Question

Unimmunized 1 yr old boy is admitted to the hospital because of fever, irritability and stiff neck. Cultures of the nasopharynx and cerebrospinal fluid grow gram-negative coccobacilli. Electron microscopic exam shows the presence of pili on the bacteria recovered from the nasopharynx, but absence of pili on the bacteria of the same species recovered from the cerebrospinal fluid. Which of the following processes shuts off expression of pili in this bacterium following invasion?

1) horizontal gene transfer
2) phase variation
3) plasmid acquisition
4) point mutation
5) transposon mutagenesis

Answer 1

Phase variation is the process that likely shuts off the expression of pili in bacteria following invasion, enabling it to adapt and potentially evade the immune system.

Step-by-step explanation:

The process that shuts off expression of pili in bacteria following invasion is known as phase variation. This refers to the reversible on-and-off switching of certain genes, allowing the bacterium to adapt to different environments, like when it invades the host tissue. Phases variation can involve changes in the expression of surface proteins, like pili, which can help the bacteria to evade the host's immune system. In the case of the 1-year-old boy presenting with meningitis symptoms, the absence of pili on the bacteria may likely be a result of phase variation, which has turned off the expression of pili to possibly help the bacterium avoid detection by the host's immune defenses.