Microbiology: Chapter 13 (Microbe-Human Interactions)

What are the two possible outcomes when microbes colonize the body?

They may become part of the normal flora or cause an infection or disease.

What is normal flora?

Microorganisms that normally live on or in the body.

Which types of microorganisms can be part of the normal flora?

Bacteria, fungi, and viruses.

Where is normal flora commonly found?

On the skin and mucous membranes, including the upper respiratory tract, gastrointestinal tract, outer urethral opening, external genitalia, vagina, external ear canal, and external eye.

Which body sites are normally free of microorganisms?

Internal tissues and organs and body fluids such as blood, urine in the kidneys, and cerebrospinal fluid.

How are newborns first exposed to normal flora?

Through exposure during passage through the birth canal.

Which microorganisms may colonize a newborn within 8–12 hours after birth?

Streptococci, staphylococci, and lactobacilli.

Which microorganisms are commonly found on the skin?

Staphylococcus, Micrococcus, Mycobacterium, and Malassezia yeast.

Which microorganisms are commonly found in the oral cavity and upper respiratory tract?

Streptococcus, Staphylococcus, Lactobacillus, Treponema, and Candida.

Which microorganisms are commonly found in the large intestine and rectum?

Bacteroides, fecal streptococci, Lactobacillus, Escherichia coli, and Candida.

Which microorganisms are commonly found in the genital tract?

Lactobacillus, Streptococcus, Mycobacterium, and Candida.

Which microorganisms are commonly found in the urinary tract?

Staphylococcus, Streptococcus, and Escherichia coli.

What are two beneficial effects of normal flora?

Protection against other microbes and nutritional benefits.

When can normal flora cause an infection?

When the host's health or defenses are compromised, allowing normally harmless microbes to cause disease.

What is the transient population of skin microbes?

Microbes that cling to the skin through routine contact but ordinarily do not grow there; their presence is influenced by hygiene.

What is the resident population of skin microbes?

Microbes that live and multiply in deeper epidermal layers, glands, and hair follicles; examples include Staphylococcus, Corynebacterium, and Propionibacterium.

What can influence the types and numbers of microbes on the skin?

Routine contact and hygiene can affect transient microbes, while resident microbes are less affected by hygiene.

Where are microbes found in the mouth?

On cheek epithelium, the tongue, the floor of the mouth, and tooth enamel.

Which Streptococcus species is mentioned as part of the oral flora?

Streptococcus salivarius.

What does the PowerPoint state about mouthwash and oral microbes?

It states that mouthwash is ineffective.

Why can human bites be dangerous?

They can introduce microbes from the mouth into tissues.

Which microorganisms are predominant anaerobes in the colon?

Bacteroides and Clostridium.

What are coliforms?

Gram-negative, lactose-fermenting, facultatively anaerobic bacteria.

Which bacterium is an example of a coliform?

Escherichia coli.

Why can eating foods such as cabbage and beans cause intestinal gas and odor?

Intestinal bacteria act on carbohydrates in these foods, producing gas and odor.

What are the main events involved in an infection?

Microbial entry, attachment, invasion or crossing barriers, multiplication in target tissue, and release.

What determines the type and severity of an infection?

The disease-causing potential of the microbe and the condition of the host.

What is a true pathogen?

A microorganism capable of causing disease in a healthy person with normal immune defenses.

What is an opportunistic pathogen?

A microorganism that causes disease when host defenses are compromised or when it enters an unusual body site.

What factors can weaken host defenses?

Extreme youth, old age, prematurity, genetic or acquired immune defects, surgery, transplants, cancer, liver malfunction, diabetes, chemotherapy, immunosuppressive drugs, and physical or mental stress.

What is Biosafety Level 1?

Work involving microbes considered not to cause disease under the conditions described; the PowerPoint example is Micrococcus luteus.

What is Biosafety Level 2?

Work involving microbes of moderate risk; the PowerPoint example is Staphylococcus aureus.

What is Biosafety Level 3?

Work involving readily transmitted or virulent pathogens; the PowerPoint example is Mycobacterium tuberculosis.

What is Biosafety Level 4?

Work involving deadly pathogens; the PowerPoint examples are rabies and Ebola viruses.

What is pathogenicity?

The potential of a microorganism to cause infection or disease.

What is virulence?

The degree of pathogenicity, related to factors such as invasion and toxin production.

What is an exogenous source of infection?

A source outside the body, such as the environment, another person, or an animal.

What is an endogenous source of infection?

A source already present on or inside the body, such as normal flora or a latent infection.

What are portals of entry?

Routes through which pathogens enter the host.

How can pathogens enter through the skin?

Through nicks, cuts, or punctures.

Which skin-entry example is given in the PowerPoint?

Herpes simplex.

How can pathogens enter through the gastrointestinal tract?

Through contaminated food or drink; Salmonella is an example.

How can pathogens enter through the respiratory tract?

Through the oral or nasal cavities when infectious particles are inhaled.

Which infections or pathogens are associated with respiratory entry in the PowerPoint?

Streptococcal sore throat, common cold, and pneumonia agents such as Streptococcus pneumoniae, Klebsiella, and Mycobacterium tuberculosis.

How can pathogens enter through the urogenital tract?

Through sexual transmission; examples given include Chlamydia and HIV.

Why are pathogens often adapted to specific portals of entry?

Their ability to establish infection depends in part on entering through a suitable route.

How do bacteria attach to host cells?

They may use fimbriae, pili, and flagella.

How do viruses attach to host cells?

They use specialized receptors.

What are virulence factors?

Microbial features that help pathogens establish infection or cause damage, including exoenzymes, toxins, and antiphagocytic factors.

How do exoenzymes help pathogens cause disease?

They damage tissues or barriers and can help microbes invade host tissues.

What are examples of exoenzymes?

Keratinase and collagenase.

What is a toxin?

A poisonous chemical product made by a microorganism.

What is an exotoxin?

A toxin secreted by a living bacterial cell.

Which bacteria can produce exotoxins?

Gram-positive or Gram-negative bacteria.

What are characteristics of exotoxins described in the PowerPoint?

They can be highly toxic in minute amounts, may affect specific cell types, and stimulate the production of antitoxins.

What is an endotoxin?

A toxin associated with Gram-negative bacteria that is released when bacterial cells are damaged or lysed.

Which bacteria are associated with endotoxin?

All Gram-negative bacteria; Escherichia coli is an example in the PowerPoint.

How does endotoxin differ from exotoxin in the PowerPoint?

Endotoxin is released when cells are damaged or lysed and is associated with Gram-negative bacteria; exotoxin is secreted by living bacterial cells and can be highly toxic in minute amounts.

What effects of endotoxin are described in the PowerPoint?

Systemic fever and inflammation, generally associated with higher doses.

What does the PowerPoint state about endotoxin and antitoxins?

It states that endotoxin does not stimulate antitoxin production.

What is antiphagocytosis?

A way pathogens avoid being engulfed by phagocytic cells.

What is leukocidin?

A toxin mentioned in the PowerPoint that is toxic to white blood cells; Streptococcus and Staphylococcus are listed as examples of producers.

How can a capsule help Streptococcus pneumoniae cause disease?

Its capsule or slime layer helps prevent the bacterium from being engulfed.

How can pathogens damage host tissues?

They can cause tissue damage and necrosis.

How can viruses damage host cells?

They multiply inside cells and can cause the cells to lyse.

What is a localized infection?

An infection that remains in one tissue or area.

What is a systemic infection?

An infection that spreads to multiple sites through tissue fluids or the bloodstream.

What is a focal infection?

An infection in which an agent spreads from a localized infection to other tissues.

What is an acute infection?

An infection that develops rapidly, is often severe, and lasts a relatively short time.

What is a chronic infection?

An infection that persists over a long period.

What is a primary infection?

The initial infection.

What is a secondary infection?

Another infection caused by a different microorganism after a primary infection.

What is the incubation period?

The period between a pathogen's entry into the host and the appearance of the first symptoms.

What happens during the incubation period according to the PowerPoint?

The pathogen multiplies at the portal of entry before the first symptoms appear.

What is the prodromal stage of infection?

The stage when vague or general symptoms appear; the PowerPoint describes it as often lasting 1–2 days.

What is the invasion stage of infection?

The stage when the pathogen multiplies extensively in target tissues and specific symptoms may appear, such as fever, cough, rash, diarrhea, or pain.

What is the convalescent stage of infection?

The stage when symptoms decline and the host recovers.

What does the PowerPoint mean by the terminal stage?

An infection that results in death.

What is a sign of disease?

Objective evidence that can be observed or measured.

What is a symptom of disease?

A subjective experience reported by the patient.

What is a syndrome?

A complex of signs and symptoms associated with a condition.

What is an example of a sign of infection involving cerebrospinal fluid?

Bacteria detected in cerebrospinal fluid.

What is an example of a symptom of infection?

A headache.

What are examples of signs associated with inflammation?

Edema and swollen lymph nodes.

What are examples of symptoms associated with inflammation?

Fever and pain, as listed in the PowerPoint.

What blood-cell changes can be signs of infection?

Leukocytosis or leukopenia.

What does asymptomatic or subclinical infection mean in the PowerPoint?

An infection with no noticeable symptoms; some signs may still be present.

What are portals of exit?

Routes through which pathogens leave an infected host by secretion, excretion, discharge, or sloughed tissue.

How can pathogens exit through the respiratory tract?

Through coughing or sneezing; the PowerPoint lists tuberculosis, influenza, chickenpox, and rabies in this context.

How can pathogens exit through skin lesions?

Through material released from lesions, such as those associated with warts.

Which portal of exit is listed for tuberculosis in the PowerPoint?

Urine.

How can pathogens exit through blood?

Through blood exposure involving ticks or needles; AIDS is listed in the PowerPoint.

How can pathogens exit through feces?

Through fecal material; worms are given as an example.

How can pathogens exit through the reproductive tract?

Through vaginal discharge or semen; AIDS is listed in the PowerPoint.

What is the relationship between portals of entry and portals of exit?

The portal of exit is often the same route as the portal of entry.