Aerobic Gram (+) Bacilli 💨 Flashcards
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An isolate with the appropriate colony and microscopic morphol- ogy may be suspected to be Bacillus anthracis if it is:
a. β-Hemolytic on SBA
b. Nonmotile
c. Catalase-negative
d. Gram-negative, non–spore forming
Nonmotile
An aerobic, gram-positive, spore-forming bacillus was isolated
from raw vegetables that were associated with an outbreak of gastroenteritis. The organism produced β-hemolysis, was cata- lase-positive, and was motile. The most likely organism is:
a. Bacillus anthracis
b. Nocardia asteroides
c. Bacillus cereus
d. Tsukamurella spp.
c. Bacillus cereus
Bacillus cereus is most noted for causing:
a. Food poisoning
b. Meningitis
c. Sexually transmitted disease
d. Urinary tract infections
a. Food poisoning
Which forms of infection are caused by Bacillus anthracis?
a. Injectional
b. Inhalation
c. Gastrointestinal d. Cutaneous
e. All of the above
e. All of the above
The functionality of lethal factor requires the presence of what other protein from Bacillus anthracis to form an active toxin?
a. Edema factor
b. D-glutamic acid c. cAMP
d. Protective antigen
d. Protective antigen
Describe the appearance of spore-forming bacteria seen with the spore stain.
In the spore stain, vegetative cells are red, but the spores stain green.
Corynebacterium species often appear as ______________ on Gram stain.
a. Pleomorphic gram-positive club-shaped bacilli that appear in palisades or in V and L formations
b. Branching gram-positive bacilli that appear as fine, intertwin- ing, delicate filaments
c. Short, thin gram-positive bacilli that appear in chains
d. Large square-ended, gram-positive or gram-variable bacilli in chains where the ends of the single cells fit snugly
together
Pleomorphic gram-positive club-shaped bacilli that appear in palisades or in V and L formations
The biochemical tests performed on a gram-positive bacillus were
consistent with Corynebacterium diphtheriae. As a definitive test, the laboratory scientist should now:
a. Perform an Elek test to determine whether the organism
produces exotoxin
b. Subculturetheorganismtocystine-telluriteagarandexamine
for black colonies
c. Prepare a methylene blue stain and examine for metachro-
matic granules
d. Gram stain the isolate and observe for its pleomorphic
morphology
Perform an Elek test to determine whether the organism
produces exotoxin
Respiratory diphtheria is common in the United States, and the
natural hosts for C. diphtheriae are humans and birds
a. True
b. False
b. False
True infections with nondiphtheria Corynebacterium spp., such as C. jeikeium or C. striatum, are often in immunocompromised patients or patients who have had:
a. Insertion of hardware or prosthetic devices
b. Coronary artery bypass surgery
c. Vitamin B12 deficiency
d. A lengthy hospital stay
Insertion of hardware or prosthetic devices
A _________ test can help to differentiate which clinically signifi- cant Corynebacterium spp. recovered from urine samples?
a. Gelatin hydrolysis; C. ulcerans
b. Reverse CAMP; C. pseudotuberculosis
c. Alkaline phosphatase; C. amycolatum
d. Urease; C. urealyticum
Urease; C. urealyticum
after birth. A gram-positive rod is recovered from blood cultures from the newborn. The isolate has the characteristics listed. What is the most likely identity of the isolate?
Weakly β-hemolytic on SBA
Gram-positive bacilli, no spores observed Catalase-positive Hydrogen-sulfide-negative
Motile at room temperature
a. Erysipelothrix rhusiopathiae
b. Listeria monocytogenes
c. Corynebacterium ureilyticum
d. Gardnerella vaginalis
Listeria monocytogenes
A commercial fisherman who had red sores on his hands was seen by his physician. Biopsy and culture of one of the lesions was performed. The culture grew an organism with the charac- teristics listed. What is the most likely organism?
Nonhemolytic on SBA
Gram-positive bacilli, no spores observed Catalase-negative Hydrogen-sulfide-production-positive
Growth in gelatin resembled a test-tube brush
a. Rhodococcus equi
b. Listeria monocytogenes
c. Lactobacillus acidophilus
d. Erysipelothrix rhusiopathiae
Erysipelothrix rhusiopathiae
A 42-year-old man from Guatemala cuts his bare feet on thorns while walking. A subcutaneous abscess develops, and when the patient is seen by a physician, his foot is swollen. When the wound is pressed by the physician, purulence is expressed along with some soft, white granules. A filamentous organism that is partially acid-fast is recovered from the granules. This is most likely an __________ mycetoma caused by ____________.
a. Actinomycotic, Pseudallescheria boydii
b. Actinomycotic, Nocardia brasiliensis
c. Eumycotic, Madurella mycetomatis
d. Eumycotic, Tsukamurella paurametabola
Actinomycotic, Nocardia brasiliensis
What other organisms can give similar clinical and laboratory findings as Listeria monocytogenes? How are these organisms differentiated from L. monocytogenes?
Streptococcus agalactiae (group B Streptococcus) and Enterococcus spp. can produce clinical laboratory findings similar to those for L. monoctogenes. Initial differentiation between L. monocytogenes and similar microorganisms can be made by the Gram stain, catalase test, and esculin hydrolysis.
A 17-year-old boy presented to an emergency department with a history of multiple episodes of febrile pharyngitis followed in 10 to 14 days with extensive desquamation of his hands and feet. The reoccurrences have followed several courses of antimi- crobial therapy including amoxicillin and cephalosporins. Rapid group A streptococci screens and cultures have been consistently negative for Streptococcus pyogenes. A specimen with a request for an alternative agent was submitted to a reference laboratory. The results listed were observed. The patient was subsequently treated with erythromycin, and he recovered. What was the etio- logic agent?
SBA: dry, wrinkled, slightly hemolytic colony, which at 48 hours is a dark spot sunken in the agar
Catalase-negative Nitrate-negative Reverse-CAMP-test-positive
a. Corynebacterium diphtheriae
b. Arcanobacterium haemolyticum
c. Listeria monocytogenes
d. Rhodococcus equi
Arcanobacterium haemolyticum
A sample is sent to the laboratory from a female patient sus-
pected to have bacterial vaginosis. Which of the following would be an appropriate medium for this specimen?
a. Loeffler medium
b. HBT agar
c. CBTA
d. BCYE
HBT agar
Remel HBT Bilayer Medium is a solid medium recommended for use in qualitative procedures for selective isolation and presumptive identification of Gardnerella vaginalis. Gardnerella vaginalis is a venereally transmitted bacterium that is associated with a clinical syndrome called bacterial vaginosis.
A 57-year-old man from New York City presents to the emer-
gency department with diarrhea, arthralgia, abdominal pain, malabsorption, and weight loss of 10 lb over the last month. A duodenal biopsy is performed, but no infectious agent is recov- ered on culture media. However, on Gram stain, a gram-positive rod is observed in macrophages in the biopsy tissue. The organ- ism is identified by 16S rRNA gene sequencing. What is the most likely identity of this organism?
a. Bacillus anthracis
b. Nocardia asteroides
c. Tropheryma whipplei
d. Erysipelothrix rhusiopathiae
Tropheryma whipplei
two spore-forming gram (+) bacilli
Bacillus spp.
Clostridium spp.
the only obligate anaerobe
Clostridium
Bacillus
- spore location
- catalase reaction
Central/subterminal spore
catalase positive
Side note:
Bacillus anthracis
✓Grampositive(+)in chains; “bamboo – fishing rod appearance”
✓capsulated (polypeptide D-glutamic acid)
✓ Grampositivearranged singly; “boxcar”
✓ central/subterminalspores
~
Bacillus spp. are motile, except
B. anthracis
B. mycoides
(+) catalase; ferments glucose; starch hydrolyzers
Clostridium
- spore location
- catalase reaction
-terminal spore
-negative catalase
– “MEDUSA HEAD” or “ground glass colonies”
✓ disturbed portion of colony stands up like “BEATEN EGG WHITE” when lifted up
o Carbohydrate fermentation (glucose, fructose, maltose, sucrose)
o GELATIN (inverted pine – tree growth); slow liquefaction
o STARCH: hydrolyzed (+)
o Vogues – Proskauer positive
o Reduced nitrates to nitrite
Bacillus anthracis
Bacillus anthracis
Polypeptide capsule (polypeptide D – glutamic acid) Anthrax toxin
✓ complex protein toxin produced in vivo responsible for the signs and symptoms of disease
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has
Protective antigen (PA);
Edema factor (EF);
Lethal factor (LF)
Bacillus anthracis
Binds to specific cell receptors; forms a membrane
channel that mediates entry of EF and LF into the cell
PROTECTIVE ANTIGEN
*an adenylate cyclase; with PA, it forms a toxin known as edema toxin
EDEMA FACTOR
with PA forms lethal toxin which is major virulence factor and cause of death in infected animal.
LETHAL FACTOR
aka Malignant Pustule
CUTANEOUS ANTHRAX
aka MILZBRAND anthrax
GASTROINTESTINAL ANTHRAX
-Most patients die from toxemia and overwhelming sepsis.
Serological:
ASOCOLI Test
ELISA
Microhemagglutination
Serological tests for Bacillus anthracis
Small shiny, compact to large, feathery, spreading type, maybe “MEDUSA head”, frosted glass colonies
o Ferments salicin; (+) lecithinase
Bacillus cereus
Bacillus cereus
Virulence Factors:
- Enterotoxins (ST and LT)
- Cerelysin
- Phospolipase C
- Pyogenic Toxin
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common LABORATORY CONTAMINANTS
Bacillus subtilis
aka “Hay Fever”
Bacillus subtilis
Culture:
Large, flat, dull with ground glass colonies, may show complete zone of hemolytic pattern, may be pigmented
Biochemical Tests:
Ferments mannitol, xylose and arabinose
Bacillus subtilis
Bacillus subtilis
Clinical Infection:
o bacteremia
o infection among immunocompromised patients o eye infection
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Bacillus subtilis
Diagnostic Tests:
i. Ascoli Test (Precipitin Test)
ii. CatalaseTest–differentiates Bacillus from Clostridium
(bacillus is gram+)
iii. Direct Fluorescent Antibody Test – (+) /POS cell wall polysaccharide and capsule antigen
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aka “Kleb-loeffler’s bacillus”
Corynebacterium diphtheriae
Corynebacterium diphtheriae
CULTURE and ISOLATION:
- Cystine–Tellurite agar -
Gray black after 48 hrs.
May be both large and small and flat or
convex - Tinsdale’s agar - Dark brown to black with brown to black halos
- Loeffler agar - Pleomorphic appearance, arranged side by side
agar that Display metachromatic granules – “ Babes-Ernst granules”
Loeffler agar
aka
* Barcoo rot
* Slow healing ulcers and membrane formation
* Complication is less common
CUTANEOUS DIPHTHERIA
a pharyngitis characterized by the development of an exudative membrane that covers the tonsils and pharyngeal wall.
* life – threatening cardiac and neurologic toxicity occur if untreated.
RESPIRATORY DIPTHERIA
Corynebacterium ulcerans
* an animal pathogen causing mastitis in domestic animals
* MOT: contact with animals and/or ingestion of unpasteurized dairy products
* Associated with diptheria-like sore throat, isolated from skin ulcers and exudative pharyngitis
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BAP: narrow zone of beta hemolysis CTBA: (+) brown halo around colonies Loeffler’s agar: (+) growth
Corynebacterium ulcerans
an animal pathogen causing granulomatous lymphadenitis in humans
Corynebacterium pseudotuberculosis
Listeria monocytogenes
“Umbrella-shaped” / “Inverted
Christmas Tree” at what temp?
at 25 deg. Celsius but not at 35 deg. Celsius
Immunosuppressed individuals and pregnant women should avoid eating soft cheeses.
o Colonized mothers may pass the organism to the fetus.
Listeria monocytogenes
ONLY catalase negative, Gram positive non-sporeforming rods that produces H2S
ONLY catalase negative, Gram positive non-sporeforming rods that produces H2S
MICROSCOPY: thin, pleomorphic rod ; form long filaments arranged in singly, short chains or in a V-shape
Erysipelothrix rhusiopathiae
Biochemical Characteristics:
o Gelatin stab culture – “pipe cleaner” or “test
tube brush” pattern at 22 deg. Celsius
o (-)/0 Catalase, Oxidase, Esculin Hydrolysis,
Nitrate reduction, VP and Urease o (+) Hydrogen sulfide
o Glucose and lactose fermenter
Erysipelothrix rhusiopathiae
CLINICAL INFECTIONS:
-Septicemia
- Endocarditis
- Erysipeloid – localized skin infection that resembles streptococcal erysipelas; self- limiting
