Abstract
Brucellosis is a worldwide zoonosis that once established, is very difficult to eradicate with persistence in animals, environment and humans. The classical Brucella species, B. abortus, B. melitensis and B. suis affect mainly cattle, small ruminants, and pigs, respectively, causing abortions and infertility. Detection of bacteria in live animal can be very challenging, since infected animals do not show systematically clinical symptoms and excretion of bacteria in bodily fluids can be rare and/or intermitted. Sampling with swabs (genitalia, tissue lesions and contaminated environments) from seropositive animals with or without clinical symptoms, can be very useful for bacterial detection and isolation in bacteriological and/or molecular diagnostics. However, no comparison of swab types has been performed in order to ensure successful detection of Brucella. The aim of this study was to compare main commercially used types of swabs for sampling and diagnostics of Brucella spp., and determine the optimal storage conditions for testing. To achieve this, we tested bacterial and molecular methods for detection of classical Brucella species using nine swab types, all with different tip materials, treated immediately after spiking, after 72 h at +4°C, and after 72 h at -20°C. Our results show how storage conditions, freezing (-20°C) vs refrigeration (+4°C), negatively affect Brucella survival even on swabs compared to direct treatment, while no impact on qPCR detection was observed. We demonstrate that Brucella recovery and detection capacity strictly depend on swab tips type, independent of the storage conditions. In particular, bacterial survival is highly variable regarding the type of swabs used for isolation and storage conditions, while molecular detection is uniform. Interestingly, a new type of flocked swab, which includes a conservation medium, showed the highest levels of recovery in both bacterial culture and qPCR, irrespective of the storage conditions (20% higher with than without protective medium). The use of this swab provide increased Brucella viability at refrigeration and freezing temperatures, which significantly increases the diagnostic sensitivity compared to the other tested swabs. To further evaluate performances of flocked swabs under field condition, a multi-centric study targeting infected animals will be conducted within the European national Laboratory Network.
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