BOC Microbiology
acid fast staining
-Carbol fuchsin is taken up by bacteria with mycolic acid (carbohydrates with two long tails) in the cell wall
A flexible calcium alginate nasopharyngeal swab is the collection device of choice for recovery of which organism from the nasopharynx?
C. diphtheriae must be recovered from the deep layers of the pseudomembrane that forms in the nasopharyngeal area. A flexible calcium alginate nasopharyngeal swab is the best choice for collecting a specimen from the posterior nares and pharynx.
Which of the following tumor markers is associated with the colon?
CEA, or Carcinoembryonic Antigen = Colon PSA, or prostate specific antigen = Prostate beta hCG, or Human chorionic gonadotropin = Testicles AFP, or Alpha-fetoprotein = Liver
Acid fast organisms
Contain wax-like, almost impermeable cell wall, which contain mycelia acid and large amount of fatty acids, waxes and complex lipids. Highly resistant to disinfectants and dry conditions. Mycobacterium tuberculosis Mycobacterium leprae and Nocardia
Cryptosporiosis
Diarrheal disease caused by parasites called cryptosporidia. They enter your body and infect your GI tract. Symptoms: Diarrhea, weight loss, dehydration, stomach cramps, fever, vomiting You can help prevent a cryptosporidium infection by practicing good hygiene and avoiding swallowing water from pools, recreational water parks, lakes and streams.
All of the following serological test results may occur in a patient experiencing a hemolytic transfusion reaction due to the presence of a clinically significant Rh antibody such as anti-c EXCEPT:
Generally, Rh antibodies do not bind complement due to the positioning of Rh antigens on the RBC surface. Rh antigens do not sit close enough to allow for Rh (IgG class) antibodies to attach. Therefore, complement-mediated intravascular hemolysis does not occur. Serological testing for Rh antibody-mediated hemolytic transfusion reactions includes optimal reactivity at 37°C and a positive DAT result due to Rh antibodies belonging primarily to the IgG class. IgG antibodies are capable of crossing the placenta and coating fetal RBCs. Additionally, Rh antibodies demonstrate dosage and may show stronger reactivity with known cells possessing a double-dose of a corresponding Rh antigen (homozygous expression).
A deficiency of platelet receptor IIb/IIIa can be found in which of the following?
Glanzmann Thrombasthenia is an inherited disorder in which the platelets are missing the receptor IIb/IIIa which is responsible for binding fibrinogen for platelet aggregation.
In which developmental stage do red blood cells begin forming hemoglobin in amounts large enough to be visualized on a Wright-stained bone marrow aspirate smear?
Hemoglobin synthesis is detectable in the basophilic normoblast, but the formation of large amounts of hemoglobin begins in the polychromatic (polychromatophilic) normoblast. On a Wright-stained bone marrow aspirate smear, the cytoplasm of the polychromatic normoblast is murky gray-blue, which is due to a mixture of pink (from hemoglobin) and blue (from RNA). The cytoplasm of the basophilic normoblast is a deep, rich blue; any amount of hemoglobin produced during this stage is masked by the presence of large amounts of ribosomes and RNA.
After birth, which of the following is the biggest concern for a newborn infant suffering from hemolytic disease of the fetus and newborn?
Hemolytic disease of the fetus and newborn leads to the destruction of fetal red blood cells cause by a maternal antibody (IgG) that is able to cross the placenta. During pregnancy the indirect bilirubin (indirect because indirect methods are needed for measuring) that is released from the red cell destruction is able to cross the placental where it is conjugated by the maternal liver and excreted by the mother. After birth the buildup of bilirubin becomes a major problem for the baby because the baby's liver is unable to conjugate the indirect bilirubin efficiently (and the maternal liver is no longer there) and therefore the bilirubin is not excreted. The indirect bilirubin can reach toxic levels (usually greater than 18-20 mg/dL) and cause damage to the infant's brain. If this is not treated permanent damage can occur (termed kernicterus).
The aseptic collection of blood cultures requires that the skin be cleansed with:
In order to attain asepsis of the skin, 70% alcohol followed by 2% iodine is used for obtaining blood cultures.
Which hemoglobin, when elevated, acts as a protection against sickling in patients with HbS?
Increased levels of HbF interfere with the polymerization of HbS, therefore inhibiting sickling of red blood cells and increasing red blood cell survival time.
What is the purpose of adding 0.025%-0.050% sodium polyanetholsulfonate (SPS) to nutrient broth media for the collection of blood cultures?
SPS is used in most commercial blood culture products because it functions as an anticoagulant and prevents phagocytosis and complement activation. In addition, SPS neutralizes aminoglycoside antibiotics. Addition of SPS may inhibit some Neisseria and Peptostreptococcus, but this can be reversed with 1.2% gelatin.
Which of the following statements are true about anti-H?
The H antigen is the precursor for A and B antigens on red blood cells. Transferases add immunodominant sugars to H precursors converting them to A or B antigens. The levels of H vary based on the ABO grouping of an individual due to differences in transferase concentration. The following is the relative amount of H present on the red blood cells based on ABO grouping: O>A2>B>A2B>A1>A1B (O has the most H and A1B has the least) Based of the above relative concentrations the correct answer is that anti-H reacts more strongly with group A2 cells than group A1 cells since A2 cells have more of the H antigen. Group O cells have the highest amount of H so anti-H would react and it would react stronger with the O cells when compared to A1 (due to more H on group O). Lastly, anti-H would react with A cells. A2 cells have the second highest relative concentration of H and would therefore react strongly with anti-H.
Modified acid fast stain
This technique is useful for the identification of oocysts of the coccidian species (Cryptosporidium, Cystoisospora, and Cyclospora), which may be difficult to detect with routine stains such as trichrome. Unlike the Ziehl-Neelsen Modified Acid-Fast Stain, this stain does not require the heating of reagents for staining. Specimen: Concentrated sediment of fresh or formalin-preserved stool may be used. Other types of clinical specimens such as duodenal fluid, bile, pulmonary samples (induced sputum, bronchial wash, biopsies) may also be stained. Reagents: There are four steps to this procedure requiring the following solutions: Absolute Methanol Acid Alcohol: 10 ml Sulfuric Acid + 90 ml Absolute ethanol. Store at room temperature. Kinyoun's Carbol fuchsin: may be purchased commercially. 3% Malachite green: dissolve 3 g of malachite green in 100 ml of distilled water. Store at room temperature. Procedure: Prepare a smear with 1 to 2 drops of specimen on the slide and dry on a slide warmer at 60°C until dry. Do not make the smears too thick! Fix with absolute methanol for 30 seconds. Stain with Kinyoun's carbol fuchsin for one minute. Rinse briefly with distilled water and drain. Destain with acid alcohol for 2 minutes. Rinse with distilled water and drain. Counterstain with Malachite green for 2 minutes. Rinse briefly with distilled water and drain. Dry on a slide warmer at 60°C for about 5 minutes. Mount with a coverslip using desired mounting media. Examine 200 to 300 fields using 40× or higher objectives. To confirm internal morphology, use 100× oil immersion objective. Quality Control: A control slide of Cryptosporidium spp. from a 10% formalin preserved specimen should be included with each staining run. Cryptosporidium spp. stains a pinkish-red color. The background should stain uniformly green.
Which of the following best describes the benefits of the RPR or VDRL tests:
While the RPR and VDRL tests are often the first screening test used to detect syphilis, a definitive diagnosis of syphilis can only be made using a specific treponemal test such as EIAs for IgG and IgM antibodies, agglutination tests such as FTA-ABS, TP-PA, and MHA-TP, or a direct detection method of the organism. The RPR and VDRL detect nontreponemal antibody proteins called reagin that the body produces in response to infection with T. pallidum. Because reagin proteins are also detected in pregnancy, old age, Lupus, and other syndromes and disease states, the RPR and VDRL tests are very sensitive but not highly specific, and so a confirmatory test specifically for treponemal organisms or antibodies needs to be performed.
Kinyoun method
a cold acid fast stain
A patient who previously had a hs-CRP of 4 mg/L was put on a statin and daily aspirin medication. She returns to the laboratory a month later, and her repeat hs-CRP is 2.3 mg/L. Which of the following is the most likely reason for the decrease in the test value?
hs-CRP is a newer marker of chronic inflammation. This new test measures low levels of CRP, (hs-CRP) and can therefore be used to monitor the risk of cardiovascular disease. Levels of <1 mg/L, 1 to 3 mg/L, and >3mg/L correspond to low, moderate, and high risk for future cardiovascular events. The medications (a cholesterol-lowering statin and the anti-inflammatory aspirin) can lower hs-CRP. A single hs-CRP value does not necessarily reflect risk.
CYP450 enzymes
most important drug-metabolizing enzymes found in liver; specialized in inactivating foreign chemicals that have been ingested
The ketone component that is measured by the nitroprusside reaction is:
Acetoacetic acid reacts with sodium nitroprusside to produce a purple color.
Biosafety levels
BSL-1: Those not known to cause Bacillus subtilis, Mycobacterium Standard microbiological practices. disease in healthy adults gordonae, soil microbes No special equipment. BSL-2: Common human pathogens Those that pose high risk of life-threatening di ease. May be transmitted by aerosols. No vaccine or therapy E. coli, Salmonella, HIV, HBV, influenza PRECAUTIONS Biological safety cabinet (BSC) I or II. Personal protective equipment (PPE). Autoclave must be available. Limited access. Most micro labs fall in this category. BSL-3: biosafety cabinets to prevent airborne transmission BSL-4: sealed, negative pressure Exhaust air is filtered twice
Unconjugated bilirubin is conjugated in the liver with which of the following substances to become water-soluble?
Bilirubin is conjugated with glucuronic acid in the liver to become conjugated bilirubin, which is water-soluble. Conjugated bilirubin passes directly from the liver into the bile duct and then into the intestine where the bacteria reduce it into urobilinogen. Urobilinogen is then oxidized and excreted in the feces as stercobilinogen or urobilin. Conjugated bilirubin can be excreted in the urine only if the bile duct is obstructed (e.g., cancer or gallstones) or if the liver is damaged (hepatic jaundice).
The progression of the maturation of the neutrophil is:
Blast- Promyelocyte- Myelocyte- Metamyelocyte- Band neutrophil- Segmented Neutrophil
Bordet-Gengou plates are used to isolate:
Bordet-Gengou plates are used to isolate Bordetella pertussis. B. pertussis is a respiratory pathogen which lives within the epithelial cells of the respiratory tract. B. pertussis is the major causative agent of whooping cough. Bordet-Gengou plates are inoculated with a swab from a patient's posterior nasopharynx when a Bordetella bacterium is thought to be present. Colonies are small and shiny, resembling mercury drops. Colonies become whitish gray with age.
Which of the following statements is true regarding CYP450 enzymes?
CYP450s are able to make compounds more water-soluble and therefore enhance excretion. CYP450s are the primary, but not the only, hepatic enzymes involved in drug metabolism. There are many CYP450s (at least 18 with possible isoenzymes of each). CYP450s are found primarily in the liver. They accept a variety of substrates and so are able to metabolize diverse compounds. Each CYP450 can metabolize several different drugs, making the CYP450 family versatile and able to address the wide range of chemical substances encountered by an individual.
Spore forming bacteria
Certain bacteria have the ability to form protective spores to survive an inactive stage (harsh environment, temperature etc). Major genera: Bacillus and Clostridium
Which lipid does not serve as a source of fuel, but can be converted to steroid hormones?
Cholesterol is an unsaturated steroid alcohol. Cholesterol is unique in that, unlike other lipids, it is not readily catabolized by most cells, and therefore, does not serve as a source of fuel. A small amount of cholesterol can also be converted by some tissue, such as the adrenal gland, testis, and ovary to steroid hormones such as glucocorticoids, mineralocorticoids, and estrogens.
Which of the following tests would be most useful in the identification of Streptococcus pneumoniae?
Optochin contains ethyl hydrocupreine hydrochloride, a compound useful in the differentiation of the alpha hemolytic streptococci, which include Streptococcus pneumoniae, the viridans streptococcus, and the alpha hemolytic members of Group D Streprococci and Enterococci. Streptococcus pneumoniae is susceptible to optochin, in contrast to viridans streptococci and alpha hemolytic group D Streptococci and the Enterococci, which are resistant.
Which of the following is considered the major transport protein for vitamin A?
Retinol-binding protein (RBP) is considered the major transport protein for vitamin A. RBP can be useful in assessing changes in nutritional status.
If a patient has a white blood count of 40,000/µL, what would be the MOST useful staining procedure to distinguish between bacterial infection and chronic myelogenous leukemia (CML)?
The LAP stain is used to determine if an increase of cells is due to chronic myelogenous leukemia or a leukemoid reaction due to infection or similar conditions. Cells from a noncancerous reaction stain positive with many intense blue granules; cells from chronic myelogenous leukemia have few blue granules.
The India ink preparation is used for presumptive identification of which organism?
The correct answer is Cryptococcus neoformans in CSF. Upon staining with India ink, C. neoformans shows distinct, wide capsules surrounding the yeast cells. C. neoformans affects predominantly immunocompromised hosts and is the most common cause of fungal meningitis worldwide. In addition, 7-10% of patients with AIDS are affected.
The number of patients correctly diagnosed for the disease or not having the disease is defined as:
The correct answer is efficiency. The efficiency is calculated by the following equation: ((TP + TN) / (TP + FP + FN + TN)) x 100 TP = True Positives TN = True Negatives FP = False Positives FN = False Negatives The efficiency is generally used in addition to the sensitivity and specificity to determine the diagnostic value of a test method.
What are the expected lab results in the condition known as "Afibrinogenemia"?
The expected lab results would be elevated PT, elevated aPTT, elevated thrombin time (TT) and elevated reptilase time. All four of these clot based-assays reflect proper function and quantity of fibrinogen, so all would be prolonged if there is a lack of fibrinogen. Patients with afibrinogenemia typically have less than 10mg/dl of fibrinogen, which would affect all four tests.
What is the difference between Ziehl-Neelsen and kinyoun stain?
The fundamental difference between the two carbolfuchsin-based methods is whether heat is used during the primary staining process. The Ziehl-Neelsen method uses heat to infuse the carbolfuchsin into the acid-fast cells, whereas the Kinyoun method does not use heat.
In order to attain asepsis of the skin, 70% alcohol followed by 2% iodine is used for obtaining blood cultures.
The iodine should remain on the skin for 1 min because instant antisepsis does not occur when cleansing the skin for a blood culture.
Nephelometry is based on the principle of:
The measurement of turbidity resulting from specific antigen-coated latex particles agglutinated by corresponding antibodies is the principle of nephelometry. In nephelometry, the light-scattering properties of antigen-antibody complexes are measured photometrically as macromolecular complexes form. Nephelometry is used in immunology to measure complement components, immune complexes, and the presence of a variety of antibodies.
Barr body
The morphology noted in the image is a Barr body. A Barr body is a small appendage, usually round, connected to the nucleus by a chromatin strand. Barr bodies are usually observed only on peripheral blood smears from females.
Which of the following contributes to specific gravity but does NOT contribute to osmolality?
The presence of large amounts of protein and glucose will alter the specific gravity and should be considered when interpreting specific gravity results. Osmolality measures the analytes in the following equation- note that protein is not included in the calculation of osmolality. Osmolality = 1.86 Na + (Glucose/18) + (BUN/2.8) + 9 (or) 1.91 Na + (Glucose/15) + (BUN/2.25).
Ziehl-Neelsen stain
Use to stain Acid-fast bacteria uses heat
Leukocyte-reduced blood products may be administered to reduce the risk of febrile reactions and what disease or condition?
present in a donated red cell unit reduces the viral load of cytomegalovirus. Leukoreduction is not successful at preventing transfusion-associated graft-vs-host disease (TA-GVHD). However, this is an uncommon route for graft-vs-host disease as it is typically transmitted through allogenic bone marrow transplantation. Malaria is found extracellularly or in red blood cells, so leukoreduction would not affect any Plasmodium species that may be present in donated red blood cells. Bacteremia exists extracellularly, so leukoreduction would not affect any bacteria present in donated red cells. The filter used in leukocyte reduction cannot filter bacteria.
malachite green
primary stain in endospore stain (Bacillus and Clostridium)
Cryptosporidium
transmitted via fecesof lifestock animals; causes waterborne illness. Identified via modified acid fast technique. Only oocytes can be identified