High virulence Proteus mirabilis strains cause acceleration of decay of fresh-cut fruits

The role of Proteus mirabilis on food safety has not been investigated before. Three P. mirabilis strains (swupm1, swupm2 and swupm3) isolated from fresh-cut fruits were shown to vary in swarming motility, with strains swupm1 and swupm2, but not swupm3 exhibiting the characteristic bull's-eye phenotype. Strains swupm1 and swupm2 grew faster and produced stronger biofilm than swupm3. These strains were all multidrug resistant and exhibited high virulence in Galleria mellonella (100% mortality at around 100 CFU inoculum) with swupm1 being the most virulent one. P. mirabilis was shown to be able to survive in fresh-cut cantaloupe at 4 °C and facilitate the growth of other bacteria. At 25 °C, P. mirabilis could significantly accelerate the decay of fresh-cut fruits. Headspace gas chromatography–ion mobility spectrometry (HS-GC-IMS) analysis showed that P. mirabilis strain swupm1 could cause dramatic changes in the volatile components of fresh-cut cantaloupe, such as ethyl acetate, ethanol and formic acid. This study indicates that P. mirabilis can accelerate the decay of fresh-cut fruits and that the virulence level of these strains seems to be closely associated with the adverse effect of such strains on food quality.