Aminoglycoside Antibiotic-Inactivating Enzymes in Actinomycetes Similar to Those Present in Clinical Isolates of Antibiotic-Resistant Bacteria

Abstract

Various species of Streptomyces possess aminoglycoside-modifying enzymes. Streptomyces kanamyceticus contains an enzyme that acetylates the 6'-amino group of kanamycin A and B, gentamicin Cla, and neomycin. Streptomyces spectabilis produces an enzyme that acetylates the 2'-amino group of the hexose ring of gentamicin Cia. These enzymes catalyze reactions identical to those catalyzed by enzymes found in gram-negative bacteria containing R(antibiotic resistance)-factors. The discovery of these enzymes suggests the possibility of an evolutionary relationship between the aminoglycosideinactivating enzymes (produced by resistance determinants) in bacteria containing R-factors and similar enzymes found in the actinomycetes.Resistance to antibiotics in clinical isolates of gram-negative and gram-positive bacteria is usually mediated by the presence of various enzymes that modify the antibiotic so that it can no longer interact with its target in the cell. The f3-lactamases hydrolyze the penicillins and cephalosporins, chloramphenicol acetyltransferase acetylates chloramphenicol, and nine enzymes acetylate, phosphorylate, or adenylylate the aminoglycoside antibiotics (1, 2). The genetic loci coding for these enzymes are usually located on extrachromosomal elements, such as the R(antibiotic resistance)-factors in gram-negative bacteria. Since these genes are not normal chromosomal components of the resistant strains, there has been considerable speculation as to their origin. Walker and Walker (3) have suggested that some R-factors might have originated in organisms that produce antibiotics.Molecular studies have shown that R-factors consist of two parts that are reversibly dissociable, these are the resistance transfer factor (RTF), and the r-determinants, genes that determine resistance to antibiotics (2). Watanabe (4) has suggested that the r-determinants exist somewhere in nature as chromosomal genes and that they are "picked-up" by promiscuous RTFs to form R-factors. The question is, where do the r-determinants originate?We have initiated a search in the actinomycetes for aminoglycoside-modifying enzymes like those that have been characterized in strains carrying R-factors (R+) in the belief that this might represent the r-determinant gene pool. their cellular dimensions, their cytology, and their genetics place them among the bacteria (5, 6). One of the most striking properties of the actinomycetes is the extent to which they produce antibiotics; most of the aminoglycoside antibiotics (streptomycin, neomycin, kanamycin, gentamicin, tobramycin, and lividomycin) are produced by them.Enzymes that modify other antibiotics have been isolated from Streptomyces species; in studies on the biosynthesis of streptomycin in Streptomyces bikiniensis, Miller and Walker (3,8) and Nimi and coworkers (9, 10) found three enzymes that phosphorylated streptomycin. In addition, Argoudelis and Coats have reported the presence of enzymes that phosphorylate lincomycin and clindamycin (11), adenylylate clindamycin (12), and acetyl...

Actinomycete integrative and conjugative pMEA-like elements of Amycolatopsis and Saccharopolyspora decoded

“…Although not shown thus far, it has been suggested that the genes responsible for the widespread resistance to aminoglycoside antibiotics in pathogens originate from soil bacteria, notably the actinomycetes, which are the most prominent aminoglycoside producers, and that the resistance genes were spread to other bacteria via horizontal gene transfer (Benveniste and Davies, 1973;Marshall et al, 1998;Grohmann et al, 2003). Several AICEs are able to mobilise chromosomal markers (Moretti et al, 1985;Hopwood et al, 1984;Brown et al, 1988b;Vrijbloed, 1996;Smokvina et al, 1988;Bibb et al, 1981), suggesting that they may play an important role in horizontal gene transfer and evolution of genome plasticity.…”

Broad host range plasmids can invade an unexpectedly diverse fraction of a soil bacterial community

“…In recent EAHEC outbreaks in Germany, recombination of a pathogenic with the plasmid of a non-pathogenic E. coli strain increased the pathogenic potential to cause a deadly combination (Brzuszkiewicz et al, 2011). Soil-borne antibiotic resistance has been found to be shared with human pathogens (Benveniste and Davies, 1973;Forsberg et al, 2012). Several organisms among the identified transconjugants belong to groups known to contain opportunistic human pathogens, providing a direct link between the plasmid encoded mobile soil resistome and opportunistic pathogens.…”

Transformation of Arthrobacter and studies on the transcription of the Arthrobacter ermA gene in Streptomyces lividans and Escherichia coli

“…Arthrobacter and S. erythreus, the gene responsible for erythromycin resistance is constitutively expressed. If antibiotic resistance genes originated in antibiotic-producing organisms (Benveniste & Davies, 1973;Walker & Walker, 1970) then it would appear that the inducibility of erythromycin resistance in non-antibiotic-producing bacteria must have been acquired later.…”