Effect of collection tubes on synovial fluid bacterial culture.
Introduction Silica sprayed tubes (SST) are often used to transport
synovial fluid samples in equine practice. They promote coagulation of
the sample. The objective of the study is to evaluate the effect of SST
on bacterial culture. Materials & methods The study was divided into
two parts: sterile saline (Part A), and synovial fluid (Part B). Four
common bacteria associated with equine synovial sepsis were used:
Streptococcus pyogenes, Escherichia coli, Staphylococcus aureus, and
methicillin-resistant Staphylococcus aureus. Three collection-tubes were
used: STT, plain (No-additives) and brain & heart infusion (BHI) broth.
Bacteria were cultured in horse blood agar plates for 48h. Outcome
variables were negative culture, positive culture, and total number of
forming colony units (FCU). Statistical analysis was performed using
Mann-Whitney U test, significance was set at p< 0.05. Results
The total number of agar plates read was 1557. Total negative cultures
were 24/779 on saline and 3/778 on synovial fluid. In broth maximum
growth FCU was achieved after 8h for both saline and synovial fluid for
all bacteria. Streptococcus pyogenes and Escherichia coli produced a
significantly lower number of FCU when in SST compared to plain or broth
after 4h. Staphylococcus aureus (ATCC & MRSA) only after 24h.
Discussion Silica containing tubes reduced bacterial proliferation,
whilst the use of a BHI broth provided the highest bacterial burden in
the sample. Use of SST may have a negative effect on bacterial
proliferation in samples obtained from clinical cases.