Exam 2: Sources and Transmission of Bacterial Infection Flashcards
Describe saprophytes
Utilize non-living organic matter for food
They are free living in either water, soil, or air habitat
Some are capable of causing disease
Describe parasites
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
What are facultative parasites capable of?
Existing as saprophytes or as parasites
Describe obligate parasites
Cannot survive outside the host
What are commensals?
Parasites that cause their host no discernible harm
What is the specialization of pathogens like?
Some are highly specialized to a particular ecological niche, while others have the ability to adapt to a wide range in environmental conditions
Describe pathogens in the environment
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
What are environmental survival strategies of pathogens?
Formation of spores
Having larger genomes and/or more complex regulatory mechanisms
Describe Listeria monocytogenes
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)
Describe Pseudomonas aeruginosa
Highly resistant to antibiotics
Infects multiple species and body systems
Genome size greater than 6 million bp
8.4% regulator genes (largest known)
What are the mechanisms of entry from environment?
Enter through a break in skin
Penetrating host mucosal membranes
What pathogens can enter through a break in skin?
Clostridium
Pseudomonas aeruginosa
What pathogens penetrate host mucosal membranes?
Listeria monocytogenes
Bacillus anthracis
What is normal flora?
Parasites that live on the epidermal and mucosal surfaces
What is resident flora?
Always present and normal
What is transient flora?
Sporadically present, but still normal
Do normal flora normally produce disease?
No, but the can be opportunistic pathogens
Most normal flora have a protective effect. What does this mean?
They prevent colonization of pathogenic bacteria by competition for receptor sites or by production of inhibitory substances
What are the body sites that we expect to find large numbers of bacteria?
Mouth Nasopharynx Rumen Large intestine Vulva Vagina Urethra Prepuce Skin External ear canal
What are the body sites with few bacteria, usually transient?
Esophagus Stomach Small intestine Trachea Bronchi Eye Udder
What are sites in the body that are normally sterile?
Bladder
Uterus
Lung below the bronchi
What does normal flora composition represent?
A dynamic balance that changes in response to activities of the host and external influences
What can the administration of antibiotics do?
Alter normal flora and cause clinical side effects
What must happen for infection to occur by opportunistic pathogens that are normal flora and live in the environment?
A predisposing condition must occur such as stress, immunosuppression, infection by another pathogen, or a break in skin or mucosal surface
What can happen with opportunistic pathogens in a stressed herd with shedding animals?
They can be rapidly transmitted and disease can spread
Describe obligate pathogens
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
How are obligate pathogens transmitted?
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
What are obligate pathogens that must penetrate skin to be transmitted?
Rickettsia
Ehrlichia
Borrelia burgdorferi
How can Mycobacterium avium be transmitted?
Feces and milk
How can Brucella abortus be transmitted?
Aborted fetus
What are examples of obligate pathogens that are transmitted through direct transmission?
Bordetella
Taylorella equigenitalis
Edwardsiella ictaluri
