S10: E-Coli & influenza

Question 1

Describe the biology of E. coli including the identification and serology

Answer 1

Escherichia coli is a gram-negative bacillus bacterium
Normal microbiota of large bowels & protects us from salmonella
Lactose-fermenting – can use MacConkey agar where the bacteria will grow into pink/red colonies (pH become acidic from breakdown of lactose into lactic acid)
Contain O, H, K & F antigens -> encode a specific structure of the bacteria

Question 2

Describe E. coli as a cause of diarrhoea including its pathogenesis & role of toxins

Answer 2

6 strains of diarrhoeagenic E. Coli

• enterotoxigenic E. Coli (ETEC) = ‘travellers diarrhoea’ through production of 2 toxins
• enteropathogenic E. Coli (EPEC) = creates a translocation tube to access & anchor into the enterocyte
• shiga toxin-producing E. Coli (STEC) = shiga toxin inhibits protein synthesis within the cell & this causes cell death
• enteroaggregative E. Coli (EAEC)
• enteroinvasive E. Coli (EIEC)
• diffusely adherent E. Coli (DAEC)

Question 3

Describe E. coli as a cause of urinary tract infections with virulence factors

Answer 3

Uropathogenic E. Coli (UPEC)

• adhesins: type 1 fimbriae
• toxins: lipopolysaccharide, a-haemolysin
• iron acquisition: bacteria produce their own iron-complexing proteins (siderophores) to acquire iron

Question 4

Describe E. coli as a cause of blood stream infections and sepsis

Answer 4

E. Coli bacteria = commonest cause of bacterial bloodstream infections
Causal factors: 50% UTIs, 21% have urinary catheters, 16% hepatobiliary infections & 7% GI infections

Question 5

Describe the management of E. coli infections

Answer 5

Diarrhoea: prevention is key – avoid food & drinks that could be contaminated with bacteria; treatment – most will recover within a few days, lots of fluids & avoid antibiotics
UTIs: trimethoprim or nitrofurantoin

Question 6

Describe the structure of the influenza virus

Answer 6

Genetic material: negative segmented sense RNA (8 genes), encoding 11 proteins including 3 RNA polymerases (high error rates)
Two surface antigens
-haemagglutinin – 18 types – binds to cells of the infected person
-neuraminidase – 11 types – releases the virus from the host cell surface

Question 7

Describe the replication of the influenza virus

Answer 7

Negative segmented sense RNA -> positive segmented sense RNA -> multiple negative segmented sense RNA
Negative segmented sense RNA -> mRNAs -> viral proteins
Negative segmented sense RNA and viral proteins are assembled into nucleocapsids

Question 8

Describe the three different types of influenza virus

Answer 8

1) influenza A = affects many animals, undergoes antigenic drift & shift and is responsible for pandemics
2) influenza B = only affects humans and undergoes antigenic drift – it mainly affects older adults
3) influenza C = affects humans & pigs and undergoes antigenic drift and produces mild disease

Question 9

Describe how influenza virus is spread

Answer 9

1) Small particle aerosols which remain suspended in air for many hours
2) Larger particles/droplets infect individuals in direct contact
3) Viral particles land on surfaces – infect others through indirect contact

Question 10

Explain how the influenza virus gains entry to the human host

Answer 10

1) Attachment of viral hemagglutinin (HA) to NANA residues on receptor (sialic acid–containing glycoproteins/glycolipids)
2) Invagination of the membrane
3) Entry occurs via receptor-mediated endocytosis

Question 11

List the clinical symptoms of influenza virus infection

Answer 11

Headache
High fever
Sore throat
Runny nose
Muscle aches & pains

Question 12

List the complications of influenza virus infection

Answer 12

Viral pneumonia
Secondary (bacterial) pneumonia
CNS syndromes
Reye syndrome

Question 13

Describe how you would diagnose flu in a clinical setting

Answer 13

Usually diagnosis from symptoms & clinical assessment

Can do a sample from a nasopharyngeal swab eg. antigen detection or nucleic acid detection

Question 14

Outline the treatments for influenza

Answer 14

1) Antivirals (rimantadine) – inhibit viral uncoating after uptake = influenza A
2) Neuraminidase inhibitors – inhibit viral release from the infected cell & cause aggregation of viral particles = influenza A & B
3) Prevention = vaccines
- formalin-inactivated vaccine by injection = influenza A & B
- live, attenuated, cold-adapted vaccine by nasal spray (CHILDREN) = influenza A & B

Question 15

What is antigenic drift?

Answer 15

Minor changes (natural mutations) in the genes of flu viruses that occur gradually over time – cause seasonal epidemics 
Refers to minor antigenic changes in H & N proteins that occur each year
Does not involve a change in viral subtype

Question 16

What is antigenic shift?

Answer 16

Major changes in the genes of flue viruses that occur suddenly when two or more different strains combine – results in a new subtype & cause widespread epidemics/pandemics
Refers to major changes in H and N proteins
Does involve a change in the viral subtype resulting in different H and N proteins

Question 17

What are the consequences of antigenic shift? Define epidemic and pandemic

Answer 17

Leads to a new subtype of influenza virus
Immune systems of many individuals have no defence against this new subtype
Epidemic = widespread occurrence of an infectious disease in a community at a particular time
Pandemic = epidemic over a very large area; affecting a large proportion of a population; often the world