6: Introduction to Microbiology

Question 1

Fungi

Answer 1

• Eukaryotes
• Unicellular: yeasts
• Multicellular: moulds

Question 2

Moulds

Answer 2

• Visible mycelium
• Many of human importance:
  > Food spoilage
  > Food products
  > Antibiotics

Question 3

Mould: Penicillium

Answer 3

• Antibiotic penicillium from mould
• Produces chemicals that prevent bacterial wall synthesis
• Cell wall becomes leaky, bacteria killed

Question 4

Fungi Pathogenesis: Superficial Mycoses

Answer 4

• Infection of outermost layer of skin or hair
• Mainly cosmetic and rarely induce immune response
• Treated topically
• Pityriasis (tinea) versicolor

Question 5

Fungi Pathogenesis: Cutaneous Mycoses

Answer 5

• Colonise skin, hair and nails
• Increased pervasive properties
• Do not pass into deep layer of skin
• Topical or oral
• Ringworm, athlete’s foot

Question 6

Fungi Pathogenesis: Subcutaneous Mycoses

Answer 6

• Entry via skin trauma
• Produce proteolytic (breaks down protein) enzymes
• Can be difficult to treat
• Candida albicans

Question 7

Fungi Pathogenesis: Systemic Mycoses

Answer 7

• Usually only affect immunosuppressed
• Entry by inhalation of spores
• Most dimorphic

Question 8

Protozoa

Answer 8

• Unicellular eukaryotes
• Size between 20-50μm but up to 1mm (some can be seen with naked eye)
• Some have flagella for movement
• Found in aqueous environments and soil
• Also exist as parasites in animals and insects

Question 9

Entamoeba Histolytica

Answer 9

• Major cause of dysentery – amoebic dysentery
• Dysentery – infection mainly of the large colon
• Pathogenic amoebae travel into intestinal wall
• Causes abscesses and ulcers
• Passed in faeces protected in a cyst

Question 10

Giardia Intestinalis

Answer 10

• Attaches to host tissues – small intestine
• Burrows in and causes release of tissue fluids
• Causes diarrhoea, malaise and lots of gas

Question 11

Malaria

Answer 11

• Caused by plasmodium parasites
• Injected into humans in mosquito saliva
• Develop in liver
• Invade red blood cells
• Rupture cells

Question 12

Multicellular Parasites: Endoparasites

Answer 12

• Live inside the body

- Helminth worms

Question 13

Multicellular Parasites: Ectoparasites

Answer 13

• Live on the surface of the body
• Fleas
• Lice
• Mites

Question 14

Helminth Worms: Flatworms

Answer 14

• Flukes

- Tapeworms

Question 15

Helminth Worms: Nematodes

Answer 15

Roundworms

Question 16

Ectoparasites: Fleas

Answer 16

• Blood-sucking parasites

- Can be hosts to pathogenic organisms e.g. Yersinia pestis (bacteria that caused the plague

Question 17

Ectoparasites: Lice

Answer 17

• Cause redness and itching

- Include Pediculus humanus (hair lice) & Phthirus pubis (crab lice)

Question 18

Ectoparasites: Mites

Answer 18

• Sarcoptes scabei – causes scabies
• Female burrows into skin and lays eggs
• Red, inflamed line indicates infection

Question 19

Function of the Cell Membrane

Answer 19

• Determines cell shape
• Protects against osmotic lysis: cell wall damage compromises bacterial survival
• Determines some staining properties
• Offers protection from some toxic substances
• Contains components that contribute to pathogenicity

Question 20

Bacterial Growth

Answer 20

• Bacteria reproduce by binary fission
• Four phases:
  > Lag
  > Exponential
  > Stationary
  > Decline

Question 21

Pathogenic Bacteria: E. coli

Answer 21

• Escherichia coli
• Very fast replication (1 – 1 million in 8 hours)
• Inhabits intestine
• Most strains harmless
• Can cause severe gastroenteritis – Escherichia coli O157:H7

Question 22

Pure Cultures

Answer 22

• Liquid media may be used initially to increase the number of bacteria in the sample
• Many grow overnight (15-18 hours)
• Follow with culture on solid media (agar) in a Petri dish
• Streak plate commonly used to isolate strains – left for 24-36 hours

Question 23

Gram Staining

Answer 23

• Gram-positive: purple

- Gram-negative: pink

Question 24

The Viral Capsid

Answer 24

• Made up of repeating protein units (capsomeres)
• Occur in distinctive shapes
• May possess distinctive antigenic structure
• Involved in attachment & entry of virion into host cell
• Resist desiccation, pH change & detergents (naked viruses)
• May be used in identification

Question 25

Viral Envelopes

Answer 25

• Outer membranous layer surrounding the capsid
• Normal host cell constituents but proteins virally encoded – when the viral progeny breaks out of the cell, the virus will attach and hijack the cell. When it breaks out of the cell, they take some of the host cell with it
• Proteins may project as spikes (peplomers) from the envelope
• Spikes involved in attachment of virus to host cells
• Determine antigenic characteristics

Question 26

H&N: Haemagglutinins

Answer 26

• Antigenic glycoproteins on viral surface
• Binds virus to host cell
• 18 different HAs – H1, H2 etc.
• ATTACHMENT

Question 27

H&N: Neuraminidase

Answer 27

• Enzymes on viral surface
• 9 different influenza NAs
• Acts on infected cell surface to release viral progeny
• RELEASE

Question 28

Viral Mutation and Strains

Answer 28

• Humans possess elaborate mechanisms to ensure DNA stability – viruses do not
• Many mutations to Viral DNA/RNA
• Results in different strains
• Very hard to ‘keep up’ with
• Makes treatment difficult

Question 29

Effects of Viral Infection on Host Cells

Answer 29

• Lysis – cell rupturing
• Change in cell behaviour – cells can swell, have functions arrested or become detached from tissue mass
• Syncytia formation – cells form together into a large multinucleated mass