Microbio Lab 2

Steps of a gram stain and what do they do

1) heat fix- adheres bacteria to slide to not wash off

2)crystal violet-stains all cells

3)grams iodine- ‘sets’ the dye

4) decolorizer- extracts lipids from gram negative cell walls, making them incapable of retaining crystal violet because of their thin peptidoglycan

5)safranin counterstain- stains all cells red

What happens in a catalase test?

catalase is a enzyme that certain bacteria produce. In a catalase test, a drop of hydrogen peroxide is added to a bacterial sample because catalase breaks down hydrogen peroxide. the formation of red principate indicates positive results. Staphylococcus species are catalase positive and streptococcus are catalase negative.

agglutination

the clumping effect due to antibody binding

Differential agar

media that allows the growth of more than one type of microorganism but results in observable morphological differences between the colonies, used to identify particular species of bacteria based on their growth properties and metabolic properties.

Selective agar

inhibit the growth of some microorganisms while allowing the growth of others. allows for isolation of individual colonies.

What do we use an MSA plate for? What type of bacteria can and can not grow on them? What color do they change with certain bacteria?

Both selective and differential. Used to isolate staphylococcus species, mainly used to identify S. Aureus. High salt content selects for Staphylococcus species which can grow in high salt content. typically red but will turn yellow at low pH. S. aureus can ferment the sugar mannitol producing acid and producing yellow halo. (gram positive)

What do we use an HEA plate for? What type of bacteria can and can not grow on them? What color do they change with certain bacteria?

Both selective and differential. Used to isolate and differentiate salmonella species from other gram negatives. E. coli produces acid and turns the normally green HEA plate bright orange. Black color is clear indicator of Salmonella because HEA plates have iron.

What do we use a MacConkey plate for? What type of bacteria can and can not grow on them? What color do they change with certain bacteria?

isolating and differentiating enteric9negative) organisms based on ability to ferment the disaccharide lactose. inhibits growth of gram positive because of bile salts. E coli will grow bright pink colonies indicating acid production. other colonies that don’t produce acid will be tan or colorless and turn the agar light brown/yellow

What is a Kirby-Bauer test used for? What can it tell you?

A kirby bauer test is used to determine susceptibility of bacteria to different antibiotics. It can tell you if a bacteria is susceptible to an antibiotic based on zones of inhibition.

What is the enzyme catalase, and what does it do?

enzymes produced by certain types of bacteria, it breaks down hydrogen peroxide.

How does a rapid Staph test work?

It detects s. aureus and different tests work differently. For the one we did in lab, we used testing paper and rapid test reagent to look for precipate formation, indicating a positive result

What does a large zone of hemolysis on blood agar indicate?

Beta hemolysis-Group A strep(GAS) are highly beta hemolytic while GBS are lesser beta hemolytic

Which Streptococcus species exhibit alpha, beta, or gamma hemolysis?

Beta-GAS and GBS to a lesser degree. Alpha- streptococcus viridians. Gamma- GDS-enterococcus faecalis

How does sterilization differ from disinfection?

Disinfection reduces the number of harmful microorganisms, however it does not eradicate them all. Sterilization kills all microorganisms.

How do antibiotics differ from disinfectants?

Antibiotics are medications that target bacterial cells while disinfectants are used to reduce the number of all microorganisms on surfaces and equipment

How do each of the types of antibiotics discussed in this lab (beta-lactam/penicillin,

macrolide/erythromycin, tetracycline, vancomycin) work? What do they target?

beta lactam/penicillin: interferes with peptidoglycan synthesis, effective against gram positive

Erythromycin/macrolide: interferes with protein synthesis by attaching to bacterial ribosomes, effective against gram positive and negative

tetracycline: interferes with protein synthesis by attaching to bacterial ribosomes, effective against gram positive and negative

vancomycin: interferes with peptidoglycan synthesis, effective against gram positive

How does bleach work as a disinfectant?

(sodium hypochlorite) damage protein to cells by causing them to clump or unravel

How does alcohol work as a disinfectant?

two ways-

1) entering cell and causing proteins to clump together

2) causing phospholipid bilayer to dissolve when at highest concentrations

How does hydrogen peroxide work as a disinfectant?

damages cell walls, membrane lipids, DNA, and some proteins

Why can't most disinfectants be used inside the human body to combat pathogenic

infections?

Disinfectants can affect human tissue and cause massive harm

When hydrogen peroxide produces bubbles, what is happening?

A species of gram positive bacteria is producing catalase, which breaks it down into water and oxygen

What is a bacterial endospore?

inactive and thick walled structures some bacterial species produce that can survive very harsh conditions

Why are bacterial endospores of particular concern in a health-care setting?

They are of particular concern because of their ability survive in such harsh conditions. They are very resistant and can lead to persistent infections, so they are especially a concern in a settings with many people who are immunely compromised.

In a clinical setting, how should disinfectants be used in a way to make them as effective

as possible?

It’s important disinfectants are used and stored correctly. For example, hydrogen peroxide may need to have a high enough concertation to be effective against catalase producing bacteria.

What is the point of streaking a microorganism on a plate of medium? What is someone

trying to do when that person completes a streak plate?

The point is to obtain pure cultures and isolated colonies

What is an antibiotic?

An antibiotic is an antimicrobial that kills bacteria or inhibits them enough for the immune system to eradicate them

What is a bacterial-lawn and how would someone prepare one

A lawn is a continuous and uniform layer of bacteria. They can be prepared by spreading a bacterial suspension over a plate.

What is a wet mount slide preparation and how does it differ from a simple stain or Gram

stain?

A wet mount slide is when a microorganism is suspended in liquid and it does not involve chemical staining. They are used to examine living microorganisms rather than view specific strucutral differences

How can you identify an erythrocyte, a lymphocyte, and a neutrophil?

In a slide, leukocytes and neutrophils are usually stained a purplish color

How does blood typing work? What antigens do each blood type express? Which

antibodies?

Type A blood: A antigens and B antibodies

Type B blood: B antigens and A antibodies

Type AB blood: AB antigens and no antibodies

Type O blood: No antigens, A and B antibodies

Rh+: Rh antigens no antibodies

Rh-: No Rh antigens and Rh antibodies

Blood typing works by viewing whether or not agglutination occurs, indicating antibodies attaching to antigens

How can you identify a fungal cell from a bacterial cel

fungal cells are generally much larger and have a nucleus

How do prevalence and incidence differ, and what does each tell you

Prevalence-the number of people in a population who have a disease at a particular time

Incidence- the number of new cases of a disease acquired by people in a population within a particular time period

How do an epidemic and a pandemic differ?

an epidemic is when an infectious disease becomes widespread in a community. A pandemic is when an infectious disease becomes widespread worldwide.

How do infection and disease differ?

an infection is the presence of a microbe in a host. a disease is a pattern of impaired bodily functions

What is an antibody and how does it work?

antibodies are y shaped molecules composed of four protein strands that can bind to specific molecules

What are the major components of human blood and what does each cell type do?

Erythrocyte- red blood cells transport gasses

Leukocytes- white blood cells are immune cells

thrombocytes- platelets are very small cell fragments that are immunologically important to the clotting response to tissue damage

How do group A, B, and D Strep differ?

Group A: strep

Group B: skin infections, vaginitis, UTI’s- meningitis in newborns

Group C: UTI and BTI

How do you score TSI slants?

Slant- Acid(A) or alkaline(K), butt (A or K), black precipice +-, gas production +-

how to calculate prevalence rates

# of cases in the population X 100,000/

total number of people in population

how to calculate incidence rates

# of new cases in the population X 100,000/ total number of people in the population