**18.1 Lactic acid bacteria**

*Pathogenic Bacteria*

The differences in the genome targeted for further screening by using mutagenesis and virulence assays in models of *in vivo* infections. The current in vivo models

Murine used for infection models that imitate the human mood of infection are

The results of current studies of pathogenicity island mutant have explained the effectiveness in finding their influence towards virulence. PAI I536–PAI V536 are five pathogenic island of *E. coli* and analyzed for their involvement in

Quorum-sensing systems controlled many virulent factors in *P. aeruginosa* such as the production of biofilm and the secretion of toxins [76]. Previously studies showed that insufficiency of the quorum-sensing systems can decrease the virulence in acute infection murine models. The use of insufficient quorum-sensing systems in a mutants murine burns injury model cause a decrease in mortality of the murine model. The ability of the bacteria to spread from the site of infection is also reduced. Lodise Jr. et al. reported the same results for a *LasR* mutant of

Quorum-sensing is a control system for coordination of gene expression in bacteria. As the level of an auto inducer goes to a threshold level, they caused the binding to specific bacterial receptors, in result gene transcription is initiated. In the result

• The wax moth *Galleria mellonella* the plant *Arabidopsis thaliana*,

commonly used for *P. aeruginosa* infection are:

*Circular representation of the* P. aeruginosa *genome.*

• The fruit fly *Drosophila melanogaster.*

not common [74].

**Figure 4.**

infection [75].

**17. Quorum-sensing**

• The nematode worm *Caenorhabditis elegans*

**24**

PAO1 [77].

Food borne pathogenic and spoilage microorganisms are affected by the lactic acid bacteria (LAB) [78, 79], for example the growth of *B. subtilis* inhibited as it spoils bread [80]. Studies showed that *Lactobacillus* strains reported an inhibitory activity against *E. coli* [81]. Proteolytic activities and lipolytic activities of psychrophilic *Pseudomonas* causing food spoilage [82]. *Lactobacillus* species produced hydrogen peroxide which inhibits the growth of *Pseudomonas* species [42].

Lactic acid functions as the natural compound having antimicrobial activity and generally recognized as safe. Lactic acid has ability to inhibit the growth of Gramnegative species of *Pseudomonadaceae* and *Enterobacteriaceae* [83]. Lactic acid is used as a bio-preservative in fermented products.

Ribosome synthesized the bacteriocin extracellularly and secreted peptide complexes or bioactive peptides havingbacteriostatic orbactericidal effect [84]. Smart et al. reported *Lactococcus lactis produced a bacteriocin called* Nisin, which is studied in detailed, and applied as stabilizer to certain foods worldwide [85]. Bacteriocins are harmless due to quick proteolytic degradation by the gastrointestinal tract enzymes [86, 87].

Four major classes of bacteriocins are


iii.Larger heat-labile proteins

iv.Complex bacteriocins [52, 88].

Most of bacteriocin are related to classes I and II. Proteinaceous compounds which are synthesized by ribosomes have bactericidal effect towards Gram-positive bacteria as compared to Gram-negative which have an additional layer composed of proteins, lipopolysaccharides and phospholipids [89–91].

Bacteriocins considered as potentially food-grade to increase food safety these can decrease the occurrence of foodborne diseases. These helped to lessen the use of chemical based preservatives and intensity of heat treatments for food preservations, resulting more naturally preserved food that is richer in nutritional and organoleptic properties [92].

Schillinger and Lucke has observed that the fact that most of bacteriocins have a narrower host range, which made them effective against closely related bacteria having same nutritive demands [93]. Lactic acid bacteria produced lactic acid functioning as a natural antimicrobial agent, having a generally known as safe to use. The growth of many Gram-negative species *Pseudomonadaceae* and *Enterobacteriaceae was* inhibited by the lactic acid bacteria. Forbio-preservation of the naturally fermented products lactic acid is used instead of other organic salts. Lactic acid is penetrates to cytoplasmic membrane of the organisms, which result in disruption of trans-membrane proton motive force and decrease in intracellular pH [94].
