Gram Pos and Neg Flashcards
Capsule
- _______ surrounding bacterial cells
- Consists of ______ made of single or multiple types of sugar residues
- Function of capsule
- Viscous gel
- Polysaccharide
- Protecting bacteria from immune system by evading phagocytosis and interfering with complement deposition
Bacterial cell wall is made of what compound?
Peptidoglycan
Bacterial plasma membranes are exceptionally _______ rich
Protein
What is the function of the bacterial plasma membrane
- Permeability and transport of solutes
- Contains proteins of ETC
- contains receptors for chemotaxis
- Site of DNA synthesis
What are the functions of the cell wall?
- Protection from mechanical disruption and turgor pressure
- Protects from toxic agents
- Permits exchange of nutrients required for growth
Describe the structure of the cell wall.
Gram Positive Bacteria
- Have a lot of ____ in cell wall
- Presence of ____ & _____
- Only ______ cell membrane
- What compound do they lack on their exterior?
- Peptidoglycan
- Teichoic & Lipoteichoic acid
- Single
- LipoPolySaccharide (LPS)
What is the function of teichoic and lipoteichoic acid in cell wall?
They anchor the cell wall to the plasma membrane
Gram Negative Bacteria
- Thickness of peptidoglycan cell wall?
- Structure of membrane compared to cell wall?
- What does the gram negative outer membrane contain?
- What is the function of the outer membrane?
- Thin (single sheet)
- Inner membrane –> cell wall –> outer membrane
- LPS
- Creates a negative charge due to LPS, which makes it harder for the host immune system to attack the bacteria. Also creates a periplasm that holds important enzymes in.
Describe how gram + and gram - bacteria appear when stained and why.
Bacteriostatic
Inhibits growth of bacteria but does not kill
Bactericidal
Inhibits growth and kills bacteria
What is the most common method of inhibition of bacterial growth?
Inhibition of cell wall synthesis and bacterial protein synthesis
Pili
- Made from what protein?
- 2 common types?
- Core of pilus?
- Pilin
- Adhesion and sex pili
- Hollow
What is flagellin?
A protein subunit that anchors flagella to bacterial cell. Each speices only has a single type and the primary protein structure differes between bacteria. They are highly antigenic.
What are spores? What are all medically important spore formers?
- Small dehydrated metabollically quiescent bacteria that are coated by a keratin like insoluble protein coat. They are heat resistant, pH resistant, and can live for a long time. They become inactive when nutritional conditions are unfavorable or depleted. They can reactive when nutrition is more available.
- Gram + rods
Shape
- Coccus?
- Bacillus?
- Coccobacillus?
- Round
- Rod shaped
- Intermediate between round and rod (oval)
When bacteria are grown on non-selective blood agar media, they may lyse the RBCs. What are the different types of hemolysis called?
What is a fastidious organism?
One that requires specialized nutrients to grow
What is MacConkey agar?
Contains bile salts that inhibit the growth of gram positive organisms. Organisms that are able to survive are gram negative and ferment lactose to form red/pink colonies.
What are the 3 virulence factors we need to know?
Adhesion
Toxins
Immune response/evasion
Are virulence factors always expressed?
No - they are often triggered by changes in environment (temp, pH, nutrient availability, osmotic pressure, hypoxia)
Only _______ have endotoxin.
Gram negative bacteria
What is an invasion type 3 secretion system?
What is endotoxin?
When gram negative cells are lysed, they release LPS, which is broken down into an O-antigen region, a core polysaccharide, and the Lipid A anchoring region. The lipid A is the portion that is toxic. At low concentrations it can cause inflammation, but at higher concentrations it can cause fever, hypotension, shock and death.
What is an AB toxin?
What is the difference between endo and exotoxin?
Endo - on the bacteria
Exo - secreted by bacteria
Cytolitic Exotoxins
- Secreted by which bacteria?
- What are 2 exotoxins to know?
- Gram + and gram -
- Phospholipase C (breaks down membrane phospholipids) and Pore-forming toxins (promote leakage and cell lysis)
What are super antigens?
- Exotoxin
- Produced mostly by Gram +
- Bind to TCR and promote uncontrolled activation of T cells –> uncontrolled cytokine release –> shock & death
Enterotoxin
- Secreted by gram (+) or gram (-)?
- Is it stable or easily degraded?
- Does it require a bacterial cell to exert its effects?
- What effect does it have on the host?
- Both
- Heat stable, resistant to gastric acid
- Do not need active replicating bacteria to have an effect
- Results in bad nausea by stimualtion of neural gut receptors
Staphylococcus aureus
- Gram staining?
- Shape?
- Hemolysis?
- Catalase test?
- Coagulase test?
- Capsulated?
- Gram +
- Cocci in clusters
- Beta
- Positive
- Positive
- Yes
What toxins are produced by gram +?
- Cytolytic (disrupt membranes and lyse cells)
- Exfoliative toxins (AB Toxin)
- Enterotoxin
Describe the pathogenesis of S. aureus.
What are the clinical presentations of S. aureus?
Streptococcous - E. coli
- Gram + or -?
- What do they ferment?
- What important enzyme do they produce?
- What are the main 3 antigens on their surface?
- Gram -
- Ferment lactose
- Produce tryptophanase
- O antigen (from LPS), K antigen from polysaccharide capsule, and H antigen from flagellar protein
E. coli - Virulence Factors
- What are the main virulence factors in E. coli (3)
- Describe the different types of pili on E. coli and how they contribute to the bacteria’s pathogenicity
- Describe the exotoxins that E.coli secrete
- Pili, Type 3 secretion system, exotoxins
- Pili
- Type 1 - binds to epithelial cells
- P pili - binds to kidney cells
- Other types bind to enterocytes and cause diarrhea
- Exotoxins
- alpha - hemolysin: pore forming cytolysin
- Shiga toxin: AB toxin that inhibits protein synthesis
Describe the pathogenesis of extraintestinal E. coli.
Describe the pathogenesis of intestinal strains of E.coli that release Shiga Toxin.
With regards to cellular structure, what features are unique to gram positive cells vs. gram negative cells?
Gram ____ cells can express beta-lactamases and these enzymes reside in the ______ space.
Negative
Periplasmic
