Factors influencing the growth and viability of Actinobacillus actinomycetemcomitans

The metabolic requirements for the routine growth of Actinobacillus actinomycetemcomitans were investigated by the addition of nutrients to conventional bacteriological and tissue culture media. Commonly used tissue culture media required fetal bovine serum as an additive to sustain bacterial growth rates comparable to those obtained with bacteriological media. The addition of increasing concentrations of yeast extract to bacteriological medium increased the growth rate of several A. actinomycetemcomitans strains. In an attempt to identify the components of yeast extract that enhanced the growth of A. actinomycetemcomitans, a number of vitamins, essential and non-essential amino acids were tested for their role in promoting growth. The addition of L-cystine resulted in bacterial growth rates comparable to those with yeast extract. Thiamine increased the growth of several A. actinomycetemcomitans strains but did not result in growth rates comparable to those with yeast extract. The addition of physiological concentrations of steroid hormones to bacteriological medium enhanced the growth of A. actinomycetemcomitans. Additional iron compounds and fat-soluble vitamins had no influence on A. actinomycetemcomitans growth. However, the requirement of iron for bacterial growth remains unclear. The optimal pH range for growth of A. actinomycetemcomitans was between pH 7.0-8.0 in a medium containing 0.5-1% NaCl. Several interesting observations on the viability of A. actinomycetemcomitans were made. A rapid reduction of A. actinomycetemcomitans viability occurred following suspension in distilled water. The presence of the detergent Triton X-100 at concentrations above 2% (v/v) also decreased the viability of A. actinomycetemcomitans within 10 min.