Isolation, characterization, and cloning of a plasmid-borne gene encoding a phosphotransferase that confers high-level amikacin resistance in enteric bacilli

Resistance to amikacin among members of the family Enterobacteriaceae at a hospital in Venezuela rose from 2% in 1979 to 5% in 1984 and 10% in 1985 as amikacin usage rose 20-fold to exceed gentamicin usage. Resistance to gentamicin remained at 25 to 27%. We examined the plasmids from 21 isolates obtained in 1984 and 1985. Nine of eleven in 1984 and three of ten in 1985 carried aacA and sul on a 3.8-kb BamHI fragment of pBWH300, a 10.4-kb nonconjugative plasmid that had been mobilized into strains of six species by at least two different coresident conjugative plasmids. Six 1985 isolates of two species carried these genes on a similar BamHI fragment of the 104-kb conjugative plasmid pBWH303. One isolate in 1984 and one in 1985 carried the 69-kb conjugative plasmid pBWH301, which had aacA as the promoter-proximal gene of an operon that also encompassed the cat and aadB resistance genes. Another conjugative plasmid, pBWH302, was found in a single isolate. It carried a different aacA allele on the functional transposon Tn654, which appeared to be closely related to Tn1331, a transposon previously isolated in Argentina and Chile. Increased selection may thus have led to dissemination of an endemic aacA allele on two endemic plasmids, one spread by mobilization, with occasional intrusion of additional aacA alleles from outside.

Section: Resultsmentioning

confidence: 99%

Nosocomial spread of an amikacin resistance gene on both a mobilized, nonconjugative plasmid and a conjugative plasmid

Hopkins

Flores

Pilar

et al. 1991

“…Nontransferable (i.e., chromosomally specified) AAC(6') production by Serratia strains resulting in amikacin resistance without concomitant gentamicin resistance has also been reported (10). Recently, two other aminoglycoside-modifying enzymes, 4'-aminoglycoside nucleotidyltransferase and a 3'-phosphotransferase, have been reported to result in resistance to amikacin without concomitant resistance to gentamicin (4,9).…”

Section: Discussionmentioning

confidence: 99%

Increased resistance to amikacin in a neonatal unit following intensive amikacin usage

Friedland

Funk

Khoosal

et al. 1992

Gram-negative isolates from blood and cerebrospinal fluid were monitored for 1 year before and for 1 year after the first-line aminoglycoside in a busy pediatric department was changed from gentamicin to amikacin.In the general pediatric wards, the switch to amikacin resulted in no change in resistance of nosocomial gram-negative infections to either amikacin (0%Yo before and after) or gentamicin (23.9% [before] versus 26.5% [after]). In the neonatal unit, the switch to amikacin was followed by an outbreak of Serratia spp. that were commonly resistant to amikacin but susceptible to gentamicin. This outbreak abated spontaneously. In the year after the change in aminoglycoside usage, the resistance to amikacin of nosocomially acquired gram-negative infections increased from 7.6 to 27.7% (P < 0.001), and the resistance to gentamicin decreased from 71.2 to 60.2% (P = 0.07). The increase in amikacin resistance of gram-negative bacilli other than Serratia spp. has persisted for more than a year after the introduction of amikacin as the sole aminoglycoside. The different effects observed in the two sections of the pediatric department may be related to the more intensive usage of aminoglycosides in the neonatal unit.The effect of predominant amikacin usage on susceptibility of gram-negative bacteria (GNB) to aminoglycosides is well documented (1, 5-7, 11, 13, 17, 19, 22-24, 28, 30). Those studies showed that frequent usage of amikacin usually results in no increase or only a slight increase in resistance to amikacin and a decrease in resistance to other aminoglycosides. However, in none of those studies were communityand hospital-acquired infections analyzed separately. Also, GNB isolated from all sites were included, and except in one study (6), invasive disease was not separated from colonization without invasion. Because all infections were combined, increases in amikacin resistance of nosocomial infections may have been "diluted" by the inclusion of large numbers of community-acquired isolates. Similarly, combining isolates from all sections of a hospital may mask significant changes in a specific area.Further motivation for this study was the lack of information on antimicrobial resistance levels in relation to aminoglycoside usage in developing countries, where overcrowded hospitals with very high rates of patient turnover are common.Because of increasing resistance of GNB to gentamicin, both the neonatal and general pediatric wards of our hospital changed to amikacin as the sole aminoglycoside for suspected GNB infections.The purpose of this study was to record prospectively the effect of intensive amikacin usage on the aminoglycoside resistance patterns of invasive hospital-acquired GNB in a busy pediatric department. MATERIALS AND METHODSPatient population. Baragwanath is the major hospital serving Soweto, South Africa (population of 1 to 2 million).

“…In addition to the ANT(4')-II described here, P. aeruginosa strains were isolated that produced a phosphotransferase that was active on amikacin and an acetyltransferase that was active on netilmicin and other aminoglycosides (unpublished data). At other institutions, substitution of amikacin for alternative aminoglycosides has not generally led to an increased prevalence of resistance (2,11,29,38), but exceptions have also been reported (7,10,25,40). In Denver, the setting was especially conducive for the emergence of antibiotic resistance.…”

mentioning

confidence: 99%

“…In P. aeruginosa and other gram-negative pathogens, enzymes conferring resistance to amikacin have included several varieties of 6'-aminoglycoside acetyltransferase (16,18,19,37), 3-aminoglycoside acetyltransferase V (5,21), and certain 3'-aminoglycoside phosphotransferases (10,22). Other 3'-aminoglycoside phosphotransferases (6,30) and ANT(2")-II (4) can modify amikacin in vitro but apparently do so at slower rates, such that amikacin resistance is not augmented in vivo.…”

mentioning

confidence: 99%

Appearance of amikacin and tobramycin resistance due to 4'-aminoglycoside nucleotidyltransferase [ANT(4')-II] in gram-negative pathogens

Jacoby

Blaser

Santanam

et al. 1990

Following the use of amikacin as the principal aminoglycoside at a Denver hospital, amikacin resistance appeared first in Pseudomonas aeruginosa and then in Escherichia coli, Klebsiella pneumoniae, and other enteric organisms from debilitated and compromised patients who had spent time in intensive care units and who had been treated with multiple antibiotics, usually including amikacin. In a P. aeruginosa isolate, resistance to amikacin and tobramycin was transferable by the IncP-2 plasmid pMG77, while in E. coli and K. pneumoniae resistance was carried by the transmissible plasmids pMG220, pMG221, and pMG222 belonging to the IncM group. Isolates and transconjugants produced an enzyme with adenyltransferase activity with substrates having a 4'-hydroxyl group, such as amikacin, kanamycin, neomycin, Sch 21768, isepamicin (Sch 21420), or tobramycin, but not with aminoglycosides lacking this target, such as dibekacin, netilmicin, sisomicin, or gentamicin C components. Genes encoding the 4'-aminoglycoside nucleotidyltransferase [ANT(4')] activity were cloned from pMG77, pMG221, and pMG222. A DNA probe prepared from the ANT(4') found in P. aeruginosa hybridized with the ANT(4') determinant found in E. coli. A probe for the ANT(4') from Staphylococcal spp., which differs in its modification of substrates, like dibekacin, that have a 4"- but not a 4'-hydroxyl group, failed to hybridize with the gram-negative ANT(4') determinant, which consequently has been termed ANT(4')-II.