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.

[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.