12 Infectious Diseases Part 1: Bacteria Flashcards
Define common terms used to describe infection.
Infection
Disease caused by microorganism
Define common terms used to describe infection.
Colonization
- Presence of microorganism w/o causing disease
- Ex: bacteria living in gut or on skin
Define common terms used to describe infection.
Pathogen
A microorganism capable of causing disease
Define common terms used to describe infection.
Virulence
- Ability of pathogen to cause disease
- Counterbalanced by host immune system
- Ex: Low virulence organsim may only cause disease in immunocompromised hosts
Define common terms used to describe infection.
Disease Manifestations:
- itis:
- emia:
-itis: Inflammation (cellulitis, lymphadenitis, meningitis)
-emia: presence in blood (bacteremia, viremia, fungemia)
- Describe the cellular basis of Gram staining.
-Gram staining is based on differences in cell structure
- Based on peptidoglycan in cell wall
- Gram positive bacteria have thick PG = Stains Purple with crystal violet
- Gram Negative: Less PG = Stains pink
- Shape and arrangement
Describe the cellular basis of Gram staining.
Five Gram-Stain Procedural Steps:
- Fixation: drying or methanol
- Primary stain: Crystal Violet
- Mordant (Iodine Tx) - Gram’s Iodine solution
- Decolourization with 95% Ethyl Alcohol
- Counterstain: Safranin
Describe the cellular basis of Gram staining.
What are the possible shapes and arrangements of Bacteria?
- Coccus
- Pairs and singles
- Chains
- Clusters
- Bacillus
- Pairs and singles
- Chains
- Flagellated Bacilli
- Spirochete
- Borrelia
- Treponema
- Spirillum
- Identify common bacterial pathogens causing human disease.
Gram Positive vs Gram Negative
Common Gram positive bacteria
* Staphylococcus (cocci)
* Streptococcus (cocci)
* Corynebacterium (bacilli)
* Listeria (bacilli)
Gram Negative Bacteria
* Neisseria (Diplococci)
* Haemophilus (coccobacilli)
* Enterobacteriaceae (enteric bacteria - Bacilli)
Define Commensal:
Commensal bacteria
- act on the host’s immune system to induce protective responses that prevent colonization and invasion by pathogens
- directly inhibit the growth of respiratory pathogens by producing antimicrobial products/signals and competing for nutrients and adhesion sites
- an organism that uses food supplied in the internal or the external environment of the host, without establishing a close association with the host
“Eat from the same dish”
Identify common bacterial pathogens causing human disease.
Staphylococcus
Shape/staining; Types; Abx resistance; area(s) of infection (common)
Cocci; Gram Positive
- Commensal residents of the skin
Axilla, groin, nares
- Staphylococcus Aureus
Range of virulence factors
Skin and soft tissue infections, bacteremia, osteomyelitis
Antibiotic Resistance: MRSA
- Coagulase Negative Staphylococci:
Not very pathogenic
Iatrogenic infections
-Iatrogenic infection was defined as an infection after medical or surgical management
-Commensal bacteria act on the host’s immune system to induce protective responses that prevent colonization and invasion by pathogens. On the other hand, these bacteria can directly inhibit the growth of respiratory pathogens by producing antimicrobial products/signals and competing for nutrients and adhesion sites.
Identify common bacterial pathogens causing human disease.
Streptococcus
Shape/Staining; Types; Abx resistance; area(s) of infection (common)
Cocci; Gram Positive
- Commensal Residents of the oropharynx
- Streptococcus pyogenes (group A strep)
Pharyngitis (strep throat), Necrotizing fasciitis (flesh eating disease)
- Streptococcus pneumoniae
Pneumonia, meningitis, otits media (ear infection)
Commensal residents of the GI Tract
- Streptococcus agalactiae (group B strep)
Neonatal meningitis
Identify common bacterial pathogens causing human disease.
Corynebacterium
Staining/shape; Types; Abx resistance; area(s) of infection (common)
Bacilli; Gram Positive
Commensal Resident of skin and mucous membranes
Corynebacterium Diptheriae
- Diptheria;
- Toxin mediated ulcerative disease of throat
- Rare now (vaccine)
other species few are pathogenic
Identify common bacterial pathogens causing human disease.
Listeria
Shape/Staining; Types; Abx resistance; area(s) of infection (common)
Bacilli; Gram Positive
Listeria Monocytogenes
- Reservoir: Animal GI flora
- Enters food chain via unwashed/undercooked produce, meat, dairy
- Pregnant people, neonates, elderly most vulnerable
- Meningitis, spontaneous abortion
- Large scale outbreaks
Neisseria spp
Shape/Staining; Types; Abx resistance; area(s) of infection (common)
Gram Negative
Diplococci
Neisseria meningitidis
- Commensal Resident of the oropharynx
- Meningitis
- Vaccine preventable
Neisseria gonorrhoeae
- Not commensal
- Sexually transmitted
- Urethritis, cervicitis
* Describe general mechanisms of antimicrobial resistance.
What is the target of Betal Lactam abx?
TARGET: Penicillin-binding proteins (PBP; transpeptidase)
β-lactam antibiotics are bactericidal
- act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls.
- PG layer is important for cell wall structural integrity, especially in Gram-positive organisms, being the outermost and primary component of the wall.
Mechanism of Action: Penicillin
What are PBPs? How are they targeted by abx
Penicillin Binding Proteins (transpeptidase)
- Group of enzymes required to build the bacterial cell wall == Bind to Peptidoglycan & allow for crosslinking of subunits
- Beta lactams (penicillins) are structurally similar to peptidoglycan - PBPs bind irreversibly to B-lactams
- Inhibition of cell wall synthesis leads to osmotic lysis and death of bacteria (bactericidal)
* Describe general mechanisms of antimicrobial resistance.
B-Lactam Abx (penicillin resistance)
- production of drug-inactivating enzymes
- modification of an existing target
- acquisition of a target by-pass system
- reduced cell permeability
- drug removal from the cell.
AMR genes refer to the genes implicated in or associated with the resistance to one or more antibiotics.
* Describe general mechanisms of antimicrobial resistance.
Target Modification:
Bacteria change structure (fit) of PBP
Modifies the target: drug can no longer bind
Via: Mutation; acquisition etc (PBP2a & MRSA)
* Describe general mechanisms of antimicrobial resistance.
Drug Inactivation
Change structure of B-Lactam
- Function of B-Lactamases ESBL, AmpC, NDM
- B-Lactamases are structurally similar to PBPs but hydrolyse B-lactam molecules and release inactvated drug
Describe the standard methods for antimicrobial susceptibility testing.
Disk Diffusion
Antibiotic diffuses from the disk into agar
Creates a concentration gradient where A = high concentraion and B = lower concentration
- An effective antibiotic will produce a large zone of inhibition (E15), while an ineffective antibiotic may not affect bacterial growth at all (TIC 75)
Describe the standard methods for antimicrobial susceptibility testing.
Gradient Diffusion (Etest)
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ETEST, the original gradient strip, consists of a predefined gradient of antibiotic concentrations immobilized on a plastic strip and is used to determine the MIC of antibiotics and antifungal agents against microorganisms tested on agar media using overnight incubation.
MIC = minimum inhibitory concentration
