FMGE 2019 — Microbiology

Q: Whipple's disease is caused by:

Bacteria. **Bacteria** - Whipple's disease is caused by the bacterium **_Tropheryma whipplei_**, a rod-shaped, gram-positive actinobacterium. - This bacterium causes a chronic, systemic infection affecting various organ systems, most commonly the gastrointestinal tract. *Virus* - Viruses are intracellular parasites that reproduce inside living cells, and they are not the causative agent of Whipple's disease. - While viral infections can cause gastrointestinal symptoms, they do not lead to the distinct histopathological findings of Whipple's disease, such as **PAS-positive macrophages**. *Helminths* - Helminths are parasitic worms (e.g., tapeworms, roundworms) that can cause intestinal and systemic infections. - These organisms are multicellular eukaryotes and are distinct from the bacterial etiology of Whipple's disease. *Protozoa* - Protozoa are single-celled eukaryotic organisms that can cause a range of infections, often gastrointestinal (e.g., Giardia, Entamoeba). - While parasitic infections can cause malabsorption, the specific **PAS-positive macrophage infiltrates** seen in Whipple's disease are characteristic of bacterial infection, not protozoan.

Q: Sporulation occurs in which phase of bacterial growth curve:

Stationary phase. ***Stationary phase*** - When **nutrients become limited** and waste products accumulate, bacteria enter the stationary phase, triggering **sporulation** in spore-forming species as a survival mechanism. - In this phase, the rate of **bacterial growth equals the rate of bacterial death**, leading to a plateau in population size. *Decline phase* - The decline phase is characterized by a **net decrease in viable cells** due to continued depletion of nutrients and high accumulation of toxic waste products. - While cells are certainly stressed, sporulation typically occurs *before* this phase, as a preventative measure to survive impending harsh conditions. *Lag phase* - During the lag phase, bacteria are **adapting to new environmental conditions** and synthesizing necessary enzymes and components. - There is no increase in cell number during this phase, and they are preparing for growth, not entering a survival state like sporulation. *Log phase* - The log phase (or exponential phase) is characterized by **rapid binary fission** and exponential increase in bacterial numbers due to optimal growth conditions and abundant nutrients. - Cells are actively dividing; sporulation, which halts active division to form a dormant spore, would be counterproductive at this stage.

Q: Which antibody is seen in recent infection?

IgM. ***IgM*** - **IgM** is the first antibody produced during a **primary immune response** to a new infection. - Its presence indicates a **recent or ongoing acute infection**. *IgE* - **IgE** is primarily associated with **allergic reactions** and defense against parasites. - It is not typically an indicator of a recent bacterial or viral infection. *IgD* - **IgD** is mostly found on the surface of **B cells** and plays a role in B cell activation. - Its function in circulating blood is not well understood, and it is not used to diagnose recent infection. *IgG* - **IgG** is the most abundant antibody in serum and represents a **secondary, more delayed immune response**. - Its presence indicates **past exposure or chronic infection**, as it provides long-term immunity.

23 Questions — Page 3 of 3

Q21

Whipple's disease is caused by:

Q22

Sporulation occurs in which phase of bacterial growth curve:

Q23

Which antibody is seen in recent infection?