Re-introduction to microbiology

Question 1

The micro-organisms

Answer 1

Protozoa (eukaryotes)
Fungi (eukaryotes)
Bacteria (prokaryotes)
Viruses
Prions (infectious 'rogue' proteins)

Question 2

Protozoa

Answer 2

Unicellular eukaryotes
2-100 μm
Many are free-living e.g. euglena (pond-water)
Several are important human pathogens (malaria)
Often affect the immunocompromised
Mainly a threat in developing countries

Question 3

Protozoa examples

Answer 3

Trypanosomiasis (chagas disease)
-South America kissing bug
Malaria
Cryptosporidium (causes diarrhoeic diseases in bad water)
-chlorinated swimming pools
Toxoplasma gondii
-crazy cat lady

Question 4

Fungi

Answer 4

Eukaryotic organisms with a variety of forms
Commercially important - baking, brewing and pharmaceuticals
External, rigid cell wall - containing chitin
Filamentous or yeast forms
Many display both - dimorphic e.g. Candida

Question 5

Bacteria

Answer 5

Most numerous organisms on earth
Adapted to inhabit almost all habitats
-even those not based on sunlight - deep sea vents
Responsible for notable worldwide epidemics - PLAGUE
Prokaryotes - no internal membranous compartments
Specialised cell walls
Produce a range of toxins - virulence factors

Question 6

Cellular forms

Answer 6

Cocci
-cocci, diplococci, tetrads, sarcina, streptococci, staphylococci
Bacilli
Extended irregular rods
Kidney bean
Corkscrew
Helical
Gram positive and gram negative

Question 7

Diplococci example

Answer 7

Neisseria

Question 8

Sarcina

Answer 8

Gram positive cocci

Genus

Question 9

Streptococci example

Answer 9

Streptococcus mutans

Question 10

Staphylococci example

Answer 10

Staphylococcus aureus MRSA

Question 11

Bacilli example

Answer 11

Bacillus subtilis

Question 12

Extended irregular rods example

Answer 12

Fusobacterium

Question 13

Kidney bean example

Answer 13

Vibrio spp.

Question 14

Corkscrew example

Answer 14

Treponema spp.

Question 15

Helical example

Answer 15

Campylobacter

Question 16

Gram positive

Answer 16

Thick cell wall made of peptidoglycan

Retain crystal violet stain

Question 17

Gram negative

Answer 17

Do not retain stain
Coloured red or pink
More resistant against antibodies because of impenetrable cell wall
Thin (single-layered) cell wall
Periplasmic space
LPS on outside with porin in between

Question 18

Peptidoglycan

Answer 18

A polymer of N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG)
Crosslinked via amino acid pentapeptides and anchored to cell wall

Question 19

Surface structures

Answer 19

Flagellum

Pili and fimbriae

Question 20

Pili and fimbriae

Answer 20

Proteinaceous filamentous structures 
Often used for attachment to host-cells or surfaces
Adhesins at the tip for host interaction
- e.g. EPEC bfp 
Can also be used for twitching motility

Question 21

Pili and fimbriae example

Answer 21

Pseudomonas spp.

Question 22

Pathogens with 2 examples

Answer 22

Disease causing bacteria

e. g. Vibrio cholera - Cholera
e. g. Yersinia pestis - Plague

Question 23

Opportunistic pathogens with 3 examples

Answer 23

Commensals that sometimes cause disease
e.g. MRSA, C. difficile, Major hospital infections
N.meningitidis- isolated epidemics in UK

Question 24

Commensals

Answer 24

The unseen hordes
Mainly harmless
Colonise surfaces and mucosa

Question 25

Commensals examples

Answer 25

Staphylococcus epidermidis: harmless commensal gram positive cocci Propionibacterium acne: gram positive bacilli- can cause acne Staphylococcus aureus: carriage in anterior nares and skin -gram positive cocci - MRSA

Question 26

Digestive tract in terms of bacteria

Answer 26

Main reservoir of bacteria within the body 1,000,000,000 per gram Around 1kg mass in bacteria

Question 27

Examples of bacteria in the digestive tract

Answer 27

``` E. Coli: -gram negative rod -essential commensal -some strains are Pathogenic Bacteroides species: -gram-negative anaerobic bacilli -most numerous in the body Clostridia species: -gram positive anaerobic spore forming bacilli -includes C. difficile an increasingly drug resistant -related to tetanus and botulism causing bacteria ```

Question 28

Mycobacterium spp. (unusual example 1)

Answer 28

Gram positive rods, unusual cell wall- mycolic acid (lipolitic sugars) Impervious to gram-staining Need Ziehl-Neelsen acid-fast staining procedure: mycobacteria in red

Question 29

Mycobacterium spp. examples

Answer 29

M. tuberculosis M. leprae -first bacteria to be clinically associated with a disease (leprosy) -Leprosy-Hansens disease

Question 30

Leper colonies

Answer 30

Leper colonies persisted until relatively recently in poorer countries, only 1 remaining in Europe (Romania - people stay there now by choice) Treatable with antibiotics- Dapsone and rifampicin NOT thalidomide

Question 31

Chlamydia (unusual example 2)

Answer 31

``` C. trachomatis Extremely unusual life cycle: -elementary body facilitates spread -reticulate body- intracellular replication Small- 0.4 microns STI -urethral and vaginal infection -conjunctivitis - trachoma -infertility (ectopic pregnancy) -asymptomatic carriage important in spread ```

Question 32

Flagellum

Answer 32

Spins around moving electrons across the membranes so can move around Electric motor built from scratch in membranes

Question 33

The carrier state + 2 examples

Answer 33

Asymptomatic carriage of pathogenic bacteria | Examples: gonnorhoea, chlamydia

Question 34

Why is the carrier state a problem?

Answer 34

Important in disease transmission esp for gon, HIV, and typhoid- gall bladder- famous example Case of Thypoid Mary - Salmonella typhi - thyphoid fever -small % remain in gall bladder --> faeces -so can transmit with poor hygiene (working with food also dangerous)

Question 35

Viruses

Answer 35

Obligate intracellular parasites Cause of major world epidemics: e.g. H1N1: 1918 Flu 20 million deaths, HIV Unable to reproduce without host factors Viral genome uses host to encode viral proteins

Question 36

Basic viral structure

Answer 36

Nucleic acid encapsulated by proteinaceous capsid Varying shape and symmetry Some further coated with lipid coat - enveloped e.g. HIV

Question 37

Lytic life cycle

Answer 37

Attach, invade, replicate, break out

Question 38

Viral latency

Answer 38

Infection does not necessarily result in lytic cycle 1. Incorporation into genome – retrovirus 2. Latent infection of host cell away from site of infection e.g. Herpes, Varicella zoster

Question 39

Retroviral replication + example

Answer 39

mRNA --reverse transcription--> DNA --> into nucleus, integration into host genome --transcription--> mRNA --> viral proteins and RNA genome e.g. HIV sits in CD4 cells

Question 40

Latent infection vs re-activcation

Answer 40

Latent e.g. Herpes simplex virus in response to mild pharygitis fever, varicella (chickenpox) Leads to recurrence Cold sore due to fever, sunlight, menstruation and zoster (shingles) due to age, immunocompromise and local injury

Question 41

Thalidomide

Answer 41

Removes symptoms but not disease | Can lead to people being born with malformed limbs

Question 42

Bacteriophage

Answer 42

Bacteria eaters Capsid head, tail and fibres Most numerous organisms on earth !!!- viruses Attack and kill bacteria- like cold virus attacks you They live in your mouths - isolated recently

Question 43

Prions

Answer 43

Heat resistant, filterable, stick to instruments Can be detected in tonsils... but not outside lymphatics so far in humans- but in animals... Scrapie, BSE, CJD (familial, variant and sporadic) Normal PrPC converted into ‘Rogue’ PrPSC Aggregate into long fibers and amyloid plaques

Question 44

Prion example

Answer 44

KURU - Papua New Guinea kuru : "trembling with fear" in Fore language Fatal brain disorder First symptoms are unsteady gait, tremors, and slurred speech Epidemic during the 1950s-60s among the Fore people

Question 45

Prions likely transmission

Answer 45

via Brain tissue

Question 46

KURU - how and why?

Answer 46

Ritualistic cannibalism Funeral rituals: -Fore cooked and ate their dead relatives. ‘the mortuary practice of consumption of the dead and incorporation of the body of the dead person into the bodies of living relatives, thus helping to free the spirit of the dead’ Brains eaten mostly by the Fore women and children. Men rarely affected (up to 40-50yrs incubation…)