Medical Microbiology Lab

Match each ingredient in mannitol salt agar with its role in the medium.

- 7.5% NaCl - Inhibits bacteria other than Staphylococci - Mannitol - Fermentable carbohydrate - Phenol red - pH indicator

Which of the following items are needed in order to set up a CAMP test? - Bacterial isolate to be identified - Mannitol salt agar plate - Optochin disc - Bacitracin disc - Blood agar plate - Staphylococcus aureus

- Bacterial isolate to be identified - Blood agar plate - Staphylococcus aureus

Not Just Another Mosquito Bite Several of Annie's mosquito bites were not healing and instead had become swollen and painful, suggestive of an infection. When the infection didn't respond to several applications of triple antibiotic ointment, Annie's mother took her to the pediatric clinic. A sterile swab was used to collect a specimen of pus from the infected site, and this was placed into a specimen transporter sleeve for transport to the microbiology laboratory. Upon arrival in the laboratory, the swab was used to inoculate a blood agar plate which was subsequently streaked for isolation. After overnight incubation, the specimen showed significant bacterial growth. A Gram stain of the bacterial colonies showed gram-positive cocci. The catalase test was negative. What two tests might be done next?

- CAMP test - Bacitracin susceptibility

Bundle of Joy: Miriam was in her 38th week of pregnancy and was surprised when after just a few mild contractions, her water broke. This was followed by a long labor, after which she delivered a healthy baby boy. About 12 hours later, the newborn became feverish, with an elevated heart rate, rapid shallow respiration, and a temperature of 38.8 degrees Celsius. Blood was collected for culture and sent to the microbiology lab. Eighteen hours later, the lab reported that the blood cultures were growing and that a Gram stain showed gram-positive cocci. Which of the following tests would be used to presumptively identify the isolate as Streptococcus agalactiae? - Catalase test - Coagulase test - Optochin susceptibility - Observation of hemolysis on blood agar - CAMP test

- Catalase test - Observation of hemolysis on blood agar - CAMP test

The following lab activities are frequently done in the medical microbiology lab. Match each of the lab activities with their purpose.

- Culture - Uses several different types of media to grow bacteria from patient specimens - Identification - Uses a variety of tests and media to determine the genus and species of a bacterial isolate - Sensitivity - Tests a microorganism with a battery of different antibiotics to determine which antibiotics are most likely to control or eliminate the infection

Which of the following are genera of gram-positive cocci frequently found as resident microbiota in humans? - Enterococcus - Streptococcus - Staphylococcus - Neisseria - Escherichia

- Enterococcus - Streptococcus - Staphylococcus

Which two bacterial species listed below include strains that are particularly problematic because of their resistance to multiple antibiotics? - Streptococcus agalactiae - Enterococcus faecalis - Streptococcus pyogenes - Streptococcus pneumoniae - Staphylococcus aureus

- Enterococcus faecalis - Staphylococcus aureus

Identify items in this list which are characteristic of all members of the genus Staphylococcus.

- Gram-positive cocci - Cells are arranged in irregular clusters - Catalase-positive - Able to grow in 6.5% NaCl

Which of the following are reasons for identifying bacteria isolated from infections? - Identification reveals the source of an infection - Identification may help with antibiotic selection - Identification may help with disease diagnosis - Identification can typically indicate the outcome for the patient - Identification may help with epidemiologic investigations

- Identification may help with antibiotic selection - Identification may help with disease diagnosis - Identification may help with epidemiologic investigations

Which of the following body sites normally have large numbers of resident microbiota? - Liver - Large intestine - Blood - Throat - Brain - Nose - Skin - Vagina

- Large intestine - Throat - Nose - Skin - Vagina

Which biochemical tests require small discs to be placed on the surface of a bacterial culture plate before incubation? - Novobiocin susceptibility - Optochin susceptibility - CAMP test - Bacitracin susceptibility - Mannitol salt agar

- Novobiocin susceptibility - Optochin susceptibility - Bacitracin susceptibility

Based on this flowchart, what is true about Staphylococcus saprophyticus?

- Possesses catalase enzyme - Does not possess coagulase enzyme - May not ferment mannitol

Which of the following correctly describe the streptococci? - Spherical cells - Cells arranged in clusters - Purple after Gram stain - Cells arranged in chains - Rod-shaped cells - Pink after Gram stain

- Spherical cells - Purple after gram stain - Cells arranged in chains

A catalase test is executed using the following steps:

- Spread a visible amount of bacteria onto the surface of a clean glass slide - Add a couple drops of hydrogen peroxide directly onto the bacteria and observe for the presence of bubbles

This image shows an unknown bacterium after 24 hour incubation on a blood agar plate. What hemolytic results is seen here?

Alpha hemolysis (The dark and green agar color seen close to the colonies is characteristic of alpha hemolysis)

An unknown bacterium was streaked on the top half of a blood agar plate and a bacitracin disc was placed on it. A vertical streak with the unknown bacterium was made, along with an intersecting horizontal streak with S. aureus. After 24 hours, your plate looked like this: What can you determine from this result?

Bacitracin resistant / CAMP positive

An unknown bacterium was streaked on the top half of a blood agar plate and a bacitracin disc was placed on it. A vertical streak with the unknown bacterium was made, along with an intersecting horizontal streak with S. aureus. After 24 hours, your plate looked like this: What can you determine from this result?

Bacitracin sensitive / CAMP negative

Which of the following tests was used to determine the response of S. agalactiae to an antibiotic? - Optochin test - Bile esculin test - Bacitracin test - Catalase test

Bacitracin test

The most reliable source of information regarding the tests that can be used to identify a particular bacterial isolate and the expected results is _______________ Manual.

Bergey's

This image shows an unknown bacterium after 24h incubation on a blood agar plate. What hemolytic result is seen here?

Beta hemolysis (The yellow transparent area that extends around the colonies is characteristics of beta hemolysis.)

This image shows an unknown bacterium after 24h incubation on a blood agar plate. What hemolytic result is seen here?

Beta-hemolytic (The yellow transparent area that extends around the colonies is characteristic of beta hemolysis)

The complete clearing or hemolysis that a bacterial isolate may produce on blood agar is called ______________ hemolysis, while partial hemolysis which produces a greenish discoloration is referred to as ________________ hemolysis.

Beta; alpha

Bile esculin medium is made selective by the incorporation of ____________________, and differential by the incorporation of ____________________ and ferric citrate.

Bile; esculin

A specific example of a medium that can be used to isolate organisms from the human body because it is enriched with compounds that support the growth of fastidious organisms is __________________ agar.

Blood

What enzyme catalyzes the breakdown of hydrogen peroxide to oxygen and water?

Catalase

Not Just Another Mosquito Bite Several of Annie's mosquito bites were not healing and instead had become swollen and painful, suggestive of an infection. When the infection didn't respond to several applications of triple antibiotic ointment, Annie's mother took her to the pediatric clinic. A sterile swab was used to collect a specimen of pus from the infected site, and this was placed into a specimen transporter sleeve for transport to the microbiology laboratory. Upon arrival in the laboratory, the swab was used to inoculate a blood agar plate which was subsequently streaked for isolation. After overnight incubation, the specimen showed significant bacterial growth. A Gram stain of the bacterial colonies showed gram-positive cocci. Which test will enable you to determine if these colonies are staphylococci or streptococci?

Catalase test

What biochemical test can readily differentiate Staphylococcus from streptococcus?

Catalase test

What test eliminated streptococci as potential agents in this case?

Catalase test

What test is used to distinguish between staphylococci and streptococci?

Catalase test

Which of the three tests conducted in this identification process did not require the use of an incubator? - Coagulase test - Catalase test - Novobiocin sensitivity test - Mannitol salt agar plate

Catalase test

Which of the following is an example of a morphological characteristic that could be used in the bacterial identification process? - Amount of colony growth - Oxygen requirement - Presence of urease enzyme - Cell shape

Cell shape

When choosing a biochemical test to run on an unknown, you should consider which of the following? - Choose any biochemical test as most tests are valuable for any type of bacteria. - Choose an easy, rapid test that is standard for its main group of bacteria. - Choose the test that takes enough time to get accurate results.

Choose an easy, rapid test that is standard for its main group of bacteria.

Which biochemical test makes use of rabbit plasma as a reagent?

Coagulase test

A __________________ key is a flowchart that can be used to identify an organism by making a series of choices until you arrive at one possibility.

Dichotomous

Bacteria Identified in Another UTI case:

E. faecalis

Which test uses a medium that is both selective and differential for members of the genus Staphylococcus?

Mannitol salt agar

Is this bacterial isolate positive or negative for catalase activity?

Negative

A microorganism that is most often harmless but may occasionally cause infection and disease if the host defenses are compromised is referred to as an ________________ pathogen.

Opportunistic

Based on the result recorded for the mannitol salt agar plate, what color was the medium after incubation?

Pink

Is this bacterial isolate positive or negative for catalase activity?

Positive

Is this bacterial strain positive or negative for mannitol fermentation?

Positive

Twelve hours after adding a sample of bacteria to rabbit plasma, your tube looks like this. Are the unknown bacteria positive or negative for coagulase activity?

Positive

You evaluate a bile esculin agar slant 24 hours after you inoculated it with your unknown bacterium. Is the bacterium positive or negative for esculin hydrolysis?

Positive

You streak your unknown bacterium onto a blood agar plate and place an optochin disc on the surface of the plate. After 24 hours, your plate looks like this. Is the unknown bacterium sensitive or resistant to optochin?

Sensitive

Not Just Another Mosquito Bite Several of Annie's mosquito bites were not healing and instead had become swollen and painful, suggestive of an infection. When the infection didn't respond to several applications of triple antibiotic ointment, Annie's mother took her to the pediatric clinic. A sterile swab was used to collect a specimen of pus from the infected site, and this was placed into a specimen transporter sleeve for transport to the microbiology laboratory. Upon arrival in the laboratory, the swab was used to inoculate a blood agar plate which was subsequently streaked for isolation. After overnight incubation, the specimen showed significant bacterial growth. A Gram stain of the bacterial colonies showed gram-positive cocci. Close observation of the growth on blood agar revealed that the colonies were beta-hemolytic. Based on this observation alone, which two organisms in the list below are the most likely agents? - Streptococcus pneumoniae - Staphylococcus aureus - Streptococcus pyogenes - Enterococcus faecalis

- Staphylococcus aureus - Staphylococcus pyogenes

Match the organisms to the infections with which they are most likely associated.

- Staphylococcus saprophyticus - urinary tract infection in young women - Streptococcus pyogenes - Scarlet fever; strep throat - Streptococcus agalactiae - Sepsis and meningitis in newborn babies - Streptococcus pneumoniae - Conjunctivitis; meningitis in young children

Some microorganisms can be identified by their sensitivity or resistance to particular antibiotics or chemicals. Match each of the following bacterial species with the chemical or antibiotic that is especially useful in its identification.

- Streptococcus pyogenes - Bacitracin - Staphylococcus saprophyticus - Novobiocin - Streptococcus pneumoniae - Optochin

Which of the following correctly describes Streptococcus agalacticae (Group B strep)? - Possesses the catalase enzyme - Synergistic hemolysis with S. aureus on blood agar (CAMP test) - No zone around bacitracin disk appears in test on blood agar - Beta-hemolytic - Alpha-hemolytic

- Synergistics hemolysis with S. aureus on blood agar (CAMP test) - No zone around bacitracin disk appears in test on blood agar - Beta-hemolytic

Which of the following infections are frequently caused by Staphylococcus species as well as Streptococcus species? - Pharyngitis - Urinary tract infection - Pneumonia - Diarrhea - Abscess - Endocarditis

- Urinary tract infection - Pneumonia - Abscess - Endocarditis

This image shows an unknown bacterium after 24h incubation on a blood agar plate. What hemolytic result is seen here?

Gamma hemolysis (The absence of hemolysis is referred to as gamma hemolysis)

According to this flowchart, what test is most useful for distinguishing between Streptococcus pyogenes and Streptococcus pneumoniae?

Hemolysis on blood agar

The field of study in which medicine and microbiology intersect is known as ___________.

Medical microbiology

Before attempting to identify an unknown bacterial species, the organism must be isolated in a _________________ culture.

Pure

What would this organism look like under the microscope?

Purple spherical bacteria in clusters

Streptococcus agalactiae would appear _________________ in color and __________________-shaped under microscopic examination.

Purple; spherical

Which of the following is a characteristics of members of the resident microbiota? - Resident microbiota often initiate allergic reactions. - Resident microbiota typically cause serious infections. - Resident microbiota can compete with and limit growth of harmful bacteria. - Resident microbiota are a major source of nutrients for our bodies.

Resident microbiota can compete with and limit growth of harmful bacteria.

Bacteria Identified in Bundle of Joy case:

S. agalactiae

Bacteria Identified in Mosquito Bite case:

S. aureus

Bacteria Identified in Ear Infection case:

S. pyogenes

From the initial isolation plate, how many more agar plates would you need to inoculate in order to determine the circled items on this flowchart?

Two

Which of the following is the quickest way to isolate bacteria from a mixed culture? - Serial dilution followed by spread plating - Loop dilution followed by pour plating - Streak plating

Streak plating

Bundle of Joy: Miriam was in her 38th week of pregnancy and was surprised when after just a few mild contractions, her water broke. This was followed by a long labor, after which she delivered a healthy baby boy. About 12 hours later, the newborn became feverish, with an elevated heart rate, rapid shallow respiration, and a temperature of 38.8 degrees Celsius. Blood was collected for culture and sent to the microbiology lab. Eighteen hours later, the lab reported that the blood cultures were growing and that a Gram stain showed gram-positive cocci. Of the organisms listed below, what is the most likely cause of this infection?

Streptococcus agalactiae

Bacteria Identified in Endocarditis case:

V. streptococci

True or False: Multiple bacterial species can have similar staining reactions and microscopic morphology.

True