Use of Carnobacterium maltaromaticum cultures and hydroalcoholic extract of Lippia sidoides Cham. against Listeria monocytogenes in fish model systems

Minimally processed refrigerated ready-to-eat fishes may offer health risk of severe infection to susceptible individuals due to contamination by the psychrotolerant bacterium L. monocytogenes. In this work, inhibition of L. monocytogenes by a plant extract and lactic acid bacteria (LAB) was studied in model fish systems kept at 5 °C for 35 days. For that, fillets of tropical fish “surubim” (Pseudoplatystoma sp.) and hydroalcoholic extract of the plant Lippia sidoides Cham. (“alecrim pimenta”) were used. Fish peptone broth (FPB), “surubim” broth and “surubim” homogenate were inoculated with combinations of L. monocytogenes and bacteriocin-producing Carnobacterium maltaromaticum (C2 and A9b+) and non bacteriocin-producing C. maltaromaticum (A9b-), in the presence or absence of extract of “alecrim pimenta” (EAP). In all model systems, monocultures of L. monocytogenes and carnobacteria reached final populations ≥ 108 CFU/ml after 35 days, except for L. monocytogenes in “surubim” homogenate (104 CFU/ml). In FPB, EAP alone and combined with cultures of LAB inhibited L. monocytogenes but carnobacteria without EAP were only weakly antilisterial. In “surubim” broth, EAP alone did not prevent L. monocytogenes growth but cultures of carnobacteria combined or not with EAP inhibited L. monocytogenes, with more pronounced effect being observed for C. maltaromaticum C2, which produced bacteriocin. In “surubim” homogenate, EAP alone and combined with cultures of C. maltaromaticum A9b− and A9b+ were strongly inhibitory to L. monocytogenes, while C. maltaromaticum C2 with EAP caused transient inhibition of L. monocytogenes. No significant inhibition of L. monocytogenes was observed for carnobacteria in “surubim” homogenate without EAP. In conclusion, it was observed that the use of EAP and cultures of carnobacteria have potential to inhibit L. monocytogenes in fish systems and the applications should be carefully studied, considering the influence of food matrix.

Research highlights
► L. monocytogenes was inhibited by “alecrim pimenta” (EAP) and carnobacteria in fish.
► EAP inhibited L. monocytogenes in fish peptone broth with or without carnobacteria.
► In “surubim” fish broth listeria was inhibited by carnobacteria with or without EAP.
► Bacteriocin was produced by C. maltaromaticum C2 only, in “surubim” fish broth.
► In “surubim” fish homogenate, EAP strongly inhibited L. monocytogenes.