Lab Review

Question 1

3 general methods to kill germs

Answer 1

1 physical (heat, radiation)
2 chem (alcohol, bleach)
3 bio (antibiotics, phage)

Question 2

which structure is mostly damaged by UV light

Answer 2

DNA

Question 3

What type of lesion UV makes in the DNA of bacteria and what does it lead to?

Answer 3

thymine dimers which leads to mutation in DNA

Question 4

What is the most lethal form of UV light and what is its wavelength?

Answer 4

UV-C (100-280 nm wavelength)

Question 5

Indicate the wavelength of UV light emitted by germicidal lamp.

Answer 5

254 nm

used for sterilization of air, surfaces, water, operating rooms

Question 6

definition of antibiotic

Answer 6

a type of antimicrobial agent that is made by a microorganism and kills or inhibit other microorganisms

Question 7

How is the efficacy of antibiotics measured?

Answer 7

Kirby-Bauer method

-tests the sensitivity of bacteria to antibiotics.

Question 8

type of agar used for Kirby-Bauer test

Answer 8

Muller-Hinton agar

Question 9

most appropriate way of washing hands to remove germs property

Answer 9

Warm water and soap for 20 seconds

Question 10

Mannitol Salt agar (MSA) is example of what type of medium

Answer 10

Selective & differential medium

Question 11

What component of the Mannitol salt agar (MSA) makes it selective

Answer 11

7.5% salt which is much higher salt concentration

normal saline is 0.9% salt

Question 12

type of bacteria that grow on MSA

Answer 12

Gram-positives

Question 13

What component of MSA makes it differential and what 2 groups of bacteria get differentiated

Answer 13

Mannitol (sugar alcohol) for GRAM POS

differentiates mannitol fermenters(phenol Red to yellow)

Question 14

staphylococci changed the color of MSA to yellow

Answer 14

Staph aureus changed the color to yellow

Question 15

Where do S. aureus and S. epidermidis found in human

Answer 15

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)

Question 16

Eosin Methylene Blue (EMB) is example of what type of medium

Answer 16

Selective & differential

Question 17

component of EMB makes it selective

Answer 17

Eosin and Methylene blue dyes

Question 18

type of bacteria grow on EMB

Answer 18

Gram-negative

Question 19

component of EMB makes it differential and what 2 groups of Gram-negative bacteria get differentiated

Answer 19

The sugar lactose which allows for differentiation between non-lactose fermenters, and heavy lactose fermenters (E. Coli)

Question 20

What is EMB used for mostly in diagnostic laboratories

Answer 20

For detection of fecal coliforms, specifically E. Coli

Question 21

coliform bacteria

Answer 21

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.

Question 22

What does presence of E. coli in water or food is indication of

Answer 22

fecal contamination

Question 23

What type of colonies E. coli makes on EMB and why

Answer 23

Dark green sheen colonies because E. coli is a rapid lactose fermenter

Question 24

typhoid pathogen

Answer 24

salmonella typhi

Question 25

How is Hydrogen peroxide (H2O2) is produced in bacterial cells and how does it damage the bacteria

Answer 25

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.

Question 26

reactive oxygen species (ROS) and what type of biological molecules are damaged by it

Answer 26

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.

Question 27

Which enzyme neutralizes H2O2. Show the reaction

Answer 27

catalase 2 H2O2 > 2 H2O + O2

Question 28

test result indicates that the organism is catalase positive

Answer 28

Generation of gas bubbles is indicative of organism being catalase

Question 29

catalase positive bacteria

Answer 29

STAPHYLOCOCCI

Question 30

function of cytochrome oxidase in bacteria

Answer 30

It is the final enzyme of electron transport chain that reduces oxygen to form H2O

Question 31

purpose of oxidase test in bacteria

Answer 31

To see if the bacterium has cytochrome oxidase in its electron transport chain

Question 32

What color does oxidase agent turns to if bacterium has cytochrome oxidase

Answer 32

DARK BLUE/PURPLE

Question 33

Which category of bacteria can be distinguished using oxidase test

Answer 33

Gram-negative rods such as pseudomonas aeruginosa

Question 34

serum

Answer 34

liquid part of the blood after it clots

Question 35

serological testing

Answer 35

using serum to specifically detect antigens or antibodies in patient’s serum

Question 36

What component of serum is commonly used in serological testing

Answer 36

antibodies

Question 37

ELISA

Answer 37

Enzyme Linked immunosorbent assay. It is a very commonly used test to use the specificity of antibodies to detect the antigen in laboratory.

Question 38

direct an indirect ELISA

Answer 38

Direct ELISA detects antigens in the patient’s serum, but Indirect ELISA detects antibodies in the patient’s serum

Question 39

INDIRECT ELISA steps

Answer 39

1 antigen of interest 2 antibody fr patient's serum 3 antihuman antibody w colorgenic enzyme

Question 40

DIRECT ELISA

Answer 40

1 antibody 2 antigen fr patients serum 3 same antibody w colorgenic enzyme

Question 41

titer

Answer 41

measurement of how much antibody an organism has produced that recognizes a particular antigen.

Question 42

indirect elisa example

Answer 42

HIV test

Question 43

direct elisa example

Answer 43

pregnancy test for HCG hormone(antigen)

Question 44

What is the purpose of standard plate count

Answer 44

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)

Question 45

How is the standard plate count is performed

Answer 45

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

Question 46

Plates containing how many colonies (CFU) are the most appropriate ones for calculation of number of bacteria in the sample

Answer 46

30-300 colonies

Question 47

epidemiology

Answer 47

study of causes, distribution, + disease in population

Question 48

outbreak

Answer 48

sudden + unexpected start of an infectious disease in an area

Question 49

3 ways food can be contaminated by harmful microbes

Answer 49

1 improper processing 2 improper storage/transport 3 improper preparation + handling

Question 50

tolerable amt of microbes in milk

Answer 50

300,000