Question

NATIONAL CENTER FOR CASE STUDY TEACHING IN S Part Il-Identifying the Pathogen A sample obtained from both Brent and Kristen was cultured using trypticase soy agar with 5% sheep red blood in the local hospital lab. The lab microbiologist observed yellow colonies characteristic of the common pathogen Staphylococcus aureus. It was also concluded that both cultures were coagulase positive, another characteristic of S aureus "So, I just had a nasty Staph infection?" Brent asked his doctor. "Yes, and I'm glad the antibiotic took care of it," said the doctor. "Me too," said Brent. "They think I just have a Staph infection," Kristen told her mom. "Yes, but why didn't your antibiotics get rid of it?" asked Kristen's mom. "I don't know. I just hope it doesn't get any worse," said Kristen. Questions 1. What do you already know about S. aureus? (See note # 1 on the Case Notes Handout.) 2. What additional info about S. aureus can you find? (Use the Internet or your textbooks). susceptible to antibiotics in Brent's case but not in 3. List hypotheses that would explain why S. aureus was Kristen's case.

Answer 1

Ans.1) Staphylococcus aureus is gram positive bacteria and round shaped. These bacteria are part of normal microbiota of skin. Its shows positive catalase test and nitrate reductase test.

Ans.2) Staphylococcus aureus is a commensal of human microbiota and also are oppurtunistic pathogen and causes skin infection, respiratory infections and degestive infections. It produces an exotoxin protein. It is a type of facultative anaerobe i.e. it is able to do anaerobic respiration in absence of oxygen otherwise it normally perform aerobic respiration.

Ans.3) Non- treatment of S. aureus infection in case of Kristen even by anti-biotics is due to infection caused by anti-biotic resistant strain. One of the example of such strain is methicillin-resistant S. aureus (MRSA). This anti-biotic resistant genes are usually found over plasmid DNA and these resistant genes are passed from resistant strain to non-resistant allele by horizontal transffer.