gi pathogens Flashcards
what is colonisation ?
the establishment of microorganism on or within a host
what is a pathogen ?
any organism that has the potential to cause diseases
how can we diagnose infection via microbiology ?
blood stool urine wound tissue cultures
describe the process in which pathogens invade
- invasion by pathogen
- incubation period (pathogen replicates in host)
- which leads to subclinical infection / the prodromal period ( early signs and symptoms )
- illness period ( clinical signs and symptoms )
- convalescent period ( reduction of symptoms )
- host may become a chronic carrier of infectious agent
what do phagocytes target ?
bacteria and fungi
what do T lymphocytes target ?
viruses, fungi, protozoa
what do antibodies and B lymphocytes target ?
viruses
what do eosinophils target ?
fungi protozoa worms
what do mast cells target ?
worms
what does the complement system target ?
bacteria
what do the macroscopic investigations include ?
colony size
shape
pattern
haemolysis
what do the microscopic investigations include ?
gram stain
organism shape
antigenic properties
why do gram + bacteria stain darker (purple/blue) ?
they have a much thicker peptidoglycan layer and so traps the crystal violet better
what are the main differences between gram + and - ?
gram + bacteria have a thick peptidoglycan layer, have no outer membrane and stain purple
gram - bacteria have a thin peptidoglycan layer, have an outer membrane and stain pink
what are the lactose fermenting gram - rods (enterobacteriacea) ?
*most common for causing infection in the gi tract
e. coli
citrobacter spp
klebsiella spp
enterobacter
what are the lactose non-fermenting gram - rods ?
morganella proteus providencia salmonella shigella
what are the gram - anaerobic bacilli ?
bacteroides
prevotella
porphyromonas
fusobacterium
what are the gram - anaerobic cocci ?
veillonella
what are the microbiological tests for enterobacteriaceae ?
- ferment glucose
- oxidase
- blood agar
- MacConkey agar (lactose fermenters turn it pink)
- CLED agar (Cysteine Lactose Electrolyte Deficient)
- chromogenic agar
characteristics of enterobacteriacea ?
gram - non spore forming grow on a variety of media ferment sugars (- produce lactase and lack oxidase) mostly facultative anaerobes increasing resistance !
how do enterobacteriacea cause disease ?
motility - flagella are motile (shigella and klebsiella are not motile though)
colonisation factors (fimbriae can tightly bind)
endotoxin (part of the outer membrane of the LPPs)
enterotoxin
what is MALDI-TOF mass spectrometry ?
- it analyses the protein composition of bacterial cell wall
- uses a database
- discriminates between highly genetically similar organisms with identical 16s rRNA
- pathogenic vs non-pathogenic E.coli may be difficult to differentiate
- some species are difficult for MALDI-TOF to differentiate between ie e.coli and salmonella
what is 16s rRNA ?
another molecular method to determine bacteria
- whole genome sequencing
- pulsed field gel electrophoresis
- multilocus sequence typing (MLST)
- multiple locus variable number tandem
what is serotyping ?
determining the immunoreactivity of various antigens
