MICROBIO 5.1

Human pathogens

Universal precautions

Sample is treated as if it’s pathogenic

How to analyze microbial samples

Observation

• morphological size & shape

• motility

Differential staining

• plate using selective or differential staining

• Gram stain status

• chemical reactions (e.g. gas production, fermentation, etc.)

Pathogenicity

ability of microbe to cause disease (yes/no question)

Virulence

EASE of pathogen (microbe that can cause disease) to infect host & cause disease

Five steps to infection

1. Pathogen enters host via portal of entry

2. Pathogen adheres to host tissue

3. Pathogen invades tissue & secures nutrients

4. Pathogen must evade host immune defenses so it can replicate

5. Pathogen must be transmitted to new host

Portal of entry

Determined by mode of transmission (e.g. if airborne transmission —> respiratory tract)

Usually mucus membrane or parenteral

Mucus membrane

Eyes, GI tract, respiratory system, urinary

Parenteral

Puncture or bloodstream directly

How does a pathogen adhere to host?

Pathogen has ligands/adhesin factors that bind to receptors on cellular target in host

*If pathogen DNA mutates & protein changes of the ligand, pathogen can use virulence

Three ways that pathogen invades tissues

1. Remain on surface of host cell

2. Reside IN cell (intracellular pathogen)

3. Invade deeper by passing thru cells OR between cells

Two main ways pathogen evades host

1. Hide

2. Undermine

Ways that pathogen HIDES from immune defenses

1. antigen-masking (cloaking antigens, which is what our immune system finds foreign)

2. antigen-mimicry (mimicking antigens of those around it)

3. antigen variation (change antigens constantly, making difficult for immune system to catch it)

Ways that pathogens UNDERMINE immune defenses

1. suppress immune function

2. avoid phagocytosis

Two main forms of transmission

Direct & indirect

Direct Contact

Transmission from direct contact between source of pathogen & host (transmission MUST come from the one in contact)

Types of direct contact

• person to person (skin/mucus membrane contact)

• animal (bite or scratch)

• environment (swimming or soil)

• vertical (in utero, vaginal delivery, breast feeding)

Indirect Contact

No direct contact between source of pathogen & host (e.g. person sick —> mosquito —> personT)

Types of indirect contact

• airborne

• vehicle (contaminated object, foodborne, needles)

• vector (carriers)

  • biological —> pathogen has part of life cycle in insect; it’s INSIDE (mosquitos, ticks)

  • mechanical —> pathogen hitch hikes (flies, cockroaches)

Standard precautions

1. Hand hygiene

2. Protective gloves

3. Face shield/barrier in splash risk

4. Disinfection of surfaces, laundry, tools

Contact precautions

Wound/skin infection, drug resistant infection, infectious diarrhea

• Limit transport

• Extra hand washing

• Gloves & gowns at all times

• single patient use equiment

Droplet precautions

Most respiratory infections (e.g. flu, pertussis); when infection does not suspend in air

• limit patient transport

• procedural mask at all times

Aireborne precuations

Microbe spreads through fine respiratory aerosols that can remain suspended in the air (TB, chicken pox, measles)

• Limit patient transport

• N95 OR comparable respirator mask

• place patient in AIIR (airborne infection isolation room) facility

  • pressurized room to keep air from escaping