Microbiology

Which of the following is a selective media recommended for the isolation of Clostridioides difficile?

Cefoxitin-cycloserine-fructose agar (CCFA)

Four specimens are received in the laboratory at the same time. The specimens are: Urine in specimen cup for urine culture Feces in preservative for stool culture Cerebrospinal fluid for culture Synovial Fluid for culture Which specimen should be processed first?

Cerebrospinal Fluid

Which of the following would be the most appropriate temperature for long term storage of specimens for viral culture?

-70° C

Observed in a stool specimen passed from a person with minor intestinal symptoms is this 8 µm in diameter cyst. Note the four nuclei and their distinctive blot-like karyosomes. Based on the microscopic appearance of this cyst, select the presumptive identification.

Endolimax nana

From the list of incubation temperatures, select the one that is currently recommended as a routine temperature of incubation for the laboratory recovery of fungi from culture specimens, being both successful and cost-effective.

30°C

A 36-year old woman is a known intravenous drug abuser, and gives a history of "several previous episodes of hepatitis". The laboratory workup is as follows: HBsAg- Reactive anti-HBs- Negative anti-HBc- Total Positive anti-HBc IgM- Negative anti-HAV- Total Positive anti-HCV- Positive anti-HAV IgM- Negative Which of the following diagnoses can be EXCLUDED based on laboratory data and current symptoms and history?

Acute hepatitis A

The colonies illustrated in the upper photograph were recovered from the aspiration of nasal secretion from a patient with acute sinusitis. The 48 hour colonies on blood agar are relatively small, entire, white, and non-hemolytic. Colonies growing on chocolate agar are also small, smooth, and entire with light yellow pigmentation. On Gram stain, pale-staining, Gram-negative coccobacilli are observed, with a tendency to form long, narrow filaments. The lower photograph reveals tube reactions with a KIA: Acid/Acid and the oxidative utilization of several carbohydrates except for xylose and mannose. Nitrate reduction is positive and ornithine and arginine decarboxylases are negative. From the observations, select from the multiple choices the genus/species name of this isolate.

Aggregatibacter aphrophilus

The colonies seen in the upper frame, grown after 48 hours of incubation aerobically at 35°C, and the accompanying Gram stain in the lower frame are of an organism uncommonly associated with human disease; however, this organism has been associated with septicemia, bronchopneumonia, osteomyelitis and other infections, particularly in intravenous drug users. What is the most likely identification of the organism?

Bacillus circulans

All of the following media types should be inoculated for cerebrospinal fluid (CSF), EXCEPT:

Brucella agar plate (BRU)

The growth of yellow-white yeast colonies with a smooth or hair-like surface within 2 - 3 days on non-selective culture media generally requires further procedures to make a presumptive identification. Microscopic observation of the subculture of colonies growing on cornmeal agar is one such approach, as illustrated in the photomicrograph. Note the spider-like colonies that appear along the streak line. From the multiple choices, select the name of the presumptive yeast identification.

Candida parapsilosis

This isolate, identified as Enterobacter cloacae, was recovered from the urine and blood cultures of a patient who had recently returned from India where he had received a total hip replacement. He presented to the ED with multiple decubiti, sinusitis, and a urinary tract infection. The Hodge Test that was performed on this organism was negative. What resistance mechanism may be identified from the KB plate and the susceptibility interpretations

Chromosomal AmpC plus Porin Mutation

A Gram stain of drainage from an open wound revealed gram-positive bacilli with spores. This description would commonly rule out which one of the following organisms?

Clostridium perfringens

Cocci may arrange as diplococci, tetrads, chains and clusters. The morphologic arrangement of the genus Staphylococcus is:

Clusters

A tissue sample is received in the laboratory for routine aerobic culture. How should the tech prepare the sample for inoculation onto agar plates?

Use a tissue grinder to homogenize the sample

A D-test is performed on gram-positive cocci to determine inducible resistance to clindamycin when the isolate is sensitive to clindamycin and resistant to which antibiotic?

Erythromycin

To accurately identify aerobic actinomycetes to the species level, the use of molecular methods, such as 16S rRNA, can be used. However, there are limitations in identifying Nocardia and other aerobic actinomycetes by molecular methods. All of the following are limitations, EXCEPT?

Extracting DNA

Each of the following characteristics will differentiate between Listeria monocytogenes and Erysipelothrix rhusiopathiae except:

Fermentation of glucose

Which of the following is also known as the Koch-Weeks bacillus?

Haemophilus aegyptius

The 70 µm ovum, illustrated in this high power microscopic view of a saline preparation, is uncommonly found in human feces. This parasite is more commonly found in rats and mice, but infections may be uncommonly transmitted to humans. Water or food contaminated with arthropod related insects within which the cysticercoid larval forms develop may be inadvertently ingested. Once in the human intestine, these larvae develop into adults that attach to the lining cells, and excrete ova that may be observed in fecal specimens. Select the name of the cestode represented by this ovum.

Hymenolepis diminuta

All of the following statements about Coxiella burnetii are true, EXCEPT:

It is best diagnosed by culture of the organism

Select from the multiple choices the specimen that is inadequate for the recovery of anaerobes and should be summarily rejected upon receipt in the microbiology laboratory.

Uterine cervical swab in Cary-Blair transport medium

Observed in the top photographs are colonies growing on blood agar after 24 hours incubation, obtained from a positive blood culture. The colonies are tiny and surrounded by narrow zones of beta hemolysis. The initial presumptive identification was that of a Streptococcus and a CAMP test was set up. A follow-up Gram stain (middle image) revealed Gram-positive bacilli in loose clusters rather than cocci. The lower image demonstrates a rectangular zone of hemolysis in the CAMP test, compared to the arrow-head shape of a control Streptococcus. From these observations, select the most likely presumptive identification of this isolate.

Listeria monocytogenes

Which of the following species of Mycobacterium might be associated with contamination of the hot water system in large institutions such as hospitals?

M. xenopi

Each of the following tests is helpful in the species identification of Staphylococcus aureus EXCEPT:

Modified dimethyl sulfoxide (DMSO) test

Multiple ring forms in red blood cells are most frequently seen in which Plasmodium species infection?

P. falciparum

Oxacillin resistance of MRSA is due to the production of which of the following penicillin-binding proteins (PBPs)?

PBP2a

Which of the following is oxidase-positive?

Pseudomonas aeruginosa

The organisms listed below are given with the most appropriate specimen for their recovery, EXCEPT:

Plasmodium falciparum - ocular secretions

Interpret the auramine fluorochrome stain image to the right:

Positive for acid-fast bacilli

The saccharolytic anaerobe that produces red fluorescing colonies when illuminated with a Wood's lamp, as shown in this photograph, is:

Prevotella bivia

The blue color seen in Simmon's citrate agar slant to the right tube shown in this photograph, indicating a positive reaction, results from:

Production of ammonia from ammonium phosphate

Examine the following test results and identify what action you would take. CAMP: Arrowhead appearance Bacitracin disk: 6mm zone of inhibition PYR: Negative Bile Esculin: Tan appearance, no darkening

Report the isolate as Streptococcus agalactiae

This Gram-positive coccus is catalase positive. The tests shown are a tube coagulase test inoculated with the isolate, and an MRSA screen plate containing 4% NaCl and 6 µg/mL of oxacillin. A 0.5 McFarland standardized inoculum of the isolate is inoculated to the plate. What step should you take next?

Report the isolate as methicillin resistant Staphylococcus aureus.

The pink-red, yeast-like colonies shown in the photograph together with the production of budding yeast cells singly and in loose clusters in the absence of hyphal formation is characteristic of which of the yeast listed below? (In the past, recovery in laboratory culture this organism was considered a contaminant; however, more recently it has been listed as an "emerging" agent of infection and cannot be considered as insignificant.)

Rhodotorula mucilaginosa

Which of the following is an obligate intracellular parasite?

Rickettsia

A yeast identification system's biotype number for an unknown isolate did not differentiate between Candida tropicalis and Candida parapsilosis. This isolate could be identified as C. parapsilosis on a cornmeal agar preparation if it produced:

Sagebrush appearance with large hyphae; blastoconidia not characteristically present.

A woman came to see her physician as she was having vaginal/vulvar itching and some pain upon urination. To obtain a diagnosis of a yeast infection, which of the following is the test of choice?

wet preparation

This suspicious form measuring 120 µm by 63 µm was recovered from a stool specimen. What is the most likely identification?

Schistosoma mansoni

You are collecting a throat swab specimen from a child with a suspected streptococcal infection. Which of the following collection techniques will ensure that only the posterior pharynx is sampled with the swab?

Sit the patient in a well-lit area. Have the patient tilt his/her head back. Use a tongue blade to depress the tongue. Access the posterior pharynx without touching the tongue, inside of the cheeks, teeth, or uvula.

The image to the right is a gram stain of a positive blood culture. The bacterial genus most likely to grow out in culture is:

Staphylococcus

Which of the following organisms is both a transient colonizer of skin, as well as the most common cause of bacterial skin infections?

Staphylococcus aureus

Which of the following organisms will give a positive coagulase test?

Staphylococcus aureus

Sulfonamides, such as sulfamethoxazole (SMZ), and trimethoprim (TMP), work by targeting:

Tetrahydrofolate synthesis; preventing bacterial DNA synthesis

An expectorated sputum specimen is received for culture at your laboratory. You are preparing to make slides and inoculate the media and are observing the gross appearance of the specimen. The specimen is a mixture of watery, bloody, and purulent material. Which area(s) of the specimen is most likely indicated for culture and slides?

The bloody and purulent areas of the specimen are most indicated for culture and slide preparation.

Acridine orange is used for:

Visualization of bacteria in specimens where debris may be present

How would you classify the organism on this Gram stain?

Yeast

Assume you perform microbiology for an institution submitting surveillance cultures for MRSA. Which isolate should receive further workup to rule out methicillin (oxacillin) resistance?

Yellow colonies on Mannitol Salt agar; catalase-positive, coagulase-positive.

The Western Blot for HIV-1 infection identification looks for HIV p24 and what other two protein bands to confirm HIV-1 infection?

gp41 or gp160

Acinetobacter spp. are similar to Neisseria spp., EXCEPT Acinetobacter spp. are generally

oxidase negative

A cerebrospinal (CSF) cell count is 1000 cells/µL. The cells on differential are predominantly lymphocytes. CSF protein is moderately elevated and the glucose is normal. No microorganisms were observed on a Gram stain smear of the CSF sediment. What is the MOST likely condition?

viral meningitis