Environmental DNA analysis of honey samples for the detection of Serratia marcescens and Malpighamoeba mellificae across Australia

The bacterium Serratia marcescens and the protozoan Malpighamoeba mellificae are opportunistic and rare pathogens, respectively, that can compromise digestive health in honey bees (Apis mellifera). To assess their presence in Australia, we applied an environmental DNA (eDNA) approach using honey (n = 135) collected across multiple states. The eDNA was extracted using an in-house optimised bead-beating silica-based method, and extraction success was confirmed by amplifying honey bee mitochondrial DNA using end-point PCR. S. marcescens was detected in 58% of the samples (78/135), while M. mellificae was not detected, highlighting honey-based eDNA analysis as a valuable surveillance tool for emerging bee health threats. This study provides the first evidence of S. marcescens in Australian apiaries and emphasises the need for targeted surveillance of M. mellificae and other understudied pathogens to strengthen early detection capacity and overall health of the managed honey bee population.