Introduction to Pathogens (Bowden) Flashcards
Commensalism of flora
neither hurt harm nor benefit host
mutualism of flora
symbiotic interactions between 2 organisms. both benefit
Most important mutualistic role of flora
microbial antagonists by providing bacterial interference
What ways does normal flora do good
prevent/suppress pathogens
synthesize vitamins (VitK)
Abs produced to commensals cross react with pathogenic Ag
Bacteriocins
Endotoxin release enhances immune response
Whay ways can normal flora be more harmful than good
can become pathogenic in tissues
penicillinase + bacteria interfere with therapy
confusion of Dxs because of resemblence to pathogens
Step vindans seeds bloodstream following dental procedure= heart valve and then infectious endocarditis
Resident flora
Interferes via competing for R, nutrients and mutual inhibition by metabolic, toxic products or bacteriocins or antibiotics
Transient flora
exposure to environment, does not cause disease or establish residency
Colonization of flora
establishment of microbial population- acquisition of new organism
How do children acquire flora
contact with adults, other children and the rest of their environment
What type of microbes are found in large intestine and why
anaerobic populations because LI kept anoxic by facultative anaerobes
How is facultative flora acquired
feces
General factors that contribute to potential pathogens
Age, immunization history, prior illnesses or coexisting illness, trauma, nutrition, pregnancy, emotional state
Medical care potential pathogens
breaching skin (intravenouse or surgery) or mucosal surfaces (endotrach tubes)
Introduction to foreign bodies
alteration of natural flora with antibiotics and Tx with immunosuppressive drugs
2 basic mechanisms of pathogens
invasion of tissue and production of toxins
What is invasiveness
ability to invade host tissue
Components of invasiveness
capsules (inhibit phagocytosis) adaptation (can alter selective tissue invasion) extracellular enzymes (degrade host tissue)
Virulence
the combination of invasiveness and toxigenicity
LD50 % dead vs dose
Is variability of virulence genotypic or phenotypic
can be both
How can infectious disease be transmitted? factors?
directly or indirectly
Source, number of infectious agents, capability of surviving host defense, % of host that is susceptible ID50 %infected vs dose
Toxigenicity. 2 types
production of toxins
Exotoxins- secreted proteins, heat labile. mainly gram + organisms
Endotoxins- LPS gram - bacteria
What is required for pathogen to be pathogenic
adhere. evade local immune system, must be able to replicate, must evade systemic immune system. must escape body for transmission to new host
Which pathogens are assoc with chronic diseases? acute?
generally intracell pathogens- chronic disease
extracell pathogens- acute disease
Stages of infections
Incubation Prodomal: non-specific symptoms Specific-illness period: signs and symptoms Recovery Latent
What is a virus
obligate intracellular parasite capable of infecting a variety of different cell types
What type of genomic material do viruses have
DNA or RNA ss or ds
What covers viruses
protecting genome is the coat protein “capsid”
some viruses also have a phopholipid envelope derived from host cell and surrounds the capsid.
Virus replication
recognize and attach to host- specific R penetration into host uncoating to release viral genome viral nucleic acids replicate new viral proteins packaged and released
Penetration of host by virus
1 translocation of PM
2 pinocytosis into cytoplasmic vacuoles
3 fusion of PM with viral envelope
3 types of infections from viruses
Abortive: when a virus invades a cell that does not permit viral replication
Cytolytic: cell lysis and release of large # of visions
Persistent: may be productive, latent or transforming
Most common virus
common cold. Rhinoviruses
2 modes of rhinovirus transmission
aerosols of respiratory droplets
contaminated surfaces
What type of genome are rhinoviruses
ss positive sense RNA and capsid- no envelope
What are bacteria
unicellular prokaryotic microorganisms found everywhere
Describe Gram + structure
thick peptidoglycan external layer with lipotoic acids. grams iodine cross links in peptidocglycan sheets
Describe gram - structure
thin layer of peptidoglycan between 2 phosopholipid bilayers. known as periplasmic space. Also have LPS and lipopolysaccharides
What is peptidoglycan
polymer of NAM and NAG
Structures of bacteria
cocci, bacilli, coccobacilli, spirochetes
How does bacteria move
flagella made of flagellins monotrichous lophotichous- several polar flagella amphitrichous several at each end peritichious- covering entire cell surface
Types of bacterial pili
Pili- surface appendages
sex pili- conjugation, transfering genetic information
common pili- means for attachment to host and important role in colonization
Endospores
resisted to heat, radiation and drying. dormant for years and years
germinate then return to vegitative state
Describe bacterial structure and what dictates it
high molecular weight polysaccharides.
capsule- adhere to cell wall
slime layer- loosely associated
Controlled by genotype and phenotype
Aerobic Bacteria
require oxygen and electron acceptor
Anaerobin bacteria
energy from fermentation reactions. O2 can be poisonous
Facultative anaerobes
grow under aerobic conditions and can also ferment
Distinctive properties of Clostridium difficile
gram +, rod shaped, spore formers, obligate anaerobes, ubiquitous saprophytes, part of normal flora
What toxins do the spores of C. difficile make
Toxin A- enterotoxin causing fluid accumulation
Toxin B- cytopathic agent
how to antibiotics affect C. difficile.
antibiotic associated colitis
diarrhea cramps pseudomembranous colitis
Basic properties of fungi
Grow as either yeast or molds
Yeast
single cell, round
form bacteria-like colonies
mold
long filament (hyphae) forms a mat (mycelium)
Thermally dimorphic fungi
at ambient temp- mold
host tissues- yeast
Which fungi is reverse temperature wise
Candidas. at ambient temp-yeast. in host tissues- mold
Are most fungi aerobes, anaerobes or facultative anaerobes
aerobes. some facultative. no strict anaerobes
What do fungi require to survive
preformed carbon sources
structure of fungi
cell wall of chitin. cell membrane contains ergosterol and zymosterol
Describe the various mycoses
Superficial (skin and hair)
Cutaneous (epidermis, hair nails)
Subcutaneous (deeper skin layers)
Systemic or deep (internal organs)
What causes subcu mycoses and where
caused by free living saprophytic fungi and located deeper layers of dermis
wide spread manifestations of chronic infections and granulomatous lesions
commonalities of mycoses
patient can remember trauma, location of problem relates to wounds, etiological agents from soil or decaying vegetation
resemble bacterial infections
Tx involves excision or amputation
Describe systemic mycoses
severe disease. immunocompromised most serious
dimorphic. no human to human transmission
geographical niche
most infections are sub clinical
Candida albicans
yeast and filamentous cells. Opportunistic.
grows in biofilms on devices.
Superficial: thrush and vaginitis
Systemic: candidemia
What is a parasite
when 2 different organisms live together and one harms the other.
Parasitic taxomonic groups
Protozoans: single cell with membrane bound nucelus
Metazoans: helminthes, nematodes etc..
Arthropods: insects
What is a definitive host
final host of host in which a parasite reaches sexual maturity
What is an intermediate host
host in which a parasite passes through its larval or asexual stage
Accidental host
host other than the usual or normal host
Reservoir host
host other than normal but parasite is capable of living and infesting
Vector
a carrier, usually arthropod, that transmits causative agent of disease to non-infected
Direct transmision examples
Ingestion
skin penetration
inhalation
person-person
Indirect transmission examples
vectors
transplantation/transfusions
Single host parasites
only human to human contact. oral-fecal
Multiple host parasites
require 2 or more hosts to complete life cycle
sexual parasitic stage in definitive host
a sexual or larval stage in intermediate host
Protozoans
most common infectious agent.
Eukaryotic, large with tru nucleus
cytoplasm:endoplasm and ectoplasm
Types of protozoans
trophozoites: active form, fragile
Cysts: dormant infective form. they are resilient
Nematodes
round worms- spindle shaped eith tough outer cuticle
Found in muscular, nervous, reproductive and GI
sexes are separate, life cycles complex
Soil transmitted helminthiases
contaminated environments.
species have different signs and symptoms but usually all can result in:
nutritional and cognitive impairment as well as conditions that require surgical intervention
Platyheliminthes
tape worms. flattened ribbon shapes. scolex on anterior end. generate proglottids which are their reproductive segments
What is the structure of platyheliminthes
no vascular or repiratory systems, no gut or body cavity
Has segmented body(strobila)
Neck (generates proglottids)
Head or scolex (sucking discs or grooves)
extensive reproductive system
