Staphylococcus aureus infection laboratory findings

Staphylococcus aureus infection Main page
Overview
Classification
Pathophysiology
Causes

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Laboratory Diagnosis

Depending upon the type of infection present, an appropriate specimen is obtained accordingly and sent to the laboratory for definitive identification by using biochemical or enzyme-based tests. A Gram stain is first performed to guide the way, which should show typical gram-positive bacteria, cocci, in clusters. Secondly, culture the organism in Mannitol Salt Agar, which is a selective medium with 7–9% NaCl that allows S. aureus to grow producing yellow-colored colonies as a result of salt utilization and subsequent drop in the medium's pH. Furthermore, for differentiation on the species level, catalase (positive for all species), coagulase (fibrin clot formation), DNAse (zone of clearance on nutrient agar), lipase (a yellow color and rancid odor smell), and phosphatase (a pink color) tests are all done. For staphylococcal food poisoning, phage typing can be performed to determine if the staphylococci recovered from the food to determine the source of infection.

Rapid Diagnosis and Typing

Diagnostic microbiology laboratories and reference laboratories are key for identifying outbreaks and new strains of S. aureus. Recent genetic advances have enabled reliable and rapid techniques for the identification and characterization of clinical isolates of S. aureus in real-time. These tools support infection control strategies to limit bacterial spread and ensure the appropriate use of antibiotics. These techniques include Real-time PCR and Quantitative PCR and are increasingly being employed in clinical laboratories.