Transcript Microbial Growth

Microbial Growth
In Cows, Humans, & Other Animals
Ruminant Microbiota
• Cows, sheep, goats, etc. evolved to
forage on grasses.
• Rumen precedes stomach.
• In developed countries, cows are fed
grain (esp. corn) to speed up growth.
• The normal microbiota are used to grass
(high fiber, low starch).
Grass-fed Microbiota
• Fibrobacter, Ruminococcus, Eubacterium,
and other genera reside in the rumen.
• They possess the enzymes to digest the
fiber into monosaccharides
• Animal cells do not
• Many of these bacteria are pH-sensitive
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Russell & Rycklik (2001). “Factors that Alter Rumen Microbial Ecology.” Science 292:
1119-22.
Switching to Grain
• Promotes new types of fermentation.
– Acetic & butyric replaced by lactic.
• Acids build up in rumen, lowering the pH.
– ~7.0 lowered to 4.6.
• Metabolism of fiber is compromised.
Altered Bacterial Profile
• Growth of new, often pathogenic,
bacteria is promoted.
• Also pathogenic in humans!
– E.coli O157:H7, Campylobacter.
• Antibiotics in animal feed.
– Bacteria evolve resistance.
Environmental Conditions
• pH
• Temperature
• Osmolarity
• Oxygen levels
• Nutrients
• Toxins
Oxygen
• Obligate aerobes – Mycobacterium
• Facultative anaerobes – E.coli, enterics
• Obligate anaerobes – Clostridium
• Aerotolerant anaerobes – Lactobacillus,
Streptococcus pyogenes
• Microaerophiles – Micrococcus luteus
See also table 6.1
(a) Obligate aerobes; (b) obligate anaerobes;
(c) facultative (an)aerobes;
(d) microaerophiles; (e) aerotolerant anaerobes
Detoxifying Oxygen
• Superoxide Dismutase (SOD), Catalase,
Peroxidase
• Superoxide free radicals: O2O2- + O2- + 2H+  H2O2 + O2 (SOD)
2 H2O2  2 H2O + O2 (catalase)
H2O2 + NADH + H+  2 H2O + NAD+
(peroxidase)
Catalase Test
Detoxifying Oxygen
• Obligate anaerobes lack all 3 enzymes
• Obligate aerobes always produce these
enzymes
• Facultative anaerobes do so under
aerobic conditions
• Aerotolerant anaerobes can produce SOD
• Microaerophiles are sensitive to high O2
The Human Gut
Genera & Species in your Gut
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Lactobacillus spp.
Bifidobacterium spp.
Bacteroides fragilis
Bacteroides oralis
Bacteroides
melaninogenicus
Clostridium perfringens
Clostridium septicum
Clostridium tetani
Pseudomonas aeruginosa
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Escherichia coli
Enterococcus faecalis
Salmonella enteritidis
Klebsiella pneumoniae
Enterobacter aerogenes
Proteus mirabilis
Staphylococcus aureus
Streptococcus spp.
Lactococcus lactis
Human Intestinal Microbiota
• 90 – 95% are obligate anaerobes
Bifidobacterium, Clostridium, Eubacterium, Fusobacterium,
Peptococcus, Peptostreptococcus and Bacteroides
• Up to 10% are facultative/aerotolerant
anaerobes
Lactobacillus, Escherichia coli, Klebsiella, Streptococcus,
Staphylococcus and Bacillus
• Pseudomonas – only known obligate aerobe
• 1011 – 1012 CFUs per ml
• ~1.2 kg
• Lactobacillus and Bifidobacterium:
– control pH.
– Produce bacteriocins.
– Take up space.
– Interact with WBCs.
– Interfere with quorum sensing.
• Intestinal microbiota produce many
vitamins and digest certain carbs.
Scientific Findings?
• Lactobacillus interferes with pathogens.
• Probiotic treatments can alleviate
symptoms of infant diarrhea.
• The Microbiome.
Conversations with the Host
• Stimulate production of mucus.
• Interact with the immune system.
• Interfere with activities of pathogens.
• Xavier & Podolsky (2000). “How to Get Along – Friendly Microbes in a
Hostile World.” Science 289: 1483-4.
• Neish et al. (2000). “Prokaryotic Regulation of Epithelial Responses by
Inhibition of Ik B- Ubiquitination.” Science 289: 1560-3.
Newer Experiments
• Germ-free mice.
– Gnotobiotic studies.
• Single organism studies.
• Microbiome transplants.
“Germ-Free” Animals
• Decreased resistance to infection.
• Chronic inflammation.
• Used for gnotobiotic studies.
“Germ-Free” Mice
The role of the immune system in governing host-microbe interactions in the intestine. Brown et al. (2013).
Nature Immunology 14, 660–667.
Bacteroides fragilis
Gram stain
Example of a single organism study.
Bacteroides fragilis
• Polysaccharide A (PSA) regulates
immune response.
• B. fragilis eases symptoms of ulcerative
colitis (induced by infection) in mice.
• So does purified PSA.
Obesity Study
• Fecal transplantation from human to
mice.
• Two groups: obese adults and lean
adults.
• Effects on mouse weight gain.
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Ridaura et al. (2013). Gut Microbiota from Twins Discordant for Obesity Modulate
Metabolism in Mice. Science 6 September 2013: Vol. 341 no. 6150.
More Connections
• Autism.
• Autoimmunity.
• Allergies.
• Diabetes.
• What else will be discovered?
Probiotics
• Foods with live microbes that promote
good health.
• Yogurt, kefir, raw sauerkraut, miso,
kombucha, and more.
• [Pasteurized products – no live beneficial
organisms.]
• OTC pills – freeze-dried, live microbes.
Probiotic Organisms
• Many Lactobacillus species
• Bifidobacterium
• Eubacterium
• Normal residents of the human GI tract.
Probiotics
• Ingestion may lead to persistent or
transient infection.
• Either result can help immune system.
• Probiotic may secrete something that
affects immune regulation.
How do they get there?
• The fetus is possibly sterile.
• Vaginal births: initial colonization (vagina has
similar microbes to the intestine).
– Vaginal fluids contain prebiotics.
• Caesarian births: altered microbial profile.
Developing Microbiota
• Breast-feeding.
– Breast milk contains probiotics and prebiotics.
– Primarily Bifidobacterium.
• Solid foods: alters microbial profile.
• Development affected by antibiotic use,
infections, diet, and more.
http://www.connecticutcenterforhealth.com/baby.html
http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/p
ro_0034.shtml