Sources and Transmission of Bacterial Infection

Question 1

Saprophytes

Answer 1

Utilize non-living organic matter for food

• free living (outside the host) in either water, soil, or air
• some are pathogenic

Question 2

Parasites

Answer 2

Live on or in animals or plants at the expense of the host

• many are host adapted and site specific
• others infect multiple species or body systems

Question 3

Facultative parasites

Answer 3

Capable of existing as saprophytes (free-living) or as parasites

Question 4

Obligate parasites

Answer 4

Cannot survive outside the host

Question 5

Commensals

Answer 5

Parasites that cause their host no discernible harm

Question 6

Degree of specialization

Answer 6

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

Question 7

Facultative parasitic bacteria environment

Answer 7

Some bacteria have the ability to survive well in the environment (saprophytic) and cause disease (parasitic)
- ex: listeria monocytogenes, pseudomonas aeruginosa, klebsiella, proteus

Question 8

Facultative parasitic bacteria are considered to be ________ pathogens

Answer 8

Opportunistic

Question 9

Facultative parasitic bacteria tend to cause _______

Answer 9

Sporadic infections rather than epidemics

- exception: L. monocytogenes in contaminated food, dairy farms with poor management

Question 10

Environmental survival strategies

Answer 10

• formation of spores (clostridium, bacillus anthracis)

- dual saprophytic/parasitic lifestyles by having larger genomes and/or more complex regulatory mechanisms

Question 11

Listeria monocytogenes

Answer 11

• resist up to 10% NaCl
• pH 4.0 to 9.5
• temperature <1 C to 45 C
• infects multiple species
• 7.3% regulatory genes

Question 12

Pseudomonas aeruginosa

Answer 12

• highly resistant to antibiotics
• infects multiple species and body systems
• genome size >6 million bp
• 8.4% regulatory genes

Question 13

Mechanisms of entry from environment

Answer 13

• enter host thru a break in the skin (species lack mechanisms for penetration of mucosal membrane, but cause disease once in tissue)
• actively penetrate host mucosal membrane (ex: L. monocytogenes, B. anthracis)

Question 14

Normal flora

Answer 14

Parasites (or commensals) that live on the epidermal and mucosal surfaces

• do not normally produce disease, but can be opportunistic
• most are protective and prevent colonization of pathogenic bacteria

Question 15

How do normal flora prevent colonization of parasitic bacteria?

Answer 15

Competition for receptor sites or by production of inhibitory substances (bacteriocins)

Question 16

______ are always present, while ______ are sporadically present

Answer 16

Resident flora; transient flora

Question 17

Body sites with many types/large numbers of bacteria

Answer 17

• mouth
• nasopharynx
• rumen
• large intestine (90% GN anaerobes)
• vulva
• vagina
• urethra
• prepuce
• skin
• external ear canal

Question 18

Body sites with few bacteria in low numbers

Answer 18

• esophagus
• stomach
• small intestine
• trachea
• bronchi
• eye
• udder

Question 19

Sterile body sites

Answer 19

• bladder
• uterus
• lung below the bronchi

Question 20

Normal flora composition

Answer 20

Represents a dynamic balance that changes in response to activities of the host and external influences
- ex: diet, age, antibiotics, stress

Question 21

Clinical implications of normal flora

Answer 21

• must interpret isolation of normal flora with caution

- administration of antibiotics can alter normal flora and cause clinical side effects (ex: diarrhea)

Question 22

Infection from normal flora

Answer 22

• some opportunistic pathogens that survive in the environment can take up residence as part of normal flora
• -> for infection to occur by one of these pathogens, a predisposing condition must occur

Question 23

Opportunistic pathogens are not “transmissable” but infection is due to _____

Answer 23

Factors affecting the host

Question 24

Transmission from other hosts (obligate pathogens)

Answer 24

• obligate pathogens do not survive in the environment well
• have reduced genome size, are highly specialized to the host and do not have ability to synthesize metabolites (rely on host to supply them)

Question 25

Examples of obligate pathogens

Answer 25

• rickettsia
• borrelia burgdorferi
• mycoplasma

Question 26

Transmission of obligate pathogens

Answer 26

• some rely on arthropod vectors to penetrate skin
• others are transmitted thru contaminated tissues/fluids
• some are capable of direct transmission and cause an epidemic in a healthy herd