Flashcards in Exam III Deck (360)
Describe a coliform
Gram negative rod
Ferment lactose with production of gas within 48 hrs at 37C
Generally associated with fecal material
Most common coliform is E.coli
The presence of coliforms are used to indicate what?
Whether a water sample has become contaminated with fecal material and therefor with potential bacterial pathogens
What method is used to determine if a water sample is contaminated with coliforms?
Most Probable Number (MPN) also known as the multiple tube fermentation method
The MPN procedure allows you to calculate what?
Total coliform counts in a water sample
The E.coli counts in a water sample
What is the first step of determining the MPN
Making a 1:10 serial dilution of the water
What is the second step of MPN
1 mL of dilution tubes is added to Lauryl Tryptose Broth (LTB)
What are the contents of LTB?
What is the purpose of Lauryl sulfate in the LTB?
Inhibits the growth of organisms other than coliforms
What is the function of lactose in LTB?
Coliforms can ferment this sugar
What is the purpose of the Durham tube in LTB?
Will indicate if gas has been produced from the fermentation of lactose
LTB is a media that is what for coliforms?
LTB gives a presumptive determination of what?
The presence of coliforms
What is the third step of MPN?
After 48 hours, broths are examined for
2. Presence of gas
The presence of growth is considered what for LTB tubes?
Positive for coliforms
Transfer how many loops of culture from every LTB tube that shows what into one of each what?
2; growth; one tube Brilliant Green Lactose Bile broth (BGLB) one tube of E.coli broth
At what temperature do you incubate the BGLB?
At what temperature do you incubate the E.coli broth (EC) at?
What are the contents of BGLB?
What is the function of Lactose in BGLB?
Coliforms can ferment this sugar
What is the function of a Durham tube in BGLB?
Will indicate if a gas has been produced from the fermentation of lactose
What is the function of the 2% bile for BGLB
BGLB is a selective media that does what?
Confirms the presence of coliforms
After 48 hours, GBLB broths are examined for the presence of what?
BGLB tube with gas are considered what?
The presence of gas in BGLB tubes is used to determine what?
The total coliform counts
What are the contents of EC broth?
EC broth is a media that is selective for what when grown at what temperature?
E.coli; 45 C
After 48 hours, EC broth is examined for the presence of what?
EC tubes containing gas are considered what?
Positive for E. coli
Positive EC broth results are used to determine what?
What is the MPN formula?
MPN/100 ml = 100P / sqrt(VnVa)
Where P is the total number of positive results either (BGLB or EC)
Vn is the combined volume of sample in LTB tubes that produced negative results in BGLB or EC
Va is the combined volume of sample in all LTB tubes
What contains one or more specific compounds that can prevent the growth of certain bacteria?
To achieve selectivity what does the media contain?
What do inhibitors adversely effect?
What contains one or more specific compounds that can distinguish between different bacterial species?
What are the two important components of differential media?
What does the substrate provide for differential media?
An energy source such as a carbohydrate that only certain bacterial species can utilize in a specific chemical reaction or set of chemical reactions
What does an indicator provide for differential media?
A visible means of showing that a specific chemical reaction has occurred (color change in media)
Selective and differential media provides what?
A simple way to screen out certain bacterial species
Some biochemical information on the organisms present in the culture (presumptive identification)
Can coliforms form endospores?
What kind of respiration do coliforms perform?
Aerobic or facultative anaerobic
What can coliforms ferment?
What kind of media is MacConkey Agar?
Selective and differential
What is MacConkey Agar used to identify?
The presence of coliforms
What are the important components in MacConkey Agar?
Bile salts (selective)
Crystal Violet Dye (selective)
Neutral Red Dye (colorless > pH 6.8; red < pH 6.8)(differential)
What role do the bile salts and crystal violet dye play in MacConkey Agar?
They inhibit the growth of Gram positive bacteria
(Only Gram negative bacteria will grow on MacConkey Agar)
How is MacConkey Agar differential?
Not all Gram negative bacteria can ferment lactose to produce acidic compounds
If acidic compounds are produced on a MacConkey agar what will happen?
The pH of the media will drop and the Neutral Red Dye (pH indicator) will cause the media to turn reddish/pink
If lactose cannot be fermented on the MacConkey agar what happens?
No acidic products are formed so there is no drop in pH which means no change in color happens
If the organism can grow on MacConkey agar and the media turns reddish/pink, what is the organism presumed to be?
If there is growth on the MacConkey agar but the media remains colorless what can be presumed about the organism?
That it is Gram negative
What type of agar is Eosin Methylene Blue (EMB) Agar?
Selective and differential
What is EMB agar used to identify?
The presence of coliforms
What are the important components in EMB agar?
Eosin Y Dye (selective and differential)
Methylene Blue Dye (selective and differential)
What do both Eosin Y and Methylene Blue dyes inhibit?
The growth of Gram positive bacteria
Why is EMB agar differential?
Not all Gram negative bacteria can ferment lactose to produce acidic compounds
Not all Gram negative bacteria produce the same amount of acidic compounds if they can ferment lactose
If there is poor to no growth on an EMB agar what does it mean?
The bacteria is Gram positive
What does it mean if there is colorless growth on an EMB agar?
Gram negative but can not ferment lactose (not a coliform)
What does it mean if the growth on EMB agar is pink and mucoidy
Small amount of acidic compounds were made by the slow fermentation of lactose (possible coliform)
What does it mean if the growth is dark purple to black with a green metallic sheen?
Large amounts of acidic compounds were made due to the vigorous fermentation of lactose (probable coliform)
What kind of agar is Hektoen Enteric Agar?
Selective and differential
What is Hektoen Enteric Agar used for?
To isolate and distinguish between Salmonella and Shigella species
Can Salmonella and Shigella break down lactose, sucrose, or salicin sugars?
Can Salmonella or Shigella reduce sulfur?
Shigella can but Salmonella cannot
What are the key components of Hektoen Enteric Agar?
Bile salts (selective)
Sodium thiosulfate (sulfur source)(differential)
Ferric ammonium citrate (differential)
Bromthymol blue dye (differential)
Acid fuchsin dye (differential)
Bile salts in the media inhibits what?
The growth of Gram positive bacteria
What does it mean if there is poor to no growth on Hektoen Enteric Agar?
Gram positive bacteria
What does it mean if the colonies are orange/yellow on Hektoen Enteric Agar?
Large amounts of acidic products made which means fermentation of the sugars happened and the bacteria is neither Salmonella or Shiegella
what does it mean if the growth is bluish/green on Hektoen Enteric Agar?
A rise in the pH indicating no fermentation but a breakdown of proteins producing alkaline products (possibly salmonella or shigella)
What does it mean if the growth is bluish green with black precipitate on Hektoen Enteric agar?
Rise in pH due to break down of proteins and thiosulfate is reduced to H2S which reacts with ferric ammonium citrate to produce an insoluble black metallic compound. (Sulfur reduction)
What is a single media that can be used to determine an organism’s ability to ferment three different sugars as well as the ability of an organism to reduce sulfur?
Triple Sugar Iron Agar (TSIA)
What is TSIA used for?
To differentiate between enteric bacteria such as Salmonella, Shigella, and E.coli
What are three important points to remember about the fermentation pathway?
Glucose is not the only carbohydrate that can be used to glycolysis
The end products of fermentation include acidic compounds
Gas can also be an end product
Most enteric bacteria use what kind of metabolism?
Facultative anaerobic respiration
In the absence of oxygen certain enteric species can use sulfur as what?
The terminal electron acceptor to produce energy
One specific biochemical pathway for sulfur reduction uses Thiosulfate as a what?
Under acidic conditions what is reduced by the enzyme thiosulfate reductase to produce sulfite and hydrogen sulfide (H2S) which is expelled from the bacterium
What can H2S be considered as which can react with metal ions to form metal sulfides?
A reducing agent
In the presence of H2S ferrous sulfate (FeSO4) is converted to what?
Ferrous sulfide (FeS)
What is a insolvable black metallic compound?
Thiosolfate is reduced to sulfite and H2S
H2S and Ferrous sulfate react to produce what?
What are the important ingredients in TSI Agar?
Low concentration of glucose .1%
High concentration of Lactose 1%
High concentration of Sucrose 1%
Sodium Thiosulfate (sulfur source)
Ferrous Sulfate (H2S indicator)
Phenol Red (pH indicator, which is red at neutral pH)
TSI agar is always prepared as a what?
The slant portion of the TSIA provides what kind of conditions?
The butt portion of the TSIA provides what kind of conditions?
If TSIA has a yellow bottom and a pink top what does it mean?
Glucose only fermentation
The glucose in TSIA is used up in how long?
~12 hours then bacteria break down amino acid in the media
If the butt is yellow and the slant is yellow in a TSIA what does it mean?
Glucose and lactose and/or sucrose fermentation
If TSIA is pink on top and bottom what does it mean?
Cracks and bubbles in TSIA indicates what?
If the bottom is yellow (acidic) and the top is pink either pink or yellow(alkaline) and there is the presence of the color black for a TSIA what does it mean?
Sulfur can be reduced under acidic conditions by thiosulfate reductase, therefore the bacteria can ferment at least one of the three sugars and can reduce sulfur
If fermentation by glucose only and the organism can reduce sulfur what color will the top be?
What kind of media is Columbia CNA with 5% Sheep Blood agar?
Selective and differential
What is CNA with 5% sheep blood used for?
To specifically grow Gram positive organisms
What is in Columbia CNA Blood Agar?
Digested animal tissue
The extremely nutrient rich content of Columbia CNA Blood agar allows for a wide variety of organisms to grow except what?
Gram negative organisms
What is in Columbia CNA Blood agar that selects against gram negative organisms?
Colistin and nalidixic acid which are antibiotics
CNA is short for Colistin Nalidixic Acid
Colistin contains many polycationic regions that can insert into what?
The outer membrane of the Gram negative bacterial cell wall
What does the insertion of colistin do?
Disrupts the integrity of the outer membrane which can lead to bacterial lysis
What does naldixic acid inhibit?
What is the function of DNA gyrase/topiosomerase?
Allows supercoiled DNA to be relaxed and reformed and is necessary for DNA replication
Nalidixic acid inhibits what in the cell?
Gram negative bacteria are more sensitive to what than Gram positive bacteria?
Different bacteria will show what when grown on agar that contains sheep’s blood?
Red blood cell hemolysis patterns
A large clearing on CNA blood agar indicates what?
Complete lysis of RBCs (red blood cells)
Partial lysis of RBCs is indicated how?
Greening of the media which is the partial lysis of RBCs
If there is no media color change or clearing on CNA blood agar what does it mean?
No lysis of RBCs
What is mannitol salt agar used for?
To identify pathogenic staphylococcus species from non pathogenic staphylococcus species
What are the three important components in MSA (mannitol salt agar)
7.5% salt (selective)
Mannitol (differential carbon source)
Phenol red (pH indicator red at neutral pH)(differential)
The high salt concentration of MSA only allows what to grow?
Only some Staphylococcus species can ferment mannitol making the media what?
If acidic products are formed in MSA the pH will drop and the media will turn what color?
Non pathogenic Staphylococcus cannot ferment what?
Mannitol (the media will remain red)
What is in regular Blood Agar?
TSA and 5% sheep blood
Many types of bacteria can produce secreted protein toxins called what?
What are able to hemolysis RBCs and destroy hemoglobin?
What are the three major types of hemolysis?
Which type of hemolysis is the complete destruction of RBCs and hemoglobin?
Which type of hemolysis is the partial destruction of RBCs and hemoglobin that produces a green coloring around a bacterial colony?
What produces the green color in alpha hemolysis?
The partial break down of hemoglobin to methemoglobin
Methemoglobin is what type of hemoglobin?
What type of hemolysis produces no destruction of RBCs?
What is DNA composed of?
Nitrogenous bases, deoxyribose sugar, and phosphates
What are linked by covalent bonds and together make up the sugar/phosphate backbone of the DNA molecule?
Ribose sugars and phosphates
What enzyme is segregated by certain bacterial species that breaks the covalent bonds between phosphate and ribose sugar molecules?
Is the presence of DNase considered a virulence factor?
The breaking of covalent bonds in the DNA backbone causes what?
One type of DNase breaks the bond between the 5’ carbon atom of the ribose sugar and the what?
A second type of DNase cleaves the bond between the phosphate and the what?
3’ carbon atom of the ribose sugar
What are the two important media components in DNase agar?
Methyl Green Dye
Because the dye binds to polymerized, uncleared DNA, the media is what color?
If there is no zone of clearing is DNase present?
If a bacteria has DNase present, what happens?
A zone of clearing is produced because the dye cannot bind to cleaved DNA
What is a medically important alpha hemolytic Streptococcus species?
Streptococcus mutants (causes dental plaque)
Beta hemolytic Streptococcus can be classified into how many groups based on the different types of carbohydrates/sugars on their surface?
Of these groups which is the most medically important beta hemolytic Streptococcus species?
Group A and Group B
Newborns with Group B Streptococcus can have what?
Pneumonia and/or meningitis
What percentage of newborns with a GBS infection die?
What percentage of newborns with GBS will suffer permanent brain damage?
Group A Streptococcus (GAS) can cause what common infection?
Occationally GAS can become invasive and cause what life threatening illness?
How can you quickly tell if the organism is a Group A Streptococcus rather than GBS or another type of non-pathogenic Streptococcus species?
What are Gram positive diplococci that generally grow/appear in short chains and show gamma hemolysis?
Enterococcus (Enterococcus faecalis)
What is a member of the normal human intestinal flora and generally considered to be an opportunistic pathogen which causes nosocomial infections (hospital required)
What can cause urinary tract infections via catheters, bacterial endocarditis via Hearst and pacemakers, and meningitis via intravenous lines?
Enterococcus faecalis has natural antibiotic what?
What are Enterococci that are resistant to vancomycin?
Vancomycin Resistant Enterococci (VRE)
What percentage of GAS and Enterococcus species produce the enzyme L-pyrrolindonyl arylamidase (PYRase)?
98% of Group A
What is a peptidase involved in the degradation of proteins?
Specifically what does PYRase do?
Removes the N-terminal pyroglutamic acid residues from polypeptides
If PYRase is present, the beta naphthylamine plus a PYR reagent will produce a Schiff base that produces what?
A red precipitate
What are substances that are produced by the natural metabolic processes of some bacteria or fungi that can inhibit or destroy other microorganisms?
What is a Gram positive rod that is commonly found in the soil that is capable of secreting the antibiotic Bacitracin?
Bacitracin in an antibiotic that is commonly found in what?
Over the counter topical first aid ointments
What does Bacitracin target?
The bacterial cell wall, specifically the incorporation of peptidoglycan in the cell wall
Bacitracin interferes with what?
The transport of peptidoglycan components across the cell membrane
Is Bacitracin effective against both Gram positive and Gram negative organisms?
Is the activity of Bacitracin bactericidal?
Yes (kills bacteria)
Which antibiotic is orally toxic to humans but very effective topically?
Normally which lipid is used to transport NAM and NAG sugars across the cell membrane during the synthesis of peptidoglycan?
Bacitracin blocks bactoprenol from transporting what?
NAM and NAG sugars
Since not all bacterial species are bacitracin reisistant what can be used for the presumptive identification of potential pathogens?
Bacitracin susceptibility test
The Bacitracin susceptibility test can differentiate between what?
Beta hemolytic Streptococcus species
Which Streptococcus species is resistant to Bacitracin and what does it cause?
Agalactiae; neonatal sepsis in newborns
Which Streptoccus species can cause strep throat and in susceptible to Bacitracin?
Bacitracin suspecptibility test can differentiate between Catalase (+/-) Gram (+/-) cocci.
What catalase positive Gram positive cocci is Bacitracin resistant and can cause minor skin infections to life threatening diseases?
What catalase positive Gram positive cocci is generally non pathogenic and part of our normal biome but are bacitracin susceptible?
Micro coccus species
What organism secrets Novobiocin?
What is a Gram positive filamentous rod that is commonly found in the solid that secretes Novobiocin?
What does Novobiocin inhibit?
Specifically what does Novobiocin do?
Binds to DNA gyrase, an enzyme that effects the degree of DNA supercoiling and is necessary for DNA replication
What is DNA gyrase?
A multi subunit enzyme that binds to and hydrolyzes ATP in order to promote DNA supercoiling
Novobiocin competes with what for the binding site on DNA gyrase and blocks what?
ATP; ATP hydrolysis reaction
Novobiocin susceptibility test can differentiate between what?
Coagulate negative Staphyloccous species
What is a Novobiocin resistant bacteria that is the second most likely cause of urinary tract infections?
What is a Novobiocin susceptible non pathogenic normal skin microbe?
What does optochin inhibit?
ATP synthase enzyme
Optochin is only used for what due to severe side effects (loss of vision)?
Differentiation of S. Pneumonia from other alpha hemolytic streptococcus
Most alpha hemolytic streptococcus are non pathogenic and optochin resistant however this streptococcus organism is a pathogen that is optochin susceptible and can cause a number of diseases including a life threatening pneumonia
To determine if an organism is resistant to an antibiotic, what must you do?
Measure the diameter of the zone of clearing and compare it to a zone diameter interpretative chart.
Who publishes the interpretative charts?
National Committee for Clinical Laboratory Standards
For bacitacin an organism is resistant if the zone of clearing is less than what?
For Novobiocin the bacteria is resistant if the diameter of clearing is less than what?
For optochin a bacteria is resistant if the zone of clearing is less than what?
S. Epidermidis is part of the normal human skin flora and is generally not considered what?
A. aureus is considered this, and can cause minor to major skin infections, pneumonia, toxic shock syndrome etc...
Name an organism that is associated with hospital acquired infections?
Methicillin-resistant S. Aureus
What two tests can be used to differentiate S. Aureus from S. Epidermidis?
Presence of coagulase
Coagulase is only present in which of the two staphylococcus?
What is a protein which binds to prothrombin?
What is involved in blood coagulation and the generation of fibrin clots?
Prothrombin is inactive and must be cleaved in order for it to be converted to what active enzyme?
Thrombin is the final portion of what?
The blood coagulation cascade
When coagulase binds with prothrombin II it produces what active enzyme?
Staphylothrombin can bind to and act on what?
Fibrinogen acting like thrombin to produce a cross-linked fibrin clot
In S. Aureus coagulase can be present in what two forms?
Bound coagulase is attached to what?
The bacterial cell wall
Bound coagulase binds to and activate prothrombin in what?
Bound coagulase can also bind to what in blood plasma?
Bound fibrinogen cleaved by coagulase activated prothrombin produces what?
What is secreted by the bacteria into the surrounding environment?
Free coagulase binds to and activates what in blood plasma?
Name the two types of coagulase test
Both types of coagulase tests require the use of what?
What is the yellow colored liquid portion of blood that the red blood cells are suspended in?
Plasma is composed of what?
90% water plus compounds such as clotting factors
Coagulase slide/clumping factor test only detects what?
Which coagulase test involves mixing bacteria with a small amount of rabbit plasma on a glass slide?
Bacteria associated with fibrin will do what on a slide?
The coagulase tube test detects what?
Both bound and fee coagulase
Which test mixes bacteria with rabbit plasma in a test tube?
In a tube test fibrin in the plasma will link together causing what to form?
What is the possible role of Coagulase as a virulence factor?
Allows the bacteria to evade the host immune response
Production of a fibrin clot around the bacteria may protect it from what?
Phagocytosis my macrophages
What term is more applicable today when referring to antibiotics?
List 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
Bacteria may not be adversely affected by what?
All the mechanisms used by antimicrobial agents
Bacteria have different patterns of what kind of susceptibility?
What factors influence the antimicrobial susceptibility of a bacterium?
Type of bacterial cell wall
Difference in metabolic pathways and/or enzymes
The environment the bacterium resides in (aerobic vs anaerobic)
The acquisition of drug resistance
What method allows for the simultaneous establishment of the susceptibility of a bacterium to several antimicrobial drugs?
Disk Diffusion (Kirby-Bauer) method
What is the term used to describe growth over the entire surface of a plate?
Immediately after the plate has been inoculated, paper disks that have been impregnated with what at a specific what are placed on the plate at a fair distance apart?
A specific antimicrobial drug; concentration
What is used in a clinical laboratory for consistency and to reduce the amount of time required for a Kirby-Bauer test?
At what temperature and time is a plate undergoing a Kirby-Bauer test subjected to for incubation?
37 C, 24 hours
During incubation, the antimicrobial drug on the paper disk does what?
Diffuses out of the disk and through the agar
Diffusion of the drug generates what?
A concentration gradient of the antimicrobial drug around the disk
Also during the incubation of a Kirby-Bauer plate, what begins to grow?
How many possible outcomes from the diffusion of antimicrobial drugs and the growth of bacteria are there?
What is it called if the bacterial lawn is around the disk
Resistance to the drug
If there is no growth around the disk we say that the bacteria is what?
Sensitive or susceptible to the antimicrobial drug
What is complete reisistance?
Growth directly around the disk
What is the area around the disk without bacteria growth called?
Zone of clearing or zone of inhibition
Moving away from the disk the antimicrobial drug concentration does what?
The periphery of the zone of inhibition is also called what?
The minimal inhibitory concentration
What do you measure in a Kirby-Bauer Test?
The diameter of the zone of clearing
After taking the diameter measurement what do you compare the diameter to?
Results on a zone diameter interpretive chart
Who develops the standards for accurate antimicrobial susceptibility tests and generates numerous charts for interpretation of these zones for many different pathogenic organisms and many different antimicrobial drugs?
The Clinical and Laboratories Standards Institute (CLSI)
What is the result if the Kirby-Bauer test is not done according to CLSI guidelines?
What is the rigorous monitoring of all components and reagents used in tests?
What are some components that are tightly monitored for quality?
The agar plates used
The concentration of bacteria used to inoculate the plates
Agar plates must be prepared at a specific what in the Kirby-Bauer test because if it fluctuates it can change the growth of the bacteria and/or the activity of the antimicrobial drug?
Agar plates used in the Kirby Bauer test must be what?
Of a specific thickness
what results if the agar plate is too thick for a Kirby Bauer test?
The diameter of the concentration gradient will be too small
A smaller zone of clearing
What results if the agar plate is too thin during a Kirby Bauer test?
The concentration gradient will be large laterally
The zone of clearing will be too big
Why must a specific concentration of bacteria be used to inoculate plates in a Kirby Bauer test?
The turbidity of the bacterial culture is compared to the turbidity of a specific McFarland standard
What are McFarland standards?
A set of reference samples of different turbidity that can be used to estimate the number of bacterial cells in a sample
As the standard number increases what increases?
The cell concentration
The turbidity of the bacterial culture used in a Kirby Bauer test is prepared so that it is equivalent to the turbidity of what McFarland standard?
If the bacterial concentration is higher than the approved McFarland standard what happens?
The drug is not as effective since it must act on a much greater number of bacteria which results in a higher concentration of drug required to kill the bacteria. The zone of clearing will be small which will produce an incorrect interpretation of results
When looking for the best antibacterial drug to use, what is desirable?
To find a drug that can kill the disease causing bacteria without killing the normal bacterial flora which can be beneficial
Besides finding a drug that does not kill beneficial bacteria what is another goal in drug choice?
Find the therapeutic dose that limits the toxicity and causes fewer side effects
What are three ways to determine susceptibility to antimicrobial drugs?
Tube dilution test
What are the advantages of the Kirby Bauer Test?
Quick and easy
Many different antimicrobial drugs can be tested simultaneously
What is the disadvantage of the Kirby Bauer test?
Does not provide any information on a therapeutic dose
What are a the advantages of the E-test (combination of disk diffusion and tube dilution)
Quick and easy
Different antimicrobial drugs can be tested simultaneously
Can give an approximate MIC
What is a disadvantage of the E-test
Cannot provide a definitive MIC
What are the advantages of the Tube dilution test?
Test can be automated
What are disadvantages of the tube dilution test?
Prior to automation it was complicated and time consuming
Prior to automation it could only test a single drug at a time
What broth was used in the laboratory during the Tube dilution test?
The first dilution tube that shows no growth during a tube dilution test is the what?
What ratio of dilutions is prepared for a MIC determination?
Each tube divides the concentration of the drug in the tube prior to it in by what?
How many results can an automated microbiology system report for MIC testing?
100 antimicrobial susceptibility plates/panels in a total of 18 hours
Who discovered penicillin?
Sir Alexander Fleming in 1928
All members of the penicillin group of drugs share the same what?
The R group is different for each penicillin group member but they all have what?
A beta lactam ring
Cephalosporins were discovered in what year?
The cephalosporin structure contains a beta lactam ring that as a different ring compound than what?
Penicillin group members
All beta lactam antibiotics target what?
The bacterial cell wall
Specifically what do beta lactam drugs affect within the cell wall?
What does peptidoglycan do for the cell?
Gives it strength which helps prevent the cell from lysis
What is the structure of petidoglycan?
A polysaccharide chain made up of two sugars NAG and NAM linked through glycosidic bonds and then cross-linked by peptide bridges
What enzyme allows for the formation of the peptide bridges?
Beta lactam drugs bind to what?
Covalently to transpeptidase
What does the binding of transpeptidase do?
Results in the inactivation of the enzyme
In 1943 what happened
Penicillin became widely available
By 1950 what percentage of S. Aureus were resistant to penicillin?
List mechanisms by which bacteria can acquire drug resistance
Natural selection/spontaneous mutations
Transfer of plasmids with resistance factors
Use of alternative metabolic pathways
Changes to drug binding sites
Activation of drug pump
Decreased bacterial cell permeability
What is a common target in beta lactam antibiotics?
The beta lactam ring for drug inactivation
Bacteria can acquire plasmids that carry what?
Antibiotic resistance genes
What do certain resistance genes encode for?
Enzymes that can specifically inactivate beta lactam antibiotics
What are enzymes that can inactive beta lactam called?
What does beta lactamase destroy?
The beta lactam ring which inactivated the antibiotic
What is nitrocefin?
A chromogenic cephalosporin that contains a beta lactam ring
Beta lactamase cleaves nitrocefin to form cephalosporanic acid resulting in a color change to what?
All electromagnetic energy travels how?
The shorter the wavelength the greater the what?
The energy it carries
Gamma rays have extremely short wavelengths as so are what?
Radio waves are longer and have considerably less what?
What includes high energy gamma and x rays?
What is the best example of nonionizing radiation?
What are highly penetrable with the exception of lead and cause the direct and complete breakage of DNA?
What are gamma rays used for?
Sterilize medical equipment and for food preservation
What is very poor at penetrating substances so bacteria must be directly exposed to be killed?
What three groups can UV be divided into?
UVA, UVB, and UVC
What is the average wavelength of UVA?
UVA includes the UV in what?
What is the average wavelength for UVB?
UVB can be used for what?
What is the average wavelength for UVC?
What is UVC used for
To kill bacteria (it is bactericidal)
How does UVC cause DNA damage?
By thymine dimer formation
What is a covalent bond that forms between 2 adjacent thymine bases?
Diners distort DNA helix making what difficult?
Replication and transcription
Formation of many thymine dimers results in what?
What are two mechanisms of thymine dimer repair?
Photoreactivation (light repair)
Excision repair (dark repair)
In photoreactivation what enzyme do bacteria possess?
The photo active enzyme DNA photolyase
DNA photolyase binds to the region of DNA that contains the dimer. Exposure to visible light activates the enzyme causing it do what?
Break the covalent bond between the thymine
What enzyme is used in excision repair?
Endonuclease, helicase, DNA polymerase, DNA ligase
What is the function of endonuclease?
Breaks bonds on either side of the DNA strand backbone that contains the dimer
What is the function of helicase?
Removes the damaged DNA segment
What is the function of DNA polymerase?
Fill in the missing nucleotides
What is the function of DNA ligase?
Joins the new segment to the old DNA strand
What is the sudden and simultaneous outbreak or increase in the number of cases of a disease in a community?
What are some examples of epidemics?
1950 polio epidemic
H1N1 flu epidemic
What are some means of transmittal of infectious disease?
Direct contact (handshakes)
Animal or insect bite
What infects many people at once?
Common source epidemic
What is an example of a common source epidemic?
Contaminated water after the severe flood in Pakistan
What is it called when a disease moves from one person to another?
The first person with the disease in propagated transmission is call the what?
In bacteria, in what three ways can gene acquisition or gene transfer occur?
What is the transfer of genetic material via bacteriophage?
What is the acquisition of DNA via direct contact between cells?
What is the uptake of foreign DNA by bacteria?
A bacterium that can take up plasmid DNA is referred to as what?
Bacteria can acquire competence naturally or what?
What are small circular DNA molecules that can be carried by bacteria?
Plasmids are distinct and independent for the bacterial chromosomal DNA and are what?
Plasmids carry what kind of genes?
That are not essential for the growth but that are beneficial to the microorganism.
What is the origin of replication (ori)
The portion of the plasmid that carries the information necessary for its DNA replication within the bacterium
What is the beta lactamase gene (bla)
The gene that encodes for the beta lactamase enzyme which can cleave beta lactam rings of members of the penicillin group
What is green fluorescent protein (GFP)?
The protein first identified in the jellyfish Aequorea Victoria and under UV light glows Green
What does araC do?
Encodes for DNA binding transcriptional regulatory protein
AraC is required for what?
Arabinose utilization in bacteria
AraC controls what?
The arabinose operon
What is a cluster of functionally related genes all under the control of a single promoter?
What is the region of DNA where transcription intimation begins?
AraC proteins bind to the DNA adjacent to the arabinose promoter doing what?
Preventing RNA polymerase to bind
If RNA polymerase cannot bind to the arabinose promoter what happens?
No transcription of the arabinose utilization gene
When arabinose is present, it binds to the AraC protein causing it to do what?
To make bacteria competent requires what?
Chilling the cells in the presence of calcium
Chilling the cells in the presence of calcium promotes what?
The binding of the plasmid DNA to the bacterial cell surface and increases the permeability of the cell membrane
What form of calcium is used?
Chilling involves placing the tubes in what?
A tray of ice
How many microliters of pGLO was added to the + tube?
Incubate the micro tubes in the ice tray for how long?
After incubation on ice you need to initiate a what?
At what temperature do you shock the microtubes?
42 C for 1 minute
After heat shock the tubes are returned back to the ice tray for how long?
How many people will acquire an infection while in the hospital?
1 patient in 20
Infection control relies on the proper use of what?
Disinfectants and antiseptics
What is a chemical that can destroy most microorganisms on inanimate surfaces like a bed rail?
What is a chemical that can destroy most microorganisms on living surfaces like your hands?
What is it called when a disinfectant can kill a wide variety of microbes?
What considerations should be made when choosing a disinfectant?
Will it be compatible with the surface (rust)
Will it still work in a protein rich environment like blood or feces
Is the disinfectant safe for the user
Is the disinfectant cost effective
A good disinfectant should be what?
able to Destroy many different microbes
Be relatively stable
Non staining and non corrosive
Easy and safe to use
What are two points that are critical to know before using a disinfectant?
What is the optimal concentration of the disinfectant to use to kill most microorganisms
What is the optimal length of time that a disinfectant needs to be in contact with a microorganism before it is destroyed
What must a chemical pass in order to serve as a hospital disinfectant?
The American Offical Anlaytical Chemist’s Use-Dilution Test