Final answer:
Chlamydia are gram-negative intracellular pathogens without a cell wall, causing diseases like chlamydia. Rickettsias are obligate intracellular parasites, with Rickettsia prowazekii causing epidemic typhus. Mycoplasmas lack a cell wall entirely, with Mycoplasma pneumoniae causing atypical pneumonia.
Step-by-step explanation:
The student is asking to describe the physical nature of three types of bacteria: Chlamydia, Rickettsias, and Mycoplasmas, as well as to provide examples of infections caused by each group. These bacteria differ from typical bacteria in their structure and method of infection.
Chlamydia
Chlamydia are gram-negative, obligate intracellular pathogens, meaning they must live within a host cell to survive. Unlike many bacteria, Chlamydias do not have a cell wall. Chlamydia trachomatis can cause infections such as chlamydia, which is a sexually transmitted disease.
Rickettsias
Rickettsias are also obligate intracellular parasites and are typically transmitted through insect vectors. Rickettsia prowazekii, for example, is the causative agent of epidemic typhus.
Mycoplasmas
Mycoplasmas are unique among bacteria as they lack a cell wall entirely, which makes them resistant to many antibiotics that target cell wall synthesis. A familiar example of a Mycoplasma infection is Mycoplasma pneumoniae, which causes atypical pneumonia.