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PYR (positive), bacitracin susceptibility (sensitive), and SXT susceptibility (resistant) tests, and immunoassay to detect group A antigen.
Three tests that could be performed to aid in the identification of Streptococcus pyogenes.
Group B Streptococci
A β-hemolytic, catalase-negative, gram-positive coccus is found to be resistant to bacitracin and sulfamethoxazole.
Staphylococcus aureus
The Christie, Atkins, and Munch-Petersen (CAMP) test is based on enhanced hemolysis between CAMP factor and β-lysin from
Bile esculin-positive and (6.5%) Salt tolerant
A nonhemolytic, catalase-negative, gram-positive coccus is pyrrolidonyl α-naphthylamide (PYR)-positive. You should also expect the isolate to be:
α-Hemolytic streptococci
The optochin test is most valuable in the identification of:
Penicillin or Erythromycin if Px is allergic to Penicillin.
What antimicrobial agent or agents are most commonly used to treat infections caused by pyogenic streptococci?
Necrotizing fasciitis and Streptococcal toxic shock syndrome.
Streptococcus pyogenes has been associated with what invasive infections?
Streptococcus pneumoniae
Which streptococcal species is the most common cause of community-acquired bacterial pneumonia?
Cause of morbidity and mortality in neonates.
What is the clinical significance of group B streptococci isolated from a vaginal culture of a pregnant woman?
Agar needs to be supplemented with pyridoxal.
How would you recover nutritionally variant streptococci from clinical samples such as blood?
Nonmotile
An isolate with the appropriate colony and microscopic morphology may be suspected to be Bacillus anthracis if it is
Bacillus cereus
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 catalase-positive, and was motile. The most likely organism is
Food Poisoning
Bacillus cereus is most noted for causing?
Injectional, Inhalation, Gastrointestinal, Cutaneous
Forms of infection that are caused by Bacillus anthracis.
Protective antigen
The functionality of lethal factor requires the presence of what other protein from Bacillus anthracis to form an active toxin?
vegetative cells are red, and the spores stain green
the appearance of spore-forming bacteria seen with the spore stain.
Pleomorphic, gram-positive, club-shaped bacilli that appear in palisades or in “V” and “L” formations
Corynebacterium species often appear as ______________ on Gram staining.
Perform an Elek test to determine whether the organism produces exotoxin.
The biochemical tests performed on a gram-positive bacillus were consistent with Corynebacterium diphtheriae. As a definitive test, the laboratory scientist should now:
Of routine use of an effective human vaccine
Diphtheria is uncommon in the United States because
Insertion of hardware or prosthetic devices
True infections with nondiphtheria Corynebacterium spp., such as C. jeikeium or C. striatum, are often in immunocompromised patients or patients who have had
Urease; C. urealyticum
A(n) _________ test can help to differentiate which clinically significant Corynebacterium spp. recovered from urine samples?
Listeria monocytogenes
A newborn female becomes febrile and will not feed for about an hour after birth. A gram-positive rod is recovered from blood cultures from the newborn. The isolate has the characteristics listed below:
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
Erysipelothrix rhusiopathiae
A commercial fisherman with red sores on his hands was seen by his physician. Biopsy and culture of one of the lesions grew an organism with the characteristics listed below:
What is the most likely identification?
Nonhemolytic on SBA
Gram-positive bacilli, no spores observed
Catalase negative
Hydrogen sulfide production positive
Growth in gelatin resembled a test-tube brush
Actinomycotic; Nocardia brasiliensis
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 ____________.
Arcanobacterium haemolyticum
A 17-year-old male presented to an emergency department with a history of multiple episodes of febrile pharyngitis followed in 10 to 14 days by extensive desquamation of his hands and feet. The reoccurrences have followed several courses of antimicrobial 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 is submitted to a reference laboratory, and the results listed below are observe: The patient was subsequently treated with erythromycin, and he recovered. What was the etiologic agent?
SBA: small, slightly hemolytic colony which at 48 hours is a dark spot sunken in the agar
Catalase negative
Nitrate negative
Reverse CAMP test positive
HBT agar
A sample from a female patient suspected to have bacterial vaginosis is sent to the laboratory. Which of the following would be an appropriate medium for this specimen?
Tropheryma whipplei
A 57-year-old man from New York City presents to the emergency department with diarrhea, arthralgia, abdominal pain, malabsorption, and weight loss of 10 lb (4.5 kg) over the last month. A duodenal biopsy is performed, but no infectious agent is recovered on culture media. However, on Gram staining, a gram-positive rod is observed in macrophages in the biopsy tissue. The organism is identified by 16S rRNA gene sequencing. What is the most likely identity of this organism?
Oxidase-positive, gram-negative diplococci
Most Neisseria species are
Pili
The virulence factor of the pathogenic Neisseria spp. that is responsible for the initial attachment of the organism to host tissues.
Pelvic inflammatory disease, Ectopic pregnancy, Fitz-Hugh–Curtis syndrome
Asymptomatic gonococcal infections in women may result in
Urethral swab
The optimal specimen to collect for the diagnosis of gonorrhea by culture in male patients.
Can accurately detect urethritis in males
Direct Gram stain for the diagnosis of gonorrhea
Modified Thayer-Martin (MTM)
A selective medium that allows the isolation of N. gonorrhoeae and N. meningitidis
Carbohydrate utilization
The test that can be used for definitive identification of both N. gonorrhoeae and N. meningitidis.
Are sensitive and do not require invasive specimens
The advantage of nucleic acid amplification tests for diagnosing gonorrhea is that the tests
Ceftriaxone & Azithromycin
What are the current recommendations for treatment of genital gonorrhea?
Lower respiratory tract infections
Moraxella catarrhalis is not often associated with:
Meningococcemia, meningitis, and Waterhouse-Friderichsen syndrome
Entrance of N. meningitidis into the bloodstream may lead to
ONPG
The test that can accurately differentiate N. lactamica from N. meningitidis is:
M. catarrhalis
Which organism is an opportunistic pathogen associated with otitis media and sinusitis in children?
N. gonorrhoeae
Erythromycin eye drops are placed into the eyes of newborns to prevent infections caused by
Negative; cannot; negative
The porphyrin test for H. influenzae would be __________ because the organism __________ biosynthesize heme. The fluorescence result of the test would be __________.
None of the above
Infections caused by β-lactamase–positive H. influenzae should be treated with which of the following?
K. denitrificans
A cervical culture for possible gonococcal infection is sent to the microbiology laboratory. After 24 hours of incubation, the modified Thayer-Martin (MTM) plate has small opaque colonies that adhere slightly to the medium. Microscopic examination reveals gram-negative coccobacilli, many with square ends. The organism ferments glucose and is superoxol and catalase negative. The most likely identification is:
Capnocytophaga spp.
A 52-year-old man who had recently received a kidney transplant was admitted to the hospital with a low-grade fever, a heart murmur, and neutropenia. He had a history of periodontal disease and recently had had two teeth extracted. Blood cultures were positive after 48 hours. The isolate grew on chocolate (CHOC) agar and sheep blood agar (SBA) in 5% CO2. The colonies were nonhemolytic, slightly adhered to the surface of the media, and had a slight yellow appearance when removed. The isolate was catalase, indole, and oxidase-negative. Microscopic morphology indicated gram-negative fusiform bacilli. The most probable identification is:
Urine
Besides respiratory tract specimens, what clinical specimen is useful for the sensitive detection of Legionella antigen?
Buffered charcoal yeast extract (BCYE) agar
What is the culture medium of choice for the recovery of Legionella spp.?
Erythromycin
The antimicrobial agent of choice for the treatment of pertussis is:
Dogs
B. bronchiseptica is considered normal oral biota in
Group D Shigella
S. sonnei
Group C Shigella
S. boydii
Group A shigella
S. dysenteriae
Group B Shigella
S. flexneri
Positive phenylalanine deaminase
Which of the following test results is most helpful in categorizing an isolate as a member of the tribe Proteeae?
Fleas
The causative agent of plague is most often transmitted to humans by:
ETEC
A 47-year-old patient who had just returned from Mexico was admitted to the hospital with a 3-day history of vomiting and diarrhea, without fever, and no fecal leukocytes were found in the stool. When he was admitted to the hospital, a stool culture grew an organism identified as Escherichia coli. Which of the following strains is the most likely cause of the infection?
Escherichia coli
A gram-negative, oxidase-negative coccobacillus was isolated from the cerebrospinal fluid of an infant in the newborn nursery. The organism produced dark pink colonies on MAC agar and had the following biochemical results: triple sugar iron, acid over acid with gas; phenylalanine deaminase-negative; sulfide-indole-motility agar, H2S-negative, indole-positive, and motile; urease-negative; and citrate-negative. The most probable identity of this organism is:
Klebsiella pneumoniae
What organism is often associated with lobar pneumonia in elderly hospitalized patients?
Escherichia coli
The most common cause of community-acquired UTIs is:
Proteus mirabilis
Which organism is an opportunistic pathogen that causes wound and urinary tract infections and may cause the production of kidney stones?
Shigella spp.
An enteric organism that is acquired by eating improperly prepared and cooked or preserved food contaminated with human feces and produces dysentery is:
Vibrio cholerae
A gram-negative bacillus isolated from a stool specimen produces clear colonies on MacConkey agar and yellow colonies on thiosulfate citrate bile salt sucrose medium. The isolate is subcultured to a sheep blood agar plate with an O/129 disk. The isolate is sensitive to O/129 and is oxidase-positive. You should suspect:
V. vulnificus
Which of the following Vibrio spp. would you expect to be most likely isolated from a blood culture?
Helicobacter
Which of the following genera is typically microaerophilic?
Gastroenteritis
Campylobacter jejuni is most noted for causing:
Fishing or swimming in ocean water
Which of the following is a risk factor for acquiring V. alginolyticus infection?
Aeromonas hydrophila
An oxidase-positive, indole-positive, β-hemolytic, gram-negative bacillus resistant to O/129, cannot grow in 6% NaCl broth, and is Voges-Proskauer positive is isolated from an adult stool culture. You should suspect:
Campylobacter
Darting motility is a characteristic of:
Hippurate hydrolysis
Which of the following tests is most helpful in differentiating C. jejuni from the other Campylobacter spp.?
Clostridium perfringens
Cause of Myonecrosis
Clostridium tetani
Cause of Tetanus
Clostridium botulinum
Cause of Botulism
Clostridioides difficile
Cause of Pseudomembranous colitis
Actinomyces spp
Cause of Actinomycosis
Aerotolerant anaerobe
An organism that can live in reduced concentrations of oxygen but prefers an anaerobic environment is known as a(n):
Superoxide dismutase
Some anaerobes are particularly susceptible to oxygen because they lack the enzyme:
Eubacterium
Endogenous anaerobes least likely to be involved in cases of bacteremia are:
Urethral swab
Which of the following specimens would be unacceptable for anaerobic culture?
Clostridium perfringens
A gram-positive bacillus was isolated from a wound specimen and had the following characteristics: double zone of β-hemolysis, lecithinase positive, lipase negative, spot indole negative. What is the most likely identification of this organism?
Fusobacterium necrophorum
An anaerobic, pleomorphic, gram-negative bacillus was recovered from a liver abscess. The special potency antimicrobial disks demonstrated that the organism was vancomycin resistant and colistin and kanamycin sensitive. Other results were as follows: chartreuse fluorescence, spot indole positive, and lipase positive. What is the most likely identification of the organism?
Auramine-rhodamine
Which of the following is (are) fluorescent stain(s) used in the detection of the mycobacteria?
M. tuberculosis
A nonpigmented mycobacterium is isolated that reduces nitrate to nitrite and is niacin positive. You should suspect:
None of the above
The causative agent of Hansen disease:
Detects a cell-mediated immune response to mycobacterial antigens
The skin test for tuberculosis:
Note
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