Gram Positive Pathogens L1 Flashcards
what are facultative anaerobes
bacteria that grow anaerobically and aerobically
what shape are cocci
round cells
what shape are bacilli
rod
examples of cocci anaerobic and aerobic bacteria
staphylococcus
streptococcus
examples of cocci anaerobic bacteria
pepstreptococcus
magnus
examples of bacilli anaerobic and aerobic
bacillus
listeria
examples of bacilli anaerobic
clostridium
lactobacillus
what colour is gram positive bacteria in blue dye
blue as thick peptidoglycan cell wall - when stain with the dye, the blue dye stuck here
what colour is gram negative bacteria in blue dye
thinner layer peptidoglycan, have outer membrane. When stained with dye, blue dye easily washed out
what colour is gram negative bacteria in pink dye
will take up pink dye so stained
what is staphylococcus
facultative anaerobe and grow well on most media
non-motile
non-sporing
catalase-positive
why do you test for coagulase positive or negative
coagulase test:
positive coagulase test has a strong correlation with pathogenicity
how do you do a catalase test
Catalyse +ve have an enzyme in cell that can break down hydrogen peroxide into water and oxygen, fizzing – ONLY STAPHYLOCOCCI FIZZ
examples of staphylococcus aureus causing clinical infections
sepsis
pneumonia
TSS
what types of infection can staphylococcus aureus cause
endogenous - from persons own flora (usually from nose to cut)
exogenous - catch off someone else
where is staphylococcus aureus found
healthy people (carriers) frequently colonised in anterior nares, axillae and groin
how many people carry staphylococcus aureus
20% persistant carriers
30% intermittent carriers
50% never carry
if you carry staphylococcus aureus when is it a problem
if move from that site to another acting as opportunistic pathogen causes problem
what can be done against staphylococcus aureus
no vaccines
methicillin resistant staphylococcus aureus (MRSA)
methicillin sensitive staphylococcus aureus (MSSA)
what is staphylococcus epidermis
what does it do
normal commensal of skin, gut, respiratory tract
acts as opportunistic pathogen - readily colonises implants as a biofilm e.g. joint replacements, intravenous devices
how is staphylococcus epidermis treated
difficult as often resistant to anti-staphylococcal agents, produce glycocalyx - sticky surface layer made of polysaccharides, DNA and proteins
sticky surface biofilm prevent antibiotics
what is staphylococcus saprophyticus
usually non-pathogenic
may cause urinary tract infection
what is streptococci
gram positive cocci in short or long chains
non-motile
sometimes capsulate
catalase negative
what do some streptococci require for growth
CO2
how are streptococci species separated
ability to haemolyse blood, by serology and biochemical tests
streptococci appearance on alpha-haemolysis
greenish
partial
Strep. pneumoniae
streptococci appearance on beta-haemolysis
complete
Strep. pyogenes
streptococci appearance on gamma hemolysis
non-haemolytic
Enterococcus faecalis
streptococci main serotyping method
Lancefield grouping
how many groups are there in the Lancefield grouping
20
what is streptococcus pyogenes
major human pathogen present in nasopharynx of healthy
what lansfield group is streptococcus pyogenes in
A
how are streptococcus pygoenes subdivided
into Griffith
based on serology of three surface protein antigens M, R, T
which streptococcus pygoenes have the M strain
those that are virulent
inhibit phagocytosis
what does streptococcus pyogenes produces
many toxins
enzymes
e.g.haemolysins
break down clots so molecules can move
what does streptococcus pyogenes cause
suppurative infections: sore throats, tonsillitis, pharyngitis, scarlet fever, etc.
invasive disease e.g necrotizing fasciitis and Streptococcal toxic shock syndrome
Non‑suppurative infections: rheumatic fever, glomerulonephritis
which lansfield group is streptococcus agalactiae in
B
where is streptococcus agalactiae present
carried by some women in gential tract
what does streptococcus agalactiae cause
important pathogen of neonates (meningitis, sepsis) also septic abortions, gynaecological sepsis
may be transferred to newborn during birth, may cause infection in mother after baby born
where is streptococcus pneumoniae found
important pathogen found as commensal of upper respiratory tract ‑ found in mouth and pharynx of carriers
what does streptococcus pneumoniae cause
Commonly causes pneumonia
Also causes meningitis
what is viridans streptococci
what does it look like on blood agar
A heterogeneous group of commensal streptococci which show greening on blood agar, but many show no haemolysis
where is viridans streptococci
mouth and oropharynx — normally of low virulence
what does viridans streptococci cause
dental caries and periodontal disease and endocarditis
what is infective endocarditis caused by
always preceded by a bacteraemia (bacteria present in blood – tooth extraction may be one cause of bacteraemia)
what is infective endocarditis
organisms may lodge in damaged or abnormal heart valves, found in rheumatic or congenital heart disease
vegetations form and valve function further impaired — high mortality rate
what lancefield group is enterococci
D
what is enterococci
non haemolytic or β-haemolytic gram +ve cocci in pairs
where is enterococci present
human and animal gut, occasionally in mouth
can grow in 40% bile salts
what type of bacteria is enterococci
pathogenicity ‑ opportunist in urinary tract infections
what are bacilli
commonly found as spores in environment e.g. soil
what is bacillus anthracis like
large non-motile grows on all ordinary media forms 'medusa head' encapsulated produces plasmid encoded toxin complex
what does bacillus anthracis cause
anthrax in humans and domestic animals
what are coryneforms
average size 3x0.3 um
phemorphic
gram+ve bacillus
snap and bend on division
what does corynebacterium diphtheriae cause
diphtheria
-may be lethal
infection occurs in throat by inhaling infected aerosol
=
what does corynebacterium diphtheriae do
produce white plaque where growing
produces a powerful toxin, spreads through body, intoxication may lead to myocarditis and peripheral neuritis
interferes with proteinsynthesis in cells
how is corynebacterium diphtheriae cured
effective vaccine based on inactivated toxin
how is corynebacterium diphtheriae detected
ELEK test used to detect toxin.
PCR now also used to detect toxin gene
what is listeria monocytogenes
short gram positive bacilli
tumbling motility at 25 degrees C
some strains are beta-haemolytic
what does listeria monocytogenes cause
may cause neonatal meningitis and sepsis — in pregnancy may lead to abortion and stillbirth
how can listeria monocytogenes frow
intracellularly in macrophages
grow well on all ordinary media
