Microbiologic Studies Related to Bacterial Resistance to Gentamicin

Weinstein, Marvin; Drube, C. G.; Moss, Eugene L.; Waitz, J. A.

doi:10.1093/infdis/124.supplement_1.s11

Cited by 54 publications

(27 citation statements)

References 6 publications

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“…Resistant variants selected by incubation with gentamicin were also resistant to amikacin (data not shown), in agreement with earlier results showing cross-resistance among different aminoglycosides (10). The results of several investigations indicate that the aminoglycoside-resistant variants differ from the susceptible members of the population in forming smaller colonies (5,14,25,27). They also grow more slowly (5,11,27), are more fastidious (27), and are more susceptible to the bactericidal effect of normal serum (24).…”

supporting

confidence: 90%

“…Aminoglycoside-resistant subpopulations in gram-negative (5,12,14,25,27) unclear, but probably involves a penetration barrier (2,15,20). In the present work bacteria resistant to up to 8 pug of gentamicin per ml were observed, but the upper level of this type of resistance is not known.…”

mentioning

confidence: 99%

“…The results of several investigations indicate that the aminoglycoside-resistant variants differ from the susceptible members of the population in forming smaller colonies (5,14,25,27). They also grow more slowly (5,11,27), are more fastidious (27), and are more susceptible to the bactericidal effect of normal serum (24). However, many of these results were obtained in experiments where the bacteria had been passaged repeatedly on antibiotic-containing media, which might change their growth properties.…”

mentioning

confidence: 99%

“…(1,8). In several reports resistant small-colony variants were shown to be apathogenic in animal models (11,27), although in one investigation the pathogenic potential of these bacteria in rats was demonstrated (16) media. In MIC determinations in solid media the resistant variants form single colonies.…”

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confidence: 99%

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Regrowth of aminoglycoside-resistant variants and its possible implication for determination of MICs

Sörén¹,

Nilsson²

1984

Antimicrob Agents Chemother

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Regrowth of aminoglycoside-resistant variants was seen when large inocula of two strains of Escherichia coli were incubated with gentamicin in concentrations well above their MICs (0.5 ,ig/ml). The extent of the selection of resistant variants was proportional to the concentration of gentamicin during incubation; after incubation with gentamicin (22 ,ug/ml for 24 h), all bacteria were resistant to at least 8 ,ug/ml. Bacteria resistant to these concentrations always formed small colonies, whereas variants resistant to lower concentrations (1 to 2 ,ug/ml) could form both small and normal colonies. The regrowth of resistant variants could be monitored by luciferase assay of intracellular ATP in cultures incubated with gentamicin (c2 ,ug/ml). In cultures incubated with higher concentrations, regrowth did occur, although this did not result in viability (CFU per milliliter) or ATP levels above those of the initial inocula. The implications of this regrowth for MIC determinations in broth and the possible clinical revelance of the resistant variants are discussed.The endpoint in MIC determinations, i.e., visible growth after overnight incubation, is the net result of a series of possible events occurring during a long period of incubation (9).These events include the initial killing of bacteria, liberation of enzymes that degrade the antibiotic, pH and other media changes that affect the activity of the antibiotic, and finally the possible regrowth of bacteria that have survived the exposure to the antibiotic. All of these factors may differ among different bacteria and antibiotics and are in general difficult to control.Regrowth of bacteria is seen quite frequently when gramnegative enteric bacteria are exposed to aminoglycosides (5). This regrowth seems to be due to the selective multiplication of resistant variants that are present in a low frequency in the initial inoculum (5,14,25). Such a regrowth obviously complicates the interpretation of MIC determinations performed in broth. The phenomenon could account for some of the following discrepancies observed in MIC determinations against aminoglycosides: (i) different MICs obtained by rapid methods and conventional methods with overnight incubation, (ii) different MICs obtained in broth and solid media (which may also be due to differences in cationic content [26]), and (iii) the pronounced effect of inoculum size on the MIC.The demonstration of regrowth by viable count is cumbersome. The possibility of monitoring the regrowth by the firefly bioluminescence assay of intracellular ATP (24) was therefore explored. Intracellular bacterial ATP increases concomitantly with viability (CFU per milliliter) (18,19), and the assay of intracellular ATP is therefore a sensitive method for monitoring bacterial growth.In this work the quantitative aspects of regrowth in aminoglycoside-exposed cultures was studied by determination of viability combined with population analysis and also by assay of intracellular ATP. (ii) Disk diffusion. Disk diffusion assays were performed with 3...

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supporting

confidence: 90%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Regrowth of aminoglycoside-resistant variants and its possible implication for determination of MICs

Sörén¹,

Nilsson²

1984

Antimicrob Agents Chemother

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“…A closer approximation to a physiological composition of culture media is desirable to improve the extrapolation from in vitro to in vivo bactericidal action of gentamicin. In one study, the 50% protective dose of gentamicin in mice challenged with P. aeruginosa correlated fairly well with resistance in tryptose-phosphate broth and less so in Mueller-Hinton broth (31). Without regard to definition of resistance and irrespective of method-dependent values, we can conclude that there was a significant emergence of strains with decreased in vitro susceptibility to gentamicin after its first clinical use in 1969, accompanied by a fourfold increase in amounts dispensed during the three subsequent years.…”

Section: Resultsmentioning

confidence: 97%

Hospital Pseudomonas aeruginosa : Surveillance of Resistance to Gentamicin and Transfer of Aminoglycoside R Factor

Maliwan

Grieble

Bird

1975

Antimicrob Agents Chemother

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). The other antimicrobials were tested in TS broth only. The strains were grown for 18 h and subcultured for 4 h before inoculation of 104 organisms into 1.0 ml of medium containing antibiotic. After overnight incubation, the tubes were observed for minimum inhibitory concentration. Nonturbid dilutions were streaked on TS agar plates, incubated, and observed for growth 18 h later. Susceptible Pseudomonas strains (Ellsworth and Hines no. 954) and a resistant strain (Hines no. 1109) were used as susceptibility test controls.All transfer experiments were done in TS media. Resistance transfer factor was sought be standard methods for conjugation (29) and replica plating (16). For recombination, overnight cultures of donor and recipient were diluted 1:10 in TS broth and incubated at 37 C for 4 h with shaking (125 rpm). Two milliliters of donor and 0.1 ml of recipient cultures were mixed in a 50-ml Erlenmeyer flask and incubated at 37 C for 4 h without agitation. Aliquots of 0.1 ml of a 10-5 dilution were spread on TS plates and incubated at 37 C overnight. TS replica plates containing 50 Ag of gentamicin and 1,000 Mg of carbenicillin per ml were incubated overnight at 37 C for selection of exconjugants. For curing of resistance, ethidium bromide was used at 6 x 10-6 M (27), and acridine orange and acriflavine neutral in a range of 1.5 to 100 Ag/ml were used (30). The dyes were used both with and without 15-s

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Importance of Adaptive and Stepwise Changes in the Rise and Spread of Antimicrobial Resistance

Fernández¹,

Breidenstein²,

Hancock³

2011

Antimicrobial Resistance in the Environment

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Microbiologic Studies Related to Bacterial Resistance to Gentamicin

Cited by 54 publications

References 6 publications

Regrowth of aminoglycoside-resistant variants and its possible implication for determination of MICs

Regrowth of aminoglycoside-resistant variants and its possible implication for determination of MICs

Hospital Pseudomonas aeruginosa : Surveillance of Resistance to Gentamicin and Transfer of Aminoglycoside R Factor

Importance of Adaptive and Stepwise Changes in the Rise and Spread of Antimicrobial Resistance

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