PoD - Medical Microbiology Flashcards
1
Q
what are the two types of cells?
A
- prokaryotes (no nucleus present - bacteria)
- eukaryotes (nucleus, more complex cell wall)
2
Q
what are the main microbial causes of infection?
A
- bacteria (prokaryotic) - round, spiral or rod shaped single celled organism
- viruses (unclassified) - a unique, acellular, metabolically inert organism that replicate within living cells
- fungi (eukaryotic) - saprophytic and parasitic spore-producing eukaryotic typically filamentous organisms; including moulds, yeasts
- parasites (eukaryotic) - an organism living within another organism
- prions (unclassified) - protein that resides on the surface of brain cells. Becomes pathogenic via mutation or an infected tissue - accumulation causes disease
3
Q
what types of specimens are taken?
A
- sterile sites - brain, CSF (if micro-organism is detected = medically significant)
- non-sterile sites - skin, intestine, stomach
4
Q
where are common specimens for bacterial cultures?
A
- urine - UTI
- sputum - respiratory TI
- throat - tonsillitis
- swabs - wound
- faeces - bacterial diarrhoea
- blood culture - septicaemia
- CSF - meningitis
- aspirate of pus - abscess
5
Q
what are common healthcare associated infections?
A
- Staphylococcus aureus and clostridium difficile
- MRSA, VRE are multi-drug resistant organisms
6
Q
what are the common characteristics of bacterium?
A
- capsule, cell wall, cytoplasmic/inner/plasma membrane, cytoplasm, ribosomes, singe chromosome, flagellum, fibriae
7
Q
differences between gram positive/negative bacteria
A
- gram +ve bacteria have plasma membrane, periplasmic space and thick peptidoglycan layer
- gram -ve bacteria have plasma membrane, periplasmic space, thin peptidoglycan layer and thick outer membrane (thick LPS layer)
- gram +ve = stained purple
gram -ve = stained pink/red
8
Q
what is on the cell surface of bacteria?
A
- penicillin binding proteins (PBP) cross links
- peptidoglycan (contribute to strength and shape of bacterium)
- lipopolysaccharide (over-expression of LPS can illicit strong immune response
9
Q
how are spores formed?
A
- mainly formed by gram +ve bacteria
- bacteria divide symmetrically and rapidly
- spores form to resist environmental stresses, however when environment returns to favourable conditions, the bacteria will continue to divide
10
Q
what is a plasmid?
A
- plasma has extrachromosomal information
- plasmids participate in process of conjugation (joins 2 bacterium)
- conjugation allows exchange of ‘genetic’ information - spread of antibiotic resistant genes
11
Q
what is a bacteriophage?
A
- virus that can eat up bacteria
- end plate binds to bacterium and tail fibres hold the virus in place
- inserts viral DNA into the bacterium and takes over bacterium DNA machinery
- viral DNA is produced, lots of phages are synthesised and burst out of the bacterium
12
Q
what is a virus?
A
- non-cellular, genetic element that cannot replicate independently of a living (host) cell
13
Q
what is a virion?
A
- a virion is required for transmission from one host cell to another - wrapped in a capsid
- the capsid is the infective form
- once the capsid binds to the target cell, the virion uncoats, shredding the lipid envelope and eventually the protein capsid
- there is replication of genomic nucleic acid (via mRNA synthesis)
- newly synthesised nucleic acid can go on to create viral proteins or more visions
14
Q
how are viruses transmitted?
A
- blood, sexual, faecal-oral, airborne, close contact, zoonotic
- host range - some viruses may only infect humans but others infect other animals
- could be transmission of a novel virus to humans or co-infection of human and animal/bird strains in one organism may lead to recombination –> generation of new strain.
15
Q
what is viral latency?
A
- following primary infection, some viruses lie dormant in the cell
- the full viral genome is retained in the host cell, but expression is restricted
- no viral particles are produced
- however, reactivation or viral replication can occur and cause disease
16
Q
are viruses and cancers associated?
A
yes
- a number of viral infections can lead to cancer
- modifies cell cycle control, prevention of programmed cell death, persistent reactive oxygen species production (damage)
17
Q
what anti-viral therapies used for?
A
- all antiviral agents are virtustatic (stops replication of virus)
- as viruses use host cell enzymes to replicate, there are limited viral proteins that are targets for antiviral drugs
- tend to be side effects
- antivirals used for prophylaxis (prevent infection), pre-emptive therapy (evidence of infection detected but before symptoms are apparent), suppressive therapy (keep viral replication below rate that causes tissue damage)
18
Q
how can viruses be prevented?
A
- immunisation
- prophylactic treatment
- infection prevention and control measures (isolation of symptomatic patients, PPE, safe use of sharps)
- blood/tissue/organ screening
- antenatal screening
19
Q
what is a parasite?
A
- an organism that lives in or on another organism, deriving nutrients at the expense of the host
20
Q
what is a vector?
A
- an organism which acts as an intermediate host for a parasite. The vector transmits the parasite to the next host
21
Q
how are parasites classified?
A
- protozoa (malaria, amoebae, flagellates)
- helminths (roundworms, tapeworms, fluke)
- ectoparasites (lice, ticks, mites)
22
Q
what are protozoa?
A
- protozoa are single celled organisms that live in humans
- protozoa live in human intestine = spread via faecal-oral route
- protozoa that live in blood or tissue = insect vector
23
Q
how does the protozoan infection - malaria - occur?
A
- malaria is a mosquito-borne disease caused by a parasite called plasmodium
- sporozoites injected by mosquito
- travel through blood and enter liver
- mature in liver and re-enter circulation as merozoites
- invade red cells, multiply and lyse cells - invade more RBCs
- can be prevented via awareness of the risk, bite prevention, antimalarial medication and prompt diagnosis
24
Q
what are helminths?
A
- worms
- nematodes (roundworms), cestodes (tapeworms), trematodes (flatworms)
25
what happens in nematode infection?
- ascaris lumbricoides (roundworm)
Ingested eggs hatch in the intestine --> ova seen in faeces by microscopy
often asymptomatic, mass of worms can obstruct small intestine
26
what happens in cestode infection?
- taenia saginata (beef)/solium (pork)
larval cysts ingested by eating raw or undercooked meat
ova in stools on microscopy
pork tapeworm cysts can form outside of the gut and cause problems in the brain
27
what happens in trematode infection?
- schistosomiasis (can affect bladder or intestine)
| can lead to complications such as liver failure and bladder cancer if left untreated
28
how are parasites diagnosed?
- Blood microscopy – thick & thin blood films for malaria
- Stool microscopy – enteric pathogens (ova, cysts or parasite itself) may be present in faeces
- Worm infection usually accompanied by excess levels of eosinophils and elevated IgE levels
- Indirect testing – serology (immune testing), rapid diagnostic tests
29
what is a fungus?
- a chemo-organotrophic eukaryote that lacks chlorophyll and forms spores
- cell wall contains polysaccharides and absorbs nutrients
- 3 groups can cause disease in humans - basidiomycetes (has spores), ascomycetes (contained in sac), zygomycetes (round)
30
what is a yeast?
- fungi that favour a unicellular habit
- significant cause of non-fatal diseases (athletes foot, thrush)
- enzymes degrade and use keratin as a nutrient source
- dermatophytosis - moulds that degrade keratin as a nutrient source
