Microbiology Exam Review Quiz Dec 2012

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Microbiology Exam Review Quiz Dec 2012 - Quiz

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Questions and Answers
  • 1. 

    Which type of microscopy is most commonly used in the direct microscopic examination of T.pallidum?

    • A.

      Brightfield Microscopy

    • B.

      Darkfield Microscopy

    • C.

      Phase Contrast Microscopy

    • D.

      Fluorescence Microscopy

    • E.

      Electron Microscopy

    Correct Answer
    B. Darkfield Microscopy
    Explanation
    Darkfield microscopy is the most commonly used type of microscopy in the direct microscopic examination of T.pallidum. Darkfield microscopy is a technique that uses a special condenser to illuminate the specimen with oblique light, making the specimen appear bright against a dark background. This technique is particularly useful for visualizing transparent or unstained specimens, such as T.pallidum, which can be difficult to see using other types of microscopy. By using darkfield microscopy, the T.pallidum bacteria can be easily observed and identified.

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  • 2. 

    The spirochetes are gram negative microorganisms.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Spirochetes are a group of bacteria known for their unique spiral shape. They are classified as gram-negative microorganisms because they have a thin peptidoglycan layer in their cell wall, which does not retain the crystal violet stain used in the Gram staining technique. This characteristic makes them appear pink or red under a microscope. Therefore, the statement that spirochetes are gram-negative microorganisms is true.

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  • 3. 

    What media is used to culture T.pallidum?

  • 4. 

    What is the purpose of the axial filaments of spirochetes such as Treponema pallidum and Borrelia spp.?

  • 5. 

    T.pallidum has a _________________ motility that can be used for laboratory diagnosis.

    Correct Answer
    corkscrew-like
    Explanation
    T.pallidum has a corkscrew-like motility, which means it moves in a twisting or spiral motion. This unique motility pattern can be used for laboratory diagnosis, as it helps differentiate T.pallidum from other bacteria that have different types of motility. By observing the corkscrew-like movement under a microscope, healthcare professionals can identify the presence of T.pallidum and make a diagnosis of syphilis.

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  • 6. 

    Identification of the causative agent of syphilis is most commonly achieved using:

    • A.

      Culture

    • B.

      Biochemical testing

    • C.

      Antigen detection

    • D.

      Serology

    • E.

      PCR

    Correct Answer
    D. Serology
    Explanation
    Serology is the most common method used to identify the causative agent of syphilis. Serological tests detect the presence of specific antibodies produced by the body in response to the infection. These tests can detect both current and past infections and are highly sensitive and specific. Culture, biochemical testing, antigen detection, and PCR are not commonly used for the identification of syphilis, as they may have limitations in terms of sensitivity, specificity, or availability. Serology, on the other hand, is a reliable and widely accessible method for diagnosing syphilis.

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  • 7. 

    The screening test used in the diagnosis of secondary and tertiary syphilis attempts to detect antibodies to ________________ whereas the specific test attempts to detect antibodies to ___________________.

    Correct Answer
    cardiolipin
    T-pallidum antigens
    Explanation
    The screening test for secondary and tertiary syphilis aims to detect antibodies to cardiolipin, a type of phospholipid found in the cell membranes of T-pallidum bacteria. This test helps identify individuals who may have been exposed to the bacteria. On the other hand, the specific test for syphilis attempts to detect antibodies specifically targeting T-pallidum antigens. This test confirms the presence of syphilis infection and is more specific than the screening test.

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  • 8. 

    Borrelia burgdorferi is the etiologic agent of ____________________.

    Correct Answer
    Lyme disease
    Explanation
    Borrelia burgdorferi is the bacterial species responsible for causing Lyme disease. Lyme disease is a tick-borne illness that affects humans and animals. It is characterized by a range of symptoms including fever, fatigue, headache, muscle and joint aches, and a characteristic skin rash called erythema migrans. If left untreated, Lyme disease can lead to more severe complications affecting the joints, heart, and nervous system. Therefore, Borrelia burgdorferi is the correct etiologic agent for Lyme disease.

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  • 9. 

    The transmission of B.Burgdorferi is mediated by:

    • A.

      Aerosols

    • B.

      Direct contact

    • C.

      Vectors

    • D.

      Fomites

    • E.

      Vehicles

    Correct Answer
    C. Vectors
    Explanation
    B.Burgdorferi is transmitted through vectors, which are organisms that can transmit the infection from one host to another. In the case of B.Burgdorferi, the primary vector is the black-legged tick (Ixodes scapularis or Ixodes pacificus), which acquires the bacteria by feeding on infected animals and then transmits it to humans or other animals during subsequent feedings. This transmission occurs through the tick's saliva, which contains the bacteria. Therefore, vectors play a crucial role in the transmission of B.Burgdorferi.

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  • 10. 

    What organs are most commonly affected during the progression of Lyme Disease?

    • A.

      Skin

    • B.

      Blood vessles

    • C.

      Brain

    • D.

      Heart

    • E.

      Joints

    • F.

      Pancreas

    • G.

      Stomach

    • H.

      Appendix

    Correct Answer(s)
    A. Skin
    B. Blood vessles
    C. Brain
    D. Heart
    E. Joints
    Explanation
    During the progression of Lyme Disease, multiple organs can be affected. The bacteria that causes Lyme Disease can spread through the bloodstream and affect various parts of the body. The skin is commonly affected, leading to rashes and skin lesions. The bacteria can also invade the blood vessels, causing inflammation and damage. The brain can be affected, leading to neurological symptoms such as memory problems and difficulty concentrating. The heart can also be affected, leading to heart rhythm abnormalities. Additionally, the joints can be affected, causing pain and swelling.

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  • 11. 

    The laboratory diagnosis of Lyme Disease is most commonly made using _____________.

    Correct Answer(s)
    serology
    Explanation
    The laboratory diagnosis of Lyme Disease is most commonly made using serology. Serology involves testing for the presence of antibodies against Borrelia burgdorferi, the bacteria that causes Lyme Disease, in a patient's blood. This is done through techniques such as enzyme immunoassay (EIA) and Western blot. These tests can detect the antibodies produced by the immune system in response to the infection. Serology is considered the most reliable method for diagnosing Lyme Disease, although it may not be accurate in the early stages of the infection.

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  • 12. 

    Name two species of Borrelia that are most commonly implicated in cases of relapsing fever. What are the vectors involved in the transmission of these species of Borrelia?

    Correct Answer(s)
    Borrelia recurrentis
    Borrelia hermsi
    Explanation
    Borrelia recurrentis and Borrelia hermsi are the two species of Borrelia commonly implicated in cases of relapsing fever. The transmission of these species of Borrelia is through vectors, specifically lice for Borrelia recurrentis and ticks for Borrelia hermsi.

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  • 13. 

    What organs are most commonly affected during severe cases of Leptospirosis?

    • A.

      Kidneys

    • B.

      Heart

    • C.

      Liver

    • D.

      Central Nervous System

    • E.

      Lungs

    • F.

      Skin

    Correct Answer(s)
    A. Kidneys
    C. Liver
    D. Central Nervous System
    Explanation
    During severe cases of Leptospirosis, the bacteria can spread throughout the body via the bloodstream, leading to multiple organ involvement. The kidneys are commonly affected as the bacteria can cause acute kidney injury. The liver can also be affected, resulting in liver dysfunction. Additionally, the bacteria can invade the central nervous system, leading to meningitis, encephalitis, or other neurological complications. Therefore, the most commonly affected organs during severe cases of Leptospirosis are the kidneys, liver, and central nervous system.

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  • 14. 

    The transmission of leptospires is most commonly via _________________________

    Correct Answer(s)
    Contaminated urine
    Explanation
    Leptospires are bacteria that cause leptospirosis, a disease that can affect humans and animals. The most common mode of transmission of leptospires is through contaminated urine. Infected animals, such as rats or livestock, excrete the bacteria in their urine, which can contaminate water sources or soil. Humans can then become infected by coming into contact with the contaminated urine, either directly or indirectly. This can occur through activities like swimming in contaminated water, handling infected animals, or consuming food or water that has been contaminated with urine.

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  • 15. 

    Identification of the causative agent of leptospirosis is most commonly achieved using:

    • A.

      PCR

    • B.

      Biochemical testing

    • C.

      Culture

    • D.

      Serology

    • E.

      Antigen detection

    Correct Answer
    C. Culture
    Explanation
    Culture is the most common method used to identify the causative agent of leptospirosis. Culture involves growing the bacteria in a laboratory setting, which allows for further testing and identification. This method is reliable and can provide a pure culture of the bacteria for further analysis. PCR, biochemical testing, serology, and antigen detection can also be used to diagnose leptospirosis, but culture is considered the gold standard for identification.

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  • 16. 

    Ticks transmit the spirochetes that cause Lyme disease within the first hour after attaching to their human host.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    It takes more than one hour, you can prevent Lyme disease by removing the ticks in the first hour.

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  • 17. 

    Spirochetes are differentiated by the number of insertion disks present.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Spirochetes are a group of bacteria that are characterized by their spiral shape. They are also differentiated by the number of insertion disks present. This means that the number of insertion disks can be used to distinguish different species or types of spirochetes. Therefore, the statement that spi rochetes are differentiated by the number of insertion disks present is true.

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  • 18. 

    Several treponeme species are considered to be normal oral and genital flora.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Some species of treponeme are considered to be part of the normal flora in the oral and genital regions. This means that they naturally exist in these areas without causing any harm or disease. Therefore, the statement is true.

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  • 19. 

    A positive ELISA test for Lyme disease should be confirmed by Western blot.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    A positive ELISA test for Lyme disease should be confirmed by Western blot because ELISA tests have a higher chance of producing false positives. The Western blot is a more specific test that can accurately confirm the presence of antibodies to the Lyme disease bacteria. Therefore, it is necessary to use the Western blot as a follow-up test to ensure the accuracy of the diagnosis.

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  • 20. 

    Diagnosis of leptospirosis is usually made by detection of IgM antibodies in acute and convalescent sera.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    The statement is true because the diagnosis of leptospirosis is typically done by detecting IgM antibodies in both acute and convalescent sera. IgM antibodies are produced by the immune system in response to an infection, so their presence indicates a recent or ongoing infection with the bacteria that causes leptospirosis. By testing for these antibodies in blood samples taken during the acute phase of the illness and again during the recovery phase, healthcare professionals can confirm a diagnosis of leptospirosis.

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  • 21. 

    Treponemes can infect the umbilical cord and cross the placenta.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Treponemes, which are a type of bacteria, have the ability to infect the umbilical cord and cross the placenta. This means that if a pregnant woman is infected with treponemes, the bacteria can pass from her bloodstream to the umbilical cord and then to the developing fetus. This can lead to serious health complications for the fetus, including congenital syphilis. Therefore, the statement "Treponemes can infect the umbilical cord and cross the placenta" is true.

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  • 22. 

    Reaginic antibodies are produced against antigens of T.pallidum.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    Antibodies are produced due to the disease process, not just the organism.

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  • 23. 

    Extreme water sports are a risk factor for leptospirosis.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Leptospirosis is a bacterial infection that is commonly transmitted through contact with water contaminated by the urine of infected animals. Extreme water sports, such as swimming or diving in freshwater lakes or rivers, increase the risk of exposure to this bacteria. Therefore, it is true that extreme water sports are a risk factor for leptospirosis.

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  • 24. 

    Human relapsing fever is caused by the bite of the human body louse.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Human relapsing fever is caused by the bite of the human body louse. This means that when a person is bitten by a human body louse, they can contract the disease known as human relapsing fever. The louse acts as a vector, transmitting the disease-causing bacteria to the human host through its bite. Therefore, it is true that human relapsing fever is caused by the bite of the human body louse.

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  • 25. 

    Susceptibility testing of Borrelia spp. to doxycycline should always be done because of the incidence of treatment failure.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    Susceptibility testing of Borrelia spp. to doxycycline should not always be done because the incidence of treatment failure is low. Doxycycline is an effective antibiotic for treating Borrelia spp. infections, and resistance to this antibiotic is rare. Therefore, routine susceptibility testing is not necessary in most cases.

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  • 26. 

    Relapsing fever is caused by:

    • A.

      L.interrogans

    • B.

      T.pallidum

    • C.

      B.burgdorferi

    • D.

      B.recurrentis

    Correct Answer
    D. B.recurrentis
    Explanation
    Relapsing fever is caused by B.recurrentis. This bacterium is transmitted to humans through the bite of infected lice or ticks. It is responsible for causing recurrent episodes of fever, along with other symptoms such as headache, muscle aches, and joint pain. B.recurrentis is primarily found in Africa, Asia, and South America, and it infects the bloodstream of its host, leading to the characteristic relapses of fever.

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  • 27. 

    Primary syphilis is characterized by the appearance of:

    • A.

      Erythema migrans rash

    • B.

      Gumma

    • C.

      Chancre

    • D.

      Gingivitis

    Correct Answer
    C. Chancre
    Explanation
    Primary syphilis is characterized by the appearance of a chancre. A chancre is a painless ulcer that typically develops at the site of infection, usually the genitals, anus, or mouth. It is the initial and most common symptom of syphilis. The chancre usually appears within 3 weeks after exposure to the bacteria and can last for 3-6 weeks. It is highly contagious and can easily transmit the infection to others. Therefore, the presence of a chancre is a key diagnostic feature of primary syphilis.

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  • 28. 

    The test for syphilis that should be performed on CSF is:

    • A.

      VDRL

    • B.

      RPR

    • C.

      ELISA

    • D.

      Western blot

    Correct Answer
    A. VDRL
    Explanation
    The VDRL test is the correct test for syphilis that should be performed on CSF (Cerebrospinal Fluid). VDRL stands for Venereal Disease Research Laboratory, and it is a screening test used to detect the presence of antibodies against the bacteria that causes syphilis. CSF is the fluid that surrounds the brain and spinal cord, and testing it for syphilis can help diagnose neurosyphilis, which is the infection of the central nervous system. Therefore, performing the VDRL test on CSF is essential for accurate diagnosis and appropriate treatment of syphilis.

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  • 29. 

    For all treponemal infections, the drug of choice is:

    • A.

      Penicillin G

    • B.

      Doxycycline

    • C.

      Tetracycline

    • D.

      Ceftriaxone

    Correct Answer
    A. Penicillin G
    Explanation
    Penicillin G is the drug of choice for all treponemal infections. Treponemal infections are caused by bacteria of the genus Treponema, including syphilis and yaws. Penicillin G is highly effective against these bacteria and is the recommended treatment due to its ability to effectively kill the bacteria and prevent further complications. Doxycycline and tetracycline are antibiotics commonly used for other types of infections, but they are not the preferred treatment for treponemal infections. Ceftriaxone is a broad-spectrum antibiotic that is effective against many types of bacteria, but it is not the first-line treatment for treponemal infections.

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  • 30. 

    What can cause false positive results in the RPR test?

    • A.

      Rheumatoid disease

    • B.

      Old age

    • C.

      Tuberculosis

    • D.

      All of the above

    Correct Answer
    D. All of the above
    Explanation
    All of the above options can cause false positive results in the RPR test. Rheumatoid disease, old age, and tuberculosis can all lead to the presence of antibodies in the blood that can be detected by the RPR test, even if the person does not have syphilis. Therefore, if any of these conditions are present, it can result in a false positive result in the RPR test.

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  • 31. 

    The anticoagulant of choice for blood cultures is EDTA

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    It is SPS - Sodium polyethanol sulfonate

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  • 32. 

    Specimens for anaerobic culture should be refrigerated if processing cannot be done immediately.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    Specimens for anaerobic culture should never be refrigerated.

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  • 33. 

    Bronchoscopy specimens should be centrifuged and the sediment used to inoculate culture media.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Bronchoscopy specimens often contain respiratory secretions and cells from the lower respiratory tract. By centrifuging the specimen, the sediment containing potential pathogens can be separated from the liquid portion. This sediment can then be used to inoculate culture media, allowing for the growth and identification of any microorganisms present in the specimen. Therefore, the statement that bronchoscopy specimens should be centrifuged and the sediment used to inoculate culture media is true.

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  • 34. 

    Urine cultures represent a semi-quantitative technique.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    They represent a quantitative culture because a known amount of material is put onto the plate.

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  • 35. 

    The presence of gram-negative diplococci in the Gram stain of a cerebrospinal fluid would be considered a critical result and should be immediately called to the attention of the clinician.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    The presence of gram-negative diplococci in the Gram stain of cerebrospinal fluid is considered a critical result because it may indicate the presence of bacteria such as Neisseria meningitidis, which is a common cause of meningitis. Meningitis is a serious infection that can lead to severe complications and even death if not promptly treated. Therefore, it is crucial to immediately inform the clinician about this finding so that appropriate treatment can be initiated as soon as possible.

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  • 36. 

    Staphylococcus species are considered:

    • A.

      Microaerophiles

    • B.

      Obligate anaerobes

    • C.

      Facultative anaerobes

    • D.

      Obligate aerobes

    • E.

      Aerotolerant anaerobes

    Correct Answer
    C. Facultative anaerobes
    Explanation
    Staphylococcus species are considered facultative anaerobes because they can survive and grow in both the presence and absence of oxygen. They have the ability to switch their metabolic pathways depending on the availability of oxygen. In the presence of oxygen, they can perform aerobic respiration, utilizing oxygen as a terminal electron acceptor. In the absence of oxygen, they can switch to fermentation or anaerobic respiration, using alternative electron acceptors. This flexibility allows Staphylococcus species to adapt to various environments, making them facultative anaerobes.

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  • 37. 

    Staphylococcus species are catalase positive.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Staphylococcus species are catalase positive because they produce the enzyme catalase, which allows them to break down hydrogen peroxide into water and oxygen. This characteristic is used to differentiate Staphylococcus from other bacteria that are catalase negative. By performing a catalase test, one can determine if a bacterium belongs to the Staphylococcus genus.

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  • 38. 

    Staphylococcus aureus has the ability to ferment ________________ which is used in the identification of this species.

    Correct Answer
    Mannitol
    Explanation
    Staphylococcus aureus has the ability to ferment mannitol, which is a type of sugar. This fermentation process produces acid, causing a change in the pH of the medium. This change in pH is used as a characteristic test to identify Staphylococcus aureus. If the organism can ferment mannitol, it will produce acid and the medium will turn yellow. If it cannot ferment mannitol, there will be no change in the pH and the medium will remain red.

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  • 39. 

    Chlorhexidine showers may be used to reduce colonization with S.aureus.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Chlorhexidine showers are commonly used to reduce the colonization of S. aureus, a bacterium that can cause various infections. Chlorhexidine is an antiseptic that has been found to be effective in killing or inhibiting the growth of S. aureus on the skin. By using chlorhexidine showers, individuals can reduce the number of S. aureus bacteria on their skin, which in turn may help decrease the risk of infection. Therefore, the statement is true.

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  • 40. 

    Staphylococci will grow on 5% sheep blood agar and chocolate agars, but not mannitol salt agar.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    Staphylococci are able to grow on mannitol salt agar.

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  • 41. 

    One way to confirm oxacillin resistance in S.aureus isolates is to test for the presence of PBP 2a.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Testing for the presence of PBP 2a is a reliable method to confirm oxacillin resistance in S. aureus isolates. PBP 2a is a penicillin-binding protein that is encoded by the mecA gene, which is responsible for methicillin resistance. Oxacillin is a type of penicillin antibiotic, so if PBP 2a is present, it indicates that the bacteria are resistant to oxacillin. Therefore, the statement "One way to confirm oxacillin resistance in S. aureus isolates is to test for the presence of PBP 2a" is true.

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  • 42. 

    The tube coagulase test should be read at 2 hours.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    It should be read every half hour for 4 hours.

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  • 43. 

    S.saprophyticus isolated from a female patient is a recognized cause of:

    • A.

      Impetigo

    • B.

      Toxic Shock Syndrome

    • C.

      Urinary tract infection

    • D.

      Folliculitis

    Correct Answer
    C. Urinary tract infection
    Explanation
    S. saprophyticus is a recognized cause of urinary tract infection (UTI) in female patients. UTIs occur when bacteria, such as S. saprophyticus, enter the urinary tract and multiply, leading to infection. This bacterium is commonly found in the genital and rectal areas, making it easier for it to enter the urinary tract in females. Symptoms of a UTI include frequent urination, burning sensation during urination, cloudy or bloody urine, and pelvic pain. Therefore, the correct answer is urinary tract infection.

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  • 44. 

    One test used to differentiate S.aureus from S.lugdunensis is:

    • A.

      PYR

    • B.

      Catalase

    • C.

      Bacitracin Sensitivity

    • D.

      Novobiocin Sensitivity

    Correct Answer
    A. PYR
    Explanation
    The PYR test is used to differentiate between Staphylococcus aureus and Staphylococcus lugdunensis. This test detects the presence of the enzyme pyrrolidonyl arylamidase, which is produced by S. aureus but not by S. lugdunensis. By observing the reaction of the test medium to the enzyme, it is possible to determine whether the bacteria being tested is S. aureus or S. lugdunensis.

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  • 45. 

    A hand wound culture produced a creamy white growth that is catalase and coagulase positive. The physician reported that the wound was caused by a dog bite. To prevent misidentification of the staph species, what additional tests should be performed?

    • A.

      Novobiocin susceptibility

    • B.

      PYR and VP

    • C.

      Tube coagulase

    • D.

      PYR and ornithine decarboxylase

    Correct Answer
    B. PYR and VP
    Explanation
    To prevent misidentification of the staph species, additional tests should be performed to confirm the identification. The PYR (pyrrolidonyl arylamidase) test is used to differentiate between Staphylococcus aureus and other staphylococci species. Staphylococcus aureus is PYR positive, while other staphylococci species are PYR negative. The VP (Voges-Proskauer) test is used to differentiate between Staphylococcus epidermidis and Staphylococcus saprophyticus. Staphylococcus epidermidis is VP positive, while Staphylococcus saprophyticus is VP negative. These additional tests will help in accurately identifying the staph species causing the wound infection.

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  • 46. 

    Selective media that can be used to isolate staphylococci includes:

    • A.

      5% Sheep blood agar

    • B.

      MacConkey agar

    • C.

      Chocolate agar

    • D.

      Mannitol salt agar

    Correct Answer
    D. Mannitol salt agar
    Explanation
    Mannitol salt agar is a selective medium that can be used to isolate staphylococci. This medium contains a high concentration of salt, which inhibits the growth of many other bacteria, allowing staphylococci to grow. In addition, mannitol, a type of sugar, is included in the agar. Staphylococci that can ferment mannitol will produce acid, causing the medium to turn yellow. This helps differentiate staphylococci from other bacteria that do not ferment mannitol. Therefore, Mannitol salt agar is an effective selective medium for isolating staphylococci.

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  • 47. 

    A gram-positive coccus that is catalase positive, coagulase negative, and resistant to novobiocin is:

    • A.

      S.aureus

    • B.

      S.epidermidis

    • C.

      S.saprophyticus

    • D.

      S.lugdunensis

    Correct Answer
    C. S.saprophyticus
    Explanation
    S.saprophyticus is the correct answer because it is the only option that meets all the given criteria. It is a gram-positive coccus, catalase positive, coagulase negative, and resistant to novobiocin. S.aureus is catalase positive and coagulase positive, S.epidermidis is catalase positive and coagulase negative, and S.lugdunensis is catalase positive and coagulase negative but not resistant to novobiocin. Therefore, S.saprophyticus is the only choice that fits all the given characteristics.

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  • 48. 

    All streptococci are negative for this test:

    • A.

      Catalase

    • B.

      Coagulase

    • C.

      PYR

    • D.

      Bile esculin

    Correct Answer
    A. Catalase
    Explanation
    Streptococci are a group of bacteria that are known to be negative for the catalase test. This means that they do not produce the enzyme catalase, which is responsible for breaking down hydrogen peroxide into water and oxygen. Other bacteria, such as staphylococci, are positive for the catalase test because they produce catalase. Therefore, if a bacterium is negative for the catalase test, it is likely to be a streptococcus.

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  • 49. 

    S.pneumoniae can positively be identified by the optochin test.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    They are susceptible

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  • 50. 

    Staphylococcus epidermidis is a member of the normal flora.

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    Staphylococcus epidermidis is a member of the normal flora because it is commonly found on the skin and mucous membranes of humans. It is a harmless bacterium that coexists with other microorganisms in the body without causing any harm. This bacterium plays a role in maintaining the balance of the microbial community and helps to prevent the colonization of harmful bacteria. Therefore, the statement "Staphylococcus epidermidis is a member of the normal flora" is true.

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