**1. Introduction**

The genus of *Pseudomonas* includes more than 140 species, most of which are saprophytic in different habitats. More than 25 species are associated with humans. Most of these bacteria are pathogenic to humans and cause opportunistic diseases. These include *Ps. aeruginosa*, *Ps. fluorescens, Ps. putida, Ps. stutzeri, Ps. cepacia, Ps. putrefaciens,* and *Ps. maltophilia*. Only two species, which are *Ps. pseudomallei* and *Ps. mallei*, produce specific human infections: glanders and melioidosis. *Ps*. *aeruginosa* and *Ps. maltophilia* account for approximately (80%) of pseudomonads recovered from clinical specimens. *Pseudomonas aeruginosa* represents the more frequently involved human infections and has extradited the most attention. It is widely distributed as a free-living bacterium and is found mostly in moist environments. Although it rarely causes infections in healthy persons, it is a significant threat to hospitalized patients, especially those with serious underlying diseases, such as cancers and burns. The high mortality associated with this infection is due to a combination of weak host defenses, bacterial resistance to antimicrobials, production of bacterial enzymes, and extracellular toxins [1].

*Pseudomonas aeruginosa* is a gram-negative opportunistic pathogen and a model bacterium for studying bacterial virulence and social traits, while it can be isolated in low numbers from a variety of environments, including soils and water, and is easily found in any human/animal-affected environment, it is a major cause of disease and death in humans with chronic conditions and immunosuppressive diseases, and the infection in these patients is difficult to treat due to a number of antibiotic resistance mechanisms and the organism's tendency to form multicellular biofilms [2]. A non-spore-forming bacterial rod is capable of causing a variety of infections in both immunocompromised and immunocompetent patients [3]. Its tendency to cause infection in immunocompromised hosts, high diversity, antibiotic resistance, and a wide range of dynamic defenses make it a very challenging organism to treat in modern medicine [4].

#### **2.** *Pseudomonas aeruginosa*

*Pseudomonas aeruginosa* is a heterotrophic, motile, gram-negative rod-shaped bacterium about 1–5μm in length and 0.5–1.0μm in wide. This bacterium is facultative aerobes that grow with aerobic and anaerobic respiration, also with nitrate as the terminal acceptor of electrons. *Ps. aeruginosa* can as well grow anaerobically *via* arginine and has limited abilities for a fermentative process that generally support quite slow or no growth. This microorganism can use more than 100 organic molecules as an origin of carbons and/or energy and as a prototroph, which generally has the capacity to grow on a medium with minimal salts and with a single origin of carbon and energy.

*Pseudomonas aeruginosa* is a heterotrophic, motile, rod-shaped gram-negative bacterium about 1–5 μm in length and 0.5–1.0 μm in width. It has a facultative antenna grown by aerobic and anaerobic respiration with nitrate as the terminal acceptor of electrons. *Ps. aeruginosa* also be grown anaerobic *via* arginine and has limited fermentation abilities that generally support highly slow or no growth. An organism can use more than 100 organic molecules as an origin of carbons and/or energy and as a primary source; it generally has the ability to grow on a minimal salt growth medium with a single source of carbon and energy. This bacterium grows well at 37°C, but can survive in temperature ranging from 4 to 42°C. They are important soil bacteria capable of breaking down PAHs, but they are also often detected in water tanks contaminated by animals and humans, such as sewage and drains, in and out of hospitals. The two most commonly used tested strains are PAO1 [5] and PA14, both of which were used to create genetic resources, including ordered and publicly available transposon mutant libraries. *Pseudomonas aeruginosa* is overwhelmingly resistant to several types of antibiotics, and this makes it a problem during infections where it is difficult to therapeutic processes. It is often called an "opportunistic" pathogen because it rarely infects healthy persons. In the clinic, the primary risk includes patients with compromised immune systems, including those with cystic fibrosis (CF), AIDS, cancer, static medical devices, eye injuries, burns, and nonhealing diabetic wounds.

Pseudomonas aeruginosa *Represents a Main Cause of Hospital-Acquired Infections (HAI)… DOI: http://dx.doi.org/10.5772/intechopen.108759*

#### **2.1 Etiology of** *Pseudomonas aeruginosa*

*Pseudomonas aeruginosa* is generally present in the environment, especially in freshwater. Reservoirs in urban communities include pools swimming. It can cause a large number of the society-acquired infections, such as puncture wounds leading to pneumonia, folliculitis, otitis externa, osteomyelitis, and others. It is usually an opportunistic pathogenic bacterium and is also an important cause of nosocomial infections, such as ventilator-related pneumonia, catheter-related urinary tract infections, and others. Reservoirs in hospitals include taps, drinking water, sinks, ice makers, toothbrushes, disinfection solutions, disinfectants, respiratory therapy equipment, soap bars, and endoscope washers [2–4].

#### **2.2 Epidemiology of** *Pseudomonas aeruginosa*

*Ps. aeruginosa* diseases are common in immunocompromised persons, such as bronchiectasis, cystic fibrosis, neutropenia, cancer, burns, organ transplant, AIDS, uncontrolled diabetes mellitus, and ICU admissions. Persons with invasive devices such as indwelling catheters and/or tubes of endotracheal are also at risk due to the organism's singular capacity to the formation of biofilms that are difficult to identify [6].

#### **2.3 Pathophysiology of** *Pseudomonas aeruginosa*

*Pseudomonas aeruginosa* possesses several mechanisms of antimicrobial resistance and a variety of virulence factors that collectively show the broad spectrum of infections it causes and the increasingly challenging treatment of the resulting antibiotic resistance. Multiple mechanisms of *Pseudomonas* antimicrobial resistance have been identified, for example, efflux systems, endogenous antibiotic resistance, and inactivated enzymes to antibiotics [6].

Endogenous antimicrobial resistance is the capacity to enclose membrane permeability to drugs. Flow systems allow *Ps. aeruginosa* to direct harmful or toxic materials out of the cell membrane. In addition, many of these bacterial isolates possess beta-lactamases and broad-spectrum beta-lactamases (ESBLs). The ability of these bacteria to form a biofilm is an important mechanism by which they can increase the resistance of antimicrobial agents as well against the defense mechanisms of the host [4, 6]. This is especially important in patients with cystic fibrosis, as most patients develop an infection in the first year of life either from the environment or from health care facilities (inpatient or outpatient).

#### **2.4 History and physical of** *Pseudomonas aeruginosa*

*Pseudomonas aeruginosa* causes a large number of infections with a variant type of severity, for example,


rubber soles. Local tenderness, purulent discharge, and other signs of infection are found; however, delay in presentation and diagnosis due to lack of symptoms initially may predispose to serious complications, such as septic arthritis and osteomyelitis [8].


## **3. Virulence factors that cause pathogenicity of** *Pseudomonas aeruginosa*

*Pseudomonas aeruginosa* possesses several virulence factors that may cause, pathogenesis that facilitates adhesion and/or disrupts host cell signaling pathways while targeting the extracellular matrix. This bacterium is capable of causing many infections that invade the organism and its immune system, resulting in diseases that are almost impossible to eradicate [15–17]. The virulence factors related to pathogenicity include lipopolysaccharide, type IV Pili, flagellum, type III secretion system, exotoxin A, proteases, biofilm formation, type VI secretion systems, and oxidant generation in the airspace. They are important factors that act in various ways to decrease the activity of the immune system.

The lipopolysaccharide (LPS) is a common component of the external membrane of *Ps. aeruginosa*. Bacterial lipopolysaccharide consists of a distal polysaccharide (or O-antigen), a non-repeating core oligosaccharide, and a hydrophobic domain known as lipid A (or endotoxin) [18]. LPS plays a specific role in the activations of the host's innate (non-specific) (NLRP1, NLRP2, NLRP3, and TLR4) and acquired (or adaptive) immune responses, and ends up causing dysregulated inflammatory responses that contribute to morbidity and mortality [19].

#### Pseudomonas aeruginosa *Represents a Main Cause of Hospital-Acquired Infections (HAI)… DOI: http://dx.doi.org/10.5772/intechopen.108759*

With regard to virulence factors, type IV capillaries *of Ps. aeruginosa* have a role in adhering to many cell types, and this is likely to be important in phenomena, such as tissue swelling and attachment to specific tissues. The triggering of biofilm formation and phagocytosis is mediated by phagocytic receptors that recognize the corresponding adhesions to microbial surfaces [20–24]. However, type III secretion system virulence factors provide a variety of secretion systems of which at least four likely play a role in virulence (types I, II, III, and IV). T3SS is one of the most intriguing virulence factors that involve flagella and basal body-associated system to deliver proteins directly from the cytoplasm of *Ps. aeruginosa* into the cytosol of host cells contributing to the avoidance of phagocytosis by *Ps. aeruginosa* as well as host tissue damage, promoting immune avoidance and bacterial proliferation [25, 26].

Exotoxin virulence factors are secreted by the mechanism of type II secretion, which uses proteolytic secretions in the extracellular environment, including phospholipase, lipase, protease, and alkaline phosphatase. Experiments with animals showed the important role of these factors in infectious patterns [27]. Furthermore, it has been shown that exotoxin A is involved in the damage and invasion of local tissues [28].

Several proteases that are produced by *Ps. aeruginosa* in the form of elastase Las B-type metal proteases destroy host tissues; thus, it plays an important role in both acute infections of the lung and burns wound [29]. Indeed, alginate virulence factors can produce a mucopolysaccharide capsule, consisting of alginate, an acetylated random copolymer of β1-4 bound to D-mannuronic acid (poly-M), and L-guluronic acid [30]. Evidence for playing this role is thought to be due to the overproduction of agents in CF intrapulmonary cell adhesion, and it is thought to be involved in host defense resistance by decreasing susceptibility to phagocytosis [31].

Quorum sensing virulence factor is a mechanism of the bacterial cell into cell communications with chemical compound diffusible. A quorum is necessary to produce enough of a secreted signaling molecule (called auto-stimulator) to stimulate

**Figure 1.**

*Mechanisms of T3SS and T6SS in regulating bacterial pathogenesis and host responses in* Ps. aeruginosa*.*

the expression of a large base [32]. In regard to the auto-stimulator, the class most commonly used by gram-negative bacteria and acyl homoserine lactones (AHL) is the class most commonly used. The mechanism spreads freely across bacterial membranes. The AHL signals produced by *Ps. aeruginosa* are oxohexanoyl-homoserine lactone and butanoyl-homoserine lactone [33, 34].

AHL signals produced by AHL synthase (LasI/RhlI) circulate in the environment. An increase in bacterial density during infection leads to an increase in the concentration of the auto-stimulator. At a specific moment, the autoinducer reaches a certain threshold and subsequently binds to a transcription activator (LasR/RhlR) that forms a complex that activates genes involved in biofilm formation and coding virulence factors [35]. Formation of a biofilm begins with the connection of free-swimming bacteria (plankton) to a surface with type IV filaments and skin, followed by twitching movement and formation of micro-colonies; then, the quorum sensing signals start to accumulate. Once a critical threshold for quorum detection signals is achieved, small colonies become embedded in the extracellular matrix (**Figure 1**) [15].

#### **Figure 2.**

*Diagrammatic representation of the main virulence factors employed by Pseudomonas aeruginosa: (a) the formation capacity of the biofilm and the composition of the extracellular matrix of the biofilms (exopolysaccharides, extracellular DNA, and proteins); (b) (QSs) the three major quorum detection systems (Las, Pqs, and Rhl); (c) flagellins FliC and FliD embedded in the flagel structure; (d) pyoverdine (PVD) siderophore as important for iron uptake system; (e) (T4P) type 4 pili; (f) (LPS) lipopolysaccharide and (OMPs) outer membrane proteins; (g) (T3SS) the type III secretion system and its four main effectors; (h) (T6SS) the type VI system of secretion; (i) (T2SS) the type II system of secretion and the compounds it releases to the extracellular milieu: lytic enzymes; proteases, lipases (PIV and AprA) and elastases (LasB and LasA), (ETA) exotoxin A, and pyocyanin [36].*

Pseudomonas aeruginosa *Represents a Main Cause of Hospital-Acquired Infections (HAI)… DOI: http://dx.doi.org/10.5772/intechopen.108759*

In this review, biofilm formation, which is a virulence factor in the first subject, is described. However, the last element of virulence discussed here is the type VI secretion system. Pathogenic bacteria often possess a number of secretion systems that function to transmit protein secretion. The T6SS is one of the more recently known examples of such secretion systems. Interest in T6SS has resulted in a rapid study of *Pseudomonas aeruginosa* in terms of structure, mechanical function, aggregation, and regulation of the secretion of *Ps. aeruginosa*. T6SS protects from other bacteria in the environment (**Figure 2**) [37, 38].

## **4. Genomic and phenotypic approaches to the study of** *Pseudomonas aeruginosa*

Genomic and phenotypic approaches to the study of *Pseudomonas aeruginosa* adaptation in the CF lung, the ubiquity of this bacterium can be strongly related to the high plasticity of the genome. *Ps. aeruginosa* has a genome of nearly from 5.2 to 7 Mbp [39, 40], with 4000 genes inside the core genome. The complete group of genes between the different *Ps aeruginosa* strains ranges from 10,000 to 40,000 genes, and it is interesting that their arrangement in the genome may differ between strains. This makes it difficult to identify areas adapted to genetic markers [39–41]. There is large detailed information about the *Ps. aeruginosa* genome, transcriptome, and proteome available from various databases: (i) the genome database of *pseudomonas* [42]; (ii) PseudoCyc [43]; (iii) (SYSTOMONAS) [44]; (KEGG) [45]; (PubChem) [46]; and (HMDB) [47].

Advances in the sequencing of genetic systems have a possible understanding of the evolution and adaptation of *Pseudomonas aeruginosa* chronic infections, such as lung cystic fibrosis (CF), revealing high levels of coexisting genetic and phenotypic diversity, including clinically important features (**Table 1**). Whole genomic sequencing of this bacterium isolates longitudinally obtained from patients with cystic fibrosis provided evidence that, during the long term of the disease, *Ps aeruginosa* undergoes adaptive processes that lead to an assemblage of mutations in infectious strains [55].

## **5. Hospital-acquired infections and antibiotic resistance of** *Pseudomonas aeruginosa*

*Pseudomonas aeruginosa* is a gram-negative bacillus belonging to the family Pseudomonadaceae [56]. In hospital environments, it can colonize damp places, including ventilators, humidifiers, oxygen respirators, sinks, taps, dialysis machines, and toilets [57]. Risk factors associated with plasmodium aeruginosa infection are COPD, diabetes, acute kidney, cystic fibrosis, immunosuppression (after organ or bone marrow transplant), liver failure, and multiple organ injury [57].

Pseudomonas infection is the most common condition treated in intensive care units (ICU), including hematology, burn units, and surgery. Clinical forms of *Ps. aeruginosa* infection are hospital-acquired pneumonia (HAP) including) urinary tract infection (UTI), ventilator-associated pneumonia (VAP and bloodstream infection (BSI), including central line-associated bloodstream infection (CLA-BSI) and wound burns, soft tissue infections, skin and surgical site infections, decubitus ulcers, eye infections, bone and joint infections, otitis media, and central nervous system infections [58].


Pseudomonas aeruginosa *Represents a Main Cause of Hospital-Acquired Infections (HAI)… DOI: http://dx.doi.org/10.5772/intechopen.108759*


*Abbreviations: PA,* Ps. aeruginosa*; CF, cystic fibrosis; CIP, ciprofloxacin; AMR, antimicrobial resistance; LPS, lipopolysaccharide; QS, quorum sensing; TCA, tricarboxylic acid cycle; T3SS, Type 3 secretion system; wgMLST, whole genome multilocus sequence typing.*

#### **Table 1.**

*Examples studies of genomic of* Pseudomonas aeruginosa *adaption and evolution.*

According to the World Health Organization, *Pseudomonas aeruginosa* is one of the antimicrobial-resistant bacteria that poses the greatest threat to human health [59]. This bacterium can have several intrinsic or acquired resistance mechanisms, often with high rates of resistance to different classes of antimicrobials [60]. *Pseudomonas aeruginosa* is substantially resistant to most antibiotics due to its selective ability to prevent different antimicrobial agents move through its outer membrane or extruding if it enters the cell. The antibiotics, which remain active, include some fluoroquinolones (e.g., levofloxacin and ciprofloxacin), aminoglycosides (e.g., tobramycin, gentamicin, and amikacin), many β-lactams (e.g., ceftazidime, piperacillin-tazobactam, cefepime, ceftazidime-avibactam, imipenem, doripenem, ceftolozane-tazobactam, and meropenem), and polymyxins. Antimicrobial resistance of *Ps. aeruginosa* can be acquired through one or more mechanisms, including modified antibiotic targets, active efflux pumps, lowering of permeability, and degradation of enzymes [61].

Endogenous and acquired antibiotic resistance makes *Pseudomonas aeruginosa* and is one of the most difficult organisms to treat. The high intrinsic antibiotic resistance of *Ps. aeruginosa* is due to several mechanisms: reduced outer membrane permeability, AmpC β-lactamase production, and the presence of several genes coding for multidrug-resistant efflux pumps [62].

A large number of acquired resistance genes encoding aminoglycoside-modifying enzymes (AME) and beta-lactamases have been observed in *Ps. aeruginosa* [63]. Extended-spectrum beta-lactamases have been increasingly reported [64–67], and metallo β lactamase has also begun to appear in *Ps. aeruginosa* [68].

Mutations in chromosomal resistance genes can occur through horizontal gene transfer, and variations in the quinolone resistance determining regions (QRDR) in genes that code for topoisomerase IV and DNA gyrase play a specific role in quinolone resistance in *Pseudomonas aeruginosa* [69]. The absence of OprD is the most common mechanism of resistance to carbapenems and is linked *via* resistance to imipenem and reduced exposure to meropenems [70]. According to the data, four efflux pump systems of the RND (resistance nodulation division) family, MexEF-OprN, MexAB-OprM, MexCD-OprJ, and MexXY-OprM, are well described and known to contribute significantly to antibiotic resistance in this bacterium [71–73]. Their overproduction

confers cross-resistance or reduced susceptibility to several β-lactams (piperacillin, ceftazidime, ticarcillin, meropenem, and cefepime), and aminoglycosides and quinolones [62]. Hyperproduction of the inducible AmpC β-lactamase is mostly due to the inactivation of the amidase AmpD [74] and two additional AmpD homologs [75], leading to an increase in inducer molecules.

#### **5.1 Resistance to β-lactams of** *Pseudomonas aeruginosa*

β-lactams, including penicillins (e.g., ticarcillin and piperacillin), cephalosporins (e.g., ceftazidime and cefepime), carbapenems (e.g., imipenem and meropenem), and monobactams (e.g., aztreonam), are commonly used in the treatment of *Pseudomonas aeruginosa* infections [76]. Resistance to these antibiotics is increasing [77] and mediated by different mechanisms, most commonly antimicrobial cleavage by β-lactamase enzymes, and antimicrobial expulsion by chromosomally encoded efflux pump mechanisms and reduced antibiotics uptake owing to loss of outer membrane porin proteins [78].

#### *5.1.1 β-lactamases*

β-lactamases, hydrolyzing enzymes that disrupt the amide bond of the traditional four-membered β-lactam ring, rendering antimicrobials ineffective, are the main identification of resistance in bacteria type gram-negative, such as *Ps. aeruginosa*. Four molecular classes of these enzymes (A–D) have been characterized, which include metal-dependent (Zn2+-requiring; class B) and metal-independent (active site serine; classes A, C, and D-lactamases reviewed, all these enzymes were reported in *Pseudomonas aeruginosa*) [79].

#### *5.1.1.1 Endogenous β-lactamases*

*Ps. aeruginosa* typically carries chromosomal genes for two β-lactamases, a class C cephalosporinase, AmpC (Lodge et al., 1990), and a class D oxacillinase, PoxB [80]. AmpC is a well-characterized β-lactamase commonly linked to β-lactam resistance in clinical isolates.

#### *5.1.1.2 Acquired β-lactamases*

Whereas the original β-lactamases were plasmid-encoded class A restriction enzymes that hydrolyze only older narrow-spectrum penicillins and cephalosporins, recently described β-lactamases in P. classes A and D capable of hydrolyzing a wide range of β-lactams, including broad-spectrum cephalosporins and monobactams, and carbapenemases (classes A, B, and D) that hydrolyze most β-lactams, include carbapenems, but not aztreonam [79].

#### *5.1.1.3 Spectrum extended of β-lactamases*

Reported more commonly in the *Enterobacteriaceae*, though also found in *Pseudomonas aeruginosa*, ESBLs typically hydrolyze and, so, provide resistance to broad-spectrum cephalosporins (e.g., the third generation of cefotaxime, oxyiminocephalosporins, and ceftazidime) and azithromycin, in addition to narrow-spectrum cephalosporins and penicillins [81].

Pseudomonas aeruginosa *Represents a Main Cause of Hospital-Acquired Infections (HAI)… DOI: http://dx.doi.org/10.5772/intechopen.108759*

#### *5.1.1.4 Carbapenemases*

Carbapenems (e.g., meropenem and imipenem) are an important class of pseudo-beta-lactams due to their stability to most β-lactamases and are of particular use in treating infections associated with ESBL and AmpC producers [82].

#### *5.1.2 Fluoroquinolones resistance of* Pseudomonas aeruginosa

Fluoroquinolones (FQs), particularly ciprofloxacin, are generally used in the treatment of *Ps. aeruginosa* diseases. Resistance against these agents, which are mediated by mutations in the enzymes of topoisomerase IV and DNA gyrase that are the targets of FQs, although flux is an important contributing factor [83], is often accompanied by target site mutations [84].

#### *5.1.3 Resistance to aminoglycosides*

A number of aminoglycosides are commonly used in the treatment of *Ps. aeruginosa* infections (e.g., tobramycin, amikacin, and gentamicin [85], especially pulmonary infections in cystic fibrosis CF patients where amikacin and, in particular, tobramycin are routinely used [86]) However, their use is associated with the development of resistance, with acquired aminoglycoside-modifying enzymes (AMEs) and rRNA methylases, the inflow mechanisms usually responsible.

#### *5.1.4 Biofilm resistance of* Pseudomonas aeruginosa

Biofilms, which are surface-mounted three-dimensional structures in which bacteria are inserted into a matrix consisting of polysaccharides, protein, and DNA, are increasingly recognized as the preferred method for bacterial growth in nature and infectious diseases [87]. This is true for *Ps. aeruginosa* [88].

#### **5.2 Efflux pumps of** *Pseudomonas aeruginosa*

In *Ps. aeruginosa*, four efflux pumps have been described, MexCD-OprJ, MexEF-OprN, MexAB-OprM, and MexXY [89]. The genes encoding these pumps are arranged as operons, with the first gene encoding a membrane fusion protein that is associated with the cytoplasmic membrane (MexC, MexA, MexX, and MexE). The second gene encodes the transporter (MexF, MexD MexY, and MexB) thought to export the substrate across the inner membrane. The third gene encodes an OM protein (OprM, OprN, and OprJ) that facilitates the passage of the substrate across the OM. Together, the three pump proteins form a channel that traverses the inner membrane and the OM and allows the target to be effluxed directly from the cytoplasm to the extracellular environment. In the case of the*mexXY* operon, there is no gene encoding the OM component; rather, MexXY appears to share the OprM channel with MexAB [90]. However, it suggests that OprM is not the OM channel for AmrAB (MexXY) [91].

As is evident from this, there is a high variation in the antibiotic susceptibility pattern against these pathogenic bacteria, and the reason for this might be linked to an antibiotics manufacturing company, purchasing without a proper prescription, prescription without laboratory guidance, misuse, and indiscriminate use, the study area and bacterial type, and resistance methods [92–95].

Pigments of blue and green, such as (Pyocyanin), as antimicrobial agents were produced by marine *Ps. aeruginosa*. Also, the technique of molecular biology was applied to know the pathways of this production. The produced pyocyanin pigments were used as antimicrobial agents against a wide range of pathogenic microorganisms [96–99].
