Normal Flora and Infection Pathogenisis

What is another name for indigenous microbial flora?

Normal or usual flora.

Approximately how many species are included in indigenous microbial flora?

Approximately species.

What are parasites?

Organisms that live at the expense of the host.

What are symbionts?

Organisms that benefit the host.

What are commensals?

Organisms that have a neutral effect on the host.

What is resident flora?

Flora that colonize an area for months or years.

What is transient flora?

Flora that are present at a body site temporarily.

Do different areas of the body contain the same microbial flora?

No. Different flora inhabit different areas in and on the body.

What factors determine where a microorganism colonizes in the body?

Nutritional status

How does the nutritional status of a body site influence microbial colonization?

It helps determine which microorganisms can colonize that site.

How can oxidation-reduction potential affect microbial colonization?

It influences which microorganisms can survive and colonize a particular site.

How can antibodies and antibacterial substances affect microbial colonization?

They can limit or prevent the growth of certain microorganisms.

How does pH influence microbial colonization?

Different microorganisms are able to colonize environments with different pH conditions.

How can established organisms interfere with newly arriving microorganisms?

Established organisms can interfere with the colonization of other microorganisms.

What are four factors that can cause microbial flora to change?

Age

How can antibiotics affect indigenous microbial flora?

They can alter the normal composition of the flora.

How can disease states affect microbial flora?

Disease can cause changes in the normal composition of microbial flora.

What can cause infections involving normal microbial flora?

An imbalance in the normal flora that allows one resident microorganism to predominate.

How can environmental organisms cause infection?

An environmental organism can enter the body and cause infection.

Who is particularly susceptible to opportunistic infections?

Immunosuppressed or immunocompromised individuals.

What may occur when the composition of indigenous flora is altered?

Pathogens or opportunistic organisms may colonize

What factors can contribute to changes in normal flora?

Age

What is the carrier state?

A condition in which a pathogenic organism establishes residence in a host without causing symptoms.

What is a carrier?

An asymptomatic host capable of transmitting an infection.

Can a carrier state be acute or chronic?

Yes.

Which organism is given as an example of a chronic carrier state?

Salmonella typhi.

Which organism is an example of an acute carrier state?

Neisseria meningitidis.

Which organism can have either an acute or chronic carrier state?

Group A Streptococcus pyogenes.

Which organism is given as an example of transient carriage?

Staphylococcus aureus.

Name two common aerobic organisms found in normal skin flora.

Staphylococcus spp. and Micrococcus spp.

What are diphtheroids?

They are listed as common aerobic organisms in normal skin flora.

Which yeast is listed among common normal skin flora?

Candida spp.

Name two anaerobic organisms commonly found on the skin.

Clostridium spp. and Cutibacterium (Propionibacterium) acnes.

Which Cutibacterium species is associated with normal skin flora?

Cutibacterium (Propionibacterium) acnes.

Name two less common aerobic organisms found on the skin.

Streptococcus spp. and Acinetobacter spp.

What percentage of skin bacteria may handwashing decrease?

Approximately 90%.

How quickly do skin bacterial numbers return to normal after handwashing?

Within a few hours.

What is a common aerobic organism in the mouth?

Staphylococcus epidermidis.

What group of streptococci is commonly found in the oral cavity?

Viridans streptococci.

Name three common Streptococcus species found in the mouth?

S. mitis

Which Streptococcus species associated with the mouth is listed in the lecture?

Streptococcus mutans.

Which genus is listed as a common aerobic member of normal oral flora?

Lactobacillus spp.

Name two common anaerobic organisms in the oral cavity.

Anaerobic streptococci and Veillonella spp.

Which Actinomyces species is listed as common oral flora?

Actinomyces israelii.

Name two anaerobic genera commonly found in the mouth.

Prevotella and Porphyromonas.

Name two spirochetes listed as normal flora of the mouth.

Treponema denticola and Treponema refringens.

Which yeast is listed as a less common organism in the mouth?

Candida albicans.

Which anaerobic organism is listed as a less common member of oral flora?

Fusobacterium nucleatum.

Name two common Staphylococcus species found in the nose and nasopharynx.

Staphylococcus aureus and Staphylococcus epidermidis.

Which Haemophilus species is commonly found in the nose and nasopharynx?

Haemophilus parainfluenzae.

Which organism listed as less common in the nose and nasopharynx can cause pneumonia?

Streptococcus pneumoniae.

Which Moraxella species is listed as less common in the nose and nasopharynx?

Moraxella catarrhalis.

Which Haemophilus species is listed as less common in the nose and nasopharynx?

Haemophilus influenzae.

Which Neisseria species is listed as less common in the nose and nasopharynx?

Neisseria meningitidis.

What type of streptococci are common aerobic flora of the oropharynx?

Alpha-hemolytic

Name two Staphylococcus species listed as common aerobic flora of the oropharynx.

Staphylococcus aureus and Staphylococcus epidermidis.

Which anaerobic genera are common in the oropharynx?

Prevotella

Which Fusobacterium species is listed among common anaerobic flora of the oropharynx?

Fusobacterium necrophorum.

Which organism is listed as a less common aerobic organism in the oropharynx?

Streptococcus pyogenes.

What are two additional less common organisms in the oropharynx?

Neisseria meningitidis and Haemophilus influenzae.

What are common organisms found in the outer ear?

Coagulase-negative Staphylococcus spp.

How can flora from the nasopharynx reach the middle ear?

Through the eustachian tube.

What is the expected microbial status of the eye?

The eye should be sterile.

Name three organisms that may contaminate the eye.

Coagulase-negative Staphylococcus spp.

What bacterial family is listed as common aerobic flora of the gastrointestinal tract?

Enterobacteriaceae.

Name two common aerobic organisms found in the gastrointestinal tract.

Staphylococcus aureus and Enterococcus spp.

Name three common anaerobic genera found in the gastrointestinal tract.

Bacteroides

Which anaerobic Streptococcus-related organisms are listed in gastrointestinal flora?

Peptostreptococcus

Which genus is a common aerobic member of genitourinary flora?

Lactobacillus spp.

Name two other common aerobic organisms found in the genitourinary tract.

Staphylococcus aureus and Enterococcus spp.

Name three anaerobic organisms commonly found in the genitourinary tract.

Bacteroides spp.

Which Group B streptococcus is listed as a less common organism of the genitourinary tract?

Streptococcus agalactiae.

Which yeast is listed as a less common organism in the genitourinary tract?

Candida albicans.

What is a pathogen?

A microorganism capable of causing disease in a susceptible host when conditions for infection are met.

What is a true pathogen?

An organism capable of causing disease in healthy

Name two examples of true pathogens provided in the lecture.

Yersinia pestis and Bacillus anthracis.

What is an opportunistic pathogen?

An organism that causes infection when host defenses are weakened.

Where can opportunistic pathogens originate?

Indigenous flora or environmental organisms.

What is an iatrogenic infection?

An infection resulting from a medical treatment or procedure.

What is virulence?

The relative ability of a microorganism to cause disease

How can virulence be measured according to the lecture?

By the infectious or infective dose.

What does a low infective dose generally indicate?

High virulence.

What organism is given as an example of a highly virulent organism requiring approximately organisms for infection?

Shigella spp.

What are virulence factors?

Organism characteristics or traits that contribute to pathogenicity and virulence.

Name three examples of virulence factors.

Capsules

What are the major microbial factors contributing to pathogenesis and virulence?

Resisting phagocytosis

What is a major role of phagocytes during bacterial infection?

Clearing bacterial infections.

How can a capsule help a microorganism resist phagocytosis?

It can inhibit engulfment.

What effect can some microorganisms have on phagosome-lysosome fusion?

They can prevent phagosome-lysosome fusion.

What are leukocidins?

Factors that damage or kill leukocytes and can inhibit chemotaxis.

How does a capsule interfere with the immune response?

It masks cell surface structures and inhibits complement.

How does Protein A interfere with phagocytosis?

It binds the Fc portion of IgG

What is the effect of Panton-Valentine leukocidin on phagocytes?

It causes discharge into the cytoplasm

What bacterial structures promote adhesion?

Fimbriae (pili) and surface polysaccharides.

Why is adhesion important for a pathogen?

It enables attachment to host surface structures and increases the ability to colonize.

What is the function of IgA proteases as a virulence mechanism?

They help microorganisms circumvent host protective mechanisms involving secretory antibody.

What is antigenic variation?

A mechanism used by microorganisms to evade host defenses.

What does lactoferrin normally bind?

Free iron.

How can meningococci use lactoferrin?

They can use lactoferrin as a source of iron.

How can microorganisms survive within phagocytic cells?

They can prevent lysosomal fusion or escape from the phagosome.