lecture 5) clinical microbiology 1 Flashcards
name 4 requirements for a disease
portal of entry
avoid host defences
establishment
damages host
what is characteristic about the main portals of entry?
they are lined with mucous membranes
what is mucuous and what is its importance?
liquid solution
composed of glycoproteins
retains moisture
what are mucous membranes protected with?
hair
skin
washing secretions
cilia
what are the main roles of mucous membranes?
protective covering
resists penetration
traps microbes
what are mucous membranes bathed in?
antimicrobial secretions
what is the main enzyme in antimicrobial secretions?
lysozyme
what type of bacteria is lysozyme?
gram positive
what does lysozyme do?
breaks glycosidic bonds in peptidoglycan
mucous contains MALT. what is MALT?
mucosal associated lymphoid tissue
what are the primary lymph organs?
bone marrow
thymus
what are the secondary lymph organs?
MALT
lymph nodes
many body fluids are not suitable for bacterial growth. why is this?
makes it inhospitable for the pathogen so it cannot cause infection
what is the importance of iron?
everything needs iron to live
how do bacteria gain iron from the host?
secrete siderophores
rip off iron and hold it
when this happens the skin becomes slightly acidic
what is the bacterial growth inhibitor found in breast milk?
lactenin
what makes lactenin a bacterial growth inhibitor?
it is selectively bactericidal
what are antimicrobial peptides?
peptide produced by bacteria that are lethal to closely related bacterial species
what do antimicrobial peptides do?
produced by bacteria
destroy the membrane
tamper with DNA and RNA
what makes antimicrobial peptides so selective?
always carry more of a negative charge on their membranes that eukaryotic cells
creates an electrostatic attraction
describe the antimicrobial peptide sakacin
produced by lactobacilli (eg liseria, gram positive)
some have been engineered for mass food production
describe the antimicrobial peptide colicin
produced by E.coli
used in polymixin antibiotics
LAST resort of antibiotics as they cause terrible collateral damage
names the defensins of the respiratory tract
beta defensins
give an example of a beta defensin found in the respiratory tract
cathelicidin
what are defensins?
cysteine rich cationic proteins that act as defensive proteins
what is cathecilidin also known as?
LL37
what cells produce cathecilidin?
neutrophils
epithelial cells
what is the mode of function of cathecilidin as a beta defensin in the respiratory tract?
have an ampithatic structure (hydrophobic and hydrophillic regions)
hydrophobic region interacts with lipids
hydrophillic regions come together
unordered structure becomes ordered which impacts pore formation
what does the stomach secrete to make the pH 2?
gastric acid
what bacteria has been found in the stomach to have links with causing stomach ulcers?
heliobacter pylori
what do the intestines secrete?
IgA
pancreatic enzymes
bile
GALT (gastrointestinal associated lymphoid tissue)
what sort of movement is carried out by the intestines?
peristalsis
where are the paneth cells found?
crypts of liberkun
what enzyme do paneth cells secrete?
lysozyme
what type of defensins are found in the GI tract?
alpha defensins
what makes the alpha defensins in the GI tract different to the beta defensins in the respiratory tract?
open-ended
argenine and cysteine residues
3 pairs of intramolecular disulphide bonds giving them a different secondary and tertiary structure
what is the major difference between gram positive and gram negative bacteria?
gram negative have an outer phospholipid bilayer whereas gram positive bacteria have a thicket peptidoglycan cell wall
what is present in gram positive bacteria that is a good vaccine target?
teichoic acid
why is it good to have a good vaccine target?
antibiotic resistance is on the rise
give 2 examples of gram positive bacteria that have teichoic acid
C. diff
S. aureus
what was the first surface protein found in gram positive bacteria?
protein M
what makes M protein a good target?
protrudes cell wall therefore good attachment
give an example of a gram positive bacteria that has M proteins
Strep. pyogenes
what acid in gram positive bacteria prevents the action of many antibiotics? give an example of a bacteria that has this acid
mycolic acid
TB
what does lipid A do in gram negative bacteria?
anchors LPS
if lipid A anchors the LPS, what happens?
heightened reaction
what type of toxin is lipid A?
endotoxin
what antigen is found in gram negative bacteria that is very variable, used in typing and that is recognised by the immune system?
O antigen
what is the name for a structure found in gram negative bacterial cell walls that is composed of polysaccharised and proteins?
glycocalyx
what is the importance of glycocalyx in the cell wall of gram negative bacteria?
creates a loose slime layer
highly organised - can make capsules so the bacteria can avoid the host’s immune cells
where are flagella and axial filaments found in gram negative bacteria?
beyond the cell wall
what is the function of flagella and axial filaments?
aids movement
name an alternative to flagella that are shorted in length
fimbrae and pili
name a mechanism that the fimbrae and pii use for immune evasion?
antigenic variation
change protein in pili
what is DNA’s contribution to antibiotic resistance?
it has caused it to spread as it has replicated the genes that have evolved to be resistant to antibiotics
components of bacterial cell walls can be targets for what?
therapeutics
what can ribosomes be targets for in bacterial cells?
antibiotics
what damage do neurotoxins cause?
damage to nervous system
cause paralysis
eg. tetnus lock jaw
what impacts to enterotoxins cause in the host?
sickness and diarrhoea AB toxin (can be both)
what impacts do cytotoxims have on the host?
cell death
neurotoxins, enterotoxins and cytotoxins are all examples of what type of toxins?
exotoxins
anthrax, diphtheria and vibrio are all examples of exotoxins. what is similar about them?
all gram positive
most exotoxins are
very bad news if you have an exotoxin that is gram negative
are exo and endotoxins gram negative or positive?
endo = negative exo = positive
where are exo and endotoxins found?
endotoxins found on the cell wall
exotoxins found extracellularly
what are the structures of exo and endotoxins
exo = polypeptide endo = LPS complex
which are more stable, exo or endotoxins?
endotoxins
which are weaker, exo or endotoxins?
endotoxins are weaker therefore have a larger lethal dose
what do endotoxins cause in the host?
fever
which are more specific, exo or endotoxins?
exo = specific endo = non-specific
name 2 compounds that streptococcus bacteria have to avoid the host’s defences?
coagulase
leukocidens
what do leukocidens kill?
white blood cells
what type of toxin are leukocidens?
cytotoxins
what group of bacteria produce leukocidens?
staph and strep
what does coagluse do?
causes fibrin blood clots in host
what makes strep more virulent than staph?
strep produces coagulase
what is the impact of antibiotics on gut microbiota?
antibiotics disturb the gut microbiota
if the gut microbiota is disturbed when using antibiotics to treat C.diff, what is the outcome?
diarrhoea
what makes a pathogen established in a host?
surface of the bug interacts with the host
what nearly always causing adhesion of the bug to the host?
proteins or carbohydrates or both (glycoproteins)
name a structure in bacteria that helps with adhesion
pili
what do pili do to help adhesion?
help bacteria attach and penetrate as they attach to receptors on the host’s surface
how do pili retract and what impact does this have on the bacteria when they are trying to establish themselves in the host?
retract via motors
bring bacteria closer to the host
