Question 1

Which specimen is most commonly collected for the laboratory diagnosis of septicaemia?

Accepted Answer

Blood is the most commonly collected specimen for the laboratory diagnosis of septicaemia as it allows for the detection and identification of microorganisms in the bloodstream. This can help in determining the causative organism and guiding appropriate antibiotic therapy. Other specimens may be collected depending on the suspected source of infection, but blood is the most important initial specimen in cases of suspected septicaemia.

Question 2

Which of the following statements concerning the laboratory diagnosis of urinary tract infections is TRUE?

Accepted Answer

A midstream specimen of urine (MSU) is usually the most appropriate specimen to collect as it reduces the risk of contamination from normal skin flora or external sources. All urine samples should not contain microorganisms unless there is an infection present. Urine is not toxic to microorganisms and can be allowed to stand after collection for laboratory testing. Any bacteria found in a urine specimen may not always indicate infection as asymptomatic bacteriuria can occur. Contamination of a urine specimen is usually due to poor collection technique and not from microorganisms in the air.

Question 3

Which specimen is most commonly collected for the laboratory diagnosis of pneumonia?

Accepted Answer

Sputum is the most commonly collected specimen for the laboratory diagnosis of pneumonia as it contains respiratory secretions and can directly reflect the organisms causing infection in the lungs. Other specimens, such as nasopharyngeal suction or throat swab, may not reflect the actual infection in the lungs and may lead to false-negative results. CSF and MSU specimens are not relevant for the diagnosis of pneumonia.

Question 4

When a single type of microorganism is grown on an agar plate it is called a(n)

Accepted Answer

A pure culture is a culture consisting of a single type of microorganism grown on an agar plate. Medium is a general term for any substance used to grow microorganisms. Streak plate is a technique used to isolate individual colonies of microorganisms from mixed cultures. Petri dish is a container used to hold agar plates. Enriched culture is a type of culture that contains added nutrients to support the growth of specific microorganisms.

Question 5

The proportion of people who do not have a disease and yield a negative test result is the ___________ of the test.

Accepted Answer

Specificity measures the proportion of true negatives among all who do not have the disease.

Question 6

A specimen collected from a patient for culture in the microbiology laboratory

Accepted Answer

Collecting the specimen before antibiotic therapy is commenced is important because antibiotics can affect the growth of microorganisms and may give a false-negative result. It is recommended to collect the specimen prior to the administration of antibiotics wherever possible.

Question 7

The results of bacterial culture and antibiotic sensitivity tests on most clinical specimens are usually available after

Accepted Answer

Results of bacterial culture and antibiotic sensitivity tests on most clinical specimens usually take 36-48 hours as it requires time for the bacteria to grow in the culture medium to a level where it can be identified and tested for sensitivity to antibiotics.

Question 8

Which of the following is NOT important when collecting specimens for microbiological investigation?

Accepted Answer

Collecting duplicate samples is not necessary for every specimen, but it may be important in some cases for validation purposes. However, time of collection, correct labelling of the container, using a sterile container, and using aseptic technique are all crucial steps in collecting specimens for microbiological investigation.

Question 9

What would be the most appropriate specimen to collect from a patient suspected of having a wound infection caused by anaerobic bacteria?

Accepted Answer

Pus from the wound is the most appropriate specimen to collect for anaerobic bacteria as they thrive in oxygen-deprived environments, such as wounds. A swab of the wound may not provide enough material for accurate diagnosis, and blood cultures or skin swabs are less likely to yield anaerobic bacteria. A nose swab would be irrelevant in this situation.

Question 10

The growth of microorganisms on agar in a petri dish is called a

Accepted Answer

The growth of microorganisms on agar in a petri dish is referred to as culture. The agar provides the essential nutrients for the growth of microorganisms. In microbiology, the term culture refers to the process of obtaining and growing microorganisms under controlled conditions.

Question 11

Laboratory diagnosis of all infectious diseases can be achieved by

Accepted Answer

Not all infectious diseases can be diagnosed using a single method; different diseases require different diagnostic approaches.

Question 12

A provisional identification of the cause of an infection can sometimes be made by direct microscopic examination of a clinical specimen.Which of the following diseases could NOT be diagnosed by this means?

Accepted Answer

The answer of A provisional identification of the cause of...

Question 13

Culture of a clinical specimen in the microbiology laboratory

Accepted Answer

Culture of a clinical specimen in the microbiology laboratory is not always an accurate or the best method for diagnosing an infection. It can take several days to obtain results, and the accuracy of the diagnosis depends on several factors such as the quality of the specimen, the type of organism present, and the expertise of the laboratory staff. Culture is generally used to identify bacterial or fungal infections, but it is not useful for detecting viruses, which require special tests. Therefore, none of the options presented in the question are true.

Question 14

Which specimen is most commonly collected for the laboratory diagnosis of meningitis?

Accepted Answer

The most common specimen collected for the laboratory diagnosis of meningitis is cerebrospinal fluid (CSF). This is because meningitis is an inflammation of the membranes surrounding the brain and spinal cord, and CSF is the fluid that surrounds and protects these structures. Analysis of CSF for bacterial, viral, or fungal agents is a key diagnostic test for meningitis. Other specimens like blood, sputum, throat swab, or MSU may be collected depending on the suspected cause of meningitis or for the identification of complications associated with the disease.

Question 15

A negative test result for a person who actually has the disease is called a

Accepted Answer

A negative test result for a person who actually has the disease is called a false negative. This means that the test has failed to detect the presence of the disease in the person, and the result is incorrect. False positives, on the other hand, occur when a person receives a positive test result for a disease they don't actually have.

Question 16

A transport medium for microbiological specimens is designed to

Accepted Answer

A transport medium for microbiological specimens is designed to prevent the specimen from drying out during transport. This helps to ensure that the specimen remains viable and can be properly analyzed once it reaches the laboratory. While some transport media may also contain additives that inhibit growth of normal microbiota organisms, the primary goal is to protect the specimen from environmental stresses that could impact its viability. Enabling the specimen to be frozen is not typically a primary function of transport media, as freezing can also damage or destroy the cells. Similarly, promoting growth and multiplication of the causative organism is not typically a goal of transport media, as this could lead to contamination or overgrowth.

Question 17

The proportion of people who have a disease and are identified as having it by a test is the ___________ of the test.

Accepted Answer

Sensitivity is the proportion of true positive results (people with the disease who test positive), so it measures how well a test detects the disease among those who have it. Specificity, on the other hand, is the proportion of true negative results (people without the disease who test negative), which measures how well a test identifies those who don't have the disease. Accuracy is a measure of how well a test correctly classifies both positive and negative results. Positivity and negativity refer to the presence or absence of a positive test result, respectively. Therefore, sensitivity is the best choice because it directly relates to the ability of the test to correctly identify those with the disease.

Question 18

Blood cultures

Accepted Answer

Blood cultures may take several days or more to produce a result due to the slow growth of bloodborne pathogens.

Answer: B 
 Blood cultures should be collected from all patients on admission to the hospital to screen for possible bloodstream infections.

Answer: C 
 Blood cultures involve the collection of blood from a patient and are not related to swab specimens.

Answer: D 
 Blood cultures typically require the collection of only 10-30 ml of blood, not 500 ml.

Answer: E 
 Blood cultures may need to be repeated if initial results are negative, if a different organism is suspected, or if there is clinical suspicion of ongoing infection.

Question 19

Three samples of blood are usually collected over a 24-48 hour period from a patient with a suspected bloodstream infection

Accepted Answer

Bloodstream infections may result in intermittent shedding of organisms into the bloodstream, so multiple samples increase the likelihood of detecting the pathogen.

Question 20

What is the approximate length of time it takes to grow colonies of most bacteria on an agar plate?

Accepted Answer

Most bacteria take approximately 18 hours to form visible colonies on an agar plate. However, the growth rate and time may vary depending on the type of bacteria and environmental conditions. Option A is too short of a time frame, and options B, D, and E are too long.

Quiz 15: Microbial Techniques for Diagnosis of Infection