Lab Review Flashcards
3 general methods to kill germs
1 physical (heat, radiation) 2 chem (alcohol, bleach) 3 bio (antibiotics, phage)
which structure is mostly damaged by UV light
DNA
What type of lesion UV makes in the DNA of bacteria and what does it lead to?
thymine dimers which leads to mutation in DNA
What is the most lethal form of UV light and what is its wavelength?
UV-C (100-280 nm wavelength)
Indicate the wavelength of UV light emitted by germicidal lamp.
254 nm
used for sterilization of air, surfaces, water, operating rooms
definition of antibiotic
a type of antimicrobial agent that is made by a microorganism and kills or inhibit other microorganisms
How is the efficacy of antibiotics measured?
Kirby-Bauer method
-tests the sensitivity of bacteria to antibiotics.
type of agar used for Kirby-Bauer test
Muller-Hinton agar
most appropriate way of washing hands to remove germs property
Warm water and soap for 20 seconds
Mannitol Salt agar (MSA) is example of what type of medium
Selective & differential medium
What component of the Mannitol salt agar (MSA) makes it selective
7.5% salt which is much higher salt concentration
normal saline is 0.9% salt
type of bacteria that grow on MSA
Gram-positives
What component of MSA makes it differential and what 2 groups of bacteria get differentiated
Mannitol (sugar alcohol) for GRAM POS
differentiates mannitol fermenters(phenol Red to yellow)
staphylococci changed the color of MSA to yellow
Staph aureus changed the color to yellow
Where do S. aureus and S. epidermidis found in human
S. epidermidis is found on the skin of 100% human population
S. aureus is found in about 25% of human population around nares (it prefers moist surfaces)
Eosin Methylene Blue (EMB) is example of what type of medium
Selective & differential
component of EMB makes it selective
Eosin and Methylene blue dyes
type of bacteria grow on EMB
Gram-negative
component of EMB makes it differential and what 2 groups of Gram-negative bacteria get differentiated
The sugar lactose which allows for differentiation between non-lactose fermenters, and heavy lactose fermenters (E. Coli)
What is EMB used for mostly in diagnostic laboratories
For detection of fecal coliforms, specifically E. Coli
coliform bacteria
bacteria that live in the environment of the intestine of many animals and humans.
Fecal coliforms such as E. Coli live primarily within intestine of all warm- and cold-blooded animals.
What does presence of E. coli in water or food is indication of
fecal contamination
What type of colonies E. coli makes on EMB and why
Dark green sheen colonies because E. coli is a rapid lactose fermenter
typhoid pathogen
salmonella typhi
How is Hydrogen peroxide (H2O2) is produced in bacterial cells and how does it damage the bacteria
H2O2 is produced by the electron transport chain during the reduction of oxygen by oxidases that reduce oxygen to for
m H2O2. It is considered a Reactive Oxygen Species (ROS) which can damage bacterial DNA, RNA, and proteins.
reactive oxygen species (ROS) and what type of biological molecules are damaged by it
Also called oxygen radicals or free radicals, ROS are types of unstable molecules that contain oxygen and can easily react with other molecules in a cell. A buildup of ROS in cells may cause damage to DNA, RNA, and proteins, and may cause cell death.
Which enzyme neutralizes H2O2. Show the reaction
catalase
2 H2O2 > 2 H2O + O2
test result indicates that the organism is catalase positive
Generation of gas bubbles is indicative of organism being catalase
catalase positive bacteria
STAPHYLOCOCCI
function of cytochrome oxidase in bacteria
It is the final enzyme of electron transport chain that reduces oxygen to form H2O
purpose of oxidase test in bacteria
To see if the bacterium has cytochrome oxidase in its electron transport chain
What color does oxidase agent turns to if bacterium has cytochrome oxidase
DARK BLUE/PURPLE
Which category of bacteria can be distinguished using oxidase test
Gram-negative rods such as pseudomonas aeruginosa
serum
liquid part of the blood after it clots
serological testing
using serum to specifically detect antigens or antibodies in patient’s serum
What component of serum is commonly used in serological testing
antibodies
ELISA
Enzyme Linked immunosorbent assay. It is a very commonly used test to use the specificity of antibodies to detect the antigen in laboratory.
direct an indirect ELISA
Direct ELISA detects antigens in the patient’s serum, but Indirect ELISA detects antibodies in the patient’s serum
INDIRECT ELISA steps
1 antigen of interest
2 antibody fr patient’s serum
3 antihuman antibody w colorgenic enzyme
DIRECT ELISA
1 antibody
2 antigen fr patients serum
3 same antibody w colorgenic enzyme
titer
measurement of how much antibody an organism has produced that recognizes a particular antigen.
indirect elisa example
HIV test
direct elisa example
pregnancy test for HCG hormone(antigen)
What is the purpose of standard plate count
The method is used around the world for estimation of the number of live microbes in a sample which is called Colony Forming Units (CFU)
How is the standard plate count is performed
First, a serial dilution of the sample is made and from each dilution, an aliquot is transferred onto agar plates and after 24 hours of incubation, the number of colonies (CFU) in each plate is counted and the number of bacteria in the original sample can be calculated by multiplying the number of colonies of the plate by the dilution factor
Plates containing how many colonies (CFU) are the most appropriate ones for calculation of number of bacteria in the sample
30-300 colonies
epidemiology
study of causes, distribution, + disease in population
outbreak
sudden + unexpected start of an infectious disease in an area
3 ways food can be contaminated by harmful microbes
1 improper processing
2 improper storage/transport
3 improper preparation + handling
tolerable amt of microbes in milk
300,000
