Detection and identification of Staphylococcus lugdunensis are not hampered by use of defibrinated horse blood in blood agar plates.

This research aims to prove that the use of defibrinated horse blood in agar plates does not inhibit the detection and identification of Staphylococcus lugdunensis, a pathogenic bacterium.

Introduction and Previous Research

• The bacterium in focus is Staphylococcus lugdunensis, a pathogen with properties resembling Staphylococcus aureus. Due to varying identification methods, the detection rates are inconsistent across different laboratories. A previously published work introduced certain criteria apt for detecting this bacterium, but these only appeared accurate when samples were cultured on Columbia sheep blood agar and not on agar with horse blood. This led to inconsistencies in detection rates across different regions.

Research Setting and Methodology

• This study was conducted at the Department of Clinical Microbiology, Central Hospital, in Växjö, Sweden. Over the span of ten years, the research team identified between 40 and 90 cases of S. lugdunensis annually, using methods such as assessing odor and colony pleomorphism, and performing a number of tests.
• The testing medium initially consisted of blood agar base with 5% human blood, but in 2009, it was changed to use 5% defibrinated horse blood instead. Following the change, the same criteria were used to identify S. lugdunensis.
• The research set out to determine S. lugdunensis’s detection rates from skin and soft tissue infection (SSTI) samples, which were then compared to the detection rates of S. aureus.

Results and Conclusions

• Even though the odor and β-hemolysis were slightly less distinct, the researchers did not witness any change in the isolation rate of either S. aureus or S. lugdunensis following the switch to the defibrinated horse blood agar. The ratios between the bacteria remained consistent, with S. aureus appearing 20 to 40 times more frequently per year.
• Overall, the study underlines that the use of defibrinated horse blood does not appear to interfere with the identification rate of S. lugdunensis, contradicting the concerns raised in some earlier studies. The authors suggest that factors other than the type of blood used in the agar may be more significant in influencing the detection of S. lugdunensis.