Effect of epinephrine on growth characteristics of Actinobacillus pleuropneumoniae field isolates.

Based on empirical observations, stressors in swine populations may contribute to outbreaks due to Actinobacillus pleuropneumoniae (App) in colonized pigs. Stress hormones as catecholamines were found to impact immune mechanism but also bacterial protein expression in vivo, so it can be hypothesized that they are key molecules in disease pathogenesis. Culturing methods to isolate App from tonsillar tissue of carrier pigs for further typing are mostly not successful. In this study the effect of epinephrine in culturing media on App growth behavior was tested. Starting cultures of different age (24-h-old or 7-day-old cultures) of three App field strains per serotypes 2, 5 and 12 were compared in their growth behavior in medium supplemented with various epinephrine concentrations. The response of App strains to epinephrine varied between strains. Highest differences in CFU/mL and in growth curve characteristics between different epinephrine concentrations were found in serotype 5 strains. Inflection points of bacterial growth curves with 24-h-old starting cultures were delayed with 100 μM epinephrine with exception of one ST5 strain. In all ST2 and ST12 as well as one ST5 strain 100 μM epinephrine led to a growth advantage in 7-day old compared to 24-h-old starting cultures. Epinephrine did not consistently enhance growth of App, so that it cannot be recommended as a supplement for growth media to facilitate isolation from colonized tonsils of subclinically infected pigs.