10. Infectious diseases

Question 1

Gastroenteritis (Gut infections) - Viral causes

Answer 1

Adults - Norovirus

Children - Rotavirus

Question 2

Gastroenteritis (Gut infections) - Parasitic causes

Answer 2

Long duration - giardia

Question 3

Gastroenteritis (Gut infections) - Bacterial causes

Answer 3

Injected or fecal-oral route

Question 4

Gastroenteritis (Gut infections) - Acute

Answer 4

Body ejects all gut contents rapidly

Question 5

Gastroenteritis (Gut infections) - Chronic

Answer 5

Organism remains causing ongoing illness

Question 6

Types of intestinal infections

Answer 6

Secretory diarrhoea

Inflammatory diarrhoea

Question 7

Secretory diarrhoea

Answer 7

No fever or low grade fever
No white blood cells in stool

Examples:
Vibrio choleroe
ETEC
EAggEC
EPEC
EHEC

Question 8

Inflammatory diarrhoea

Answer 8

Fever
White blood cells in stool

Examples:
Campylobacter jejuni
Shigella spp.
Non typhoidal salmonella serotype
EIEC

Question 9

Vibrio cholera: Secretory diarrhoea - Method

Answer 9

1. Normal ion movement - Na+ from lumen to blood and no net Cl- movement
2. Activation of epithelial adenylate cyclase by cholera toxin
3. Na+ movement blocked and net movement of Cl- to lumen
4. Massive water movement tolumen (Cholera symptoms)

Question 10

Vibrio cholera: Secretory diarrhoea - Major Symptom

Answer 10

Waterborne

Rice water bacteria

Question 11

Vibrio cholera: Secretory diarrhoea - Major virulent factor

Answer 11

Cholera toxin (AB type)
1A and 5B encoded on phage genome

Question 12

Signs of acute/innate infection

Answer 12

Rubor
Calor/heat
Tumor
Dalor/pain
Change in function

Question 13

Signs of acute/innate infection - Rubor definition

Answer 13

Increased blood flow due to vasodilation

Question 14

Signs of acute/innate infection - Calor/heat definition

Answer 14

Increased blood flow due to vasodilation

Question 15

Signs of acute/innate infection - Tumor definition

Answer 15

Increased plasma movement from blood to tissue

Question 16

Signs of acute/innate infection - Dalor/pain definition

Answer 16

Pain due to localised swelling from tumor formation.

Fluid stretches nerved and pain receptors

Question 17

Signs of acute/innate infection - Change in function definition

Answer 17

Due to pain and change in tissue structure, usually reduced mobility

Question 18

Methods of adaptive immunity: Specific and Memory

Answer 18

Host mediated response to target.

Repeat response is quicker

Question 19

Methods of adaptive immunity: Humoral immunity

Answer 19

B cell produces antibodies

Question 20

Methods of adaptive immunity: Cellular immunity

Answer 20

T cells attack intracellular pathogens

Question 21

Methods of adaptive immunity: ADCC

Answer 21

Antibody dependent cell mediated cytotoxicity

Question 22

Heliobacter pylori

Answer 22

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

Question 23

Streptococcus

Answer 23

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

Question 24

Staphylococcus

Answer 24

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

Question 25

Immunity

Answer 25

Innate - Immediate, rapid response | Adaptive - Develops though exposure, bespoke weapons of defence.

Question 26

Inflammation

Answer 26

``` A non-specific reaction Induced by cytokines EG Interleukina and TNF-α Accumulation of neutrophils EG Fluid accumulation/release during diarrhoea ```

Question 27

Bacteremia

Answer 27

Bacteria in the bloodstream | Exploited to reach other organs

Question 28

Septicaemia

Answer 28

``` 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. ```

Question 29

Timeline of S.Enterica infection

Answer 29

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.

Question 30

How bacteria get into the body

Answer 30

Ingested (EG Listeria monocytes) Bites (EG Ticks/fleas deliver Yersinia pestis, Lyme disease) Wounds/Surgical points/Catheters (Streptococcus and Staphylococcus)

Question 31

General-purpose media

Answer 31

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

Question 32

Enrichment media

Answer 32

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.

Question 33

Selective media

Answer 33

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

Question 34

Differential media

Answer 34

General purpose media with chromogenic substrate additives. | Tests for the presence or absence of enzymes.

Question 35

Selective/differential media

Answer 35

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

Question 36

CLED Agar - differential for urine analysis

Answer 36

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)