Microbiology Flashcards
What does S. pyogenes cause?
haemolysis
What are the features of eukaryotes?
- complex
- multi-cellular
- linear chromosomes with histones
- introns
- 80S ribosomes
What are the features of prokaryotes?
- simple
- single-celled
- circular chromosome
- 70S ribosomes
- cell wall
- rapid cell cycle
What is the structure of the cell wall in prokaryotes?
- made of peptidoglycan or murein
- rigid barrier
- for gram +ve there is a multi-layer
- for gram -ve there s an outer membrane, periplasm and thinner PG layer
What are the special features of the gram negative organisms?
many lipopolysaccharides (LPS) which have a structural role and role in antigens and bacterial toxins
What are the differing structures added on to gram positive or negative organisms?
gram +ve have fimbriae which are non-flagella protein appendages
gram -ve plus aren’t a motor and have piling repeat unit
What are the differences in ribosomes between eukaryotic and prokaryotic organisms?
70S in prokaryotes
80S in eukaryotes
these are very different so drugs can tailor their effect to the ribsome
What are the different factors needed for prokaryotic growth?
- Food= C, O, H, salts, vitamins
- Temperature (mesophiles work at body temperature)
- [H+]
- Osmotic protection
- Oxygen
What are the phases of bacterial growth?
- lag
- exponential
- stationary
- decline
How can microorganisms be classified?
- appearance
- growth requirements
- enzyme/metabolic tests
- molecular tests
What structures can cocci form?
division in one plane to make chains
division in three planes to make clumps
What are curved rods always?
gram negative
What can spiral shaped bacteria be?
- rigid spirillum
- flexible spirochaete
What colours do gram negative and positive stain?
- gram negative stain pink with LPS on outer membrane
- gram positive stain purple with multi-layered peptidoglycan
What are obligate aerobes, obligate anaerobes and facultative aerobes?
- obligate aerobes need oxygen
- obligate anaerobes are killed by oxygen
- facultative aerobes tolerate oxygen
What are selective and differential media?
- selective permits growth of one organism over another
- differential allows adding of chemicals to produce changes that help with identification
What haemolysis does streptococcus give?
- green alpha partial haemolysis
- complet beta haemolysis
- no gamma haemolysis
What makes up a microbiome?
endogenous and exogenous mircroorganisms
What is virulence?
the capacity of a microbe to cause damage to the host so its pathogenicity
What is commensal bacteria?
part of the normal flora, endogenous, mutualistic
What is an example of a protozoa and fungus?
malaria = protozoa
yeast and candida = fungus
What is an example of gram -ve cocci?
neisseria meningitides
neisseria gonorrhoeae
What are coliforms and what are they treated with?
gram -ve bacilli like E.coli which are aerobes
treated with Gentamicin
What type of membrane do endotoxins have?
gram -ve
How does endotoxic shock come about?
- endotoxin binds to macrophage receptors and B cells
- acute cytokines cause endotoxic shock and fever
How is fever brought about?
- cytokines to anterior hypothalamus
- prostaglandin E increases the body’s thermal set point
- this causes fever
What happens in sepsis?
- leaky small blood vessels
- decreased blood volume so increased HR
- poor perfusion
- blood clotting so increases risk of haemorrhage
What are streptococcus, enterococcus and staphylococcus?
gram +ve
What is streptococcus pneumonia?
gram +ve
alpha haemolytic cocci
Are enterococci haemolytic?
no they are non-haemolytic
What is the gram state of staph aureus and epidermis and what is their coagulase state?
- staph aureus is gram +ve and coagulase +ve
- staph epidermis is gram +ve and coagulase -ve
- both are in clusters
What are the features of clostridium?
gram +ve
anaerobic bacilli
produce exotoxins
What are the key gram -ve organisms?
Neisseria spp (STI and meningitis) Escherichia coli (GI)
What are the key gram +ve organisms?
Streptococcus, Staphylococcus and C. diff
How do viruses infect cells?
- attach ligand to receptor on a cell
- viral and cell envelope fuse which can be mediated by a viral enzyme
- viral uncaring to realise viral nucleic acid then host ribosomes used to make nucleic acids and proteins
How can viruses be released?
- enveloped viruses release by budding
- other viruses release by lysis
How do antibiotics target bacteria?
- ribosomes
- growing bacterial cell wall
- enzymes
How do anti-viral drugs work?
- target viral nucleic acid polymerase
- other viral enzymes
- uncoating
- attachment
- release
How is antiviral resistance analysed?
genotypical not phenotypically
How does a virus cause pathogenesis?
cells can die due to lysis/hijacking of cell, immune system or proliferation
How do cytotoxic T lymphocytes work?
- recognise cell-surface proteins as foreign
- start cell death
How does viral persistence work?
- virus can either remain latent then reactivate or remain active and only cause complications later on
What are the ways to detect a virus?
detect either the virus itself of the antibody against the virus
What are the antibodies produced in repose to infection?
- IgM initially but then levels of this will drop to 0
- IgG will be produced after and levels will remain low after rise in the blood
What will be blood components of recent infection?
IgM, rising titre of IgG and very high IgG
How can virus detection be done?
PCR or antigen detection
What is bacteriostatic?
inhibit the growth of bacteria
What is bactericidal?
kill bacteria
What are the features of the ideal antibiotic?
remains for a long time
minimal toxicity to host
kills bacteria
What are the groups of cell wall antimicrobials?
- Penicillins (beta lactam)
- Cephalosporins (beta lactam)
- Carbapenems (beta lactam)
- Glycopeptides (not beta lactam)
What do beta lactams target?
Penicillin Binding Proteins (PBPs)
How do beta lactam antibiotics work?
beta lactam ring on penicillin binds to bacteria to unhurt cross-linking and its ability to make new cell walls
What are the features of Penicillins?
\+ few side effects \+ safe in pregnancy - resistance - patients can be allergic - few side effects
What are the common types of penicillins and their features?
- Amoxicillin: safe, oral, good tissue perfusion, works on gram +ve and -ve
- Co-amoxiclav: IV/oral, beta lactam and beta lactase inhibitor, works on gram -ve and +ve
- Flucloxacillin: narrow spectrum, staph and strep, gram +ve
- Temocillin: gram -ve, beta-lactamase resistant, active against coliforms and ESBL-producing organisms
What do Cephalosporins do?
- inhibit cell wall synthesis
- bactericidal
- more resistant to beta lactamases
- broad spectrum
- cause C. diff
- kidney and urine excretion
- eg Cephoxitin
What do Glycopeptides do?
- bactericidal
- not beta lactam
- act on substrate so enzyme can’t attach
- reduced cross-linking
- weakened cell wall
- only active on gram +ve
- IV only
How do antibiotics that inhibits protein synthesis work?
attach to ribosomes
bacteriostatic as synthesis resumes when antibiotics are stopped (with the exception of aminoglycosides)
What are the main types of antibiotics that inhibit protein synthesis?
- Aminoglycosides: IV, binds to ribosomes, bactericidal, gram -ve, urine excretion eg Gentamicin
- Tetracyclines: bacteriostatic, bind to ribosomes, broad spectrum, eg doxyclycine
- Macrolides: liver excretion, eg clarithromycin, azithromycin and azithromycin
What is the side effect of Gentamicin?
damage to cranial nerve VIII
damage to kidneys
What are the main antibiotics that affect nucleic acids?
- Metronidazole: against anaerobes, rare resistance
- Quinolones: bactericidal, indirectly inhibit DNA synthesis
- Fluoroquinolones: bactericidal, good orally, gram -ve and +ve
What is the main class of antibiotics that affects folic acid synthesis?
- Timethoprim: gram -ve and +ve, used in UTIs
folic acid is needed for the synthesis of key cellular components
What is the side effect of Ciprofloxacin?
tendonitis
What is the side effect of Metronidazole?
alcohol interaction
What are the 4 Cs to avoid?
- Cephalosporins
- Co-amoxiclav
- Cirprofloxacin
- Clindamycin
What are biofilms?
organisms behaving as part of a multi-cellular community that are resistant to antimicrobial agents and host defences
What are the features of persister cells?
tolerance not resistance
very slow growth
enriched in biofilms
What are the main steps of resistance transfer?
variation –> selective pressure –> evolution resistance –> gene transfer
How can horizontal gene transfer occur?
bacterial transformation
transduction
conjugation
What are the antimicrobial drug resistance mechanisms?
- altered permeability (altered efflux or influx)
- inactivation (beta lactamases)
- altered target site
- replacement of a sensitive pathway
What are the types of beta lactamase?
penicillinase
extended spectrum beta lactamases
carbapenemase
What does SICPs stand for?
standard infection control procedures
What is the chain of infection?
- infectious microbe
- reservoir
- portal of exit
- modes of transmission
- portal of entry
- susceptible host
- infectious microbe
- repeat
What are the five Is of infection spread?
Inhalation Ingestion Inoculation Intercourse (mother to) Infant
What is disinfection?
reducing the number of microorganisms to a level which is safe
What is sterilisation?
killing the microorganisms so they are incapable of causing infection
