Zoonotic Infections: A Case Study

Treatment of zoonotic infections in both animals and humans is not only a humanitarian action, but also shortens the length of sickness and, hence, the period of communicability, thereby providing a valuable measure in countering and controlling of the spread of zoonotic diseases (Mantovani, 1992; Webber, 2005). However, the diminishing utility of current antibiotics in the face of rising bacterial resistance and the stagnant development of new antibiotics constitute the main obstacles for achieving an effective treatment which further underscores the urgent need for the development of alternative therapeutic options (Mohamed et al., 2014). This scourge is further compounded by intracellular zoonotic pathogens, such as Mycobacterium, Salmonella, Listeria, and Brucella that reside and thrive inside mammalian cells (Seleem et al., 2009a, 2009b; Nepal et al., 2015). Treatment of infections caused by these intracellular pathogens is very challenging because most antibiotics are unable to access intracellular replicative niches and achieve the optimum therapeutic concentrations within the infected cells (Seleem et al., 2009a, 2009b). For instance, the mortality rate in human listeriosis remains high (20-30%) even

with the early interference with antibiotics (Hamon et al., 2006; Swaminathan and Gerner-Smidt, 2007; Watson, 2009).
These challenges have sparked efforts to target intracellular zoonotic agents utilizing different approaches (Alajlouni and Seleem, 2013; Kuriakose et al., 2013; Nepal et al., 2015).

One potential novel alternative therapeutic approach to treat infections caused by intracellular zoonotic pathogens that has shown promise in recent years is silencing essential genes with a peptide nucleic acid (PNA) (Alajlouni and Seleem, 2013; Rajasekaran et al., 2013). In addition to the hybridization affinity to their target DNA and RNA sequence, and specificity of PNA molecules to silence genes, these molecules are characterized by chemical and enzymatic stability conferred by their pseudopeptide backbone as well as low toxicity to host tissues (Good and Nielsen,

1998a).
However one significant limitation of these hydrophilic macromolecules is that their cellular uptake is controlled by the high selectivity imposed by cellular membranes (De Coupade et al., 2005; Munyendo et al., 2012); this constitutes a major challenge for the successful utilization of PNA gene inhibition therapeutics to target intracellular pathogens (Tan et al., 2005). Additionally, effective delivery of such large molecules across stringent bacterial cell walls can be a daunting task. Therefore, there is a need for an appropriate carrier system to deliver PNAs specifically to intracellular replicative niches and eliminate resident pathogen(s) effectively. Cell-penetrating peptides (CPPs), consisting of positively charged residues, have emerged as extremely efficient and crucial allies to PNAs and a wide range of cell-membrane impermeable cargos. These agents help molecules, such as PNAs, overcome challenging delivery barriers to permit their entry into infected cells (Mishra et al., 2009).
The present study was undertaken to:
- Assess the ability of the anti-rpoA PNAs to inhibit gene expression in Listeria at pure culture.
- Examine the ability of the anti-rpoA PNAs to inhibit Listeria gene expression in infected macrophages.
- Study the impact of anti-rpoA PNAs on expression of Listeria virulence genes.
- Determine the pathogenicity of different Listeria monocytogenes strains to C. elegans.
- Explore the in vivo efficacy of the anti-rpoA PNAs in treatment of Listeria infected C. elegans.