Comparative evaluation of VITEK 2 for antimicrobial susceptibility testing of group B Streptococcus

OBJECTIVES:Intrapartum antibiotic prophylaxis is recommended to prevent neonatal group B streptococcal (GBS) disease in colonized women, and penicillin or aminopenicillin constitute the first-line antibiotics. Most isolates are resistant to tetracycline, and resistance to macrolide-lincosamide-streptogramin (MLS) antibiotics is increasing. Therefore, laboratory testing for MLS resistance in GBS is now recommended for penicillin-allergic patients. The aim of this study was to compare the antimicrobial susceptibility of GBS as determined by the VITEK 2 system (bioMérieux, Marcy l'Etoile, France), agar diffusion methods and PCR-genotypic detection of resistance genes.METHODS:One hundred and ten unrelated selected GBS clinical isolates were studied. The antibiotics tested (VITEK 2 and agar diffusion method) were benzylpenicillin, ampicillin, erythromycin, clindamycin, co-trimoxazole, tetracycline, kanamycin, streptomycin and vancomycin. A standardized double-disc (DD) diffusion test was performed for MLS antibiotics. Genotypic characterization of tetracycline, MLS and aminoglycoside resistance genes was performed by PCR.RESULTS:All strains were susceptible to benzylpenicillin, ampicillin and vancomycin [category agreement (CA) between VITEK 2 and the diffusion method was 100%]. Ninety-five (86%) strains were resistant to tetracycline (CA was 98.9%). Eighty-one strains (73.6%) harboured an MLS resistance phenotype; 50 (61.8%) an MLS(B)-constitutive phenotype, 25 (30.8%) an MLS(B)-inducible phenotype and 6 (7.4%) an M phenotype. The agreement between data of VITEK 2 and the DD diffusion test for the detection of MLS(B)-constitutive, MLS(B)-inducible and M phenotype isolates was 76%, 36% and 100%, respectively. Almost all discrepancies were due to failure to detect erythromycin resistance by VITEK 2.CONCLUSIONS:VITEK 2 allows accurate determination of GBS susceptibility for the majority of antibiotics, but has to be improved for erythromycin. Thus, the DD diffusion test remains the most simple and reliable method for macrolide resistance detection among this streptococcal species

A preliminary survey of M. hyopneumoniae virulence factors based on comparative genomic analysis

Mycoplasma hyopneumoniae is the etiological agent of porcine enzootic pneumonia (PEP), a major problem for the pig industry. The mechanisms of M. hyopneumoniae pathogenicity allow to predict the existence of several classes of virulence factors, whose study has been essentially restricted to the characterization of adhesion-related and major antigenic proteins. The now available complete sequences of the genomes of two pathogenic and one non-pathogenic strain of M. hyopneumoniae allowed to use a comparative genomics approach to putatively identify virulence genes. In this preliminary survey, we were able to identify 118 CDSs encoding putative virulence factors, based on specific criteria ranging from predicted cell surface location or variation between strains to previous functional studies showing antigenicity or involvement in host-pathogen interaction. This survey is expected to serve as a first step towards the functional characterization of new virulence genes/proteins that will be important not only for a better comprehension of M. hyopneumoniae biology, but also for the development of new and improved protocols for PEP vaccination, diagnosis and treatment