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PubMed1983

Inhibition of lysosomal phospholipases by aminoglycoside antibiotics: in vitro comparative studies.

Aminoglycoside antibiotics induce an early and characteristic lysosomal phospholipidosis in cultured fibroblasts and in kidney tubular cells. We have recently demonstrated an inhibition of lysosomal phospholipases A1 and A2 by gentamicin and amikacin in vitro. In vivo, gentamicin decreases the activity of phospholipase A1 (Laurent et al., Biochem. Pharmacol. 31:3861-3870, 1982). In the present study, we examined 14 aminoglycosides for in vitro inhibition of phospholipases. To mimic the situation prevailing in lysosomes, the enzymatic activities were assayed with phospholipid vesicles (liposomes) with a composition similar to that of lysosomal phospholipids (phosphatidylcholine, sphingomyelin, phosphatidylinositol, cholesterol; 4:4:3:5.5, molar ratio). We measured the hydrolysis of 1-palmitoyl-2-[1-14C]oleoyl phosphatidylcholine contained in the liposomes by a soluble fraction of highly purified lysosomes isolated from rat liver. Similar IC50S (concentrations causing 50% inhibition of enzymatic activity) were observed for dibekacin, gentamicin (with no major difference between C1, C1a, or C2), netilmicin, tobramycin, and kanamycin B. Sisomicin was slightly more inhibitory. Kanamycin A, N1-(L-4-amino-2-hydroxy-1-oxobutyl)dibekacin, and amikacin showed increasing IC50S. Streptomycin caused the least inhibition. Octa- and tetramethylkanamycin A are much less inhibitory than the parent drug. These results point to the number, the nature, and the respective positions of the cationic groups as essential determinants in causing inhibition of phospholipid breakdown. The binding of three aminoglycosides (gentamicin, amikacin, streptomycin) to the liposomes at pH 5.4 was also measured by gel permeation and was found to be related to the respective inhibitory potency of each drug. Insofar as lysosomal phospholipidosis is an early sign of intoxication by aminoglycosides, these results may serve as a basis for the development or screening of less toxic compounds in this class of antimicrobial agents.

Aminoglycosides↗
PubMed1983

Self-transmissible plasmids in staphylococci that encode resistance to aminoglycosides.

High-level resistance to gentamicin, tobramycin, and kanamycin was transferred between staphylococci of the same and different species by filter mating. Resistance and transfer proficiency were mediated by plasmids ranging from 38 to 54 kilobases in size. All of the plasmids encoded intermediate resistance to amikacin and netilmicin and resistance to ethidium bromide; some encoded beta-lactamase production. None of these plasmids carried resistance to other antibiotics or heavy metals. Transfer of antibiotic resistance occurred by a mechanism similar to that of conjugation, because it was DNase resistant, required cell-to-cell contact, and did not appear to involve phage. The participation of phage in transfer appeared to be unlikely because mijtomicin C-induced lysates of donor isolates did not mediate transfer, filter mating transfer proceeded at high frequency between nonlysogenic donor and recipient cells, and transfer of the aminoglycoside resistance plasmid mobilized the transfer of as many as five additional plasmids. All 17 gentamicin-resistant Staphylococcus aureus and all 6 Staphylococcus epidermidis isolates obtained from an outbreak of staphylococcal infections in a newborn nursery contained conjugative plasmids, as did all 6 gentamicin-resistant S. aureus isolates from bacteremic adults. However, only 3 of 10 gentamicin-resistant S. epidermidis isolates from colonized cardiac surgery patients and 1 of 2 S. epidermidis isolates from patients with prosthetic valve endocarditis transferred gentamicin resistance by filter mating. The recent increase in nosocomial infections caused by gentamicin-resistant staphylococci may be partially explained by the evolution of self-transmissible plasmids in these isolates.

Aminoglycosides↗
PubMed1984

Relation between aminoglycoside 2"-O-nucleotidyltransferase activity and aminoglycoside resistance.

The relationship between plasmid-coded aminoglycoside 2"-O-nucleotidyltransferase [ANT(2")] activity and the minimum inhibitory concentration for aminoglycosides was studied. ANT(2") was very unstable, and therefore, procedures for handling this enzyme were optimized. Escherichia coli L58058.1 producing ANT(2") was resistant to gentamicin, sisomicin, kanamycin, tobramycin, and dibekacin but susceptible to netilmicin, amikacin, and neomycin. However, only amikacin and neomycin were not modified by ANT(2"). A correlation between the substrate profile of the enzyme tested at 0.15 mM and the minimum inhibitory concentrations of the aminoglycosides could not be demonstrated. The substrate concentration-dependent enzyme activity curves proved to be a better alternative than a substrate profile based on tests at one concentration. At concentrations of greater than 10(-2) mM, ANT(2") demonstrated substrate inhibition that explains the discrepancy between ANT(2") activity and the minimum inhibitory concentrations. A close correlation was found between the physiological efficiency (Vmax/Km ratio) of ANT(2") and the minimum inhibitory concentrations for the enzyme-producing strain.

Aminoglycosides↗
PubMed1984

In vitro synergistic activities of aminoglycosides and new beta-lactams against multiresistant Pseudomonas aeruginosa.

The in vitro interactions between amikacin, netilmicin, tobramycin, gentamicin, and various antipseudomonal beta-lactams were studied by the agar dilution checkerboard technique against 30 Pseudomonas aeruginosa strains resistant to all tested antibiotics. Amikacin produced more frequent synergy both at the total and clinically applicable level. Among the beta-lactams, clinically relevant synergistic interactions were obtained in the following order: ceftazidime and ceftriaxone greater than moxalactam greater than aztreonam greater than cefotaxime greater than azlocillin greater than cefoperazone greater than cefsulodin greater than carbenicillin.

Aminoglycosides↗
PubMed1984

Identification of aminoglycoside-acetylating enzymes by high-pressure liquid chromatographic determination of their reaction products.

A method to identify the aminoglycoside-acetyltransferase (AAC) enzymes AAC(3), AAC(2') and AAC(6') by high-pressure liquid chromatographic characterization of their products of reaction with tobramycin or sisomicin is described. Conditions are given for the chromatography of kanamycin A, netilmicin, neomycin, and apramycin, and their products of reaction, if any, with the three AAC enzymes are listed.

Acetylation↗
PubMed1984

Susceptibilities of 45 clinical isolates of Proteus penneri.

Patterns of susceptibility of 45 Proteus penneri clinical isolates to 14 antimicrobial agents were evaluated by a macrobroth dilution method. All strains were highly susceptible to ceftizoxime, ceftazidime, moxalactam, cefoxitin, gentamicin, tobramycin, netilmicin, and, with few exceptions, to amikacin, piperacillin, and cefoperazone. Most strains were susceptible to cefotaxime and ceftriaxone. All strains were resistant to cefazolin and cefsulodin.

Anti-Bacterial Agents↗
PubMed1984

Synergism at clinically attainable concentrations of aminoglycoside and beta-lactam antibiotics.

We evaluated the in vitro synergistic activity at clinically attainable concentrations of combinations of aminoglycoside and beta-lactam antibiotics against 30 gentamicin-resistant clinical isolates of gram-negative bacilli. All 56 pairs of 4 aminoglycosides and 14 beta-lactams were evaluated. Combinations with amikacin demonstrated inhibitory synergistic activity in 29% of the assays, as compared with 22% for netilmicin (P = 0.018), 17% for gentamicin (P less than 0.001), and 13% for tobramycin (P less than 0.001). Among the beta-lactams, combinations with cefoperazone, ceftriaxone, or cefpiramide (SM-1652) demonstrated inhibitory synergistic activity most often (39, 38, and 35% of the assays, respectively) and with ceforanide, cefsulodin, and imipenem least often (less than or equal to 8% each). The most active combination was amikacin and ceftriaxone, with which 67% of the assays demonstrated inhibitory synergism. Isolates with high-level resistance to either antibiotic in a combination were unlikely to be inhibited synergistically by the combination. Further, combinations generally demonstrated little synergistic activity against isolates highly susceptible to beta-lactams.

Aminoglycosides↗
PubMed1985

In vitro antibacterial activities of antibiotics against Pseudomonas aeruginosa in peritoneal dialysis fluid.

Intraperitoneal antibiotics are used to treat Pseudomonas aeruginosa peritonitis, a serious complication of continuous ambulatory peritoneal dialysis. However, P. aeruginosa killing is often inefficient despite low MBCs. Broth dilution MIC/MBC and time kill curves of tobramycin, amikacin, netilmicin, azlocillin, piperacillin, ceftazidime, cefsulodin, and ciprofloxacin were determined in peritoneal dialysis fluid (PDF), buffered PDF, fluid recovered from patients on continuous ambulatory peritoneal dialysis (RPF), and cation-supplemented Mueller-Hinton broth. MBCs of all antibiotics were 8 to 16 times greater in PDF and RPF than in Mueller-Hinton broth or buffered PDF. Use of the time kill curve technique and Mueller-Hinton broth showed that aminoglycosides killed greater than or equal to 99.9% of P. aeruginosa at 1 h, ciprofloxacin killed greater than or equal to 99.9% at 2 h, and beta-lactams killed greater than or equal to 99.9% at 6 h. In contrast, killing was not demonstrated in PDF by any drug at 6 h and by aminoglycosides only at 24 h. Bactericidal activity was optimal in RPF for ciprofloxacin at 1 h and for aminoglycosides at 2 h; bactericidal activity was not demonstrated in RPF with any beta-lactam (no kill by penicillins; less than 99% kill by cephalosporins). Slow bacterial growth, increased protein binding, and glucose concentrations and other inhibitors may interfere with beta-lactam activity in RPF. These considerations and reported clinical failures and toxicity of aminoglycoside therapy warrant further study of quinolones and drug combinations in P. aeruginosa peritonitis.

Anti-Bacterial Agents↗
PubMed1985

Comprehensive evaluation of ciprofloxacin-aminoglycoside combinations against Enterobacteriaceae and Pseudomonas aeruginosa strains.

The in vitro activities of antibiotic combinations containing ciprofloxacin and either gentamicin, sisomicin, netilmicin, amikacin, or tobramycin were evaluated by checkerboard assay (agar dilution method). A total of 220 strains of Enterobacteriaceae and Pseudomonas aeruginosa (11 species, 20 strains each) were tested. Synergistic or antagonistic effects were observed in less than 1% of the tests performed; they appeared to represent method-dependent fluctuations rather than true antibiotic interactions. No significant differences among the five aminoglycosides tested were seen. Time-kill experiments performed with three representative strains of Escherichia coli and Serratia marcescens showed additive combination effects with respect to the kill rates and inhibition of bacterial regrowth. Exposure of Serratia strains to either ciprofloxacin or gentamicin before the addition of the second drug had little influence on the combination effects observed. No antagonistic drug interactions were seen in vivo when combination therapy with ciprofloxacin and gentamicin was evaluated in a model of E. coli thigh muscle infection in neutropenic mice. Comparable therapeutic effects were obtained, regardless of whether the two compounds were administered simultaneously or sequentially at 1- or 2-h intervals.

Aminoglycosides↗
PubMed1986

In vitro activity of piperacillin, ticarcillin, and mezlocillin alone and in combination with aminoglycosides against Pseudomonas aeruginosa.

A total of 103 isolates of Pseudomonas aeruginosa were studied to compare the in vitro effectiveness of three beta-lactam antibiotics (piperacillin, ticarcillin, and mezlocillin) when used alone and in combination with four aminoglycosides (tobramycin, gentamicin, amikacin, and netilmicin). All drugs were tested as single agents against a standard inoculum (5 X 10(5) CFU/ml). The three antipseudomonal penicillins were also tested against the isolates at a higher inoculum concentration (10(7) CFU/ml). Synergy testing was performed by the two-dimensional checkerboard method and was defined by a fractional bactericidal index of less than or equal to 0.5 and bacterial killing accomplished at antibiotic concentrations no greater than those achievable in serum. All combinations were assessed for synergy. The degree of synergy was further analyzed by dividing the isolates into groups based on their susceptibility and resistance to the individual agents in the combination. The overall effectiveness of the various aminoglycoside-antipseudomonal penicillin combinations was assessed regarding their ability to kill the isolates either as single agents or through synergy. Piperacillin was the most active antipseudomonal penicillin, and tobramycin and amikacin were the most active aminoglycosides when used as single agents. When tested against isolates at a higher inoculum concentration, ticarcillin was significantly more active than the other beta-lactams. The highest degree of overall synergy was noted with gentamicin-ticarcillin (78.2% of strains) and amikacin-piperacillin (77% of strains). When assessed for overall effectiveness, all combinations containing amikacin were the most active. The combination of amikacin-piperacillin was the most effective, with activity against 96% of all isolates.

Aminoglycosides↗
PubMed1986

Membrane perturbation by aminoglycosides as a simple screen of their toxicity.

A simple test to assess the toxicity of aminoglycosides was designed based on the interaction of these drugs with phosphatidylinositol bisphosphate. The fluorescent probe 1-anilino-8-naphthalene sulfonate was incorporated into liposomes composed of L-alpha-phosphatidylcholine and phosphatidylinositol bisphosphate (4:1 molar ratio), and changes in fluorescence induced by the aminoglycosides were measured. The magnitude of these changes correlated well with the intrinsic ototoxicity of the drugs previously established in cochlear perfusions: neomycin greater than gentamicin approximately equal to tobramycin greater than amikacin approximately equal to kanamycin approximately equal to netilmicin greater than neamine approximately equal to spectinomycin. Correlations were not accurate when other phospholipids were substituted for phosphatidylinositol bisphosphate. An alternative in vitro test, measurement of the zeta potential of liposomes, ranked the drugs according to their electrostatic charge but not their toxicity. These results suggest that: a simple screen for aminoglycoside toxicity can be established and perturbation of membranes containing phosphatidylinositol bisphosphate is a key step in aminoglycoside ototoxicity.

Aminoglycosides↗
PubMed1987

Correlation between renal membrane binding and nephrotoxicity of aminoglycosides.

The kinetics of aminoglycoside binding to renal brush border and basolateral membrane vesicles from rat renal cortex were studied by using [3H]amikacin. [3H]amikacin binding to renal membranes was found to be a rapid, saturable process with a fourfold greater affinity for basolateral membranes than for brush border membranes (Kd basolateral = 607 microM; Kd brush border = 2,535 microM). Renal membranes prepared from immature rats (2 to 3 weeks old) exhibited a significantly lower affinity compared with membranes from adults (Kd basolateral = 2,262 microM; Kd brush border = 6,216 microM). Additionally, the inhibitory behavior of several aminoglycosides versus [3H]amikacin binding to brush border membranes revealed the following rank order of potency: neomycin greater than tobramycin approximately gentamicin approximately netilmicin greater than amikacin approximately neamine greater than streptomycin. The relative insensitivity of immature rats to aminoglycoside-induced nephrotoxicity in vivo and the comparative nephrotoxicity of the various aminoglycosides suggest that renal membrane-binding affinity is closely correlated to the nephrotoxic potential of these antibiotics.

Aminoglycosides↗
PubMed1987

In vitro susceptibility of Citrobacter species to various antimicrobial agents.

The in vitro activities of 16 antimicrobial agents against 14 clinical isolates of Citrobacter diversus and 27 isolates of Citrobacter freundii were studied. C. freundii isolates were more resistant, being susceptible only to amikacin, netilmicin, gentamicin, imipenem, ciprofloxacin, and enoxacin. C. diversus isolates were susceptible to many more of the agents tested.

Anti-Bacterial Agents↗
PubMed1988

In vitro activity of LY146032 alone and in combination with other antibiotics against gram-positive bacteria.

The antibacterial activity of LY146032 alone and in combination with other drugs was assayed against gram-positive isolates. Synergism was found when LY146032 was combined with netilmicin, amikacin, imipenem, and fosfomycin by both checkerboard and time-kill tests. Indifference predominated when LY146032 was combined with teicoplanin, vancomycin, and rifampin. Under no circumstances and with no combinations was an antagonistic effect detected.

Anti-Bacterial Agents↗
PubMed1988

Aminoglycoside resistance among Pseudomonas aeruginosa isolates with an unusual disk diffusion antibiogram.

In recent years, a number of clinical microbiology laboratories have isolated Pseudomonas aeruginosa with the unusual aminoglycoside disk diffusion result of resistance to both amikacin and gentamicin but susceptibility to tobramycin (ArGrTs). A total of 39 isolates of P. aeruginosa reported to have this resistance pattern were retested by the standard National Committee for Clinical Laboratory Standards disk diffusion procedure; 30 strains (77%) were confirmed to be ArGrTs. These 30 isolates were further examined for susceptibility to those aminoglycosides by agar dilution and broth micro- and macrodilution methods. Only 27, 27, and 23% of the isolates appeared to be ArGrTs by agar, broth microdilution, and broth macrodilution testing, respectively. Most of the remaining isolates were resistant to all three aminoglycosides when tested by broth dilution and resistant only to gentamicin when tested by agar dilution. The percentages of strains resistant to any particular aminoglycoside by agar dilution, broth microdilution, and broth macrodilution, respectively, were 43, 80, and 70 for amikacin, 97, 93, and 100 for gentamicin, 100, 100, and 100 for netilmicin, 30, 87, and 93 for sisomicin, and 13, 57, and 50 for tobramycin. These results indicate that strains showing the unusual aminoglycoside antibiogram are less susceptible to aminoglycosides in general and should probably be considered borderline resistant to all aminoglycosides. The efficacy of aminoglycosides in the treatment of infections produced by these strains is unknown.

Amikacin↗
PubMed1989

Isolation, characterization, and DNA sequence analysis of an AAC(6')-II gene from Pseudomonas aeruginosa.

The gene encoding a 6'-N-acetyltransferase, AAC(6')-II, was cloned from Pseudomonas aeruginosa plasmid pSCH884. This gene mediates resistance to gentamicin, tobramycin, and netilmicin but not amikacin or isepamicin. The DNA sequence of the gene and flanking regions was determined. The 5'- and 3'-flanking sequences showed near identity to sequences found abutting a variety of different genes encoding resistance determinants. It is likely that the current structure arose by the integration of the 572-base-pair sequence containing the AAC(6')-II gene into a Tn21-related sequence at the recombinational hot spot, AAAGTT. We have compared the sequence of the AAC(6')-II gene to genes of other 6'-N-acetyltransferases. An AAC(6')-Ib protein (encoded by the aacA4 gene; G. Tran Van Nhieu and E. Collatz, J. Bacteriol. 169:5708-5714, 1987) that results in resistance to amikacin but not gentamicin was found to share 82% sequence similarity with the AAC(6')-II protein. We speculate that these two genes arose from a common ancestor and that the processes of selection and dissemination have led to the observed differences in the spectrum of aminoglycoside resistance.

Acetyltransferases↗
PubMed1989

Do double-beta-lactam combinations prolong neutropenia in patients undergoing chemotherapy or bone marrow transplantation for hematological disease?

The total period of neutropenia was assessed in 174 episodes after chemotherapy or bone marrow transplantation in which patients received antibiotics for fever in a randomized prospective trial. Log rank analysis demonstrated no significant difference in the total duration of neutropenia between patients receiving netilmicin plus either piperacillin or azlocillin and those given ceftazidime plus either piperacillin or azlocillin. Of 86 patients in the single-beta-lactam group, 27 had a persistent neutrophil count of 0.1 x 10(9) per liter during treatment compared with 27 of 88 patients in the double-beta-lactam group, and 29 of 68 patients treated with the single-beta-lactam combination had a total period of neutropenia greater than 30 days versus 36 of 75 in the double-beta-lactam group. The use of two beta-lactam antibiotics rather than one does not appear to prolong neutropenia in patients undergoing treatment of hematological malignancy. However, in order to determine the effect of a single-beta-lactam combination, a similar carefully controlled prospective randomized study in which such treatment is compared with a non-beta-lactam-containing regimen is required.

Adult↗
PubMed1989

Antimicrobial susceptibility of Plesiomonas shigelloides from patients with diarrhea.

Antimicrobial susceptibility testing was performed on 72 fecal isolates of Plesiomonas shigelloides from patients with diarrhea by using a standard agar dilution technique. All isolates were obtained from a single geographic location. Based on the in vitro activities demonstrated in this study, norfloxacin, ciprofloxacin, and trimethoprim may be effective as oral agents in the treatment of P. shigelloides diarrheal disease. For the parenteral treatment of extraintestinal infection, netilmicin and the cephalosporins had the best in vitro activity.

Anti-Bacterial Agents↗