Ch 11: Host-Microbe Interactions Flashcards
How are host microbes acquired?
during and after birth through contact with people, food and the environment
Which body sites are colonized mainly by bacteria?
skin upper respiratory GI tract external genitalia outer urethra vagina external ear & eye
Sterile sites in the body contain no microbes in a healthy host. What are these areas?
internal tissues and organs
- heart, lungs, liver, etc.
- upper reproductive tract
- sinuses & middle ear
fluids
- blood
- CSF
- urine, saliva, semen
- amniotic fluid
What are the benefits of normal flora?
microbial antagonism
What are probiotics?
supplements of live beneficial microbes (e.g. Lactobacillus)
What can normal flora deficiencies lead to?
antibiotic superinfections
infant botulism
What are the adverse effects from normal flora?
endogenous infections by opportunists
- staph infections (wounds, surgical sites)
- urinary tract infections (UTIs) are often caused by intestinal bacteria (fecal contamination)
In a healthy host, normal flora bacteria are expected to be found in all the following locations EXCEPT:
A. Oral cavity B. Vaginal tract C. Urinary bladder D. Skin E. Colon
C. Urinary bladder
“Good” bacteria, or _____ , can be ingested to boost the normal flora of GI tract.
probiotics
What are the biosafety levels?
BSL-1 (non-pathogens) - Open bench BSL-2 (opportunists) - Gloves & coats BSL-3 (treatable true pathogens) - Safety cabinets & vaccinations BSL-4 (untreatable true pathogens) - Isolation & decontamination
What factors influence infection?
microbial pathogenicity
- virulence factors (e.g. adhesins, toxins) promote infection
condition of host defenses
- healthy or compromised
What is the difference between true and opportunistic pathogens?
true pathogens cause infection in anyone
opportunistic pathogens cause infection in compromised hosts
compromised hosts are more susceptible to infection. What can compromise the host?
injury or surgery age immune deficiencies other disease or infections drug therapies pregnancy stress
What does a host provide for a pathogen?
host provides resources for the pathogen’s reproduction and transmission
What must a pathogen be able to do?
a pathogen must be able to…
- access portal of entry
- colonization
- survive host defenses
- causing damage
- access portal of exit
What are the portals of entry a pathogen must access to get into host?
skin & eyes
gastrointestinal tract
respiratory tract
genitourinary tract
What is the infectious dose?
the minimum number of microbes at the portal of entry required to establish infection
What are adhesion factors?
Factors affecting pathogen colonization
bacteria
- glycocalyx
- fimbriae
viruses
- spikes
What are the features of surviving host defenses?
antiphagocytic factors prevent elimination by host phagocytes
leukocidin is a toxin that kills WBCs (S. aureus)
capsule prevents adherence to phagocytes (S. pneumoniae)
some bacteria can survive inside phagocytes (M. tuberculosis)
What are the antiphagocytic factors of S. aureus?
coagulase produces a protective fibrin “shield” around the bacteria
phagocytes cannot eat bacteria
staphylokinase dissolves clot and releases the bacteria after multiplication
and the process repeats…
How do pathogens cause damage to host?
Exoenzymes
Endotoxins
Exotoxins
What are exoenzymes?
damage host tissues and promote invasion
- mucinase
- hyaluronidase
- collagenase
What are exotoxins?
proteins excreted by some G+ & G- that are toxic in small doses and specific to cell type
What are the types of exotoxins?
CYTOTOXINS
cell lysis/tissue damage
invasion, nutrients, weaken host, transmission
anthrax and whooping cough
NEUROTOXINS
paralysis
weaken host
tetanus and botulism
ENTEROTOXINS
fluid secretion and peristalsis in GI tract
transmission
food poisoning
What are endotoxins?
lipopolysaccharide (LPS) released from outer membrane of dead G- bacteria is toxic in large doses and produces general damaging effects
What are the effects of endotoxins?
inflammation
fever
coagulation
What are the portals of exit for a pathogen?
Used to transmit to other hosts
Feces Urine Open lesions Coughing/Sneezing Insect Bites
Which enzyme is produced by Staphylococcus aureus that hides the bacteria from host phagocyte?
coagulase
When lipopolysaccharide is released from dead gram-negative bacteria, it is called ______ because it causes inflammation and fever.
endotoxin
What is a disease reservoir?
can be living or nonliving
where the pathogen survives and multiplies
allows transmission to host
What are the characteristics of a human disease reservoir (carrier)?
asymptomatic incubating convalescent chronic passive
What are the characteristics of a animal disease reservoir (carrier)?
zoonotic infections
- Rabies from animal bite
- Salmonellosis from eating contaminated poultry
- Lyme disease from deer/mice via ticks
What are some examples of non-living disease reservoirs?
soil
- tetanus
water
- cryptosporidiosis
What are the types of transmission?
communicable or noncommunicable
- contagious
direct or indirect
- vehicle
horizontal or vertical
- placental or perinatal
What are examples of direct transmission?
A to B
contact
- touching, kissing, biting, sex
droplet
- sneeze, cough
- <1 m distance between reservoir and host
What are biological vectors?
Method of direct transmission
- blood-feeding arthropods
- ticks, mosquitoes, fleas, etc.
What are examples of indirect transmission?
A to B to C using vehicles
fomites blood, serum, & tissues soil & water food fecal-oral transmission
What is a nosocomial infection?
healthcare-acquired (HA)
How do nonsocomial infections occur?
compromised hosts
pathogens
chain of transmission
How do we prevent nosocomial infections?
WASH HANDS! universal precautions PPE microbial control isolation monitor for outbreaks
An inert object or surface, like a doorknob or money, that serves indirectly transmit infection is called a:
fomite
Rabies is a ______ infection because it is acquired from an animal reservoir.
zoonotic
What are koch’s postulates?
systematic method used to establish the etiologic agent of disease
- Find evidence of a particular microbe in every case of a disease.
- Isolate that microbe from an infected subject and cultivate it in pure culture in the laboratory (b); perform full microscopic and biological characterization (a).
- Inoculate a susceptible healthy subject with the laboratory isolate (c) and observe the same resultant disease (d).
- Reisolate (f) the same agent (e) from this.
Why did Warren & Marshall win the 2005 Nobel Prize in Physiology or Medicine?
showed that gastric ulcers were caused by a bacterium called H. pylori
What is epidemiology?
the study of disease in populations
frequency & distribution data
What is the difference between incidence and prevalence?
incidence
- new cases in time period (per 100,000)
prevalence
- total existing cases (% of population)
What was recommended once it was learned that the pertussis vaccine only protected for 10 years?
Booster shot
What was recommended once it was learned that mosquito-borne WNV was spreading westward?
Eliminate standing water
Spray for mosquitoes
Monitor birds for WNV
Warn public
What terms can be used to describe the incidence of disease?
endemic - only among specific group of people
sporadic - occasional
epidemic - widespread in community
pandemic - worldwide
What are the types of epidemics?
point-source epidemic: e.g., contaminated food at party
common-source epidemic: e.g., contaminated town water supply
propagated epidemic: eg. TB is spread person-to-person
Warren and Marshall discovered the link between H. pylori and gastric ulcers. What observation did NOT follow Koch’s postulates?
A. H. pylori was isolated from the stomachs of patients with ulcers
B. When Marshall drank a H. pylori culture he developed ulcers
C. When H. pylori was eliminated with antibiotics, the ulcers went away
D. Some people who did not have ulcers had H. pylori in their stomachs
D. Some people who did not have ulcers had H. pylori in their stomachs
When John Snow discovered a sewage-contaminated well was the source of a cholera outbreak, he asked city officials to remove the Broad Street water pump handle. This epidemic can be described by all the following EXCEPT:
A. Common-source epidemic B Fecal-oral transmission C. Vehicle transmission D. Indirect transmisison E. Nosocomial infection
E. Nosocomial infection
