Mcdb 139: Lecture 1

Front 1

Gram Stain

Back 1

- Determines if Gram + or Gram - based on cell wall composition

Front 2

Process of Gram Stain

Back 2

01: Add crystal violet
02: Add iodine: all will be purple, Iodine acts as a mordant to set stain
03: Decolorize with alcohol, rinse immediately with water
04: Add safranin

Results:
Gram + cocci = purple
Gram - rods = red (pink)

Front 3

4 Possible Outcomes of Gram Stain

Back 3

Gram +: Cells retain crystal violent stain- PURPLE; cell wall thick layer of peptidoglycan


Gram -: cell walls do not retain crystal violet because of thin cell wall = PINK

Gram Non-reactive: Do not stain or stain poorly (ex. myobacteria -- TB)

Gram Variable: Stain unevenly

Front 4

Salmonella

Back 4

- can live in intestines of animals asymptomatically
- outbreak in eggs, recall of PB

Front 5

Intensive Agriculture

Back 5

- agricultural production characterized by high inputs of capital, labour, or heavy usage of pesticides or chemical fertilizers

Front 6

Intensive Animal Farming

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- large animals raised on limited land
- require large amounts of food, water, and medical inputs (keep animals healthy in cramped and stressed conditions -- lowers immune systems)
- Factory Farming: large indoor confined livestock operations

Front 7

Contaminated Food: Culprits and Symptoms?

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- Bacteria, parasites, viruses
- Symptoms range mild to serious: age dependent, type of bacteria, dose, etc.
- Harmful bacteria most common cause from raw meat, fruits, and vegetables

Front 8

What happens in the body after microbes that produce illness are swallowed?

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01: Incubation Period: bacteria migrates to primary site of infection --> intestines
02: Colonize intestinal wall and release toxins
03: Some are invasive and may penetrate other organs

Symptoms depend on type of microbe, usually great overlap: diarrhea, abdominal cramps, nausea

Front 9

Escheria Coli

Back 9

- more than 700 serotypes identified
- serotypes distinguished by their O and H Ags on bodies and flagella
- most do not cause disease in humans
- Most serotypes responsible for symptoms from contaminated food are those that produce the Shiga toxin

Front 10

Shiga Toxin (Stx)

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Causes harmful E. Coli in humans

Virtually identical to that produced in Shigella dysenteria type 1

One of most potent toxins known to man

Likely was transferred by a bacteriophage to otherwise harmless E. coli bacteria

Front 11

E. coli O157:H7 Disease Symptoms

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- severe bloody diarrhea
- abdominal cramps
- symptoms 2-8 days post ingestion
- most likely occur in kids < 5 yrs and elderly (weaker immune systems)
- no evidence ABs effective
- complication: hemolytic uremic syndrome -- toxin destroys RBCs and damages kidneys, 3-5% mortality

Front 12

How do humans become infected with E. coli?

Back 12

- oral-fecal transmission
- can live intestines of healthy cattle
- toxin requires highly specific receptors on cell surface in order to attach and enter cell
- cattle, swine, and deer do not have these receptors and can harbor the toxigenic bacteria asymptomatically and shed them in their feces
- meat contaminated during slaughter and butchering, orgs mixed into beef when ground into burger
- bacteria also present on cow's udders or on equipment that may get into raw milk (unpasteurized)

Front 13

Modes of Transmission

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- undercooked hamburger
- lettuce, spinach
- non-pasteurized milk and juices
- salami
- drinking or swimming in sewage contaminated water

Front 14

Washing of Leaves (Spinach)

Back 14

Place in vats of lightly chlorinated water, then another washing of more chlorinated water, and then the last wash is a rinse to remove smell of chlorine

Chlorinated water kills 90-99% microbes

12/36 failed to meet chlorination standards past 6 yrs

Front 15

Biological Role of Pilus

Back 15

Function: Attachment structure
Purpose: exchange genetic info with other bacteria

Front 16

Structure of E. coli/ Salmonella

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- Facultative Gram - Rods
- Lipopolysaccharide O side chainsy
- Capsule: protects against phagocytosis, is hydrophilic so repels hydrophobic surface of phagocytic cell and also prev AB binding
- Pilus, Flagella
- Enteric: found in gut

Please see slide!

Front 17

Facultative vs. Obligate Anaerobe

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Facultative can survive in both presence and absence of O2

Obligate can only survive in presence of O2

Front 18

Endotoxins

Back 18

Lipopolysaccharide (LPS) or lipoligosaccharidte

Found outer membrane of various Gram - bacteria

Important component in ability to cause disease

Activity depends on lipid A component of LPS which is released at cell lysis.

Front 19

Lipid A

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Part of LPS that determines of activity of endotoxin

Released at cell lysis

Causes many symptoms of Gram - bacterial infections:
- complement activation
- release of cytokines
- fever
- shock

Front 20

Cytokines

Back 20

proteins that act as signals for infection

recruits other immune cells to fight at site of infection and triggers WBCs to release more cytokines