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ASCP MLS BOC - MediaLab - Questions Missed on CATs (1-5)

Terms in this set (142)

Francisella tularensis; Sub blood culture bottle to a media with cysteine for optimal growth

Francisella tularensis is a slow growing, pleomorphic Gram-negative coccobacilli. The most common clinical presentation is ucleroglandular disease where the organism is transported to the lymph nodes and then disseminated in the blood stream. Blood cultures that grow poorly or fail to grow on blood agar and show Gram-negative coccobacilli in the Gram stain, should have the organism subcultured to a media that contains cysteine (such as chocolate agar, modified Thayer Martin agar, cysteine heart agar, or buffered charcoal-yeast extract agar) to enhance growth of the organism. Growth may also be increased with additional CO2 incubation.
Campylobacter jejuni is mostly seen in gastrointestinal infections, not commonly in blood cultures. Other species of Campylobacter such as C. coli or C. fetus subsp. fetus, can be been in blood cultures. Campylobacter species require a microaerophilic environment as well as incubation at 42 degrees. However, the Gram stain rules out Campylobacter species, which shows a curved Gram-negative bacillus via Gram stain.
Yersinia pestis can be seen in blood cultures but is more common in respiratory cultures or aspirates from lesions. Yersinia pestis does grow better at room temperature, however, the Gram stain rules out Yersinia pestis, which show plump Gram-negative bacilli, typically with bipolar staining via Gram stain.
Streptococcus pneumoniae can be seen in blood cultures but is more common in respiratory cultures. This organism does have an autolytic property, which is used with the bile solubility test for identification. However, the Gram stain rules out Streptococcus pneumoniae, which would be Gram positive cocci.
Ribonucleic protein (RNP) antibodies

Ribonucleic protein (RNP) antibodies are not specific for Systemic Lupus Erythematosus (SLE). In addition, Anti-Sjögren's syndrome antigen A (SSA, or Ro) and anti-Sjögren syndrome antigen B (SSB, or La) antibodies and histone antibodies are not specific for SLE. Anti-ribosomal P (anti-P) is associated with neurolupus but not particularly useful in management or diagnosis of neuropsychiatric lupus. Chromatin antibodies detection is of primary use in the diagnosis of drug-induced lupus not SLE.
The initial laboratory results demonstrated a positive ANA test, or anti-nuclear antibody, which is a screening test for Lupus erythrematosus; an RA test, or rheumatoid factor, screening assay for the presence of an antibody linked with rheumatoid arthritis and other conditions, such as lupus erythematosus. Renal disease in patients with Systemic Lupus Erythematosus is indicated by an assessment of the levels of C3 and C4. In this case, there was a decreased level. A decrease in complement proteins indicates that the classic complement pathway may have been activated resulting in immune complexes, a clinically significant indication of tissue damage, particularly renal disease. Patients with SLE are characterized by the presence of antibodies to multiple antigens but some of these antibodies are not exclusive to SLE.
An extractable nuclear antibody, Smith (Sm) antibody, is highly specific for SLE, but occurs in only 20-30 or35% of cases.
Double-stranded DNA (dsDNA) antibodies (titer >1:10) detected by immunofluorescence assay (IFA) is seen in up to 50-60% of patients with Systemic Lupus Erythematosus (SLE). These antibodies indicate an active disease.

- acquired by natural exposure in response to an infection or a natural series of infections, or through intentional inject of an antigen

Passive immunity can be artificially or naturally acquired. Artificial passive immunity is achieved by infusion of serum or plasma containing high concentrations of antibody or lymphocytes from an actively immunized individual. Passive immunity via preformed antibodies in serum provides immediate, temporary antibody protection against microorganisms such as hepatitis A. Passive immunity can be acquired naturally by the fetus through the transfer of antibodies thru the maternal placental circulation in utero during the last 3 months of pregnancy. The amount and specificity of maternal antibodies depend on the mother's immune status to infectious diseases that she has experienced.
Adaptive immunity is a type of body defense. If a microorganism overwhelms the body's natural, innate resistance, a third line of defense exists, adaptive immunity. Characteristics of adaptive immunity compared to innate immunity include: presence of memory lymphocytes, the physical barrier of lymphocytes in epithelial cells, antibodies secreted at epithelial surfaces, the presence of specific antibodies, and the action of lymphocytes.
Natural immunity (inborn or innate resistance) is one of the ways that the body resists infection after microorganisms have penetrated the body's first line of defense of unbroken skin and mucus membranes. Characteristics of innate immunity include: absence of lymphocytes, skin and mucosal epithelial as physical barriers, presence of antimicrobial chemicals, the presence of complement, and the protective actions of macrophages, neutrophils, and natural killer cells.
Provides rapid results

The assay takes 2 to 3 days to obtain results. It does not provide rapid results.
CCNA was developed to detect the presence of C. difficile toxin B in fecal samples. A filtrate of stool sample is prepared and inoculated onto sensitive tissue culture cells. If toxin is present, it causes the cells to round up in a characteristic cytopathic effect (CPE). To verify the CPE is caused by C. difficile toxin, the filtrate is also inoculated onto a second set of tissue culture cells, to which C. difficile specific anti-toxin has been added. Absence of CPE in the second set of cell cultures proves the cellular changes in the first set were caused by C. difficile toxin B.
Although CCNA is considered one of the best testing methods for the detection of C. difficile toxin, it is labor intensive, requires the use of cell cultures, and requires at least 48 hours incubation.
Clostridioides (formerly Clostridium) difficile is the most common cause of pseudomembranous colitis. The organism is part of the normal enteric flora in about 5% of people with higher colonization rates of up to 20% in long term care facilities. When patients are given antibiotics, the other normal flora may be killed, allowing this organism to produce high levels of two toxins, A (an enterotoxin) and B (a cytotoxin). The colon mucosa may experience necrosis due to Toxin B resulting in the bloody diarrhea see in pseudomebranous colitis. This organism is frequently transmitted in healthcare facilities and is a nosocomial concern.
Antibody immunoassay to differentiate HIV-1 and HIV-2

The testing recommendations and algorithm for HIV has been changed in recent years. Specimens positive for HIV-1 or HIV-2 antibodies should be tested with an immunoassay that will differentiate the antibodies, if the initial screening immunoassay does not already do so. Initial screening assays should be 4th generation, in that they not only detect HIV-1/HIV-2 antibodies, but also the p24 antigen.
The HIV-1 immunofluorescence assay was formerly recommended as a confirmation method when HIV antibodies were identified in a patient sample. The former recommendation for using IFA was based on the inability of early immunoassays to correctly identify antibodies in specimen. Improvements in immunoassays have led to the removal of this assay as confirmation in the recommended testing algorithm; however, in the even that an immunoassay to differentiate HIV-1 and HIV-2 is not available, IFA is an acceptable alternative.
The Western blot is no longer included in the recommended testing algorithm. The use of Western blot for confirmation may demonstrate a false negative result, especially during seroconversion. Western blot has also been shown to misidentify HIV-2 infections as HIV-1. Improvements in HIV-1/HIV-2 antibody immunoassays have led to the removal of this assay as confirmation in the recommended testing algorithm; however, in the even that an immunoassay to differentiate HIV-1 and HIV-2 is not available, Western blot is an acceptable alternative.
After confirmation of HIV infection, specimens should be tested for HIV viral load by nucleic acid amplification to determine the weight of infection and treatment options.
None; considered non-pathogenic

This image shows a trophozoite of Chilomastix mesnili. C. mesnili is a pear-shaped trophozoite that averages 8-15 µm in length. There is a single nucleus located at the anterior end of the organism. There is also a small karyosome that can be centrally or eccentrically located. Peripheral chromatin is not present. C. mesnili has 4 flagella, three of which extend out of the anterior end of the organism. The fourth flagellum is seen extending from the cytostome of the organism (rudimentary mouth found near the nucleus). Bordering the cytostome are cytosomal fibrils that resemble a "shepherd's crook", a predominant feature of C. mesnili. Finally, a spiral groove is present on the posterior end of the organism and gives the posterior end a curved appearance as seen in the image.
Chilomastix mesnili is non-pathogenic. It has been seen in areas of poor sanitation and transmission occurs through ingestion of the cyst form, through hand-to-mouth or food and drink that are contaminated. However, it is not known to cause human disease and is thus not associated with any parasitic condition.
Amebiasis and amebic hepatitis are both caused by Entamoeba species, most commonly E. histolytica. Entamoeba species trophozoites are typically larger, with an average size of 12-25 µm. The trophozoites are typically amoeboid shape with pseudopods, not pear-shaped. Entamoeba species do have a single nucleus with a karyosome (placement different depending on species), but does contain peripheral chromatin, unlike C. mesnili. Also, Entamoeba species are amebas and move via, pseudopodia, not flagella. Flagella are not present in any Entamoeba species. E. histolytica can migrate into the blood and then are removed by the liver. The organisms can then reside in the liver and cause abscesses and symptoms similar to hepatitis and other liver infections.
Traveler's diarrhea typically refers to infection with Giardia intestinalis, but can also refer to infections with bacterial species as well. Giardia intestinalis is also a flagellate and the trophozoite can be pear-shaped. The size is also about the same with a range of 8-20 µm in length. The difference between the two is that G. intestinalis is bilaterally symmetrical with two nuclei present.
Trichomonas tenax trophozoite

The image of the organism shows a pear-like shape, typical of a trophozoite form versus a cyst form, which is more circular. There are predominant flagella that extend from the anterior end of the organism, which puts it into the flagellate group of organisms. There is one nucleus present with a predominant axostyle, which runs the length of the organism and wraps around the nucleus. The nucleus is filled with chromatin granules. The organism is identified as Trichomonas tenax trophozoite. It also has an undulating membrane that is two-thirds the length of the organism. T. tenax can range in size from 5-14 µm. The organism is found in mouth scrapings, tonsillar crypts, and pyorrheal pockets.
Trichomonas hominis has no known cyst form, only trophozoite forms. The trophozoite can be differentiated from T. tenax by the position of the nucleus and axostyle. The nucleus is present in the anterior portion of the organism, instead of more centralized in T. tenax, and also contains a central karyosome. The axostyle extends down from the nucleus, and does not wrap around the nucleus. T. hominis also has a full body length undulating membrane. The organism is typically found in contaminated milk and recovered from the stool, but is considered a non-pathogen.
Entamoeba gingivalis trophozoite is in the ameba group, not the flagellates. Since is is an ameba, the organism moves via pseudopodia instead of flagella. The flagella present in this picture rules out Entamoeba gingivalis. The organism does live around the gum line of teeth and in tartar, gingival pockets, and tonsillar crypts.
Trichomonas vaginalis also has no know cyst form, only trophozoite forms. The trophozoite can be differentiated from T. tenax because it typically has granules present along the axostyle. Also, T. vaginalis has a very short undulating membrane, about half the total length of the organism. T. vaginalis is a sexual transmitted organism and can cause urethritis and vaginitis.