Lecture 12: Medical Microbiology Flashcards
_______: The collection of all the microorganisms living in association with the human
body (microflora, microbiota)
human microbiome
T/F: microorganisms outnumber our human cells, and have wayyyy more genes
true!
outnumber us 10^14>10^13
20000<20000000
T/F: Colonization begins immediately after birth
true!
colonized through vaginal canal and breastfeeding
T/F: Every exposed area in/on the surfaces of the body are colonized with bacteria
true
skin and mucous membranes
T/F: Internal tissues should be free of microbes
true
what are some examples of internal tissues that should be free of microbes?
peritoneum, pericardium, pleura, blood, muscles, organs
what is the beneficial product that E. coli produces for us?
vitamin K in our colon
T/F: most bacteria in/on our body are harmless commensals (that can always turn bad) and many contribute to our health
true
T/F: Different areas of the skin vary in chemical composition and moisture
content
true
what are the three different microenvironments of the skin?
dry, moist, sebaceous
each have different microbial populations
_______ (skin microbiota):
Forearms, hands
* High numbers of Betaproteobacteria
* Known from 16 rRNA genes
* Rarely cultured and their role isn’t known
* Second highest is corynebacteria
* Most are harmless commensals
* Some may cause skin infections
* Ex) Corynebacterium diphtheriae
* Can cause non-healing ulcers of the skin: cutaneous diphtheria
dry skin
where do we have high numbers of Betaproteobacteria
also corynebacteria
dry skin
______ (skin microbiota):
Armpits, nostrils
* High numbers of corynebacteria and staphylococci
* Most are harmless commensals
* Ex) Staphylococcus epidermidis
* Most frequently isolated from skin
* Some are important pathogens
* Ex) Staphylococcus aureus
* Cause of boils, abscesses, wound infections
moist skin
where are there high numbers of corynebacteria and staphylococci
moist skin
armpits and nostrils
_____ (skin microbiota):
Sebaceous skin
* Oily skin around the nose, on the upper chest and back
* High numbers of propionibacteria
* Anaerobic Actinobacteria that produce propionic acid as an end-product of
fermentation
* Ex) Propionibacterium acnes
* Lives in hair follicles, and eats oil secreted by skin (sebum)
* Overgrowth can trigger inflammation
* Inflammatory acne
sebaceous skin
where do we have high numbers of propionibacteria (species: acne)
on our sebaceous skin (oily skin)
_____ are anaerobic actinobacteria that produce propionic acid as an end-product of fermentation
propionibacteria
_______ has antimicrobial enzymes:
* Lysozyme
* Lactoperoxidase
* Catalyzes production of superoxide radicals O2
-
* Oxidative damage to invading microbes
Saliva
_______: Catalyzes production of superoxide radicals O2-
* Oxidative damage to invading microbes
lactoperoxidase
The mouth is home to a complex microbial community including
_________
aerobes and anaerobes
______ mucosa:
* Aerobic
* Lives on mucous membranes like the tongue
Neisseria mucosa
_________:
* Aerotolerant anaerobe
* Produces a sticky dextran slime layer that lets it
stick to surfaces
* Forms biofilms in crevices around the teeth
* Produces lactic acid as an end-product of
fermentation
* Degrades tooth enamel
* Dental carries (cavities)
* Can lead to inflammation along the gum line:
* Gingivitis
Streptococcus mutans
Low pH and proteolytic enzymes make the ______ inhospitable to most
microbes
* Some bacteria do colonize the _______
stomach
_________: Cause of stomach ulcers
* Colonizes surface of the mucous membrane
* Membrane is protected from stomach acids by mucous
* Has a number of virulence factors:
* Urease neutralizes surrounding acidity
* Exotoxin: kills cells of the mucous membrane
* Endotoxin: triggers an inflammatory response
* Treated with antibiotics – tetracycline
helicobacter pylori
helicobacter pylori produce both exo- and endo-toxin… what do they both do?
exotoxin: kills cells of the mucous membrane
Endotoxin: triggers an inflammatory response
because the helicobacter pylori produces endotoxin it must be…
a gram negative
helicobacter pylori produces ____, which neutralizes the surrounding pH to 7, which degrades the bicarbonate/mucous wall of the stomach that protects membrane from stomach acid…. causing stomach ulcers (considered a carcinogen!)
urease
______: Area of rapidly changing pH
* As pH becomes slightly alkaline the quantity and variety of bacteria found
in the gI tract substantially increases
small intestine
T/F: As pH becomes slightly alkaline the quantity and variety of bacteria found
in the gI tract substantially increases
true! more types can survive in higher pH
_______:
* Genus of Gram positive lactic acid bacteria
* Opportunistic pathogen
* Frequent cause of nosocomial infections
* Example: blood borne infection
* Develop antibiotic resistance readily
* Vancomycin resistant ____
* Spread resistance genes on to other Gram positive bacteria
* Horizontal gene transfer
Enterococcus
what does horizontal gene transfer mean?
genes transfer buddy-buddy, instead of passing down through daughter cells
_______: pH is neutral
* Environment is anoxic
* Enormous number of microbes ~ 10^11 cells/g of feces
* Mostly anaerobes and facultative aerobes
large intestine
why are most of the bacteria in the large intestine anaerobes/facultative aerobes?
because oxygen is super lucrative! only a little bit even makes it through, so then its used super fast!!
______: Most cultured bacterium from feces
* Indicator of fecal contamination
* Most strains are non-pathogenic
* May stimulate the immune system
* Produce vitamin K
E. coli
T/F: 16S rRNA gene sequences reveal that E. coli
probably makes up < 1% of bacteria in the large
intestine
true
Largest group of bacteria in large intestine are strict anaerobes
from the genera _______
Bacteroides and Clostridium
explain how high numbers of methanogens in the gut have led to obesity (mouse studies)
Studies compared normal mice with germ
free mice:
* Germ free mice had 40% less body fat
Inoculated germ free mice with microbes
from healthy mouse intestines
* Inoculated mice quickly gained weight
Compared the microbiomes of normal weight
mice to genetically obese mice
* Genetically obese mice had fewer
Bacteroidetes, more Firmicutes and way
more methanogens
* Suggested that methanogens use up H2
which promotes bacterial fermentation
* Bacterial fermentation makes
nutrients available to the host
which bacteria are more present in lean mice? less?
more: bacteroidetes
less: firmicutes, methanogens
which bacteria are more present in obese mice? less?
more: firmicutes, methanogens
less: bacteroidetes
how does the presence of methanogens affect obesity?
they use up H2 which promotes bacterial fermentation… which makes more nutrients available for absorption… increases caloric intake
T/F: Changing the microbiota of the large intestine
can affect human health
true! if antibiotics are taken and normal flora is wiped out, opportunistic pathogens can take over
what happens with Antibiotic associated colitis?
Clostridium difficile grows
* Inflammation of the colon results
Treatment:
* Further antibiotics
* Probiotics
* “Transpoosition”
______: Home to a variety of bacteria including Staphylococci,
Streptococci and Corynebacteria
* Some people harbor pathogens among their normal
microflora
* Carriers
* Ex. Staphylococcus aureus
upper respiratory tract
________
* No resident microflora
* Mucous, lysozyme, ciliated cells, Secretory IgA,
alveolar macrophages
Lower respiratory tract
what three types of bacteria do we have in our upper respiratory tract?
staphylococci
streptococci
corynebacteria
______: kidneys, bladder
* Normally free of microorganisms (should be mostly sterile)
Upper urinary tract
Some members of the normal microbiota can act as opportunistic pathogens when transferred to urinary tract… like?
E. coli
most common pathogen that causes UTIs
the ______ in the reproductive/urinary tract is home to some Gram neg. bacteria
urethra
why are men less likely to get UTI’s compared to women?
their anatomy! much harder for bacteria to survive when urine is constantly flushing them out
plus urinary tract is so much further from rectum
______ in the vagina
produces lactic acid from glycogen
* Lowers pH and prevents growth of other
microbes (kills bacteria and STIs)
Lactobacillus acidophilus
T/F: If normal microbiota is disturbed secondary
to a course of antibiotic therapy
* Yeasts can overgrow and cause yeast
infections
true! because yeasts are eukaryotic they aren’t targeted by antibiotics, opportunistic growth!
______: growth of microbes that are not normally present in the host
(regardless of whether or not the host is harmed)
Infection
______: damage or injury that impairs regular host functions
Disease
______: a microbe that is able to cause disease
Pathogen
________: a microbe that causes disease only in the
absence of normal host resistance
Opportunistic pathogen
Streptococcus pneumoniae and E. coli are both ______
Opportunistic pathogens
________: the ability to cause disease
Pathogenicity
_______: the severity of the disease that is caused
Virulence
whats the LD50 value?
Number of pathogenic cells or dose of a toxin that will cause death in 50%
of inoculated animals
if the LD50 value is lower is it more or less virulent?
more virulent… less cells needed to cause 50% deaths
_______: the process by which a disease develops
Pathogenesis
steps that lead to an infection and tissue damage
_______: genetically encoded traits that contribute to a
pathogen’s ability to cause disease
Virulence factors
______: The ability of a pathogen to stick to a surface and begin colonization
adherence
what are two non-covalent adherence factors?
capsules and slime layers
_______ uses slime layer to stick to teeth and form a biofilm
Streptococcus mutans
______ uses capsule to stick to cells in the lungs
Streptococcus pneumoniae
how do capsules protect cells from phagocytes?
phagocyte can’t recognize bacteria in capsule, can’t destroy it
what is the other adherence factor?
adhesins
_____: specific surface molecules that allow
selective adherence to particular cell types
Adhesins
Strains of enterotoxigenic E.coli produce
_____ allowing specific adherence to
enterocytes in the intestine (adhesin)
fimbriae
Neisseria gonorrhoeae produces _____
that allow it to attach to mucosal epithelial
cells (adhesin)
fimbriae
how does neisseria gonorrhoeae bring itself closer to enterocyte membrane?
retracts its fimbriae, then opas proteins can specifically attach to certain receptors on the host cell
T/F: Some pathogens can colonize and grow on the surface of tissues, others need to invade tissue
true
______: the ability of a pathogen to enter into host cells or spread
through tissues
Invasiveness
what are some virulence factors that promote invasiveness?
siderophores
exoenzymes
invasins
what are siderophores?
iron binding molecules
* Host proteins transferrin and lactoferrin sequester iron, making it
unavailable for microorganisms
* Limit the growth of invaders
* Siderophores rip iron out of tissues to be used by bacteria (competes with us for growth!)
why is bacteria that are invasive so bad?
they’re no longer localized!! can’t target them as efficiently
what are exoenzymes?
proteins that are excreted by bacteria to degrade host
tissues
what are the five types of exoenzymes?
hyaluronidase
collagenase
proteases, nucleases, lipases
fibrinolysin
coagulase
_______: hydrolyzes hyaluronic acid (a connective tissue component
that holds animal cells together)
* Allows pathogen to spread between cells
Hyaluronidase
_______: degrades collagen (extremely abundant connective tissue in
animals)
* Allows pathogen to spread through tissues
Collagenase
_______:
* Degrade host macromolecules
Proteases, nucleases and lipases
______: dissolves fibrin clots
Fibrinolysin
______: induces fibrin clots
Coagulase
why does Streptococcus pyogenes makes streptokinase (a fibrinolysin)?
to escape clots that try to trap them
Staphylococcus aureus produces coagulase to protect it from phagocytes, why?
if it can induce clots to surround it, it can hide from immune system!
_____: proteins that allow bacteria to invade and enter directly into
host cells
Invasins
_______:
non-lactic acid, non-spore forming
psychrotolerant member of the Firmicutes
* Can be found in unpasteurized dairy products, improperly packaged
processed meats
* Produces invasins that promote phagocytosis by macrophages
* Hijacks the cytoskeleton to escape the phagolysosome
* Spreads from cell to cell avoiding the
humoral immune response
Listeria monocytogenes
_____: bacteria in the blood
Bacteremia
can be carried to different organs and tissues
______: bacteria multiplying in the blood
Septicemia
Can lead to Sepsis
* Widespread systemic inflammation
* Septic shock
* Can be caused by Gram negative bacteria (Ex: Gram negative
sepsis)
* Also by Gram positives: Staphylococci and Enterococci
why do we never want bacteria in our blood?
blood has perfect conditions for growth… and can take the bacteria EVERYWHERE in our body!
why can septic shock be caused by any gram negative bacteria?
because they produce the endotoxin
which gram positives cause septic shock?
staphylococci and enterococci
______: Proteins released by growing bacteria
* Inhibit host cell function or kill host cells
* Usually heat labile
* Can be extremely toxic
exotoxins
Bacillus anthracis releases…
exotoxin
has several virulence factors:
* Capsule, exoenzymes and the anthrax toxin
* Interferes with the immune response and kills macrophages
what are the three categories of exotoxins?
Cytoxins, AB toxins, Superantigens
______, a type of exotoxin, Disrupt cytoplasmic membrane integrity
* Cell lysis and death
cytotoxins
what are the three types of cytotoxins?
hemolysins
Lecithinase or phospholipase
Leukocidins
_______:
* Lyse many cells (not just red blood cells)
* Ex. Streptococcus pyogenes
* Produces streptolysin: attacks sterols in the cell membrane
Hemolysins
__________:
* Dissolves membrane lipids
* Ex. Clostridium perfringens
* α-toxin (gas gangrene)
Lecithinase or phospholipase
_____: destroy white blood cells
* Ex) Staphylococcus aureus: staphylococcal α-toxin
* Toxin subunits insert into the membrane and oligomerizes to form a heptamer
* A membrane spanning pore
* Cell contents leak out and the cell dies
Leukocidins
what are the two subunits of AB toxins?
Two subunits: Active subunit and Binding subunit
__________ (Corynebacterium diphtheriae)
* Subunit B: specifically binds to a protein on animal cells
* Subunit A: moves across the membrane
* Interferes with protein synthesis
* Gene for diphtheria toxin is not encoded on the chromosome, but instead on
a virus
Diphtheria toxin
T/F: Gene for diphtheria toxin is not encoded on the chromosome, but instead on
a virus
true!
gene is delivered to bacteria, but cannot be passed down to daughter cells
what are three other examples of AB toxins?
tetanus, botulism and cholera toxins
_______: Activate T cells to elicit an extreme immune response
superantigens
_______: Bind to MHC molecules and TCRs outside the antigen binding sites
* Bridge the gap and mimics proper antigen presentation
* Huge number of T cells can be activated
* T cells produce cytokines
* Extreme immune response
* Extreme fever, systemic inflammation, shock, death
superantigens
Staphylococcus aureus cause _____, when super antigen exotoxin builds up over time
toxic shock
syndrome toxin (TSST)
______: Lipopolysaccharide from the Gram negative outer membrane
* The toxic part is: Lipid A
* Only released when cells die
* Generally considered less toxic than exotoxins
* A lot is needed to cause symptoms
endotoxin
which kind of bacteria has endotoxin?
gram negative
______- colonizes the intestine and multiplies producing a huge number of
bacteria
* As these bacteria die they release endotoxin
* Causes fever, diarrhea, generalized inflammation
Salmonella
when is Lipid A released from gram negative bacteria?
when they die- and lipopolysaccharides breakdown
Gram negative sepsis is an example of _____ release
endotoxin
Gram negative bacteria multiply in the blood
* Killed by immune system, releasing endotoxin
* Massive inflammation leads to septic shock and death
