10. Infectious diseases Flashcards
Gastroenteritis (Gut infections) - Viral causes
Adults - Norovirus
Children - Rotavirus
Gastroenteritis (Gut infections) - Parasitic causes
Long duration - giardia
Gastroenteritis (Gut infections) - Bacterial causes
Injected or fecal-oral route
Gastroenteritis (Gut infections) - Acute
Body ejects all gut contents rapidly
Gastroenteritis (Gut infections) - Chronic
Organism remains causing ongoing illness
Types of intestinal infections
Secretory diarrhoea
Inflammatory diarrhoea
Secretory diarrhoea
No fever or low grade fever
No white blood cells in stool
Examples: Vibrio choleroe ETEC EAggEC EPEC EHEC
Inflammatory diarrhoea
Fever
White blood cells in stool
Examples: Campylobacter jejuni Shigella spp. Non typhoidal salmonella serotype EIEC
Vibrio cholera: Secretory diarrhoea - Method
- Normal ion movement - Na+ from lumen to blood and no net Cl- movement
- Activation of epithelial adenylate cyclase by cholera toxin
- Na+ movement blocked and net movement of Cl- to lumen
- Massive water movement tolumen (Cholera symptoms)
Vibrio cholera: Secretory diarrhoea - Major Symptom
Waterborne
Rice water bacteria
Vibrio cholera: Secretory diarrhoea - Major virulent factor
Cholera toxin (AB type) 1A and 5B encoded on phage genome
Signs of acute/innate infection
Rubor Calor/heat Tumor Dalor/pain Change in function
Signs of acute/innate infection - Rubor definition
Increased blood flow due to vasodilation
Signs of acute/innate infection - Calor/heat definition
Increased blood flow due to vasodilation
Signs of acute/innate infection - Tumor definition
Increased plasma movement from blood to tissue
Signs of acute/innate infection - Dalor/pain definition
Pain due to localised swelling from tumor formation.
Fluid stretches nerved and pain receptors
Signs of acute/innate infection - Change in function definition
Due to pain and change in tissue structure, usually reduced mobility
Methods of adaptive immunity: Specific and Memory
Host mediated response to target.
Repeat response is quicker
Methods of adaptive immunity: Humoral immunity
B cell produces antibodies
Methods of adaptive immunity: Cellular immunity
T cells attack intracellular pathogens
Methods of adaptive immunity: ADCC
Antibody dependent cell mediated cytotoxicity
Heliobacter pylori
Gram negative, motile (polar flagella), spiral shaped.
Causes infection in the stomach.
Diseases: Gastritis, Gastric ulcers, Gastric cancer
Spread by close contact: host-host, food/water sources.
Can detect urea in breath = Key diagnosis UBT
Streptococcus
Gram positive
Cocci
Chains
Infection sites: Throat, mammary glands, skin, middle ear, lungs, blood.
Diseases: Paryngitis (strep throat), mastitis, impetigo/cellulitis, necrotizing fasciitis, otidis media, pneumonia, scarlet fever
Staphylococcus
Gram positive
Cocci
Grape-like clusters
Infection from: Asymptomatic to susceptible person.
Infection sites: Skin, blood/systemic, lungs, bones, stomach, brain.
Diseases: Pimples, impetigo in wounds, toxic shock syndrome, septicaemia, pneumonia, osteomyelitis, gastroenteritis (inflammatory), meningitis
Immunity
Innate - Immediate, rapid response
Adaptive - Develops though exposure, bespoke weapons of defence.
Inflammation
A non-specific reaction Induced by cytokines EG Interleukina and TNF-α Accumulation of neutrophils EG Fluid accumulation/release during diarrhoea
Bacteremia
Bacteria in the bloodstream
Exploited to reach other organs
Septicaemia
Blood borne, systemic Septic shock Bacteria, organisms or Ior toxins Severe response: Blood vessels leak, lowers BP, can damage vital organs (brain and kidneys) Massive cytokine release. Immune system overdrive: -High temperature -Lethargy (extreme tirednes) -Violent chills/shivering -Faintness (low BP) -Pale, clammy skin -Rapid but shallow breathing -Petechiae (pinprick bruises on skin) -Purple blotches (purpura) which don't fade under glass.
Timeline of S.Enterica infection
0 mins - Ingest contaminated food
15 mins - Invasion of epithelial cells.
1 hour - Neutrophils appear, increased vascular permeability.
3 hours - Neutrophil-induced tissue damage and inflammatory-induced fluid accumulation.
8 hours - Massive effusion of neutrophils and fluid in intestinal lumen.
24-48 hours - Evident tissue damage, diarrhoea and more fluid like accumulation.
How bacteria get into the body
Ingested (EG Listeria monocytes)
Bites (EG Ticks/fleas deliver Yersinia pestis, Lyme disease)
Wounds/Surgical points/Catheters (Streptococcus and Staphylococcus)
General-purpose media
General cultivation uses LB agar generally (Luria-Bertani) contains yeast exract, salts, water and agar.
Grows both fastidious (fuddy/with heeds) and non-fastidious bacteria (and yeast/fungi).
Often a starting point to look for unexpected organisms
Enrichment media
Dependent on the symptoms and sample site.
For fastidious bacteria, often supplement media with sheep blood.
In a mixed sample this allows the causative organism to grow faster.
Selective media
Mixed bacterial population.
Blood based agar, contains antimicrobials.
Incubated at 42°c in microaerobic (low O2) conditions.
Inhibits growth of most enteric bacteria.
Allows growth of campylobacter
Uses not only media but growth conditions as selection.
Once isolated can use other serological tests
May use antibiotic selection
Differential media
General purpose media with chromogenic substrate additives.
Tests for the presence or absence of enzymes.
Selective/differential media
MacConkey agar detects bacilli and enteric bacteria.
Contains bile salts and crystal violet that inhibit Gram-positive bacteria.
pH indicators allow for fermentation of sugars to be monitored.
Traditionally contains lactose to identify:
-Lactose fermenting (E.coli)
-Lactose non-rementing (Salmonella)
Fermentation of sugars (xylose, lysines, deoxynolate)
-E.coli, simple sugars
-Shigella cannot use xylose, salmonella can
Additional metabolism produces H2S
CLED Agar - differential for urine analysis
Cysteine-lactose-electrolyte deficient.
C = Enhances growth of slow growing coliforms.
L = pH indicator is bromothymol blue
Fermentaters = yellow
Can use for quantification of bacterial load (EG UPEC)
