micro and viro BOC review

The Gram stain of a sputum specimen is unremarkable but the culture reveals many small gram-negative rods that are able to grow only on charcoal yeast extract agar. What is the MOST likely diagnosis?

Legionnaire's disease

Which modified PCR technique or other method of amplification is used to detect Mycobacterium tuberculosis?

Transcription-Mediated Amplification

is a Gram-negative bacillus that shows bipolar staining in a Gram stain. Characteristics of the organism include oxidase negative, catalase-positive, and non-lactose fermenting colonies on MacConkey.

yersinia

Specimen handling from patients with symptoms consistent with tularemia requires work in a biological safety cabinet. Although PCR may confirm infection with Francisella tularensis, the following culture characteristics and tests aid in presumptive identification:

No growth on MAC, slow growth on CHOC; oxidase negative, positive catalase and ß-lactamase

causes cutaneous infection after the organism enters the skin or subcutaneous tissues. It is the most frequent cause of nocardiosis, which is usually seen in the hands and feet as a result of outdoor activity.

Nocardia brasiliensis

sporulation is characterized by the production of short urn-shaped phialides with a narrow bottle-like opening derived laterally from the sides of the hyphae. Spherical or oval-shaped, yellow-pigmented conidia are produced from within each phialide, forming loose aggregates at the terminal opening.

Phialophora verrucosa

this fungal species produces phialides with distinct flattened or saucer-like collarettes. several dematiaceous hyphae with long, flask-shaped, tapered phialides that have flat saucer-like terminus are seen

Pleurostomophora richardsiae

A blood culture yielded an organism with the following reactions: TSIA: K/A, gas (+), H2S (+) Citrate: Positive Indole: Negative Lysine: Positive Ornithine: Positive Motility: Positive Phenylalanine: Negative ONPG: Negative Urease: Negative

Salmonella

Distinctive are the lavender-pink pigmented colonies growing on MacConkey agar and the tiny coccobacilli observed in gram stains, simulating those of Neisseria species. The oxidative production of acid from most carbohydrates (saccharolytic) and negative oxidase reaction are additional key identifying characteristics (oxidase negative group of non-fermenters).It is a common isolate from a variety of nosocomial infections in hospitalized patients.

Acinetobacter baumannii

Which of the following markers would you expect to find in the serum of a patient who has recently recovered from Hepatitis B infection?

Anti-HBs

The colonies growing on the surface of this 5% sheep blood agar plate, with ß-hemolysis, were recovered from a throat swab of a 19-year-old girl with acute pharyngitis. Gram stain revealed club-shaped Gram-positive bacilli with rudimentary branching. What is this species?

Arcanobacterium hemolyticum

mold form produces short conidiophores with a single, round conidium. It gives the appearance of a "lollipop". This organism causes a significant systemic infection that typically begins in the respiratory tract. In the U.S., the reservoir for the organism is in the Mississippi, Missouri, and Ohio River Valleys.

Blastomyces dermatitidis

A patient grew out Mycobacterium tuberculosis (MTB) from an acid-fast bacilli (AFB) sputum culture. The physician called requesting information on alternative choices for the treatment of MTB since the patient had tested resistant to the primary drugs of choice. Which of the following antitubercular agents would be recommended for treatment?

Ciprofloxacin

Colonies are slow-growing and are not specific. Distinctive for making the identification of cladosporium-type sporulation, as seen in microscopic mounts, are hyphae giving rise to long chains of dark-staining, elliptical conidia each separated by a scar called a dysjunctor. Its colony is gray-green to black with a black reverse.

Cladophialophora carronii

also produces large macroconidia which are club-shaped and contain 3 - 5 cells separated by transverse septa. The outer walls of the macroconidia are thin and smooth, devoid of echinulate spikes. Microconidia are not produced.

Epidermophyton floccosum

Which is the first marker (antigen or antibody) which will become positive after exposure to Hepatitis B?

HBsAg

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

Haemophilus aegyptius

rarely produces macroconidia. Rather, a mixture of club-shaped, spherical microconidia in varying sizes are produced. These microconidia are borne laterally in small, irregular clusters from septate hyphae.

Trichophyton tonsurans

A gram-positive bacillus grew as a diffusely beta-hemolytic colony from a newborn. It was catalase-positive and had tumbling motility on a hanging drop preparation. The image shows how the organism grew in the motility medium. What is the most likely diagnosis?

listeria

Characteristic is the production of spindle-shaped (fusiform) multi-celled macroconidia that are pointed at the tip and may be slightly turned to one side. The outer wall is slightly thickened with a prickly(echinulate) surface. causes ringworm

microsporium canis

The relatively rapid growth of indented gray-yellow colonies on chocolate agar in five days is suggestive of

nocardia

are anaerobes most commonly recovered from human infections, and commonly associated with parappendiceal abscesses. This organism group grows readily on BBE agar in an anaerobic atmosphere and produces gram-negative bacilli with rounded ends, as seen in the photograph.

Bacteroides fragilis

produces a large cyst and trophozoite entirely covered in cilia. Both stages are also known to contain a kidney-bean-shaped macronucleus and a small, round micronucleus.

Balantidium coli.

colonies growing on blood agar vary from smooth and mucoid to dry and wrinkled, simulating those of Pseudomonas stutzeri, but can be distinguished by having a distinct pungent earthy odor. Acid is also produced from most carbohydrates (saccharolytic). Oxidase is positive. A key distinguishing chemical reaction is the positive nitrate reduction with the production of gas.

Burkholderia pseudomallei

This isolate is typically recovered from a skin abscess at the site of a dog bite; or may be recovered from blood cultures in cases where the infection may spread.

Capnocytophaga canimorsus

A presumptive identification can be made based on the observation of variable staining cocco-bacilli that often line up in rosette-like clusters. More definitive identification can be made by demonstrating positive oxidase and indole reactions, and negative reactions for catalase, nitrate, and urease

Cardiobacterium hominis

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? (Choose the BEST response.)

Clostridium perfringens

a coccidian protozoa, has been reported worldwide causing disease in humans. Most cases are seen in the tropics and subtropic areas. The incubation period is approximately one week. Symptoms present as severe watery diarrhea, weight loss, nausea and vomiting, low-grade fever, and fatigue. Cysts may be identified in fresh stool by wet mount preparation or trichrome stain. The cysts, however, are small (7µm x 10µm), are not easily detected in a wet mount, and do not hold trichrome stain well. Specimens stained with modified acid-fast or safranin stain produce improved visualization of the organism's morphology.

Cyclospora cayetanensis

Unique is the pitting of the agar surrounding the colonies particularly on chocolate agar, with a light gray-white pigmentation of the adjacent agar. Gram stains reveal slender, straight gram negative bacilli with rounded ends.

Eikenella corrodens

this fungal species produces long, slender, tapered phialides that may appear roughened at the tip where the rings or annelids have formed.

Exophiala jeanselmei

produces large, tuberculated, macroconidia. The infection is typically associated with the aerosolization of bird or bat excrement.

Histoplasma capsulatum

The Major Histocompatibility Complex (MHC) I genes encode for:

Human Leukocyte Antigens (HLA)-A,B,C

The red/pink color of the colonies seen on this MacConkey agar plate is an indication of:

Lactose-fermenting gram-negative bacilli

Which of the following organisms has been isolated from nasal secretions and causes atrophic rhinitis, a tissue-destructive disorder in the nose?

Klebsiella pneumoniae subsp. ozaenae

The 48-hour growth of small pinpoint gray-white, smooth colonies on chocolate agar (right plate) are most commonly recovered as normal upper respiratory flora but may cause otitis media and sinusitis. There was no growth on Thayer Martin media (left plate). Growth on MacConkey agar is also absent. Short, plump, Gram-negative cocci lying singly and in loose clusters are seen in Gram stain, as illustrated in the lower photomicrograph. This non-fermenter is non-motile, oxidase-positive, and does not utilize carbohydrates (assacharolytic). Nitrates are reduced and DNAse is positive. From these observations, select from the multiple choices the presumptive identification of this isolate.

Moraxella cattharalis

is a Gram-negative coccobacilli, catalase, and oxidase-positive, reduces nitrate to nitrite, and is differentiated from other Moraxella species by the ability to liquefy gelatin. Causes pink eye

Moraxella lacunata

Which Pseudomonas species will have yellow colony pigmentation on blood agar?

Pseudomonas fulva

The tiny colonies seen in the upper photograph are surrounded by a narrow zone of beta hemolysis. The lower photomicrograph confirms that the isolate is a streptococcus. The small size of the colonies and the butterscotch odor are clues to the identification of ______________, which characteristically carries the F antigen.

Streptococcus anginosus (S. milleri in the European literature)

In order to differentiate Nocardia species, reactions for casein, tyrosine, and xanthine hydrolysis on casein agar can be used. Nocardia _________ is negative for all these tests and relatively inert biochemically.

asteroides

Which of the following Hepatitis viruses is (are) transmitted through the fecal oral route and may be implicated in infections transmitted through contaminated food and water?

hepA