Survival of Staphylococcus and other bacteria in skin prick test antigens solutions

Skin prick tests are commonly used for human allergy testing and determination. Because solutions are kept at 4 degrees C and patient's skin is cleaned, the same solutions are used on many patients with the same applicators without sterilization.

Our objectives were to determine whether a model bacteria could survive in antigen solutions and whether bacteria from patient's skin could be found in clinical antigen solutions.

Unused antigen solutions were spiked using Staphylococcus epidermidis. Concentration was followed from time = 0 to time = 21 days. Clinical samples consisted of antigen solutions used on a daily basis, from different hospital centers (n = 146). These were tested for total bacterial counts and detection of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci. Isolates were identified by 16S rDNA sequencing.

The concentration of S epidermidis remained stable over the 21 days. Twenty-three percent of the clinical antigen solutions contained bacteria. As expected, species like S aureus, S hominis, S epidermidis, and Micrococcus luteus were highly represented (62.5%) within a total of 20 different species.

Skin bacteria can survive in antigen solutions used in skin prick tests. Moreover, even if no MRSA were observed in field samples, nosocomial infections could be a concern if pathogens were present on the skin of some tested patients.