gastrointestinal bacterial infections Flashcards
gastric acidity high ph kills majority of bacteria, how is gastric acidity disturbed
by drugs and gastric surgery
age and autoimmune conditions
intestinal motility in the fluid absorptive process maintains appropriate distribution of indigenous enteric flora
in ridding host of pathogenic micro-organisms.
how is intestinal motility disturbed
surgery and drugs opoids
mucosal integrity acts as a physical barrier and is essential for maintaining proper gut function such as digestion nutrient absorption and assimilation,
how is mucosal integrity disturbed
malignancy
inflammatory bowel disease
what are protective mechanisms at epithelial level
mucins
anti microbial peptides
commensal bacteria
innate immunity
which part of the gi tract has the most normal flow of bacterial flora
caecum
10^12
what does normal commensal flora do to protect the gi tract
aids development of intestinal immunity
resists colonisation by pathogens
produces antibacterial substances such as colicins( produced by ecoli and toxic to some ecoli strains, type of bacteriocin which is released to prevent competition from other bacterial strains)
interfere with virulence of pathogens
induce antimicrobial peptides
promote epithelial expression of lectins
how does innate immunity protect at the epithelial level
innate immune system
active against a large amount of pathogens
epithelial cell can recognise bacterial molecular structures such as lipopolysaccharide, peptidoglycan via toll like receptors
how do mucins protect at the epithelial cell level
glycoproteins consisting on a protein core with multiple oligosaccharide side chains
secreted and membrane bound forms
produced by goblet cells in the epithelium
multiple functions including a protective layer on epithelial surfaces
how do antimicrobial peptides protect at epithelial level
20-40 amino acid peptides
produced by a wide range of cells and on many different epithelial surfaces as well as by neutrophils
in the GIT secreted by paneth cells
alpha defensins, beta defensins, cathelicidins,
often act by forming pores in membranes interfering with metabolism and cytoplasmic components
also immunomodulatory actions
mucosal system of the gi tract
intestinal epithelial barrier
lamina popria (connective tissue under mucosal layer)
gut associated lymphoid tissue
peyers patchers isolated lymphoid follicles and mesenteric lymph nodes
inductor and effector sites
inductive sites, antigen sampled at mucosal layer and then activates naive and memory b t lymphocytes
effector sites where effector cells work
intestinal epithelial cell family
columnar m cells endocytose protein and peptide antigens, transport them into underlying tissue
taken up by dendritic cells and macrophages
these cells can present them to T cells in the GALT leading to appearance of immunoglobulin A secreting plasma cells in the mucosa
dendritic cells below epithelium can also sample luminal antigens
via pseudopods pushed between epithelial cells
also present enterocytes, endocrine cells, goblet cells, paneth cells
how does the adaptive immune system protect the gi tract
peyers patches
lymphoid follicles, located in the mucosa extend into submucosa of the small intestine especially the ileum
secretory IgA is transported into the lumen
interferes with adhesion and invasion of bacteria
small amounts of igG and IgM
t cells exposed to antigen at peyers patches migrate into the lamina popria and the epithelium, then mature into cytotoxic t cells
what are other host factors
personal hygiene
access to
systemic immunity
genetic/acquired
breastfeeding
vaccination
what are the sources of gi bacterial tract infections
person to person- helicobacter pylori, shigella
water (usually from faecal contamination) e,g vibrio cholerae
organisms present within food from the start
gut flora contaminating meat during slaughter campylobacter, E coli
shelfish contaminated by water supply e.g enteroviruses
contamination of vegetables with gut flora e.g fertilisers
organisms introduced into food during processing
contaminated processing plant e.g salmonella contaminated ingredients e.g some salmonella
contaminated food worker staphylococcus aureus
what is typhoid mary
