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