lec 5-6 - clinical microbiology Flashcards
mucous
solution containing glycoproteins and proteins
MALT is found in most mucous membranes
MALT
mucosa-associated lymphoid tissue
primary lymphoid organs
thymus
bone marrow
mechanical protection of mucous
hairs
skin
bacteria in blood
septicemia
what type of bacteria has outer phospholipid bilayer
gram -ve
antimicrobial secretions in GI tract - stomach
- gastric acid
- acidic pH2
helicobacter pylor causes stomach ulcers
paneth cells
secrete lysozyme
found at the end of the crypts of Lieberkühn
intestinal glands
natural bacteria that colonize mucous membranes
have their own antimicrobial peptides so are more effective
interfere with membranes
form pores
enter cells and affect RNA
why do antimicrobial peptides attach better to bacteria
acidic on outside of membrane
no cholesterol
leukocidin
cytotoxin produced by bacteria to kill macrophages
exotoxins
formed and secreted by bacteria
most are gram +ve
split into 3 groups
very potent
3 groups of exotoxins
neurotoxins
enterotoxins
cytotoxins
neurotoxin
exotoxin that is destructive to nerve tissue
causes lockjaw/tetanus
enterotoxin
exotoxin produced in and affecting the intestines
causes vomiting and diarrhoea
cytotoxin
exotoxin or antibody
has specific toxic actions causing cell death
endotoxin
normally gram -ve
not secreted - released when cells are disrupted
heat stable
less potent and less specific than exotoxins
capsules
important in preventing phagocytosis
allows infection process to continue
proteinaceous components of cell not seen
4 requirements for disease
portals of entry
establishment (adherence factors)
avoiding host defences
damaging host
mucous membranes
form protective covering that resists penetration and traps microbes
bathed in antimicrobial secretions
how do we protect our mucous membranes
wash with secretions - e.g. saliva, tears, mucous, urine
filter hairs in nasal passage
cilia in respiratory tract
skin
keratinised tough mechanical barrier slightly acidic pH - fatty acid chains high NaCl conc. subject to periodic drying
lactenin
proteins in breast milk
protect against mastitis
bacteriocidal against streptococcys pyogenes
antimicrobial secretion sin GI tract - intestines
pancreatic/intestinal enzymes bile GALT (Gut associated lymphoid tisue) secretory IgA paneth cells - produce lysozymes, cryptins
genitourinary tract
low pH of urine and vaginal epithelia
toxic metabolites (urea) present in urine
hypertonic kidney medulla
flushing with urine and mucous
3 types of antimicrobial peptides
defensins
cationic peptides
bacteriocins
defensins
antimicrobial peptides
rich in arginine and cysteine
function:
- defend from pathogens
- shape microbiota
- protect stem cells
bacteriocins
antimicrobial peptides
lethal to closely related species
e.g. colicins, sakacins
peyer’s patches
patches of lymphatic tissue
monitor intestinal bacteria and prevent growth of pathogenic bacteria in small intestine
coagulate mechanisms for evading host defence systems
cause fibrin clots in blood of host
fibrin walls off the infection
anatomical structures outside bacterial cell wall
glycocalyx
fimbriae and pili
flagella and axial filaments
glycocalyx
polysaccharides and proteins
thin surrounding slime layer
can form a capsule
fimbriae and pili
involved in adherence
found on gram -ve
aids motility
flagella and axial filametns
protrudes beyond cell wall and glycocalyx
aids movement to distal tissues
can produce rotational movement of whole organism
4 main types of HCAIs
UTIs
surgical site infections
bloodstream infections
pneumonia
5 ways to determine the cause of an infection
rapid tests and immunoassays molecular testing biochemical tests culture microscopy
3 types of stain based microbiology
gram stain
acid fast stain
PAS
gram stain
differentiates between gram +ve and -ve
gram +ve stains purple
acid fast stain
ziehl-neelson stain
specific
no need for culture
performed directly on sputum
sputum
saliva/mucous coughed up and used to test for infection
PAS
periodic acid schiff
stains for polysaccharides and glyoproteins
disadvantage - high background
selective media
support growth of one type of organism while inihbiting growth of another
e.g. mannitol salt agar
agglutination assays
uses immune system to tell us what weve got
doesnt require a culture
detection of viral infections
lack of agglutination can be used as the measure of infection
mass spectrometric methods
MALDI TOF
ESI
cheaper than sequencing
reliant on databases of known patterns
NAATs
nucleic acid amplification techniques
doesnt detect live or dead cheap sensitive no standard for comparison prone to error in set up
