**1. Introduction**

Nowadays, aminoglycoside antibiotic regimen remains as a prevailing therapy for the treatment of *Pseudomonas aeruginosa* pathogen, predominantly for respiratory complications in cystic fibrosis patients. However, *P. aeruginosa* strains are emergent multidrug-resistant. Bacteria develop resistance to aminoglycosides by producing aminoglycoside-modifying enzymes such as acetyltransferase, phosphorylase, and adenyltransferase [1]. The bacterial ribosome is a primary antibiotic target, but bacteria can acquire resistance by modification of drug-binding sites. More than 50 years of studies in *Escherichia coli* have shown that 16S and 23S rRNAs have methylated nucleotides (**Figure 1**). These molecular modifications are performed by methyltransferases (MTases), which take in charge the transfer of a methyl group from a methyl donor S-adenosyl-l-methionine, better known as AdoMet or SAM [2]. These RNA MTases are diverse in posttranscriptional RNA modification, where single RNA nucleosides are chemically transformed. SAM-dependent MTases are involved in biosynthesis, signal transduction, protein repair, chromatin regulation, and gene silencing [3]. More recently, it was shown that aminoglycoside resistance in *E. coli* has its primary target within the decoding

#### **Figure 1.**

*Ribonucleotides methylated where the methyl moiety is located either in 16S or 23S ribonucleotides: m6 A [66, 67], m6 2A [68], m5 C [67], m4 Cm [69], m2 G [66], m7 G [70], m3 U [67, 71], m5 U [72], and Ψ [68]. Molecules are designed using the figures on the next web page, https://mods.rna.albany.edu/mods/modifications/search/. The structure shows clearly the methyl (CH3-) but in the last structure bottom does not show this methyl.*

**53**

*The Role of Pseudomonas aeruginosa RNA Methyltransferases in Antibiotic Resistance*

16S rRNA and 14 methylated nucleotides in 23S rRNA [4].

region of 16S and 23S rRNAs and it is known to have 10 methylated nucleosides in

Different methylation sites have been identified within the 16S rRNA which yield different aminoglycoside resistance phenotypes [5]. One type group of 16S rRNA methylases is produced by istamycin producer *Streptomyces tenjimariensis*,

synthesized by gentamicin producer *Micromonospora purpurea* that methylates residue G1405; nonetheless, in *P. aeruginosa* the modification takes place in helix 44, with a secondary target in 23S rRNA helix 69 [6]. They bind specifically to the aminoacyl site (A-site) of 16S rRNA within the prokaryotic 30S ribosomal subunits

Probably RNA methylation began prior to DNA methylation in the early forms of life evolved on Earth [8], allowing to hypothesize perhaps that methylases appeared before polymerases. Ribonucleotide can be methylated by methyltransferases or demethylated by demethyltransferases. The structure of the bacterial ribosome has a molecular mass of 2.5 mega Daltons. In *E. coli*, the 50S subunit is composed of 23S rRNA (2904 nt), 5S rRNA (120 nt), and 33 ribosomal proteins, while the 30S subunit is composed of 16S rRNA (1542 nt) and 21

The 16S rRNA resistance methyltransferases modify only intact 30S subunits, but the molecular details of their target recognition mechanisms are not quite elucidated yet. Such studies are becoming all the more necessary [10]. RNA methylation has been observed in different types of RNA species, viz., mRNA, rRNA, tRNA, snoRNA, snRNA, miRNA, and tmRNAs. Specific RNA methyltransferases are synthesized by cells to label these RNA species according to their needs and prevailing environmental conditions surrounding the cells, and this molecular labeling system is a constituent of epigenetics. New molecular structures provide crucial new insights that may provide a starting point for strategies to suppress these emerging causes of pathogenic bacterial resistance to aminoglycosides [11]. Nonetheless, bacteria develop resistance to aminoglycosides by producing aminoglycoside-modifying enzymes such as acetyltransferase, phosphorylase, and adenyltransferase. These enzymes, however, cannot confer a broad aminoglycoside

*P. aeruginosa* has a large genome among *Gamma proteobacteria*, which allows it to improve many resistance mechanisms in a versatile way, for example, by transmissible plasmids or integrons. *P. aeruginosa* derepresses the chromosomal AmpC cephalosporinase [12, 13]; it also acquires genes for AmpC enzymes, class A carbenicillinases or *β*-lactamases, class D oxacillinases, and class B carbapenem-hydrolyzing enzymes [14], as it occurs in other bacteria like *E. coli* and *K. pneumoniae*. Other mechanisms include modifying the structure of topoisomerases II and IV to become quinolone resistant [15], decreasing outer membrane permeability by the partial or total failure of OprD proteins [12], overexpressing the active efflux systems with broad substrate patterns [16, 17], or

synthesizing aminoglycoside-modifying enzymes as adenylyltransferases,

The range of antibiotic resistance in *P. aeruginosa* is wide, and it represents a major difficulty for health care by its unsuccessful treatment, as a consequence of its low intrinsic antibiotic susceptibility, an effect of the interaction between multidrug

A1408 residue. Another group of 16S rRNA methylases is

*DOI: http://dx.doi.org/10.5772/intechopen.85185*

and interfere with protein synthesis [7].

ribosomal proteins (S1–S21) [9].

**2. Antibiotic resistance**

resistance spectrum due to its substrate specificity [1].

acetyltransferases, and phosphoryltransferases [18].

which methylates m1

#### *The Role of Pseudomonas aeruginosa RNA Methyltransferases in Antibiotic Resistance DOI: http://dx.doi.org/10.5772/intechopen.85185*

region of 16S and 23S rRNAs and it is known to have 10 methylated nucleosides in 16S rRNA and 14 methylated nucleotides in 23S rRNA [4].

Different methylation sites have been identified within the 16S rRNA which yield different aminoglycoside resistance phenotypes [5]. One type group of 16S rRNA methylases is produced by istamycin producer *Streptomyces tenjimariensis*, which methylates m1 A1408 residue. Another group of 16S rRNA methylases is synthesized by gentamicin producer *Micromonospora purpurea* that methylates residue G1405; nonetheless, in *P. aeruginosa* the modification takes place in helix 44, with a secondary target in 23S rRNA helix 69 [6]. They bind specifically to the aminoacyl site (A-site) of 16S rRNA within the prokaryotic 30S ribosomal subunits and interfere with protein synthesis [7].

Probably RNA methylation began prior to DNA methylation in the early forms of life evolved on Earth [8], allowing to hypothesize perhaps that methylases appeared before polymerases. Ribonucleotide can be methylated by methyltransferases or demethylated by demethyltransferases. The structure of the bacterial ribosome has a molecular mass of 2.5 mega Daltons. In *E. coli*, the 50S subunit is composed of 23S rRNA (2904 nt), 5S rRNA (120 nt), and 33 ribosomal proteins, while the 30S subunit is composed of 16S rRNA (1542 nt) and 21 ribosomal proteins (S1–S21) [9].

The 16S rRNA resistance methyltransferases modify only intact 30S subunits, but the molecular details of their target recognition mechanisms are not quite elucidated yet. Such studies are becoming all the more necessary [10]. RNA methylation has been observed in different types of RNA species, viz., mRNA, rRNA, tRNA, snoRNA, snRNA, miRNA, and tmRNAs. Specific RNA methyltransferases are synthesized by cells to label these RNA species according to their needs and prevailing environmental conditions surrounding the cells, and this molecular labeling system is a constituent of epigenetics. New molecular structures provide crucial new insights that may provide a starting point for strategies to suppress these emerging causes of pathogenic bacterial resistance to aminoglycosides [11]. Nonetheless, bacteria develop resistance to aminoglycosides by producing aminoglycoside-modifying enzymes such as acetyltransferase, phosphorylase, and adenyltransferase. These enzymes, however, cannot confer a broad aminoglycoside resistance spectrum due to its substrate specificity [1].
