Systematic difference in the methylation of ribosomal ribonucleic acid from gram-positive and gram-negative bacteria

A survey of gram-positive and gram-negative organisms was performed to compare the distributionof N6-methylated adenine. It was found that (i) all the gram-positive strains tested, Staphylococcus aureus, Sarcina lutea, Bacillus stearothermophilus, Bacillus subtilis, and Bacillus megaterium, contain neither N6-monomethyl adenine (m6A) nor N6-dimethyladenine (m26A) in 23S ribosomal ribonucleic acid (rRNA). In the case of S. aureus and Streptococcus pyogenes, strains which are clinically resistant to erythromycin contain m26A. (ii) The gram-negative strains Salmonella typhimurium, Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, and Klebsiella pneumoniae all contain m6A but not m23A in 23S rRNA. These observations suggest the existence of at least one systematic structural difference between the ribosomes of the two classes of bacteria. Because of the demonstrated relationship between N6-dimethylation of adenine in 23S rRNA and clinical resistance to macrolide, lincosamide, and streptogramin B-type antibiotics in staphylococci and streptococci, the observed systematic differences found in rRNA methylation combined with greater cellular permeability may be related to the relatively greater efficacy of macrolide, lincosamide, and streptogramin B-type antibiotics in treating infections caused by gram-positive organisms.