15. Host microbe interactions

Question 1

What are humans like as bacterial hosts? 5

Answer 1

1. humans are ecosystems harbouring 10^14 bacteria, called microbiota
2. these are permanent interactions
3. our microbiota are individual and unique to us, plus we have bacteriophages that predate on them
4. we have growth factors, optimum temp and pH for them
5. they have enzymes which break down complex carbs into sugars, plus fatty acids, which help us gain more calories form food
6. out microbiota coats gut surfaces, plus helps immune system

Question 2

What are conditions like in the host? 4

Answer 2

1. animal and human bodies provide organic nutrients
2. also, constant osmotic pressure
3. surface varies eg. skin, respiratory tract, gI tact
4. majority of our faeces is bacteria

Question 3

What are the different host surfaces? 6

Answer 3

1. surfaces select for the best adapted bacteria for ecological niche
2. skin is dry, salty and acidic eg. staphyloccocus epidermis, a grame positive bacterium
3. fewer bacteria live on skin than in gut
4. the lungs are usually sterile but have o2 for the aerobe mycobacterium tuberculosis. the nasopharynx is good at getting rid of bacteria
5. the large intestine is good for anaerobes, incl species of clostridium, a gram positive spore former
6. some places in the body are v good at supporting bacteria, others at expelling it

Question 4

What are bacterial systems around the body? 4

Answer 4

1. epithelial cells desquamate, so only small numbers of bacteria can attach to any cell
2. they then have to reattach to new cells underneath
3. eyes have a few bacterial systems eg. crying flushes out bacteria
4. bacteria coverage varies over the skin, they prefer warm, moist places eg. axillary fossa

Question 5

what are sites of infection in hosts? 5

Answer 5

1. mucous membranes - 400m2
2. include mouth, respiratory tract, gi tract
3. all have an normal flora
4. combinations of bacteria present vary massively between sites
5. majority of body is sterile eg, blood, organs, lymph, nerve systems

Question 6

what is the normal flora? 6

Answer 6

1. skin (2m2) has restricted biodiversity in sweat glands plus on skin - 180spp
2. some resident bacteria eg. staphylococcus epidermis and proprionibacterium acnes etc. live there all the time
3. 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
4. dental plaque - bacteria living interlocked forming a structured bacterial community
5. nasal commensal organisms eg. streptococcus spp achiomyces spp etc which cause diseases like meningitis coloize and make you ill if immune system is colonised

Question 7

describe the colonization of teeth. 6

Answer 7

1. MICROCOLONIES OF BACTERIA FORM ON TOOTH SURFACE -ATTACH TO SALIVARY PELLICLE RECEPTORS
2. other bacteria then bind to these, building a thick biofilm with a thick anaerobic under and aerobic surface
3. this takes around two days and the resulting network consists of primary and secondary colonizers
4. in mature plaque we see corncob formations - streptococcus bacteria surround a central bacterial rod
5. there is a metabolic exchange between them - mutualistic relationship
6. streptococcus mutants cause cares at tooth surface

Question 8

describe some research into gut bacteria. 6

Answer 8

1. recent explosion of research in this area
2. . obesity has been linked with gut flora
3. blooms and production of neruological chemicals seems to be connected to mental health
4. these bacteria depend on how you were born
5. flora depends on interaction with environment and diet
6. comparison is totally diet dependent

Question 9

what are stomach bacteria? 6

Answer 9

1. stomach is ph2 and creates a barrier to the gi tract
2. few bacteria, no significant bacterial flora except helicobacter pylori colonies, which has coevolved with us since cavemen
3. h. pylori is gram negative, motile rod with 5 polar flagella and colonizes mucosa of stomach in more than half of people
4. 80% of gastric ulcer patients carry h. pylori, develop due to problem in matching
5. h. pylori can lead to gastritis which can lead to gastric cancer
6. aslo stimulates grelin production, an appetite suppressant. antibiotics have a worldwide association with obesity

Question 10

Describe small intestine flora. 4

Answer 10

1. ph 4-5
2. low bacterial biomass
3. bacteria in colon do not back up into small intestine due to valve, therefore don’t eat out food
4. eeg. enterococci and lactobacilli

Question 11

Describe colon flora. 6

Answer 11

1. specialised fermentation vessel with ph7, huge bacterial biomass, 10^10-11 cells per gram
2. facutative aerobes can grow anaerobically and can use oxygen, use all o2 in gut and create anaerobic atmosphere eg. ecoli, enterococcus faecalis
3. 99% are obligate anaerobes
4. 1/3 of all faecal biomass is bacteria and we all have 1.5kg/3lbs in out gut
5. 1000 different spp in gi tract
6. diet dependent and difficult to change - takes on year plus for permanent change, although transient blooms can occur

Question 12

how is the microbiota associated with obesity? 4

Answer 12

1. normal mice consume less than germ free mice but have 42% more fat
2. microbes breakdown food to suagrs and short chain fatty acids, body gains calories
3. if you colonise germ free mice, they have 50% fat increase and become diabetic in 2 weeks
4. the mice are on the same diet, but their food wasn’t giving as much sugars or calorific value previously

Question 13

How doies the content of the bacterial flora contribute to obesity? 4

Answer 13

1. microbial flora in obese mice is different to in lean mice
2. GE obese mice have more fermicutes than bacteriodetes
3. heterozygotes have fewer fermicutes and more bacteriodetes compared to obese
4. treating obese mice with vancomycin, a strong antibiotic, causes mice to lose weight

Question 14

what are faecal microbiota transplants? 6

Answer 14

1. clostridium difficile infections were a multi drug resistant hospital problem
2. infections are more common and hard to get rid of
3. taking gi flora from a healthy donor and transplanting into person with infection means flora outgrows and outcompetes infection
4. one lady with normal bmi received a transplant from her obese sister
5. her diet didn’t change but she got fat
6. now, must match bmi of donor and recipient

Question 15

how do antibiotics interact with normal flora? 6

Answer 15

1. oral antibiotics inhibit normal flora and are being used inappropriately
2. giving to young children can cause long term detrimental effects
3. some cause sterilization of gi tract - wide spectrum antibiotics now recommended to be taken with probiotics
4. oppurtunistic pathogens invade eg. clostridium spp
5. c. difficile can casue colitis, where whole surface of gi tract is removed and causes diarrhea and ulcers, life threatening
6. can create a germ free environment on vagina with antibiotics, which leads to thrush casued by canolida albicans (yeast)

Question 16

what are the benefits of normal flora? 6

Answer 16

1. Synthesise and excrete vitamins eg k and b12, bifidobacterium is essential for this
2. prevent colonization by pathogens, compete for attachment sites and saturate potential sites
3. also compete for nutrients
4. antagonise other bacteria by production of bacteriocins to protect their niches
5. these are toxins that kill closely related bacteria, creating inhinibtion zones
6. they also help to establish immune defences