Media Lab Microbiology
Which of the following statements is correct regarding the glutamate dehydrogenase (GDH) assay for Clostridioides difficile? The GDH test can differentiate toxin-producing strains of C. difficile from nontoxigenic strains. The GDH assay is a valuable confirmatory test for C. difficile. Detection of the GDH gene and 16srRNA genes for C. difficile without the presence of a toxin gene indicates a carrier or nonpathogenic state. GDH assays can be used as stand-alone assays.
Detection of the GDH gene and 16srRNA genes for C. difficile without the presence of a toxin gene indicates a carrier or nonpathogenic state.
The recommended temperature/time/pressure for routine steam sterilization of media is: The correct answer is highlighted below 121° C for 8-10 minutes @ 10 psi 121° C for 12-15 minutes @ 15 psi 220° C for 8-10 minutes @ 10 psi 220° C for 12-15 minutes @ 15 psi
121° C for 12-15 minutes @ 15 psi Sterilization of media occurs when it is autoclaved with high-pressure steam. The recommended temperature, time, and pressure of steam sterilization for media is 121° C for 12-15 minutes @ 15 psi. Sterilization of media is required so contaminating organisms from the water or powder used to prepare the media do not grow while trying to recover bacteria from the patient's specimen. Once the sterilization process is complete, the agar is allowed to cool slightly then poured into sterile petri plates. The agar is then allowed to further cool and solidify.
Which of the following serological tests would be used for the diagnosis of Q-fever? Weil-Felix test Quellung test EIA or indirect immunoflourescence Cold agglutinin test
EIA or indirect immunoflourescence Discussion: reference method due to its high specificity and sensitivity in both acute and chronic infections. It is also reliable, cost-effective, and easy to perform. The Weil-Felix test detects cross-reacting rickettsia antibodies by using Proteus vulgaris. The Quellung test utilizes antibodies to bind to the bacterial capsule, which can be used to identify serotypes of Streptococcus pneumoniae. Cold agglutinins are autoantibodies that cross-react with red blood cells (RBCs). They cause RBCs to clump together when the person is exposed to cold temperatures and increases the chances of those RBCs getting destroyed.
All of the following Mycobacterium species produce pigments, EXCEPT? Mycobacterium scrofulaceum Mycobacterium marinum Mycobacterium kansasii Mycobacterium fortuitum group
Mycobacterium fortuitum group
Immunosuppressed or diabetic patients with ketoacidosis may present with symptoms of a brain abscess caused by which of the following? Metabolic acidosis Phycomycosis Hyperglycemia Metabolic alkalosis
Phycomycosis Discussion: Phycomycosis is the correct answer because immunosuppressed or diabetic patients in ketoacidosis may develop a rapidly progressive fungal infection (phycomycosis) of the sinuses that migrates up to the brain. Phycomycosis is also known as Mucormycosis an infection caused by the species Mucor or Rhizopus. A patient that is immunocompromised does not have the full capability of the immune system to help fight off infections and a patient who is in diabetic ketoacidosis has an increased amount of glucose in their system that serves as a food source for invasive organisms. Both causes contribute to a favorable environment for organism growth.
You are processing a Level 1 specimen for culture when two other specimens arrive for processing. The two specimens are: Sputum for sputum culture Urine in a boric acid transport tube for urine culture How would you handle the processing of these two new specimens? Stop processing the Level 1 specimen and process the sputum culture Place the sputum culture in the refrigerator, leave the urine at room temperature, and continue processing the Level 1 specimen Leave the sputum and urine specimens at room temperature and continue processing the Level 1 specimen Stop processing the Level 1 specimen and process the urine culture
Place the sputum culture in the refrigerator, leave the urine at room temperature, and continue processing the Level 1 specimen Discussion: Level 1 specimens in the laboratory are related to life-threatening illnesses and should be processed before other specimens. Urine specimens that are preserved (boric acid) are considered a Level 4 specimen. Since the specimen is preserved, it is stable for 24 hours and should be set up last in priority. Sputum specimens are considered a Level 2 specimen because there is no preservative and degradation of the sample or overgrowth of normal flora contaminants can occur. Since the two specimens that arrived are at lower priority levels, they should be stored appropriately to eliminate the possibility of specimen degradation of organism overgrowth. The urine is preserved in boric acid, which makes the specimen stable at room temperature for 24 hours. The sputum specimen is unpreserved and must be refrigerated in order to prevent organism overgrowth until processing can occur. The sputum specimen is a Level 2 priority, thus the Level 1 specimen would still have top priority and processing should not be stopped. Since the urine is preserved, that specimen can be left at room temperature. However, leaving the sputum at room temperature can cause the overgrowth of normal flora organisms to occur. The urine specimens, since preserved, are a Level 4 priority, and thus, the Level 1 specimen processing should not be discontinued.
The ability of streptococci to spread within the tissues and cause rapidly advancing cellulitis is due to the production of several virulence factors. Each of the following correctly describes the effects of the specific virulence factor EXCEPT: Streptokinase causes the hydrolysis of fibrin clots. Streptolysin O is toxic to many cell types, including neutrophils and monocytes. Streptolysin S is associated with the rash of scarlet fever and the pathogenesis of the streptococcal toxic shock-like syndrome. Hyaluronidase depolymerizes the ground substance in connective tissue.
Streptolysin S is associated with the rash of scarlet fever and the pathogenesis of the streptococcal toxic shock-like syndrome. Discussion: Streptococcal pyrogenic exotoxins (SPEs) and not Streptolysin S are associated with the rash of scarlet fever and the pathogenesis of the streptococcal toxic shock-like syndrome. Streptolysin S is toxic to a variety of cell types, including erythrocytes. The "spreading factors" produced by streptococci include streptokinase which hydrolyzes any clots that may hinder spreading and may, thus, prevent the formation of fibrin barriers. Streptolysin O is toxic to many cell types, including neutrophils and mononuclear phagocytes, allowing the uninhibited proliferation of the bacterial cells. Another spreading factor is hyaluronidase, which depolymerizes the ground substance of the connective tissue removing any barriers to the spread of the bacterial cells.
A urine culture contains the following organisms: Proteus mirabilis: 2,000 CFU/mL Klebsiella pneumoniae: 10,000 CFU/mL In which of the following urine sources would both organisms be worked up with a full sensitivity? Catheterized urine Midstream clean catch urine Nephrostomy Suprapubic aspiration
Suprapubic aspiration
A 6-year-old girl was seen in the emergency department with pain and tenderness in her lower right quadrant. A CBC showed a high white blood cell count with increased segmented neutrophils and bands. The child was admitted to surgery with a diagnosis of appendicitis. During surgery, the appendix appeared normal, but an enlarged node was removed and cultured. A diagnosis of mesenteric lymphadenitis was made. Gram-negative rods were isolated. Which of the following biochemical results are most likely produced by the suspect organism? The correct answer is highlighted below Triple sugar iron agar (TSIA) acid over acid, H2S negative, lysine positive, indole positive, urea negative TSIA acid over acid, H2S negative, lysine negative, indole variable, urea positive TSIA alkaline over acid, H2S positive, lysine negative, indole negative, urea variable TSIA acid over acid, H2S positive, lysine positive, indole variable, urea negative
TSIA acid over acid, H2S negative, lysine negative, indole variable, urea positive Discussion: The correct answer is TSIA acid over acid, H2S negative, lysine negative, indole variable, urea positive. This case is typical of Yersinia enterocolitica and the biochemical reactions listed are consistent for this organism. Y. enterocolitica generally presents as severe lower abdominal pain mimicking appendicitis, but infects the mesenteric lymph nodes and may infect the appendix and ileum. TSIA acid over acid, H2S negative, lysine positive, indole positive, urea negative is typical of Escherichia coli. TSIA alkaline over acid, H2S positive, lysine negative, indole negative, urea variable, as well as TSIA acid over acid, H2S positive, lysine positive, indole variable, urea negative are both H2S positive, which is not descriptive of Y. enterocoliti
