**4. Bacteriocins**

#### **4.1 Briefly definition and characteristics**

Bacteriocins are defined as a group of ribosomally produced antimicrobial peptides synthesized by both Gram-positive and Gram-negative bacteria. These molecules are characterized by its ability to act against closely related bacteria (narrow spectrum) or a diverse group of bacteria (broad spectrum) [82]. Bacteriocins can be dived in two general groups: Class I composed by peptides with post translational modifications and Class II composed by unmodified peptides. The production of bacteriocins is considered as a competition mechanism that allows bacteria to kill other bacteria that can compete with it for a certain niche or for nutrients. This suggests that many bacterial groups produce at least one bacteriocin, which means that there are still many bacteriocins to be discovered [83, 84]. Bacteriocins have a great antimicrobial capacity against their targets at nanomolar concentrations and exerts its activity by membrane permeabilization [85].

In recent years these molecules have received much interest in general and in particular their application in the food chain. The main reason is the search for alternatives to antibiotics due to the emergence of antimicrobial resistance [86]. While the use of antibiotics to treat enteric pathogens can cause harm to commensal bacteria in the intestinal microbiota, narrow-spectrum bacteriocins can be used in such a way that only the target bacteria are affected by the treatment [86]. On the other hand, the bacteriocins can be used as modular of the intestinal microbiota. For example, they can be used to establish a microbiota that favors the fattening of the chickens and therefore as natural substitutes for antibiotics as growth promoters [87]. In addition, today consumers are demanding food products where the use of chemicals is reduced to a minimum, and natural alternatives such as bacteriocins would be welcomed. Finally, another advantage is that the bacteriocins can be used directly or bacteriocin-producing probiotic cultures can be used resulting in the production of these molecules in situ. This would eliminate the process of production and purification of bacteriocins making their application more economical. But bacteriocins can be also useful to inhibit and eradicate biofilm biofilms in the food production chain (**Figure 3**).

#### **4.2 Applied studies on** *Salmonella* **biofilms**

One of the first studies in this field, two concentrations of enterocin AS-48 (25 and 50 mg/L) produced by *Enterococcus* were tested in combation with antibiotics and biocides against four *Salmonella* strains [88]. Concentrations of 25 mg/L of bacteriocin in combination with antimicrobials highly inhibited the growth of *Salmonella.* This bacteriocin also have effects on sessile biofilm cells. Preformed biofilms were treated with different combinations of bacteriocin and antimicrobials. Enterocin AS-48 at 50 mg/L had a synergic effect in combination with some

**Figure 3.**

*Mode of action of bacteriocin and bacteriocing-producing bacteria to inhibit and/or eradicate* Salmonella *biofilms.*

biocides. But the results differ between strain tested. In another study, Bag and Chattopadhyay [89] tested the antibiofilm activity of nisin alone or in combination with essential oil components. *S.* Typhimurium preformed biofilms were treated with MIC doses of nisin alone or in combination with ρ-coumaric acid. MIC doses of nisin only reduced in 20% biofilm formation. However, in combination with ρ-coumaric acid were reduced in almost 80%. This study demonstrated that nisin by itself have a low antibiofilm activity. Kim et al. [90] tested the crude bacteriocin DF01 derived from *Lactobacillus brevis* DF01 against *S.* Typhimurium biofilms. The incubation of this pathogen with bacteriocin DF01 reduced *S.* Typhimurium biofilm formation in almost 47%. However, the treatment of preformed biofilms with bacteriocin did not reduce biofilm mass. Therefore, the main action of DF01 bacteriocin is interfere in the biofilm formation process. In a similar study, Seo and Kang [91] evaluated the antibiofilm effect of bacteriocins purified from *Pediococcus acidilactici* K10 and HW01 in *S.* Typhimurium biofilm formed in stainless steel and chicken meat. Crystal violet staining method and fluorescence microscopy showed that those two bacteriocins reduces *S.* Typhimurium biofilm formation. In contrast to previous studies, this work demonstrates the ability of bacteriocins to also reduce the formation of biofilms in the food matrix itself.

In addition, instead of bacteriocins, the bacteriocin-producing bacteria themselves can also be used as alternative way to reduce *Salmonella* biofilm formation through competition, exclusion and displacement [92]. Das et al. observed that *L. plantarum* KSBT 56 isolated from Indian traditional food reduces in 2 log CFU/mL the cells present in *S.* Enteritidis biofilms [93]. Gómez et al. [94] used potential probiotic lactic acid bacteria (LAB) to inhibit the formation of food-borne pathogens biofilms. In this study they evaluated both bacteriocinogenic (sakacine and nisin producer strains) and non-bacteriocinogenic *Lactobacillus* and *Lactocococcus* strains against *S.* Typhimurium. The researchers preformed biofilms of LAB and after formation added a culture of *S.* Typhimurium. Preformed biofilms of LAB significantly reduced the attachment and biofilm formation of *Salmonella* in comparison to control. However, it is important to note that this reduction was not influenced by the production of bacteriocins. In another interesting study, the adhesion of food-borne pathogens as *S.* Typhimurium to wood commonly used in traditional cheese production in Sicilia was evaluated. The results showed that indigenous milk LAB highly adhere to wood surfaces while in samples artificially contaminated with *S.* Typhimurium, no adherence of this food-borne pathogen was observed. The researchers propose that biofilms formed by LAB in wood surfaces have a protective effect in biofilm formation by food-borne pathogens [95].

*An Overview of* Salmonella *Biofilms and the Use of Bacteriocins and Bacteriophages… DOI: http://dx.doi.org/10.5772/intechopen.98208*
