Micro Chapter 14 Practice Questions

Which of the following body sites is normally considered strictly sterile in a healthy human?

Cerebrospinal fluid

What is a primary reason Gram-positive bacteria are generally more successful at colonizing the skin than Gram-negative bacteria?

They are more resistant to salt and dryness.

Which bacterium is renowned for its ability to survive the highly acidic environment of the stomach by utilizing the enzyme urease?

Helicobacter pylori

What is the approximate ratio of strictly anaerobic organisms to facultative organisms in the human distal intestine?

1000:1

How do gut microbiota, such as Bacteroides thetaiotaomicron, primarily benefit the host's nutritional status?

By breaking down complex carbohydrates into usable products.

Which term describes a laboratory animal in which all the microbial species present are completely known, or the animal is completely germ-free?

Gnotobiotic

What structural feature of the blood-brain barrier is most critical for preventing pathogens from entering the central nervous system?

Extremely tight junctions between endothelial cells.

Which pathogenic bacterium is notable for its ability to cross the maternofetal (placental) barrier and infect a developing fetus?

Listeria monocytogenes

By what mechanism do host cells of the innate immune system recognize the presence of microbiota to keep them in check?

By detecting microbe-associated molecular patterns (MAMPs) using pattern recognition receptors (PRRs).

The 'hygiene hypothesis' (or disappearing microbiota hypothesis) suggests that the rise in modern allergic and metabolic diseases is most likely linked to:

The loss of 'ancestral' microbiota due to improved sanitation and widespread antibiotic use.

What is the primary function of tight junctions in the context of the human microbiome?

They act as molecular glue between epithelial cells, preventing microbiota from accessing deeper tissues.

Which intestinal condition is characterized by the formation of an exudative plaque on the intestinal wall caused by a toxin produced after antibiotic therapy?

Pseudomembranous enterocolitis

What specific term describes an unhealthy imbalance in the composition of a microbiome at any body site?

Dysbiosis

How does heavy initial colonization by Bifidobacterium species specifically benefit breast-fed infants?

It easily digests human milk oligosaccharides and produces metabolic products that protect against intestinal pathogens.

The 'gut-brain axis' allows for bidirectional communication between the central nervous system and gut microbiota. Which major neural pathway plays a crucial role in this physical connection?

The vagus nerve

Which of the following describes a beneficial function performed by normal skin microbiota?

They promote the expression of host tight-junction proteins and secrete antimicrobial peptides.

What role do methanogenic archaea, such as Methanobrevibacter smithii, potentially play in host weight gain?

They oxidize hydrogen gas in the gut, allowing bacteria to ferment more efficiently and produce more calories for the host to absorb.

Which increasingly mainstream clinical treatment is currently approved to correct severe dysbiosis caused by recurrent Clostridioides difficile infections?

Fecal microbiota transplants (FMT)

How do bacteria within the microbiome communicate with each other to alter gene expression based on their population density?

Quorum sensing

Why is the lower respiratory tract (the trachea and deep lungs) no longer considered a completely sterile environment?

Because low numbers of normal microbiota, such as Prevotella and Streptococcus, have been detected there.

The human virome consists largely of bacteriophages, but surprisingly, the viromes of healthy infants often include which of the following?

Viruses associated with diarrheal disease

How does Cutibacterium acnes contribute to the formation of acne on the skin?

It degrades triglycerides in sebum into free fatty acids, which promotes inflammation.

Why is the surface of the eye (conjunctiva) generally hostile to heavy microbial colonization?

Tears constantly rinse the surface and contain antimicrobial factors like lysozyme.

In patients with a heart mitral valve prolapse (heart murmur), transient bacteremia from a dental procedure can lead to a serious condition known as:

Subacute bacterial endocarditis

Why are malnourished populations significantly more susceptible to severe epidemics of cholera (Vibrio cholerae)?

They often suffer from achlorhydria (loss of stomach acid), allowing the acid-sensitive bacteria to survive passage to the intestine.

The duodenum and jejunum of the small intestine are difficult environments for most microbes to colonize. Which trait allows specific Gram-positive Bacillota to survive there?

They possess a bile salt hydrolase enzyme that destroys bile salts if they enter the cell.

By adulthood, over 90% of the bacteria in a healthy human gut microbiome belong to which two phyla?

Bacteroidota and Bacillota

Which organism is a critical member of the healthy vaginal microbiome because it produces lactic acid to maintain a protective, mildly acidic environment?

Lactobacillus crispatus

Bacterial proteins such as catalase can act as 'immunomodulins.' What is the function of an immunomodulin?

They modify the secretion of host immune system regulatory proteins, such as cytokines.

Faecalibacterium prausnitzii is considered a highly beneficial gut microbe primarily because it:

Produces large amounts of butyrate, which serves as energy for colonic cells and inhibits inflammation.

In the landmark Gordon lab study transferring human twin feces into germ-free mice, what happened when an 'Obese-microbiome' mouse was cohoused with a 'Lean-microbiome' mouse?

The obese mouse gained less weight because the lean microbiome successfully invaded and displaced the obese microbiome.

Which of the following describes an opportunistic pathogen?

A microbe that causes disease only when introduced to an unusual location or in an immunocompromised host.

According to the text, the widely used herbicide glyphosate (Roundup) has been linked to intestinal dysbiosis associated with which human condition?

Celiac disease

What is the key functional difference between a prebiotic and a probiotic?

Prebiotics are plant fibers that humans cannot digest but beneficial microbes can, whereas probiotics are the living microbes themselves.

Which specific substance freely diffuses across the blood-brain barrier without requiring a carrier system?

Oxygen

By what specific mechanism do bacteria within a microbiome communicate their population density to one another?

By secreting targeted autoinducer molecules into their environment.

The microbial product indole (produced when E. coli degrades tryptophan) has what important communication effect on host intestinal epithelial cells?

It signals the host to tighten tight junctions and increase production of anti-inflammatory interleukin 10 (IL-10).

Research in microbial endocrinology indicates that host stress hormones (epinephrine and norepinephrine) can have what effect on the microbiome?

They stimulate the growth of pathogenic and nonpathogenic E. coli in vitro and influence their adherence to the mucosa.

How might intestinal dysbiosis potentially contribute to the development of Parkinson's disease?

By increasing gut levels of lipopolysaccharide (LPS), triggering inflammation that forms Lewy bodies in the vagus nerve, which travel to the brain stem.

What is considered a significant evolutionary advantage of using phage therapy over traditional antibiotics for treating infections?

Because bacteriophages coevolve with bacteria, it is easier to identify a new phage to infect a resistant bacterium than to discover a brand-new antibiotic drug.

Skin

Mostly Gram-positive (Staphylococcus, Bacillus, Propionibacterium).

Acidic pH (4–6) and high salt inhibit most growth.

Mouth

500+ species; Streptococcus, Actinomyces, Lactobacillus.

Microbes form biofilms (dental plaque) and can cause endocarditis if they enter the blood.

Respiratory

Mucociliary escalator sweeps microbes out of the lungs.

Once thought sterile; now known to contain low numbers of Prevotella and Streptococcus.

Stomach

Extremely acidic (pH 1–4).

Helicobacter pylori survives by using urease to raise local pH; it can cause ulcers or cancer.

Intestine

Highest bioburden (10^11/cm in colon).

1,000 anaerobes for every 1 facultative organism. Predominantly Bacteroidota and Bacillota.

Urogenital

Lactobacillus crispatus maintains acidic pH (4.5) to inhibit pathogens in vagina.

Distal urethra contains S. epidermidis and Enterococcus.

True or False

Most internal organs, blood, and cerebrospinal fluid should harbor bacteria; their lack of presence indicates infection.

False

Which of the following is not a physical barrier included in host-microbe interactions?

Mucous Membranes

Tight Junctions

Formed between epithelial cells to prevent microbes from breaching mucosal barriers.

Blood-Brain Barrier (BBB)

Extremely tight junctions in brain capillaries protect the CNS from toxins and pathogens.

Maternofetal Barrier

The placenta separates maternal and fetal circulation to protect the fetus.

Host cells use ___ to recognize Microbe-Associated Molecular Patterns (MAMPs) like peptidoglycan.

Pattern Recognition Receptors (PRRs)

PRRs used by host cells to recognizes MAMPs triggers ___ to control microbial populations.

Cytokine production

Which of the following is NOT a defensive response triggered by PRR’s recognising MAMPs?

Adaptive antibody generation

The Gut-Brain Axis

A bidirectional communication pathway connecting the CNS to the intestinal tract via the vagus nerve, affecting mood and behavior

Which of the following is the gut-brain axis comprised of?

All of the above

Which of the following is NOT microbial antagonism?

Bacteria causing disease

True or False

Microbiota is constantly being sampled by mucosal cells of the immune system to keep itself sharp.

True

Immunomodulin

A protein made by normal microbiota that influences the host immune response by modifying the secretion of host proteins (i.e. cytokines)

Bacterial proteins like ___ can act as immunomodulins to influence immune response.

Catalase

Which of the following is not true for Faecalibacterium prausnitzii?

Gram-Negative

True or False

Faecalibacterium prausnitzii’s effects on human immune cells includes secreted bacterial factors and interactions with Toll-like receptors.

True

True or False

Bacterial factors from F. prausnitzii can increase inductions of the inflammatory cytokine IL-8 while decreasing the numbers of anti-inflammatory T-cell lymphocytes.

False

Lacking F. prausnitzii leads to what condition?

Crohn’s disease

F. prausnitzii is NOT associated with which of the following?

Hemochromatosis

Which of the following is NOT an attribute of Candidatus Savagella?

Gram-negative

Gnotobiotic Animal

Germ-free or colonized by a known set of microbes

Axenic

Germ-free

To develop a gnotobiotic colony or germ-free animals, which of the following is NOT the correct action?

Natural birth

Germ-free animals are more susceptible to infections for which reason?

All of the above

The most successful microbial invaders in the cohoused mice were ___ from the ___ mouse.

Bacteroides; lean

Which of the following is NOT a step that methanogens go through to collaborate with metabolic weight gain?

Methanogens consume the fermentation end products produced, like fatty acids, to produce methane.

True or False

Normal microbiota breaching human defenses will not cause any problems as they are not true pathogens.

False

Serum Complement

A host defense system that attacks bacterial membranes and attracts phagocytes to an infection

Immunocompromised Host

An animal with a weakened immune system

Opportunistic Pathogens

A microbe that normally is not pathogenic but can cause infection or disease in an immunocompromised host organism

True or False

The intestine is considered an incubator for antibiotic resistance.

True

True or False

Indiscriminate use of antibiotics will not lead to stronger bacteria, rather it will throw them off and be more effective as a treatment.

False

Which of the following is the method used by bacteria to pass antibiotic resistance genes?

All of the above

Dysbiosis (Definition)

An imbalance in the composition of a microbiome that can be brought on by stress or antibiotic therapy

May cause some human diseases or even influence behaviors

Which of the following bacteria has NOT been associated with intestinal health?

Staphylococcus

Which of the following bacteria has been associated with intestinal health?

Bacteroides

True or False

Research suggests that specific members of a microbiome are more important than the presence of a core set of genes among different members of the microbiome.

False

Which non-antibiotic drug also disturbs the microbiome balance?

All of the above

Glyphosate (Roundup)

Linked to a form of intestinal dysbiosis associated with celiac disease

Prebiotic

A food or nutritional supplement

Provides fibers that can be digested by beneficial bacteria

Probiotic

A food or nutritional supplement

Contains live microorganisms that promote beneficial gut bacteria

The benefits of having a microbiome include which of the following?

Interfering with pathogen colonization

A germ-free animal is characterized by which of the following?

Thin intestinal walls

When does an infant’s microbiome begin to compose?

At birth

Microbial colonization typically occurs when a newborns ___.

Tissues come into contact with the external environment

Which of the following is NOT supposed to be sterile?

Eyes

Metagenomic DNA Sequencing

Next-gen sequencing method that analyzes all genetic material directly from complex environmental or clinical samples

Virome

All the viruses that inhabit a particular organism or environment

Human viruses in the virome does not include those that can cause ___.

None of the above

Which of the following is NOT a disease that causes diarrhea?

Erythroparvoviruses

Epidermis

The outer protective cell layer in most multicellular animals.

Skin has a(n) ___ pH.

Acidic

Which part of the skin does not harbor enough moisture to support microbial growth?

Hand