General Bacteriology + Gram Positive Flashcards
Bacteria are grouped and named based on their…
- Morphological differences
- Biochemical/metabolic differences
- Immunologic characteristics
- Genetic characteristics
All organisms have a name with two parts, consisting of ____ and _____
- Genus
- Species
What are the three major shape categories of bacteria?
- Cocci (coccus)– spherical, oval
- Typically arranged in clusters or chains
- Bacilli (bacillus)– rods
- May be straight or curved
- Short bacilli – coccobacilli
- Spiral – comma shaped, s-shaped, or true spiral
What are the steps to performing a gram stain?
1) Smear the substance onto a slide (sputum, drainage, etc)
2) Heat it to fix the bacteria to the slide
3) Pour on crystal violet stain (blue dye) and wait 60 sec
4) Wash off with water and add iodine solution and wait 60 sec
5) Wash off with water and add ethyl alcohol or acetone to decolorize
6) Add safranin to counterstain (red dye), wait 30 sec and wash off with water
What give gram positive bacteria their color?
- Very thick peptidoglycan
- Extensive cross-linking
- Holds on to purple/blue color = Gram stains blue
- Allows low molecular weight compounds to come through
- Substances that target the cytoplasmic membrane (like PCN) can pass through
What give gram negative bacteria their color?
- Thinner – much less peptidoglycan
- Simple cross-linking
- Blue gets washed away, red gets absorbed = Gram stains red
- Does block low molecular weight compounds
- It has an outer membrane of lipopolysacharide (LPS)
- LPS contains lipid A – toxic to humans
- Lipid A is known as the “gram-negative endotoxin”
What are two examples of bacteria that do not stain well? What technique is used instead?
- Mycobacterium tuberculosis has extra lipids that cause it to resist uptake of stains –> Acid-fast
- Treponema pallidum are too thin to be seen without special lighting of microscope –> Gram negative
What is the bacterial cell wall made of?
Peptidoglycan
What is transpeptidase?
- Enzyme that creates the linkage formation of the cell wall
- Located in the cell membrane
What does the antibiotic penicillin inhibit?
Transpeptidase
What are the classic COCCI Gram-Positives bacteria?
1) Streptococcus – forms strips of cocci
- A (Group A strep) Streptococcus pyogenes
- B (Group B strep) Streptococcus agalactiae
- Streptococcus viridans
- Streptococcus pneumoniae
2) Enterococcus– forms strips of cocci
- D Enterococci
3) Staphylococcus – forms clusters of cocci
- Staphylococcus saprophyticus
- Staphylococcus aureus
- Methicillin-resistant Staphylococcus aureus (MRSA)
- Staphylococcus epidermidis
What are the classic BACILLI Gram-Positives bacteria?
1) Bacillus – spore-forming
- Bacillus cereus
- Bacillus anthracis
2) Clostridium – spore-forming
- Clostridium botulinum
- Clostridium tetani
- Clostridium perfringens
- Clostridium difficile
3) Corynebacterium – not spore-forming
- Corynebacterium diptheriae
4) Listeria – not spore-forming
- Listeria monocytogenes
What are the classic Gram-Nevative bacteria?
- Most GN organisms are rods or pleomorphic. 1 cocci + 1 spirochete
1) Neisseria - Diplococci - Neisseria meningitis
- Neisseria gonorrhoeae
- Moraxella catarrhalis
1) Spirochete - Treponema pallidum
Define virulence.
- Virulence – the degree of an organism’s pathogenicity
- Virulent organism – one that can cause disease
What determines virulence?
Virulence factors, such as…
- Presence of certain cell structures (Flagella, Pili, Capsules, Endospores, Biofilms)
- Bacterial endotoxin (lipid A)
- Bacterial exotoxins
Describe flagella, pili, and capsules.
-Flagella: Protein filaments that move the bacterium around
-Pili: Straight filaments arising from bacterial cell wall
-Capsules: Protective gel-like wall around the cell wall
Major function – protection from immune system
Ex: Streptococcus mutans – makes a gel in the presence of sugar = cavities
Describe the clinical correlation of antibodies directed towards bacterial capsules.
-They bind to the capsule (opsonization) and our macrophages and neutrophils can then bind to and digest the bacteria
- Example: Streptococcus pneumoniae has a capsule
- A vaccine against Streptococcus pneumoniae contains antigens and causes an immune response against the antigens, triggering the production of antibodies
- These antibodies then protect the individual from future infections
Describe endospores
- Metabolically dormant structures produced by some bacteria (Resistant to heat, cold, drying, and chemicals)
- Form when there is a shortage of nutrients
- Can lie dormant for years
-Formed by only 2 types of bacteria, both gram-positive
Bacillus
Clostridium
Describe biofilms (glycocalyx, slime layer).
- Extracellular polysaccharide network
- Protects bacteria from attack by antibiotics and the immune system
- Allows bacteria to bind to prosthetic devices (such as IV catheters)
-Staphylococcus epidermidis
Known to cause bacteremia, catheter-related sepsis, and infection of prostheses
Describe endotoxin in Lipid A
- Piece of outer membrane of the lipopolysaccharide (LPS) of gram-negative bacteria
- Released when the bacterial cell undergoes lysis – part of the cell that fragments off
- Can also be steadily shed from living bacteria
What is the clinical correlation of septic shock?
- Common, deadly response to both gram-negative and gram-positive infection
- Bacteremia – bacteria in the bloodstream (w/ or w/out symptoms)
- Sepsis – bacteremia that causes a systemic immune response to the infection
Describe exotoxins.
- Proteins secreted by bacteria
- Can cause severe disease manifestations
-Botulism toxin, tetanus toxin (neurotoxins) made by Clostridium
Act on nerves and motor end plates to cause paralysis or contraction
-Cholera toxin (enterotoxin) made by Vibrio cholerae
Massive diarrhea in cholera
Describe GENERAL streptococci characteristics and how they are categorized.
- Line up like a strip
- “catalase-negative”
- Alpha-hemolytic streptococci = partially lyse RBCs
- Beta-hemolytic streptococci = lyse RBCs completely
- Non-hemolytic streptococci = cannot lyse RBCs
- Classified by the presence of a carbohydrate antigen on their cell wall. Named A through U (Lancefield antigen)
- There are more than 30 different species of Streptococci, but only 5 are significant human pathogens
Give me streptococcus pyogenes details.
- Group A beta-hemolytic streptococci
- Clinical correlation: Streptococcal pharyngitis
- Classic strep throat
- Rapid strep test (RADT) – rapid antigen detection test
- Can detect group A carbohydrate antigen in minutes
- Penicillin treats it effectively
