Lab 15: Normal Flora and Opportunistic Pathogens

Normal Flora

Microorganisms residing in the human body.

Resident Microbes

Microbes acquired shortly after birth.

Commensality

Mutualistic relationship between microbes and host.

Opportunistic Pathogens

Normal flora causing infection in unusual locations.

Blood Agar

Nutrient medium enriched with 5% sheep blood.

Alpha Hemolysis

Incomplete RBC breakdown, green coloration around colonies.

Beta Hemolysis

Complete RBC breakdown, clear area around colonies.

Gamma Hemolysis

No RBC breakdown, no change in medium.

Mannitol Salt Agar

Selective medium for isolating pathogenic staphylococci.

Halophilic

Organisms thriving in high salt concentrations.

Streptococcus viridans

Typical pharyngeal flora, prefers high CO2.

Streptococcus pyogenes

Beta-hemolytic pathogen causing strep throat.

Throat Culture

Sample taken from pharynx for microbial analysis.

Candle-Jar Incubation

Technique providing high CO2, low oxygen.

Staphylococcus epidermidis

Common skin and nasal cavity flora.

Staphylococcus aureus

Pathogenic strain causing skin lesions and food poisoning.

Clean Catch Urine Sample

Midstream urine collection method to avoid contamination.

Colony-Forming Units (CFU)

Measurement of viable bacterial colonies per ml.

Urinary Tract Infection (UTI)

Infection caused by normal flora entering urethra.

E. coli

Most common UTI-causing organism.

Dental Caries

Cavities caused by bacteria in the mouth.

Plaque

Gummy substance of bacteria on tooth enamel.

Lactobacillus acidophilus

Bacteria associated with dental caries.

Snyder Test Agar

Medium to test susceptibility to dental caries.

Bromcresol Green

pH indicator changing color with acidity.

Susceptibility to Dental Caries

Measured by time for Snyder agar to turn yellow.

High Susceptibility

Snyder agar turns yellow in 24-48 hours.

Moderate Susceptibility

Snyder agar turns yellow in 72 hours.