Bacteriology 2: Physiology And Metabolism Flashcards
Hektoen enteric agar
-isolation species
-selective ingredients
-differential diagnosis
It is designed to differentiate between bacteria that ferment certain sugars and those that produce hydrogen sulfide (H₂S). =Sulfur reducer
-used to differentiate between pathogenic and non-pathogenic enteric bacteria in stool samples. It is also used to screen for Salmonella and Shigella contamination in food and water samples.
differential diagnosis
-gram negative lactose fermenter: Organisms that ferment these sugars produce acid, causing a yellow color change in the medium.
Non-fermenters: Pathogens like Salmonella and Shigella and proteus do not ferment these sugars and form black colonies. Therefore H2S producer- Gram (-)
Macconkey’s agar
-isolation species
-selective agents
-differential ingredients
Bile salts and crystal violet: These inhibit the growth of Gram-positive bacteria, allowing only Gram-negative organisms to grow.
differential ingredients
-this dye detects acid production from lactose fermentation. color red at pH less than 6.8 (acidic conditions)= lactose positive E.coli = (double pink) lactose positive vs. salmonella = lactose negative (no color)
isolate and differentiate Gram-negative bacteria, particularly (E. coli, Salmonella) based on their ability to ferment lactose.
It is commonly used to detect bacteria from stool, urine, or water contamination.
Eosin methylene blue agar
-isolation specie
-selective ingredients
-differential ingredients
Eosin Methylene Blue Dyes: These dyes inhibit the growth of most Gram-positive bacteria, making the medium selective for Gram-negative organisms. especially useful for detecting lactose fermenters like Escherichia coli and distinguishing them from non-lactose fermenters.
differential ingredients
(also act as pH indicators): These dyes not only inhibit Gram-positive bacteria but also form a complex with fermentation products, causing distinct color changes in the colonies based on the level of acid produced.
-Escherichia coli and other strong lactose fermenters produce acid as they ferment lactose. The acid lowers the pH, causing a metallic green sheen to form on the surface of colonies (especially E. coli) due to the precipitation of the eosin-methylene blue complex.
-Other fermenters like Enterobacter may form pink or purple colonies without a metallic sheen. = Small amount of acid production-typically for enterobacter aerogenes
-Salmonella, Shigella, and other non-lactose fermenters do not produce acid. These bacteria form colorless or pale colonies as there is no acid production to alter the color of the dyes.
Mannitol-salt agar
-isolation specie
-selective ingredients
-differential ingredients
commonly used for the isolation of Staphylococcus species, particularly Staphylococcus aureus. It is designed to select for salt-tolerant organisms and differentiate those capable of fermenting mannitol.
selective agent
-The high salt concentration inhibits the growth of most bacteria except for salt-tolerant organisms like Staphylococci, making the medium selective for these species.
differential diagnosis
-Mannitol: A fermentable sugar alcohol used to differentiate species based on their ability to ferment mannitol.
Phenol Red (pH indicator): This pH indicator detects acid production from mannitol fermentation. It turns yellow in acidic conditions (pH < 6.8) and remains red in neutral or basic conditions.
SUMMARY
Selective for: Salt-tolerant bacteria, particularly Staphylococcus species, due to the high salt concentration.
Differentiates: Mannitol fermenters (like Staphylococcus aureus) that produce yellow colonies from non-fermenters (like Staphylococcus epidermidis) that do not change the medium’s color.
Blood agar plates
-key components
-types of Hemolysins (are able to destroy RBC)
Differential medium that supports the growth of a wide variety of bacteria. They are particularly useful for identifying hemolytic bacteria, based on their ability to break down red blood cells (RBCs). The medium contains 5-10% sheep blood, which allows for the detection of hemolysis (the breakdown of RBCs).
*Sheep Blood (5-10%): Provides nutrients for bacteria that require enriched conditions and allows for the visualization of hemolysis.
Blood agar allows the identification of bacteria based on the type of hemolysis they produce:
Beta (β) Hemolysis:
-Complete lysis of red blood cells and hemoglobin in the surrounding medium.
-Appearance: This results in a clear, transparent zone around the bacterial colonies where RBCs have been completely lysed.
-Examples of β-Hemolytic Bacteria:
Streptococcus pyogenes (group A strep, causes strep throat)
Staphylococcus aureus
Alpha (α) Hemolysis:
Partial lysis of red blood cells, with the reduction of hemoglobin to methemoglobin.
-Appearance: This produces a greenish or brownish discoloration around the colonies, known as “green hemolysis.”
-Examples of α-Hemolytic Bacteria:
Streptococcus pneumoniae
Viridans streptococci
Gamma (γ) Hemolysis:
No hemolysis; bacteria do not break down RBC
-Appearance: There is no change in the color or appearance of the medium around the colonies.
-Examples of γ-Hemolytic Bacteria:
Staphylococcus epidermidis
Biochemical tests for microbial ID:
-Carbohydrate breakdown
-citrate utilization
-decarboxylases and deaminases
-ability to produce acidic metabolic products (fermentatively or oxidatively)
-able to use citrate
-use of aa
Catalase test
-Reaction
-purpose
-positive result
-benefit of this bacteria
-the catalase test is used to identify organisms that produce the enzyme catalase, which breaks down hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂).
-test to differentiate catalase-positive organisms, such as Staphylococci (e.g., Staphylococcus aureus), from catalase-negative organisms like Streptococci.
-Immediate production of bubbles (O₂ gas), indicating the presence of catalase when H2O2 is added
-benefit = they can survive b/c they can convert toxic chemicals into O2
Oxidase test
-Reaction
-purpose
-positive result
-The oxidase test detects the presence of cytochrome c oxidase, an enzyme in the electron transport chain that participates in cellular respiration in certain bacteria.
-The test helps distinguish oxidase-positive bacteria (e.g., Pseudomonas, Neisseria, Vibrio) from oxidase-negative bacteria (any aerobic)
-A purple color appears within seconds, indicating the presence of cytochrome c oxidase.
Neumonic:
-Oxidase = oxidation phosphorylation has cytochromes = “p” = purple
Coagulase test
-reaction
-purpose
-positive results
-The coagulase test is used to detect the production of coagulase, an enzyme that converts prothrombin and fibrinogen in plasma to fibrin, leading to clot formation.
-This test differentiates coagulase-positive bacteria like Staphylococcus aureus from coagulase-negative species like Staphylococcus epidermidis.
-In the tube test, bacteria are incubated with plasma.
Positive result: The plasma clots, indicating the presence of free coagulase.
Urease test
-reaction
-purpose
-positive result
-The urease test detects the enzyme urease, which catalyzes the hydrolysis of urea into ammonia (NH₃).
-This test is used to identify urease-positive bacteria such as Helicobacter pylori (H. Pylori), Proteus.
-Bacteria are grown in a medium containing urea and a pH indicator.
Positive result: The production of ammonia raises the pH, turning the medium pink (alkaline conditions).
Oxygen concentration and pH for the 3 ecological niches
-supragingival plaque (teeth)
O2 = high/low
pH = neutral/acidic
-subgingival plaque (gingival crevice)
O2 = low
pH = neutral/weekly alkaline
-tongue coating
O2 =high/low
pH = neutral/acidic
What are 3 of the ecological niches in the oral cavity?
-Supragingival Plaque (TEETH)
-Saliva- coated teeth
forms on the exposed surfaces of teeth
-Subgingival Plaque (GINGIVAL CREVICE)
-GCF-coated teeth and epithelial
The gingival crevice, or sulcus, is the space between the teeth and gums, creating an environment with low oxygen levels where anaerobic bacteria thrive.
-Tongue Coating
-Saliva-coated epithelia
The surface of the tongue provides a unique habitat due to its papillae (small projections), which create numerous crevices and grooves where bacteria can adhere and colonize.
Subgingival plaque
-low [O2]
Tongue coating
-high/low [O2]
What oral bacteria acts as cavity prevention? What are the reactions?
Nitrate and hypotheocyanate (OSCN-) production
nitrate
NO3 —> NO2-
By nitrate reductase
Hypotheocyanate
SCN-thiocyanate —> OSCN-
By Salivary peroxisase
