Phenotypic and genotypic characterization of Streptococcus agalactiae in pregnant women: first study in a province of Argentina

Group B Streptococcus (GBS) is the leading cause of neonatal infections. Our purpose was to characterize GBS colonization in pregnant women, current serotypes, resistance phenotypes and genes associated with virulence. In Misiones, Argentina, there are no previous data on this topic. Vaginal-rectal swabs from 3125 pregnant women were studied between 2004 and 2010. GBS strains were identified by conventional and serological methods (Phadebact Strep B Test, ETC International, Bactus AB, Sweden). Serotypes were detected using Strep-B Latex (Statens Serum Institut, Denmark). Resistance phenotypes were determined by the double-disk test. Genes were studied by PCR. Maternal colonization was 9.38%. Resistance to erythromycin was 11.6%, and the constitutive phenotype was the predominant one. Serotype Ia was the most frequent, whereas serotypes IV, VI, VII and VIII were not detected. The lmb, bca and hylB genes were detected in more than 79% of the strains. In this study, the colonization rate with GBS and the serotype distribution were compared with studies reported in other areas of the country. The high resistance to erythromycin in Misiones justifies performing antibiotic susceptibility testing. The serotype distribution, the genes encoding putative virulence factors, and the patterns of resistance phenotypes of GBS may vary in different areas. They thus need to be evaluated in each place to devise strategies for prevention.

Simultaneous Determination of Various Macrolides by Liquid Chromatography/Mass Spectrometry

Macrolides are frequently used in veterinary medicine as therapeutic and preventive agents for various diseases. It is difficult to determine macrolides simultaneously with conventional methods due to their similar structures. A simultaneous analysis for erythromycin, roxithromycin, tiamulin and tylosin with LC/MS has been developed. Separation was performed on C18 reversed phase column. Mobile phase was gradiently flowed with 10 mM ammonium acetate and methanol. The mass spectrometer was run in the positive mode and selective ion monitoring mode. The molecular ions were [M+H]+ form at m/z 837.5 for erythromycin, at m/z 859.5 for roxithromycin, at m/z 494.2 for tiamulin and at m/z 916.7 for tylosin. Limits of detection were in the range from 0.001 to 0.01 microgram/g lower than their MRLs.