Effect of culture conditions on the susceptibility of enteroaggregative Escherichia coli to human serum and polymorphonuclear leucocytes

Abstract

Recent work has indicated that the pathogenicity of enteroaggregative Escherichia coli (EAggEC) is strictly regulated by environmental conditions. The growth conditions, susceptibility to the bactericidal activity of serum, and polymorphonuclear leucocytes (PMN) using strains of EAggEC grown in two different culture conditions were examined. Strains of EAggEC grown in casamino acids-yeast extract (CYE) broth at 37 degrees C for 20 h showed resistance to killing by human serum (86.8 +/- 6.9% survival by 2 h) and PMN (67 +/- 5.1% survival by 2 h). In contrast, these strains grown in nutrient broth (NB) showed sensitivity to serum (98.9 +/- 0.5% killing by 2 h) and PMN (98.9 +/- 0.5% killing by 2 h). EAggEC strains cultured in NB became resistant to killing by serum when mixed with extracellular material extracted from the bacteria grown in CYE broth. These results indicate that the growth condition may modulate the sensitivity of EAggEC, and the promotion of extracellular material formation in CYE broth is responsible for the resistance to killing by serum and PMN.