Question

As an LPN working on a medical floor, I read the order for my patient that the physician had just written: “Obtain throat culture for C&S.” I knew that this meant the physician wanted a throat swab collected for culture and sensitivity testing. Culturing refers to identification of the bacteria causing the patient’s symptoms, while sensitivity will determine what antibiotic the bacteria identified will be sensitive to—in other words, which antibiotic has the ability to kill the bacteria.

I gathered the necessary items, including the appropriate culture materials—in this case, a sterile swab that comes with a container filled with a transport medium that will keep the bacteria alive until they are processed in the lab. I entered the patient’s room, introduced myself, and informed the patient what I was going to do. I asked the patient not to close her mouth when the specimen was being taken, so as not to contaminate the specimen. I washed my hands, donned gloves, and asked Mrs. S. to open her mouth. I noted that her throat was very red and there was pus visible on her tonsils. I introduced the swab into her throat and gently swabbed the areas where pus was visible. I removed the swab and placed it into the provided container filled with transport medium, ensuring the lid was secure. I thanked Mrs. S., labeled the swab with her name and identification information, and carried the swab to the lab. I then removed my gloves and washed my hands.

In the lab, the laboratory technician received the patient’s throat culture and logged it in. Being careful not to contaminate the specimen, the lab tech inoculated a blood agar plate using the swab supplied by the nurse. The blood agar plate was covered and stored at 35°C to 37°C for 48 hours.

After 24 hours, the lab tech observed that the majority of colonies were surrounded by clear zones in which there was no red pigment, indicating that hemolysis had occurred. Based on this characteristic appearance, the lab tech identified a group A hemolytic streptococcus as being the cause of the patient’s symptoms.

The lab tech then re-streaked a different agar plate, containing small discs of different antibiotics, to determine which antibiotic would be effective in treating the organism identified. Penicillin was identified as being the antibiotic most effective for treating the patient’s strep throat. After a 10-day course of penicillin, the patient was fully recovered.

Research and Review

Locate this article in a library collection or through a database:Martin JM et al. 2002. Erythromycin-resistant group A streptococci in schoolchildren in Pittsburgh. N Engl J Med 346: 1200-1206. Read the article thoroughly and then answer the questions that follow here linking the case file, the chapter content, and this case report.

• Discuss the common antibiotics used for the treatment of group A streptococcal infections in 2001, as pointed out in the background of the article.
• Beginning in January of 2001, what phenomenon did physicians identify in group A streptococcus isolates from the throats of children?
• Which type of agar was used to culture the throat swab specimens? Based upon the information you've learned, why was this type of medium used to identify group A streptococcus isolates?
• Based upon your knowledge of the 5 I's of microbiology, which type(s) of tests were used in this study to identify the group A streptococci in the specimens collected? How were the other four I's also used in this study? Give specific examples.
• The researchers hypothesized that if resistant strains of group A streptococci existed in schoolchildren, they probably are circulating in the general public as well. Describe how they tested this hypothesis and discuss the results of this experiment.
• Conduct additional research and discuss how group A streptococcal infections are treated today based upon the information learned from this research study in 2001 and recent studies.

Answer 1

1).Penicillin or amoxicillin is the antibiotic of choice to treat group A strep pharyngitis. There has never been a report of a clinical isolate of group A strep that is resistant to penicillin.

Throat culture. The group A streptococci have long been recognized as the Streptococcus sp. associated with acute pharyngitis. In a positive throat culture, group A streptococci appear as beta-hemolytic colonies among other normal throat flora which are usually alpha- or nonhemolytic on 5% sheep blood agar. S. pyogenes may appear as highly mucoid to nonmucoid; colonies are catalase negative. Optimal recovery of group A streptococci may be achieved by use of blood agar plates containing sulfamethoxazole-trimethoprim to inhibit some of the normal flora and growth under anaerobic conditions to enhance streptolysin O activity . Throat culture is still recognized as the most reliable method for detecting the presence of group A streptococci in the throat. Presumptive identification of the beta-hemolytic group A streptococci relies on susceptibility to bacitracin or a positive pyrrolidonylarylamidase test.

Serological identification of the organism involves testing for the presence of group-A-specific polysaccharide in the bacterium's cell wall using the Phadebact test is used for the presumptive identification of group A beta-hemolytic streptococci.

The other Four I's used like

Incubation- storing the plate at 35°c to 37°c for 48 hours

Inspection - while assessing the client or Mr.S mouth contains redness and Puss

Inoculation - inoculating a blood agar plate using the swab.