Part 7: Normal Human Microbial Interactions Flashcards
Human microbiome
The collection of all the microorganisms living in association with the human body
Number of human cells in the human body
10^13
Number of microorganisms in the human body
10^14
Number of genes in the human genome
20,000
Number of genes in the microbiome
20,000,000
When does colonization begin?
After birth
Where do microbiota live?
Every exposed area of the body i.e., skin and mucous membrane
What area is free of microbes?
Internal tissues i.e., blood, muscles, organs
How do microbiota contribute to health?
Produce beneficial products
Inhibit the growth of pathogens
Benefit of Lactobacillus acidophilus
Protects the female reproductive tract
Dry skin areas
Forearms, hands
Dry skin has high numbers of
Betaproteobacteria
Betaproteobacteria
Known from 16 rRNA genes
Rarely cultured
Second highest bacteria on dry skin
Corynebacteria
Corynebacterium diphtheriae
Can cause non-healing ulcer of the skin - cutaneous diphtheria
Moist skin
Armpits, nostrils
Moist skin has a high number of
Corynebacteria and staphylococci
Most frequently isolated bacteria on skin
Staphylococcus epidermidis
Staphylococcus aureus
Pathogen that causes boils, abscesses, wound infections
Sebaceous skin has a high number of
Propionibacteria
Propionibacteria
Anaerobic Actinobacteria that produce propionic acid as an end product of fermentation
Propionibacterium acnes
Lives in hair follicles, and eats sebum - oil secreted by skin
Overgrowth can trigger inflammation - inflammatory acne
Antimicrobial enzymes in saliva
Lysozyme and lactoperoxidase
Lactoperoxidase
Catalyzes production of superoxide radicals O2 - oxidative damage to invading microbes
What kinds of microbes does the mouth have?
Aerobic and anaerobic
Neisseria mucosa
Aerobic
Lives on mucous membranes like the tongue
Streptococcus mutans
Aerotolerant anaerobe
Streptococcus mutans produces
A sticky dextran slime layer that lets it stick to surfaces - forms biofilms in crevices around the motor
Streptococcus mutans produces what end-product
Lactic acid as an end-product of fermentation
Streptococcus mutans degrades
Tooth enamel - dental carries
Streptococcus mutans leads to
Inflammation along the gum line - gingivitis
Stomach environment for microbes
Low pH and proteolytic enzymes make the stomach inhospitable to most microbes
Helicobacter pylori
Colonizes surface of membrane, protected from stomach acid by mucous
Helicobacter pylori
Exotoxin - kills cells in the membrane
Endotoxin - triggers inflammation
What is the cause of stomach ulcers?
Helicobacter pylori
What is helicobacter pylori treated with?
Antibiotics - tetracycline
Small intestine environment
Area of rapidly changing pH
As pH becomes more neutral, bacterial numbers increase
Enterococcus
Genus of gram positive lactic acid bacteria
Opportunistic pathogen
What is the cause of nosocomial infections?
Enterococcus
Enterococcus mechanism
Develop antibiotic resistance readily
Spread resistance genes on to other gram positive bacteria - horizontal gene transfer
Large intestine environment
pH is neutral, environment anoxic
Enormous number of microbes ~ 10^11 cells/g of feces
Mostly anaerobes and facultative aerobes
E. coli
Most cultured bacterium from feces - indicator of fecale contamination
E. coli strain is
Non-pathogenic
May stimulate the immune system
Produce vitamin K
What makes up less than 1% of bacteria in the large intestine?
E. coli
What reveals E. coli is less than 1% of the large intestine?
16S rRNA
Largest group of bacteria are strict anaerobes are from the genera
Bacteroides and Clostridium
What roles does Bacteroides and Clostridium play?
Role in digestion
High number of methanogens play
A role in obesity
Germ free mice vs. normal mice body fat
40% less body fat
Innoculated germ free mice with microbes from healthy mouse intestines led to
Mice quickly gained weight
Microbiomes of normal weight mice vs. genetically obese mice
Genetically obese mice had fewer Bacteroidetes, more Firmicutes and way more methanogens
What do methanogens use to promote bacterial fermentation?
H2
What does bacterial fermentation do for the host?
Make nutrients available
Antibiotic associated colitis
Clostridium difficile grow
Inflammation of the colon
Treatment of antibiotic associated colitis
Further antibiotics
Probiotics
“Transpoosition”
Upper respiratory tract environment
Home to a variety of bacteria including staphylococci, streptococci, and corynebacteria
What pathogen lives in normal microflora?
Staphylococcus aureus
Lower respiratory tract environment
No resident microflora
Mucous, lysozyme, ciliated cells, secretory IgA, phagocytes
Upper urinary tract environment
Normally free of microoganisms
Urethra environment
Home to some gram-negative bacteria
Normal microbiota in urinary tract
Can act as opportunistic pathogens
E. coli in the urinary tract causes
Urinary tract infections
Lactobacillus acidphilus in the vagina produces
Lactic acid from glycogen
Lactic acid does what in the vagina
Lower pH and prevents growth of other microbes
If normal microbiota in the vagina is disturbed
Yeast can overgrow and cause yeast infections
