Microbiology quiz questions

What is true of a pure culture?

we obtain it from an isolated colony which has grown from a single cell

What is the total magnification for a 40x objective lens?

400x

Why do we use aseptic technique in the lab?

to prevent experimental bacterial cultures from being contaminated with microbes from the environment

What is the purpose of oil when using the 100x lens?

to increase resolution and minimize bending of the light that passes through the sample

What is the main reason agar is preferred over gelatin as a solidifying agent in solid media?

agar remains solid at 37 degrees celsius

What is true of facultative anaerobes?

They can grow without O2 and use O2 in their metabolism as well as produce a catalase that breaks down H2O2

What is the function of the iris diaphragm?

it adjusts the amount of light that reaches the specimen

What could happen if you over-decolorize your sample?

gram positive bacteria may appear gram negative

What best describes the difference between genotype and phenotype?

genotypes is the genetic makeup, phenotype is the observable trait

What result is a student most likely to see when they forget to use iodine during a gram stain?

all cells appear pink

Why do we make dilutions when trying to determine the concentration of cells in a culture?

The dilutions help to distribute the cells so that they are easier to count or determine

Obligate anaerobe

cannot grow in the presence of oxygen

Obligate aerobe

requires oxygen for growth

Facultative anaerobe

can use oxygen if present but does not require it for growth

Microaerophile

requires oxygen for growth but can only tolerate specific amounts

How does UV irradiation cause bacterial death?

it causes pyrimidine dimers

What organisms are known to produce endospores?

clostridium perfringens and bacillus anthracis

Sulfonamides are a ______ inhibitor of the ______ biosynthesis pathway.

competitive, folate

A bacteriostatic drug

growth

A bactericidal drug

no growth

If a physician suspects a patient has strep throat (caused by the bacterium Streptococcus pyogenes) and swabbed their throat, what would be the most effective agar for a preliminary identification?

Blood agar as it is differential for hemolysis and S. pyogenes will demonstrate β-hemolysis

Transduction process

bacterial DNA is carried in a phage

Conjugation process

transferred by cell to cell contact through a sex pilus

Transformation

naked DNA is taken up directly from the environment

What is wild type acinetobacter?

a naturally competent prototroph that can grow on minimal media

What would a urine sample with more than 3 different colony types most likely indicate?

a poorly collected specimen contaminated with skin microbiota

What is the name of the cycle in which phage infection leads to the lysis of the host cell?

lytic cycle

What is the enzyme that catalyzes the oxidation reaction in Aliivibrio fischeri called?

luciferase

Characteristics of coliforms

they ferment lactose to produce acid and gas and are gram negative rods

What normal microbiota was used to monitor fecal pollution?

indicator organisms

what is the minimal number of colony types you should expect to see on a blood agar plate?

2

what is the minimal number of colony types you should expect to see on a MacConkey agar plate?

1

What test should you perform on a gram positive cocci?

catalase

What happens in the ouchterlony immunoprecipation method if an antibody recognizes an antigen?

they will create a visible opaque line in the gel and they will cross link creating an insoluble lattice of protein

Why can we use antigen-antibody to identify components of a mystery meat?

because antibodies bind specifically to antigens and placing meat extracts and known antisera into wells on an agar plate, both diffuse and form a visible line of precipitation if they match

When monitoring water for contamination why do public health agencies look for indicator organisms rather than individual pathogens?

pathogens are often present in very low numbers and there is no single method to isolate all pathogens

What are EMB plates differential for?

lactose fermentation

What are EMB plates selective for?

gram negative rods

What is the strain characteristics of enterobacter aerogenes on EMB plates?

lighter with a dark center

What is the strain characteristics of e.coli on EMB plates?

dark, flat colony with green metallic sheen