BLOOD AND BONE MARROW
A cancer patient was admitted to the hospital with fever, tachycardia, and a drop in blood pressure. Due to the patient being treated for cancer, her chemotherapy had been administrated through an intravenous catheter. To rule out a catheter-related infection, the physician ordered two sets of blood cultures with one set being collected from the catheter site and the second set being collected by venipuncture. After 48 hours, the patient had positive blood cultures that grew Staphylococcus epidermidis. How will the physician know if the Staphylococcus epidermidis present is due to an infected catheter or is a contaminant?
Both blood culture sets (catheter and venipuncture) will be positive
The Gram stain shown in the image was prepared from a positive anaerobic blood culture bottle after 36 hours incubation. Based on the morphology of the bacterial cells (some with spores, noted by the blue arrows), what is the most likely identification?
Clostridium septicum
If a Brucella species is suspected in a blood culture, it should be held for a maximum of how many days on a commercial blood culture system?
10-14
A mucoid alpha hemolytic translucent colony suspected of being Streptococcus pneumoniae was isolated from a blood culture. All of the of the following are appropriate tests to make a presumptive or definitive identification of this organism EXCEPT?
Bacitracin susceptibility
Which of the following is MOST often determined to be the cause of sepsis?
Bacteria
A 40-year-old man with a prosthetic valve developed intermittent bouts of low grade fever. A changing cardiac murmur suggested the possibility of endocarditis; however, repeat blood cultures over a two week period were all negative. Bacteria resembling those seen in the lower image were finally seen in Gram stain of a positive bottle. Colonies were recovered when broth was subcultured to a blood agar plate with a staph streak, as shown in the upper image. What is the most likely bacterial species?
Abiotrophia defectiva
A budding yeast with pseudohyphae and clusters of gram positive staphylococci were observed in a Gram stain smear prepared from a positive blood culture. What is the MOST likely source of the infection?
An indwelling catheter
Which of the following instrument-based systems are considered a continuous monitoring system?
BACTEC
A laboratory recently purchased a continuous monitoring system for blood culture analysis. The system is able to detect CO2 production by growing organisms and as a result will produce a color change in the sensor located at the bottom of the blood culture bottle. The instrument will detect this color change and alert the staff that a blood culture is positive for bacterial growth. Which of the following instruments uses this methodology?
BacT/ALERT
The colonies seen growing on the surface of the blood agar plate shown in the upper photograph were recovered from a blood culture after 36 hours of aerobic incubation at 35° C. A Gram stain prepared from one of the colonies is shown in the lower photomicrograph. The most likely identification is:
Bacillus circulans
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
Which one of the following pathogenic anaerobic bacteria is MOST frequently isolated in clinical laboratories?
Bacteroides fragilis
Since Brucella species are facultative intracellular organisms that infect the reticuloendothelial system, specimens of choice for recovery include:
Blood and bone marrow
What is the one principle that is conserved between all continuous monitoring blood culture systems?
CO2 detection
A technologist subcultures a positive blood culture and notes the following characteristics on the isolated colonies displayed in the image below: Growth of non-hemolytic colonies with a ground-glass appearance, displaying a "Medusa Head", as indicated by the arrows Gram stain reveals a large, gram-positive rod with central and subterminal spores that do NOT swell the cells Catalase positive Non-motile What would be the MOST likely conclusion and action?
Cannot rule out Bacillus anthracis, refer isolate to your Laboratory Response Network (LRN) Reference Laboratory
An anaerobe was recovered from a blood culture after 92 hours incubation. A gram stain of the isolate is illustrated in the photomicrograph. The most likely identification is:
Cutibacterium (Propionibacterium) acnes
The Carba NP confirmatory test is used to detect all of the following carbapenemases EXCEPT?
ESBL (Extended Spectrum Beta-Lactamase)
A microbiology laboratory recently purchased a rapid identification instrument that uses a laser on the microorganisms, which produces an ion cloud. These ions are then separated in a tube and travel within the tube to a detector. The time of travel will be measured and a mass spectrum will be produced. Which of the following techniques uses this methodology?
MALDI-TOF
The upper image is a photomicrograph of a Gram stain prepared from a positive blood culture obtained from a 68 year old female with an indwelling urinary bladder catheter. Smooth, gray, faintly beta hemolytic colonies were recovered in subcultures of the positive bottle. The tubes shown in the lower photograph are: an esculin slant (left) displaying intense brown coloration a 6.5% sodium chloride broth (right) showing cloudy growth The most likely identification is:
Enterococcus faecalis
Which of the following instruments is used for continuous monitoring of mycobacterial growth?
MGIT 960
What is the methodology used for detecting the presence of bacteria in blood samples that are loaded onto a BACTEC analyzer?
Fluorescent change
An autopsy of a 1-year-old female admitted to the emergency room 4 hours prior to her death revealed Waterhouse-Friderichsen syndrome. Blood and nasopharyngeal cultures taken prior to her death should reveal an oxidase-positive, Gram-negative diplococcus with the following biochemical reactions:
Glucose positive, Maltose positive, Lactose negative and Sucrose negative
All of the following organisms have been linked to cause endocarditis EXCEPT?
Hemophilus influenzae
Which one of the following organisms can be isolated from bone marrow specimens?
Histoplasma capsulatum
Blood culture bottles used in continuous monitoring systems, such as the BacTec, uses resins or charcoal to do which of the following?
Inactivates and absorbs out antimicrobial agents
The purpose of the additive SPS (sodium polyanethol sulfonate) that is in continuous monitoring system blood culture bottles, is all of the following EXCEPT?
Inactivates and absorbs out antimicrobial agents
The bacterial species shown on the blood agar plate illustrated in the photograph was recovered from a blood culture of a patient with fever. The most likely source of infection is which of the following?
Indwelling catheter
The condition most likely to predispose a person to septicemia by viridans streptococci is:
Poor oral hygiene
The most common organism that causes septic arthritis in patients under 30 years of age is:
Neisseria gonorrhoeae
The bacterial species shown in this composite photograph of a chocolate agar plate and accompanying gram stain, recovered from an autopsy blood culture of a patient dying with Waterhouse Friderichsen syndrome is most likely:
Neisseria meningitidis
Which of the following is a rapid latex agglutination method for detecting Methicillin-Resistant Staphylococcus aureus (MRSA)?
PBP2a
What virulence factor is not inherent to bacterium?
Production of opsonins
A patient had a transfusion reaction to red blood cells and the remains from the unit of blood were sent to the microbiology laboratory for culture. The organism that grew was a gram-negative bacilli that was catalase and oxidase positive and was negative for gelatin hydrolysis. The organism was inoculated on a Pseudo F agar slant and incubated for 24 hours. Fluorescence was observed when using a UV light as seen in the image. This organism is most likely:
Pseudomonas putida
Abiotrophia defectiva (formerly Streptococcus defectivus) and Granulicatella adiacens (formerly S. adjacens, then A. adiacens) are the names currently given to two species of what were previously called nutritionally variant streptococci (NVS). What supplement must be added to blood culture medium to recover these organisms in cases of "culture negative endocarditis?"
Pyridoxyl
History records an outbreak with the sudden onset of high fever, headache, and abdominal pain among 93 persons who had attended a public church dinner the week before. The photograph of an XLD agar plate is representative of the organism that may have been recovered from blood cultures from any one of these 93 persons. The most likely identification is:
Salmonella serotype Typhi
Which of the following is characterized by hypotension due to systemic infection that does not respond to fluid resuscitation (an attempt to replenish body fluid)?
Septic shock
A patient is showing signs of an intravenous catheter associated infection. The physician has removed the catheter and sent the catheter tip along with a skin swab of the catheter site to the laboratory for testing. The physician ordered a Gram stain of the skin entry site and a culture of the catheter tip. On which of the following media should the catheter tip be plated?
Sheep Blood Agar and Thioglycollate Broth
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
A Staphylococcus species recovered from a blood culture was found to produce acid from sucrose and maltose and showed alkaline phosphatase activity. The Staphylococcus was also coagulase negative. The same organism was also found in a culture from the central line tip. The most likely identification is:
Staphylococcus epidermidis
Which of the following is the most common etiologic agent identified in prosthetic valve endocarditis?
Staphylococcus epidermidis
A D-test is performed to determine if Staphylococcus aureus or Streptococcus agalactiae has an inducible resistance to clindamycin. This inducible resistance is due to which of the following mechanisms?
erm gene
All of the following statements about blood cultures are correct EXCEPT?
If two separate sets (two bottles each set) of blood cultures are requested, draw them both from the same site at the same time.
The colonies growing on the surface of a thiosulfate citrate bile sucrose (TCBS) agar plate (the green color indicates lack of sucrose fermentation) were identified as Vibrio vulnificus. The serious complication of infections with this bacterial species is:
Life-threatening septicemia
A 30-year-old Hispanic pregnant female developed fever and signs and symptoms of meningitis following ingestion of cheese sent by relatives in Mexico. The colonies recovered from a positive blood culture is shown in the upper photograph; the microscopic features in the lower photograph. The most likely identification is:
Listeria monocytogenes
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
Infections of the bone marrow are not only caused by bacteria and fungi, they can be caused by viruses as well. Which of the following viruses can often be isolated from bone marrow specimens?
Parvovirus B19
Observe the Optochin "P" disc reaction Illustrated in the upper left photograph on the surface of blood agar. Heavy growth of tiny, alpha hemolytic colonies are observed growing on the agar surface that extend to the outer margins of the paper disc. The Gram stain presented in the lower photomicrograph reveals small Gram positive cocci lying singly, in small clusters, and more typically in long chains. This isolate has been recovered from blood cultures in cases of post-valvular endocarditis. Select the presumptive identification of this isolate.
Streptococcus viridans
Organisms such as coagulase-negative Staphylococcus, Corynebacterium, and alpha streptococcus species are all found on the skin and represent normal skin flora. All of the following are functions of normal skin flora EXCEPT?
They aid in the transmission of nosocomial infections
Brucella suis and Salmonella typhi can commonly infect the spleen, liver, and bone marrow. Which of the following reasons allow these two organisms to cause a systemic infection?
They are both ingested by monocytes and/or macrophages within the spleen, liver, and bone marrow
Which of the following is considered a normal skin flora organism?
Bacillus subtilis
The small, slowly growing gray-white colonies seen on the blood agar plate were recovered from a blood culture of a 40-year-old farm worker who developed fever and chills leading to septicemia, following ingestion of contaminated milk. The Gram stain of this organism is seen in the lower image revealing small gram-negative coccobacilli in loose clusters. Key to the identification of this blood culture isolate is the rapid urease reaction. From these observations, select from the choices the presumptive identification of this isolate.
Brucella species
A patient was admitted to the hospital for fever, chills, weight loss, headaches, and fatigue. The patient mentioned that he had cut his hand while hunting wild boar a couple of weeks ago. Blood cultures were received in the microbiology laboratory and several days later a bone marrow specimen on the patient was received. The blood culture was positive after 5 days and the bone marrow grew a small, convex, smooth colony after 48 hours on sheep blood and chocolate agar. A gram stain was performed and demonstrated small Gram negative coccobacilli organisms. Which of the following organisms is the cause of infection for this patient?
Brucella suis
The flat, spreading gray-white colonies with an outer zone of beta hemolysis as observed on the surface of an anaerobic blood agar plate shown in the upper image were recovered from a blood culture of an elderly man leading to a potential diagnosis of cancer of the colon. Observed in the gram stain are short gram-positive bacilli, some with distinctive central and sub-terminal spores. From these observations, select the most likely isolate.
Clostridium septicum
This non-hemolytic organism was isolated from the blood culture of a patient. The image shows the organism's reactions in 6.5% NaCl broth and on bile esculin agar. With further testing, this isolate will most likely be identified as:
Enterococcus spp.
Observed on the surface of blood agar are smooth, white, 48-hour-old colonies incubated at 37oC, demonstrating a positive catalase reaction and a negative coagulase reaction. The sample was taken from an intravenous catheter. In the photomicrograph are gram positive cocci distinctly arranged in loose clusters and in tetrad formation. From these observations, select the presumptive identification of this isolate.
Staphylococcus epidermidis
