Pathogens

Question 1

Give an example of the binomial classification

Answer 1

Escherichia coli

Question 2

Recall the Linnaean classification system

Answer 2

Domain
Kingdom
Phylum
Class
Order
Family
Genius
Species
Strain 
Isolate

Question 3

Describe viruses: size, genome size

Answer 3

most are 20 nm to 300 nm

• genome size 9Kb- 300Kb

Question 4

Describe the structure of viruses

Answer 4

DNA or RNA genome linear, segmented, single or double stranded

• protein nucleocapsid - individual capsomeres. Helical, cubic, or complex arrangement
• Enveloped or non-enveloped may have components derived from host cell
• No cytoplasm

Question 5

What is the difference between non-enveloped and enveloped viruses?

Answer 5

Non-enveloped is much more robust and survive on viruses

Membraned once are easily degraded

Question 6

Common viral infections in the UK community…

Answer 6

• Upper respiratory tract infection - rhinovirus, influenza, RSV
• Gastroenteritis e.g. Norovirus (SRSV), adenovirus(non-enveloped virus), rotavirus
• Rashes e.g. varicella zoster virus (chickenpox), measles
• Meningitis e.g. enterovirus, bacteria meningitis is lethal
• Hepatitis virus e.g. HepB
• Human Papilloma virus (HPV) - genital warts

Question 7

Healthcare-associated Infections (Hospital Acquired)…

Answer 7

• Norovirus, flu
• Influenza
Surface haemagglutinin allow it to adhere to cells and form component vaccines against flu. Eg Influenza

Question 8

What virus causes these muco-cutaneous lesions?

Answer 8

• Human Herpes simplex Type 1

* Chicken pox virus is herpes virus with similar shape

Question 9

Describe the structure of bacteria

Answer 9

• Size: 0.5 μm to 3 μm
• Structure: Prokaryotic. Haploid DNA, circular genome. no nucleus
• usually have rigid cell wall made of peptidoglycan of sugars outside cytoplasmic membrane
• some bacteria have capsules of polysaccharide that block antibody binding and other pathogens
• Fimbria(pilli) allow bacteria to attach to surfaces.
• Polar flagella on bacteria is on one side and allow it to migrate
• no mitochondria.

Question 10

What is the difference in staining of gram negative and positive bacteria?

Answer 10

gram positive- dark purple

Gram negative: pink

Question 11

What was the 1st influenza to be sequenced?

Answer 11

Haemophilus influenze

Question 12

Describe fungi

Answer 12

• Size: over 2 μm
• Structure: Eukaryotic. Haploid or diploid DNA
• Single or multiple nuclei

Question 13

Describe the cell wall structure of fungi

Answer 13

• Rigid chitinous cell wall outside cytoplasm

Question 14

What is the filamentous form of fungi?

Answer 14

• Filamentous form/moulds. – hyphae (e.g. Aspergillus spp) multinucleate branching hyphae forming mycelium

Question 15

What is classification of fungi based on?

Answer 15

morphology (growth form),

2. mode of reproduction (sexual or asexual)
3. disease caused: 70,0000species ~300 human pathogens

Question 16

What are the types of infection caused by fungi? Give examples of each. (3)

Answer 16

• Superficial mycoses: Skin, nail hair and mucous membranes (dermatophytes) or thrush (Candida albicans)
• Cutaneous - e.g. Tanea – aka ringworm
• Systemic mycoses: e.g Histoplasmosis. Histoplasma capsulatum pores that can be breathed in

Question 17

What is oral candidiasis?(3)

Answer 17

• most common oral fungal infection
• carriage rates 20% - 75% without any symptoms.
• Usually Candida albicans

Question 18

Describe yeast infections (3)

Answer 18

• normal constituent of the digestive and vaginal tracts
• Generally, no problems in healthy people
• Opportunistic pathogens

Question 19

Describe opportunistic infections in AIDS(3)

Answer 19

• (Previously classified as a protozoan)
o PCP(Pneumocystis pneumonia) in AIDS
o Single cells
o forms cysts containing sporescapsule

Question 20

What can Cryptococcus neoformans cause in AIDS?

Answer 20

Fungal yeast like form – encapsulated – large Block out canals in the cerebral spinal fluid

Question 21

Describe parasites

Answer 21

• Eukaryotic organisms – Protozoa and Helminths
• Term parasite - sometimes applied to any microbe that lives in or on another animal host, causing it harm.
• Different morphology and sizes at different life cycle stages
• They can be microscopic or visible to the eye
• Multicellular

Question 22

Describe protozoa

Answer 22

• Single cells 5 to 300 μm
• Single or multiple nuclei
• Haploid DNA
• Morphology varies throughout life cycle
• May have flagella.
• Trophozoites, cysts and other morphotypes – complex life cycles

Question 23

Give examples of protozoa

Answer 23

• Entamoeba histolytica - amoebic dysentery
• Giardia lamblia – giardiasis (steatorrhea)
• Toxoplasma gondii
• Cryptosporidium spp - swimming pools - diarrhoea
• Trichomonas vaginalis –common STI

Question 24

What are the groups of parasites?

Answer 24

• Cestodes are tapeworms e.g. Taenia saginata
• Trematodes are flatworms or flukes and include Schistosoma haematobium
• Nematodes which are roundworms e.g. Ascaris lumbricoides

Question 25

What are helminths?

Answer 25

These are multicellular parasitic worms • Different morphology and sizes at different life cycle stages • They can be microscopic or visible to the eye • Multicellular