Microbiology Flashcards
Function of the bacterial cell wall
strong outer cover that maintains bacterial shape & protects against osmotic pressure
Ways bacteria may use its morphology to survive (3)
- having a **capsule** that protects against phagocytosis
- flagella (longer) or pili / fimbriae (shorter) that enables them to move or deliver toxins to host
- **two membranes** for protection
Describe the variations in cell wall structure accounting for gram-positive and negative staining
pos = single ; neg = double
gram positive = thick, single peptidoglycan layer made of repeating sugar subunits cross linked by peptide chains in cell wall
gram negative = thin peptidoglycan layer & an additional outer membrane containing lipopolysaccharides = endotoxins
Function of flagella on bacteria
allows for movement
Function of fimbriae / pili on bacteria
- allow bacteria to adhere to cell surfaces & exchange plasmids with other bacteria
- allows for the delivery of endotoxins to host (?)
Ways bacteria can be classified
Shape, staining, biochemical tests, sensitivity tests & culture techniques
Round, spherical bacteria are known as?
Coccus / cocci
Rod bacteria are generally known as?
Bacilli
Curved rod bacteria are known as?
vibrio
Spiral rod bacteria are known as?
spirochaete
Temperature range for bacterial survival, and for spores>
-80 to +80 degree Celcius, spores = up to 120 degree Celcius
How do you measure growth rate of bacteria?
Measured by shining light on bacteria and measuring absorption
Briefly describe the three ways bacteria performs gene transfer
- transformation - pick up DNA from environment - via plasmid
- transduction - when virus infects bacteria - via phage
- conjugation - exchange of plasmid between bac cells - via sex pilus
How does bacteria achieve genetic variation (3+3)
- mutations: baseline substitution, deletion, insertion
- gene transfer: transformation, transduction, conjugation
How does the gram stain differentiate bacteria?
PINK = negative = double membrane bacteria = endotoxins and exotoxins
PURPLE = positive = single membrane bacteria = exotoxins only
Briefly describe the gram staining technique?
- heat fix sample to slide
- add methyl violet (blue / purple)
- add iodine → fixes methyl violet to gram pos samples
- add alcohol to decolorize gram neg samples
- counterstain with basic fuschin (red)
What does it mean if the gram stain returned positive?
- sample will be purple
- sample is a single membraned bacteria which will produce exotoxins only
What does it mean if the gram stain returned negative?
- sample will be pink
- sample is a double membraned bacteria which will produce both exo and endotoxins
What are endotoxins?
- Component of the outer membrane of bacteria that is released when bac is damaged
- Specific components of this is recognised by the immune system → will have huge reaction = endotoxic shock
- Work is non-specific
What are exotoxins?
- proteins secreted by both bacteria.
- action is specific: inhibit (botulism) or stimulate (tetanus) nervous system
- unstable exposure to heat
- can be converted to a toxoid → non-active toxin
What colour will the bacteria stain with Gram stain if it only produces exotoxins?
Purple = gram-positive bacteria = single membrane
What colour will the bacteria stain with Gram stain if it produces both endotoxins and exotoxins?
Pink = gram-negative bacteria = double membrane
When should you not use the gram stain to group bacteria (i.e. when will it not work)
- for cell walls that contains mycotic acids (‘acid fast bacilli’) which the gram stain cannot get in to
- e.g. mycobacteria spp.
→ Ziehl-Neelsen staining should be used
What stain is used for mycobacteria spp.?
Ziehl-Neelsen staining
result = red or blue
What does it mean if an organism stains blue on Ziehl-Neelsen stain?
= non acid fast bacteria = not mycobacteria spp.
What does it mean if an organism stains red on Ziehl-Neelsen stain?
= mycobacteria spp as they are acid fast so will retain the red/pink dye
Why is gram staining not used for mycobacteria spp.?
cell wall of mycobacteria contains mycolic acids - hard to penetrate for gram stain
6 species of gram positive bacteria
(Sexy Students Can Look Bad Come morning!)
Streptococcus, staphylococcus, corynebacterium, listeria, bacillus, clostridium
sexy students can look bad come morning
Ideas for gram positive bacilli?
- bacillus
- corynebacteria
- listeria
& anaerobic bacilli
Ideas for gram positive cocci?
- Staphylococci
- Streptococci
- Enterococci
What will the gram test results be for Streptococcus spp. ?
- positive (purple) (single layer)
What does the catalase test differentiate between?
- Staphylococci → positive
- Streptococcus & enterococci → negative
What is the catalase test?
Catalase = enzyme following 2H2O2 → 2H2O + O2
Tests if bacteria produces the catalase which protects Staphylococci against hydrogen peroxide (converts it to gas and water = gas bubbles)
Which bacteria spp will test positive for the catalase test and how will it return?
Staphylococci → positive
When placed in hydrogen peroxide it will produce gas bubbles where others will have no reaction
Which bacteria spp will test negative for the catalase test and how will it return?
Streptococcus & enterococci → negative
When placed in H2O2 it will not have any reactions
What is haemolysis and what will the test for?
haemolysis = RBC breakdown in blood agar
tests are done in blood agar, if positive it is mostly to group bacteria according to antigen groups (e.g. alpha, beta & gamma), or no haemolysis
What is the optochin test and what does it test for?
- Optochin = chemical used for identification of streptococcus pneumoniae from other alpha haemolytic streptococci
- disc is placed in agar & formation of inhibition zones (lysis) is the test
formation = positive = strep pneumoniae;
no inhibition = other alpha haemolytic strp
How will streptococci spp. test for
- catalase test?
- optochin test?
catalase: ❌ negative (only staph is pos)
optochin:
strep pneumoniae will be ✅ positive
other alpha haemolytic strep will be ❌ negative
How would you differentiate between the alpha and beta haemolytic groups of strep?
Using the blood agar (mammalian blood)
How would alpha haemolytic (viridians) streptococci present on blood agar?
greenish white colonies
due to partial erythrocyte and Hb breakdown
How would beta haemolytic streptococci present on blood agar?
yellowish white, opaque colonies
due to complete erythrocyte lysis
strep pyogenes & agalactiae!
How would gamma haemolysis present on blood agar?
dotted / no colonic growth
How would you further classify alpha haemolytic streptococci?
Optochin test - differentiates stroptococci pneumoniae from other alpha haemolytic streptococci
How will the optochin separate streptococci pneumoniae from the rest?
Streptococci pneumoniae are sensitive to optochin → lysis (clear zone no growth) = positive
How will other alpha haemolytic streptococci appear on optochin?
there will be growth as not sensitive = no lysis
How would you further classify beta haemolytic streptococci?
Lancefield grouping, by detecting surface antigens
(so, aka Antigenic grouping)
Important groups in Lancefield Grouping & ex?
A - Strep pyogenes
B - Strep agalactiae
D - Enterococcus genus
Strep pneumoniae - tests? diseases? tx?
gram pos, optochin sensitive
community acquired pneumonia, bacterial meningitis, COPD exacerbate, sinusitis, otitis media
penicillin or erythromycin
alpha haemolytic streptococcus - test? disease? tx?
group
alpha haemolysis = green colonies on blood agar
bacterial endocarditis, dental caries
penicillin / amoxicillin
b. endocarditis = penicillin & gentomycin
enterococcus spp. - test? diseases? tx?
non haemolytic, Lancefield group D, McConkey growth
Infective - endocarditis, UTI, wound, IV catheter
penicillin / vancomycin (± gentamycin)
🌟 General treatment options for streptococcus spp.?
penicillin / amoxicillin
erythromycin if allergic
erythromycin / vancomycin if resistant
What does the MacConkey agar test for?
isolates & identifies enteric bacteria,
as it contains
bile salts - only permits growth of enteric bacteria
lactose & pH indicator - fermentation fo lactose produces an acidic environment → red / pink color
What does the color change mean on MacConkey agar?
pH indicator, as if lactose fermenting, will produce an acidic environment
Which bacteria will grow red / pink colonies on MacConkey agar?
E coli, Enterococcus spp., Klebsiella spp.
Which bacteria will turn MacConkey agar clear / yellowish but will grow in colonies?
Salmonella spp., Shigella spp., Psuedomonas spp
Which bacteria will turn MacConkey into a pinkish colour but will have no growth?
Staphylococcus aureus (latin for gold!)
Which test separates Staphylococcus aureus from other staph spp.?
Coagulase test
How does a coagulase work?
coagulase = enzyme causing fibrin to clot, preventing phagocytosis;
so test is bacteria sample + plasma
only staph aureus will form a clot, every other staph = no clot
Staphylococcus aureus. - test? disease? tx?
catalase positive, coagulase positive (only staph to be)
skin infections, osteomyelitis, septic arthritis, septicaemia, bac endo, conjunc, pneumonia, toxic shock!
flucloxacillin, if MRSA = vancomycin
Listeria spp. - tests, diseases, tx?
gram pos
- *pregnancy** - miscar and still-b;
- *young old immunecomp** - pneumonia, meningitis, encephalitis, sepsis
tx ampicillin / erythromycin and gentamycin
Tetanus - bac name, transmission, present, treat?
clostridium tetani - transmit through spores entering open wounds!
tx - human tetanus immunoglobulin, benzodiazepines!
How would tetanus present?
SPASMS and CONTRACTS
- locked jaw - trismus
- if sustained - sardonic smile - risus sardonicus
- persistent spam of the back muscles - opisthotonos
- painful contraction and spasms at site of injury
- flunctuating BP, tachy, arrhy, fever
Tx tetanus?
IV high dose benzodiazepine for spasms
human tetanus immunoglobulin
antimicrobial to mop up remaining: penicillin, metronidazole
Benzodiazepine - ex, mechanism?
facilitate and enhance binding of GABA to receptor → systemic synaptic transmission depression
ex diazepam, lorazepam, midazolam
clostridium difficile - disease, transmission, tx?
pseudomembranous colitis - diarrhoea following antibiotic therapy
trans - spores via faecal-oral route
tx vancomycin
clostridium botulinum - disease, transmission, tx?
botulinism - descending paralysis secondary to botulinum toxin
trans - food ingest, wound contamination
tx - vancomycin or metronidazole
Free card
Gram negative stains?
pink!
6 important gram neg bacteria?
neisseria spp
enterobacteriaceae
parvobacteria
helicobacter spp.
vibrio spp.
pseudomonas spp.
gram negative cocci - ideas?
neisseria
moraxella
anaerobic cocci
gram negative bacilli - ideas?
e. coli
campylobacter
pseudomonas
salmonella
shigella
proteus
If a gram negative bacilli is lactose fermenting what could they be?
in pink colour!
e coli or klebsiella pneumoniae!
If a gram negative bacilli stains pale / yellow in McConkey agar with growth what could they be?
Shigella, salmonella, proteus
If a gram negative bacilli does not grow or turn MacConkey agar into any colour what could they be?
Pseudomonas or vibrio
Neisseria meningitidis - special presenting feature?
If meningitis triad (fever, headache, neck stiffness / leg pains, photophobia) + purpuric rash = this bacteria as it is most likely to cause rash
or septicaemia :’)
tx neisseria meningitidis?
cefotaxime or benzylpenicillin
close contacts rifampicin, ciprofloxacin or ceftriaxone
vaccine for A & C strain available
Neisseria gonorrhoea - disease, trans, tx?
direct mucosal contact
gonorrhoea, reiter’s syndrome (urethritis, conjunctivitis and arthritis)
tx ciprofloxacin or cefixime
free card
e coli treatment is dependent on site
UTI: trimethoprim
Pneumonia: Cephalosporin
Klebsiella pneumonia - disease, tx?
Hospital acquired pneumonia, UTI, neonate meningitis
tx cephalosporins
Typhoid & paratyphoid - cause, aka, trans, tx?
Salmonella typhi and paratyphi (A, B & C)
aka enteric fever
trans - faecal oral
tx - ciprofloxacin
Salmonella enteritidis - disease, trans, tx?
causes ‘salmonella’ or gastroenteritis ± bacteraemia
inadequately cooked food contaminating w/ infected animal faeces, e.g. poultry & eggs
self limiting disease!
Shigella dysenteriae - trans, disease, tx?
faecal-oral
bacillary dysentry
ciprofloxacin
Campylobacter jejuni & coli - trans, disease, tx?
trans - contaminated poulty (jejuni) or pig meat (coli), unpasteurised milk
most common cause of diarr in england + wales!!!!
gastroenteritis ± dysentery / reactive arthritis / guillan barre (watery diarr + CNS)
tx - self limiting but if severe cirpofloxacin
summary of food poisoning / diarrhoea related bacteria (and virus?) !
salmonella, shigella, campylobacter jejuni, norovirus (elderly), rotavirus (child)
Proteus mirabellis - disease, tx?
UTI in young females (‘mirabelles’), wound and IV catheter infection
tx trimethoprim
Haemophilius influenza - disease, tx, special?
mening, pneumo. osteomy + septic arth. acute epiglottitis, otitis media, cellulitis
cefotaxime or ceftriaxone
if children + non-typable = this. rare tho coz HiB vaccine
Whooping cough - cause, trans, tx?
NOTIFIABLE
bordetella pertussis
airborne droplet transmission
diagnose ELISA for pertussis toxin
tx clarythromycin, erythromycin
Severe pneumonia with a high fever, has been near warm water (AC units, water tanks) recently - bacteria, trans, tx?
Legionella pneumophila
= Legionnaires disease (pneumonia), also causes Pontiac fever = flu like illness
inhalation of aerosolised droplet (also holiday home shower)
tx - erythromycin but if severe rifampicin or cirpofloxacin
Helicobacter pylori - everyone’s fav
disease, trans, tx
chronic gastritis, duodenal and gastric ulcers
tx Clarithromycin, amoxicillin / metronidazole + PPI (omeprazole)
Cholera - type of bacteria, location, trans, present, tx?
vibrio cholerae
in water & seafood, transmit through faecal-oral & seafood
present = rice water diarrhoea, up to 25 litres fluids lost per day
tx = rehydrate, severe = ciprofloxacin
pseudomonas aeruginosa - diseases, trans, tx?
pneumonia esp in those with cystic fibrosis
UTI & catheter infections
wound / burn / IV line infect
trans is hand borne & thru direct contact
tx fentamycin or ceftazidime
if child with CF / adult with bronch then ciprofloxacin
