Growth of pure cultures of Verocytotoxin-producing Escherichia coli in a range of enrichment media.

This study compared the growth of different strains of Verocytotoxin-producing Escherichia coli (VTEC) in a range of selective enrichment media. Turbidometric and impedance methods were used to determine the growth of VTEC in pure culture in different enrichment media. Ten strains failed to grow in buffered peptone water + vancomycin, cefsulodin, cefixime at 42 degrees C and some failed to grow, or grew poorly in E. coli (EC) medium supplemented with 20 mg l(-1) novobiocin and modified EC supplemented with 20 mg l(-1) novobiocin at 37 degrees C and 42 degrees C. Individual VTEC strains were sensitive to the selective agents in some media. Statistical analysis of the conductance detection times of 10 strains showed no overall effect of temperature alone (P = 0.66) but there were significant (P < 0.001) effects as a result of the combination of medium and temperature and these two factors were influenced by strain. Growth of VTEC during enrichment is dependent on different factors alone or in combination. These include medium type, presence of certain selective agents or antibiotics, incubation temperature and the initial population of VTEC. Sensitivity to these conditions can be strain related. This study highlighted differences in the ability of some enrichment media to support the growth of VTEC, making them unsuitable for the isolation of VTEC, especially low numbers of non-O157 strains.