Experiment 2: Phage Detection Under Field Conditions Using the ISO 6579:2017

As result from the experiment 1, the aim of experiment 2 was to assess the feasibility of isolating new phages from poultry field samples collected according to the Salmonella NCP using the MRSV as a screening media. To this end, in 2021, 93 MSRV agar plates suspected to be positive to Salmonella, corresponding to 49 different farms, different poultry production and type of samples, were selected (Table 2).

Distribution of field sample types by production method.

To establish the optimal sampling spot from MSRV plates and bearing the results from experiment 1 in mind, a sample was taken with an inoculating loop from the lytic halo zone (n = 67) together with media samples from the milky-looking bacterial growth around the inoculum (n = 93). These plates were categorized as “plates suspicious for phage detection” (Figure 1B). In this sense, plates that did not show whitish growth or pale appearance, and therefore were not suspected to be positive for Salmonella, were not selected for the experiment. A total of 160 plate samples were recovered and analyzed for phage isolation. Each plate sample was tested against the 9 Salmonella serovars through spot test assay with the double-layer agar technique, as described above in the experiment 1, performing a total of 1,440 analysis.