The study illustrates that ESBL-producing E. coli, as well as plasmids carrying ESBL genes of clinical interest, can be easily transferred among horses, humans and flies living in close contact.

The agar dilution method was used to investigate the sensitivity to pleuromutilins of 100 isolates of Brachyspira hyodysenteriae isolated from 63 pig farms between 1997 and 2001. In the period under investigation, MICs to both tiamulin and valnemulin increased, with differences between the periods 1997-98 and 1999-2001 being statistically significant (P , 0 . 001 for tiamulin and P , 0 . 0001 for valnemulin). Between 1997 and 2001, the MIC 50 and MIC 90 of tiamulin increased from 0 . 062 and 0 . 25 ìg ml À1 , respectively, to 1 . 0 and 4 . 0 ìg ml À1 . Valnemulin MIC 50 and MIC 90 were < 0 . 031 ìg ml À1 in 1997 and by 2001 were respectively, 2 . 0 and 8 . 0 ìg ml À1 . The increase in MICs of tiamulin and valnemulin demonstrated in this study reflect the intensity of pleuromutilin use in the treatment of swine dysentery in the Czech Republic.

The exosubstance of Rhodococcus equi in a prepurified form strongly enhanced the hemolytic effect of certain strains of Listeria monocytogenes. The strains which produced positive synergic hemolysis with this exosubstance were also pathogenic for guinea pigs and white mice. The other strains, which remained nonhemolytic in the presence of the R. equi exosubstance, were apathogenic for those animals. A routine test was devised for the in vitro determination of the pathogenicity of L. monocytogenes strains.