15. Host microbe interactions Flashcards
1
Q
What are humans like as bacterial hosts? 5
A
- humans are ecosystems harbouring 10^14 bacteria, called microbiota
- these are permanent interactions
- our microbiota are individual and unique to us, plus we have bacteriophages that predate on them
- we have growth factors, optimum temp and pH for them
- they have enzymes which break down complex carbs into sugars, plus fatty acids, which help us gain more calories form food
- out microbiota coats gut surfaces, plus helps immune system
2
Q
What are conditions like in the host? 4
A
- animal and human bodies provide organic nutrients
- also, constant osmotic pressure
- surface varies eg. skin, respiratory tract, gI tact
- majority of our faeces is bacteria
3
Q
What are the different host surfaces? 6
A
- surfaces select for the best adapted bacteria for ecological niche
- skin is dry, salty and acidic eg. staphyloccocus epidermis, a grame positive bacterium
- fewer bacteria live on skin than in gut
- the lungs are usually sterile but have o2 for the aerobe mycobacterium tuberculosis. the nasopharynx is good at getting rid of bacteria
- the large intestine is good for anaerobes, incl species of clostridium, a gram positive spore former
- some places in the body are v good at supporting bacteria, others at expelling it
4
Q
What are bacterial systems around the body? 4
A
- epithelial cells desquamate, so only small numbers of bacteria can attach to any cell
- they then have to reattach to new cells underneath
- eyes have a few bacterial systems eg. crying flushes out bacteria
- bacteria coverage varies over the skin, they prefer warm, moist places eg. axillary fossa
5
Q
what are sites of infection in hosts? 5
A
- mucous membranes - 400m2
- include mouth, respiratory tract, gi tract
- all have an normal flora
- combinations of bacteria present vary massively between sites
- majority of body is sterile eg, blood, organs, lymph, nerve systems
6
Q
what is the normal flora? 6
A
- skin (2m2) has restricted biodiversity in sweat glands plus on skin - 180spp
- some resident bacteria eg. staphylococcus epidermis and proprionibacterium acnes etc. live there all the time
- some transient bacteria eg. e. coli and viruses that wont live on skin eg. hands for long
4, oral cavity - very high biodiversity, 300+spp - dental plaque - bacteria living interlocked forming a structured bacterial community
- nasal commensal organisms eg. streptococcus spp achiomyces spp etc which cause diseases like meningitis coloize and make you ill if immune system is colonised
7
Q
describe the colonization of teeth. 6
A
- MICROCOLONIES OF BACTERIA FORM ON TOOTH SURFACE -ATTACH TO SALIVARY PELLICLE RECEPTORS
- other bacteria then bind to these, building a thick biofilm with a thick anaerobic under and aerobic surface
- this takes around two days and the resulting network consists of primary and secondary colonizers
- in mature plaque we see corncob formations - streptococcus bacteria surround a central bacterial rod
- there is a metabolic exchange between them - mutualistic relationship
- streptococcus mutants cause cares at tooth surface
8
Q
describe some research into gut bacteria. 6
A
- recent explosion of research in this area
- . obesity has been linked with gut flora
- blooms and production of neruological chemicals seems to be connected to mental health
- these bacteria depend on how you were born
- flora depends on interaction with environment and diet
- comparison is totally diet dependent
9
Q
what are stomach bacteria? 6
A
- stomach is ph2 and creates a barrier to the gi tract
- few bacteria, no significant bacterial flora except helicobacter pylori colonies, which has coevolved with us since cavemen
- h. pylori is gram negative, motile rod with 5 polar flagella and colonizes mucosa of stomach in more than half of people
- 80% of gastric ulcer patients carry h. pylori, develop due to problem in matching
- h. pylori can lead to gastritis which can lead to gastric cancer
- aslo stimulates grelin production, an appetite suppressant. antibiotics have a worldwide association with obesity
10
Q
Describe small intestine flora. 4
A
- ph 4-5
- low bacterial biomass
- bacteria in colon do not back up into small intestine due to valve, therefore don’t eat out food
- eeg. enterococci and lactobacilli
11
Q
Describe colon flora. 6
A
- specialised fermentation vessel with ph7, huge bacterial biomass, 10^10-11 cells per gram
- facutative aerobes can grow anaerobically and can use oxygen, use all o2 in gut and create anaerobic atmosphere eg. ecoli, enterococcus faecalis
- 99% are obligate anaerobes
- 1/3 of all faecal biomass is bacteria and we all have 1.5kg/3lbs in out gut
- 1000 different spp in gi tract
- diet dependent and difficult to change - takes on year plus for permanent change, although transient blooms can occur
12
Q
how is the microbiota associated with obesity? 4
A
- normal mice consume less than germ free mice but have 42% more fat
- microbes breakdown food to suagrs and short chain fatty acids, body gains calories
- if you colonise germ free mice, they have 50% fat increase and become diabetic in 2 weeks
- the mice are on the same diet, but their food wasn’t giving as much sugars or calorific value previously
13
Q
How doies the content of the bacterial flora contribute to obesity? 4
A
- microbial flora in obese mice is different to in lean mice
- GE obese mice have more fermicutes than bacteriodetes
- heterozygotes have fewer fermicutes and more bacteriodetes compared to obese
- treating obese mice with vancomycin, a strong antibiotic, causes mice to lose weight
14
Q
what are faecal microbiota transplants? 6
A
- clostridium difficile infections were a multi drug resistant hospital problem
- infections are more common and hard to get rid of
- taking gi flora from a healthy donor and transplanting into person with infection means flora outgrows and outcompetes infection
- one lady with normal bmi received a transplant from her obese sister
- her diet didn’t change but she got fat
- now, must match bmi of donor and recipient
15
Q
how do antibiotics interact with normal flora? 6
A
- oral antibiotics inhibit normal flora and are being used inappropriately
- giving to young children can cause long term detrimental effects
- some cause sterilization of gi tract - wide spectrum antibiotics now recommended to be taken with probiotics
- oppurtunistic pathogens invade eg. clostridium spp
- c. difficile can casue colitis, where whole surface of gi tract is removed and causes diarrhea and ulcers, life threatening
- can create a germ free environment on vagina with antibiotics, which leads to thrush casued by canolida albicans (yeast)
