**3.8 Target modification**

*Pseudomonas aeruginosa* - Biofilm Formation, Infections and Treatments

**3.5 Aminoglycoside-modifying enzymes**

(resistant to tobramicin and gentamicin) [67].

**3.6 Low outer membrane permeability**

may cause membrane impermeability [69].

mechanisms are observed in cumulative resistance.

resistance that can be observed in *P. aeruginosa.*

**3.7 Active efflux pumps**

transferable aminoglycoside modifying enzymes (AMEs), low permeability of the outer membrane, active efflux and, in rare cases, target modification [62–64].

AMEs inactivate the aminoglycoside by adding the antibiotic molecule to a phosphate, adenyl or acetyl radical, and thus modified antibiotics minimize the binding affinity of the bacterial cell (30S ribosomal subunit) to its target [65, 66]. Aminoglycoside phosphoryl transferases (APHs), aminoglycoside adenylyl transferases (also known as nucleotidyltransferases) (AADs or ANTs) and aminoglycoside acetyltransferases (AACs) are three types of AMEs involved in aminoglycoside alteration. The following AMEs are most commonly expressed by *P. aeruginosa:* AAC(69)-II (resistant to gentamicin, tobramycin and netilmicin), AAC(3)-I (resistant to gentamicin), AAC(3)-II (resistant to gentamicin, tobramycin and netilmicin), (69)-I (resistant to tobramycin, netilmicin and amicacin) and ANT(29)-I

Membrane impermeability or reduced permeability is a mechanism known to provide resistance to many antibiotic forms, including aminoglycosides, β-lactams and quinolones [68]. For instance, this resistance mechanism is often encountered in cystic fibrosis isolates that are continually under antibiotic attack. Several mechanisms, such as lipopolysaccharide (LPS) modifications, alteration of membranous proteins involved in substratum absorption, and inactivation of enzymatic complexes involved in the energetic membrane necessary for transport system activity,

The combination of low membrane permeability and active efflux pumps is partially due to the natural resistance of *P. aeruginosa* to many groups of antibiotics. *P. aeruginosa's* efflux systems involved in antibiotic resistance belong to the family of resistance-nodulation-division (RND) [70]. In order to confer resistance to several antibiotics, four major efflux systems have been described: MexAB-OprM, MexCD-OprJ, MexEF-OprN and MexXY-OprM. These systems consist of three proteins: (1) the efflux pump protein found in the cytoplasmic membrane (MexB, MexD, MexF and MexY), (2) the pore-acting outer membrane protein (OprM, OprJ and OprN) and (3) A protein in the periplasmic space that bridges the cytoplasmic and outer membrane proteins (MexA, MexC, MexE and MexX). In both natural and acquired resistance, MexAB-OprM and MexXY-OprM are active, whereas only the other two

Acquired resistance is observed following mutations in the regulatory systems

that can be caused by antibiotic pressure and that can confer resistance to all groups of antibiotics upon over-expression of these efflux systems. Polymyxins, except [69]. Resistance to multiple groups of antibiotics that are substrates of these efflux systems can be caused by exposure to a single antibiotic. Quinolones are substrates of all efflux systems and are an important trigger factor that can generate cross-resistance to efflux systems of several major classes of antibiotics, including β-lactams and aminoglycosides, for pseudomonal therapy [71]. It is understood that efflux systems confer a moderate degree of resistance, but they typically act simultaneously with other mechanisms of resistance, thus taking part in the high-level

**82**

Due to the low affinity of the drug to the bacterial ribosome, bacteria may be resistant to aminoglycosides. This can be achieved by 16S rRNA methylation by target modification. Various 16S rRNA methylases have been identified for *P. aeruginosa*: RmtA, first reported in clinical isolates of *P. aeruginosa* resistant to aminoglycosides and conferred resistance to all parenterally administered aminoglycosides, including amicacin, tobramycin, isepamicin, kanamycin, arbecacin and gentamicin, secondary 16S rRNA methylases including RmtB, ArmA and RmtD [72].

## **3.9 Resistance to fluoroquinolones**

Resistance to fluoroquinolones arises by mutation in the DNA gyrase or topoisomerase 1 V coding bacterial chromosome gene or by successful drug transport out of the cell [73]. Topoisomerase 1 V mutations can occur in gyrA / gyrB genes within the motif of the quinolone-resistant determinative region (QRDR), which is considered to be the active site of the enzyme. This contributes to the altered amino acid sequences of the subunits A and B, and hence to the altered topoisomerase II with a low affinity for quinolone molecules. As a result of point mutations in parC and parE genes encoding the ParC and ParE enzyme subunits, modifications of a secondary target (topoisomerase IV) occur. The over-expression of efflux includes other types of fluoroquinolone tolerance in *Pseudomonas*. Mutations in the nalB, nfxB and nfxC genes, resulting in overexpression of MexA-MexB-OprM, MexC-MexD- OprJ and MexE- MexF- OprN fallowing efflux [74].

## **3.10 Biofilm-mediated resistance**

A biofilm is an aggregate of microorganisms that bind to each other on a living or non-living surface and are embedded in an extracellular polymeric (EPS) matrix of self-produced substances, including exopolysaccharides, proteins, metabolites, and eDNA [75, 76]. The microbial cells grown in biofilms are less sensitive than the cells grown in free aqueous suspension to the antimicrobial agents and the host immune response [77]. Even bacteria that are deficient or lack protective mutations in their intrinsic resistance, when they grow in a biofilm, they can become less susceptible to antibiotics [78]. The general mechanisms of biofilm-mediated resistance that protect bacteria from antibiotic attack include antibiotic penetration prevention, altered microenvironment that induces slow biofilm cell growth, adaptive stress response induction, and differentiation of persistent cells [78–80].

*P. aeruginosa* causes chronic lung infections in CF patients and, through the production of DNA, proteins and exopolysaccharides, forms a biofilm on lung epithelial cell surfaces. The regulation of the formation of *P. aeruginosa* biofilm is multifactorial and mainly depends on quorum sensing systems, GacS / GacA and RetS / LadS two-component regulatory systems, exopolysaccharides and cdi- GMP [81]. Quorum sensing is a form of communication between bacterial cells and cells that regulates gene expression in response to changes in cell population density. *P. aeruginosa* has three major systems of quorum sensing, LasILasR, RhlI-RhlR, and PQS-MvfR, all of which contribute to mature and differentiated biofilm formation. During biofilm formation, *P. aeruginosa* undergoes numerous physiological and phenotypic changes [82]. For example, *P. aeruginosa* strains convert to a mucoid phenotype in CF chronic infection that displays upregulated production of alginate driven by the CF microenvironment, enabling the formation of colonies of biofilms. Due to its ability to show swarming and twitching motility, *P. aeruginosa* flagellum is important for the initiation of biofilm formation. However, *P. aeruginosa* significantly

decreases flagellum expression after surface attachment and may also permanently lose the flagellum due to genetic mutations, reducing host immune response activation, allowing *P. aeruginosa* to evade immune detection and phagocytosis [83].

## **4. The global economic scenario of antibiotic resistance**

It is still an immense global challenge to quantify the exact economic effect of resistant bacterial infections. Measuring the distribution of the disease associated with antibiotic resistance is a crucial prerequisite in this situation. A major economic burden for the entire world is antibiotic resistance. In the USA alone, 99,000 deaths are caused annually by antibiotic-resistant pathogen-associated hospital-acquired infections (HAIs). Approximately 50,000 Americans died in 2006 because of two popular HAIs, namely pneumonia and sepsis, costing the US economy around \$8 billion [84]. Patients with antibiotic-resistant bacterial infections need to remain in the hospital for at least 13 days, creating an extra 8 million hospital days each year. There have been estimates of costs of up to \$29,000 per patient infected for an antibiotic-resistant bacterial infection. In total, economic losses of approximately \$ 20 billion were recorded in the US, while losses of approximately \$35 billion per year were also recorded in terms of loss of productivity due to antibiotic resistance in health care systems [85].

A worst-case scenario could emerge in the coming future, according to the analysts of the Research and Development Corporation, a US non-profit global organization, where the planet could be left without any effective antimicrobial agent to treat bacterial infections. In this case, the global economic burden will be nearly \$120 trillion (\$3 trillion per annum), roughly equal to the entire actual annual health care budget of the United States. In general, the world population will be significantly affected: about 444 million people will succumb to infections as of 2050, and birth rates will decrease rapidly in this scenario [86, 87]. These losses are calamitous, but these estimates reflect imperfect images of the economic costs of antibiotic resistance due to data limitations such as the inclusion of total conditions and resistance-susceptible diseases. The use of antibiotics in the livestock and food industries is another very critical trait of antimicrobial resistance (AMR), that was missing from the investigation. It is an important player in the rising AMR, likely causing its own projected economic losses. There is also a misappropriation of the use of antimicrobials as growth promoters in many developing countries. This activity has been outlawed in the European Union since 2006 [88, 89].

#### **5. Novel alternative antimicrobial therapy for** *P. aeruginosa* **treatment**

The overuse and misuse of antibiotics, which can lead to unwanted side effects and the production of drug-resistant bacterial strains, is a growing public health issue. The production of new antibiotics, in addition, is very limited and timely. The development of innovative therapeutic approaches to the treatment of infections with *P. aeruginosa* is therefore highly desirable and has received further interest over the past decade. These innovative therapeutic techniques, which involve antimicrobial peptides, phage therapy, inhibition of quorum sensing as well as the use of iron chelation, nanoparticles, probiotics and vaccine strategies.

#### **5.1 Antimicrobial peptides**

A number of species, from bacteria to animals, develop antimicrobial peptides (AMPs), also called host defense peptides, and they are active against a wide range

**85**

*Chemotherapy and Mechanisms of Action of Antimicrobial Agent*

of microorganisms [90]. There is no complete understanding of the mode(s) of operation of AMPs. It is widely agreed that the cytoplasmic membrane is attacked by AMPs, leading to cell death [91]. AMPs have also been shown to possess anti-biofilm and immunomodulatory properties, in addition to antimicrobial activity, AMPs have been proposed as an alternative to traditional antibiotics to battle bacterial infections as a result of their broad-spectrum activity; AMPs exhibit rapid killing kinetics, low mediated resistance levels, and low host toxicity [92]. Many antimicrobial peptides, including GL13 K, LL-37, T9W, NLF20, cecropin P1, indolicidin, magainin II, nisin, ranalexin, melittin, and defensin, have demonstrated powerful antimicrobial effects of either direct bactericidal effects or biofilm disruption against *P. aeruginosa* [93]. In addition, by facilitating antibiotic absorption, disrupting biofilm formation or inhibiting bacterial quorum, some AMPs have demonstrated synergy with traditional antibiotics against several bacteria, including *P. aeruginosa* [94]. For instance, it has been shown that the clearance of *P. aeruginosa* biofilm was increased by a combination of GL13 K with tobramycin [95]. In 2017, Zheng et al. [96] observed that when combined with tetracycline in vitro, the minimum inhibitory concentration of cecropin A2 against clinical isolates of *P. aeruginosa* was reduced 8-fold.

By inducing lysis, bacteriophages (phages) are viruses that infect and destroy bacteria [97]. In 1915, the British bacteriologist Frederick Twort first discovered phages. Two years later, Félix d'Herelle made a similar discovery independently in Paris and presented the phage therapy notion. With the advent of antibiotic therapy, phage therapy was abandoned in several countries, but has been continuously developed in Eastern European countries with facilities in Warsaw, Poland, and Tbilisi, Georgia [98]. Shotgun metagenome sequencing showed that there were antipseudomonal phages in the phage cocktails sold in pharmacies in Georgia and Russia [99]. The successful treatment of infections with MDR *P. aeruginosa* has been reported in a few case reports from Belgium and the US, but has not gained broad acceptance in the Western world [100]. Phage therapy has many benefits, including replication at the infection site, high precision for attacking bacteria without effects on commensal flora, less side effects than other therapies, antibiotic-resistant bacteria bactericidal activity and simple administration [101]. The use of phages as an alternative to antibiotics has been extensively studied for the treatment of *P. aeruginosa* infections. There are 137 different phages that have been characterized to date that target the *Pseudomonas* genus [102]. Many in vitro and in vivo studies have been performed to test the efficacy of phages against chronic infections of *P. aeruginosa*. For instance, co-incubation of phage PA709 with the clinical strain *P. aeruginosa* 709 has been shown to significantly reduce the viability of *P. aeruginosa*. Another research found that intranasal administration of P3-CHA bacteriophage to mice receiving a lethal dose of *P. aeruginosa* strain CHA substantially improved the

rate of survival and reduced the bacterial load in the lungs [103].

identified during these clinical trials [106].

Another benefit of phage therapy is that phages can be genetically modified as vehicles to transport bacteria with antimicrobial agents, thus increasing treatment efficacy [104]. While phages have been shown to be successful in vitro and in animal models against bacterial infection, only a small number of phage therapy clinical trials have been performed to date. The reasons for this include: safety issues about post-treatment phage clearance and impurity of phage preparations; poor stability of phage preparations; and lack of knowledge of the comprehensive phage mode of action and bacterial resistance to phage growth [105]. In clinical trials, the use of phages against *P. aeruginosa* infections has been studied in patients with venous leg ulcers, burn wounds and otitis, and no adverse reactions have been

*DOI: http://dx.doi.org/10.5772/intechopen.95476*

**5.2 Phage therapy**

*Chemotherapy and Mechanisms of Action of Antimicrobial Agent DOI: http://dx.doi.org/10.5772/intechopen.95476*

of microorganisms [90]. There is no complete understanding of the mode(s) of operation of AMPs. It is widely agreed that the cytoplasmic membrane is attacked by AMPs, leading to cell death [91]. AMPs have also been shown to possess anti-biofilm and immunomodulatory properties, in addition to antimicrobial activity, AMPs have been proposed as an alternative to traditional antibiotics to battle bacterial infections as a result of their broad-spectrum activity; AMPs exhibit rapid killing kinetics, low mediated resistance levels, and low host toxicity [92]. Many antimicrobial peptides, including GL13 K, LL-37, T9W, NLF20, cecropin P1, indolicidin, magainin II, nisin, ranalexin, melittin, and defensin, have demonstrated powerful antimicrobial effects of either direct bactericidal effects or biofilm disruption against *P. aeruginosa* [93]. In addition, by facilitating antibiotic absorption, disrupting biofilm formation or inhibiting bacterial quorum, some AMPs have demonstrated synergy with traditional antibiotics against several bacteria, including *P. aeruginosa* [94]. For instance, it has been shown that the clearance of *P. aeruginosa* biofilm was increased by a combination of GL13 K with tobramycin [95]. In 2017, Zheng et al. [96] observed that when combined with tetracycline in vitro, the minimum inhibitory concentration of cecropin A2 against clinical isolates of *P. aeruginosa* was reduced 8-fold.

#### **5.2 Phage therapy**

*Pseudomonas aeruginosa* - Biofilm Formation, Infections and Treatments

**4. The global economic scenario of antibiotic resistance**

activity has been outlawed in the European Union since 2006 [88, 89].

chelation, nanoparticles, probiotics and vaccine strategies.

**5. Novel alternative antimicrobial therapy for** *P. aeruginosa* **treatment**

The overuse and misuse of antibiotics, which can lead to unwanted side effects and the production of drug-resistant bacterial strains, is a growing public health issue. The production of new antibiotics, in addition, is very limited and timely. The development of innovative therapeutic approaches to the treatment of infections with *P. aeruginosa* is therefore highly desirable and has received further interest over the past decade. These innovative therapeutic techniques, which involve antimicrobial peptides, phage therapy, inhibition of quorum sensing as well as the use of iron

A number of species, from bacteria to animals, develop antimicrobial peptides (AMPs), also called host defense peptides, and they are active against a wide range

decreases flagellum expression after surface attachment and may also permanently lose the flagellum due to genetic mutations, reducing host immune response activation, allowing *P. aeruginosa* to evade immune detection and phagocytosis [83].

It is still an immense global challenge to quantify the exact economic effect of resistant bacterial infections. Measuring the distribution of the disease associated with antibiotic resistance is a crucial prerequisite in this situation. A major economic burden for the entire world is antibiotic resistance. In the USA alone, 99,000 deaths are caused annually by antibiotic-resistant pathogen-associated hospital-acquired infections (HAIs). Approximately 50,000 Americans died in 2006 because of two popular HAIs, namely pneumonia and sepsis, costing the US economy around \$8 billion [84]. Patients with antibiotic-resistant bacterial infections need to remain in the hospital for at least 13 days, creating an extra 8 million hospital days each year. There have been estimates of costs of up to \$29,000 per patient infected for an antibiotic-resistant bacterial infection. In total, economic losses of approximately \$ 20 billion were recorded in the US, while losses of approximately \$35 billion per year were also recorded in terms of loss of productivity due to antibiotic resistance in health care systems [85]. A worst-case scenario could emerge in the coming future, according to the analysts of the Research and Development Corporation, a US non-profit global organization, where the planet could be left without any effective antimicrobial agent to treat bacterial infections. In this case, the global economic burden will be nearly \$120 trillion (\$3 trillion per annum), roughly equal to the entire actual annual health care budget of the United States. In general, the world population will be significantly affected: about 444 million people will succumb to infections as of 2050, and birth rates will decrease rapidly in this scenario [86, 87]. These losses are calamitous, but these estimates reflect imperfect images of the economic costs of antibiotic resistance due to data limitations such as the inclusion of total conditions and resistance-susceptible diseases. The use of antibiotics in the livestock and food industries is another very critical trait of antimicrobial resistance (AMR), that was missing from the investigation. It is an important player in the rising AMR, likely causing its own projected economic losses. There is also a misappropriation of the use of antimicrobials as growth promoters in many developing countries. This

**84**

**5.1 Antimicrobial peptides**

By inducing lysis, bacteriophages (phages) are viruses that infect and destroy bacteria [97]. In 1915, the British bacteriologist Frederick Twort first discovered phages. Two years later, Félix d'Herelle made a similar discovery independently in Paris and presented the phage therapy notion. With the advent of antibiotic therapy, phage therapy was abandoned in several countries, but has been continuously developed in Eastern European countries with facilities in Warsaw, Poland, and Tbilisi, Georgia [98]. Shotgun metagenome sequencing showed that there were antipseudomonal phages in the phage cocktails sold in pharmacies in Georgia and Russia [99]. The successful treatment of infections with MDR *P. aeruginosa* has been reported in a few case reports from Belgium and the US, but has not gained broad acceptance in the Western world [100]. Phage therapy has many benefits, including replication at the infection site, high precision for attacking bacteria without effects on commensal flora, less side effects than other therapies, antibiotic-resistant bacteria bactericidal activity and simple administration [101]. The use of phages as an alternative to antibiotics has been extensively studied for the treatment of *P. aeruginosa* infections. There are 137 different phages that have been characterized to date that target the *Pseudomonas* genus [102]. Many in vitro and in vivo studies have been performed to test the efficacy of phages against chronic infections of *P. aeruginosa*. For instance, co-incubation of phage PA709 with the clinical strain *P. aeruginosa* 709 has been shown to significantly reduce the viability of *P. aeruginosa*. Another research found that intranasal administration of P3-CHA bacteriophage to mice receiving a lethal dose of *P. aeruginosa* strain CHA substantially improved the rate of survival and reduced the bacterial load in the lungs [103].

Another benefit of phage therapy is that phages can be genetically modified as vehicles to transport bacteria with antimicrobial agents, thus increasing treatment efficacy [104]. While phages have been shown to be successful in vitro and in animal models against bacterial infection, only a small number of phage therapy clinical trials have been performed to date. The reasons for this include: safety issues about post-treatment phage clearance and impurity of phage preparations; poor stability of phage preparations; and lack of knowledge of the comprehensive phage mode of action and bacterial resistance to phage growth [105]. In clinical trials, the use of phages against *P. aeruginosa* infections has been studied in patients with venous leg ulcers, burn wounds and otitis, and no adverse reactions have been identified during these clinical trials [106].

## **5.3 Quorum sensing inhibition**

Quorum sensing is a mechanism that enables bacteria to regulate the expression of genes in a manner based on cell density. To control virulence and biofilm formation, *P. aeruginosa* utilizes quorum sensing [107]. Las and Rhl are two major *P. aeruginosa* quorum-sensing systems responsible for the synthesis of the signal molecules of N-acyl homoserine lactone (AHL), N-(3-oxododecanoyl)-L-homoserine lactone (3O-C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL). 3O-C12-HSL and C4-HSL bind to and activate their LasR and RhlR cognate transcription factors, respectively, inducing the formation of biofilms and the expression of various virulence factors, including elastase, proteases, pyocyanin, lectins, rhamnolipids, and toxins [108]. The third *P. aeruginosa* quorum-sensing system, PQSMvfR, has been reported to facilitate the formation of biofilms in addition to the LasI-LasR and RhlI-RhlR systems. This mechanism regulates the development of the *Pseudomonas* quinolone signal (PQS), 2-heptyl-3-hydroxy-4-quinolone, by the transcriptional regulator MvfR, also known as PqsR, by controlling the pqsABCDE operon. In addition, PqsA and PqsD proteins have been implicated in the development of biofilms [82].

A promising technique for treating *P. aeruginosa* infections is known to be the inhibition of quorum sensing. This approach is capable of preventing or decreasing the formation of biofilms, reducing bacterial virulence and has a low risk of bacterial resistance growth. In addition, this strategy has a small scope, such that any unwanted inhibitory effects on beneficial bacteria are impossible. For the Las and Rhl systems, quorum sensing inhibitors may be either natural or synthetic and are capable of reducing the activity of AHL synthase, inhibiting the development of AHL, degrading AHLs or competing for AHL receptor binding [109]. In recent years, the use of quorum sensing inhibitors for the treatment of infections with *P. aeruginosa* has been intensively studied. The carotenoid zeaxanthin, typically found in plants, algae and lichens, for example, reduced the formation of biofilms in *P. aeruginosa* by binding to the signal receptors for quorum sensing, lasR and RhlR, and blocking the expression of virulence genes, lasB and rhlA [110]. Flavonoids are a class of naturally developed plant metabolites that have acted as LasR and RhlR antagonists and substantially decreased their ability to bind to the *P. aeruginosa* promoters of quorum sensing-regulated genes [111].

#### **5.4 Iron chelation**

Iron is important for bacterial growth and is involved in a number of cellular processes, such as the production of electricity, the replication of DNA and the transport of electrons [112]. Compared to healthy people, the iron content of human sputum was found to be substantially elevated in CF patients, indicating that an increased amount of iron promotes chronic CF lung infection [113]. *P. aeruginosa* utilizes pyoverdine and pyochelin siderophores to obtain iron from the extracellular environment [114]. Therefore, a technique to fight *P. aeruginosa* infections is to limit the concentration of extracellular iron or disrupt iron uptake by *P. aeruginosa*. Several studies have related iron metabolism to the pathogenesis of chronic infections, indicating that iron analogues and chelators may work against *P. aeruginosa* as potential therapeutic agents. For example, iron chelators, 2,2′ dipyridyl (2DP), diethylenetriaminepentacetic acid (DTPA) and EDTA, have been reported to impair growth and biofilm formation of *P. aeruginosa* and have been more effective under anaerobic conditions [115].

Gallium is a nonredox iron III analog that disrupts the metabolism of bacterial iron by acting in several biological processes as an iron replacement, so it is a US

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*Chemotherapy and Mechanisms of Action of Antimicrobial Agent*

FDA-approved medication for cancer-associated hypercalcemia treatment [116]. In 2007, Kaneko et al., reported that gallium was able to inhibit the growth of *P. aeruginosa*, prevent the development of biofilms, and manifest excellent bactericidal activity in vitro by reducing the uptake of bacterial iron and repressing the synthesis of pyoverdine mediated by the transcriptional regulator PvdS. In addition, in mouse infection models, gallium has also been found to remove *P. aeruginosa*

Currently, a variety of diseases, including cancer and bacterial infectious diseases, have received significant attention from nanoparticles to treat them. Nanoparticles are small materials that have been used in a number of chemical, biological and biomedical applications, having a size of less than 100 nm and a large surface area to mass ratio [117]. The nanoparticles used for their antimicrobial activity are highly penetrable in the bacterial membranes, may interfere with the formation of biofilms, have several antimicrobial mechanisms, and are strong antibiotic carriers [118]. For the prevention of *P. aeruginosa* infections, metallic and antimicrobial agent-loaded nanoparticles have been extensively examined. Silver nanoparticles, for example, are powerful antimicrobial agents that generate silver ions responsible for the inhibition, like DNA synthesis, of bacterial enzymatic systems. Silver nanoparticles have shown important antimicrobial effects on the clinical strains of *P. aeruginosa*, killing *P. aeruginosa* effectively and inhibiting its in vitro growth. In addition, silver nanoparticles have demonstrated low mammalian

cell cytotoxicity, although this requires more in vivo research [119].

ampicillin-attached nanoparticles [120].

inhibitory effect on biofilm formation.

**5.6 Probiotic as an alternative antimicrobial therapy**

Nanoparticles are capable of delivering antimicrobial agents such as antibiotics to bacteria, as described earlier. Kwon et al., developed porous silicon nanoparticles with a novel antimicrobial peptide fused with a synthetic bacterial toxin, containing membrane-interacting peptides. This engineered nanoparticle was discovered in a mouse model of *P. aeruginosa* lung infection to increase the survival rate and bacterial clearance. Moreover, it has been found that the binding of antibiotics to nanoparticle surfaces greatly improves the effectiveness of both antibiotics and nanoparticles. In this respect, silver ampicillin-attached nanoparticles have a higher rate of in vitro killing of ampicillin-resistant *P. aeruginosa* isolates compared to silver

Probiotics are living microorganisms which, when ingested in appropriate quantities, provide health benefits [121]. The majority of probiotic bacteria are grampositive, and their primary functions are related to intestinal tract health regulation and maintenance (e.g., *Lactobacillus* and *Bifidobacterium*) [122]. The probiotics in the intestines that colonize the human host are the most numerous. The commensal intestinal microbiome leads to enhanced infection tolerance, differentiation of the host immune system, and nutrient synthesis [123]. The probiotic *Pediococcus acidilactici* HW01 was studied against *P. aeruginosa* and observed decreased *P. aeruginosa* motility as well as decreased pyocyanin development, decreased protease and rhamnolipid production, and decreased stainless steel surface biofilm formation. Another research conducted by Moraes et al., showed that *Lactobacillus brevis* and *Bifidobacterium bifidum* were effective against *S. aureus* biofilms grown on titanium discs. The findings showed a decrease in *S. aureus* growth on titanium discs when both probiotics were used, but *L. brevis* strains was shown to have the greatest

*DOI: http://dx.doi.org/10.5772/intechopen.95476*

effectively.

**5.5 Nanoparticles**

FDA-approved medication for cancer-associated hypercalcemia treatment [116]. In 2007, Kaneko et al., reported that gallium was able to inhibit the growth of *P. aeruginosa*, prevent the development of biofilms, and manifest excellent bactericidal activity in vitro by reducing the uptake of bacterial iron and repressing the synthesis of pyoverdine mediated by the transcriptional regulator PvdS. In addition, in mouse infection models, gallium has also been found to remove *P. aeruginosa* effectively.
