Intro Flashcards
define pathogen
Organism that causes or is capable of causing disease
define commensal
Organism which colonises the host but causes no disease in normal circumstances
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 asympomatic carriage
Disease is carried harmlessly at a tissue site
what is bacterial nomenclature
genus then species
what is round bacteria called
coccus
what is rod like bacteria called
bacillus
two main groups of bacteria
gram positive
gram negative
gram positive colour?
purple
gram negative colour?
pink
what is diplococcus
two cocci that grow together
structure of basic bacteria cell
cell envelope- phsopholipid membrane w layer of peptidoglycan
capusle
inner membrane
outer membrane
purpose of flagella/ pilli
to stick to host cells
swim / movement
what bacteria does not show up with GRAM staining and what would you use isntead
TB
Ziehl- neelsen stain
structure of gram + bacteria
Has a capsule with
Thick peptidoglycan linked to phospholipid membrane
structure of gram - bacteria
two phospholipid membrane
perisplamsic space- thin phosphilipid layer
endotoxin-
what is endotoxin
Component of the outer membrane of bacteria, eg lipopolysaccharide in Gram negative bacteria
what is exotoxin
Secreted proteins of Gram positive and Gram negative bacteria
characteristics of exotoxin
protein
specific
labile to heat
strong antigenicity
produced by gram + & -
methods of gene transfer
transformation
transduction
conjugation
what does gram staining do
seperates bacteria into gram positive and negative depending on the thickness of peptidoglycan
what structure does staph usually appear
clusters
what structure does strep usually appear in
chains
what does the catalase test show
differentiates between staphylcoccus and streptococcus genus
what would catalase + show
staph
what would catalase -ve show
strep
3 types of haemolysis and what they show
alpha- partial
beta- complete
gamma- none
what does mackonkey agar show
bacteria that can digest lactose
examples of bacteria that are non- fermenters gram -ve
salmonella, shigella, pseudomonas aurerginosa
optochin -ve and +ve would show
-ve = strep viridans
+ve= strep pneumonia
which strep is susceptible to optochin
s pneumoniae
structure of c difficile
gram +ve bacilli
what does the coagulase test do
differentiates staph aureus which produces the enzyme coagulase from S epidermis and S saprophyticus which do not produce coagulase
what would coagulase +ve show
staph aureus
what would coagulase -ve indicate
staph epidermis or sapro
method for the coagulase test
apply rabbit plasma to a small sample or pure colony, observe for fibrin clot clumps
what does the lancefield grouping rely on ?
relies on the different group specific carbohydrates antigen present on the bacterial cell wall
what group in the lancefield classification would s.pyogenes be
GROUP A
what agar would you use for streptocuccus
blood
what agar would you use for fastidious neisseria
chocolate
what agar would you use for differentiating lactose status
MacConkey
what agar would you use to isolate salmonella and shigella
XLD AGAR- xylose lysine deoxycholate agar
What diseases does s pyogenes cause
Tonsillitis
Pharyngitis
Impetigo
Cellulose of the foot
