Symbiosis and resident normal flora

mutualism

both partners benefit

commensalism

one partner benefits, one partner not affected

amensalism

one partner is harmed, one partner not affected

parasitism

one partner benefits, one partner is harmed

Normal microbiota

• colonize body’s surface

• do not normally cause disease

• dynamic and diverse bacterial strains

• acquired from birth and environment

  • breastmilk, vaginal delivery

  • skin contact, food, water, pets

• can change

  • dynamic, not static

types of normal microbiota

Resident microbes

• part of normal microbiota

• inhabit body sites for extended time periods

Transient microbes

• temporary inhabitation of body sites

Commensal organisms of resident microbiota

• oral

• respiratory

• gut

• vagina

• skin

Microbes not usually found in

• brain

• CNS

• blood

• lungs

• middle/inner ear

why are microbes different in different locations?

• different ranges of nutrients

• pH levels differ (increase as you move further down torso)

Our resident microbes provide:

• prevention of disease

• nutrition and metabolites

• commensalism with host and microbes

GI microbiota is beneficial

Fecal flora reconstitution:

• restores vitamins

• stimulates immune system

• Competitive exclusion: creates antagonistic environment for pathogens —> probiotics

Fecal microbiota transplantation (FMT)

• treat Clostridium difficile infections (spore-forming, resistant to antibiotics)

• transplant fecal material from healthy donor

• beneficial bacteria to fight the infection

Hemolytic patterns of Streptococcus

• Beta: complete lysis of RBC, clear zone around colonies

• Alpha: conversion of hemoglobin into methehemoglobin, development of green/brown zone around colonies

• Gamma: no lysis of RBC, no zone around colonies (not really hemolytic)

Serotypes of streptococcus

1. Streptococcus pyogenes

   1. Group A strep

   2. acute infections

2. Streptococcus agalactiae

   1. Group B strep

   2. neonatal sepsis and meningeal infection

3. Streptococcus pneumoniae

   1. pnemococcus

   2. bacterial pneumonia

Gnotobiotic animals

• “germ-free animals”

• require vitamins K and B

• poor immune system

• increased susceptibility to pathogens

Which of these organisms is capable of causing disease?

(Pick all that apply)

A. Members of your resident normal flora

B. Members of your transient normal flora

C. Commensal organisms

D. Pathogenic organisms

E. None of these

F. I don’t know

A,B, C, D

Name one mechanism that could allow a non-pathogenic bacteria to acquire a virulence factor

horizontal gene transfer

True or false: Most pathogenic organisms can colonize and infect

any location in the body

False

• most pathogens are site-specific

What is the most common portal of entry and infection site for a

pathogen of humans?

A. Through the skin

B. Through the mucus membranes of the respiratory tract

C. Through the mucus membranes of the digestive tract

D. Through the mucus membranes of the urogenital tract

E. Through the placenta

F. Through the

B

Organisms that live inside a cow’s rumen help the cow by

breaking down hay and grass into useable nutrients for the cow.

In return, the bacteria get a place to live and a continuous source

of food. This is an example of which type of symbiosis?

A. Mutualism

B. Commensalism

C. Amensalism

D. Parasitism

E. I don’t know

A

You pick up a Campylobacter infection from contaminated food.

You end up with diarrhea and the Campylobacter get food and

housing.

A. Mutualism

B. Commensalism

C. Amensalism

D. Parasitism

E. I don’t know

D

A beneficial member of your normal gut microbiota picks up a

toxin gene from a lysogenic phage. The toxin allows the bacteria

to gain nutrients by lysing red blood cells.

A. Mutualism

B. Commensalism

C. Amensalism

D. Parasitism

E. I don’t know

D