Bacterial Structure and Function Flashcards
Exception to the Gram Positive/Negative Rule
Organisms in the genus MYCOPLASMA
- Simplest bacteria
- Do not have a peptidoglycan layer
- ONLY A LIPOPROTEIN MEMBRANE
DO NOT STAIN AT ALL*
Bacterial Cell Membrane
- Functions (5)
- Energy production
- Nutrient processing
- Brings in nutrients, gets rid of nutrients - Selective Transport of Molecules
- Osmotic Barrier
- Site of Secretion of toxins and enzymes
Beta-Hemolytic Streptococci Examples
GROUP A - Streptococcus Pyrogenes
- Strep throat, can cause ‘flesh eating disease’
GROUP B - Streptococcus Aglactaea
- Called so because it used to cause a form of mastitis in cows, causing the tits to swell up
- Normal colonizer of the female genital tract, 50% of women will have it occurring naturally and is usually benign
MUST BE SCREENED FOR DURING PREGNANCY
- If positive, will be given antibiotic
- One of the major causes of meningitis, pneumonia, and bacteraemia
Also includes Group C, F, and G
Clinical Example of Mycoplasma
Mycoplasma pneumoniae
- Walking pneumonia or ‘100 day cough’
- Leads to lower lung infection, though pt is largely functional but with a persistent cough
- The lack of peptidoglycan layer means that therapeutics targeting one cannot be used
- Instead, tend to use therapeutics that target DNA/RNA
15% resistance to first line antibiotics, this past year 1 in 5 pts failed regimen
Clinical Significance of Key Components
Key components of bacteria, viruses, fungi etc mentioned throughout the course are targeted by therapeutics. Understanding of the key components allows for understanding of the therapeutics best used to treat them
Coagulase Negative Staphylococcus
Anything that is not an aureus
- Most are just skin flora
- Can cause serious but typically opportunistic infections, rarely primary
Examples
1. S. Epidermis
2. S. hominus
3. S. warneri
4. S. hemolyticus
5. S. capitis
Common Clinical Examples of Acid-Fast (Mycobacteria) Bacilli
Mycobacterium tuberculosis (TB)
Mycobacterium leprae (leprosy)
TB is most prevalent in northern Ontario indians etc
Describing Bacteria - Gram Stain + Steps
Gram Stain
Gram Positive
- Appears purple on gram stain
Negative
- Appears pink on the gram stain
Steps
1. Crystal violet (primary stain)
- Both will appear purple
- Both cell walls stain with dye
- Gram’s Iodine (mordant — forms complex w primary die, allows it to adhere more strongly to the target material)
- Dye crystals become trapped in gram positive cell
- Gram negative unaffected - Alcohol (decolourizer)
- Dye crystals will remain trapped in gram positive cell, stay purple
- Outer membrane of gram negative cell weakened, allowing cell to lose dye, become colourless - Safarin (Red dye counterstain)
- Gram positive will remain purple
- Gram negative will be stained
Describing Bacteria - Shape (4)
Cocci = round
Bacilli = Rod/stick shaped
Curved
Spiral
Exception to the Gram Positive/Negative Rule
Bacteria of the genus Mycobacterium
- Eg Mycobacterium tuberculosis
Fecal Veneer
Theoretical construct that the world is covered with a ‘thin layer of feces’
We aerosolize bacteria when we breathe, sweat, pass gas, defecate etc.
Genus Staphylococcus
- Morphology
- Two major groups
GRAM POSITIVE COCCI found on the skin but are also highly pathogenic organisms
TWO MAJOR GROUPS
1. Coagulase Positive Staphylococcus
- S. aureus
- Found in two areas: nose and perianal region (two swabs)
- Hand hygiene the most effective method of reducing risk
- Coagulase Negative Staphylococcus
- Kind of everywhere
- On epidermis, capitis
Gram Negative Bacteria - Composition of Outer Membrane
- Definition
- Structure
- Mechanism
- Effects
- Clinical Significance
Outer membrane is composed of lipopolysaccharides (LPS) endotoxin
- Definition: Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria. It acts as an endotoxin that can trigger a strong immune response in the host.
- Structure:
• Lipid A: The toxic component; anchors LPS to the bacterial membrane.
• Core Polysaccharide: Links Lipid A to the O-antigen.
• O-Antigen: A variable polysaccharide chain; used for bacterial identification. - Mechanism:
• When Gram-negative bacteria lyse, LPS is released.
• Lipid A activates the immune system via Toll-like receptor 4 (TLR4) on immune cells.
• This triggers the release of cytokines (e.g., IL-1, TNF-α), leading to inflammation. - Effects:
• Low levels: Fever, localized inflammation.
• High levels: Septic shock, hypotension, multi-organ failure. - Clinical Relevance: LPS is a major cause of complications in Gram-negative bacterial infections like E. coli and Salmonella.
Gram Positive - Cell Wall Composition + Significance for Treatment
Peptidoglycan layer is cross-linked between
- N-acetyl Glutamine (NAG)
- N-acetyl Muramic Acid (NAM)
This is what penicillin and penicillin-like antibiotics target, the crosslinkages between NAG and NAM
Gram Positive vs Gram Negative
GRAM POSITIVE
- Cell has a thick peptidoglycan layer
- Between the peptidoglycan layer and the cell membrane is the PERI-PLASMIC SPACE
- Peptidoglycan layer poses challenge in killing them
GRAM POSITIVE, THINK ANTIBIOTICS
GRAM NEGATIVE
- Very thin outer membrane that surrounds a thin peptidoglycan layer
Medically Relevant Gram Positives - Streptococci Sp.
Medically Relevant Gram Positive
Cocci in chains, clustered, typically of low virulence
Usually found in the mouth and oropharynx
Notable example is Streptococci Pyrogenese, causing strep throat
MRSA PTs
- Every pt that comes in is swabbed twice, nostrils and perianal area.
- If MRSA positive, put in isolation with contact precautions
- Want to avoid a colonized PT with no obvious signs of infection from spreading it to others
Mycobacterium
- Classification name
- Structure
- Visualization
- Known as ACID FAST bacteria
- Have a
- Thick membrane capsule
- massive mycolic acid cell wall
Makes them impermeable to most things
Visualized by the Zeihl-Neilson Stain
Naming Convention for Bacteria
Gram Stain + Shape + Morphology
Naming Convention for Bacteria
- Genus/Species
Kings Play Chess On Fancy Green Squares
Kingdom, Phylum, Class, Order, Family, Genus, Species
Genus name is always capitalized
- Eg Staphylococcus
Species name is never capitalized
- Eg Aureus
So together Staphylococcus aureus (italicized) would then become S. aureus
Similarities in Gut Bacteria
Gut bacteria of partners tends to be quite close. Gut bacteria between a dog and their owner is closer than that between the owner and their neighbour.
Staphylococcus Aureus
- Clinical Significance
- Can cause several infections, some serious, but also part of the normal flora of various areas of the body
- Serious infections can occur in
- Heart
- Lungs
- Bone marrow
- Skin
- Intestines - ALWAYS clinically significant when found in sterile site
- MRSA (Methicillin resistant Staphylococcus Aureus) superbug
Streptococci sp. — 3 Classifications
Classified based on how the organisms grow on blood agar (5%)
CLASSIFICATIONS
- Alpha Hemolysis
- Partial lyses of blood cells in the agar
- Blood goes green - Beta Hemolysis
- Complete lysis of blood cells in agar - Gama-Hemolysis
- No lysis of blood cells in agar
Streptococcus Classification - Alpha Hemolytic Examples
Two Types
- Viridians Streptococci
- Not very pathogenic
- Part of the normal oral flora - Streptococcus Pneumoniae
- Part of the normal oral flora
- NUMBER ONE CAUSE OF COMMUNITY-ACQUIRED PNEUMONIA
- as well as: bacteraemia, meningitis, otitis media
TWO PRESENTING PHENOTYPES OF STREPTOCOCCUS PNEUMONIAE
1. Respiratory
2. Urinary Tract
Structural Differences between Gram Positive, Gram Negative, and Acid Fast Bacteria
Three Medically Relevant Gram Positive Cocci (GPC)
- Staphylococci
- Streptococci
- Single Cocci
Two Ways of Describing Bacteria
- Shape
- Gram Stain
What is a Bacteria?
- Cell Components
Cell Components
- Single celled
- Contains BOTH DNA AND RNA
- DNA changes frequently
- Ribosomes (metabolic activity, production of proteins)
- Cytoplasm with NO NUCLEUS
What is a Bacteria?
- Reproduction and timeline
Reproduction and Timeline
- Reproduction by binary fission
- Exponential
- Four generations of (some) bacteria in one hour
- Fast reproduction time = fast evolutionary changes, posing problems with therapeutics
What is Bacteria?
- Clinical Significance (2)
Bacteria produce proteins via RNA for their own signalling. Leads to production of toxins which, when released, cause numerous diseases.
Fast reproduction, fast evolutionary changes, poses problems wrt adaptations to therapeutic treatments
