Question

A 20-year-old, sexually-active female presents at her family physician's office with fever, painful arthritis of the right knee, and several small pustules on her extremities. Material from the pustules and joint fluid were collected for culture on modified Thayer-Martin medium. Which of the following results are consistent with a diagnosis of gonococcal infection? A. Growth of small colonies consisting of gram-negative diplococci. Bacteria grown on plates are catalase and oxidase positive. B. Growth of small colonies consisting of gram-positive cocci. Bacteria growth on plates are catalase and oxidase positive. C. Growth of small colonies consisting of gram-negative diplococci. Bacteria growth on plates are catalase and oxidase negative. D. Growth of large mucoid colonies consisting of gram-negative bacilli. Bacteria growth on plates are catalase and oxidase negative. E. Growth of gram-negative diplococci within polymorphonuclear leukocytes. Bacteria can utilize glucose and maltose as a carbon sources.

Short answer

The correct result that is consistent with a diagnosis of gonococcal infection is A. Growth of small colonies consisting of gram-negative diplococci. The bacteria grown on plates are catalase and oxidase positive.

Step-by-step solution

Identify the phenotypic traits of the causative bacteria

The causative agent of gonococcal infection, Neisseria gonorrhoeae, is known to be gram-negative, diplococci in shape, and positive for both catalase and oxidase reactions. Furthermore, they can grow on modified Thayer-Martin medium and can be present within polymorphonuclear leukocytes.

Review the answer choices

Each of the answer choices should be reviewed and compared against the known phenotypic traits of N. gonorrhoeae. Answer choices that don't match these traits can be ruled out.

Eliminate incorrect options

From the known traits, options B, C, and D can be ruled out as they describe bacteria that are either gram-positive (B), catalase and oxidase negative (C and D), or are bacilli in shape (D).

Choose the correct answer

After the process of elimination, options A and E remain. Both of them describe bacteria that are gram-negative, diplococci and either catalase and oxidase positive (A) or present within polymorphonuclear leukocytes (E) - both of which are known traits of N. gonorrhoeae. However, option E also mentions the ability to utilize glucose and maltose as a carbon source, which is a characteristic of Neisseria meningitidis, not N. gonorrhoeae. So, option A is the correct answer.

Key concepts

Neisseria gonorrhoeae Characteristics

When discussing the organism responsible for the sexually transmitted infection gonorrhea, Neisseria gonorrhoeae steals the spotlight. This bacterium has several distinctive features that are crucial for its identification. For starters, N. gonorrhoeae are gram-negative bacteria, meaning they don't retain the crystal violet stain used in gram staining due to their thinner cell wall structure. They are also described as diplococci because of their shape, resembling two round cells that appear to be 'kissing' or joined together.

Another significant characteristic is their ability to grow in a specialized environment provided by modified Thayer-Martin medium. They thrive in this medium because it contains antibiotics that inhibit the growth of other bacteria that are not of medical significance. Furthermore, they exhibit positive results for both catalase and oxidase tests, which are biochemical assays used to identify bacterial species. Being able to distinguish this bacterium based on these tests is essential for accurate diagnosis.

Moreover, the clinical presentation of gonorrhea often involves painful arthritis and pustules among other symptoms. When these signs are coupled with the identification of N. gonorrhoeae through the methods mentioned, the diagnosis becomes much clearer and enables appropriate treatment to commence.

Thayer-Martin Medium Culture

The Thayer-Martin medium is not your ordinary agar—it is a superhero in the world of microbiology, particularly when it comes to isolating Neisseria species. This medium is a type of Mueller-Hinton agar that has been modified to be selective, and it includes antibiotics such as vancomycin, colistin, nystatin, and trimethoprim. The purpose of these antibiotics is to create an exclusive party where unwanted bacterial guests, commonly found as normal flora or contaminants, are not allowed to grow.

VIP Treatment

Only a select group of bacteria can grow on this medium, which usually includes Neisseria gonorrhoeae and Neisseria meningitidis. These Neisseria species are like VIPs in this exclusive culture medium due to their resistance to the included antibiotics.

Isolation and Identification

When a sample, such as one from a suspected gonococcal infection, is plated on this medium, the growth of small colonies that are gram-negative diplococci can indicate the presence of N. gonorrhoeae. The absence of other bacteria makes the identification process more straightforward and less noisy.

Gram-negative Diplococci Identification

In the microscopic world of bacteria, shape and staining characteristics are like fingerprints, uniquely identifying various species. Gram-negative diplococci are a particular group that is characterized by their pink color under a gram stain and a pairing arrangement that looks like two coffee beans sitting side by side.

To identify these bacteria properly, a few laboratory steps are followed. Firstly, a sample is taken from the site of infection and is stained using the gram staining procedure. This step will reveal whether the bacteria are gram-positive or gram-negative, based on the color they retain. Once it is established that we are dealing with a gram-negative organism, which does not retain the crystal violet and instead appears pink or red after a counterstain, the focus shifts to their shape—diplococci.

Then, further biochemical tests like the oxidase test, which checks for the presence of certain enzymes, and the catalase test, which examines the bacteria’s ability to decompose hydrogen peroxide, assist in narrowing down the identification. If these tests come back positive and the bacteria are observed within polymorphonuclear leukocytes from the patient's specimen, the finger can often be pointed confidently at Neisseria gonorrhoeae as the culprit of the infection.