Characterization of the chromosomal aac(6')-Ic gene from Serratia marcescens

Abstract

The DNA sequence of the chromosomal aac(6')-Ic gene from Serratia marcescens, which had been previously cloned (H. M. Champion, P. M. Bennett, D. A. Lewis, and D. S. Reeves, J. Antimicrob. Chemother. 22:587-596, 1988) was determined. High-pressure liquid chromatographic analysis of extracts prepared from Escherichia coli carrying the chromosomal aac(6')-Ic gene on a plasmid confirmed the presence of 6'-N-acetyltransferase activity in this strain, which was suggested by the aminoglycoside resistance profile. DNA sequence analysis of the cloned 2,057-bp PstI fragment revealed several regions of homology to previously characterized sequences from GenBank, including the rpoD and tRNA-2 genes of E. coli. Subcloning experiments confirmed the coding sequence of the aac(6')-Ic gene to be at positions 1554 to 1992. The predicted amino acid sequence of the AAC(6')-Ic protein suggested that it was the third member of a family of AAC(6') proteins which included a coding region identified between the aadB and aadA genes of Tn4000 and an AAC(6') protein encoded by pUO490, which was isolated from Enterobacter cloacae. Primer extension analysis suggested that the -35 region of the aac(6')-Ic promoter overlapped a large palindromic sequence which may be involved in the regulation of the aac(6')-Ic gene. Hybridization experiments utilizing a restriction fragment from the aac(6')-Ic gene showed that all S. marcescens organisms carried this gene whether or not the AAC(6')-I resistance profile was expressed. Organisms other than Serratia spp. did not hybridize to this probe.

Characterization and transcriptional regulation of the 2'-N-acetyltransferase gene from Providencia stuartii

“…The majority of AAC proteins are plasmid encoded; however, an important exception has been identified in Serratia marcescens, in which the 6'-N-acetyltransferase gene [aac(6')-Ic] is chromosomally encoded (4,19,28). Surprisingly, the aac(6')-Ic gene has been shown by DNA hybridization studies to be universally present in S. marcescens strains, regardless of their aminoglycoside resistance profiles (28).…”

“…The majority of AAC proteins are plasmid encoded; however, an important exception has been identified in Serratia marcescens, in which the 6'-N-acetyltransferase gene [aac(6')-Ic] is chromosomally encoded (4,19,28). Surprisingly, the aac(6')-Ic gene has been shown by DNA hybridization studies to be universally present in S. marcescens strains, regardless of their aminoglycoside resistance profiles (28). Although evidence suggests that some aminoglycoside resistance genes originated from producing organisms, such as the actinomycetes (2), it is evident that other genes are intrinsic to gram-negative bacteria, as is the aac(6')-Ic gene in S. marcescens. A second chromosomally encoded acetyltransferase, the 2'-N-acetyltransferase, has been found in Providencia stuartii (6,21,22,33).…”

Identification and analysis of aarP, a transcriptional activator of the 2'-N-acetyltransferase in Providencia stuartii

“…In gram-negative bacteria, chromosomal acetyltransferases such as the aac(2Ј)-Ia gene product in Providencia stuartii, the aac(6Ј)-Ig gene product in Acinetobacter haemolyticus, and the aac(6Ј)-Ic gene product in Serratia marcescens appear to be intrinsic to these species and confer aminoglycoside resistance when overexpressed (6,30,31,33,40). In P. stuartii, studies on aac(2Ј)-Ia regulation have shown that wild-type strains express the aac(2Ј)-Ia gene at low levels; however, mutants with increased expression can be selected in the presence of aminoglycosides at frequencies of 10 Ϫ6 to 10 Ϫ7 (31).…”

Aminoglycoside 2′‐N‐acetyltransferase genes are universally present in mycobacteria: characterization of the aac(2 ′)‐Ic gene from Mycobacterium tuberculosis and the aac(2 ′)‐Id gene from Mycobacterium smegmatis

“…These two genes are chromosomally located and present in all strains of their respective species. The aminoglycoside 6Ј-N-acetyltransferase genes isolated from different bacteria are also chromosomally located and most of them are species-specific as described in Enterococcus faecium (Costa et al, 1993), Serratia marcescens (Shaw et al, 1992), Acinetobacter haemolyticus (Lambert et al, 1993), Acinetobacter sp.13 and Acinetobacter sp.6 (Rudant et al, 1994).…”

“…In addition to aminoglycoside modification, another role in other cellular processes or metabolism has been proposed in actinomycetes (Benveniste and Davies, 1973a;Ló pez-Cabrera et al, 1989) and in Providencia (Shaw et al, 1992;Rather et al, 1993) for the chromosomally encoded AAC enzymes. Recently, it has been demonstrated that the enzyme AAC(2Ј)-Ia from P. stuartii contributes to the O-acetylation of peptidoglycan (Payie et al, 1995).…”