Lecture 2.1: Infection and Disease Flashcards
What is Symbiosis?
A close relationship between two different type of organisms in a community
Types of Symbioses (3)
Mutualistic
Commensalism
Parasitism
Mutualistic Symbiosis: Effects and Examples
Species A and Species B Benefit
E.coli in human intestine
Commensalism Symbiosis: Effects and Examples
Species A Benefit and Species B Unaffected
Microbes on Human Skin
Parasitism Symbiosis: Effects and Examples
Species A Benefit and Species B Harmed
TB, Fungi, Helminiths
What is Infection?
Refers to the presence and growth of microorganism in a host, not including normal flora
An infection may or may not cause a disease
What is a Pathogen?
An organism that causes damage to the host
Types of Pathogens (3)
• Opportunistic
• Primary
• Zoonotic
Opportunistic Pathogens
A group of microorganisms that do not usually infect healthy hosts
But can produce infections in hospitals, to immuno-depressed persons or those patients presenting underlying diseases as cystic fibrosis, which favours infection
Primary Pathogens
They can cause disease in a host regardless of the host’s resident microbiota or immune system
Zoonotic Pathogens
A zoonosis is an infectious disease that has jumped from a non-human animal to humans
Zoonotic pathogens may be bacterial, viral or parasitic
They may also involve unconventional agents and can spread to humans through direct contact or through food, water or the environment
What is Pathogenicity?
The ability of microorganism to cause disease
Phases of Infection (5)
• Incubation Stage
• Prodrome Stage
• Illness/ Specific Symptoms
• Recovery
• Health
Phases of Infection: Incubation Stage
The time between the acquisition of the pathogen and the onset of symptoms
Phases of Infection: Prodrome Stage
Nonspecific symptoms, such as fever or tiredness, occur
Phases of Infection: Disease Specific Symptoms
Increase rapidly
Phases of Infection: Recovery
As the host immune system and/or treatments effectively reduce the number of pathogens, symptoms decrease
This also called the convalescence stage
Phases of Infection: Health
• Ultimately, symptoms disappear and the individual returns to health
• However, some individuals may become chronic carriers of the infectious
agents or develop latent infections that can reoccur
What is a Symptom?
Experienced by the individual affected by the disease
What is a Sign?
Can be detected by someone other than the individual affected by the disease
What is a Portal of Entry?
It is a site through which microorganisms enter the susceptible host and cause infection
What are some examples Portal of Entry?
• Mucous Membranes
• Skin
• Placenta
• Respiratory Tract
• Gastrointestinal Tract
What is Virulence?
The degree of pathogenicity
What is the Virulence Factor?
Enable a host to replicate and disseminate within a host in part by subverting or eluding host defences
How do Virulence Factors help bacteria?
• Invade the host
• Evade host defences
• Cause disease
What is included in Virulence Factor? (5)
- Attachment (via adhesins)
- Colonisation (& Enzymes)
- Invasiveness
- Toxins (& Enzymes)
- Inhibition of Phagocytosis
Staphylococci Infection
• Gram-positive cocci that grow in clumps
• Yellow-ish crust around mouth
• Staph. aureus is one of the most important
pathogen
• Causing a variety of pyogenic infections and
toxin-mediated illnesses
• Antibiotic Resistance
Coagulation as a Defence against Microbes
• Coagulation is an innate defence mechanism
against microbial pathogens
• It traps and immobilises invading bacteria in a
clot
Coagulase as a Virulence Factor
• S. aureus secretes two proteins that promote coagulation
• Coagulase (Coa) and von Willebrand factor binding protein (vWbp)
• Promote similar modifications of the coagulation cascade during host infection
• Both of these proteins activate prothrombin nonproteolytically
Coagulase Test
Fibrinogen Plasma + Coagulase
If Coagulase is present then a Fibrin Visible Clot can be seen
What is key about coagulase-negative staphylococci?
Coagulase-negative staphylococci are generally considered non-pathogenic
apart from Staph. epidermidis and Staph. saprophyticus
Virulence Factor: Invasin
• Hyaluronidase enzyme is produced by Staphylococcus aureus
• It is responsible for the spread of then organism during infection
• Hyaluronidase enzyme is capable of degrading hyaluronic acid (HA)
• This is an essential component of the extracellular matrix of human tissues
Streptococcus
• Gram positive spheres (cocci) like staphylococci
• Streptococci appear in strips (chains) on gram stain not clusters
• 1µm in diameter and usually capsulated
• Facultative anaerobes
• They are catalase negative
• Non-sporing bacteria and non-motile
Pharyngitis
• A variety of bacteria can cause infection in the pharynx
• A classic infection is strep throat
• Caused by Streptococcus pyogenes
• Contains M proteins which inhibits phagocytosis
• Produces pyrogenic toxins which cause the symptoms seen with pharyngitis
• Group A streptococci can cause abscesses on the tonsils
• S. pyogenes can cause scarlet fever and toxic shock syndrome
Virulence Factor: Streptococcus
• Secretes a hemolysin that causes haemolysis
• Haemolysis is the breakdown of red blood cells (RBC)
• Beta haemolysis is caused by two haemolysins O and S
• Alpha haemolysis is caused by hydrogen peroxide produced by the
bacterium, oxidising haemoglobin to green methemoglobin
Name Post Streptococcal Illnesses (4)
• Glomerulonephritis
• Streptococcal Toxic Shock Syndrome
• Scarlet Fever
• Acute Rheumatic Fever
Staphylococcus aureus: Gram? Shape? Where do they infect?
• Gram Positive
• Cocci
• Bacteria colonise skin and nasopharynx
Staphylococcus aureus: How do they evade host defences? (3)
• Using Protein A
• Coagulase (forms fibrin clot)
• Haemolysins and Leukocidins (destroy RBC AND WBC)
Staphylococcus aureus: How do they carry out deep invasion?
• Hyaluronidase (breaks down connective tissue)
• Staphylokinase (lyse clots)
• Lipase (breaks fat)
• Can produce an A-B Toxin (TSS, Scalded Skin Syndrome)
Streptococcus pyogenes: Gram? Shape? Where do they infect?
• Gram Positive
• Cocci
• Skin
Streptococcus pyogenes: What Virulence Factors does it have? (6)
• Hyaluronidase (breaks down connective tissue)
• Dnase
• M protein
• Streptokinase (plasminogen -> plasmin ->fibrinolyisn)
• Lipase (breaks fat)
• Can produce an A-B Toxin (TSST, Scalded Skin Syndrome)
Streptococcus pyogenes: What can make it change from normal skin flora to pathogenic? (6)
- Trauma inoculates bacteria into skin
- Bacteria colonise
- Inflammation
- Pustular lesions and honeycomb like crust
- Deeper infection
- May lead to anti-streptoccal Ab reactions glomerulonephritis
Signs & Symptoms of Streptococcal Respiratory Diseases
• Sore throat
• Difficulty swallowing
• May progress to scarlet or rheumatic fever
How and when are Streptococcal Respiratory Diseases Spread?
• Spread via respiratory droplets
• Occurs most often in winter and spring
How to treat Streptococcal Respiratory Diseases?
• Often confused with viral pharyngitis
• Penicillin is an effective treatment
When does Pathogenesis of Streptococcal Respiratory Diseases occur?
• When normal microbiota are depleted
• Large inoculum is introduced
• Adaptive immunity is impaired
What causes Scarlet Fever?
Caused by Group A streptococci
Who is most commonly affected with Scarlet Fever?
Usually seen in children under age of 18 years
What are Symptoms of Scarlet Fever? (8)
• Symptoms usually begin with appearance of a rash
• Tiny bumps on the chest and abdomen (can spread to whole body)
• Appears redder in armpits and groin
• Rash lasts 2-5 days
• Very sore throat with yellow or white papules
• Fever of 101˚F/38.3˚C or higher
• Lymphadenopathy in neck
• Headache, body aches, and nausea
