1.5. Normal bacterial flora & colonization resistance Flashcards
normal flora (microbiota)
microbes which exist on body surfaces (skin & mucous membranes)
resident flora
microbes that usually occupy a particular body site
transient flora
microbes that colonize a site transiently only (even for hours to weeks)
Commensalism:
the microbe derives benefit from the host and the host is not harmed
Mutualism:
- Both the host and the microbe benefit from the interaction
•Digestion and fermentation of carbohydrates (NB. Short chain fatty acids)
•Production of vitamins
•Development of gut-associated lymphoid tissue (GALT)
•Polarization of gut-specific immune responses
•Prevention of colonization by pathogens
Parasitism:
The microbe benefits at the expense of the host
which local and systemic processes do gut micrbiota influence?
- Gut-to-brain communication
* Proper functioning of the gut microbiota is dependant on a stable cellular composition
Dysbiosis
-disturbance in composition and function of microbiota.
-Alterations can persist for prolonged periods and often the initial state is not completely recovered.
•Several exogenous and endogenous factors can affect the composition of the gut microbiota
•Use of antibiotics: Suppression of (components of) the normal flora and changes in metabolism in the gut
•Diet: high sugar, high fat and low amounts of fermentable fibre
•Impact of dysbiosis can be far-reaching: loss of colonization resistance, risk/severity of auto-immune conditions, neurological disorders and metabolic disorders
which factors alter host-normal flora relationship?
- dysbiosis
- change in host local non-specific defence mechanisms
- systemic immune-compromise
Upper Respiratory Tract Normal Flora
- Gram-positive facultative aerobic bacteria
•Viridans streptococci, β-haemolytic streptococci,
*Staphylococcus aureus(10-40% of individuals are nasal carriers), Streptococcus pneumoniae(5-60% of individuals), diphtheroids, lactobacilli - Gram-negative facultative aerobic bacteria
•Haemophilus species,Moraxella catarrhalis, Neisseria spp - Anaerobic bacteria
•Fusobacteriumspp, Actinomycesspp - Yeasts
•Candida albicans - Viruses
•Enteroviruses, Adenovirus
Gastrointestinal Tract Normal Flora
- Stomach: Salivary microbes (streptococci, lactobacilli, Candida spp)
- Upper small bowel: Usually sparse flora; salivary microbes
- Ileum: Escherichia coli, enterococci, and equal numbers of obligate anaerobes
- Colon: Abundant microbes; predominantly obligate anaerobes (Bifidobacterium spp, Bacteroides fragilis, Peptostreptococcus spp) . E.coli, other Enterobacterales (Enterobacter spp, Klebsiella spp), enterococci, streptococc
Genitourinary Tract
- Lower urethra: Enterobacterales, streptococci, enterococci
- Vagina: As above, plus Lactobacillus spp, anaerobes
Skin Normal Flora
Coagulase-negative staphylococci (CNS), Bacillus spp, diphtheroids, Propionebacterium spp, *Staphylococcus aureus (perineum and axilla in some individuals), Streptococcus viridans, Micrococcus spp
what is colonization resistance?
Normal flora play an important role in protecting the host from colonization and invasion by pathogenic microbes(microbes that are able to cause infections)
name the direct mechanisms that influence normal flora composition
- Competition for the same nutrients
- Competition for the same receptors on host cells
- Production of secreted products that are toxic to other organisms (for example, bacteriocins)
name the indirect mechanisms that influence normal flora composition
- Enhancement of epithelial barrier function
- Stimulation of innate immune system
- Stimulation of adaptive immune system
what are probiotics?
live microorganisms which, when consumed in adequate amounts, confer a health benefit to the host
what GIT and other diseases can probiotics treat?
- Acute gastroenteritis
- Antibiotic-associated diarrhoea
- Clostridium difficile-associated diarrhoea
- Necrotizing enterocolitis
- Urinary tract infections
- Eczema
- Inflammatory bowel disease
- Obesity-related disorders
- Liver disease
what are the most commonly studies probiotic organisms?
Bifido bacterium and Lactobacillus genera
what are probiotic mechanisms of action?
- Remodelling of microbial communities and suppression of pathogens (includes factors discussed under colonization resistance)
- Promotion of intestinal barrier function
- Immunomodulation
- Effects on epithelial cell differentiation
future research on probiotics
- Characterize probiotics and their mode of actions against specific pathogens
- Identification of vulnerabilities within target pathogens to aid probiotic design
