[Relatedness of methicillin-resistant coagulase-negative staphylococci]

Many identification and relatedness studies methods had been commonly used for epidemiological studies in microbiological laboratories. Apart from phenotypic methods, genotypic are also often used. The aim of this study was to compare, obtained by PFGE chromosomal DNA patterns of methicillin-resistant S. epidermidis strains isolated from clinical material. 46 methicillin-resistant S. epidermidis strains were included in this study. Most of them were isolated from wound swabs (65.2%) and catheters (19.6%) from different surgical clinics (76.1%). To identify strains and receive biochemical profiles, ID 32 Staph tests and GPI cards of Vitek 1 system were used. Pulsed-field gel electrophoresis and Tenover et al. interpretation were used to compare chromosomal DNA patterns of examined strains. 44 and 42 PFGE patterns of chromosomal DNA were received, using visual interpretation classifying two pairs of strains as the same, two pairs as closely related and three pairs as probably related. Strains classified as identical and similar in visual evaluation were indistinguishable in Molecular Analyst DST interpretation, probably due to tolerance in bands location pattern. Strains probably related in visual interpretation represent at least 96% similarity in Molecular Analyst DST but different susceptibility and biochemical profiles obtained by ID 32 Staph and Vitek 1. PFGE analysis had foremost capacity to distinguish methicillin-resistant S. epidermidis strains using visual interpretation and Molecular Analyst DST (Bio-Rad) program and seems to be useful method in epidemiological studies. Strains with the same PFGE pattern, had different susceptibility and biochemical profiles.

Evaluation of methicillin resistance by cefoxitin disk diffusion and PBP2a latex agglutination test in mecA-positive Staphylococcus aureus, and comparison of mecA with femA, femB, femX positivities

Methicillin resistance in staphylococci is primarily due to the presence of a mecA gene which encodes the novel penicillin binding protein2a. Some chromosomal factors such as femA and femB also participate in the expression of methicillin resistance. This study was designed to detect methicillin resistance by cefoxitin disk diffusion and penicillin binding protein2a latex agglutination methods, and to compare mecA, femA, femB and femX gene positivities. A total of 60 MRSA isolates were included in the evaluation. PCR analysis showed that all isolates were positive for mecA and femA genes. Seven of these isolates tested negative by the latex agglutination test. Fifteen isolates were positive for femB and 28 isolates for femX gene. This study implicated that for the determination of methicillin resistance, latex agglutination test is the least reliable method when compared to PCR and cefoxitin disk diffusion test. femA gene shows more correlation than femB and femX with methicillin resistance.

[Application of multiplex pcr for identification of MRSA and MRCNS strains in medium of automatic blood culture system]

Rapid detection and identification ofmethicillin-resistant staphylococci in patient's blood is essential for the prompt antimicrobial therapy of infection. Molecular-based diagnosis, in comparison to conventional methods, allows to increase sensitivity and to reduce time necessary to achieve positive results and also enable to test susceptibility. The aim of the study was the use of multiplex PCR to detect region of the 16S rRNA that is unique to staphylococci, the S. aureus-specific clfA gene and the mecA gene which is a determinant of methicillin resistance, in a medium of the BACTEC blood culture system. Three different extraction methods were examined in order to ascertain the most suitable method to isolate staphylococcal DNA. The only method which removed PCR inhibitors contained in BACTEC blood culture material use Triton X-100 and lysostaphyin to lysis bacterial cells. The use of High Template Preparation Kit failed to yield a positive result in all investigated probes. Third of the methods, based on alkali lysis, resulted in DNA which could be amplified by PCR only in case of S. aureus blood culture. The findings of our study suggest that not all DNA extraction methods are appropriate because some of them may not remove potent amplification inhibitors found in blood and medium of system BACTEC.

A novel gene, fudoh, in the SCCmec region suppresses the colony spreading ability and virulence of Staphylococcus aureus

Staphylococcus aureus colonies can spread on soft agar plates. We compared colony spreading of clinically isolated methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). All MSSA strains showed colony spreading, but most MRSA strains (73%) carrying SCCmec type-II showed little colony spreading. Deletion of the entire SCCmec type-II region from these MRSA strains restored colony spreading. Introduction of a novel gene, fudoh, carried by SCCmec type-II into Newman strain suppressed colony spreading. MRSA strains with high spreading ability (27%) had no fudoh or a point-mutated fudoh that did not suppress colony spreading. The fudoh-transformed Newman strain had decreased exotoxin production and attenuated virulence in mice. Most community-acquired MRSA strains carried SCCmec type-IV, which does not include fudoh, and showed high colony spreading ability. These findings suggest that fudoh in the SCCmec type-II region suppresses colony spreading and exotoxin production, and is involved in S. aureus pathogenesis.

[Molecular typing of methicillin-resistant Staphylococcus aureus isolated from hospitalized patients in Qingdao]

OBJECTIVE

To explore the molecular types of methicillin-resistant Staphylococcus aureus (MRSA) strains present in major hospitals in Qingdao area, using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) methods, trying to find out the epidemiological characteristics of these MRSA isolates. Correlation of the PFGE types with microbiological phenotypes and clinical data was also studied.

METHODS

360 isolates of MRSA were procured during 2003 to 2007 from major hospitals in Qingdao. PFGE technology was applied to comparatively analyze the chromosomal DNA digested with endonuclease SmaI. Comparison of DNA fragments patterns from each MRSA strain and cluster analysis were performed with the Bionumerics version '2.0' software. A dendrogram was generated using PFGE macrorestriction fragments on gel images. Data was used to predict the possibility of each PFGE type via SPSS software version 11.0, using the variables as predictors including groups on patient's age, gender, source and the site where MRSA was isolated. Antibiotic sensitivity patterns of these MRSA isolates were determined by K-B tests, and a correlation between these patterns and PFGE types was investigated. Housekeeping genes were amplified with PCR and sequenced in representative strains of variant PFGE types to identify their allelic profile.

RESULTS

5 types of PFGE patterns (M0-M4) were identified with M1 being the predominant and M2 next to it which was significantly correlated to the isolates from wounds. M3 type strains were mainly isolated from ICU wards and there were a few cases complied with M4 type with no correlated variant factors found in this study. A unique pattern of MRSA isolates with its M0 distinct from other types had not been reported. No significant association was found between PFGE individual types, gender or age groups. M1 and M2 types were the major proportional PFGE patterns among different hospitals. No vancomycin-resistant isolates were detected among 360 MRSA strains. No significant association was found between individual antibiotic resistance and specific PFGE types. Data from MLST analysis showed that the allelic profiles of M1 and M3 type strain had the same ST239 linage which was commonly present in China. For M2 and M4 representative strains, the allelic profiles were ST5 and ST240, respectively. ST45 and ST398 were corresponding to two PFGE patterns clustered as M0 type.

CONCLUSION

Nosocomial infection due to MRSA was evenly distributed among different age groups and no gender bias was observed. The PFGE types of MRSA strains isolated in major hospitals in Qingdao were highly correlated with the sources of isolates and ST239 isolate seemed the prevalent and widespread one. Strategies should be designed to further monitor and prevent or minimize the spread of ST5 MRSA isolates and the like, in Qingdao area.

Antimicrobial resistance of old and recent Staphylococcus aureus isolates from poultry: first detection of livestock-associated methicillin-resistant strain ST398

The susceptibilities of 12 antimicrobial agents for two collections of Staphylococcus aureus, isolated in the 1970s and in 2006 from poultry, were determined. For eight antibiotics, the percentage of resistance was significantly higher in the recent isolates. Ten recent isolates were methicillin resistant and had spa types t011 and t567, belonging to multilocus sequence type 398. This is the first report of "livestock-associated" methicillin resistant S. aureus from healthy poultry.

Phenotypic and genetic antibiogram of methicillin-resistant staphylococci isolated from bovine mastitis in Korea

Staphylococcus aureus belongs to the group of major contagious mastitis pathogens, whereas the coagulase-negative staphylococci (CNS) are also capable of causing opportunistic bovine mastitis. Many of these strains are resistant to penicillin or ampicillin because of the long-term use of beta-lactam antibiotics in agricultural and healthcare settings. Based on the simple and highly specific coagulase genotyping by PCR-RFLP used for discriminating among Staph. aureus strains, the relationship between phenotypic antibiogram and the polymorphism of coagulase gene was determined in this study. The staphylococci strains (835 Staph. aureus and 763 CNS) were isolated from 3,047 bovine mastitic milk samples from 153 dairy farms in 8 provinces from 1997 to 2004 in the Republic of Korea. Twenty-one (2.5%) Staph. aureus and 19 (2.4%) CNS strains were resistant to methicillin [oxacillin minimum inhibitory concentration (MIC) > or = 4 microg/mL]. The mecA gene was also found in 13 methicillin-resistant Staph. aureus (MRSA) and 12 methicillin-resistant CNS (MRCNS) isolates with a significantly higher detection rate of the mecA gene in MRSA with high MIC (> or = 16 microg/mL) compared with those with MIC < or = 8 microg/mL. Methicillin-resistant Staph. aureus and MRCNS were also more resistant to other antibiotics (ampicillin, cephalothin, kanamycin, and gentamicin) than methicillin-susceptible staphylococci. Among 10 different coa PCR-RFLP patterns (A to J) in 706 Staph. aureus strains, the main types were A (26.9%), B (17.0%), G (10.5%), and H (15.4%), with the frequent observation of the A and H types (6 and 10 isolates) in MRSA. This study indicates that major epidemic Staph. aureus clones may be spread between different dairy farms, and the profile of coa genotype can be applied for epidemiological investigations and control of bovine mastitis, particularly one caused by MRSA with specific prevalent coa types.

Genetic characterization of Staphylococcus aureus isolates carrying Panton-Valentine leukocidin genes in Bangladesh

To assess the spread and genetic characteristics of Panton-Valentine leukocidin (PVL) gene-carrying Staphylococcus aureus in Bangladesh, we investigated 59 strains (49 isolates from clinical specimens and 10 isolates colonized in the nasal cavities of medical staff), including 26 methicillin-resistant S. aureus (MRSA) strains. The PVL gene was detected only in methicillin-susceptible S. aureus (MSSA) strains (7 clinical strains and 2 colonizing strains). PVL gene-positive MSSA strains were found to belong to coagulase serotypes III or VI and were classified into sequence types ST88 (CC88), ST772, and ST573 (CC1) by multilocus sequence typing, and agr types 2 or 3. These types were different from those determined for MRSA (coagulase serotypes I and IV, ST240 and ST361, and agr type 1). PVL gene-positive MSSA possessed a larger number of virulence factor genes than MRSA, although they were susceptible to more antimicrobials. These findings suggest that the PVL gene is distributed to limited populations of S. aureus clones with specific genetic traits that are distinct from MRSA in Bangladesh, but genetically close to CA-MRSA clones in the CC1 lineage reported in the United States and European countries.

Horizontal gene transfers link a human MRSA pathogen to contagious bovine mastitis bacteria

BACKGROUND

Acquisition of virulence factors and antibiotic resistance by many clinically important bacteria can be traced to horizontal gene transfer (HGT) between related or evolutionarily distant microflora. Comparative genomic analysis has become an important tool for identifying HGT DNA in emerging pathogens. We have adapted the multi-genome alignment tool EvoPrinter to facilitate discovery of HGT DNA sequences within bacterial genomes and within their mobile genetic elements.

PRINCIPAL FINDINGS

EvoPrinter analysis of 13 different Staphylococcus aureus genomes revealed that one of the human isolates, the hospital epidemic methicillin-resistant MRSA252 strain, uniquely shares multiple putative HGT DNA sequences with different causative agents of bovine mastitis that are not found in the other human S. aureus isolates. MRSA252 shares over 14 different DNA sequence blocks with the bovine mastitis ET3 S. aureus strain RF122, and many of the HGT DNAs encode virulence factors. EvoPrinter analysis of the MRSA252 chromosome also uncovered virulence-factor encoding HGT events with the genome of Listeria monocytogenes and a Staphylococcus saprophyticus associated plasmid. Both bacteria are also causal agents of contagious bovine mastitis.

CONCLUSIONS

EvoPrinter analysis reveals that the human MRSA252 strain uniquely shares multiple DNA sequence blocks with different causative agents of bovine mastitis, suggesting that HGT events may be occurring between these pathogens. These findings have important implications with regard to animal husbandry practices that inadvertently enhance the contact of human and livestock bacterial pathogens.

grlA and gyrA mutations and antimicrobial susceptibility in clinical isolates of ciprofloxacin- methicillin-resistant Staphylococcus aureus

OBJECTIVE

To determine grlA and gyrA mutations in ciprofloxacin- methicillin-resistant Staphylococcus aureus isolates and their susceptibility to current antimicrobials, including a newer fluoroquinolone gatifloxacin, glycopeptides vancomycin, teicoplanin and oxazolidinone linezolid.

METHODS

A total of 56 methicillin-resistant S. aureus (MRSA) isolates were collected during 2003-2006 from inpatients of Süleyman Demirel University Hospital. The isolates were confirmed to be MRSA by the production of coagulase, showing resistance against cefoxitin and having the mecA gene and tested by disk diffusion for susceptibility to vancomycin, teicoplanin and linezolid. The minimum inhibitory concentrations (MICs) of ciprofloxacin and gatifloxacin were measured using the E-test. The quinolone resistance determining regions (QRDRs) of isolates were amplified by PCR and mutations in grlA and gyrA genes were identified by direct sequencing.

RESULTS

Sequencing data revealed that 96% of our isolates had mutations in both grlA and gyrA genes. Among these, the grlA mutation of Ser-80-Phe or Tyr and the gyrA mutation of Ser-84-Leu were the most dominant ones being detected in 50 (89%) and 40 (71%) isolates, respectively. Although 96% of isolates were highly resistant to ciprofloxacin (MIC, >or=32 mg/l), only 54% of ciprofloxacin-resistant MRSA isolates were resistant to gatifloxacin and exhibited lower-level resistance (MIC, <or=6 mg/l). Of the isolates tested, 46% were found to be susceptible to gatifloxacin (MIC, <or=0.5 mg/l). Full susceptibility was observed for vancomycin, teicoplanin and linezolid.

CONCLUSIONS

This study provided information on grlA and gyrA mutations and current antimicrobial susceptibility in clinical MRSA isolates. The results indicated that gatifloxacin is still effective against MRSA isolates and might be useful for treatment of less serious MRSA infections but careful monitoring of susceptibility is required.

Staphylococcal chromosome cassette evolution in Staphylococcus aureus inferred from ccr gene complex sequence typing analysis

Staphylococcal chromosome cassette mec (SCCmec) elements within major lineages of healthcare- and community-associated methicillin-resistant Staphylococcus aureus (MRSA) clones were characterised using intra-SCCmec multilocus sequencing. A strong correlation was observed between sequence- and PCR-based typing methods (p <0.001). However, phylogenetic analysis of the SCCmec locus using concatenated sequences evidenced few recombination events. Sequence type (ST)-SCCmec1 was found in SCCmec elements types I and IV, suggesting the evolution of an SCCmecI element into an SCCmecIV element. This coincided with the spread of the clone harbouring this SCCmec element into the community. No correlation was observed between ST-SCCmec lineage and MRSA lineage, confirming multiple acquisitions of SCCmec by S. aureus. This was exemplified by the SCCmecIV ST-SCCmec10 element, which was detected in all of the clonal complexes examined, including healthcare- and community-associated MRSA. The acquisition of this SCCmec element was five- to ten-fold more common than that of others. Models of MRSA clone evolution suggest that this SCCmec was first found in the paediatric clone.

[Community acquired infections with methicillin resistant strains of Staphylococcus aureus: report of five cases]

Community acquired infections with methicillin resistant strains of Staphylococcus aureus (MRSA) infections have a more aggressive clinical course and involve mostly skin and lungs. These infections appear as outbreaks among prisoners, sportsmen, men having sex with men and military personnel. The higher aggressiveness of these strains is due to the production of several toxins, mainly Panton- Valentine leukocidine. The detection of the gene that codes for this toxin is a distinctive feature of these strains. We report five patients with community acquired MRSA infections. The clinical presentation was a skin infection in all. One patient had a pleuropneumonia in addition. Apart for resistance to beta-lactam antimicrobials, the strains were resistant to erythromycin and ciprofloxacin. Patients were treated with vancomycin, clotrimoxazole or intravenous clindamycin with a good evolution. An epidemiological surveillance for community acquired MRSA strain infections should be started and measures to adequately treat infected patients and avoid dissemination should be implemented.

[Genetic types of three community-acquired methicillin-resistant Staphylococcus aureus isolates]

OBJECTIVE

To investigate the genetic features of the community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) prevalent in West China.

METHODS

Three CA-MRSA isolates obtained in Chengdu, Sichuan, underwent SCCmec (Staphylococcal Cassette Chromosome mec) multi-PCR, Staphylococcal protein A (spa) typing and multi-locus sequence typing (MLST) method, and their Panton-Valentine leucocidin (PVL) gene was also detected.

RESULTS

All 3 CA-MRSA isolates were positive of mecA gene (147 bp), and the other PCR product of 750 bp was confirmed to be type IVa SCCmec. Spa typing showed that the MRSA strains s29635 and s35301 were typed as t437, and the strain s19165 was typed as t008. MLST showed that the MRSA strains s29635 and s35301 were typed as ST59, and the strain s19165 was typed as ST8. The strains s19165 and s35301 were all positive for PVL gene, and the strain s29635 was negative for PVL gene.

CONCLUSION

CA-MRSA clones ST8-t008 and ST59-t437 have been isolated in West China.

Molecular typing of clinical Staphylococcus aureus isolates from northern India using coagulase gene PCR-RFLP

Molecular typing of total 84 Staphylococcus aureus clinical isolates was performed using coagulase gene PCR. Out of 84 S. aureus strains total 33 different types of S. aureus strains were prevalent in this hospital and community. Types 2-7 and 9 were the most prevalent S. aureus strains accounting for more than 53% of total isolates. This technique is relatively inexpensive and is simple to perform and analyze.

Strain-relatedness of methicillin-resistant Staphylococcus aureus isolates recovered from patients with repeated infection

Invasive disease following methicillin-resistant Staphylococcus aureus (MRSA) detection is common, regardless of whether initial detection involves colonization or infection. We assessed the genetic relatedness of isolates obtained > or =2 weeks apart representing either repeated infections or colonization-infection sets to determine if infections are likely to be caused by previously harbored strains. We found that MRSA infection following initial colonization or infection is caused by the same strain in most cases, suggesting that a single successful attempt at decolonization may prevent the majority of later infection.

Methicillin resistance in Staphylococcus aureus and coagulase-negative staphylococci: epidemiological and molecular aspects

Infections caused by the genus Staphylococcus are of great importance for human health. Staphylococcus species are divided into coagulase-positive staphylococci, represented by S. aureus, a pathogen that can cause infections of the skin and other organs in immunocompetent patients, and coagulase-negative staphylococci (CNS) which comprise different species normally involved in infectious processes in immunocompromised patients or patients using catheters. Oxacillin has been one of the main drugs used for the treatment of staphylococcal infections; however, a large number of S. aureus and CNS isolates of nosocomial origin are resistant to this drug. Methicillin resistance is encoded by the mecA gene which is inserted in the SCC mec cassette. This cassette is a mobile genetic element consisting of five different types and several subtypes. Oxacillin-resistant strains are detected by phenotypic and genotypic methods. Epidemiologically, methicillin-resistant S. aureus strains can be divided into five large pandemic clones, called Brazilian, Hungarian, Iberian, New York/Japan and Pediatric. The objective of the present review was to discuss aspects of resistance, epidemiology, genetics and detection of oxacillin resistance in Staphylococcus spp., since these microorganisms are increasingly more frequent in Brazil.

Development and validation of microarray-based assay for epidemiological study of MRSA

We have developed a microarray-based assay for the genotyping of Staphylococcus aureus strains. A DNA microarray consisting of 221 genes with 390 oligonucleotide probes was designed to identify characteristic genes or gene alleles of S. aureus. The 221 genes were chosen on the basis of the following criteria: (i) genes used as control for the microarray system, (ii) virulence genes, (iii) resistance genes and their regulators, and (iv) genes constituting genomic islands, e.g., SCCmec. The microarray system was established by determining the method to prepare targets by random-primer labeling with chromosomal DNA and the conditions for hybridization. We verified the system by using DNAs of seven strains, the genome of which has been fully sequenced. Furthermore, the presence of 32 genes and the types of SCCmec elements and coagulase genes carried by another 27 strains were examined and compared with the results of PCR. As a result, the presence or absence of 182 genes out of the 221 genes was verified. Our data showed the usefulness of the oligonucleotide microarray based assay in identifying important marker sets, such as toxin genes, resistance genes, SCCmec elements, and coagulase genes, for the molecular epidemiology of S. aureus.

[Evaluation of IDI-MRDA assay on a collection of community-acquired methicillin-resistant Staphylococcus aureus isolates and on carriage specimens]

The efficacy of infection control measures against MRSA is linked to the rapid detection of MRSA. With the conventional diagnosis by culture the response delays vary from 48 to 72 hours. In contrast molecular techniques give results within hours.

OBJECTIVE

The objective of the present study is to perform the IDI-MRSA PCR test (BD Diagnostic GeneOhm) on a collection of characterized community-acquired MRSA (CA-MRSA) isolates and on carriage specimens. COLLECTION OF ISOLATES: Fifty-two isolates of CA-MRSA previously characterised by their toxinotype and SCCmec type cassette were analysed. All of them were identified as MRSA by the IDI-MRSA test.

SPECIMENS

Seventy screening specimens from 35 different patients were tested in comparison with the culture on specific media (MRSA ID, BioMérieux). Among those 70 specimens, 24 were from nose, 25 from cutaneous sites (axillar; groin) and 21 from other sites. Sensitivity and specificity were 86.4 and 91.3% respectively; positive and negative predictive values were 93.3 and 82.6% respectively.

RESULTS

Three of four false-positive results came from specimens collected during a decolonisation treatment. Without taking account those specimens, specificity and positive predictive reach 97.9 and 95% respectively. This study shows that IDI-MRSA is an interesting additional test for the diagnosis of MRSA carriage.

[Clonal transmission of methicillin-resistant S. aureus (MRSA) strain in two surgical wards in Lódź]

OBJECTIVE

Phenotypic and genotypic characteristics of S. aureus strains isolated from selected operative wards.

METHODS

A group of 50 strains were analysed. Bacterial strains were isolated from three operative wards of Pirogow Specialistic Hospital in Lódź in a year. Biochemical properties and drug resistance were estimated using standard microbiological techniques. PCR MP technique was used for genotypic analysis.

MAIN OBSERVATIONS

A convergence of genotyping results and antibiotic resistance profiles among MRSA strains was observed. Thus, the antibiogram may serve as the instrument for the preliminary typing of S. aureus strains that may be related. However, this hypothesis has to be verified, for example by using PCR MP technique.

RESULTS

Methicillin-resistance was demonstrated in 24 out of 50 S. aureus isolates. Most MRSA strains (19 out of 24) presented multidrugresistance. Twelve various profiles of enzymatic activity and fifteen different genotypes (A-O) were singled out among the investigated strains. Profile A, recorded in 20 strains, was most frequent (Dice Coefficient: 0.80-0.94).

CONCLUSIONS

1. S. aureus strains present high resistance to antibiotics frequently showing multidrug-resistance coupled with methicillin-resistance 2. Genetically related MRSA strains present a stable drug-resistance pattern 3. Clonal transmission of MRSA strain was observed in two operative wards 4. The disc-diffusion method for testing antibiotic-resistance and PCR MP technique are useful in epidemiological investigation for S. aureus.

[Investigation of the virulence genes in methicillin-resistant Staphylococcus aureus strains isolated from biomaterial surfaces]

Staphylococci are the most important agents of nosocomial infections originating from biomaterials. The aim of this study was to investigate the presence of virulence genes and their phenotypic expressions in 11 methicillin-resistant Staphylococcus aureus strains isolated from the surfaces of clinically used biomaterials of 48 thorasic intensive-care unit patients. By the use of specific primers, the presence of genes encoding the attachment and biofilm production (icaA, icaC, bap), methicillin resistance (mecA), enterotoxins A-E (sea, seb, sec, sed, see), toxic shock syndrome toxin (tst), exfoliative toxins A and B (eta and etb), alpha- and beta-hemolysins (hla and hlb), staphylococcal exotoxin-like protein-1 (set1), proteases (sspA, sspB, aur, serine proteaz gene), lipase (geh) and the regulatory genes (sarA and agrCA) were investigated by polymerase chain reaction (PCR). The phenotypic properties of the isolates such as biofilm formation, antibiotic susceptibility, extracellular protease and lipase production were also evaluated. None of the isolates were found to be biofilm and/or slime producers, however, all strains were found to have icaA gene which is responsible for biofilm formation. Nevertheless the presence of icaC and bap genes that are also responsible for biofilm formation were not detected. All the strains have had mecA gene and were resistant to oxacillin, penicilin G and gentamicin, while 10 were also resistant to erythromycin and nine were also resistant to ofloxacin. The isolates were susceptible to vancomycin, teicoplanin and co-trimoxazole. Screening of toxin and regulatory genes revealed that all the strains harboured sea, set1, hla, hlb and sarA genes. The phenotypic tests for the determination of extracellular protease production revealed that all the strains formed very weak zones on skim milk and milk agar plates, and yielded negative results on casein agar plates. Furthermore, all strains were found to harbour sspA, sspB, aur and serine protease genes. Tween 20, Tween 80 and tributyrin containing media were used to detect lipase production and all strains gave late-positive results (on the third day of incubation), although they all lacked for lipase gene (geh). As a result, S. aureus strains isolated from biomaterial surfaces yielded positivity for some of the tested virulence genes, of which some of them have not been expressed phenotypically. Although there were some limitations in the study, it could be concluded that the presence of these virulence genes in S. aureus strains might be considered as potential threats especially in intensive care unit patients.

[Susceptibility of Staphylococcus aureus to new macrolide antibiotics]

A total of 73 isolates of Staphylococcus aureus (26 - MRSA, 47 - MSSA) were tested for their susceptibility to macrolide antibiotics and new derivatives (azalide - azythromycin and ketolide -telithromycin). We observed a high - level resistance of MRSA isolates to all tested antibiotics. Over 96% of isolates were resistant to macrolides and azalides and 92,3% to ketolides. Majority of MSSA isolates (93.6%) demonstrated a high-level susceptibility to telithromycin. Mechanisms of resistance to macrolide antibiotics (34 - MLSB and 1 - MSB) were found among 47,9% Staphylococcus aureus isolates. All of MSSA (100%) and 40% MRSA isolates with induction phenotype of resistance (MLSB(I)) were sensitive to telithromycin. Isolates with constitutive phenotype of resistance (MLSB(K)) were resistant to all of the tested antibiotics.

Accessory gene regulator (agr) typing of Staphylococcus aureus isolated from human infections

Staphylococcus aureus is a major hospital and community acquired pathogen. A total of one hundred strains were investigated. They were collected from January 2004 to July 2006 in the laboratory of microbiology at Charles Nicolle University hospital of Tunis. The isolates were identified by conventional methods. Methicillin resistance was confirmed by amplification of mecA gene by PCR. The agr groups were identified by multiplex PCR. The agr groups were distributed as follows: 19 strains belonged to group I, 16 to group II and 65 to group III. Among methicillin resistant S. aureus (MRSA), 9 (16.4%) belonged to group 1, 8 (14.5%) to group II and 38 (69.1%) to group IlI. For methicillin susceptible S. aureus (MSSA), only 10 strains (22.2%) belonged to group I, 8 (17.8%) to group II and 27 (60%) to group III. A preferential link was observed between agr group I and invasive infections (P=0.003) especially bacteremia (P=10(-4). Besides, agr groups II and III were closely related with non invasive infections (P=0.003). No association was found between other types of infections and agr groups. Likewise, no correlation was observed between agr groups, age or sex of patients and type of infections.