biology and classificaiono bacteriatf Flashcards
define pathogen
organism that causes or is capable of causing disease
define commensalism
organism which colonises the host but causes no disease in normal circumstance
define opportunist pathogen
microbe that only causes disease if host defences are compromised
define virulence/pathogenicity
the degree to which a given organism is pathogenic
define asymptomatic carriage
when a pathogen is carried harmlessly at a tissue site where it causes no disease
3 areas that need to be kept microbe free
gall bladder
lungs
kidney
how can bacteria look
- coccus (spherical)
- bacillus (rod)
describe stain of gram positive bacteria
purple
describe cell membrane of gram positive bacteria
double cell membrane
what colour does gram negative bacteria stain
pink
describe cell membrane of gram negative bacteria
2 cell membranes
an inner and outer membrane, which are separated by lipoprotein, periplasmic space and peptidoglycan
structure of gram positive bacteria
cytoplasmic membrane - single membrane made of lipids
peptidoglycan - this links to membrane via liptotechoic acid
capsule at top
structure of gram negative bacteria
double membrane - inner and outer
in between membranes:
lipoprotein, periplasmic space, peptidoglycan
lipopolysaccharide in middle
capsule at top
describe bacterial environment
temp
<-80C to +80C
ph
<4-9
water/desiccation
2 hours - 3 months
light
UV
growth rate of most viruses
more than an hour doubling rate
in cells
growth rate of e. coli, S aureus
20-30 mins doubling rate
in broth or solid media
growth rate of mycobacterium TB
24 hours doubling rate
in broth or media
growth rate of fungi
30 min doubling rate
in broth or media
growth rate of mycobacterium leprosariums
2 weeks doubling rate
in broth or media
2 types of bacterial toxins
endotoxin
exotoxin
what are endotoxins
component of the outer membrane of bacteria, e.g. lipopolysaccharide in gram negative bacteria
what are exotoxins
secreted proteins of gram positive and gram negative bacteria
describe exotoxins
composition - protein
action - specific
effect of heat- labile
antigenicity - strong
produced by - gram positive & gram negative
convertibility to toxoid - yes
describe endotoxins
composition - lipopolysaccardie
action - non specific
effect of heat- stable
antigenicity - weak
produced by -LPS - gram negative
convertibility to toxoid - no
how big is bacterial chromosome
typically 2-4 x103 kb
structure of plasmid
transfer promotion genes
plasmid maintenance genes
antibiotic or virulence determinant genes
2 types of genetic variation in bacteria
mutation
gene transfer
3 types of mutations
base substitution
deletion
insertion
3 types of gene transfer
transformation eg via plasmid
transduction eg via phage
conjugation eg via sex pilus
describe transduction
bacteriophages (viruses that infect bacteria) mediate transfer of DNA between via transduction, whereby DNA from a donor bacterium is packaged into a virus particle and transferred into a recipient bacterium during infection
describe transformation
some bacteria are abel to take up free DNA from the environment and incorporate it into their chromosome
describe conjugation
the mechanism of gene transfer responsible for the most concerning aspects of anti microbial resistance
a sex pilus (small tube) forms between two bacterial cells through which a plasmid is transferred from one tot he other
first step of classification of bacteria
obligate intracellular bacteria
OR
bacteria that may be cultured on artificial media
3 types of obligate intracellular bacteria
Rickettsia
Chlamydia
Coxiella
how to classify bacteria that may be cultured on artificial media
with a cell wall
OR
no cell wall
which bacteria that may be cultured on artificial media have no cell wall
molllicutes
how to classify bacteria with a cell wall
growing as single cells
OR
growing as filaments
3 examples of bacteria growing and filaments
actinomyces
nocardia
streptomyces
3 types of bacteria growing as single cells
rods
cocci
spirochaetes
3 types of spirochatees
leptospira
treponema
borrelia
what are the gram negative cocci
anaerobic - veillonella
aerobic - neisseria
what are the gram positive cocci
aerobic - staphylococcus & streptococcus
anaerobic - peptostreptococcus
types of streptococcus
beta - haemolytic
alpha haemolytic
non haemolytic
enteroccocus
6 bacterial morphology
diplococcus
chain of cocci
cluster of cocci
chain of rods
curved rod
spiral rod
which bacteria stain with ziehl- neelsen stain
mycobacteria eg M TB
anaerobic gram positive rods
clostridium
proniobacterium
aerobic gram positive rods
corynebacterium
listeria
bacillus
anaerobic gram negative rods
bacteroides
aerobic gram negative rods
coliforms
pseudomonads
vibrio
parvobacteria
how to do gram stain
- Apply a primary stain such as crystal violet (purple) to heat fixed bacteria
- Add iodide which binds to crystal violet and helps fix it to the cell wall
- Decolourise with ethanol or acetone
- Counterstain with safranin (pink)
what is coagulase test
Distinguishes S.aureus from other staphylococci – coagulase positive
what is alpha haemolysis
haemolysis causing by production of hydrogen peroxide oxidising haemoglobin – the agar appears green
what is beta haemolysis
haemolysis results because of lysis of red blood cells by haemolysis such as Streptolysin O produced by S.pyogenes
what is gamma haemolysis
haemolysis implies no haemolysis
what is oxidase test
Tests if micro-organism contains a cytochrome oxidase – implies organism able to use oxygen as the terminal electron acceptor
