Comparison of final OD readings and colony forming units (CFUs) among three strains.

<p>D7S-1S, SCC1398S, and D11S-1S were grown in TSBYE, TSBYE + 50% human serum, or TSBYE + 50% horse serum for 23 h. All samples were prepared with a starting cell number of 0.5 × 1.0⁸–1.0 × 1.0⁸/ml. <b>(A).</b> D11S-1S reached the highest OD when incubated in human serum. The OD reading of D11S-1S in human serum was 2-fold higher than the readings for two low-responder strains incubated under the same condition. <b>(B).</b> D11S-1S incubated in 50% human serum for 23 h yielded the lowest number of recovered CFUs, representing only 18%-25% of the same strain incubated in either horse serum or TSBYE alone (<i>P</i> < 0.01). The recovered CFUs from D11S-1S grown in 50% human serum were less than 15% of either D7S-1S or SCC1398S incubated under the same condition (<i>P</i> < 0.01).