BIOL 2051 - MOCK EXAM #3

Why does the presence of mycolic acid make Mycobacterium species inherently resistant to many antibiotics?

It forms a thick, hydrophobic barrier that is impermeable to many antibiotics.

How do acid-fast bacilli (AFB) appear under a microscope following a successful acid-fast stain?

They appear as pink rods

What physical property defines "acid fastness" in certain bacterial genera?

The ability to resist decolorization by acids during staining procedures

List three specific species within the Mycobacterium genus mentioned in the text.

M. leprae, M. tuberculosis, and M. smegmatis.

Besides Mycobacterium, which other genus is identified as displaying acid-fastness?

Genus Nocardia as it also characterized by a unique cell wall containing high concentrations of mycolic acids. This waxy lipid layer makes both genera acidfast positive, meaning they retain carbolfuchsin stain even when washed with acid-alcohol.

Why might a child's gastric washings show acid-fast bacilli when their sputum examination is negative?

It suggests extrapulmonary TB or earlystage pulmonary TB with a low bacterial load in the lungs.

What is the primary functional reason a capsule is considered a "virulence factor"?

It allows pathogenic bacteria to evade the host immune system by avoiding phagocytosis

Why is heat-fixing strictly avoided during the preparation of a capsule stain?

To prevent the capsule from shrinking or being destroyed.

Describe the "halo effect" observed in a successful Maneval’s capsule stain.

The capsule appears as a clear, bright halo between the dark background and the colored cell.

In Maneval's stain, which specific dye colors the background, and what is its chemical nature?

Congo red, which is an acidic stain.

How does the capsule of Bacillus anthracis differ chemically from that of Azotobacter vinelandii?

B. anthracis has a polypeptide capsule, while A. vinelandii has a polysaccharide capsule.

What specific role does the capsule of Streptococcus mutans play in the development of dental caries?

It uses dextrans to stick to tooth enamel, forming a biofilm

Describe the "Wzx/Wzy-dependent" pathway for glycan synthesis.

Sugar units are built on a lipid carrier, flipped by Wzx, and stitched together outside by Wzy.

What is the unique characteristic of the ABC transporter-dependent pathway for polysaccharide export?

The entire polysaccharide chain is completed inside the cytoplasm before being exported with the help of ATP hydrolysis

How does the "Synthasedependent" pathway differ from the other two glycan export models?

A single protein both polymerizes and exports the polysaccharide simultaneously.

In the cps gene arrangement of Neisseria, what are the specific roles of Regions A, B, and C?

Region A: synthesis; Region B: transport; Region C: translocation. N. meningitidis that lacks the cps locus or cannot express the capsule (nonencapsulated) is typically rendered nonpathogenic or significantly reduced in virulence.

What environmental factor triggers Azotobacter vinelandii to produce a physically thicker, more compact alginate capsule?

High oxygen stress/tension. Recall the image of the electron micrograph

Why must Azotobacter protect its dinitrogenase reductase enzyme?

Because dinitrogenase reductase is inactivated by oxygen and is highly sensitive to O2.

Identify two main methods Azotobacter uses to protect its nitrogen-fixing enzyme from oxygen.

Has intense aerobic metabolism consumes oxygen so rapidly at the cell membrane that it prevents oxygen from entering the cytoplasm and also a conformational protection protein and an oxygen-retarding alginate capsule.

Why is mannitol used as the sole carbon source in the enrichment culture for Azotobacter?

Azotobacter can readily utilize it, while many other microbes cannot

Why does the broth medium for isolating Azotobacter lack an added nitrogen source?

he mannitol broth medium used for isolating Azotobacter lacks an added nitrogen source to create a selective environment that only allows nitrogen-fixing microorganisms to grow. Because Azotobacter species are capable of fixing atmospheric nitrogen into usable ammonia through the enzyme nitrogenase, they can thrive in nitrogen-free media, while most other soil microorganisms cannot

What visual cue identifies Azotobacter vinelandii under UV light?

A distinct yellow-green, fluorescent pigment.

What are the drought-resistant, dormant structures produced by Azotobacter called?

Presence of cysts (ovoid-shaped, dormant, drought-resistant structures produced by Azotobacter which may be visible in Gram stain)

Where are Lactobacillus and Bifidobacterium typically found in the human body?

Lactobacillus in the small intestine; Bifidobacterium in the colon.

List three ways probiotic EPS can promote health benefits for the host.

Modulating immune responses, influencing gut microbiota, and protecting against pathogens.

How does EPS increase intestinal barrier integrity?

By the upregulation of tight junctions.

Define dysbiosis and list two diseases linked to this condition

An imbalance in the gut microbial community; linked to IBS and IBD.

What is the specific energy source for the rotation of the bacterial flagellar motor?

The Proton Motive Force (PMF).

What are the two components of the Proton Motive Force?

Electrical potential difference (membrane potential) and chemical potential difference (pH gradient)

Distinguish between amphitrichous and lophotrichous flagellar arrangements

Amphitrichous: flagella at both opposite ends; Lophotrichous: a tuft/cluster at one site

What is the flagellar arrangement of Escherichia coli?

Peritrichous.

What is the purpose of TTC in a motility test medium?

It is reduced by motile bacteria to form formazan, a red pigment.

Chemically, what is red formazan the result of?

The reduction of 2,3,5- triphenyltetrazolium chloride (TTC).

What unique enzyme does Helicobacter pylori use to survive the acidic stomach?

Urease. Urease catalyzes the breakdown of urea (found in the stomach from dietary sources) into ammonia and carbon dioxide.

What is the primary function of FATPase in the bacterial plasma membrane?

To synthesize ATP using the Proton Motive Force (PMF).

Is the F-ATPase the same as the flagellar motor? Explain

No; F-ATPase maintains the gradient, while the flagellar motor directly uses the flow of protons to rotate

What is the consequence of damaging the fliA gene?

Failure to assemble the outer parts of the flagellum due to lack of the sigma28 factor. complete loss of motility, significant reduction in virulence

Define chemotaxis in the context of bacterial behavior.

The movement of bacteria toward or away from chemicals/stimuli.

What is the specific role of the CheY protein in chemotaxis?

It controls the direction of flagellar rotation switching clockwise or counterclockwise direction (determining "run" vs. "tumble").

What do MCPs act as in the bacterial cell?

Methyl-accepting chemotaxis proteins (MCPs) sensors that function as transmembrane sensors (chemoreceptors) that detect external chemical signals, such as nutrients or toxins.

What are pili (fimbriae) chemically made of?

Proteinaceous pilins or fimbrins.

What is the role of the "sex pilus" (conjugative pilus)?

It facilitates the transfer of DNA from a donor cell to a recipient cell.

what are tra genes?

Genes typically found in the transfer region (tra) of region of conjugative plasmids, best example is the F plasmid, aid in gene transfer and conjugation via T4SS.

What is a critical function of Type IV competence pili in Vibrio cholerae?

They bind to extracellular doublestranded DNA via their tips and retract to initiate DNA uptake during natural transformation.

Which specific pilus type is associated with nosocomial UTIs caused by Proteus mirabilis?

MR/P pili.

(Mannose Resistant – MR)

What environment triggers the expression of the pH6 antigen (PsaA) in Yersinia pestis?

Acidic conditions (around pH 6.7) found in host macrophage phagolysosomes.

List five bacterial components that serve as antigenic factors.

Peptidoglycan, LPS, Mycolic acid, Capsule, and Flagella.

Distinguish between reversible and irreversible attachment in biofilm formation.

Stage A is reversible; Stage B is irreversible.

Why is quorum sensing vital for biofilm survival?

It acts as a bacterial communication system to coordinate population density, enabling the shift from individual behavior to a collective, organized community. Example activating gene expressions to initiate EPS secretion, QS regulate increase biofilm resistance to stressors like antibiotics, dehydration, and environmental toxins!

What term describes immobile microbial communities attached to surfaces?

Sessile communities.

What term describes free-floating bacteria?

Planktonic bacteria

What visual indicator suggests a stronger biofilm in a crystal violet assay?

A denser, darker purple ring or spot.

Write the breakdown reaction of urea by the enzyme urease.

Urea → Ammonia NH3 and Carbon Dioxide CO2

Explain how P. mirabilis creates a "crystalline" biofilm

Ammonia raises urine pH, causing magnesium and calcium phosphates to precipitate into crystals

What morphological changes occur when a P. mirabilis swimmer cell becomes a swarmer cell?

It becomes exceptionally long, polyploid, and hyperflagellated (thousands of flagella)

What is the role of flhDC in Proteus mirabilis?

It is the class 1 flagellar master regulator gene

Define siderophores and their affinity level

High-affinity iron-binding molecules are used by some pathogenic bacteria to scavenge iron like Fe3+ away from humans

Name two host proteins that tightly bind iron to hide it from bacteria

Transferrin and Lactoferrin.

How does adding lemon juice to a salad affect iron absorption?

It converts iron from Fe3+ (ferric) to Fe2+ (ferrous) for better absorption.

List the two internalins L. monocytogenes uses to adhere to host receptors

Internalin A (InlA) and Internalin B (InlB).

What is the specific role of Listeriolysin O (LLO)?

It facilitates the escape of Listeria from the host cell's vacuole (vacuolar lysis).

How does Listeria achieve movement within the host cytoplasm?

It uses the ActA protein to induce actinbased motility.

Why is cell-to-cell spread advantageous for Listeria?

It allows the bacterium to spread to adjacent cells without leaving the cytoplasm or exposure to the extracellular environment.

What is the function of the "Housekeeping" sigma factor?

It initiates transcription of most genes needed for basic cell function

Give three examples of conditions that activate alternative sigma factors

Starvation, sporulation, and heat-shock response

Provide the full equation for biological nitrogen fixation

N_2 + 8e^- + 10H^+ + 16 ATP + 16 H_2O → 2NH_4^+ + H_2 + 16ADP + 16P_i

What is the microbial process that is the reverse of nitrogen fixation?

Denitrification.

Why does Azotobacter grow at the surface of a flask interface?

Because it is an aerobic organism that requires oxygen

What two functions does the Proteus toxic agglutinin (Pta) serve?

Cytotoxin and agglutinin.

What type of molecule is HpmA and what does it do to host cells?

It is a hemolysin that creates pores in host cell membranes

What happens during the "swarming" phase of the Proteus bull's-eye pattern?

Swarmer cells stop moving and revert back to the shorter, swimmer morphotype

What does Vitamin C neutralize to help iron absorption?

Iron-blocking compounds like phytates. Enhances non-heme iron absorption in intestine by reducing ferric iron to ferrous iron

Why are endospores typically not considered antigenic factors?

They are dormant structures and are typically not active in causing disease or triggering immune responses.

What is a unique feature of bacterial gene expression involving ribosomes and RNA polymerase?

Transcription and translation are coupled in bacteria

What is required for all bacterial gene transcription to initiate?

A specific sigma factor, depending upon the environmental condition.

What is the role of the "housekeeping" sigma factor (sigma-70)?

It initiates the transcription of most genes needed for basic cell function.

Under what specific environmental conditions might alternative sigma factors be activated?

Starvation, sporulation, stationary phase, nitrogen metabolism, and heat-shock response.

Beyond resisting decolorization, why can't acid-fast bacteria be stained with a standard Gram stain?

Their cell wall is resistant to penetration by water-soluble stains like the Gram stain.

Why is microscopic examination of sputum alone sometimes insufficient to rule out active tuberculosis?

Sputum results can be negative in extrapulmonary TB or earlystage pulmonary TB with a low bacterial load.

Why does the bacterial capsule remain unstained during a negative staining procedure?

Because the capsule is nonionic and does not take up acidic or basic stains.

Identify two specific acidic stains used to color the background in capsule staining.

India ink or Congo red.

Identify two specific basic dyes used to color the bacterial cell itself in capsule staining

Crystal violet or methylene blue.

True or False: Bacterial capsules can serve as a reserve energy store.

True

In the Wzx/Wzy-dependent pathway, where are the individual sugar repeat units initially built?

On a lipid carrier at the cytoplasmic membrane.

What form of energy is required to export completed polysaccharide chains through an ABC transporter

Energy in the form of ATP.

Which specific region of the Neisseria meningitidis genome is involved in capsule transport?

Region B.

Which specific region of the Neisseria meningitidis genome is involved in capsule translocation?

Region C.

How does the molecular weight of the alginate change in A. vinelandii under high oxygen stress?

It increases to create a physically thicker and more compact capsule.

Why is the enzyme dinitrogenase reductase specifically vulnerable in Azotobacter?

It is an enzyme that is inactivated by oxygen.

Why is Azotobacter sold commercially as a bio-fertilizer?

Because it enriches soil nitrogen by converting gaseous nitrogen into ammonia and organic nitrogen.

Who discovered Azotobacter and what technique did they use?

Martinus Beijerinck in 1901 using an enrichment culture technique.

Where in a flask would you expect to see Azotobacter growth, and why?

At the surface/air interface because it is an aerobic microbe

What is the Gram stain result and cellular shape of Azotobacter?

It is a Gram-negative, bacillusshaped (rod-shaped) bacterium.

What term describes specific fibers that act as "food" for beneficial gut bacteria?

Prebiotics.

What does the safety acronym GRAS stand for in the context of microbial exopolysaccharides?

Generally Recognized As Safe.

List four industrial roles for microbial EPS in food or cosmetic products.

Thickener, stabilizer, emulsifier, and gelling agent.

What is the primary protein subunit that makes up the bacterial flagellar filament?

Flagellin.

How is torque generated in the bacterial flagellar motor?

By the flux of ions (ion-motive force) across the cell membrane.

Which specific bacterial types might utilize a Sodium Ion Gradient (Na+ motive force) for motility?

Bacteria in extreme environments or haloalkaliphiles. (name a bacteria)

To which general protein secretion category does flagellar protein secretion belong?

Type III secretion system (T3SS).