Clinical microbiology Flashcards
requirements of disease
Portals of entry, establishment, avoiding host defences, damaging the host
portals of entry
mucous membranes
how are mucous membranes protected
(1) washing with secretions .e.g tears, saliva, mucus, and urine
(2) filtet hairs in nasal passages prevent entry of large particles
(3) cilia in respiratory tract pushes mucous and microbes upwards
non specific innate mechanisms: mechanical factors
keratinized surface of skin- touch- acts a barrier against entry i.e. mechanical barrier to microbial invasion.
mucous membranes
forma protective covering that resists penetration and traps many microbes. often bathed in antimicrobial secretions which contain a variety of antimicrobial substances
Mucosal associated lymphoid tissue(MALT)
is a diffuse system of small concentrations of lymphoid tissue found in various submucosal membrane sites of the body, such as the gastrointestinal tract, thyroid, breast, lung, salivary glands, eye, and skin.
primary lymph organs
thymus and the bone marrow
antimicrobial secretions
many body fluids e.g. the blood are not suitable;e for microbial growth due to the presence/ absence of various factors
why some body fluids aren’t suitable for microbial growth
1) normal iron is not bioavailable in blood or breast milk
2) long chains of fatty acid (oleic acid) occur in slight acidic secretions of the skin (pH4-6) and these ar lethal to many bacteria
3) lactenin- proteins present in breast milk which are selectively bactericidal for streptococcus pyogene, protect against mastitis (inflammation of the mammary gland)
lactenin
nitrogenous substance present in milk. It has antimicrobial properties.
mastitis
inflammation of the mammary glad
what do lysozyme do
hydrolyse bonds connecting sugars in peptidogylcans- action of lysozyme on the cel wall of Gram +ve bacteria. Peptidoglycan backbone , B(1-4) bonds connecting alternating N-acetylgucosamine and N-acetylmuramic acid (NAM) residues
what secretions are antimicrobial in stomach
gastric acid
what secretions are antimicrobial in intestine
-pancreatic enzymes, bile, intestinal enzymes, GALT, peristalsis
what secretions are antimicrobial in large intestine
- shedding of columnar epithelial cells
- secretory IgA
- normal microbiota
- Paneth cells
paneth cells in the large intestine produce
lysozyme and cyptins
what protects the genitourinary tract
- low pH of urine and vaginal epithelia
- urea and other toxic metabolic end products in urine.
- hypetonic nature of kidney medulla.
examples of antimicrobial peptides
defensives, cationic peptides, bacteriocins
defensins
peptides that are open ended, rich in arginine and cycsetine and disulphide linked (quaternary structure).
- they are highly hydrophobic and hydrophilic regions
where are defensives found
neutrophils, intestinal Paneth cells and intestinal and respiratory epithelial cells
function of defensives:
(1) defend from pathogens
(2) shape microbiota
(3) protect stem cells
cationic peptiden example
Cathelicidin
cathelicidin
produced by a variety of cells e.g. neutrophils and respiratory epithelial cells
bacteriocins
peptides produced by bacteria including normal microbiota. lethal to closely related species
examples of bacteriocins
e.g. Colitis produced by E.coli e.g. Saracens produced by lactobacilli
establishment of bacteria in host cell
attachment is usually far away and then tightens
mechanism of adherence of Mycoplasma pneumoniae
forms a protein rich tip organelle
mechanism of adherence of streptococcus pneumoniae
Riga, Pillin tip protein; PsaA
mechanism of adherence of Neisseria meningitidis
adhesion complex protein ACP: FBP
mechanism of adherence of Treponema pallidum
FBP and LBP in genitourinary tract
mechanism of adherence of Neisseria gonorrhoeae
Type IV pilli
mechanism of adherence of Shigella species
mechanism not known
mechanism of adherence of Escheichia coli
bundle forming pilli
mechanism of adherence of Vibrio cholerae
OmpU
adherence factors are associated with
establishment of infection
the bacterial cell wall: gram positive
thick peptidoglycan level, with lipoteichoic acid and wall techie acid
the bacterial cell wall: gram negative
Lipid A anchors LPS to the outer phospholipid bilayer. Release of this leads to a heightened immune reaction- endotoxin.
-O-antigen is highly variable and recognised by the immune system- can be used in typing.
glycocalyx
made of polysaccharide and proteins. If loosely attached referred to as a slime layer
if the glycocalyx is highly ordered
known as a capsule
capsules
important in preventing phagocytosis edna allowing the infection process to continue
e.g. encapsulated Klebsiella anthraces and Strep are not infectious if un-encapsulated
Fimriae and pilli
Involved in adherence e..g bundle forming pili from E.coli. Typically found on gram negative bacteria. Aids in motility, so is therefore a potential vaccine candidate
s pilli
secreted fragments that soak up antibody
flagella and axial filaments
- protrudes far beyond cell wall and glycocalyx
- aids in movement to distal tissues
- H.pylori uses flagella to penetrate through gastric mucous
axial filaments
can oriduce a rotational movement of the whole organism