Exam 2: Sources and Transmission of Bacterial Infection

Question 1

Describe saprophytes

Answer 1

Utilize non-living organic matter for food
They are free living in either water, soil, or air habitat
Some are capable of causing disease

Question 2

Describe parasites

Answer 2

Live on or in animals or plants at the expense of the host
Many are host adapted and site specific
Others can infect multiple species or body systems

Question 3

What are facultative parasites capable of?

Answer 3

Existing as saprophytes or as parasites

Question 4

Describe obligate parasites

Answer 4

Cannot survive outside the host

Question 5

What are commensals?

Answer 5

Parasites that cause their host no discernible harm

Question 6

What is the specialization of pathogens like?

Answer 6

Some are highly specialized to a particular ecological niche, while others have the ability to adapt to a wide range in environmental conditions

Question 7

Describe pathogens in the environment

Answer 7

Facultative parasitic bacteria
Some bacteria have the ability to survive well in the environment and cause disease
Considered opportunistic pathogens
Tend to cause sporadic infections rather than epidemics

Question 8

What are environmental survival strategies of pathogens?

Answer 8

Formation of spores

Having larger genomes and/or more complex regulatory mechanisms

Question 9

Describe Listeria monocytogenes

Answer 9

Resistant up to 10% NaCl, pH 4.0 to 9.5, and temperature less than 1 to 45 deg. C
Infects multiple species
7.3% regulatory genes (2nd largest known)

Question 10

Describe Pseudomonas aeruginosa

Answer 10

Highly resistant to antibiotics
Infects multiple species and body systems
Genome size greater than 6 million bp
8.4% regulator genes (largest known)

Question 11

What are the mechanisms of entry from environment?

Answer 11

Enter through a break in skin

Penetrating host mucosal membranes

Question 12

What pathogens can enter through a break in skin?

Answer 12

Clostridium

Pseudomonas aeruginosa

Question 13

What pathogens penetrate host mucosal membranes?

Answer 13

Listeria monocytogenes

Bacillus anthracis

Question 14

What is normal flora?

Answer 14

Parasites that live on the epidermal and mucosal surfaces

Question 15

What is resident flora?

Answer 15

Always present and normal

Question 16

What is transient flora?

Answer 16

Sporadically present, but still normal

Question 17

Do normal flora normally produce disease?

Answer 17

No, but the can be opportunistic pathogens

Question 18

Most normal flora have a protective effect. What does this mean?

Answer 18

They prevent colonization of pathogenic bacteria by competition for receptor sites or by production of inhibitory substances

Question 19

What are the body sites that we expect to find large numbers of bacteria?

Answer 19

Mouth
Nasopharynx
Rumen
Large intestine
Vulva
Vagina
Urethra
Prepuce
Skin
External ear canal

Question 20

What are the body sites with few bacteria, usually transient?

Answer 20

Esophagus
Stomach
Small intestine
Trachea
Bronchi
Eye
Udder

Question 21

What are sites in the body that are normally sterile?

Answer 21

Bladder
Uterus
Lung below the bronchi

Question 22

What does normal flora composition represent?

Answer 22

A dynamic balance that changes in response to activities of the host and external influences

Question 23

What can the administration of antibiotics do?

Answer 23

Alter normal flora and cause clinical side effects

Question 24

What must happen for infection to occur by opportunistic pathogens that are normal flora and live in the environment?

Answer 24

A predisposing condition must occur such as stress, immunosuppression, infection by another pathogen, or a break in skin or mucosal surface

Question 25

What can happen with opportunistic pathogens in a stressed herd with shedding animals?

Answer 25

They can be rapidly transmitted and disease can spread

Question 26

Describe obligate pathogens

Answer 26

Do not survive in the environment well
Have reduced genome size
Highly specialized to host
Do not have the ability to synthesize metabolites and rely on the host to supply them

Question 27

How are obligate pathogens transmitted?

Answer 27

Some do not have the ability to actively penetrate host mucosal membranes and rely on arthropod vectors to penetrate skin
Others can be transmitted through contaminated tissues/fluid
Some are capable of direct transmission and can cause an epidemic in a health herd

Question 28

What are obligate pathogens that must penetrate skin to be transmitted?

Answer 28

Rickettsia
Ehrlichia
Borrelia burgdorferi

Question 29

How can Mycobacterium avium be transmitted?

Answer 29

Feces and milk

Question 30

How can Brucella abortus be transmitted?

Answer 30

Aborted fetus

Question 31

What are examples of obligate pathogens that are transmitted through direct transmission?

Answer 31

Bordetella
Taylorella equigenitalis
Edwardsiella ictaluri