5.2 Lab

Question 1

why is sheep blood used for blood agar?

Answer 1

-sheep RBCs are most sensitive to the hemolytic toxins released by bacterial cells, thus causing hemolytic zones around the colonies

Question 2

approaches for detecting bacteria in feces, exudate, excretion, secretion, tissue, blood, and hair

Answer 2

isolation: gram stain, biochemical tests, MADLI-TOF
direct detection: antigen or nucleic acid

Question 3

approaches for detecting bacteria using blood

Answer 3

indirect detection: antibodies (serological tests)

Question 4

strategies for identifying bacterial genus/species?

Answer 4

biochemical tests (old school)
MALDI-TOF mass spectrometry: 20 minutes!

Question 5

what type of bacteria can grow on MacConkey agar?

Answer 5

gram negative, eg. E. coli

Question 6

why does E. coli turn pink on MacConkey agar?

Answer 6

pink due to lactose fermenting (lactose in as ingredient in MacConkey agar)

Question 7

what grows on phenylethyl alcohol agar?

Answer 7

gram + (eg. S. pseudointermedius)
-inhibits growth of gram-negative organisms by interfering with DNA synthesis

Question 8

what makes MacConkey agar selective for gram - bacteria?

Answer 8

the selective action of this medium is attributed to crystal violet and bile salts, which are inhibitory to most species of gram-positive bacteria

Question 9

what is thioglycolate broth?

Answer 9

enrichment non-selective media
-supports the growth of anaerobes, aerobes, microaerophilic, and fastidious bacteria

Question 10

is it possible to isolate bacteria from an animal that received antibiotics in the past days/weeks? How?

Answer 10

yes, however you should let the lab know about the antibiotic regimen (can alter results)
>lab can put swab thioglycolate broth: very good for growth

Question 11

what can we look for when examining cultures?

Answer 11

-is there growth?
-morphology
-mixed colonies?
-colour
-hemolysis

Question 12

what is the use of biochemical tests for bacteria? how do they work?

Answer 12

ID bacteria
-the difference in protein and fat metabolism, carbohydrate metabolism, enzyme production, compound utilization ability, etc.

Question 13

How does MALDI-TOF work and what does it do?

Answer 13

Matrix-Assisted Laser Desorption/Ionization-Time of flight (MALDI-TOF) mass spectrometry (MS)

Identification of genus/species and subspecies based on protein mass patterns
>compare with data base

Question 14

advantages of MALDI-TOF

Answer 14

-single colony is needed
-easy preparation
-rapid
-high throughput
-low exposure risk
-high specificity (some exceptions)

Question 15

disadvantages of MALDI-TOF

Answer 15

-initial investment $$
-maintenance
-closely related organisms
-database entries
-future: susceptibility testing

Question 16

peracute anthrax signs in cattle, sheep, goats

Answer 16

-staggering, trembling, difficulty breathing, convulsions, death
-progression of the disease is rapid, signs may go unnoticed
-often animals are found dead and bloated

Question 17

what is the pathogenesis of anthrax?

Answer 17

-Vegetative forms are shed after death in the oozing blood through nose, mouth, or anus
-sporulate on exposure to O2

-Spores can be:
>inhaled (spore laden dust)
>cutaneous (via lesion)
> gastrointestinal (infected meat, contaminated water)
»ingested through grazing, browsing, drinking, or spore laden dust

-biting flies can also transmit bacteria from terminally infected animal or carcass after death

-germination and multiplication in lymphatics and spleen

Question 18

virulence factors of anthrax

Answer 18

capsule
lethal toxin: cell destruction, shock
edema toxin

Question 19

structure of a bacterial spore from inside to outside

Answer 19

-core (DNA ribosomes, glycolytic enzymes)
-cytoplasmic membrane
-spore wall (normal peptidoglycan)
-cortex (think layer of less cross-linked peptidoglycan)
-keratin spore coat (protein)

Question 20

how does CFIA recommend disposing of carcasses and contaminated materials from anthrax?

Answer 20

CFIA does not recommend burying with quick lime, but burning/incineration and use of formaldehyde

Question 21

what is the major source of anthrax infection?

Answer 21

spores in the environment

Question 22

what type of pathogen in bacillus anthracis?

Answer 22

gram + rod, very large rod with thick capsule

Question 23

why is anthrax a reportable disease?

Answer 23

zoonotic and potential for large economic impact

Question 24

where do we see anthrax in canada and why?

Answer 24

more common in west >Ab, Sask

Question 25

what are the key virulence determinants of Bacillus anthracis?

Answer 25

-capsule
-lethal toxin
-edema toxin

Question 26

what is septicemia?

Answer 26

Septicemia, or sepsis, is the clinical name for blood poisoning by bacteria. It is the body’s most extreme response to an infection.

Question 27

what is toxic shock?

Answer 27

Toxic shock syndrome (TSS) is a cluster of symptoms that involves many systems of the body. Certain bacterial infections release toxins into the bloodstream, which then spreads the toxins to body organs. This can cause severe damage and illness.

Question 28

what is an opportunistic pathogen?

Answer 28

An opportunistic pathogen can only cause disease in situations that compromise the host’s defenses, such as the body’s protective barriers, immune system, or normal microbiota.

Question 29

what is a bacterial spore? why is it important?

Answer 29

-unable to grow or reproduce but can help the bacteria to survive in an environment that is unfavourable for growth.

Under harsh environmental conditions, such as loss of a nutritional requirement, some bacteria can convert from a vegetative state to a dormant state, or spore.

The spore is a dehydrated multishelled structure that protects and allows the bacteria to exist in “suspended animation”. It contains a complete copy of the chromosome, the bare minimum concentrations of essential proteins and ribosomes, and a high concentration of calcium bound to dipicolinic acid. The spore has an inner membrane, two peptidoglycan layers, and an outer keratin–like protein coat.

Question 30

what is a latent infection?

Answer 30

A latent infection is an infection by an organism that remains inactive in the body. A latent infection typically causes no symptoms, but the inactive organism may reactivate and cause sickness.

Question 31

what is a reportable disease and how does it get to be reportable?

Answer 31

important in the planning and evaluation of disease prevention and control programs, in the assurance of appropriate medical therapy, and in the detection of common-source outbreaks.