Week 8 Flashcards

Question

What are the 4 components of the type II secretion system?

Answer 1

cytoplasmic ATPase (GspE) IM platform (four membrane proteins - GspC, GspF, GspL, GspM) periplasmic pseudopilus (GspG) OM complex (GspD) aka ‘secretin’

Answer 2

Type II Secretion System (T2SS) consists of 12-15 protein, called general secretion pathway (Gsp) proteins in enterotoxigenic Escherichia coli.

Answer 3

In other bacteria GspC and GspD interact to insert the substrate protein into the secretin channel, through which it is pushed in piston-like as the pseudopilus extends.

Answer 4

Twin-arginine translocation system

Answer 5

SecYEG transports unfolded proteins into the PM. Tat transports fully folded proteins into the periplasm

Answer 6

In free-living bacteria T2SS secretes enzymes that degrade compounds in the environment (including proteases, lipases, chitinases)

Answer 7

T2SS is required for virulence of some animal/human pathogens, e.g. Yersinia enterocolitica yts1E (ATPase-) mutants show reduced infection in mouse

Answer 8

Pectate lyase, endo- and exo- enzymes (at least 9 enzymes) Pectin acetylesterase Pectin methylesterase (2) Polygalacturonase Cellulase (2) Endoxylanase Protease (at least 4)

Answer 9

Multi-protein nano-machine, structurally related to bacterial flagella Transfers effector proteins from the bacterium into the host cytoplasm

Answer 10

Hexameric ATPase (InvC) Sorting platform (SpaO, OrgA,OrgB) Secretin (InvG) Needle (PrgI)

Answer 11

Effectors Translocator proteins - forms pores in cellular membranes Class 1 and 2 chaperones which binding and folding proteins

Answer 12

Shigella flexneri T3SS effector IpaB induces apoptosis in macrophages ipaB mutant has 0% cytotoxity compared to ~70% cytotoxicity in wildtype Shigella flexneri

Answer 13

Several Hrp proteins form a pilus through which effectors (including Avrs) are translocated

Answer 14

Seen with immuno-gold labelling of effector AvrPto

Answer 15

Proteases and Ubiquitine ligase shows that they have a function of degredation

Answer 16

AvrBs3, PthA, AvrXa7 and related proteins from Xanthomonas species make up the TALE family TALE: transcription activator-like effectors Exhibit sequence-specific DNA binding Act as transcriptional activators in the plant cell nucleus

Answer 17

Each 33-35 amino acid repeat binds a single nucleotide. Specificity is determined by a two amino acid sequence. HD binds C, NN binds G, NG binds T, NI binds A (H,D,N,G,I are amino acids)

Answer 18

Xcv AvrBs3 targets Bs3 gene in pepper which is a resitance gene

Answer 19

Detects the presence of flagella Greats a signalling cascade which triggers immunity-related transcription PAMP-triggered immunity

Answer 20

AvrPto AvrPtoB AvrPphB

Answer 21

AvrPtoB causes degradation of FLS2 by tagging it with ubiquitine

Answer 22

Agrobacterium tumefaciens

Answer 23

Type 4 secretion system inserts T-DNA found in the Ti Plasmid into wounded cells and moves into nucleus, integrating randomly into a nucleus. This induces uncontrolled cell division --> crown gall

Answer 24

Produce unusual amino acids - Octopine and Nopaline (Opines) which is an energy source only the bacteria can use

Answer 25

LB: left border repeat; RB right border repeat: (C/T)GGCAGGATATA(T/A)C(A/(A/G)TTGTAA(A/T)T aux: auxin biosynthesis genes cyt: isopentyl transferase (involved in cytokinin biosynthesis) tm1: tumour size regulation ocs: octopine synthase

Answer 26

VirA and VirG sense chemicals from wounded plant cell Expression of virulence proteins ss-T-DNA forms a complex VirD2 which is transported through a pore by a VirB protein into plant cell The T-DNA integrates into the host DNA

Answer 27

Extracellular polysaccharide (EPS) Form a capsule around most bacterial cells Used to hides cell surface molecules

Answer 28

Exopolysaccharide required for virulence of some animal pathogens, e.g. Klebsiella pneumoniae K antigen (capsular polysaccharide): Bacteria mixed with polymorphonuclear leukocytes (PMNL) Bacteria which lacked capsular polysaccharide were quickily killed off (within 30 mins), wildtype increased in number over 90 mins

Answer 29

Exopolysaccharide (= extracellular polysaccharide, EPS) is required for virulence of some plant pathogens, e.g. Xanthomonas campestris pv. campestris (Xcc): Capsule minus bacteria died off after 3 days compared to capsule plus which increased in number over 3 days

Answer 30

EPS suppresses Ca2+ signalling and thus the expression of plant defence genes like PR1.

Answer 31

The B subunit of the toxin binds to GM1 gangliosides on the surface of gut epithelial cells. The A subunit is internalised, binds to a G protein and activates adenylate cyclase. Converts AMP to cAMP Increased intracellular cyclic AMP levels over activate protein kinase A. PKA phosphorylates cystic fibrosis transmembrane conductance regulator (CFTR) causing loss of Cl-, Na+, K+, and HCO3− and H2O from the cell

Answer 32

Toxin, Pathovar, structure, target/action, symptoms Syringomycin, syringae, Cyclic lipodepsipeptide, Pores in PM, Necrosis Syringopeptin, syringae, Cyclic lipodepsipeptide, Pores in PM, Necrosi

Answer 33

Toxin, Pathovar, structure, target/action, symptoms Tagetitoxin, tagetis, Hemithioketal, Inhibitor of chloroplastic RNA Pol, Chlorosis Tabtoxin, tabaci and others, B-lactam dipeptide, Inhibitor of glutamine synthase, chorosis

Answer 34

Mimics of the plant hormone jasmonic acid Suppresses stomatal closure (a consequence of PTI), by forcing them open to allow for bacteria to enter leaf

Answer 35

Polyketide and cyclised amino acid

Answer 36

Glycinea impacts soybeans and others

Answer 37

Poisoning by mushroom

Answer 38

Poisoning by fungi (on other food stuffs)

Answer 39

Mycetism, results from the ingestion of a mushroom that contains preformed toxic metabolites Examples include ibotenic acid from Amanita muscaria and amatoxins from Amanita phalloides (Death cap)

Answer 40

A. muscaria produces ibotenic acid. This is an unstable thermolabile amino acid which can be decarboxylated to muscimol. ibotenic acid activates the glutamate receptor Muscimol activates the gaba receptor Both affect neurotransmission signalling

Answer 41

Symptoms similar to acute alcohol intoxication. Victim staggers, becomes delirious and loses consciousness. Death results in only 1% of cases, but when it does occur it is from respiratory failure. Muscimol has insecticidal properties; the common name for this fungus is the fly agaric because it was used to kill flies.

Answer 42

Amanita phalloides produces amatoxins There are at least 9 known amatoxins Among the most deadly poisons in nature α-Amanitin is a potent inhibitor of RNA polymerase II. It causes kidney failure, liver failure, coma and death. One mushroom or less may be fatal.

Answer 43

Treatment needs to be quick, even before the mushroom has been identified. Evacuation of the gastrointestinal tract is performed by inducing vomiting, stomach lavage/ and or enemas. Carbon may be given to absorb toxins. Kidneys and liver function are monitored

Answer 44

This is the intoxication following ingestion of fungi producing toxins (mycotoxins) when growing on foodstuffs. Associated with a specific food. Seasonal, non-transmissible and unresponsive to drug and antibiotic treatment. >100 species of filamentous fungi are known to produce mycotoxins

Answer 45

In 1960 more than 100,000 Turkeys died within a few months in a 100 mile radius around London. The new disease was called Turkey X It was caused by aflatoxins produced by Aspergillus flavus, present in the peanut meal used in turkey feed. Aflatoxins are the most dangerous mycotoxins, mainly effecting animals

Answer 46

The feed had been prepared with contaminated peanut meal from which a mycotoxin was extracted. Most reports of aflatoxins refer to stored foodstuffs such as mouldy peanuts, cottonseed, coconuts and corn. They have been found in dried fermented fish and identified in the milk of animals eating contaminated feed.

Answer 47

There are four principle aflatoxins B1, B2 G1 and G2. They are produced by a range of fungi including Aspergillus flavus, Aspergillus parasiticus, Aspergillus ostianus, plus other species of Aspergillus and Penicillium.

Answer 48

Children are more sensitive than adults and development may be impaired. The characteristic effect of high-level aflatoxin poisoning is liver damage – necrosis, cirrhosis and carcinoma. Aflatoxins intercalate into DNA, causing DNA damage (alkylation) and chronic exposure increases risk of cancer, especially of the liver and gall bladder.

Answer 49

Approximately 300 species of fungi cause human disease. Most are soil saprophytes. They are facultative parasites, infecting hosts when the opportunity arises. Combined, they kill more than either malaria or TB

Answer 50

Disease, location, estimated life threatening infections, mortality rates Cryptococcosis (Cryptococcus neoformans), worldwide, >1,000,000, 20-70%, opportunistix invasive mycoses Penicillious (Penicillium marneffei), Southeast Asia, >8,000, 2-75%, endemic dimorphic mycoses

Answer 51

In 2022 the WHO released the first list of fungal pathogens of particular concern eg critical group includes

Answer 52

In 2022 the WHO released the first list of fungal pathogens of particular concern eg critical group includes Cryptococcus neoformans

Answer 53

Dimorphism, is where fungi can exist in tissues as either single cells (yeast) or a mycelial form. Dimorphic fungi which are pathogenic in animals are more likely to exist outside the host in a mycelial form. Conditions inside the host cause the conversion of the mycelium to the yeast form. eg Elevated temperatures, High CO2 and low O2, Levels of nutrients

Answer 54

Superficial Cutaneous Subcutaneous Systemic

Answer 55

Fungi which cause cutaneous damage are called dermatophytes

Answer 56

Tinea corporis, ringworm. Lesions are red, raised, itchy, and often circular (hence ‘ringworm’). Tinea pedis, athletes foot. The most common type. Typically found in the toe webbing.

Answer 57

Trichophyton rubrum, Trichophyton mentagrophytes Epidermophytom floccosum

Answer 58

The fungi gain entry to the subcutaneous tissue by wounds, typically scratches caused by thorns. These diseases tend to be prevalent in rural and tropical regions. Localised and form abscesses called mycetomas. Examples include Sporothrix schenckii, which occurs in farmers and gardeners Tissue damage is variable, but can be very disfiguring.

Answer 59

Sporothrix schenckii There have also been outbreaks among building workers exposed to heavily infected timbers.

Answer 60

The fungus spreads from one internal organ to another often via the bloodstream Frequently systemic mycosis originates in the lungs by the inhalation of spores. If a vital organ such as the brain becomes involved it frequently leads to death.

Answer 61

This is based on clinical observation and laboratory investigation. Specimens should be taken from as many sites as possible, including urine and sputum. A lung biopsy may need to be performed for pulmonary mycotic infections.

Answer 62

Most pathogenic fungi are easy to grow in artificial culture. The agar medium most commonly used is Sabouraud’s glucose agar and 4% malt extract agar

Answer 63

For dimorphic fungi agar such as brain-heart infusion agar and blood agar are effective for yeast phase growth.

Answer 64

A variety of treatment and staining techniques can be used. Add a drop of CSF to a drop of India Ink

Answer 65

Capsule is seen as a clear halo around the yeast Round yeast with mucopolysaccharide capsule

Answer 66

Serological (antibody-based) methods are used to detect fungal antigens Types of test include: immunodiffusion enzyme-linked immunosorbent assay (ELISA)

Answer 67

Organism-specific primers are employed. Care must be taken in the interpretation of results, as the sensitivity of PCR may lead to false positive results.

Answer 68

Causes aspergillosis Very effective pathogen in immunocompromised patients and patients with lung disease (including cystic fibrosis, tuberculosis, asthma).

Answer 69

Initial siter of infection is the lungs. A type of aspergillosis in which a ‘fungus ball’ (compact ball of mycelia) may form in an existing cavity in the lung, particularly old tuberculosis lesions May cause no symptoms or may cause bleeding (which can be severe or even fatal). Systemic infection occurs via the bloodstream – the fungus can disseminate to the brain, liver and kidneys. Liver and kidney failure can be rapid and may be fatal.

Answer 70

Most common fungal infection Most Candida species are commensals – part of the human GI and skin microbiomes in healthy people There is a concerning emergence of multi-drug resistant Candida strains Oral thrush is common in new-born babies, resulting from infection during birth

Answer 71

Causes candidiasis when the immune system is weakened or the equilibrium of the microbiome is disrupted (e.g. by antibiotics)

Answer 72

Survives phagocytosis by forming hyphae and puncturing the cell – also used to disrupt epithelial cells. When get to blood stream in gut the tranform into yeast form and spread arounf the body It is a very effective pathogen in immunocompromised patients Easily adapts to different nutrient availabilities It forms biofilms, particularly on implanted foreign surfaces, helping it survive internally

Answer 73

Cryptococcus species are yeasts that cause cryptococcosis HIV/AIDS sufferers are particularly at risk The fungus can persist for years in the lung, reactivating only upon weakened immune surveillance

Answer 74

Infection occurs from inhalation of particles from soil or bird droppings – colonises the lungs Easily disseminates via the blood to the central nervous system (cryptococcal meningitis), and also encephalitis

Answer 75

Brain abcesses Focal absesses (lung and liver) Endocarditis Retinitis

Answer 76

It protects from phagocytosis and can even trigger macrophage death This is suggested to be the way Cryptococcus crosses the blood-brain barrier, although the actual mechanism is not yet confirmed

Answer 77

The treatment is often difficult, since both the host and the parasite are eukaryotic. Hard to attack the fungus without damaging the host cells. There are very few antimycotic compounds which can be used in human treatment.

Answer 78

Polyene macrolide antibiotics are produced by Streptomyces spp and include amphotericin B, nystatin and pimaricin. They have in common a large ring structure. Bind specifically to the sterol in the fungal membrane (ergosterol). They increase the permeability of the plasma membrane --> leakage of the cellular constituents, lysis and cell death

Answer 79

Amphotericin B is administered intravenously in a bile salt suspension and is active against most fungi. It is used to treat systemic infections and severe superficial mycosis. At low concentrations this antibiotic can also boost the immune system. Unfortunately in higher concentrations it is toxic to the kidneys

Answer 80

Nystatin is too toxic to be administered intravenously, and cannot be absorbed by the digestive tract it is therefore along with pimericin used topically to treat superficial infections such as thrush (Candida albicans).

Answer 81

Of the newer anitifungal drugs the imidazoles and the triazoles are the most effective. They have a broad spectrum and effect the ergosterol in the plasma membrane.

Answer 82

Ketoconazole can be absorbed through the gastrointestinal tract and inhibits the synthesis of ergosterol. Another advantage is that it is non-toxic to human cells

Answer 83

Despite these new drugs Amphotericin B still remains the drug of choice when faced with life-threatening mycosis.

Week 8 Flashcards

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