Chapter 6, Problem 28ESP

Bacterial conjugation, mediated mainly by conjugative plasmids such as F, represents a potential health threat through the sharing of genes for pathogenicity or antibiotic resistance. Given that more than 400 different species of bacteria coinhabit a healthy human gut and more than 200 coinhabit human skin, Francisco Dionisio [(2002) Genetics 162:1525–1532] investigated the ability of plasmids to undergo between-species conjugal transfer. The following data are presented for various species of the enterobacterial genus Escherichia. The data are presented as “log base 10” values; for example, –2.0 would be equivalent to 10^–2 as a rate of transfer. Assume that all differences between values presented are statistically significant.

1. (a) What general conclusion(s) can be drawn from these data?
2. (b) In what species is within-species transfer most likely? In what species pair is between-species transfer most likely?
3. (c) What is the significance of these findings in terms of human health?