Microflora Flashcards
how many microbial cells are there in our body?
10^14 - this is 10x the amount of human cells
what is meant by organisms density varies at different sites of our body?
dry, exposed areas of skin harbour far fewer organisms that protected, moist areas of the skin such as groin, armpits or toes. The highest density is in the oral cavities and colon.
what is meant by normal flora/microbiota?
organisms found in a given location in a state of health
what is meant by colonisation?
establishment in a site of the body
what is meant by microbiota?
all the organisms in a given community
what is meant by microbiome?
all the genes present within the microbiota
what is meant by symbiosis?
two or more organisms that co-exist in close physical association - human host and normal flora have a symbiotic relationship
what is an example of mutualism?
nitrogen fixing bacteria and legumes
what is commensal flora?
normal flora
why is it difficult to define the extent to which human microbe relationships are commensalistic or mutualistic?
it is unclear what the role of flora is currently
what is commensalism?
when one organisms benefits but the other derives no benefit or harm
what is mutualism?
when both organisms benefit
what is parasitism?
when one organisms benefits at the expense of the other
what is neutralism?
when neither organism derives any benefit or harm
what is a non sterile site?
it is a site that has normal flora that is exposed to the environment either directly or indirectly.
why do non sterile sites exist?
until birth sterility is maintained but the baby is born and acquisition of normal flora begins. There is no mechanism to maintain sterility.
where are there differences in the acquisition of non sterility?
through C section compared to birth canal and through breast feeding (lactobacillus and bidiobacteria) and bottle feeding (enterobacteriacae)
what are sterile sites?
they have no normal flora - sterility is maintained through cleaning surfaces, physical separation from non sterile sites and barriers
what is special about barriers for sterility maintenance?
they have uni-directional flow - adjacent to non sterile sites e.g. upper genital tract separated by cervix
what influences locations of growth?
microenvironments and tissue tropisms
where are the microenvironments?
within a tissue or at different sites
what is tissue tropism?
propensity for a particular organism to grow in a particular habitat
what physical variables influence what organisms grow where?
oxygen availability temperature moisture pH nature of surface
what are the characteristics of skin?
dry variable temperature different component exposed aerobic subject to abrasion nutrient poor 2m^2 in adults
what is the gingival crevice?
it is in the mouth and is moist, constant temperature and has few physical challenges. It is an anaerobic environment with a mucosal surface component that is bathed in nutrients
why is there such a diversity of microbes in the mouth?
there are different ecological systems - soft tissue, non-epithelial, anaerobic
where are you most likely to find Actinomyces in mouth?
on the teeth - non-epithelial surface
how do humans adapt to the environment?
mouth, skin and nasopharyngeal flora, vagina and GIT
what is found in skin flora?
propionibacterium species (acne), coagulase-negative-staphylococci and staphylococcus aureus
what happens near a body orifice?
the skin flora will be similar to those in the orifice
what bacteria is found in the mouth flora?
viridans, oral streptococci and anaerobes
why is there a mutualistic relationship between human host and mouth flora?
mouth flora gain benefit from nutrients in host, but give the host vitamins that are synthesised and normal flora can prevent the colonisation of pathogenic
what does overflow of oral streptococci lead to?
biofilms on teeth converting sugars to lactic acid resulting in enamel damage and erosion of teeth
what comprises the naopharyngeal flora?
nostrils - skin flora - S aureus (40% of it)
pharynx - neisseria meningitidis, Strep. pneumoniae, pyogenes, haemophilius influenzae and S aureus
how can the pharyngeal flora cause infection in the LRT?
the respiratory epithelium can become compromised - bronchitis or pneumonia
what comprises the vaginal flora?
pre puberty - skin an dlower GIT flora - mainly E coli
post puberty - glycogen is produced due to circulating oestrogens - lactobacillus species (acidophilus) - ferment glycogen maintaining pH at 3 preventing the overgrowth of species, skin flora and a few C albicans - overgrowth if the pH is not maintained causes opportunistic infections and thrush
what comprises the GIT flora?
low gastric pH inhibits bacterial growth but there are mainly anaerobic bacteria until caecum where aerobic - acid tolerant lactobacilli and H pylori - counts increase distally
how many bacteria are in the GIT flora?
10^9-10^11 - over 400 species
bacteroides, clostridium and bifidifobacteria species
what is enteric gram negative bacilli and E coli?
aerobic bacteria
how is H pylori adapted?
it produces urease and converts urea into ammonia and CO2 and therefore is acid tolerant
what are the functions of normal flora?
metabolism, preventing colonisation, induction of cross reactive antibodies and nitric oxide production
how do normal flora help metabolism?
synthesis of secondary metabolites or vitamins - enteric bacteria secrete vit K and B12, and will ferment unused energy substrates (SCFA)
how do flora resist colonisation?
environmental manipulation such as maintaining a low pH and antibacterial agents - colicins, bacteriocins, FA, metabolic waste products
why is the induction of cross reactive ABs good?
may have a protective effect
what is E coli good for?
producing vitamin k for bone metabolism and blood clotting
what is butyrate for?
preventing bowel cancer and modulating the immune response
what is propionate for?
lowers cholesterol, anticarcinogenic activities, promotes satiety and prevents lipid lipidogenesis
what is nitric oxide used for and how is it produced?
vascular health - 25% of nitrate is returned to mouth, oral bacteria reduce it to nitrite which is absorbed and converted to Nitric oxide, and nitrate is good for reducing BP
what is acetate used for?
producing short chain FAs
what are acetate, butyrate and propionate used for collectively?
help to inhibit enteropathogens, provide energy to coloncytes or epithelial cells, promotes mucin production and affects gut hormone production for appetite modulation
what is a benefit of diversity?
redundancy of microbiota - other organisms can also perform same role
what is C. Difficile infection?
it is a HCAI that is due to antibiotic use largely - pertubation of normal colonic microbiota leads to C difficle overgrowth and leads to toxins and diarrhoea
what is the basis of Crohns?
with IBD there is less diversity of gut bacteria particularly antiinflammatory, immunemodulating and mucus disrupting - use Fecal F. prausnitzil to monitor as is commonly absent in Crohns
what is a fecal transplant?
use of bowel derived material to treat disease
what can this be used to improve?
MS, CFS, IBS, UC, diabetes, ideopathic thrombotic purpur
how is obesity related to microbiota?
obesity is associated with diminished bacterial diversity - increased antibiotic use in infancy is associated with higher early years BMI
what is the pathology of normal flora?
1) overgrowth - excessive in normal site
2) translocation - presence in wring site as spread, from one surface to another and inoculation into a normally sterile site
3) cross-infection
what is an example of overgrowth?
vaginal thrush - could have been recently treated with broad spectrum antibiotics - inhibition of colonisation resistance and therefore excessive growth of candida
what is conjunctivitis?
it is a translocation (e.g. from haemophilius influenza) from one surface to another. It presents as red eyes and purulent conjunctival discharge (following URTIs) with a cough and running nose
what is intravascular catheter infection?
it is a translocation of normal flora inoculating a normally sterile site. It presents with spiking fevers and is associated with administration of IV drugs. It could be due to coagulase-negative-staphylococci and is resolved by removing line
what is MRSA?
it is a multiresistant infection - methicillin resistance S, Aureus. Can result in pneumonia and is then grown in respiratory secretions - initially can colonise nose - cross infection
why is it difficult to determine the clinical significance of normal flora present in a sample?
opportunity for contamination is high in a sample, it is often difficult to determine if they are there for benign causes or pathogenic, could be acute or latent
what conditions are caused by normal flora?
pneumonia, endocarditis, urogenital infections, abscesses, dental caries, peridontal disease and pharyngitis, gastroenteritis and peritonitis
