Ba310

Sediment samples were rinsed on a sieve (0.5 mm) with tap water and the remaining material was sorted under a stereoscopic microscope Leica EZ4. Isolated macroinvertebrates were placed in separate vials with 70% ethanol. A similar procedure was applied for macrophytes with additional careful examination and cleaning of each macrophyte sample.
For the identification of chironomid larvae, native slides for immediate inspection were prepared using ethanol as a mounting medium, and for some specimens, it was necessary to prepare permanent slides in Berlese mounting medium. Identification keys: Caspers and Cranston,⁴⁸
Wiederholm,⁴⁹
Schmid,⁵⁰
Brooks et al.,⁵¹
Moller Pillot,^{52 –54 (link, link)} Bitušík and Hamerlík,⁵⁵
and Vallenduuk⁵⁶
were used for identification to the lowest possible taxonomic level, under a Motic BA310 microscope.

A total of 42 Listeria spp. strains were considered as reported in Table 1. Part of these strains, belonging to the European Union Reference Laboratory (EURL) set, were supplied by the National Reference Laboratory for Listeria monocytogenes (strains from 1 to 25), while the other strains belong to the internal laboratory collection and were isolated from food of animal origin (strains 26 to 31) or environmental samples (strains from 34 to 42). Also two American Type Culture Collection (ATCC) strains were used (strains 32 and 33). Strain stocks were kept at -80°C until a loop (~10 μL) was transferred in Tryptic Soy broth tubes, subsequently incubated at 37°C for 48h. At the end of the incubation period, cells were harvested in exponential growth phase, defined as a relative change in optical density (OD) of 0.05-0.2 at 540 nm (6320D spectrophotometer; Jenway, Staffordshire, UK). Cell concentration of each bacterial strain suspension was calculated by counting under a phase-contrast microscopy (BA 310, Motic, Barcelona, E) and, if necessary, was diluted in sterile saline water (0.85% NaCl), to obtain a concentration of 8 Log CFU/mL.