MLS 418: Clinical Microbiology I – Urine Cultures Unit

True or False: Urine in the bladder of a healthy person is sterile.

True

Urine becomes contaminated when it passes through the _________.

urethra

The route(s) of infection for a UTI can include:

a. use of a catheter

b. area around the urethra becoming colonized with enteric organisms

c. blood stream

d. all of the above

all of these

Cystitis is the infection of the ___________.

bladder

The number one cause of UTIs is:

Escherichia coli

An acceptable urine specimen for culture that is easy to collect, has minimal contamination if patient is properly instructed, and yields an accurate colony count is:

clean catch midstream urine

The urine specimen that utilizes the most sterile technique for collection but is the most invasive is:

suprapubic urine

What temperature should urine be stored at if it will be cultured within 30 minutes?

25ºC (room temp)

What temperature should urine be stored at if it will be cultured within 24 hours?

4ºC (refrigerated)

What temperature should urine be stored at if it is placed in transport media, such as boric acid?

25ºC

What kind of a container should urine be stored in?

sterile and leak-proof container

The majority of urine cultures performed in the laboratory will have:

either no growth or growth of contaminants only

The microbiologist counted 75 colonies of a gram-negative bacillus isolated on the MacConkey plate. There were 70 colonies of the same gram-negative bacillus on the BAP. The 0.001 calibrated loop was used to set up this culture. What should be reported for the colony count?

75,000 cfu/mL (always use the higher count when there is a difference)

A colony count for a straight catheterized urine specimen is >100,000 cfu/ml of a gram-negative bacillus. This organism should be treated as a:

pathogen with a complete workup performed

A clean-catch midstream urine was cultured on a child. The following organisms grew:

- 12,000 cfu/ml diphtheroids

- 52,000 cfu/ml LF GNRs

- 18,000 cfu/ml coag-neg Staphylococcus

How should this culture be evaluated?

report organisms as contamination with no further workup

What media do all labs generally use for setting up urine cultures?

sheep blood agar and MacConkey agar

The primary purpose of setting up a colony count on a urine culture is to:

quantitate growth to aid in the interpretation of the culture

The 0.01 ml calibrated loop should be used for the colony count when setting up what type of urine culture?

suprapubic urine

The best incubation conditions for the MAC when setting up a urine culture is:

35ºC in ambient air

Results of a clean catch urine sample after 18 hours incubation from a 16-year-old female:

Sheep Blood Agar:

- Isolate # 1 >100,000 cfu/ml beta-hemolytic cream yellow colonies

- Isolate # 2 50,000 cfu/ml non-hemolytic grey colonies

- Isolate # 3 35,000 cfu/ml beta-hemolytic grey colonies

- Isolate # 4 10,000 cfu/ml dry white colonies

MacConkey Agar:

- 35,000 cfu/ml pink colonies

What is your next best step?

no further work up is necessary

A urine culture and colony count is ordered on a clean catch urine collected from an 8-year-old female seen in the emergency room. The unpreserved urine specimen collected in a sterile cup is received in the lab at 1900. The culture will not be set up until 0700 the next morning. The next best step is to:

store the specimen at 4ºC until the culture can be set up

On Monday, you report a clean catch urine on a 19 year-old female: 5,000 cfu/ml lactose fermenting GNR

On Tuesday, a second specimen was submitted on the same patient has a colony count of 12,000 cfu/ml of lactose fermenting GNR.

The next best step is:

perform an ID and susceptibility on the 12,000 cfu/mL LF GNR

A physician wants to request a urine culture to include culturing for anaerobes and inquires about what type of specimen to submit for this culture. The best response is:

suprapubic urine submitted in a sterile, capped syringe with all the air expelled

What is the urine colony count if a 0.01 ml calibrated loop was used and 65 colonies are isolated when plated on a sheep blood agar plate?

6,500 cfu/mL

Results of a clean-catch urine culture at 18 hours incubation:

- BAP: >100,000 cfu/ml beta-hemolytic gray colonies

- MAC: >100,000 cfu/ml dark pink colonies

The next best step to provide a abbreviated identification is to perform a/an:

oxidase and spot indole

Quality control procedures in a microbiology laboratory must include:

daily monitoring of temperatures of each refrigerator, incubator, and heating block

A GNR that is oxidase negative, that swarms on a BAP, produces a clear colony on MacConkey agar, and is spot indole positive can be identified by abbreviated methods as:

Proteus vulgaris

Which of the following can produce a false positive result when performing the catalase test?

scraping up the sheep blood agar from the plate when obtaining colonies

Results of a clean catch urine sample at 18 hours of incubation:

- BAP has >100,000 cfu/mL gray, non-hemolytic colonies

- MAC is NG

- Gram Stain is GPC in chains

What is your next step?

What should you do if that next step is negative?

catalase test; run a PYR

True or False: Susceptibilities should be performed on Enterococcus species when identified as a potential pathogen, as there are no known susceptibility patterns.

True

A 37 year old's clean catch urine grew >100,000 cfu/mL, with beta-hemolytic gray colonies on the BAP. Shiny, metallic green colonies were seen on the EMB agar. Based on the colony morphology, this organism can be identified as:

Escherichia coli

If a clean catch urine sample has many white colonies growing on a BAP and has NG on a MAC, what should you perform next?

a Gram stain

True or False: Susceptibilities for Staphylococcus saprophyticus from urine cultures should be reported as there are no known susceptibility patterns.

False

If you suspect yeast from a gram stain, what should you perform next? If that test is positive, what should you report the organism as?

a germ tube; report as Candida albican/dubliniensis

Routine stool cultures in the United States should be examined at minimum for the presence of:

Salmonella, Shigella, and Campylobacter species

Which of the following specimens is unacceptable for stool culture?

a. stool specimens cultured within 1 hour of collection

b. stool submitted in enteri transport media

c. stool submitted with a small amount of urine present

d. stool submitted in unsterile, but clean container

stool submitted with a small amount of urine present

The purpose of a HE (Hextoen Enteric) agar is to determine if the organism is:

a lactose and/or sucrose fermenter

The purpose of a stool culture is to screen for the presence of stool pathogens using selective, differential and routine media. If an organism produces an orange to salmon pink colony on HE (Hextoen Enteric) agar it is a:

non-stool pathogen

Observation of colonies on a routine stool culture show clear colonies on MacConkey and blue-green colonies with black centers on Hextoen Enteric agar. What is your next step in the culture process?

screen the suspicious colonies with a GNR ID panel

Observation of colonies on a routine stool culture show clear colonies on MacConkey and blue-green colonies with black centers on Hextoen Enteric agar. What organism do you suspect as the pathogen?

Salmonella species

Transport of stool for Clostridium difficile toxin testing will be delayed from a near-by hospital clinic. What is the best transport method of the stool specimen?

refrigerate the specimen and transport it on ice

What is he most common cause of antibiotic-associated pseudomembranous colitis?

Clostridium difficile

True or False: A gram stain is routinely performed on stool specimens for the presence of bacteria.

False

True or False: The CDC recommends screening stool cultures for E. coli O157:H7 by culture only.

False

True or False: When inoculating stool culture media, always inoculate selective media first.

False; always inoculate non-differential media first

True or False: GN broth is used to enhance the growth of small numbers of normal stool flora.

False; it is used to enhance the growth of small number of pathogenic stool organisms

What media is set up, at minimum, for a routine stool culture?

sheep blood agar, MAC, HE agar, and Campy-BAP

If at 24 hours of incubation, the MAC agar for a routine culture is growing many LF GNRs and some NLF GNRs, what is the next best step?

work up the clear colony type, as it is suggestive of Salmonella or Shigella species

Cefsulodin-irgasan-novobiocin (CIN) agar is routinely incubated at ___ºC to recover the _________________.

22/Yersinia species

Suspicious colonies on MacSorbital agar will appear ___________, which is consistent with ______________.

clear/E. coli O157:H7

The preferred method for laboratory diagnosis of antibiotic-associated pseudomembranous colitis caused by Clostridium difficile can be made by detection of:

C. difficili toxin in the stool

The preferred stool sample to test for C. difficili toxin is:

unformed stool that takes the shape of the container

A molecular Gastrointestinal panel for bacteria, virus and parasites was positive for Salmonella species. The public health laboratory requires the laboratory to attempt recovery of the organism from the stool for epidemiological purposes. Serotyping Salmonella isolates aids in the detection of outbreaks in the community. The stool is plated to a HE and MAC. Which colony should be worked up to recover Salmonella from the culture?

the clear colony with the black center growing on HE agar

A stool culture from a 4 year-old boy had the following results:

- HE agar: Moderate clear colonies with black centers

- HE agar: Few yellow colonies

- MAC agar: Few pink colonies

- MAC agar: Moderate clear colonies

An identification was performed on the moderate clear colonies with black centers from the HE agar. The identification was Citrobacter freundii.

The next step is:

report as moderate normal stool flora

We suspect Campylobacter species based on the following:

Tan, smooth, mucoid looking colonies that are gnr with a gull wing morphology; colonies were both catalase positive and oxidase positive.

What test should be performed to identify this organism as Campylobacter jejuni?

Na Hippurate hydrolysis

If a bacteria is growing on CVA agar from a routine stool culture, is a Gram variable rod with a spiral, catalase positive, and oxidase positive, it is most consistent with:

the Campylobacter species

List the pathogens commonly isolated in urine:

- E. coli (most common!)

- Proteus species

- Enterobacterales

- Enterococcus species

- Beta-hemolytic Strep (S. pyogenes and S. agalactiae)

- Staph. saprophyticus, Staph. aureus, and Staph. epi

- P. aeruginosa, Acinetobacter, and other NLF GNRs

- Candida species (yeasts)

- Aerococcus species (pure isolate with >100,000 cfu/mL)

List the potential contaminants that are commonly isolated in urine:

- Diphtheroids

- Coag-negative staph other than S. saprophyticus

- Alpha-hemolytic and non-hemolytic strep

- E. coli when mixed

- Bacillus species

- Non-pathogenic Neisseria

What does Staphlycoccus aureus often cause?

- skin infections

- pneumonia

- osteomyelitis

- wound infections

- toxin mediated illness

- opportunistic infections

What does Staph. epidermidis often cause?

infections associated with prosthetic devices (catheters, shunts, etc.)

What does Staph. saprophyticus often cause?

UTIs (especially in young women)

What does Group B Strep/Strep. agalactiae usually cause?

UTIs

What does Enterococcus species usually cause?

UTIs

What does Bacillus cereus cause?

Food poisoning

What does Corynebacteriium urealyticum cause?

UTIs

Key infections due to the Enterobacterales order:

- Opportunistic/nosocomial infections

- UTIs

- Typhoid fever (Salmonella typhi)

- Hemolytic uremic syndrome (HUS), E. coli

What is Pseudomonas aeruginosa known to cause?

nosocomial infections and UTIs

What does Campylobacter jejuni cause?

gastroenteritis

What does Helicobacter pylori cause?

gastritis and peptic ulcer disease

What does Aeromonas hydrophila cause?

gastroenteritis

What does Plesiomonas shigelloides cause?

gastroenteritis

what does Clostridium difficile cause?

antibiotic-associated pseudomembranous colitis

What does Candida albicans/dublinensis cause?

in urines, it is seen with UTIs and vaginitis

What does the Candida species cause when associated with urine?

opportunistic infections

What does Candida glabrata cause?

UTIs