Chapter 7: Fundamentals of Microbial Growth and Decontamination

What process is used by most prokaryotes to divide? Is it a sexual or asexual process?

asexually through binary fission

What process do certain fungi and some bacteria divide? Is it a sexual or asexual process?

asexually through budding or spore formation

List the four phases of bacterial growth and briefly describe what occurs in each

1. lag phase - cells adjust to new environment, alter gene expression but usually no population growth

2. log phase - exponential bacterial growth

3. stationary phase - number of cell growth equals number of cells dying, population growth rate slows

4. death phase - waste buildup and decreasing nutrients, cells die exponentially

Which type of bacteria grows at human body temperature (37oC)

mesophiles

Observe the temperature ranges of thermophiles and extreme thermophiles; Using this information, what do you think the term thermophile means?

love high temperatures

List the names and pH ranges for prokaryotes grouped by pH requirements

acidophiles - 1 to 5

neutralophiles - 5 to 8

alkaliphiles - 9 to 11

What type of bacteria would you expect to find living in the Great Salt Lake of Utah?

halophiles

Define extremophile

organisms that live in extremes of pH, temperature, and/or salt and that are exposed to a combination of stresses

Many aerobic bacteria remediate reactive oxygen species (ROS) using enzymes that convert the reactive intermediates into nonreactive products. What reaction does the enzyme catalase perform? What reaction does the enzyme superoxide dismutase perform?

catalase - convert hydrogen peroxide to water

superoxide dismutase - convert reactive superoxide ions to hydrogen peroxide

The degree to which an organism can detoxify reactive oxygen species (ROS) is directly related to how much oxygen it can tolerate. Which of the following organisms do you think has no ability to detoxify ROS? Answer choices: obligate aerobe, obligate anaerobe, aerotolerant anaerobe, facultative anaerobe

obligate anaerobe

How do heterotrophs obtain carbon?

extract carbon from an external source of organic carbon such as sugars, lipids, and proteins

How do autotrophs obtain carbon?

self feeding that use carbon fixation to convert inorganic carbon into organic carbon

What do phototrophs use for energy?

light energy

What do chemotrophs use for energy?

break down chemical compounds for energy

List three physical states of growth media and state the main use for each

liquid - aka broth media, ideal for growing large batches of microbes

solid - useful for isolating colonies and observing specific culture characteristics, isolate bacteria into pure cultures using the streak plate isolation technique

semisolid - used for the motility test to determine if an isolated specimen is able to move

Define complex media

aka enriched media, contain a mixture of organic and inorganic nutrients that are not fully defined, they contain more complex ingredients like blood, milk proteins, or yeast extract

Define defined media

aka synthetic media, media with a precisely known composition, each organic and inorganic component is completely known and quantified

What is the purpose of differential media?

so that we can visually distinguish one microbe from another based on how they metabolize media components

Which agar media differentiates between microbes that can or cannot lyse red blood cells (RBCs), and if the microbe can lyse RBCs, it distinguishes the extent to which they can do so

blood agar

Differentiate between alpha, beta, and gamma hemolysis. What do each look like? What do each indicate about their ability to lyse red blood cells?

alpha - do not lyse red blood cells and instead just oxidize hemoglobin, the oxygen-carrying component of blood; they turn blood agar a green color

beta- make hemolysins and can therefore lyse red blood cells and generate a yellow zone around colonies growing on blood agar

gamma - do not lyse red blood cells

Mannitol salt agar (MSA) is a selective and differential media. What kind of organisms does MSA select for? What ability are organisms differentiated by?

selects for bacteria that can tolerate high salt concentrations

Eosin methylene blue agar (EMB) is a selective and differential media. What kind of organisms does EMB select for? What ability are organisms differentiated by?

selects for gram negative bacteria through the dyes eosin and methylene blue and and differentiate through their ability to ferment the sugar lactose

What type of organism would you be growing if you added thioglycolate to the media?

anaerobic organisms

What is the purpose of the streak plate technique when starting with a mixed culture?

culture is diluted on an agar plate in such a way that individual cells are separated from one another

Define colony

as a cell divides the population increases to form a mound of cells

List three direct methods of counting bacteria. List three indirect methods of counting bacteria

manual cell counting, viable plate count, coulter counter

What is the downside of using the turbidity measurement for enumerating bacteria?

both living and dead cells account for turbidity in the growth medium

What is the difference between disinfection and sterilization?

disinfection - reduces microbial numbers

sterilization - eliminates all bacteria, viruses, and endospores

What is decimal reduction time (DRT)?

the time in minutes that it takes to kill 90% of a given microbial population at a set temperature

What is thermal death time?

the shortest period of time that a given temperature must be help to kill all microbes in a sample

What is thermal death point?

the minimum temperature needed to kill all microbes in a sample within ten minutes

What process uses heat, steam, and pressure to sterilize microbial media and lab instruments?

autoclave

Boiling water for 5 minutes kills which types of microbes? What does boiling water not destroy?

pathogenic bacteria, protozoans, and viruses

it does not destroy endospores

What process used by the dairy industry reduces the number of bacteria in milk?

pasteurization

What type of sterilization is used when a microbiologist flames an inoculation loop using a Bunsen burner?

dry heat

What microbial decontamination method is utilized when using a LifeStraw?

filtration

What is the difference between disinfectants and antiseptics?

disinfectants - used to treat inanimate objects

antiseptics - applied to living tissue

What is the difference between microbiocidal and microbiostatic germicides?

microbial - germicides that kill microbes

microbiostatic - germicides that inhibit microbial growth but do not kill microbes

What is the mode of action of alcohols such as ethanol or isopropanol?

target proteins and lipid membranes

The disinfectant Lysol contains what type of chemical?

phenols

What is one of the most widely used halogen disinfectants?

chlorine bleach

Detergents are amphipathic molecules. What does that mean?

have both a hydrophilic and hydrophobic end, allows then to remove water soluble and water insoluble substances

Which two chemical agents kill Mycobacterium?

glutaraldehyde and hydrogen peroxide

What is the most effective endospore elimination method?

autoclaving

How are naked viruses usually inactivated?

chlorine based agents

How are prions eliminated?

combination of chemical treatments and increased temperature and pressure during autoclaving