6 Bacterial Growth, Nutrition, and Differentiation Supplemental Case History

Scenario Caitlyn is a very social high school sophomore. Her worried mom often asks her if she is having sex with any of the boys she hangs out with. As an answer, Caitlyn usually sighs, rolls her eyes, and says she’s not having sex with anyone. Many people, especially teenagers, consider genital intercourse to be “sex” and oral intercourse to be something else.

Signs and Symptoms Caitlyn came home from school complaining about a sore throat that had persisted for a few days. Her mother, who suspected it was strep throat, took Caitlyn to her primary care physician. The physician noted that Caitlyn has a low-grade fever and her throat is red and inflamed, with several white spots producing a whitish/yellowish discharge. A rapid strep test was performed, and the result was negative. Throat swabs were sent to a reference laboratory for cultures and additional tests. A “rapid strep test” or RST is a point-of-care test used to assist in the diagnosis of bacterial pharyngitis caused by group A streptococci (such as Streptococcus pyogenes). The test detects the presence of group A streptococcal (GAS) antigens in the throat of a patient with suspected strep throat. This test is very specific for GAS antigens, with a reported sensitivity ranging from 90–95%, depending on the type of test used. However, false positives and false negatives are possible.

Testing A smear was made from the throat swab, which was Gram stained and observed with a light microscope at 1,000×. Answer 1: Gram negative diplococci, encapsulated. This observation is highly indicative of infection with Neisseria or Moraxella, which both may be found in the pharynx. Gonorrhea image, “Gonorrhea” by the CDC http://www.cdc.gov/nchhstp/newsroom/images/Gonorrhea.jpg Interpret the Gram stain results

Testing Throat swabs were plated on culture media, including blood agar, chocolate agar, and Thayer-Martin agar. On the blood agar plate, α-hemolytic streptococci grew abundantly (result not shown). Why is Thayer-Martin considered a selective medium, while blood agar and chocolate agar are considered differential media? Is it significant that α-hemolytic streptococci were observed on the blood agar plate? Interpret the pattern of growth observed on the chocolate agar and Thayer-Martin agar plates. Answer 1: Thayer-Martin contains a combination of antibiotics that inhibits the growth of most types of bacteria, except Neisseria. Answer 2: The observation of α-hemolytic streptococci is most likely not a significant finding in this case. Normal flora streptococci that inhabit the oral cavity and pharynx are typically α-hemolytic Answer 3: Combined with the Gram stain results, growth on chocolate agar indicates Hemophilus or Neisseria. Growth on Thayer-Martin agar indicates Neisseria. Hemophilus or Neisseria image, “Neisseria gonorrhoeae 01” by the CDC http://commons.wikimedia.org/wiki/File:Neisseria_gonorrhoeae_01.png

Testing An oxidase test was also performed on the culture of the Gram-negative diplococci on the chocolate agar plate. Answer 1: Oxidase test is positive, which indicates Neisseria. Answer 2: A positive test for oxidase means that the bacteria produce a type of cytochrome oxidase, a membrane-associated enzyme in the electron transport system. This result means that the bacteria have a respiratory type of metabolism with oxygen as the final electron acceptor. This result also indicates that the bacteria are strict aerobes. Oxidase Test image, “Oxidase Test” by the CDC. http://www.cdc.gov/std/gonorrhea/lab/ngon.htm Interpret the oxidase test result—is it positive or negative? What does this test result indicate about the metabolism of this bacterium?

Diagnosis When the laboratory results come back, the physician asks to speak with Caitlyn without her mom present. Once alone, Caitlyn admits she has given oral sex to several of the boys she hangs out with, ending with “I didn’t think it was a big deal, since I can’t get pregnant!” Based on the clinical and laboratory findings in this case, what is the diagnosis? Answer 1: The diagnosis is pharyngeal gonorrhea, caused by Neisseria gonorrhoeae. Many people, especially teenagers, presume oral sex to be "safe" sex, largely because there is no risk of pregnancy. However, roughly 50% of chlamydial infections and over 60% of gonococcal infections occur at a nongenital site. Oral sex, therefore, does not prevent transmission of sexually transmitted viruses, bacteria, or other pathogens.

Caitlyn was given a single dose of ceftriaxone by IM injection. Treatment Confident of the diagnosis, the physician administered the medically recognized standard of care for treating gonococcal infections. Disease symptoms resolved fully in a few days. Caitlyn was given a single dose of ceftriaxone by IM injection. Answer 1: Treatment guidelines for uncomplicated gonococcal infections are the same for either body region. Treatment Source: aafp.org Should pharyngeal gonococcal infections be treated differently than genital gonococcal infections, since the bacteria are not infecting the same body region?

Additional Considerations Once the diagnosis was confirmed, the physician reported the case to the state’s Department of Health for disease surveillance. Name 2 additional sexually transmitted bacterial infections that can be passed to either partner by oral sex. What additional actions should be taken with regard to Caitlyn’s sexual contacts? Answer 1: Chlamydia and syphilis. Answer 2: All of the sexual contacts should be notified, tested, and treated if there is evidence of disease.

This concludes the Lecture PowerPoint presentation for Chapter 6 PowerPoint slides by Holly Ahern SUNY Adirondack