Phenotypic and genotypic study of Streptococcus agalactiae in vagina of pregnant women in Argentina.

Streptococcus agalactiae (GBS) is a leading cause of serious neonatal infection. In this study we determine the prevalence, serotype distribution and genomic diversity of GBS in vagina of pregnant women. Vaginal swabs of 531 pregnant women were cultured on Columbia Agar Base Blood, GBS Agar Base and Todd Hewitt Broth. GBS were characterized by group and type-specific agglutination. Genomic polymorphism was studied by random amplification of DNA (RAPD). Seventeen patients (3.2%) were positive for GBS, resulting serotype III the most frequent. RAPD detected 16 different RAPD profiles from 21 GBS studied, revealing a good discriminatory power. In this sense, this method showed different genotype from GBS serotype III recovered from successive samples of two patients, suggesting reinfection. In conclusion, the combination of RAPD and serotyping appear promising for epidemiological studies. Finally, findings of reinfection after therapy during pregnancy, led us to suggest performing prenatal GBS screening and intrapartum prophylaxis in order to reduce neonatal risk.

Characterization of clinical isolates of Streptococcus agalactiae by random amplified polymorphic DNA using degenerate oligonucleotides.

Epidemiological studies of Streptococcus agalactiae strains have been limited by the lack of sensitive and discriminatory methods for comparing clinical isolates. Serotyping, albeit a widely used methodology, has been shown to possess low capability to distinguish between epidemiologically related and unrelated isolates. We have employed here a random amplification of polymorphic DNA (RAPD) assay, using degenerate oligonucleotides as primers, to characterize S. agalactiae isolates from related or unrelated clinical samples. Epidemiologically-related isolates (mother-infant pairs) showed identical profiles by this methodology. On the contrary, 12 epidemiologically-unrelated isolates (classified into 5 different serotypes) resulted in 11 distinct RAPD patterns. This suggests that the proposed modified RAPD assay provides a highly discriminatory tool for the analysis of genomic diversity among isolates from pathogenic organisms.

Methicillin resistance study in clinical isolates of coagulase-negative staphylococci and determination of their susceptibility to alternative antimicrobial agents.

AIMS: To achieve reliable detection of methicillin resistance in clinical isolates of coagulase-negative staphylococci. METHODS AND RESULTS: Strains (105) were evaluated by normatized antimicrobial susceptibility methods, and for the presence of the methicillin resistance-determining mecA gene, using the polymerase chain reaction. Correlation between phenotypic and genotypic methods was obtained in 87.6% of the samples. Six strains, classified as methicillin-susceptible by phenotypic assays, revealed the presence of the mecA gene, indicating that methicillin resistance expression was probably repressed. Another seven isolates failed to show mecA amplification after displaying methicillin resistance in phenotypic evaluations. The susceptibility of the methicillin-resistant isolates to other antimicrobial agents was variable. CONCLUSION: Genotypic determination of the mecA gene proved to be the most reliable method for detection of methicillin resistance. SIGNIFICANCE AND IMPACT OF THE STUDY: Correct assessment of methicillin resistance, such as that attained through genotyping, is essential for defining therapeutic strategies, particularly when treating severely compromised patients.

[Importance of the bacterium-host interaction in coagulase-negative staphylococci isolated from neonates]. / Importancia de la relación huésped-parásito en estafilococos coagulasa negativa aislados de neonatos.

OBJECTIVE: Neonates represent a high risk population for infections by coagulase-negative staphylococci (CNS). To have a better understanding of these process our purpose was to compare the expected result of the bacterium-host interaction given by the neonates' risks factors and the micro-organisms' virulence factors with the condition of infecting or colonising strain that emerge from the diagnosis on the basis of the clinical symptoms. METHODS: We studied 24 neonates who were submitted to an epidemiological control establishing as risk factors: catheters, vesicle sounds, previous surgery and immunodepressed conditions. In the CNS recovered from clinical samples we determined the following virulence factors: synergistic hemolysis, slime production, adherence to Teflon catheters and hydrophobicity. RESULTS: We found correlation between the clinical diagnosis and the expected result of the bacterium-host interaction in 21 patients (87.5%). Among them, in 8 patients infection didn't occurred in spite of having the micro-organisms 3 from 4 virulence factors since the patients didn't have risk factors. CONCLUSIONS: A microbiological study based entirely on identification and treatment can alter the biological context. It is necessary to understand the bacterium-host interaction for an appropriate comprehension of the bacterial diseases.