Exam 3 Flashcards
Selective Media
Contains 1 or more specific compounds that can PREVENT the GROWTH of certain bacterial species.
How do you achieve selectivity in media?
Media contains INHIBITORS
What might inhibitors have an effect on?
DNA synthesis, gene expression, enzymatic activity, or even membrane permeability
Differential Media
contains one ore more specific compounds that can DISTINGUISH between DIFFERENT bacterial species
What are the two important components in differential media?
Substrates and Indicators
What are substrates in differential media?
can be a carbohydrate that only certain bacterial species can utilize in a specific chemical reaction or a set of chemical reactions
What are indicators in differential media?
They provide a visible means of showing that a specific chemical reaction has occurred (e.g., a color change in a media)
What is presumptive identification?
Some biochemical information on the organisms present in a culture provided by selective and differential media
Can media be both selective and differential?
YES
Describe coliforms
bacteria that reside in the guts of birds and all mammals (including humans);
most well known coliform in E. coli;
indicator of fecal contamination
General characteristics of coliforms
Gram negative rods;
non-spore forming bacteria;
aerobes or facultative anaerobes;
can FERMENT LACTOSE
What is MacConkey agar?
selective and differential media used to identify the presence of coliforms
Enzyme secreted by certain bacterial species and breaks covalent bonds between phosphate and ribose sugar molecules
DNase
Breaking of covalent bonds in the DNA backbone causes _____ of DNA into short nucleotide chains
Depolymerization
How many types of DNA enzymes
2
DNase agar 2 important components
1- DNA
2- Methyl Green Dye
What is the color of the DNA media originally?
Blue/green
DNase NEGATIVE result
- blue/green after incubation
- no zone of clearing around organism
What does methyl green dye bind to?
Polymerized DNA
DNase POSITIVE result
- bacteria shows growth
- zone of clearing
to get a positive DNase result what happens?
- DNA cleaves to remove bound dye
- DNase is secreted and cleaved the DNA around the bacteria
Alpha-hemolytic Streptococcus species
- S. Pheumoniae (pneumonia)
- S. Mutans (dental plaque)
BETA- hemolytic streptococcus species are classified into how many groups?
7 (based off the different types of carbs/sugars on their surface)
The most medically important BETA-hemolytic strep species belong to what two groups?
Group A and B
Group B Streptococcus (GBS)
- women can carry in genital tract
- can pass it on to newborns
- newborns that get it can have pneumonia or meningitis
- 20% new borns die
- 30-50% suffer from brain damage
Group A Streptococcus (GAS)
- in throat or on skin
- “strep throat”
- Can cause necrotizing fasciitis (flesh-eating disease)
PYR TEST
SLIDE 6 QUESTION??
Medically important species in the Enterococcus genus is
Enterococcus faecalis
Enterococcus Faecalis can cause
- opportunistic pathogen
- causes nosocomial infections
- UTI’s via catheters
- bacterial endocarditis via heart valves & pacemakers
- meningitis via intravenous lines
What is the drug of choice for enterococcus infections
Cancomycin-Resistant Enterococci (VRE)
Why doesn’t VRE work for E. Faecalis
it has a naturally antibiotic resistance
98% of Group A streptococcus species and 96% of enterococcus species produce what enzyme?
L-pyrrolidonyl arylamidase (PYRase)
What is PYRase
Peptidase involved in the degradation of proteins
what is the PYR reagent
p-dimethylaminocinnamaldehyde
What color show a positive PYR test
Red
PYRase negative is what color
no color
what bacteria is part of the human skin flora and is generally not considered pathogenic
S. epi
Opportunistic pathogen that can cause minor to major skin infections, pneumonia, and toxic shock
S. aureus
What 2 tests can differentiate S. aureus and S. epi
1- mannitol fermentation
2- presence of coagulase
Coagulase is only present in..
S. aureus
What is coagulase?
protein which binds to prothrombin
What is prothrombin involved in
blood coagulation and generation of fibrin clots
Prothrombin is what type of enzyme
Inactive
what is the active version of prothrombin
thrombin
Coagulase + prothrombin =
Staphylothrombin
what does staphylothrombin do?
catalyzes fibrinogen cleavage
What 2 forms can coagulase be present in, in S. aureus?
1- Bound coagulase
2- free Coagulase
characteristics of bound coagulase
- attached to cell wall
- binds to/activates prothrombin and fibrogen in plasma
characteristics for free coagulase
- secreted by bacteria into environment
- binds to/activates prothrombin in plasma
What are the two types of coagulase tests?
1- slide
2- tube
What do both coagulase test require?
Plasma
What does the coagulase slide test detect?
ONLY bound coagulase
What will bacteria associated with fibrin do in the coagulase slide test?
Clump together
What does the coagulase tube test detect?
Bound and free coagulase
What happens if the bacteria is coagulase NEGATIVE
No clot is formed and plasma is LIQUID
What happens if the bacteria is coagulase POSITIVE
CLOT is formed and plasma Is THICK
Transfer of genetic material viz bacteriophage
Transduction
Acquisition of DNA via direct contact between cells “bacterial sex”
Conjugation
Uptake of foreign DNA by bacteria
Transformation
A bacterium that can take up plasmid DNA is referred to as
Competent
How can bacterium be made competent?
by exposing the organisms to specific chemical solutions and specific environmental conditions
What is the most common type of foreign DNA?
Plasmid DNA
Characteristics of plasmids
- Small and circular
- distinct, independent, self-replicating
- carry genes that aren’t essential for growth but are beneficial to organism
In the lab bacterial Transformation what is the foreign DNA
pGLO
Ori
portion of plasmid that carries that info necessary for DNA REP within the bacterium
bla
encodes for the beta-lactamase enzyme
bacteria that produce the B-lactamase enzyme are ____ and grow in the presence of antibiotics
resistant
Under UV light what color does GFP glow?
Green
araC encodes what?
DNA binding transcriptional regulatory protein
a cluster of functionally related genes all under the control of a single promoter
Operon
the region of DNA where transcription initiation begins
Promoter
Is there a need for arabinose utilization genes to be expressed when arabinose is not present? pGLO system
NO
What happens when arabinose is taken in by the bacterium, binds to the AraC protein? pGLO system
Changes shape
with pGLO if arabinose is present
- arabinose binds to AraC
- AraC shape change
- RNA polymerase can bind to arabinose promoter
- transcription gfp gene—> GFP protein
what is step 1 of the pGLO system
preparation of competent bacterial cells
What do you have to do to make bacteria competent in the pGLO system
chill the cells in presence of CALCIUM
Why do the cells have to be chilled by calcium in the pGLO system
because the cell membrane become more permeable and more efficient in binding plasmid DNA
how long do you incubate the micro tubes in the ice tray for the pGLO system
10 mins
what does the incubation do in the pGLO system
allows the plasmid DNA to bind to the surface of the competent cells
What is step 3 in the pGLO system
Heat shock
where do you place the tubes after the ice bath in the pGLO system
42 degree bath for 1 minute then ice bath for 2 mins then room temp
What is referred to as heat shock in the pGLO system
moving tubes quickly from ice to the bath
what does heat shock do in the pGLO system
permits the plasmid DNA to be taken up by the bacteria
After the heat shock in the pGLO system what does the bacteria now contain
pGLO which carries b-lactamase gene
What does the addition of a rich broth and incubation at room temp allow in the pGLO system
allows the permeability of the bacterial cell membrane to recover and return to normal state
What would you see on a LB plate in pGLO system
bacterial colonies and no pGLO
What would you see on a LB/ampicillin plate without pGLO
no colonies and no pGLOW
What would you see on a LB/ampicillin plate with pGLO
colonies
does the LB/ampicillin plate with pGLO have b-lactamase
yes
what would you see on LB/ampicillin/arabinose plate with pGLO
colonies will be fluorescent green under UV
Components of MacConkey Agar
Bile salts (selective), Crystal violet dye (selective), Neutral red dye (colorless >ph6.8, Red <pH6.8) (differential), Lactose (differential)
What does the bile salts and neutral red dye in MacConkey agar do?
They are selective; they inhibit the growth of gram positive bacteria (only gram negative bacteria will grow on this agar)
Describe the differential characteristics of macConkey agar
Not all gram negative bacteria can ferment lactose, BUT if they do, acidic products are made and pH will drop below 6.8, and the neutral red dye will cause media to turn REDDISH/PINK.
If cannot ferment lactose, then there will be no acidic products, no drop in ph, and no color change
Possible results observed on macConkey agar:
growth and reddish/pink color = gram negative bacteria that can ferment lactose therefore PRESUMED COLIFORM
growth but opaque/colorless (no fermentation) therefore NOT A COLIFORM
What is Eosin Methylene Blue agar (EMB)?
Selective and differential agar used to identify the presence of coliforms (gram negative lactose fermentors)
What are the components of EMB agar?
Eosin Y dye (selective and differential), Methylene Blue Dye (selective and differentia), Sucrose (differential), Lactose (differential)
What do Eosin Y dye and Methylene blue dye in EMB agar do?
They inhibit the growth of gram positive bacteria
Why is EMB agar differential?
NOT all gram negative bacteria can ferment sucrose or lactose to produce acidic compounds, SOME can ferment sucrose and/or lactose, NOT all gram negative bacteria produce the same amount of acidic compounds if they can ferment sucrose or lactose
Possible results observed on EMB agar:
Poor to no growth: gram positive bacteria
growth but colorless: gram negative but no fermentation of lactose OR sucrose so no change in ph and therefore no color change; NOT A COLIFORM
growth and pink/mucoidy: gram negative, slight change in pH; small amount of acidic products, SLOW fermentation of lactose; POSSIBLE COLIFORM
growth and green/purple to black with possible green metallic sheen: gram negative, large drop in ph, large amounts of acidic products made, vigorous fermentation of lactose and/or sucrose; PROBABLE COLIFORM
What is Hektoen Enteric Agar?
selective and differential agar used to isolate and distinguish between Salmonella and Shigella species
Characteristics of salmonella and shigella:
Salmonella and shigella CANNOT breakdown lactose, sucrose, or salicin sugars
Salmonella but NOT shigella CAN reduce sulfur
Components of Hektoen Enteric agar:
Bile salts (selective), sucrose (differntial), sucrose (differential), salicin (differntial), lactose (differential), sodium thiosulfate (sulfur source), ferric ammonium citrate (differential), bromothymol blue dye (differential), acid fuchsin dye (differential)
Possible results observed ok Hektoen enteric agar:
Poor to no growth: gram positive bacteria
growth and orange/yellow: gram negative but neither salmonella nor shigella because lots of fermentation happening
growth and bluish/green: gram negative and no fermentation happening, but breakdown of proteins making alkaline products raises pH: POSSIBLY SALMONELLA OR SHIGELLA
growth, bluish/green, with black precipitate: thiosulfate in media reduced to H2S which reacts with ferric ammonium citrate in media to make insoluble black metallic compound (sulfur reduction); POSSIBLY SALMONELLA
What is triple sugar iron agar?
single media used to determine an organism’s ability to ferment 3 different sugars as well as its ability to reduce sulfide
TSIA used to help differentiate between enteric bacteria such as salmonella, shigella, and e. coli
Sulfur reduction in enteric bacteria (TSIA)
most enteric bacteria are facultative anaerobes and can grow under anaerobic conditions
in the absence of O2, sulfur can be used as a terminal electron acceptor to produce energy
one specific pathway for sulfur reduction used THIOSULFATE as an electron acceptor
under acidic conditions, thiosulfate is reduced by the enzyme thiosulfate reductase to produce sulfite and hydrogen sulfide (h2s) which is expelled from the bacterium
Hydrogen sulfide and metal ions (TSIA):
H2S is a reducing agent that can react with metal ions to form metal sulfides, one reaction that occurs in the presence of H2S is the conversion of ferrous sulfate to ferrous sulfide
ferrous sulfide in an insoluble BLACK metallic compound
Sulfur reduction equation
Thiosulfate—– (thiosulfate reductase, acidic conditions)——>sulfite and H2S
H2S——–> ferrous sulfide (black precip)
components of triple sugar iron agar:
low [glucose]=0.1% high [lactose]=1% high [sucrose]=1% sodium thiosulfate (sulfur source) ferrous sulfate (H2S indicator) phenol red (pH indicator, which is red at neutral pH)
preparation of TSIA
always prepared as a slant, slant portion provides aerobic conditions, the butt portion provides anaerobic conditions
how TSIA is inoculated
an inoculating needle is used
butt is first stabbed with needle and then needle is pulled up the slant on the way out
possible results observed on TSIA
glucose only fermentation: acidic products formed, lower pH, media turns yellow w/in a few hours, glucose is low concentration so used up in about 12 hours, bacteria now begins to break down amino acids in the media, producing ammonia; this raises the pH and media turns red color (REVERSION), slant turns red because enough alkaline product made in slant to neutralize pH, butt remains yellow
alkaline slant (red)/acid butt (yellow)
TSIA results con’d:
glucose and lactose and/or sucrose fermentation: 2 or 3 of sugars can be fermented and acidic products made, lower the pH, media turns yellow, high concentrations of sucrose and lactose ensure that sugar supply will not be exhausted, NO reversion, media remains yellow
butt and slant = yellow
Tsia results cont’d
NO fermentation: bacteria cannot ferment sugars, but can break down amino acids, making ammonia, raising pH, cause media to turn REDDER in color than uninoculated control
alkaline slant/alkaline butt
tsia results con’td
GAS PRODUCTION: gas may be produced from fermentation, lifting of media from bottom of the tube and cracks or bubbles in butt portion of media indicates gas production
tsia results con’t
sulfur reduction: bacteria can ferment at least one of the sugars, makes acidic products, lowers pH, media turns yellow, under acidic conditions if thiosulfate reductase present will reduce thiosulfate in media to H2S, which will react with ferrous sulfate in media to make black precip (ferrous sulfide)
What is the multiple tube fermentation method?
Most Probable Number (MPN), used to determine if a water sample is contaminated with coliforms
What does the MPN procedure allow one to calculate?
TOTAL coliform counts in a water sample, the E. coli counts in a water sample
What is Laurel tryptose broth (ltb)?
media selective for coliforms and gives presumptive identification of presence of coliforms
components of LTB:
lauryl sulfate (inhibits growth of gram positive bacteria), lactose (coliforms can ferment lactose), durham tube (will indicate if gas has been produced from lactose fermentation)
During MPN, what does growth and gas present in LTB indicate?
probable coliforms
What is Brilliant green lactose broth (bglb)?
selective media that CONFIRMS presence of coliforms
components of bglb:
lactose (coliforms can ferment this sugar), durham tube (will indicate if gas has been produced from the fermentation of lactose), 2% bile (inhibits non-coliforms)
gas produced after incubation confirms presence of coliforms
What is E. coli broth?
media that is selective for E. coli when grown at 45 degree celsius
components of e. coli broth:
lactose (coliforms ferment lactose), durham tube (gas can be produced from lactose fermentation), bile salts ( inhibits non-coliforms).
gas present after incubation confirms presence of e. coli
formula used to calculate MPN
MPN/100mL = 100P divided by square root of (VnVa)
P= total # of positive results (BGLB or EC) Vn= combined volume of sample in LTB tubes that produced negative results in BGLB or EC Va= combined volume of sample in all LTB tubes
What is columbia CNA with 5% sheep blood agar used for?
used to specifically grow gram positive organisms such as staphylococci, streptococci, and enterococci
What is in columbia CNA blood agar?
digested casein, digested animal tissue, beef extract, yeast extract, corn starch, and sheep blood
What does the presence of all these compounds in CNA do?
makes the media EXTREMELY nutrient rich which should allow for the growth of a wide variety of organisms except gram negative organisms
What are colistin and nalidixic acid?
antibiotics that act as selective agents AGAINST gram negative organisms in Columbia CNA
Describe the function of colistin
contains many polycationic regions that can insert into the outer membrane of the gram negative bacterial cell wall
the insertion of colistin into this outer membrane disrupts the integrity of the outer membrane, which can lead to bacterial lysis
what does nalidixic acid do?
inhibits DNA gyrase/ topoisomerase (which allow supercoils DNA to be relaxed and reformed and is necessary for DNA replication)
therefore nalidixic acid inhibits DNA synthesis
what does the sheep blood in columbia CNA blood agar do?
makes the media differential: different bacteria can show different RBC hemolysis patterns when grown on agar with sheep’s blood
what are the three different hemolysis patterns and what do they indicate?
alpha: partial lysis of RBCs
gamma: no lysis of RBCs
beta: complete lysis of RBCs
What is mannitol salts agar used for?
used to help identify pathogenic staphylococcus species from non pathogenic staphylococcus species
components of mannitol salts agar (MSA):
7.5% salt (selective), mannitol (carb, differential), phenol red (pH indicator, RED at neutral pH, differential)
Is MSA selective, differential, or both?
Both
selective because high salt concentration only allows growth of staphylococcus species,
differential because pathogenic species will ferment the mannitol making acid products lowering the pH and changing color to yellow, while non pathogenic species will not ferment the mannitol and there will be no color change
What is blood agar?
tryptic soy agar with 5% sheep blood
What is blood agar used for?
makes nutrient rich environment and useful when attempting to culture fastidious organisms (organisms requiring strict physiological conditions)
can also be used to differentiate bacteria based on an organism’s hemolytic characteristics
What are hemolysins?
secreted protein toxins that can lyse RBCs and destroy hemoglobin (gives blood its red color)
Describes 3 different hemolysis patterns:
Beta: complete RBC and hemoglobin destruction; zone of clearing present
alpha: partial destruction; produces green coloring around colonies; H2O2 secreted by bacteria diffuses through agar oxidizing hemoglobin to methemglobin which is green in color; OXIDIZED hemoglobin
gamma: zero destruction
What are compounds produced naturally by the metabolic processes of certain bacteria or fungi called?
antibiotics
Compounds can now be produced in a variety of ways (from live organisms or synthetically in a lab) so what term is more applicable?
antimicrobials
What are several mechanisms of antimicrobial agents?
disruption of the bacterial cell wall, inhibition of protein synthesis, inhibition of nucleic acid replication, disruption of folic acid metabolism, disruption of the bacterial cell membrane
Can a bacterium have different patterns of antimicrobial susceptibility?
yes
What are factors that can influence the antimicrobial susceptibility of a bacterium?
type of bacterial cell wall, differences in metabolic pathways and/or enzymes, the environment the bacterium resides in (i.e., aerobic vs anaerobic), the acquisition of drug resistance
What method is used to simultaneously establish the susceptibility of a bacterium to several antimicrobial drugs?
Kirby-Bauer method
describe the disks used during the kirby-bauer method
paper disks that have been impregnated with a specific antimicrobial drug at a specific concentration
What happens during incubation when the kirby-bauer method is being performed?
diffusion of the drug generates a concentration gradient of the antimicrobial drug around the disk
bacteria is beginning to grow
possible results occurring during kirby-bauer method
growth occurring regardless of concentration of the drug= resistance to the drug
grow occurring but sensitive or susceptible to drug; at high concentration of drug, the bacteria will be killed, as concentration decreases there will be a point where the bacteria can survive the concentration of the drug and will grow.
What is the minimal inhibitory concentration?
The periphery of the zone of clearing is the lowest drug concentration that can kill or inhibit bacterial growth
To determine whether an organisms is susceptible or resistance to an antimicrobial drug wha must be measured?
the diameter of the zone of clearing; zone diameter interpretive chart is then used to analyze the results
what must be applied to ensure consistency during the kirby-bauer test?
quality control
what is quality control?
rigorous monitoring of ALL components and reagents used in the test
Bacillus licheniformis
gram positive rod, commonly found in soil, can secrete anitibiotic Bacitracin
What does bacitracin do?
targets bacterial cell wall, specifically the incorporation of peptidoglycan in the wall; interferes with the transport of peptidoglycan components across the cell membrane; no peptidoglycan available to make up the cell wall for replicating bacteria; effective against gram positive and gram negative bacteria; effective topically for people but orally fairly toxic
Bactoprenol
lipid used to transport NAM and NAG sugars across cell membrane during the synthesis of peptidoglycan
how bacitracin effects bactoprenol
if it is present it blocks bactoprenol from transporting the NAM and NAG sugars across cell membrane thereby inhibiting further synthesis of peptidoglycan
bacitrancin resistant pathogenic bacteria include:
streptococcus pyrogenes (causes strep throat), stapyhlococcus species (includes aureus, which can cause skin infections like necrotizing fascitis)
bacitracin susceptibility test
bacterium inoculated onto a blood agar plate such that a bacterial lawn will be produced after incubation; paper disk impregnated with bacitracin placed onto plate and incubated overnight; bacitracin will diffuse out making a concentration graident decreasing as it moves away from the disk;
how can you presumptively differentiate btwn streptococcus pneumoniae and other alpha hemolytic streptococcus species?
ONLY streptococcus pneumoniae is sensitive to the antibiotic OPTOCHIN
what does optochin do?
inhibits the ATP synthase enzyme, which results in lack of ATP production and cell death
What is the target of all beta lactam antibiotics?
ALL of these guys target the bacterial cell wall, specifically peptidoglycan
structure of peptidoglycan
polysaccharide chain made up of NAM and NAG sugars linked together by glycosidic bonds and then cross-linked by peptide bridges to form a strong lattice structure
what allows formation of peptide bridges?
transpeptidase; catalyzes formation of the cross-linked peptide bonds
beta lactam mode of action
covalently bind to transpeptidase, which results in the inactivation of the enzyme; without peptide crosslinks cell wall loses its structural integrity
mechanisms by which bacteria can acquire drug resistance
drug inactivation main one
plasmids
carry antibiotic resistance genes that code for enzymes that can specifically inactivate beta lactam antibiotics “beta lactamases”
nitrocefin
chromogenic cephalosporin compound, contains beta lactam ring, test paper can be impregnated with this drug;
uncleaved beta lactam ring: yellow
cleaved ring: pink/red
What is a disadvantage to the Kirby-Bauer Method?
Doesn’t provide any information on a therapeutic dose
How do yo determine the result of the kirby-bauer method?
measure the zone of clearing
What is an advantage of the E-test?
Can give an approximate MIC
what is a disadvantage to the E-test?
can’t provide a definitive MIC
what does the E-strip contain?
different concentrations of the drug at various points
What is the MIC in the E-test?
area around the strip where bacterial growth begins
What is an advantage of the tube dilution test?
Can give a precise MIC and can be automated
What is the MIC in the tube dilution?
The tube with the lowest antimicrobial drug concentration that shows no growth
characteristics of gamma rays
- highly penetrable
- causes direct and complete breakage of DNA
UV light
- poor at penetrating substances
- cant penetrate through plastics
- bacteria must be directly exposed to be killed
Wavelength of bactericidal UV
wavelength 100-280 nm
How does UVC cause DNA damage?
thymine dimer formation
photoreactivation
- light repair
- a photoreactive enzyme
excision repair
dark repair
what does endonuclease do
breaks bonds on either side of the DNA strand backbone that contains the dimer
what does helicase do
removes the damaged DNA segment
What does DNA polymerase do
fills in the missing nucleotides
What does DNA ligase do
join the new segment to the old DNA strand
Infection control relies on the proper use of ________ and _______
disinfectant and antiseptic
Disinfectant = a chemical that can destroy most microorganisms (with the possible exception of spores) on _____________ like a bed rail
inanimate surface
ANTISEPTIC = a chemical that can destroy most microorganisms (with the exception of spores) on _____ _____ like your hands
living surfaces
A disinfectant that can kill a wide variety of microbes
Broad Spectrum
Two points that are CRITICAL to know before using a disinfectant:
1) What is the optimal concentration of the disinfectant to use to kill most microorganisms?
2) What is the optimal length of time that a disinfectant needs to be in contact with a microorganism before it is destroyed?
To serve as a hospital disinfectant a chemical must pass the American Official Analytical Chemist’s ___-___ ____
Use-Dilution Test
Use-Dilution Test examines how well a disinfectant works against a _____ ______ of a known microorganism dried onto a __-____ _____
High concentration, non-porous object
STEP 1 of Germicide:
Sterile __-_____ objects (glass beads) are placed into a broth of growing bacterial culture
Non-porous
STEP 2 of Germicide:
Non-porous objects moved to an empty sterile Petri plate to aie dry so that a____ ____ ___ over the object
bacterial film forms
STEP 3 of Germicide:
Non-porous object covered with the dried bacterial film is submerged into a ______ ______ of disinfectant for __ minutes
specific concentration, 10
Tubes after Germicide exeriment:
1) NO GROWTH means…
2) GROWTH means…
1) If NO growth in tube:
The concentration of disinfectant used was effective in killing the bacteria
2) If growth in tube:
The concentration of disinfectant used was NOT effective in killing the bacteria
Disinfectant Lab: the class will examine \_\_\_ different disinfectants all at the \_\_\_ \_\_\_ concentrations to determine the most effective concentration for each disinfectant in destroying E. coli and Pseudomonas aeruginosa (Gram negative organisms), and S. epidermidis and Bacillus cereus (Gram positive organisms)
3, same 3
a sudden and simultaneous outbreak or increase in the number of cases of a disease in a community
Epidemic
Common source epidemic = infects ____ _____ at _____
many people at once
Disease moves from one person to another
Propagated transmission
The first person with the disease (the one to be identify in this exercise
Index case
