Human microbe interactions

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Human microbe interactions Helpful or harmful.

• What makes the difference?

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Normal Microbiota and the Host

• Transient microbiota may be present for days,
  weeks, or months
• Normal microbiota permanently colonize the host

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Types of interactions between Humans and Microbes
Commensalism- Microbes that do not help or harm
us are commensals most of the normal flora
Mutualism- microbes and host benefit, for example
a microbe producing vitamins in the intestine
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Parasitism- microbe benefits and harms the
host Example pathogens
Opportunistic pathogen- normally harmless
organism becomes pathogenic in a compromised host
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What parts of the body are inhabited?
Figure 14.2
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Skin
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Normal Microbiota and the Host

• Microbial antagonism is competition between
  microbes.
• Normal microbiota protect the host by
• occupying niches that pathogens might occupy
• producing acids
• producing bacteriocins
• Probiotics are live microbes applied to or
  ingested into the body, intended to exert a
  beneficial effect.

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Some body parts should have few if any microbes
present
Solid organs Blood Cerebrospinal
fluid Urine Lower respiratory tract
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Steps to infection
Normal Flora pathogens
Infection Disease
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The Battle

Host Defenses
Microbial Weapons
Physical

Virulence Factors
Chemical
Capsules
Normal Flora
Enzymes
Nonspecific Internal responses
Toxins
Siderophores
Specific Immune responses
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Host defenses
Physical
Skin, mucous, enzymes
Chemical
pH
Enzymes, anti-microbial proteins, inflammation,
fever and immune responses
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What defense mechanisms are used to defend these
regions of the body?
Skin Mouth Nose Lungs Stomach Intestinal
tract Urinary Tract Genital regions male and
female
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Non-specific Immune Responses
Includes physical and chemical defenses that
prevent attachment and penetration
Internal nonspecific responses
Inflammation response- phagocytic white blood
cells
Fever
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The Battle

Host Defenses
Microbial Weapons
Physical

Virulence Factors
Chemical
Capsules
Normal Flora
Enzymes
Nonspecific Internal responses
Toxins
Siderophores
Specific Immune responses
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Steps to infection
Normal Flora pathogens
Pathogens
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What makes a pathogen?
Virulence Factors
Factors that improve attachment
Pili, capsules, fimbriea
Factors that allow penetration
Enzymes- hyaluronidase, proteases
Factors that improve colonization
Siderophores
Toxins- damage host
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Virulence factors important in Salmonella
pathogenesis
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Salmonellosis
diarrhea, fever, and abdominal cramps 12 to 72
hours after infection
lasts 4 to 7 days
Examples
S. enteritidis
S. typhi
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Toxins
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Effects of Toxins
Toxins disrupt normal host functions
Examples
Botulinum toxin
Tetanus toxin
Enterotoxin
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Botulinum toxin
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Tetanus toxin
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Cholera enterotoxin
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Result - Diarrhea
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Virulence- the degree of pathology caused by the
organism
Infectious Dose- The number of organisms needed
to make a person ill or a carrier
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Streptococci
Indiana State University
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Streptococcus pyogenes
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Indiana State University
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What makes the difference?
Number and types of virulence factors
Physiology of the pathogen
Health of the host
Route of infection
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Predisposing Factors of the Host

• Make the body more susceptible to disease
• Short urethra in females
• Inherited traits such as the sickle-cell gene
• Climate and weather
• Fatigue
• Age
• Lifestyle
• Chemotherapy