BIOL 261: CH. 24 - MICROBIAL SYMBIOSES WITH HUMANS

What microbes are associated with parts of the body exposed to the outside world?

Various microbes are found on the skin, in the upper respiratory tract, stomach, intestines, colon, and genital tract.

What type of bacteria are found on the skin?

On the skin, common bacteria include Staphylococcus epidermidis, Micrococcus luteus, and Bacillus species.

What is the appearance of Staphylococcus epidermidis?

Staphylococcus epidermidis appears as G+ cocci arranged in clusters.

What is the appearance of Micrococcus luteus?

Micrococcus luteus is a G+ cocci that forms yellow-colored colonies and arranges in tetras.

What type of bacteria is Bacillus, and how does it come into contact with the skin?

Bacillus is a G+ rod that often resides in soil.

• It can be transient on the skin, typically picked up from the environment or hands.

What is normal flora, or normal microbiota?

Normal flora, or normal microbiota, refers to the microorganisms that naturally inhabit the body without causing harm.

What bacteria are found in the upper respiratory tract?

The upper respiratory tract contains Streptococcus species, which are G+ cocci that form chains.

What is the role of Helicobacter pylori in the stomach?

Helicobacter pylori is a G- rod that lives in the stomach, where it neutralizes stomach acid using urease, allowing it to survive and potentially cause infection.

What is the pH of the stomach?

The pH of the stomach is around 2, which is very acidic.

How does Helicobacter pylori affect the pH of the stomach?

Helicobacter pylori neutralizes the stomach’s acidic pH by converting urea into ammonia, raising the pH locally and allowing the bacteria to grow.

What is the role of bacteria in the intestines?

Bacteria in the intestines help with digestion, especially in breaking down complex carbohydrates and fermenting sugars.

What do bacteria in the intestines produce when they ferment sugars?

When bacteria ferment sugars in the intestines, they produce acids and gases.

What types of bacteria are found in the colon?

The colon contains G- rods, such as Escherichia coli, Enterobacter aerogenes, and Proteus species, as well as G+ cocci like Enterococcus faecalis.

What pathogens are present in the colon?

Pathogens like Salmonella typhi and Shigella dysenteriae are present in the colon and are G- rods that do not ferment lactose.

What is the role of bile salts in the intestines?

Bile salts are selective for G+ rods in the intestines, promoting the growth of certain bacteria while inhibiting others.

What is culture and sensitivity testing?

Culture testing involves growing out a pathogen and identifying it, while sensitivity testing determines the most effective antibiotic for treating the infection.

How is culture testing performed?

Culture testing involves growing the pathogen in a pure culture and conducting biochemical tests to identify the bacteria.

What are dichotomous keys used for in microbiology?

Dichotomous keys are used to help identify bacteria through a series of yes/no questions based on their characteristics.

What is the Kirby-Bauer test?

The Kirby-Bauer test is a sensitivity test that determines the best antibiotic for treating an infection by measuring the zone of inhibition around antibiotic discs.

What does the zone of inhibition indicate in the Kirby-Bauer test?

The zone of inhibition indicates the effectiveness of an antibiotic.

• A larger zone means the antibiotic is more effective at preventing bacterial growth.

What is the microbiome like in utero?

In utero, the fetus does not have any normal flora or microbiome.

When does the microbiome begin to develop?

The microbiome begins to develop after birth, as the newborn is exposed to various microorganisms.

What microbes are found in the vaginal tract?

The vaginal tract contains normal flora, such as Lactobacillus species.

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What type of bacteria is Lactobacillus?

Lactobacillus is a G+ rod bacterium.

How does Lactobacillus affect the pH of the vaginal tract?

Lactobacillus produces lactic acid by fermenting lactose, which lowers the pH of the vaginal tract, helping to prevent harmful microbial growth.

What part of the body does not have normal flora due to macrophages being present to phagocytize bacteria and viruses?

Lower respiratory tract.

Why is the bladder considered to have no normal flora?

Because urine, which is a great growth medium containing water, salt, sugar, and protein, has no other bacteria to compete with.

Why is cerebrospinal fluid (CSF) free from normal flora?

Because anything that gets into the CSF, which surrounds the brain and spinal cord, can grow there, leading to conditions like meningitis.

What condition is caused by inflammation of the meninges due to the growth of organisms in the CSF?

Meningitis.

Why does the circulatory system lack normal flora?

Blood contains white blood cells (WBCs) that are part of the immune system and protect against infections.

Why is bone marrow free from normal flora?

Bone marrow contains stem cells, which are the precursors to all blood cells and do not harbor normal flora.

Which organs in the body do not contain normal flora?

All internal organs.

What are some future benefits of knowing the human microbiome?

• The development of biomarkers for predicting predisposition to diseases.

• Designing targeted therapies.

• Personalized drug therapies and probiotics.

How are most bacteria identified if they cannot be cultured?

Advanced sequencing techniques allow for the identification of different microbiota at different body sites.

What are facultative anaerobes?

Facultative anaerobes are bacteria that can live with or without oxygen.

What was discovered in the 1980s and is found in approximately 50 percent of the world’s population?

Acid-resistant Helicobacter pylori.

Where is Helicobacter pylori found when present?

It is found in the gastric mucosa.

What significant influence do microbial metabolites or transformation products have on host physiology?

They influence vitamin production, modification of steroids, and amino acid biosynthesis.

Which vitamins are produced by caiforms in the gut?

B₁₂ and K.

What amino acid-related benefit do caiforms provide in the gut?

They help in amino acid biosynthesis.

What does it mean to be lactose intolerant?

It means lacking the enzyme needed to break down lactose found in milk, dairy, and ice cream.

What role does E. coli play in lactose digestion for lactose-intolerant individuals?

E. coli loves lactose and produces acid and gas when it interacts with lactose.

How does Beano help with digestion?

Beano is an enzyme that breaks down complex carbohydrates, pre-digesting food to ease digestion.

What is the oral cavity in terms of its microbial habitat?

The oral cavity is a complex, heterogeneous microbial habitat.

What does saliva contain that helps with antimicrobial activity?

Saliva contains antimicrobial enzymes, including lysozyme.

What is the role of lysozyme in saliva and tears?

Lysozyme breaks beta 1-4 linkages in the peptidoglycan cell wall of bacteria.

Why do high concentrations of nutrients near surfaces in the mouth promote microbial growth?

High concentrations of nutrients near surfaces in the mouth provide an environment that supports localized microbial growth.

What does a tooth consist of?

A tooth consists of a mineral matrix (enamel) surrounding living tissue, including dentin and pulp.

What is the process of biofilm formation on teeth?

The formation of biofilms on teeth (dental plaque) is an ordered process of microbial assembly.

What types of bacteria are involved in the formation of dental plaque?

Dental plaque primarily contains Gram-positive cocci in chains, such as streptococcus species.

How do bacteria contribute to dental cavities?

Bacteria produce glycan, a sticky substance that helps them adhere to teeth.

What happens when bacteria grow on teeth?

As bacteria grow, they produce acids that weaken the enamel of the teeth.

How does weakened enamel lead to dental cavities?

The acids produced by the bacteria slowly break down the enamel, leading to an infection and the formation of dental cavities.

What bacteria frequently cause urinary tract infections, especially in women?

E. coli and P. mirabilis frequently cause urinary tract infections, especially in women.

What is the role of Lactobacillus acidophilus in the vagina?

Lactobacillus acidophilus ferments glycogen in the vagina, producing lactic acid.

How does Lactobacillus acidophilus contribute to the vaginal environment?

Lactobacillus acidophilus helps maintain a healthy vaginal environment by producing lactic acid through the fermentation of glycogen, which helps lower the pH and inhibits the growth of harmful bacteria.

What bacteria are commonly associated with bladder infections?

E. coli and Proteus.

What type of bacteria are E. coli and Proteus?

They are Gram-negative rods.

Are E. coli and Proteus motile?

Yes, they are motile, meaning they can move, often through flagella.

Why are females more susceptible to bladder infections?

Females are more susceptible because they have a shorter urethra.

What is the human virome?

The human virome refers to the collection of viruses present in and on the human body.

What types of viruses can be found in the human virome?

The human virome includes animal viruses, bacteriophages, and possibly plant viruses.

What diseases can viruses in the human virome cause?

Some viruses in the human virome can cause severe diseases like hepatitis and severe acute respiratory syndrome.

What are some examples of milder infections caused by viruses in the human virome?

Viruses in the human virome can also cause milder acute infections such as influenza and the common cold.

Are all viruses in the human virome harmful?

No, some viruses in the human virome are completely benign and do not cause harm.

Which type of viruses are the most abundant in the human body?

Bacteriophages are the most abundant viruses in all body sites.

Are bacteriophages animal viruses?

No, bacteriophages are not animal viruses; they infect bacteria instead.

What is Inflammatory Bowel Disease (IBD)?

Inflammatory Bowel Disease (IBD) is a chronic inflammation of the gut and disruption of homeostasis, also known as dysbiosis.

How does antibiotic use affect the risk of developing IBD?

Antibiotic use increases the risk of developing IBD.

Can IBD be transmitted between family members?

Yes, once developed, IBD may be transmissible between family members.

How does the gut microbiome diversity of individuals with IBD compare to others?

Individuals with IBD have lower gut microbiome diversity.

What is the correlation between IBD and the Western diet?

There is a strong correlation between IBD and the typical Western diet, which is rich in animal protein.

What does Streptococcus mutans cause?

Streptococcus mutans causes dental cavities.

What does Streptococcus mutans produce that helps it stick to teeth?

Streptococcus mutans produces a sticky substance that allows it to stick to your teeth, grow, and make a biofilm.

What happens when oral antibiotics are used in the human gut?

Oral antibiotics decrease all microbes in the human gut, both target and non-target.

What infection is associated with antibiotic use?

Clostridium difficile infections are associated with antibiotic use.

What is a newer therapy for Clostridium difficile infection?

A newer therapy for Clostridium difficile infection is a fecal transplant.

What type of bacteria is Clostridium difficile?

Clostridium difficile is a Gram-positive rod that forms endospores and is anaerobic.

What causes the bloody diarrhea in Clostridium difficile infections?

Clostridium difficile produces a toxin that causes bloody diarrhea, and the colon may eventually rupture.

How do antibiotics affect Clostridium difficile?

Antibiotics kill the bacteria, including Clostridium difficile, as broad-spectrum antibiotics target both Gram-positive and Gram-negative bacteria.

What is an example of a broad-spectrum antibiotic and how does it work?

An example of a broad-spectrum antibiotic is penicillin, which blocks the crosslinking of peptidoglycan cell walls in bacteria.

What is the purpose of fecal transplants?

Fecal transplants are used to introduce healthy bacteria into the gut, often to treat conditions like C. difficile infections.

How do fecal transplants create competition with C. difficile?

Fecal transplants introduce beneficial microbes that outcompete the harmful C. difficile bacteria, helping to restore a healthy microbial balance in the gut.

What happens when C. difficile goes into spore form?

When C. difficile goes into spore form, it becomes more resistant to environmental conditions, including antibiotics, and can survive in the gut, potentially causing an infection again if conditions allow.

What are probiotics?

Probiotics are live organisms that provide health benefits to the host.

What form do probiotics usually come in?

Probiotics typically come in the form of live bacteria, often lyophilized (freeze-dried).

What happens when lyophilized probiotics are rehydrated?

When lyophilized probiotics are rehydrated, the bacteria come back to life and begin to grow.

What are common species of bacteria used as probiotics?

Bifidobacterium and Lactobacillus are common species of bacteria used as probiotics.

Where are probiotics commonly found?

Probiotics are commonly found in yogurt and probiotic drinks.

What are examples of probiotic foods?

Examples of probiotic foods include yogurt with "active culture" and fermented foods.

How do probiotics benefit the gut?

Probiotics benefit the gut by taking up space or nutrients, which limits the ability of pathogens to colonize.

What are prebiotics?

Prebiotics are carbohydrates that are indigestible by humans but provide nourishment for gut bacteria.

How do prebiotics benefit the gut?

Prebiotics benefit the gut by feeding the fermentative bacteria in the intestines, promoting a healthy microbiome.

What types of foods are prebiotics found in?

Prebiotics are found in nutrient-dense foods like complex carbohydrates and fibers.

Why are prebiotics important for gut health?

Prebiotics are important because they nourish gut bacteria, helping maintain a balanced and healthy microbiome.

Dysbiosis

an alteration or imbalance of an individual’s microbiome relative to the normal, healthy state, primarily observed in the microbiota of the digestive tract or the skin

Fecal Transplant

the transfer of microbiota from the colon of one individual into the colon of another

Host

an organism that can harbor pathogenic or beneficial (micro)organisms

Human microbiome

the total microbial content in and on the human body