility group.

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Molecular typing of Salmonella typhi strains from Dhaka (Bangladesh) and development of DNA probes identifying plasmid-encoded multidrug-resistant isolates.

The presence of antibodies to staphylococcal enterotoxins (enterotoxins A through F) in sera of healthy subjects (n = 567) and in sera of patients with toxic shock syndrome (n = 20) was determined Furthermore, production of enterotoxins by Staphylococcus aureus isolated from humans was investigated In 46, 86, 78, 41, 20, and 91% of the sera of healthy subjects, antibodies were found against enterotoxins A, B, C, D, E, and F, respectively The high percentage of sera with antibodies against enterotoxin F correlated with the relatively high frequency of enterotoxin F-producing S aureus isolated from humans (one-third of the isolates produced enterotoxin F) In patients with toxic shock syndrome, antibodies against enterotoxin F were not present or were present only at very low levels An increase of antibodies after onset of the disease was observed in two of eight patients investigated From the results, it can be concluded that only those humans who show low levels of antibodies are susceptible to toxic shock syndrome

Serum antibodies to enterotoxins produced by Staphylococcus aureus with special reference to enterotoxin F and toxic shock syndrome.

A patient with chronic myelogenous leukemia became colonized with a Staphylococcus haemolyticus strain and experienced a septic episode caused by this strain during a cytostatic course. The strain was multiply resistant to antibiotics; the MIC and MBC of vancomycin were 2 and 4 mg/liter, and the MIC and MBC of teicoplanin were 4 and 16 mg/liter, respectively. We performed a surveillance study on the carriage of S. haemolyticus in medical and nursing staff of the hospital ward where the patient was treated. S. haemolyticus was isolated from 18 sites on 12 of the 39 people tested. A number of typing methods were performed in order to investigate the possible relationships among the isolates. Methods used were immunoblotting of staphylococcal peptides, plasmid analysis, restriction fragment length polymorphism of chromosomal DNA, and pulsed-field gel electrophoresis of total DNA. Compared with the immunoblotting technique, the molecular methods were more discriminative. The strain colonizing the patient showed a consistent pattern by all typing methods during isolation. When the immunoblot technique was used, similar patterns were found with isolates from hospital staff and isolates from unrelated sources. With the molecular techniques, no evidence of a local spread of the patient's strain was found. However, plasmid profiles and restriction fragment length polymorphism and pulsed-field gel electrophoresis patterns showed that S. haemolyticus isolates collected from hospital ward personnel were related, which was not the case with isolates collected from unrelated sources. Restriction fragment length polymorphism analysis was more discriminative when IS431 was used as a DNA probe instead of a probe based on the 16S rRNA gene. S. haemolyticus, as in this case, may develop resistance to vancomycin and teicoplanin. These antibiotics are considered the last-resort drugs for the therapy of nosocomial gram-positive infections. Thus, local spread of staphylococci resistant to these drugs is an important problem, which should be prevented by strict hygienic measures and antibiotic policy.

W. J. Van Leeuwen

Papers

Molecular typing of methicillin-resistant Staphylococcus aureus on the basis of protein A gene polymorphism

Discrimination of epidemic and nonepidemic methicillin-resistant Staphylococcus aureus strains on the basis of protein A gene polymorphism.

Molecular typing of Salmonella typhi strains from Dhaka (Bangladesh) and development of DNA probes identifying plasmid-encoded multidrug-resistant isolates.

Serum antibodies to enterotoxins produced by Staphylococcus aureus with special reference to enterotoxin F and toxic shock syndrome.

Nosocomial infection by Staphylococcus haemolyticus and typing methods for epidemiological study.