Ch. 23 Flashcards
Most microorganisms are ___.
Benign
Humans are colonized by ___ at birth.
Microorganisms
Microorganisms usually found associated with human ___ ___.
Body tissue
Pathogens -
Microbial parasites
Pathogenicity -
The ability of a parasite to inflict damage on the host (cause disease)
Virulence -
Measure of pathogenicity (attachment structures, enzymes, toxins)
Opportunistic pathogen -
Causes disease only in the absence of normal host resistance
Infection -
Situation in which a microorganism is established and growing in a host, whether or not the host is harmed
Disease -
Damage or injury to the host that impairs host function
___ provide a favorable environment for the growth of many microorganisms.
Animals
Infections frequently begin at sites in the animals ___ ___.
Mucous membranes
The ___ surface varies greatly in chemical composition and moisture content.
Skin
Skin
Three microenvironments:
- dry skin
- moist skin
- sebaceous skin
Dry skin:
Forearms and palms of hands
Moist skin:
Inside of nostrils, armpits, umbilicus
Sebaceous skin
Side of the nose, back of scalp, upper chest and back
Skin microflora examined by molecular ___ methods.
Ecology
Skin microflora examined by molecular ecology methods.
How many phyla detected?
19
Each microenvironment shows a unique ___.
Microbiota
The skin microflora
Composition is influenced by:
- environmental factors
- host factors
The ___ ___ is a complex, heterogeneous microbial habitat.
Oral cavity
Saliva contains ___ enzymes.
Antimicrobial
High concentrations of nutrients near surfaces in the mouth promote what?
Localized microbial growth
The ___ consists of a mineral matrix surrounding living tissue.
Tooth
Enamel -
Mineral matrix in teeth
Dentin and pulp -
Living tissue in teeth
How do bacteria colonize tooth surfaces?
Bacteria colonize tooth surfaces by first attaching to acidic glycoproteins there by saliva.
___ analysis of human microflora shows a complex microbial community.
Metagenomic
Human microflora
- most microorganisms are facultatively aerobic
- some are obligately anaerobic
- some are obligately aerobic
The human gastrointestinal (GI) tract consists of:
Stomach, small intestine, and large intestine
What is the GI tract responsible for?
Digestion of food, absorption of nutrients, and production of nutrients by the indigenous microbial flora
The GI tract contains how many microbial cells?
10^13-10^14
Microbial populations in different areas of the GI tract are influenced by…
Diet and the physical conditions in the area
The ___ of the stomach and the duodenum of the small intestine prevents many organisms from colonizing the GI tract.
Acidity
Functions and products of intestinal flora.
Compounds produced include:
- vitamins
- gas, organic acids, and odor
- enzymes
A restricted group of organisms colonizes the upper ___ ___.
Respiratory tract
Examples of organisms that colonize the upper respiratory tract:
Staphylococci, steptococci, diphtheroid, bacilli, and gram-negative cocci
Staphylococcus aureus and Streptococcus pneumoniae can be found in the __ of some healthy individuals.
Nasopharynx
The lower respiratory tract lacks microflora in ___individuals.
Healthy
Upper respiratory tract:
- sinuses
- nasopharynx
- pharynx
- oral cavity
- larynx
Lower respiratory tract:
- trachea
- bronchi
- lungs
The ___ is typically sterile in both males and females.
Bladder
Urogenital tract
Altered conditions (such as change in pH) can cause potential pathogens in the urethra (such as ___ ___ and ___ ___) to multiply and become pathogenic.
Escherichia coli and Proteus mirabillis
E. coli and P. mirabilis frequently cause what in women?
Urinary tract infection
The ___ of the adult female is weakly acidic and contains significant amounts of glycogen.
Vagina
___ ___, a resident organism in the vagina, ferments the glycogen, producing lactic acid.
Lactobacillus acidophilus
___ ___ maintains a local acidic environment.
Lactic acid
What are pregnant women tested for?
Group B Strep
Virulence can be estimated from experimental studies of the ___.
Lethal dose 50 (LD50)
Lethal dose 50
The amount of an agent that kills 50% of the animals in a test group
Highly virulent pathogens
Show little difference in the number of cells required to kill 100% of the population as compared to 50% of the population
Attenuation -
The decrease or loss of virulence
Toxicity -
Organism causes disease by means of a toxin that inhibits host cell function or kills host cells
Exotoxins:
Cytotoxin
Neurotoxin
Enterotoxin
___ can travel to sites within host not inhabited by pathogen.
Toxins
Invasiveness -
Ability of a pathogen to grow in host tissue at densities that inhibit host function
___ can cause damage without producing a toxin.
Invasiveness
Many pathogens use a combination of toxins, invasiveness, and other virulence factors to enhance ___.
Pathogenicity
Bacteria and viruses that initiate infection often adhere specifically to epithelial cells through what?
Interactions between molecules on the surfaces of the pathogen and the host cell
Bacterial adherence can be facilitated by:
- extracellular macromolecules that are not covalently attached to the bacterial cell surface (slime layer, capsule)
- fimbriae and pili
The ___ ___ of a pathogen is insufficient to cause host damage.
Initial inoculum
The pathogen must multiple and colonize the ___.
Tissue
What is most important in affecting pathogen growth?
Availability of nutrients
Pathogens may grow locally at the site of invasion or may…
Spread throughout the body
Bacteremia -
The presence of bacteria in the bloodstream
Septicemia -
Bloodborne systematic infection
Septicemia may lead to..
Massive inflammation, septic shock, and death
Infection requires..
Attachment to surface as well as growth
Attachment and growth have been well studied in the formation of ___ on tooth surfaces.
Biofilms
Acidic ___ from saliva form a thin film.
Glycoproteins
Streptococcus sobrinus and streptococcus mutans are common agents in __ __.
Tooth decay
Dental plaque -
Extensive growth of oral microorganisms, especially streptococci, results in a thick bacterial layer
As plaque continues to develop, ___ bacterial species begin to grow.
Anaerobic
Dental caries -
As dental plaque accumulates, the microorganisms produce high concentrations of acid, resulting in decalcification of the tooth enamel
Pathogens produce enzymes that:
- enhance virulence by breaking down or altering host tissue to provide access to nutrients
- protect the pathogen by interfering with normal host defense mechanisms
Example of enzyme that enhances virulence by breaking down or altering host tissue to provide access to nutrients?
Hyaluronidase
Example of enzyme that protects the pathogen by interfering with normal host defense mechanisms?
Coagulase
___ species encode a large number of virulence factors.
Salmonella
Salmonella also contains ___ plasmids.
Resistance (R plasmids)
Several genes that direct invasion are clustered together on the chromosome as ___ ___.
Pathogenicity islands
Three categories of exotoxins:
Cytotoxins
AB toxins
Superantigen toxins
Exotoxins -
Proteins released from the pathogen cell as it grows
Cytotoxins (cytolytic toxins) -
Work by degrading cytoplasmic membrane integrity, causing cell lysis and death
Toxins that lyse red blood cells are called ___.
Hemolysins
Staphylococcus alpha-toxin
Kills nucleated cells and lyses erythrocytes
AB toxins
- consist of two subunits, A and B
- work by binding to a host cell receptor (B subunit) and transferring damaging agent (A subunit) across the cell membrane
Examples of AB toxins
- diphtheria toxin
- tetanus toxin
- botulinum toxin
Clostridium tetani and clostridium botulinum produce AB exotoxins that affect ___ ___.
Nervous tissue
Botulinum toxin
Consists of several related AB toxins that are the most potent biological toxins known
Tetanus toxin
Also an AB protein neurotoxin
Enterotoxins
Exotoxins whose activity affects the small intestine
- generally cause massive secretion of fluid into the intestinal lumen, resulting in vomiting and diarrhea
Example of enterotoxin
Cholera toxin
Endotoxin
The lipopolysaccharide portion of the cell envelope of certain gram-negative bacteria, which is a toxin when solubilized
Endotoxins generally ___ toxic than exotoxins.
Less
Presence of endotoxin can be detected by the …
Limulus amoebocyte lysate (LAL) assay
Hosts have innate resistance to most pathogens:
- natural host resistance
- tissue specificity
- physical and chemical barriers