Infection Flashcards
Where do we have normal flora?
Skin, Vagina, Upper and Lower Bowel, Nasopharynx
What important organisms make up the flora of the nasopharynx?
- Streptococci
- Haemophilus
- Neisseria
- Mixed anaerobes
- Candida (fungus)
- Actinomyces
What important organisms make up the flora of the skin?
- Staphylococci
- Streptococci
- Corynebacteria
- Propiniobacteria
- Yeasts
What important organisms make up the flora of the upper and lower bowels?
• Upper Bowel - Enterobacteriaceae - Enterococci - Candida • Lower Bowel - Clostridium - Bifidobacteria - Bacteroides - Peptosteptococci
What important organisms make up the flora of the vagina?
- Lactobacilli
- Streptococci
- Corynebacteria
- Candida
- Actinomyces
- Mycoplasma hominis
What are the components of the bacterial cell envelope?
- cytoplasmic membrane
- cell wall
- capsule
- flagella
- pilli
What are the properties of the bacterial cytoplasmic membrane?
- Functions to synthesise and export components of the cell wall
- functions in respiration, secretion of extracellular enzymes and toxins, and uptake of nutrients by active transport mechanisms.
What are the properties/functions of the bacterial cell wall?
- protective against osmotic or mechanical stress
- barrier against certain toxic chemicals
- often the source of antigens
Describe the Gram+ and Gram- cell envelopes
- Gram+ (2 layers) contains a plasma membrane and a thick peptidoglycan layer. There can also be additional carbohydrates and proteins depending on the species of organism.
- Gram- (3 layers) contains a plasma membrane, a thin peptidoglycan layer and an outer membrane (which contains outer membrane phospholipids and LPS)
What are the properties/functions of the bacterial capsule?
- Contains capsular K antigens
- Protects against phagocytosis
- Helps with adhesion
- used in laboratory diagnostic tests
Describe the process of Gram staining
- Methyl violet (blue) + Lugol’s iodine is added. This is taken up by both Gram+ and Gram-
- Acetone is used to decolourise, by removing the stain from the outer membrane of the Gram-
- Methyl red (paler pink) is used to colourise the Gram- bacteria red.
Describe the classification of Gram+ cocci that form clusters
Clusters (catalase+):
- Staphylococcus Aureus (coagulase+)
- Staphylococcus epidermidis and saptrophyticus are coagulase-
Describe the classification of Gram+ cocci that form chains
B-haemolysis:
- Group A Strep = Streptococcus Pyogenes
- Group B Strep = Streptococcus agalacitae
- Group D = Enterococci
A-haemolysis:
- Streptococcus Pneumoniae (optochin resistant)
- Viridans Step
Describe the classification of Gram+ rods
Aerobes:
- Spores = Bacillus Athracis or Bacillus cereus
- Non spores: Listeria is motile in room temperature. Corynebacterium and Pallisaids
Anaerobes:
- Spores = Clostridium species such as botunilium, difficile and tentani.
- Branching = Acintomyces
What infections are caused by Staphylococcus Aureus?
- skin/soft tissue infections
- endocarditis
- osteomyelitis
- Toxic Shock Syndrome
What infections are caused by Streptococcus Epidermidis and Saprophyticus?
skin commensals of low pathogenic potential. However, are usually the cause of line, pacemaker and prosthetic infections.
What infections are caused by Staphylococcus Pyogenes?
- Causes quinsy (a painful puss-filled inflammation of the tonsils and the surrounding tissues)
- Causes cellulitis (inflammation of tissue bellow the skin)
- Toxic Shock Syndrome
What diseases are caused by Bacillus Anthracis?
- Cutaneous (Hide porter’s disease) - black eschar, oedema and swelling
- Gastrointestinal
- Inhalational
What are the components of the innate immune system?
- Physical barriers such as skin and mucociliary escalator
- Cellular barriers
- Circulating effector leucocytes such as monocytes/macrophages, neutrophils and NK cells
- Circulating components such as complement, collectins and pentraxins, and antimicrobial peptides
- Commensal organisms (microbiome)
- Cytokines
- Local enzymes
How are NK cells activated?
Natural Killer cells are specialised T-cells. They are stimulated by IL-12 and IL-15. They are activated by Syk and Zap70 protein kinases.
They kill infected and malignant cells particularly if lost normal MHC Class I molecule.
What is the function of NK cells?
- They kill infected and malignant cells particularly if lost normal MHC Class I molecule.
- secrete INF-y, which is an important activator of macrophages.
How do phagocytes recognise pathogens?
Phagocytosis is carried out by macrophages/monocytes and neutrophils. They detect pathogens through Pattern Recognition Receptors (PRR), which recognises molecular structures produced by microbial pathogens, called PAMPs (Pathogen Associated Molecular Patterns).
Phagocytes can also recognise and phagocytose opsonised pathogens, either by complement (especially C3) or antibodies. Phagocytosis usually involves ingestion into a vesicle that later becomes a phagolysosome.
What are the functions of cytokines?
- pro-inflammatory
- chemoattractant
- Regulatory (activates adaptive immune response)
- Down-regulatory
What are the important pro-inflammatory cytokines?
TNF-a
IL-1
What are the important chemoattractant cytokines?
IL-8
What are the important regulatory cytokines?
INF-y
IL-12
What are the important down-regulatory cytokines?
Il-10
TGF-b (Transforming Growth Factor beta)
What are the main receptor types of the innate immune system?
- PRRs
- Complement Receptors
- Fc Receptors
- NK Receptors
What are the main types of PRRs?
- Toll-like Receptors
- Nod-like Receptors
- Rig-like Receptors
- C-type Leptin-like Receptors
What do NLRs detect?
Bacterial cell wall peptidoglycan
What do RLRs detect?
Viral RNA
What do CLRs detect?
Mannose and fructose
Describe the TLR
Transmembrane receptors that consist of an extracellular recognition domain and an intracellular TIR (Toll-interleukin receptor) domain.
The TIR recruits MyD88 or TRIF adaptor proteins.
What TLRS recognise bacterial lipids?
TLR1, 2, 4 and 6
What TLRS recognise viral RNA?
TLR3, 7 and 8
What TLRS recognise bacterial DNA?
TLR9
What TLRS recognise bacterial and parasite proteins?
TLR5 and 10
What TLR detects LPS?
TLR4
What are the anatomical and physiological barriers?
- Skin
- Mucocilliary escalator
- Low pH environment
What are the phagocytic cells?
- Neutrophils
- Macrophages
- Dendritic cells
What are the states a macrophage can exist in?
- resting
- primed
- hyperactivation
Describe the role of the neutrophil
Engulf and breakdown pathogentic components via oxygen dependent and independent killing mechanisms.
Also release cytokines as well as other destructive chemicals.
Describe the resting macrophage
‘garbage collectors’ with few MHC Class II molecules
Describe the primed macrophage
Upregulation of MHC Class II and macrophages acting as APCs following detection of INF-y from Thelper and NK cells