Microbio Lab - Second Half

Antigen

Protein/sugar marker on the surface of Red Blood Cells (RBCs) that determines blood type (A, B, Rh)

Antibody (Ab)

Protein found in the serum (plasma) that attacks foreign antigens

Agglutination

The clumping together of antigens and antibodies; this is the positive result indicating the antigen is present in blood typing

Incompatibility

Occurs when a recipient receives blood with new antigens, leading to the immune system attacking the cells (can cause shock, kidney failure, or death).

Type A Blood

Has A Antigens on RBCs and produces Anti-B Antibodies in serum.

Type O blood

Has Neither A nor B Antigens on RBCs and produces Both Anti-A and Anti-B Antibodies in serum.

Type AB Blood

Has A and B Antigens on RBCs and produces Neither Anti-A nor Anti-B Antibodies in serum.

Rh Positive (+)

Indicates the Rh antigen is present; blood clotted (+) in the Rh well.

Rh negative (-)

Indicates the Rh antigen is absent; blood did not clot (-) in the Rh well. (Produces Anti-Rh Abs only upon exposure).

Universal donor

Type O- (Has no A, B, or Rh antigens, so it won't be attacked by recipient antibodies).

Universal recipient

Type AB+ (Has all A, B, and Rh antigens, so it produces no ABO or Rh antibodies to attack donor blood).

Rules for receiving blood (recipient)

You cannot receive blood with new antigens you don't already have; your existing antibodies must not attack the donor's RBCs.

Rule for donating blood (donor)

You can only donate if the recipient's body already "expects" your antigens (or if you have no antigens, like Type O).

Rh Factor Donation Rule

Rh (-) blood can donate to both (+) or (-) recipients, but Rh (+) blood can only donate to other (+) recipients.

Clumping result

Means the antigen is present (positive result)

No clumping result

Means the antigen is not present (negative result)

Donated component in transfusion

Red blood cells (RBCs)

transfusion

transferring blood from one person to another

Alcohol mechanism of action

Kills bacterial cells by denaturing proteins and damaging cell membranes.

Alcohol vs. Hand soap effectiveness

Alcohol generally removes or kills more bacteria than standard hand soap; its action is rapid.

Antisepsis

The primary goal of alcohol application (e.g., prep before a needle/catheter), intended to reduce the level of skin contaminants.

Microbes alcohol is ineffective against

endospores and some naked viruses

Reason alcohol fails to fully sterilize

It loses effect due to evaporation, is ineffective against endospores/some viruses, and bacteria hide in skin crevices.

Bacterial refuges on skin

Pores and crevices of the skin, where bacteria (like Micrococci) hide and resist alcohol treatment.

Most common skin bacteria

gram-positive micrococci

Sterlization

The complete elimination of all microbial life (which alcohol cannot fully achieve).

Experimental control of fingerprints on agar

The left thumb plate, showing bacteria removed just by the physical act of touching the agar (initial contamination level).

Antimicrobial drug

Any compound that kills or inhibits the growth of microorganisms (e.g., Sulfa drugs).

Antibiotic

An antimicrobial agent naturally produced by a microorganism (fungus or bacterium) to kill or inhibit other microbes (e.g., Penicillin).

Broad spectrum antimicrobial

Effective against a wide range of both gram positive and gram negative bacteria

Narrow spectrum antimicrobial

Effective against a limited group or only one type of organism (e.g., Sulfa drugs).

Reason antibiotics don't work on viruses

Antibiotics target bacterial-specific structures like the cell wall that viruses lack

Five cellular targets of antibiotics

Cell wall synthesis, DNA/RNA synthesis, Protein synthesis, Folic acid synthesis, and Plasma membrane disruption.

Mechanism for Gram-Negative Resistance (Cytoplasmic Drugs)

The outer membrane acts as a permeability barrier, restricting the entry of the antimicrobial agent.

Mechanism for Gram-Positive Resistance (Membrane Disruptors, e.g., Polymyxin B)

The thick peptidoglycan cell wall remains stable and protects the cell even when the underlying plasma membrane is disrupted.

Zone of Inhibition

The clear area around a drug disk in the Kirby-Bauer test where bacteria cannot grow; indicates the drug's effectiveness.

Factors Influencing Zone Size

Diffusibility of the agent, size of the inoculum (amount of bacteria), and type/depth of the medium.

Required Medium for Susceptibility Testing

Mueller-Hinton Agar

Using Drugs with Intermediate Resistance

The drug can still be successful if the dosage is increased.

Considerations for Best Treatment (Sensitive Organism)

Strength of effectiveness, cost of the drug, and patient allergies or conditions.

Coliforms

Bacteria (like E. coli) that naturally occur in the intestines of humans and warm-blooded animals.

Significance of coliforms in food/water

They are the primary indicator of fecal contamination, suggesting a high potential for the presence of serious pathogens (e.g., Salmonella, cholera).

Why Coliforms are Found in Meat

Fecal material from the animal's intestines contaminates the muscle during the butchering process.

Hamburger Cooking Safety

Should be cooked medium-well to well-done because pathogens are thoroughly mixed throughout the meat during the grinding process.

Steak cooking safety

The interior of the meat is typically sterile; contamination is limited to the outer surface.

Safe Thawing Procedure

Thawing should take place in the refrigerator (not warm water) to prevent rapid bacterial growth.

Refrigeration Limits

Not a guaranteed means of prevention; some pathogens (psychrophiles) can still grow at refrigerator temperatures.

Pasteurization

A process that significantly reduces the bacterial load in food but does NOT kill all bacteria.

Fermented Foods (e.g., Cheese, Yogurt)

Foods that safely contain high bacterial counts because the bacteria are beneficial and used for production.

Coliforms (Definition)

Gram-negative, non-spore forming bacilli that posses the enzyme B-gal

Coliform Biochemical Action

Ferments lactose (due to B-gal), producing acids and gases

Coliform Indicator Significance

Their presence in water is the primary indicator of fecal contamination.

Membrane Filter (MF) Method

Standardized technique to determine coliform counts in water by filtering a known volume through a small pore size filter.

Membrane filter pore size

0.45 micrometers

Minimum Water Sample Volume (MF)

At least 100 mL must be filtered; more is used if bacteria/turbidity are low.

Incubation conditions for MF

Filter is placed on Endo broth and incubated for 24 hours at 35C

What is endo-broth (Selective etc)

Selective AND differential

Endo Broth (Selective Property)

Selective because it inhibits most Gram-positive bacteria using sodium lauryl sulfate, basic fuchsin, and sodium sulfite.

Endo Broth (Differential Property)

Differential because it uses lactose and basic fuchsin to distinguish lactose fermenters from non-fermenters.

Coliform Appearance on Endo Broth

Red colonies with a characteristic green metallic sheen.

Non-Coliform Appearance on Endo Broth

Colorless colonies (cannot ferment lactose).

Pathogens Indicated by Coliforms

E. coli, Klebsiella, and Enterobacter.

EnteroPluri-Test system

A self-contained, multi-chambered plastic tube used for rapid identification of bacteria in the Enterobacteriaceae family using multiple biochemical tests.

Advantage of Multitest Systems

Fast identification (18-24 hours), high efficiency (many tests in one tool), minimal media prep, and reliable results

Disadvantage of Multitest Systems

Limited scope (only available for certain families/groups) and potential need to confirm questionable results.

Prerequisite Test for EnteroPluri-Test

The Oxidase Test.

Reason for Oxidase Test in enteropluri-test

Nearly all Enterobacteriaceae are oxidase-negative rods; a negative result confirms the isolate belongs to the family, validating the use of the test.

Expected Oxidase Result for Enterobacteriaceae

Oxidase negative - validates using rapid system

Test efficiency of enteropluri-test

Running many distinct biochemical tests (often $12 or more) using only one tool.

Streptococci cell arrangement

Isolate in CHAINS

Staphylococci Cell Arrangement

Isolate in irregular CLUSTERS (like grapes).

Catalase Test Result for Streptococci

Catalase Negative (they LACK the enzyme).

Catalase Test Result for Staphylococci

Catalase Positive (they HAVE the enzyme).

Alpha hemolysis

Partial Lysis; causes a greenish clearing around the colony

Beta Hemolysis

Complete Lysis; causes a clear, transparent yellow zone around the colony.

Gamma hemolysis

No Lysis; causes no change in the medium color or appearance.

Lancefield classification system

Serological method for grouping beta-hemolytic streptococci based on differences in their cell wall carbohydrates.

Basis for Lancefield classification

Distinct CARBOHYDRATES (polysaccharides) are present in the bacterial cell wall.

Streptococci Group Causing Dental Caries

Viridans streptococci group.

Mechanism of Dental Caries Formation

The bacteria ferment sugars in the mouth, producing acids that degrade the tooth enamel.