microbiology exam 2

What is the human microbiome?

The vast and diverse communities of microorganisms that colonize various sites on and within the human body, including the skin, mouth, urogenital tract, and gastrointestinal system, integral for health.

What are the roles of the human microbiome?

Maintaining health, supporting immune function, aiding digestion, and preventing colonization by pathogenic organisms.

What is dysbiosis?

An imbalance or disruption in the microbial communities, which can lead to disease states.

Which prominent bacterium resides in skin sebaceous glands and metabolizes oily substances?

Cutibacterium acnes (formerly Propionibacterium acnes).

How does C. acnes contribute to an acidic skin environment?

By metabolizing oily substances from sebaceous glands, producing fatty acids that create an acidic pH.

How does C. acnes lead to acne?

Colonization by different strains or an overgrowth can lead to inflammation triggered by immune responses to C. acnes or its metabolic products.

Which beneficial bacteria reinforces skin cell tight junctions and acts as a barrier against pathogens?

Staphylococcus epidermidis.

What microbial imbalance is often seen in eczema?

Dysbiosis, leading to an increase in Staphylococcus aureus overgrowth, which contributes to inflammation and skin barrier breakdown.

How many bacterial species typically inhabit the oral cavity?

Approximately 250 bacterial species.

Which oral bacterium metabolizes sugars into acids that demineralize enamel, leading to cavities?

Streptococcus mutans.

How does Streptococcus dentisani promote oral health?

It produces antimicrobial molecules capable of killing Streptococcus mutans, a major contributor to tooth decay.

Which bacterial species predominantly compose the vaginal microbiota?

Lactobacillus species.

What is the role of Lactobacillus in vaginal health?

They maintain an acidic vaginal pH (around 3.5-4.5) by producing lactic acid, which prevents pathogenic bacteria and fungi.

What happens when the vaginal pH rises?

Pathogenic bacteria can colonize the vagina, increasing the risk of infections like bacterial vaginosis or yeast infections.

Where is the largest microbial population in the human body primarily located?

The gut microbiota (mainly in the large intestine).

Name three functions of gut microbes.

Assisting in digesting dietary fiber, producing vitamins (e.g., K and B vitamins), and generating short-chain fatty acids (SCFAs).

What are the benefits of short-chain fatty acids (SCFAs) produced by gut bacteria?

They have anti-inflammatory effects and help prevent the growth of harmful bacteria.

How has research demonstrated a link between gut microbiota and obesity?

Transferring gut microbes from obese or lean individuals into germ-free mice showed that microbes from obese donors induced weight gain, while those from lean donors did not.

How does dietary fiber impact gut microbiota?

Dietary fiber is fermented by gut bacteria to produce vitamins and SCFAs, which decrease inflammation, inhibit harmful bacteria growth, and support immune health.

What is the difference between prebiotics and probiotics?

• Prebiotics: Foods rich in fibers or compounds that feed beneficial bacteria (e.g., inulin). - Probiotics: Live beneficial bacteria consumed via foods like yogurt or supplements, which help restore or maintain a healthy microbiome.

What is Clostridium difficile infection, and how is it often treated?

A severe antibiotic-associated diarrhea caused by an opportunistic pathogen allowed to colonize due to gut dysbiosis. It is effectively treated with Fecal Microbiota Transplantation (FMT).

Distinguish between catabolism and anabolism.

• Catabolism: breakdown of molecules to release energy. - Anabolism: synthesis of complex molecules using energy

What is ATP?

ATP (adenosine triphosphate) is the universal energy currency in cells, synthesized from ADP and inorganic phosphate during energy-yielding reactions, powering various cellular processes.

What does the ATP cycle involve?

Continuous synthesis of ATP during energy-generating reactions and hydrolysis of ATP to release energy for cellular work.

What are exergonic reactions?

Reactions that release energy, such as ATP hydrolysis.

What are endergonic reactions?

Reactions that require energy input, such as the biosynthesis of macromolecules.

Define oxidation and reduction in redox reactions.

• Oxidation: loss of electrons. - Reduction: gain of electrons.

Name three important energy carriers (electron carriers) in cellular metabolism.

NADH, NADPH, and FADH2.

What is the function of enzymes in metabolic reactions?

Enzymes are biological catalysts that lower activation energy, increasing the rate of reactions without being consumed.

What are the two main forms of microbial growth outcomes?

• Discrete colonies: derived from a single cell. - Biofilms: complex, surface-attached communities.

Name five characteristics used to describe bacterial colony morphology.

Shape, margin, elevation, size, texture, pigmentation, or optical properties.

What temperature range do most mesophilic bacteria thrive in?

Between 30^ ext{o} ext{C} and 37^ ext{o} ext{C}.

How does pH affect bacterial growth?

pH affects biomolecular stability and enzyme activity; Neutrophiles grow best near neutral pH (\sim7), Acidophiles prefer acidic environments (3.5-4.5), and Alkaliphiles thrive in alkaline conditions.

Which type of bacteria is favored by high salt concentrations, and which medium demonstrates this?

Salt-tolerant species, such as Staphylococci, are favored, as seen in Mannitol Salt Agar (MSA).

Distinguish between obligate aerobes and obligate anaerobes.

• Obligate aerobes: require oxygen for growth. - Obligate anaerobes: cannot survive in oxygen.

What are the key steps in biofilm development?

Secretion of extracellular polymeric substances, attachment to surfaces, communication among microbes, and cooperation and genetic exchange.

Why are biofilms medically significant?

Biofilms are highly resistant to antibiotics and disinfectants, complicating the treatment of infections on medical devices, prosthetic joints, and other body sites.

What is bioremediation?

The employment of microbes for environmental cleanup, such as treating wastewater, cleaning oil spills, and restoring contaminated sites.

How do bacteria produce ATP through aerobic respiration?

Aerobic respiration involves glycolysis, the citric acid cycle, and the electron transport chain, culminating in oxygen reduction as the terminal electron acceptor.

How do bacteria produce ATP through anaerobic respiration?

Anaerobic respiration replaces oxygen with alternative electron acceptors like Nitrate ( ext{NO}3^-), Sulfate ( ext{SO}4^{2-}), or Carbonate allowing energy production in oxygen-limited environments.

What is glycolysis?

The initial metabolic step that breaks down glucose into pyruvate, producing ATP and NADH, and serving as the foundation for both aerobic and anaerobic energy pathways.

What is the function of the electron transport chain in aerobic respiration?

It transfers electrons from NADH and FADH2 to oxygen, creating a proton gradient across the membrane, which drives ATP synthesis via oxidative phosphorylation.

When does fermentation occur in bacteria?

When an electron transport chain is unavailable; bacteria switch to fermentation, producing ATP solely through glycolysis.

Name five food products made through fermentation.

Beer, wine, bread, cheese, yogurt, sauerkraut, kefir, soy products, kombucha, tempeh, tamari, soy sauce, and vinegar.

What is the purpose of biochemical testing for bacterial speciation?

To analyze bacterial metabolic capabilities, such as fermentation patterns and respiration modes, to identify species accurately, aiding in diagnostics and research.

What is quorum sensing (QS)?

A chemical communication system that bacteria use to detect their population density via autoinducers, which, when reaching a threshold, activate genes for group behaviors like biofilm formation or virulence.

Describe the mechanism of quorum sensing.

Bacteria secrete autoinducers; when these molecules reach a critical concentration, they bind to specific receptors on bacterial surfaces, triggering gene expression changes relevant to population density.

Name and define the three main types of symbiotic relationships between microbes and hosts.

• Mutualism: both organisms benefit (e.g., algae-fungi in lichens). - Commensalism: one benefits, the other is unaffected (e.g., Staphylococcus epidermidis on skin). - Parasitism: one benefits at the host's expense (e.g., pathogenic bacteria).

What is the purpose and function of selective media?

Selective media inhibit certain bacteria while supporting the growth of others, aiding in microbial isolation (e.g., MacConkey agar suppresses gram-positive bacteria).

How do differential media and pH indicators work?

Differential media contain specific chemicals and pH indicators that reveal biochemical capabilities (e.g., sugar fermentation). Lactose fermentation, for instance, produces acid, lowering pH and changing the medium's color.

How is MacConkey agar both selective and differential?

It selectively supports gram-negative bacteria growth while differentiating lactose fermenters (which turn colonies red or pink due to acid production) from non-fermenters (which remain colorless or yellow).

How is Mannitol Salt Agar (MSA) both selective and differential?

It selectively favors salt-tolerant Staphylococci and differentiates mannitol fermenters (which produce acid, turning the medium yellow) from non-fermenters (which do not change the medium's color).

What is blood agar used for, and what can it indicate?

It is an enriched medium for culturing fastidious bacteria and allows observation of hemolytic activity, which aids in bacterial identification.

Describe the three types of hemolysis observed on blood agar.

• Beta-hemolysis (\beta): complete lysis of red blood cells, producing clear zones. - Alpha-hemolysis (\alpha): partial lysis, producing a greenish discoloration. - Gamma-hemolysis (\gamma): no hemolysis, with no change in the blood agar.

What is the human microbiome?

The vast and diverse communities of microorganisms that colonize various sites on and within the human body, including the skin, mouth, urogenital tract, and gastrointestinal system, integral for health.

Mutualism

both organisms benefit (e.g., algae-fungi in lichens).

Commensalism

one benefits, the other is unaffected (e.g., Staphylococcus epidermidis on skin).

Parasitism

one benefits at the host's expense (e.g., pathogenic bacteria).

Obligate aerobes

require oxygen for growth.

Obligate anaerobes

cannot survive in oxygen.

Beta-hemolysis (\beta)

complete lysis of red blood cells, producing clear zones.

Alpha-hemolysis (\alpha)

partial lysis, producing a greenish discoloration. 

Gamma-hemolysis (\gamma)

no hemolysis, with no change in the blood agar.

Prebiotics

Foods rich in fibers or compounds that feed beneficial bacteria (e.g., inulin).

Probiotics

Live beneficial bacteria consumed via foods like yogurt or supplements, which help restore or maintain a healthy microbiome.

Catabolism

breakdown of molecules to release energy.

Anabolism

synthesis of complex molecules using energy.

Oxidation

loss of electrons.

Reduction

gain of electrons.

Discrete colonies

derived from a single cell.

Biofilms

complex, surface-attached communities.

In Situ Bioremediation

treating contamination at the site

ex situ bioremediation

removing the contaminated material to treat it elsewhere

three types of pollutants that microbes can help remove from the environment

Hydrocarbons

Peticids

Heavy metals 

Nitrogen

key component of proteins and enzymes, essential for bacterial growth ans ,metabolism

phosphorous

cricial for energy production (in the form of ATP) and the creation of cell membrane, which are vital for bacterial life

Idenella sakaoensis

two enzymes petase and MHETase works together to break down (pet) which is used in bottles and packaging

Acidophiles

acid loving

<5.5

Neutrophiles

neutral

5.5-8.0

Alkaliphiles

Basic Phs 

>8.0

Psychrophlic

cold loving organisms

0-20

Mesophilic 

moderate or middle temp.

20-45

Thermophilic 

heat-loving organsns 

50-55