Sources and Transmission of Bacterial Infection Flashcards
Saprophytes
Utilize non-living organic matter for food
- free living (outside the host) in either water, soil, or air
- some are pathogenic
Parasites
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
Facultative parasites
Capable of existing as saprophytes (free-living) or as parasites
Obligate parasites
Cannot survive outside the host
Commensals
Parasites that cause their host no discernible harm
Degree of specialization
Some microorganisms are highly specialized to a particular ecological niche, while others have the ability to adapt to a wide range of environmental conditions
Facultative parasitic bacteria environment
Some bacteria have the ability to survive well in the environment (saprophytic) and cause disease (parasitic)
- ex: listeria monocytogenes, pseudomonas aeruginosa, klebsiella, proteus
Facultative parasitic bacteria are considered to be ________ pathogens
Opportunistic
Facultative parasitic bacteria tend to cause _______
Sporadic infections rather than epidemics
- exception: L. monocytogenes in contaminated food, dairy farms with poor management
Environmental survival strategies
- formation of spores (clostridium, bacillus anthracis)
- dual saprophytic/parasitic lifestyles by having larger genomes and/or more complex regulatory mechanisms
Listeria monocytogenes
- resist up to 10% NaCl
- pH 4.0 to 9.5
- temperature <1 C to 45 C
- infects multiple species
- 7.3% regulatory genes
Pseudomonas aeruginosa
- highly resistant to antibiotics
- infects multiple species and body systems
- genome size >6 million bp
- 8.4% regulatory genes
Mechanisms of entry from environment
- 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)
Normal flora
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
How do normal flora prevent colonization of parasitic bacteria?
Competition for receptor sites or by production of inhibitory substances (bacteriocins)
______ are always present, while ______ are sporadically present
Resident flora; transient flora
Body sites with many types/large numbers of bacteria
- mouth
- nasopharynx
- rumen
- large intestine (90% GN anaerobes)
- vulva
- vagina
- urethra
- prepuce
- skin
- external ear canal
Body sites with few bacteria in low numbers
- esophagus
- stomach
- small intestine
- trachea
- bronchi
- eye
- udder
Sterile body sites
- bladder
- uterus
- lung below the bronchi
Normal flora composition
Represents a dynamic balance that changes in response to activities of the host and external influences
- ex: diet, age, antibiotics, stress
Clinical implications of normal flora
- must interpret isolation of normal flora with caution
- administration of antibiotics can alter normal flora and cause clinical side effects (ex: diarrhea)
Infection from normal flora
- 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
Opportunistic pathogens are not “transmissable” but infection is due to _____
Factors affecting the host
Transmission from other hosts (obligate pathogens)
- 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)
