## 4 Discussion  
The results obtained in the present study indicate that _P. dendriiformis_ UJA2219 produces antimicrobial activity against bacteria at risk in foods as _E. coli_ E19, _S. enterica_ CECT 3197, _S. aureus_ CECT 976 and _B. cereus_ LWL1. The antibacterial activity can be recovered from cultured broths by cation exchange chromatography and also by reversed-phase chromatography. To study the antimicrobial effect of these partially purified fractions, a food model was chosen, which was a homemade vegetable puree. Previous studies carried out in our group [6] indicated that the _Paenibacillus_ genus presented antimicrobial activity and modified the growth of pathogens present in food. The annotation of the genome of _P. dendriiformis_ UJA2219 ([PERSON] et al., in preparation) suggests that this bacterial strain may produce secondary metabolites identified as 1 RiPP protein (paeinodin) and NRP proteins, such as paeinibacterium, peligpectin and paeinlamicin. It could be that the addition of _P. dendriiformis_ or any of its metabolites to a food model, in this case a homemade vegetable puree, generates an antimicrobial effect and/or a modification of microbial biodiversity. The results obtained on microbial counts in puree inoculated with _P. dendriiformis_ UJA2219 indicated that the bacterium failed to inhibit the puree microbiota, except for the weak decrease of presumptive _Enterobacteriaceae_ detected at day 7 of incubation at 25 \({}^{\circ}\)C. These results could be due to a low production of antimicrobials in the puree by the inoculated strain. In situ production of antimicrobial substances is markedly influenced by many factors, such as pH, aeration, incubation temperature, time of incubation, available nutrients, the food matrix and the competing microbiota [35]. In published studies of the efficacy of other _Paenibacillus_ strains in food, it has been shown to reduce the populations of _Bacillus subtilis_ and _Listeria_ in milk, which makes it promising for the biopreservation of dairy products [36]. However, strain UJA2219 did not show antilisteria activity in the  
Figure 6: Principal coordinates analysis of puree samples treated with elutes or with _Paenibacillus dendriiformis_ UJA2219. C, untreated controls. P, puree inoculated with _P. dendriiformis_ UJA2219. E, puree treated with partially-purified extract (1.5 M eluate). A, puree treated with partially-purified extract (60% acetonitrile). preliminary tests. Another _Paenibacillus_ strain was effective against _Clostridium botulinum_ in purere [37]. Most of these studies are based on assays performed with the strain in question, not with the purified fractions. In the present study, the treatments carried out indicated that partially-purified preparations from _P. dendriiformis_ UJA2219 cultured broths exerted an antimicrobial effect on the vegetable purece incubated at 4 \({}^{\circ}\)C and 25 \({}^{\circ}\)C that depended on the bacterial group. Antibacterial activity was more pronounced at 25 \({}^{\circ}\)C than under refrigerated conditions, suggesting that it could help the preservation of these purees outside of refrigeration. At 25 \({}^{\circ}\)C, for all mesophilic aerobic bacteria and lactic acid bacteria, an efficacy of the eluate from NaCl was observed during the first two days, but not after 7 days. For presumptive _Bacillus_, an efficacy of the two eluates (A and E) was observed after 7 days. However, from the inhibitory spectrum of the eluates, we would expect a greater reduction of the _Bacillus_ population. Nevertheless, we should consider that there may be great differences in strain sensitivity, and that the possible _Bacillus_ strains found in the puree may not necessarily be as sensitive as the LWL1 strain used in the assays of antibacterial activity.