What does a zone of inhibition suggest?
high concentrations of this mutagen is toxic
What is extreme temperatures used for?
to control the growth of microbes
How is heat sensitivity genetically determined and reflected?
in the optimal growth ranges
Dry heat
denatures enzymes, dehydrates microbes, and kills by oxidation
effects. Methods of dry heat:
Hot-air ovens
Incineration
(i.e. flaming loops)
Moist Heat
denatures enzymes more efficiently due to transfer of heat energy
from moisture. Methods of moist heat:
Pasteurization
Boiling
Autoclaving
Pasteurization
temperature is maintained at 63°C for 30 minutes or 72°C for 15 seconds
Boiling
temperature is maintained at 100°C for 10 minutes to kill vegetative bacterial cells but does NOT inactivate endospores.
Autoclaving
uses steam under pressure for sterilization, usually kills endospores; standard conditions are 15 psi at 121°C for 15 minutes.
Thermal death time (TDT)
the length of time required to kill all bacteria in a liquid culture at a given temperature
Thermal death point (TDP)
the temperature required to kill all bacteria in a liquid culture in 10 minutes
Decimal reduction time (DRT)
the time, in minutes, in which 90% of a population of bacteria at a given temperature is killed
psychrophilic
0-20
psychrotrophic
20-30
mesohilic
25-40
thermophilic
45-65
hyperthermophilic
80 or higher
Antimicrobial Agents
available for controlling the growth of microbes
Disinfectants
chemical agents used on inanimate objects to lower the level of microbes on their surfaces
Bactericidal agents
those that result in bacterial death
Bacteriostatic agents
those causing temporary inhibition of growth
American Official Analytical Chemist's use-dilution test
standard method for measuring the effectiveness of a chemical agent
Antibiosis
against life
Antibiotic
a substance produced by a microorganism that inhibits other microorganisms
Antimicrobial drugs
antimicrobial chemicals used internally, whether natural or synthetic
Pathogen
disease causing organism
How does the clinical laboratory determine its pathogen's sensitivity to antimicrobial agents?
isolate the pathogen from a clinical sample
Disk-diffusion method
a Petri plate containing agar growth medium is inoculated uniformly over its entire surface
Zones of inhibition
clear area where bacteria doesn't grow
How can effectiveness of an agent be measured?
zones of inhibition
Kirby- Bauer test
performed in many clinical laboratories with strict quality controls to minimize the variance between laboratories
Minimum inhibitory concentration (MIC)
an antibiotic is determined by testing for bacterial growth in dilutions of the antibiotic in nutrient broth
Is the disk-diffusion technique measuring bacteriostatic or bacteriocidal activity?
Bacteriostic until we can perform a subcultural to determine if it was bacteriocidal
In which growth phase is an organism most sensitive to an antimicrobial agent?
log phase
Why is the disk-diffusion technique not a perfect indication of how the drug will perform in vivo? What other factors are considered before using the antimicrobial agent in vivo?
variations in pH, patient nutrition, side effect, other medical conditions, additional drug interactions
In every infectious disease...
the pathogen must come in contact with the host
Communicable disease
can be spread either directly or indirectly from one host to another
Noncommunicable disease
they cannot be transmitted from one host to another
Epidemiology
science that deals with when and where diseases occur and how they are transmitted in the human population
Endemic diseases
constantly present in the population
epidemic disease
many people in a given area acquire the disease in a relatively short period of time
Index case
the first reported patient in a disease outbreak
case defintion
include the typical symptoms of patients included as cases in an outbreak investigation
Direct contact methods
droplet infection
fomites
vectors
mechanical transmission
biological transmission
Droplet infection
occurs when microorganisms are carried on liquid drops from a cough or sneeze
Fomites
contact with contaminated inanimate objects
Vectors
insects and other arthropods that carry pathogens
mechanical transission
insects carry a pathogen on their meet and may transfer the pathogen to a person's food
Biological transmission
transmission of a disease by an anthropod's bite
reservoir
the continual source of an infection
carriers
humans who harbor pathogens but who do not exhibit any signs of disease
Epidemiologist
compiles data on the incidence of a disease and its method of transmission and tries to locate the source of infection to decrease the incidence
Epidemic curve
gives a visual display of the outbreak's magnitude and time trend
secondary cases
the infected family members
Could you be the "infected" individual and not have growth on your plate? explain
yes, you could be a carrier who has the disease but doesn't show any of the signs or symptoms
Do all people who contact an infected individual acquire the disease?
not necessarily, it depends on the person's immune system and the level of infection along with the type of disease
How can an epidemic stop without medical intervention?
each individual either overcomes the infection or dies, so they are no longer a source of infection
Are any organisms other than the culture assigned for this experiment growing on the plates? How can you tell?
Yes, the gloves were not sterile which allowed for other growth
What was the method of transmission of the "disease" in this experiment?
the disease was spread by skin to skin contact when shaking hands with other peers
Morbidity
illness due to a specific disease
Morbidity =
# of cases per period / susceptible population size at midpoint of period X K
Mortality
the second epidemiological measurement and refers to the number of deaths within a specified period among people having a particular disease
Mortality =
# disease - related deaths per period/ # of people with the disease X K
Incidence
compares the number of new cases of a disease during specified period to the size of the susceptible population during that period
Incidence =
# new cases/ susceptible population size at midpoint of period X K
sporadic
occurring at regular intervals or only in a few places
Epidemic
a widespread occurrence of an infectious disease in a community at a particular time
Endemic
regularly found among particular people or in a certain area
Pandemic
prevalent over a whole country or the world