Bacterial Pathogenesis Lecture 20

Front 1

Colonisation is mediated by external structures called adhesins. what are some egs of adhesins?

Back 1

pili/fimbriae
afimbrial adhesins
capsules

Front 2

the tip of pilus can be made up of ____________ or _____________ which confers host specificity

Back 2

pilin
proteins

Front 3

pili can be found either at one end of cell (___________) or ____________

Back 3

(polar)
petrichous

Front 4

afimbrial adhesins are organised protein structures
t/f

Back 4

false. afimbrial adhesins are proteins structures that are not organised into pili/fimbriae.

Front 5

what is an example of afimbrial adhesin?

Back 5

bordetella pertussis

Front 6

what is the bordetella adhesin made up of

Back 6

filamentous haemagglutinin

Front 7

casules adhere to cell surfaces because....?

Back 7

they have a sticky surface

Front 8

what are capsules made up of

Back 8

polysaccharide

Front 9

what are the 4 functions of bacterial invasions

Back 9

1/ they are obligate intacellular parasites, meaning they have to infect cell to replicate
2/escape normal flora so they dont have to compete for nutrients
3/hide from immune response
4/disseminate into deeper tissues (find niche)

Front 10

Giardia lamblia is transmitted by ....?

Back 10

zoonosis

Front 11

giardia lamblia has two stages in its life cycle what are they

Back 11

cyst- infectious and dormant
trophozoite - actively growing, disease causing

Front 12

how does trophozoite attach to cell surface

Back 12

surface lectins

Front 13

bacteria always invades host cell true or false

Back 13

false

Front 14

infectivtiy assay is the method of quantitating infectious virus by plaque formation. what are the steps involved

Back 14

growing cells in dish
adding virus and agar layet
wait several days
wash and stain

Front 15

what are the steps involved in assembly and release for non-enveloped and enveloped viruses?

Back 15

non-enveloped:spontaneous assembly of capsi poteins around nucleic acid genome, proteolytic cleavage, virions accumulate in cytoplasm/nucleus and cell lyses.

Front 16

what are involved in assembly and release of enveloped virus?

Back 16

1) budding from cell surface. viral envelope glycoproteins accumulate in plasma membrane, capsid proteins and nucleic acid condense directly adjacent to cell membrane, membrane surrounding nucleocapsid then bulges out and becomes 'nipped off'
2) cellulor secretory pathway virus particles bud into golgi-derived vesicles and are released to outside of cell when transport vesicle fuses with cell membrane.

Front 17

what can halt the infectious process of viruses?

Back 17

antibody, killing of infected cell by CTL, Nk cells , Ab mediated mechanisms, blocking replication cycle by antiviral drugs, IFN- anti-viral cytokines

Front 18

what cytopathic effects are commin in virally infected cells?

Back 18

1) inclusion bodies which represent accumulated virions or unassembled viral components
2) syncytia- fusion of neighbouring cells, formation of multi-nucleate cells
3) some viruses encode oncogenes: uncontrolled proliferation of infected cell and tumour devt

Front 19

what properties do viruses which infect intestinal tract have?

Back 19

1) hardy- can withstand bile and acid
2) no envelope
3) can replicate extensively in intenstinal tract and cause diarrhea or use this site to gain entry to body to cause generalised disease.

Front 20

an example of a virus that infects the alimentary tract and goes on to spread systemically is...?

Back 20

Hep A virus

Front 21

What are the steps involved in PCR?

Back 21

1. target DNA containing the sequence to be amplified is heat denatured to make it ss
2. temperature is lowered so that primers can anneal via H bonds to the DNA on both sides of target seq
3. DNA pol extends the primers and synthesizes copies of the target DNA seq using dNTPs.

Front 22

what cytocidal effects do viruses have on cells?

Back 22

1. necrosis- cell death due to viral replication
Rotavirus kills enterocytes while poliovirus destroys the neurons in spinal cord.
2. viruses can trigger apoptosis- programmed cell death to prevent viral replcation

Front 23

what non-cytocidal effects do viruses have on cells?

Back 23

some viruses do not directly kill cells but lead to persistent and latent infections. cells may lose their ability to perform particular functions (rhinovirus and cilial stasis).
cells may become transformed, virus replication may affect cellular version of oncogene- tumor devt

Front 24

why do viruses make us feel sick?

Back 24

1. viral damage to tissues and organs
2. immunopathology(fever, inflammation, kill infected cells eg liver damage in hepatitis) and immunosuppression. (HIV)

Front 25

how does bacteria avoid complement factors?

Back 25

1. capsules to prevent complement activation
2. Neisseria gonorrhoeae generate serum resistance. these bacteria have modified lipooligosaccharides on their surface that interfere with the proper formation of MAC during complement cascade.
3. bacteria can bind to AB at Fc end so complement cannot bind to Fc. Staphylococcal protein A and G of S. pyogenes interferes with AB mediated opsonization by binding to Fc part of Ig

Front 26

how does bacteria avoid detection of ABs?

Back 26

1. remain inside host cells.
2. host mimicry eg N. meningitidis capsule type B is made up of sialic acid
3. coat with host proteins- allowing binding of Fc end of AB with FcR
4. colonise priveldged site that has poor access of ABs. - conceal antigens
5. antigenic variation- mutation and gene switching

Front 27

how does bacteria avoid phagocytosis?

Back 27

1.prevent opsonisation
2. prevent contact with phagocyte - capsule

Front 28

how does bacteria prevent opsonisation?

Back 28

1. prevent complement activation (S. pyogenes breaks down C5a)
2. prevents AB binding
3. coating with host proteins (S.aureus produce protein A interfering with AB mediated opsonization by binding to Fc portion of Ig)

Front 29

what two ways are used by bacteria to survive in phagocytes?

Back 29

inhibit phagolysosome fusion
escape into cytoplasm
resist killing by producting antioxidants and inhibiting respiratory cell burst.

Front 30

what is an example of bacteria that can inhibit phagolysosome fusion?

Back 30

chlamydia
salmonella tryphimurium

Front 31

how do pathogens resists killing by the respiratory burst?

Back 31

1. produce catalase- breaks down toxic products
2. prevent activation of respiratory burst
eg salmonella tryphymurium prevents assembly of NADPH oxidase

Front 32

define epidemiology

Back 32

the study of occurrence and distribution of disease in a population

Front 33

a disease that occurs occasionally and at irregular intervals

Back 33

sporadic disease

Front 34

when a disease is maintained at a low level, steady frequency at a moderately time interval

Back 34

endemic ( common cold)

Front 35

Whats the difference between pandemic and epidemic?

Back 35

Pandemic is when there is an increase in disease occurrence within a large population over a very wide region (H1N1) while an epidemic is an outbreak affecting many people at once eg influenza

Front 36

how may animals transmit diseases (zoonosis) to humans?

Back 36

1. when animals come into direct contact with diseased animal flesh- inoculation of infected animals to human's broken skin
2. drinking contaminated cow's milk
3. inhaling duct particles contaminated by animal excreta or products
4. eat insufficiently cooked infected flesh

Front 37

what is a mechanical vector

Back 37

pathogen is carried on the body surface of a vector. carriage is passive with no growth during transmission eg shigella and Yersinia pestis

Front 38

what is a biological vector?

Back 38

pathogen goes through a morphological / physiological change within the vector - malarial parasite

Front 39

what are some indirect contact ways of transmission of pathogens?

Back 39

fomites, vectors, water/food

Front 40

staphylococcal food poisoning has short/long incubation period

Back 40

short. food poisoning is due to preformed toxin in food while infection is due to bacteria multiplying in host/food

Front 41

salmonella food infection has a __________ incubation period

Back 41

long

Front 42

norovirus is transmitted by......?

Back 42

contaminated food or liquids, aerosols and fomites

Front 43

how is rotavirus transmitted?

Back 43

1. mether to fetus
2. person to person
3. water and food (resistant to chlorination)
4. faecal-oral route
5. asymptomatic shedding
6. nosocomial

Front 44

there is a vaccine for norovirus but not for rotavirus t/f

Back 44

false. there is a vaccine for rotavirus as immunity follows after infection but no long term immunity for norovirus.

Front 45

immunity from rotavirus can be attained after 2 years old.

Back 45

true

Front 46

how do you differentiate staphylococcal aureus from staphylococcal

Back 46

it is positive for a slide coagulase test. oxalated plasma is added to one of the two saline suspensions prepared on both sides of a slide. positive reactions show clumping

Front 47

streptococcus pyogenes and staphylococcus aureus. which test differentiates between the two

Back 47

catalase test which is positive in staphylococci (bubbles seen) while shown -ve

Front 48

how do you identify streptococcus pneumoniae?

Back 48

sensitive to optochin. when incubated aerobically at 37 degree celcius, greening or parial haemolysis results

Front 49

is S. aureus and streptococcus pyogenes sensitive to penicillin

Back 49

S. aureus is resistant but strep. pyogenes is sensiive to penicillin hence S.pyogenes can be treated with penicillin.

Front 50

an example of a bacteria that produces toxins and pili

Back 50

Etnterotoxigenic Escherichia coli (ETEC)

Front 51

Streptococcus pyogenes produce only immediate damage

Back 51

false- there is post streptococcal hypersensitivity

Front 52

what happens in penumonia?

Back 52

rapid multiplication of Streptococcus pneumoniae
invasion of alveolar tissues
in flow of fluid into alveoli and gas exchange canonot occur
alveolar inflammation and alveolar fills with fluid
altered permeability of cells and entry of fluids
inflammatory response reduces lung function
bacteria spread by blood

Front 53

influenza is part of the __________ family

Back 53

orthomyxoviridae

Front 54

rhinovirus is part of the _________________ family

Back 54

picornaviridae

Front 55

why do some vaccines fail?

Back 55

1. wrong sort of immune response
2. responses too low.
3. respones are induced to wrong target
4. immature immune system
5. non-responders in population
6. immunosuppression
7. immune evasion- antigenic variation
8. attentuated vaccines can cause full-blown illnesses in indiv whose immune system is compromised
9. attenuated virus can mutate in ways that restore virulence

Front 56

how is communication between microbes carried out?

Back 56

1. quorum sensing: cell to cell communication mediated by small signals
2. biofilm: how microbes create their own microenvironments and niches . organised microbial systems consist of layers of microbial cells associated with surfaces

Front 57

what are some factors that can affect normal flora?

Back 57

climate/geography
age
hospitalisation
personal hygiene
diet
medical treatments/interventions

Front 58

what are some benefits of the normal flora?

Back 58

1. supplies some metabolites like Vit D and K
2. GIT physiology- digestion eg modify bile acids
3. prevents establishment of pathogens by outcompeting pathogens for nutrients
4. stimulates devt of immune system as microbiota is controlled by the innate immune response.

Front 59

how is diagnosis of syphilis carried out?

Back 59

dark ground or flourescent microscopy on vesicle fluid, Serology screening then specific test
Organism is not cultured

Front 60

how is diagnosis of gonorrhoeae done?

Back 60

gram staining
culture on selective medium
penicillin resistance
PCR on urine sample

Front 61

how is herpes treated

Back 61

acyclovir

Front 62

is the incubation period of herpes long or short?

Back 62

short

Front 63

__________ is a small DNA virus that has >60 serotypes

Back 63

papillomavirus

Front 64

what can be used to treat chlamydia?

Back 64

azithromycin - single dose
doxycycline- 7 days

Front 65

what are the complications that chlamydia is associated with

Back 65

pelvic inflammatory disease and infertility

Front 66

which STIs have high incidence of asymptomatic carriers?

Back 66

chlamydia, gonorrhoeae

Front 67

_____________ has an unusal developmental cycle- retinaculate and developmental bodies

Back 67

Chlamydia trachomatis

Front 68

what defines someone as HIV positive?

Back 68

1. test positive for HIV antibody
2. CD4 t cell count <200/ml whole blood
3. variety of oppurtunistic fungal, protozoal, bacterial or viral infection

Front 69

how is HIV diagnosed?

Back 69

detect antibody by EIA
confirm by Western blot (immunoblot)
window of 1-3 mths before AB seen

Front 70

How is HIV acquired?

Back 70

1. sexual intercourse
2. risk higher for anal sex
3. Injecting drug user
4. perinatal
5. blood transfusion, organ transplant, artificial insemination

Front 71

why is it difficult to control HIV?

Back 71

1. long asymptomatic IP
2. no effective vaccine because vaccines evades immune system
3. chemothreapy can reduce viral loads but does not eliminate completely
4. cost and unpleasant side effects of chemo

Front 72

how is pure culture of bacteria cultivated?

Back 72

1. streak dilution- streak plate where cells are picked up by a sterile wire loop and wiped off by streaking along surface of a solid medium.
2. spread plate: 1:10 000 dilution of bacterial culture in broth, pour 0.1ml onto surface of pre-poured agar: colonies appear only on surface
3. pour plate:1ml taken from 1:10000 dultion of culture in broth, mixed thoroughly with melted agar, cooled to harden and incubated: colonies appear abov and below

Front 73

what are some factors affecting bacterial growth?

Back 73

physical factors include pH, temp, oxygen conc, hydrostatic pressure, osmotic pressure, radiation, moisture

Nutritional factors includ availability of C, N, S, P , trace elements and vitamins

Front 74

spectrophotometer is used for..??

Back 74

measure bacterial growth by determining degree of light transmission through the culture.

Front 75

describe how temperature affects bacterial growth.

Back 75

obligate: organism must have specified environmental conditions
facultative: organism able to adjust and tolerate to envt condition but able to live in other conditions
bacteria can be classified to psychrophiles (15-20), mesophiles (25-40), thermophiles (50-60

Front 76

why do halophiles require sodium?

Back 76

1. cells require sodium to maintain a high intracellular K+ conc for enzymatic function
2. cells need sodium to maintain integrity of cell walls.

Front 77

what types of culture media are there?

Back 77

natural, selective, synthetic, complex, differential, enrichment

Front 78

what is a complex medium

Back 78

contains reasonably and familiar material but varies slightly in chemical composition from batch to batch

Front 79

selective medium- what is it and give an eg.

Back 79

encourages growth of some organisms but suppresses growth of others eg antibiotics

Front 80

differential medium- what is it and give an eg

Back 80

contains a constituent that causes an observable change - MacConkey's agar

Front 81

enrichment medium-what is it and give an eg

Back 81

contains special nutrients that allow growth of a particular organism that might not otherwise be present in sufficient nos. to allow it to be isolated and identified.

Front 82

how are obligate anaerobes cultured?

Back 82

all molecular O2 must be removed so agar plates are incubated in sealed jars containing chemical substances that remove O2 and generate CO2 or water

Front 83

what is a plasmid?

Back 83

circular, covalently closed DNA molecules that replicate independently from chromosome. they often dont carry genes that are essential to life of a bacterium in all envronments.

Front 84

what are the functions of plasmids?

Back 84

1. bacteria needs to be able to replicate quickly so to have non-core functions optional is a smart move
2. flexibility- huge range of functions not maintained by each cell so this significantly broadens niches available
3. plasmids can give DNA a selective advantage: protect against unwanted phages/transposons and for repair- DNA repair switched on same time as those for competence; recombination (mixing up of DNA)

Front 85

what is teh uptake of naked DNA by bacteria

Back 85

transformation

Front 86

what is transduction

Back 86

the accidental transfer of bacterial DNA by bacteriophages. during packaging of phage, some DNA included

Front 87

describe transposons.

Back 87

they can move between genera- (on phages or on plasmids)
range in size
contain indirect and direct repeats
target site may not be specific
seq varies from Tn to Tn but size will be characteristic of particular Tn
net result is that Tn appears in a different region of DNA - cut and inserted elsewhere, copied and inserted (replicative transposition)

Front 88

conjugation- what is it

Back 88

transfer of a plasmid from one bacterium to another by a F factor
1. bacteria attached to each other by pilus
2. two strands separate- one is transferred into the recipient
3. transfer happens thru a channel- tube that connects donor and recipient.
4. ssDNA is replicated
5. when replication is finished, the recipient cell is known as a transconjugant.