Passage IV

The amoeba Entamocba histolytica can infect the human digestive tract. Scientists conducted 2 experiments to study the amoebicidal (amoeba-killing) activity of human milk.

Experiment 1

Ten milliliters of a mixture of nutrient medium (NM) and saline solution(SS) that was 5% SS by volume was put in a test tube. This procedure was performed twice more except that the percents by volume of SS were 10% and 15%, respectively. Ten milliliters of only NM was put in fourth test tube. Next, 1 × 10⁷ E. histolytica were added to each test tube. Then, a second set of test tubes was likewise prepared, except that human milk was substituted for SS. All 8 test tubes were incubated at 37° C for 1 hr. At the end of incubation, the percent survival (percent of the adde E. histolytica that were still alive) was determined for each test tube (see Figure 1).

Experiment 2

A sample of human milk was separated into 3 fractions: casein (a protein), lipids, and noncasein proteins. Ten milliliters of a mixture of NM and SS that was 10% SS by volume was put in a test tube. This procedure was repeated 3 times, except that each time a different human milk fraction was substituted for SS. Next, 1 × 10⁷ E. his­tofytica were added to each of the test tubes. Then, 2 more sets of 4 test tubes were likewise prepared. Each set of test tubes was incubated at 37°C for a different period of time: 3 hr, 6 hr, or 9 hr. At the end of incubation, the percent sur­vival was determined for each test tube (see Figure 2).

Figure adapted from Nidia León-Sicairos et al., "Amoebicidal Activity of Milk, Apo-lactoferrin, slgA and Lysozyme." ©2006 by Marshfield Clinic.