USA Biology Olympiad (USABO) Practice Exam

If bacteria with a plasmid containing genes for sex pilus construction and tetracycline resistance undergo conjugation, what is the likely outcome?

1. Loss of antibiotic resistance

2. Rapid spread of tetracycline resistance

3. Increased virulence

4. Decreased reproductive rate

The correct answer is: Rapid spread of tetracycline resistance

The scenario describes bacteria that possess a plasmid with genes for constructing a sex pilus and for tetracycline resistance. When these bacteria undergo conjugation, they can transfer their plasmid to other bacteria nearby through direct contact. This process effectively allows for horizontal gene transfer, which is a significant mechanism by which antibiotic resistance spreads among bacterial populations. The presence of the sex pilus facilitates the connection between the donor and recipient bacterial cells, allowing for the transfer of genetic material—specifically, the plasmid that carries the gene for tetracycline resistance. This means that recipient bacteria can acquire the ability to resist tetracycline, leading to a rapid increase in the number of resistant strains within a community of bacteria. Consequently, this amplifies the prevalence of tetracycline resistance in the bacterial population, which is a major public health concern, as it can render common antibiotic treatments ineffective. The rapid propagation of tetracycline resistance is a clear and direct result of the conjugation process described in the question.