Correlation between esterase electrophoretic types and capsular polysaccharide types 5 and 8 among methicillin-susceptible and methicillin-resistant strains of Staphylococcus aureus

Epidemiologic and Clinical Utility of Typing Systems for Differentiating Among Strains of Methicillin-Resistant Staphylococcus aureus

Typing systems for differentiating among strains of methicillin-resistant Staphylococcus aureus (MRSA) can be valuable tools for the epidemiologist and the clinician. Specific criteria for evaluating such systems are typeability, reproducibility, and discriminatory power. An ideal typing system also would be rapid, inexpensive, technically simple, and readily available. Systems based on the detection of phenotypic variations include antimicrobial susceptibility testing, bacteriophage typing, multilocus enzyme electrophoresis, and electrophoretic methods such as protein eletrophoresis and immunoblotting. Systems that directly detect genotypic variations include plasmid profile analysis, restriction enzyme analysis of plasmid DNA, restriction enzyme analysis of chromosomal DNA, Southern blot analysis of specific restriction fragment length polymorphisms, and pulse field gel electrophoresis. in general, the more widely available typing systems based on phenotypic assays and plasmid analysis have limitations in typeability and/or discriminatory power.The chromosomal DNA-based techniques, although promising, are unproven approaches still under active investigation.

Staphylococcus aureus: Immunopathogenesis and Human Immunity

Considering a large number of pathogen factors that enable high virulence of a microorganism such as Staphylococcus aureus (S. aureus), it is essential to see them through the continuous adaptation to the newly acquired mechanisms of the host immune response and efforts to overcome these, allowing the bacteria a perfect ecological niche for growth, reproduction, and location of new hosts. Past efforts to create a vaccine that would provide effective protection against infections caused by S. aureus remained without success. The reasons for this stem from the outstanding adaptability skills of this microorganism to almost all environmental conditions, the existence of a numerous virulence factors whose mechanisms of action are not well known, as well as insufficient knowledge of the immune response to S. aureus infections. This review article deals with this issue from another perspective and emphasizes actual knowledge on virulence factors and immune response to S. aureus.

The comparison of Staphylococcus aureus types 5 and 8 with respect to methicillin resistance in patients admitted to Al-Zahra Hospital by PCR

BACKGROUND

Staphylococcus aureus is a common human pathogen in community- and hospital-acquired infection, and its capsule is involved in pathogenesis. The predominance of 2 capsular polysaccharides types 5 and 8, on the surface of clinical isolates, led to the development of conjugate vaccine (Staph VAX) based on capsular polysacchrides types 5 and 8 conjugated to a carrier protein. The aim of this study was to determine the prevalence of capsular polysaccharides types 5 and 8 Staphylococcus aureus strains among isolates and their comparison with respect to methicillin resistance.

MATERIALS AND METHODS

We studied the capsular genotypes of 193 isolates that encompassed both hospital- and community-acquired infection in Al-Zahra Hospital of Isfahan city from 2008 to 2009. Cap5 and 8 genes were detected by PCR method. Methicillin resistance was determined by PCR (mecA) and disk diffusion methods as well.

RESULT

In this population (193 cases), most of the clinical isolates (73%) expressed capsular polysaccharide type 5 (24%) and 8 (49%), whereas 27% were non-typeable. The prevalence of MRSA in type 8 was 67.9%, whereas MRSA isolates in the capsular genotype 5 were 22.2%.

CONCLUSION

This study Staphylococcus aureus confirms that the prevalence of capsular polysaccharide types (5 and 8) are predominant, and Staphylococcus aureus type 8 is more resistant to methicillin compared to type 5.

Complication of radiation therapy among patients with positive S. aureus culture from genital tract

AIM

The main goal of this investigation was to evaluate the influence of positive Staphylococcus aureus culture from the genital tract on patients receiving radiation therapy, suffering from carcinoma of the uterus. The other aim was to observe radiation therapy complications.

BACKGROUND

Radiation therapy of patients suffering from cervical cancer can be connected with inflammation of the genitourinary tract.

MATERIALS AND METHODS

In years 2006-2010 vaginal swabs from 452 patients were examined. 39 women with positive S. aureus cultures were analysed.

RESULTS

Complications and interruptions during radiation therapy were observed in 7 (18.9%) of 37 patients with positive vaginal S. aureus culture. One of them, a 46-year-old woman developed pelvic inflammatory disease. None of the six patients who received palliative radiotherapy showed interruption in this treatment. Isolated S. aureus strains were classified into 13 sensitivity patterns, of which 8 were represented by 1 strain, two by 2 strains and three by 13, 8 and 6 strains. One strain was diagnosed as methicillin resistant S. aureus (MRSA).

CONCLUSIONS

The results of the present study show that S. aureus may generally be isolated from the genital tract of female patients with neoplastic disease of uterus but is not often observed as inflammation factor of this tract. Comparison of species' resistance patterns may be used in epidemiological studies in order to discover the source of infections and therefore be of profound significance in the prevention of nosocomial infections.

Genetic relationship between methicillin-sensitive and methicillin-resistant Staphylococcus aureus strains from France and from international sources: delineation of genomic groups

Cluster analysis of the SmaI patterns, generated by pulsed-field gel electrophoresis, of 44 methicillin-resistant (MRSA) and 118 methicillin-sensitive (MSSA) Staphylococcus aureus strains isolated in various French hospitals and 61 MRSA and 48 MSSA strains from 20 other countries revealed 20 genomic groups distributed into four distantly related phylogenic branches. Eighty-three of the 105 MRSA strains (79%) were clustered in the six genomic groups of phylogenic branch I; and 154 of the 166 MSSA strains (92.8%) were clustered in the 14 genomic groups of phylogenic branches II, III, and IV. Agreement between genomic group and two other markers, esterase type and phage group, was obtained, emphasizing the clonal structure of the population. The genomic groups were delineated by esterase type. The distribution of the strains within the genomic groups was independent of their geographical origin; French strains were clustered with strains from other countries. The three types of the staphylococcal cassette chromosome mec (SCCmec) complex were distributed according to genomic groups. Most of the time, type I and type II SCCmec complexes were found in the MRSA strains belonging to the same genomic groups. In contrast, the type III SCCmec complex was specific to the MRSA strains belonging to the three genomic groups characterized by a common esterase type.

A Shared noncapsular antigen is responsible for false-positive reactions by Staphylococcus epidermidis in commercial agglutination tests for Staphylococcus aureus

Many of the commercial slide agglutination tests for Staphylococcus aureus incorporate antibodies against cell surface antigens associated with methicillin resistance, including capsular polysaccharides and an uncharacterized antigen, serotype 18. These tests are more sensitive than the first-generation agglutination procedures that detected only bound coagulase and protein A, but they suffer from false-positive reactions with some coagulase-negative staphylococci. The aim of this study was to elucidate the mechanism for false-positive agglutination by S. epidermidis in these tests. A group of methicillin-resistant S. aureus (MRSA) isolates, including a serotype 18 strain, that were not detectable in the first-generation tests were found to be of capsular polysaccharide type 8. All of these isolates were deficient in bound coagulase and/or protein A, and they possessed a heat-stable, proteinaceous antigen that was absent from a prototype capsule type 8 strain. Enzyme-linked immunosorbent assay and agarose gel immunodiffusion experiments demonstrated that this proteinaceous antigen was also present on both methicillin-sensitive and methicillin-resistant S. epidermidis clinical isolates. S. epidermidis strains that gave false-positive agglutination test results had a considerably higher level of this antigen than strains that gave the correct negative result. These findings reveal the importance of the careful selection of MRSA strains for raising anti-capsular type 8 antibodies for use in agglutination tests. Strains devoid of the antigen shared with S. epidermidis should be used to eliminate potential cross-reactions with this coagulase-negative coccus.

Comparison of DNA fingerprinting by PFGE and PCR-RFLP of the coagulase gene to distinguish MRSA isolates

Staphylococcus aureus isolates were collected from epidemiologically unrelated clinical sources in Japan between 1991 and 1993. A total of 40 isolates, five each of eight coagulase types, were analysed by polymerase chain reaction (PCR) of the coagulase gene, PCR-restriction fragment length polymorphism (RFLP) after AluI digestion, and pulsed-field gel electrophoresis (PFGE) of chromosomal DNA after SmaI digestion. The efficiency of discrimination among the isolates increased in the order of PCR < PCR-RFLP < PFGE, yielding five, 13 and 31 different types, respectively. To assess the clinical use of these methods, 42 additional methicillin-resistant S. aureus (MRSA) isolates collected from 27 inpatients in a hospital were analysed. PFGE and PCR-RFLP were able to discriminate 11 and four types, respectively. PFGE analysis detected cross-infection between four postoperative patients in an intensive-care unit, and in six neonates in intensive care. We conclude that of the three methods tested, PFGE analysis currently allows the most effective discrimination of MRSA strains.

Methicillin-resistant Staphylococcus aureus subtyping: interest of combined antibiotyping and esterase electrophoretic typing

Ninety-four methicillin-resistant Staphylococcus aureus isolates (MRSA) were characterized by means of two typing methods, antibiotyping and esterase electrophoretic typing. Antibiotyping, recorded on the basis of susceptibility testing of 13 antimicrobial agents, allowed the description of 18 antibiotypes, four of which comprised 30, 14, 14 and 12 strains respectively. Esterase electrophoretic typing, based on esterase activity against seven synthetic substrates after polyacrylamide-agarose gel electrophoresis, led to the description of 12 electrophoretic types, two of which were predominant with 60 and 20 strains respectively. The combined use of both typing methods yielded 32 combinations, three of which were predominant with 21, 12 and 11 strains respectively. A good differentiation of strains was achieved, particularly when the antibiotype was correlated to the electrophoretic type. Thus, the combination of antibiotyping with esterase electrophoretic typing may be proposed as a well-suited method for the characterization of MRSA strains.

Molecular genotyping of methicillin-resistant Staphylococcus aureus via fluorophore-enhanced repetitive-sequence PCR

Methicillin resistance in Staphylococcus aureus is a frequent cause of nosocomial and community-acquired infections. Accurate, rapid epidemiologic typing is crucial to the identification of the source and spread of infectious disease and could provide detailed information on the generation of methicillin-resistant S. aureus (MRSA) strains. The high degree of genetic relatedness of MRSA strains has precluded the use of more conventional methods of genetic fingerprinting. A rapid DNA fingerprinting method that exploits PCR amplification from a DNA repeat sequence in MRSA is described. The random chromosomal distribution of this repeat sequence provides an ideal target for detecting DNA fragment patterns specific to individual MRSA strains. Two PCR fingerprinting methods which use an oligonucleotide primer based on a repetitive sequence found in Mycoplasma pneumoniae are presented. The repetitive element sequence-based PCR (rep-PCR) and fluorophore-enhanced rep-PCR (FERP) can identify epidemic strains among background MRSA. The combination of oligonucleotide primers labeled with different fluorescent dyes allowed simultaneous FERP fingerprinting and mecA gene detection. Eight different fingerprint patterns were observed in MRSA strains collected from different sources. These techniques provide a rapid discriminatory means of molecular epidemiologic typing of MRSA involved in nosocomial infections.

Epidemiology of Staphylococcus aureus in patients with cystic fibrosis

Seven hundred and thirty-four isolates of Staphylococcus aureus, recovered from the sputum of 238 cystic fibrosis patients in six French hospitals, were characterized by esterase electrophoretic typing, capsular polysaccharide serotyping and phage typing and tested against 14 antibiotics for sensitivity. Thirty-four esterase electrophoretic types were found with a genotypic diversity coefficient of 0.91. Five hundred and forty-eight (78.7%) isolates produced capsular polysaccharide and 350 (50.3%) were type 8. Four hundred and sixty isolates (66.6%) were phage typable and 202 (28.2%) were lysed by group III bacteriophages. No esterase electrophoretic type, capsular type or phage type was specific to cystic fibrosis. Isolates belonged to a wide range of types, similar to strains acquired outside hospitals. Eighty-five patients had three or more consecutive isolates over at least 6 months. The ability of S. aureus to persist for long periods of time has been demonstrated in 73% of them. Methicillin-resistance was encountered among 73 strains (9.8%) which were also multiresistant. Two hundred and eighty-nine (39.9%) strains were sensitive to all antibiotics tested except to penicillin. Pristinamycin and co-trimoxazole were the most effective antibiotics. These results could contribute to the elaboration of a rational approach to the prophylaxis and therapy of respiratory staphylococcal infections in cystic fibrosis patients.

Molecular epidemiology for local outbreaks of methicillin resistant Staphylococcus aureus (MRSA). The need for several methods

Subtyping isolates may be useful for epidemiological studies of methicillin-resistant-Staphylococcus aureus (MRSA) outbreaks. Among subtyping methods, DNA-based techniques have been applied very effectively for this purpose. An outbreak of MRSA infections took place in one hospital in Barcelona early during 1991. From the beginning of the outbreak to December 92, 70 MRSA isolates from different patients and sources were collected. All strains were evaluated by restriction endonuclease analysis of plasmid DNA (REAP) and macrorestriction endonuclease analysis of genomic DNA using Sma I and pulsed-field-gel-electrophoresis (PFGE). Plasmid screening and REAP using Hind III demonstrated two plasmid subtypes: subtype A showing a large plasmid, and subtype B showing the same large plasmid plus a smaller one. Subtypes A and B corresponded to the more recent and older isolates, respectively, suggesting the loss of the small plasmid during the epidemic. PFGE using Sma I displayed two closely related profiles (PFGE subtype A and A'; CS = 0.90). These subtypes were different from those subtypes exhibited from 4 methicillin-susceptible-Staphylococcus aureus (MSSA) isolates from the same hospital and from 2 epidemiologically unrelated MRSA isolates. Almost all isolates showing PFGE subtype A preceded those isolates showing PFGE subtype A'. This fact and the similarity between both subtypes suggested minor chromosomal DNA rearrangement during the outbreak from a unique strain. While PFGE using Sma I is a useful tool in evaluation of clonal dissemination, our data suggest epidemic or local outbreaks may need several methods to best delineate the source and spread of MRSA strains. The reproducibility and discriminatory power of REAP makes it a useful adjunct in this context.

Use of commercial particle agglutination systems for the rapid identification of methicillin-susceptible and methicillin-resistant Staphylococcus aureus

The performance of a recently introduced Staphylococcus aureus identification system (Slidex Staph-Kit) was compared with that of currently available systems (Immuno Scan Staphlatex, Staphyloslide, Staphaurex and SeroSTAT II) for the identification of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible Staphylococcus aureus. The new system, which detects a capsular antigen common in MRSA, performed with equal or greater sensitivity than the other systems. None of the commercial systems was adversely affected by the methicillin susceptibility of the staphylococci when isolates were recovered from non-selective media. The greatest advantage of the anti-capsular monoclonal reagent was its improved performance on isolates recovered from selective media.

Typing of Staphylococcus aureus by pulsed-field gel electrophoresis, zymotyping, capsular typing, and phage typing: resolution of clonal relationships

Sixty-nine Staphylococcus aureus isolates from two epidemiologically unrelated sources were typed by pulsed-field gel electrophoresis after SmaI digestion of chromosomal DNA (genome typing), and the results were compared with those obtained by other typing methods: phage typing with the international set of phages, capsular serotyping with monoclonal antibodies against capsular polysaccharides type 5 and 8, and zymotyping by polyacrylamide agarose electrophoresis for esterase polymorphism. A good correlation of S. aureus types was found by these four typing methods. Differentiation increased in the order capsular typing < zymotyping < phage typing < genome typing, yielding 2, 10, 20, and 26 different S. aureus types, respectively. Five of the 26 genome types were further divided into several subtypes revealing clonal relationships. When 36 French S. aureus isolates were compared with 33 German S. aureus isolates, 3 strains representing clonal populations were identical in both groups. S. aureus isolates from patients with cystic fibrosis were also typed at the beginning and the end of a 4-week summer camp for these patients. The results suggested a possible strain transmission during the summer camp. We conclude that genome typing by pulsed-field gel electrophoresis is a powerful tool not only for strain identification but also for the resolution of the clonal relationships of S. aureus strains.

rRNA gene restriction patterns as an epidemiological marker in nosocomial outbreaks of Staphylococcus aureus infections

rRNA gene restriction patterns (ribotyping) were compared with phage typing, serotyping, enterotoxins and exfoliatin production in the analysis of 26 Staphylococcus aureus strains isolated from two different nosocomial outbreaks. Total DNA was cleaved by EcoRI restriction endonuclease. After agarose gel electrophoresis and Southern transfer, the hybridization of the membranes was done with radiolabelled 16S rRNA gene from Bacillus subtilis inserted into a plasmid vector. Six to 13 fragments were visualized. A core of common fragments was discerned for all strains tested. A full correlation between ribotyping and conventional markers was observed in only one of the outbreaks studied. In both outbreaks, ribotyping proved helpful in characterizing otherwise untypable strains.

Epidemiologic typing and delineation of genetic relatedness of methicillin-resistant Staphylococcus aureus by macrorestriction analysis of genomic DNA by using pulsed-field gel electrophoresis

To evaluate the usefulness of phenotypic and genotypic analyses for the epidemiologic typing of methicillin-resistant Staphylococcus aureus (MRSA), we characterized 64 epidemic MRSA isolates and 10 sporadic methicillin-susceptible S. aureus isolates from a university hospital and 18 MRSA isolates from hospitals in different geographical areas. Chromosomal DNA macrorestriction analysis with SstII was resolved by pulsed-field gel electrophoresis and compared with antibiotype analysis, phage type analysis, and standard genomic DNA restriction analysis with BglII. Indices of the discriminatory ability of these methods were 0.982, 0.959, 0.947, and 0.959, respectively. Macrorestriction patterns of 94% of MRSA isolates from patients, personnel, and the environment associated with a nosocomial outbreak were closely related (similarity coefficient, 85 to 100%). In contrast, methicillin-susceptible S. aureus isolates showed a marked diversity of macrorestriction patterns (median similarity, 41%). MRSA isolates from other geographical areas showed diverse macrorestriction patterns, with the exception of four isolates displaying identical or closely related patterns; these isolates were associated with concurrent outbreaks in four other Belgian hospitals. A concordance of genomic DNA macrorestriction typing with phenotypic methods was observed for 60 to 65% of MRSA isolates, and a concordance with standard DNA restriction analysis was found for 79 to 98% of these isolates. In conclusion, genomic DNA macrorestriction analysis was a useful complement to phenotypic methods for delineating epidemic isolates of MRSA, for identifying their nosocomial reservoirs, and for tracing their intra- and interhospital spread. The genetic relatedness of MRSA isolates, as estimated by this technique, appeared to correlate with their space-time clustering.

DNA polymorphisms in methicillin-susceptible and methicillin-resistant strains of Staphylococcus aureus

Restriction fragment length polymorphisms in methicillin-susceptible and methicillin-resistant (MRSA) strains of Staphylococcus aureus isolated in the same hospital over a 4-month period were studied by using SmaI and ApaI digestion of genomic DNA and pulsed-field gel electrophoresis. Each of the 20 methicillin-susceptible strains had a unique SmaI pattern, but the 27 MRSA strains showed only seven SmaI patterns. More than half of the SmaI fragments in all of these seven patterns were identical, as were those in the patterns from two unrelated MRSA strains. Digestion with ApaI, which cuts staphylococcus DNA into at least twice as many fragments, confirmed the results obtained with SmaI. Lastly, the plasmid contents of MRSA strains showing identical SmaI and ApaI electrophoretic patterns were not identical. These results are interpreted as supporting the hypothesis that all MRSA strains arose from a single clone and emphasize the need to use several methods in epidemiological investigations of MRSA outbreaks.

Epidemiologic typing of Staphylococcus aureus by DNA restriction fragment length polymorphisms of rRNA genes: elucidation of the clonal nature of a group of bacteriophage-nontypeable, ciprofloxacin-resistant, methicillin-susceptible S. aureus isolates

Analysis of DNA restriction fragment length polymorphisms of rRNA genes (ribotyping) was employed to assist in the epidemiologic investigation of the emergence and spread of ciprofloxacin-resistant Staphylococcus aureus at the Atlanta VA Medical Center because many isolates of interest were nontypeable by phages and harbored few plasmids useful as strain markers. Chromosomal DNAs of selected S. aureus isolates were digested initially with 20 different restriction enzymes. EcoRI appeared to give the best discrimination of hybridization banding patterns (ribotypes) and was used with all study isolates. Overall, 15 different ribotypes were seen among the 50 S. aureus isolates studied (7 ribotypes among 13 methicillin-susceptible S. aureus [MSSA] isolates and 9 ribotypes among 37 methicillin-resistant S. aureus [MRSA] isolates). Seven of eight ciprofloxacin-resistant MSSA (CR-MSSA) patient isolates had identical antibiograms, were nontypeable by phages, and had a single 22-MDa plasmid. Six of these seven CR-MSSA isolates had an identical ribotype pattern. Ribotyping distinguished this CR-MSSA strain or clone from MRSA and other MSSA isolates, including nontypeable isolates that contained a 22-MDa plasmid. Five ciprofloxacin-susceptible MSSA isolates studied had five ribotypes; one pattern was identical to the CR-MSSA clone. Twenty-three CR-MRSA isolates recovered from the Atlanta VA Medical Center had four different ribotypes. Ribotyping proved to be a useful molecular epidemiologic tool in the study of S. aureus because it differentiated isolates which were indistinguishable by more traditional methods. In addition, this technique demonstrated that at our institution, ciprofloxacin resistance emerged in multiple strains of MRSA, as opposed to primarily a single strain or clone of MSSA.

Epidemiologic and clinical utility of typing systems for differentiating among strains of methicillin-resistant Staphylococcus aureus

Typing systems for differentiating among strains of methicillin-resistant Staphylococcus aureus (MRSA) can be valuable tools for the epidemiologist and the clinician. Specific criteria for evaluating such systems are typeability, reproducibility, and discriminatory power. An ideal typing system also would be rapid, inexpensive, technically simple, and readily available. Systems based on the detection of phenotypic variations include antimicrobial susceptibility testing, bacteriophage typing, multilocus enzyme electrophoresis, and electrophoretic methods such as protein electrophoresis and immunoblotting. Systems that directly detect genotypic variations include plasmid profile analysis, restriction enzyme analysis of plasmid DNA, restriction enzyme analysis of chromosomal DNA, Southern blot analysis of specific restriction fragment length polymorphisms, and pulse field gel electrophoresis. In general, the more widely available typing systems based on phenotypic assays and plasmid analysis have limitations in typeability and/or discriminatory power. The chromosomal DNA-based techniques, although promising, are unproven approaches still under active investigation.

Epidemiological markers for epidemic strain and carrier isolates in an outbreak of nosocomial oxacillin-resistant Staphylococcus aureus

An outbreak of nosocomial infections occurring in a postoperative intensive care unit was caused by a single strain of oxacillin-resistant Staphylococcus aureus. Six patients were infected, or colonized, by this strain, which was traced by using the following four epidemiological markers: antibiogram, bacteriophage type, capsular polysaccharide type, and esterase electrophoretic type. This strain was compared with S. aureus isolates obtained from the noses of 13 carriers from a group of 42 staff members. A good correlation in terms of phenotypic markers was found between the epidemic strain and a strain isolated from one carrier. Both exhibited the same pattern of multiple resistance as well as the same phage type, 77, capsular polysaccharide type, 5, and esterase electrophoretic type, 6. In contrast, an oxacillin-resistant strain, isolated from another carrier, differed from the epidemic strain by susceptibility to rifampin and by susceptibility to four additional bacteriophages. The other 11 strains isolated from carriers were susceptible to oxacillin and exhibited widely different phenotypes. These results confirm the interest of using several epidemiological markers to trace the spread of epidemic S. aureus strains and to delineate the carrier strains.