Emergence of Pseudomonas aeruginosa strains producing metallo-beta-lactamases of the IMP-15 and VIM-2 types in Mexico.

Eighty-six carbapenem non-susceptible Pseudomonas aeruginosa isolates collected in the National Institute of Respiratory Diseases of Mexico City were screened for the presence of metallo-beta-lactamase (MBL) activity using both E-test strips and a microbiological assay with EDTA-imipenem. Genomic comparisons and sequence analyses conducted with these isolates revealed the presence of bla(VIM-2) in two clonally related isolates, and bla(IMP-15) in a clonally unrelated isolate. Both genes were found to be carried by class 1 integrons, and bla(IMP-15) was additionally present on a broad host-range plasmid. This is the first report of co-existing P. aeruginosa strains producing different MBLs in a Mexican hospital, highlighting the necessity of appropriate surveillance to prevent dissemination of carbapenem resistance.

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.