Microbiology

Question	Answer
What is the most common limiting factor for bacterial replication?	Iron availability
What is O-Antigen?	LPS
What is H-Antigen?	Flagella
What is K-Antigen?	Capsule (seen in G+ves consists of polysaccharide)
What is an advantage of a coagulase producing bacteria?	Coagulase converts fibrinogen to fibrin - bacteria will coat itself in fibrin and be more resistant to phagocytosis.
What do mycoplasma lack?	Cell wall
What are two examples of gram positive enterobacteria aci?	Strep and staph
What are two examples of gram -ve enterobacteria aci:	E.coli and salmonella
Name two gram negative protobacteria?	Proteus and Neisseria
What TLR does LPS act through to cause toxic shock?	TLR-4
Define antimicrobials?	Low molecular weight microbial metabolites which can kill/inhibit growth of susceptible bacteria.
Why do bacteriostatic antibiotics have lower risk associated with them than bacteriocidal?	Because when a bacteria is killed, they release lipid as they die which can lead to sepsis/toxic shock
How will action of antibiotic differ for anaerobic and aerobic E. coli?	Anaerobic E. coli lacks a specific oxidative transporter which makes gentamycin entry harder.
Why do bacteria in a biofilm have altered antibiotic efficacy?	Antibiotics cannot penetrate biofilm.
Why are UTIs easier to treat than bladder?	Because antibiotic free in urine will target UTI but can only access bladder via circulation.
Why might an abscess affect antimicrobial entry?	Pus may bind drugs so drain abscess first
How might menigitis affect drug distribution?	Decrease BBB barrier function (increases permeability) allowing entry of normally blocked drugs.
Why aren't aminoglycocides given orally?	Because they are absorbed by fecal material.
How are tetracyclines contraindicated in pregnancy?	Bound to proteins in milk?
For which group of antibiotics does rate of killing increase with concentration above MIC?	Aminoglycocides and Fluroquinolones (concentration-dependent)
How can rifampicins cause contraception to be ineffective?	They induce P450 pathway which increases metabolism of pill. Makes it have shorter half-life ==> bad.
What's another name for PBP?	Transpeptidase
What spectrum is penicillin G?	narrow
What ring is attached to beta lactam ring in penicillin?	5 sided
What ring is attached to beta lactam group in cephalosporin?	6 sided
In which type of bacteria (ie gram pos or neg) does the beta lactam require porin to access the cell wall?	Gram negative
Describe the classification of cephalosporins in terms of gram positives and negatives.	1st gen - target gram positives and few negatives 2nd gen - more gram neg, less gram pos 3rd gen - more gram neg, less gram pos 4th gen - used in human med only: more active against gram pos again
Name a cell wall antibiotic which is not a beta lactam? How is it administered and why?	Bacitran - applied topically or in ophthalmic preparations as it is nephrotoxic
which bacteria is polymixin derived from?	bacillus polymyxa
What is the only bacteriocidal ribosome binding Antibiotic?	Aminoglycocides
Which ribosomal binding antibiotics target the 30s region?	Aminoglycodies and tetracyclines
Which target the 50s region?	Chloramphenicol, Lincosamides, Macrolides and pleuromutilins.
Which ribosome binding antibiotic is excreted by the biliary system?	Tetracyclines
What bacteria is intrinsically resistant to lincosamides?	Facualative anaerobes due to methylation of 50s
In which animals can't you use lincosamides?	Not in herbivores, especially horses.
Which macrolide can be bacteriocidal at high doses?	erythromycin
Which disease can chloramphenicol not target?	Chlamydia
Which ribosome binding agent is exclusively veterinary use?	Pleuromutilins
How can resistance occur to ribosome binding agents?	Intrinsic: Methylation of subunit (binding site), lack of receptor/domain. Extrinsic: Possession of degradation enzyme
What is THF (dihydrofolate) important for?	THF is required for DNA synthesis in bacteria.
Which two antibiotics inhibit THF production?	Sulphonamide and Trimethoprim.
Which enzyme in particular does sulphonamide inhibit?	Dihydrofolate synthase so that PABA cannot be added to DHF to make THF
What is DNA gyrase?	It is what gives DNA strands the super-coiling effect. If you inhibit this, bacteria cannot function.
What group of antibiotics target DNA gyrase?	Fluoroquinolones.
Why can fluoroquinolones cause cartilage erosion in horses?	Because it has a high Vd and good penetration into CSF bones and cartilage.
Why do you give penicillin with clavulonic acid?	Clavulonic acid reduces beta-lactamase activity therefore reduces resistance to Penicillin.
What would you give commonly for a G+ve infection?	B-lactams (specifically penicillin G and 1st gen cephalosporins) or macrolides e.g. erythromycin.
What do you tend to use for G-ve spp?	Aminoglycocides but not gentamycin in production any because it has no MRL.
Name some broad spectrum antibiotics?	B-lactam, Sulphonamides, fluoroquinolones, tetracyclines.
What is SARSS?	suspected adverse reactions surveillance scheme
In what 3 circumstances would BS agents not have an effect?	Site of infection (e.g. endocarditis), nature of infection and if host is immunosuppressed e.g. host with FeLV)
When should you not use fluoroquinolones?	In horses <3yo --> Joint dz
What is the standard withdrawal period for meat when antibiotics have been given?	28 days.
What is the standard withdrawal period for milk if antibiotics have been given?	7 days.
What type of bacteria is intrinsically resistant to Vancomycin?	G-ve because they have an outermembrane.
Why are enterococcus resistant to cephalosporins?	Cephalosporins have low affinity to the enterococcus PBP
How does spontaneous resistance spread through a population of bacteria.	It is not transferred within bacteria, rather the resistant ones just outgrow the susceptible ones when challenged with antibiotic.
Name two ways in which bacteria can acquire resistance?	Conjugation or transformation between 2 closely related bacteria.
Give some examples of plasmid-mediated resistance?	B-lactamase enzymes, heavy metal resistance, aminoglycocide enzymes.
Name the three aminoglycocide modifying enzymes?	N-acetyl-transferase O-adenyl-transferase O-phospho-transferase
What is the most common form of aminoglycoside resistance?	Enzyme modification
Name 5 major superfamilies of the bacterial efflux transporters?	Major facilitator super-family (MFS), ATP-binding cassette superfamily (ABC), Small Multidrug resistant family (SMR), Resistance nodulation cell division superfamily (RND), Multi-antimicrobial extrusion protein family (MATE)
Which antibiotics can efflux?	Tetracyclines, aminoglycocides, fluoroquinolones, chloramphenicol, erthryomycin and some B-lactams
How are enterococci resistant to vancomycin?	Transposon mediated, the van gene hops about onto plasmids, aiding its transfer.
Give 2 examples of chromosomal mutations?	Mutation in DNA Gyrase inferring quinolone resistance, or mutation in PBP with lower affinity for B-lactam.
What is disc diffusion also known as?	Kirby-Bauer
How long would you incubate a kirby-bauer agar plate for?	37oC for 24hr.
Name 2 experiments to determine MIC?	Dilution test and E-Strip.
What is the difference between breakpoint assays and kirby-bauer?	K-b has bacteria in agar, antibiotic on disk, break point has antibiotic in agar, and bacteria on disk.
What drug is contraindicated in dobermanns?	Sulphonamides
What is a risk of gentamycin?	Nephrotoxicity
Name 3 common successful prophylactic treatment?	Dry cow therapy, strangles in horses (quarantine/treat) and Leptospira in cattle (remove carriers)
Name 3 deleterious uses of prophylaxis?	Growth promotion with fluoroquinolones in spain, neomycin and tetracyclin in calves increases D+, intrauterine treatment of neomycin to prevent metritis affects fertility.
Antivirals should not be used against which type of virus? Why?	RNA - as they are prone to mutations >> resistance!
What is the mainstay of preventing viral disease?	Vaccines
What are the potential (general) drug targets for an antiviral?	Entry, uncoating, replication, assembly and release
What are the types of antiviral therapies and which is safest?	Drugs which target viral proteins = SAFEST Drugs which target host proteins e.g. blocking receptors Drugs which enhance host defences e.g. interferons
Describe the normal way in which a virus enters a cell	Virus binds to CD4 on cell membrane >> viral envelope protein changes to expose fusion protein >> viral and cell membranes fuse and process of entry begins. CAN TARGET VIRAL FUSION PROTEIN OF CD4 RECEPTOR OF CELL
How are viruses normally uncoated? How can drugs target viral uncoating?	Protons enter virus via M2 channel, causing a change in the shape of the viral core, releasing the genome from this core. Drugs block M2 channels hence inhibit uncoating
Give an example of an M2 channel blocker	Amantdaine
Give examples of viral polymerases which can be inhibited by drugs to prevent genome replication	DNA polymerase RNA retrovirus reverse transcriptase
How do nucleotide analogues preven genome replication in virus? Give 2 examples	They are incorporated into viral genome and prevent elongation of the DNA hence prevent replication e.g. Acyclovir (herpes virus) Zidovudine (HIV)
How are nucleotide analogues used as antivirals, specific?	They are pro-drugs, activated by viral enzymes only
Where do non-nucleotide reverse transcriptase inhibitors bind?	Near catalytic site of reverse transcriptase
Give an example of a non-nucleotide reverse transcriptase inhibitor	Nevirapine
Why are non-nucleotide reverse transcriptase inhibitors highly specific?	Do not bind to host enzymes
Why does resistance develop rapidly in non-nucleotide reverse transcriptase inhibitors?	Only requires a single amino acid substitute
How do integrase inhibitors work? Which virus can they target?	Bind to viral integrase to prevent viral cDNA from being inserted into host genome. Used against HIV
Name an antiviral classification that inhibits virus assembly, and describe the way in which it does this	Protease inhibitor Viruses are produced as polypeptides that must be cleaved by proteases to be activated Inhib of protease therefore results in inhib virus activation
How do neuraminidase inhibitors target viruses?	Inhib release of virus Normally haemagglutinin binds to receptor containing sialic acid and neuraminidase will cleave this receptors, allowing release of virions Neuraminidase inhibitor cleaves sialic acid therefore stops the binding of the haemagglutinin, therefore virions cannot exit cell
What trend will you see in the level of virus n blood when you use multiple drug therapy?	The more drugs, the bigger the reduction of the virus in the blood, and the slower resistance develops!
Give an e.g. of a TLR stimulant, used to treat equine sarcoids	Imiquimod (stim TLR 7 and 8)
Name 2 retroviruses in cats	FIV and FeLV
Name a licensed drug used in feline retrovirus therapy	Feline interferon omega (virbagen omega)
Do you treat Herpes virus in cats?	Yes, particularly in acute cases where corneal ulcers are developing
Are there any licensed drugs to treat Herpes virus in cats?	NOOOO!
What does coranavirus cause in cats?	FIP
What can be used to treat Equine herpes virus (EHV1)?	Valacyclovir - expensive and not licensed
What can potentially be used to treat EEHV1 (killer in baby elephants)?	Famicyclovir - often given by rectal route, unlicensed, shown to work in a few cases!
What is the main component of the BBB?	Endothelium
What is a mycose?	A fungal infection
When can a subcutaenous mycose become life threatening?	If it spreads to internal organs via blood or lymphatics.
What are the 5 broad groups of anti-fungals?	Azoles, pyrimidine analogues, polyenes, allylamines, Echinocandins
Which 'other' group of anti-fungal is used to treat ringworm?	Griseofulvin
What components of the fungal cell wall are present in fungi but not animals?	Chitin, B-glucans.
Name a membrane disrupting agent?	Amphotericin B
How does Amphotericin B disrupt the cell membrane?	Binds to ergosterol and disrupts membrane by forming pores.
Give 2 examples of fungi which amphotericin B is active IN VITRO against?	Candida and aspergillus
How can you reduce intrinsic toxicity of Amphotericin B?	Make oil based formulations.
Under which of the 5 main groups of anti-fungal does amphotericin B belong?	Polyene
How is amphotericin B released from it's liposome?	Requires uptake by macrophages
How to Azoles inhibit ergosterol synthesis?	Inhibit fungal p450 and act through an unhindered nitrogen
Are azoles fungicidal or fungistatic?	Only fungistatic - see less budding/hyphae
Accumulation of which intermediate makes azoles toxic?	Methyl-Ergostadiene-diol
What are the two groups of Azoles?	Imidazoles and Triazoles.
What is another Ergosterol synthesis inhibitor?	Allylamines
How do Allylamines work?	Target Erg-1 (enzyme) whereas Azoles target Erg-11
What is an echinocandin an example of (we think)?	Glucan synthase inhibitor
Which genes do Echinocandins inhibit in glucan synthesis?	FSK1, 2 + 3
Inhibition of B-glucan synthase can lead to secondary reduction in what?	Ergosterol and Lanosterol
Are echinocandis fungistatic or fungicidial?	Fungicidal but non-toxic
Where do Echinocandins act on the fungus?	They act at apical tips of hyphae as this is where glucan synthase is located.
What are the echinocandins registered for oral use?	Caspofungin, micafungin and anidulafungin
What enzyme does nikkomycin inhibit?	Chitin synthase
To what group does 5-FC belong?	Pyrimidine analogue
What does cytochrome deaminase do?	Converts 5-FC (prodrug) -> 5-FU which is the active drug.
Are flycocytosines useful in monotherapy?	NO - need another drug to first 'open the door' - combine with amphotericin B or fluconazole
What halogen compounds are frequently used as disinfectants?	Chlorine and Iodine
What is the action of chloride compounds?	Activity through electronegative denaturing proteins.
What are chloride compounds often used in?	Water treatment and the food industry
What is the most widely used chlorine containing disinfectant?	Sodium Hypochlorite
What must you never mix with Sodium Hypochlorite?	Ammonia - will make chlorine gas.
What determines the activity of Sodium Hypochlorite?	Amount of free chlorine in solution
What are iodine solutions often dissolved in?	Ethyl alcohol (tincture of iodine)
What can inactivate iodine solutions?	QACs and organic debris
What is quickly replacing Inorganic iodine solution?	Iodophors
What ARE iodophors?	Iodine complexes with increased solubility and sustained release of iodine.
What is the relation between dilution and activity in iodophors?	The more dilute, the more free iodine and the more activity.
What are the only things that QACs are effective against?	Mycoplasma, G+ve and G-ve bacteria.
How do QACs work?	They are cationic and attack negative charges on surfaces of microorgansims. Effect cell permeability.
What are QACs toxic to?	Fish.
What is the most common QAC?	Benzalkonium. Used in food industry as non toxic (except fish)
Name some Phenolic compounds?	Coal-tar extracts or synthetic formulations.
why are phenolic compounds being phased out?	Environmental concerns, taint food, concentrations above 2% highly toxic!
Name some oxidising compounds?	Hydrogen peroxide, virkon, peracetic acid and Ozone.
Is hydrogen peroxide a pollutant? Why?	No - breaks down into water and oxygen.
Why can some bacteria become tolerant to H2O2?	Because they can have peroxidases
What is an issue with peracetic acid?	Corrosive, hazardous and may be carcinogenic because oxygen reacts with DNA.
What components are in Virkon-S?	Potassium peroxymonosulphate and sodium chloride. (peroxygen molecule, organic acid and surfactant molecule)
What are peroxide vapours replacing?	Formaldehyde fumugation
What oxidising compound is used in water systems for feeders?	Ozone

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