Introduction to Infection and Microbes

Question 1

Define infection

Answer 1

An invasion of a host’s tissues by microorganisms causing a disease (pathological change/damage)

Question 2

What causes the disease in an infection?

Answer 2

Microbial multiplication
Toxins
Host response

Question 3

Define zoonoses

Answer 3

Infectious diseases of animals that can naturally be transmitted to humans

Question 4

What are the 3 ways of horizontal transmission?

Answer 4

Contact (direct, indirect, vectors)
Inhalation (droplets, aerosols)
Ingestion (faecal-oral)

Question 5

What is vertical transmission?

Answer 5

Transmission of an infection from mother to child before or after birth (eg. HIV)

Question 6

Give some examples of types of exotoxins

Answer 6

Cytolytic
AB toxins
Super antigens
Enzymes

Question 7

What are the 4 types of microbe?

Answer 7

Viruses
Bacteria
Parasites
Fungi

Question 8

What is the key characteristic of all microbes?

Answer 8

They multiply

Question 9

What is a viral envelope made of?

Answer 9

Lipopolysaccharides and lipids

Question 10

What is the difference between gram positive and gram negative bacteria?

Answer 10

Gram positive bacteria have a very thick peptidoglycan wall whereas gram negative have a thinner peptidoglycan wall and 2 membranes. Gram positive bacteria hold the gram stain.

Question 11

What are obligate anaerobes?

Answer 11

Microbes that require oxygen free environments to survive

Question 12

How do we name bacteria?

Answer 12

Linnaean taxonomy

Genus then species eg. Staphylococcus aureus

Question 13

Give an example of gram positive cocci

Answer 13

Staphylococcus aureus
Streptococcus pneumoniae
Enterococcus faecalis

Question 14

Give an example of gram negative cocci

Answer 14

Neisseria meningitidis

Mortadella catarrhalis

Question 15

Give an example of gram positive bacilli

Answer 15

Listeria monocytogenes

Bacillus cereus

Question 16

Give an example of gram negative bacilli

Answer 16

Escherichia coli (E-coli) 
Klebsiella pneumoniae
Salmonella typhi 
Pseudomonas aeruginosa
Haemophilus influenzae

Question 17

Name a yeast

Answer 17

Candida albicans (thrush) 
Cryptococcus neoformans (meningitis)

Question 18

Name a mould (fungi)

Answer 18

Aspergillus species (lung infection)

Question 19

Name a protozoa (single celled) parasite

Answer 19

Giardia lamblia

Plasmodium falciparum

Question 20

Name a helminth (worm, multicellular)

Answer 20

Roundworms
Tapeworms
Flukes

Question 21

What are the beneficial effects of normal flora?

Answer 21

Sheer number in bowel make it hard for invading pathogen to compete for nutrients and site
Some produce antimicrobials
Helps develop the immune system
Can provide nutrients (vitamin K)
Can aid in digestion and absorption of nutrients

Question 22

What are mycoplasma?

Answer 22

Small, prokaryotic organisms with no peptidoglycan in their cell walls
Have a single plasma membrane
Extremely small so frequently pass through filters

Question 23

Describe chlamydiae

Answer 23

Small bacteria that are obligate intracellular parasites
Grow in cytoplasmic vacuoles
Have 2 lipid bilayers

Question 24

Describe rickettsia

Answer 24

Small, rod-like or coccobacillary shaped
Double layered, gram negative cell wall
Transmitted by arthropods (eg. Fleas)

Question 25

What does positive RNA mean?

Answer 25

Directly encodes for mRNA

Question 26

What does negative RNA mean?

Answer 26

Does not directly encode for mRNA

Question 27

Why is HPV linked to cervical cancer?

Answer 27

Direct carcinogen as it express E6 and E7 proteins that inhibit p53 and pRB protein function (important for cell proliferation)

Question 28

What is the normal range for CRP?

Answer 28

< 5

Question 29

What bacteria causes cellulitis?

Answer 29

Staph aureus | Strep pyogenes

Question 30

Briefly describe strep pyogenes

Answer 30

Gram positive Group A streptococcus Beta haemolytic (complete destruction of RBCs on blood agar)

Question 31

What is the sweep test?

Answer 31

Performed when looking for necrotising fasciitis | If the fascia is dead then there will be no resistant to sweeping the finger around in a small surgical incision

Question 32

What is the treatment for necrotising fasciitis?

Answer 32

Supportive care - IV fluids, analgesia, antypyretics Antibiotics ITU referral - high mortality condition Surgery - drain pus, remove infected source, amputation

Question 33

Why can't necrotic tissue recover?

Answer 33

Lack of blood supply

Question 34

What do we think about when choosing an Abx?

Answer 34

Severity of infection Site of infection Likely pathogen(s) Route of administration Possible adverse effects - allergy, interactions with other drugs, renal/hepatic impairment Ecological impact - don't select for other organisms

Question 35

What is the likely bacterial cause of NF?

Answer 35

Strep pyogenes | Group A beta haemolytic

Question 36

Describe alpha haemolysis and bacteria that do it

Answer 36

Produces a green appearance on agar Strep viridans group Strep pneumoniae

Question 37

Describe the virulence factors of strep pyogenes

Answer 37

``` M proteins - antiphagocytic Exotoxins - streptolysin for cell lysis Streptokinase - lysis of clots Streptodornase - DNAases to promote spread C5a peptidase - inactivate complement ```

Question 38

Which Abx are active against streptococci?

Answer 38

``` Beta lactams (penicillins, cephalosporins, carbapenems) Glycopeptides (vancomycin) ```

Question 39

What is toxin-mediated disease treatment?

Answer 39

Anti-toxin therapy - high dose immunoglobulin | Interfere with toxin production - Abx that inhibit protein synthesis

Question 40

What is the empiric treatment for strep infections?

Answer 40

Tazocin and clindamycin

Question 41

If group A strep is identified, which Abx do we use?

Answer 41

Benzylpenicillin and clindamycin

Question 42

Name some group A strep diseases (other than cellulitis and NF)

Answer 42

``` Acute pharyngitis/tonsillitis Scarlet fever Impetigo Erysipelas Puerperal sepsis ('childbed fever') ```

Question 43

What are some consequences post-strep infections?

Answer 43

Acute rheumatic fever - cross reaction between heart/joint tissue and strep antigens - valve damage/pericarditis/endocarditis etc Acute glomerulonephritis - antigen-antibody complexes on basement membrane

Question 44

Which bacteria falls under non-haemolytic 'strep'?

Answer 44

Enterococcus faecalis

Question 45

Name some common staph skin infections

Answer 45

Impetigo Furuncle (boil) - hair follicles Surgical wound infection

Question 46

Is staph aureus coagulase positive or negative?

Answer 46

Positive

Question 47

What colours do coagulase positive and negative tests produce?

Answer 47

``` Positive = gold Negative = white ```

Question 48

Describe some features of coagulase negative bacteria

Answer 48

Low violence Generally don't cause infections in otherwise healthy people Can create biofilms

Question 49

Which of staph and strep is typically localised and which is spreading?

Answer 49

``` Staph = localised Strep = spreading ```

Question 50

What Abx do we use for staph?

Answer 50

Flucloxacillin Beta lactam combinations eg. Coamoxiclav and tazocin Vancomycin for flucloxacillin resistant strains

Question 51

Why is flucloxacillin generally a good choice?

Answer 51

Resistant to staph beta lactamase