Microbiology & Immunology Practice Questions

Question 1

Which virus causes both varicella and herpes zoster?

Accepted Answer

Reactivation from a sensory ganglion follows a dermatomal distribution

Answer

Viral oncoproteins disrupt p53 and retinoblastoma tumor-suppressor pathways

Answer

Primary infection is widespread, whereas recurrence favors keratinized sites

Answer

Axonal reactivation carries latent virus back to the orolabial epithelium

Question 2

Which three organisms constitute the classic red complex?

Accepted Answer

Late anaerobic colonizers correlate strongly with pocket depth and bleeding

Answer

Orange-complex bridging precedes and supports late red-complex colonization

Answer

Tissue invasion by spirochetes accompanies a dysbiotic anaerobic consortium

Answer

Coaggregation and oxygen consumption prepare a niche for strict anaerobes

Question 3

What best describes ecological succession in dental plaque?

Accepted Answer

Ordered community replacement — metabolic cooperation changes the niche rather than merely adding random species; plaque succession is an ordered process: pioneer organisms attach, alter oxygen and nutrients, and provide receptors for coaggregation.

Answer

Continuous epithelial shedding — a non-shedding tooth permits stable accumulation unlike renewing mucosa; oral mucosa continually sheds superficial epithelial cells, limiting persistent biomass and favoring organisms able to adhere to epithelial receptors.

Answer

Taxa or functions shared broadly among healthy people — functional overlap can persist even when strain-level membership varies; the core microbiome denotes organisms or, more robustly, microbial functions commonly found across individuals.

Answer

Taxa differing with host and environment — lifestyle-sensitive species vary more than widely shared microbial functions; the variable microbiome reflects differences arising from genetics, diet, hygiene, medication, smoking, geography, and disease.

Question 4

What does aciduricity mean in mutans streptococci?

Accepted Answer

Ability to function at low environmental pH — proton tolerance provides selection after acid production changes the habitat

Answer

Reducing the frequency of fermentable carbohydrate — changing the selective pressure can restore a less aciduric community

Answer

They neutralize plaque acids through ammonia production — base generation opposes selection for strongly aciduric organisms

Answer

Environmental selection of an aciduric community — low pH creates feedback that favors acid-producing and acid-tolerant taxa

Question 5

What does a negative biological indicator demonstrate?

Accepted Answer

Direct microbial challenge evaluates lethality beyond package exposure alone

Answer

Mycolic acids increase chemical resistance beyond most vegetative bacteria

Answer

Unusual protein stability requires specialized prion reprocessing procedures

Answer

A high-resistance target supplies a conservative margin for routine bioburden

Question 6

Which oral finding is associated with secondary syphilis?

Accepted Answer

Hematogenous dissemination creates highly infectious multifocal mucosal lesions

Answer

Disrupted tooth development creates a late stigma of transplacental infection

Answer

Granulomatous organization reflects a T-cell response to persistent mycobacteria

Answer

Contiguous spread ignores anatomic boundaries and produces chronic suppuration

Question 7

Which organism commonly acts as a bridge between early and late plaque colonizers?

Accepted Answer

Fusobacterium nucleatum — broad adhesin compatibility links streptococci with later anaerobes; fusobacterium nucleatum coaggregates with numerous early and late colonizers.

Answer

Viridans streptococci — pioneer streptococcal adhesins permit attachment before bridging species arrive; early colonizers include Streptococcus sanguinis, S.

Answer

Reduced activity of growth-dependent targets — metabolic dormancy creates phenotypic tolerance without a resistance mutation; many antibiotics act best on active biosynthesis or division.

Answer

Stable multispecies spatial organization — a climax community persists through structured cooperation and nutrient exchange; mature plaque is not a random bacterial layer.

Question 8

Which fungal infection is especially associated with uncontrolled diabetes and ketoacidosis?

Accepted Answer

Rhinocerebral mucormycosis — angioinvasive broad nonseptate hyphae cause thrombosis and tissue infarction

Answer

Yeast-to-hyphal transition — hyphae enhance penetration while adhesins and proteases support persistence

Answer

Continuous overnight denture wear — occlusion and retained moisture favor a Candida-rich denture biofilm

Answer

White plaques that wipe away — a superficial mass of hyphae and debris can be removed from the epithelium

Question 9

What is the main role of Toll-like receptors in periodontal tissues?

Accepted Answer

Pattern-recognition signaling initiates innate defense without prior sensitization

Answer

Continuous neutrophil migration restrains biofilm invasion but also releases enzymes

Answer

B-cell maturation converts antigen recognition into high-rate antibody secretion

Answer

The same recruited cells and mediators provide defense and collateral destruction

Question 10

Which adhesion protein is targeted in pemphigus vulgaris?

Accepted Answer

Desmoglein in epithelial desmosomes — loss of keratinocyte adhesion creates suprabasal acantholysis

Answer

Delayed T-cell-mediated inflammation — sensitized T lymphocytes recruit inflammation without an antibody effector

Answer

Cytotoxic T lymphocytes — direct cell-mediated attack on basal cells produces interface mucositis

Answer

At the basement membrane zone — autoantibodies against hemidesmosomal components create a subepithelial split