Combined Activity of Sulfamethoxazole, Trimethoprim, and Polymyxin B Against Gram-Negative Bacilli

Nonpigmented multiply drug-resistant Serratia marcescens caused an extensive outbreak of infection at the Nashville Veterans Administration Hospital. Isolates were of one serotype resistant to all currently available antimicrobial agents for therapy of systemic infections except for occasional susceptibility to chloramphenicol and kanamycin. Frequently strains were susceptible to nalidixic acid, and all were susceptible to amikacin (BB-K8). Drug-resistant strains caused 130 infections, 12 bacteremias, and 7 infection-associated deaths. Combinations of antimicrobial agents were evaluated for synergism against Serratia strains from infected patients. “Checkerboard” isobolograms indicated in vitro static synergism between sulfamethoxazole, trimethoprim, and polymyxin (STP). Killing curves using clinically achievable concentrations of STP verified the bactericidal effect of STP against these strains. In a daily dosage of 1,600 mg of sulfamethoxazole and 320 mg of trimethoprim orally in combination with 100 to 300 mg of colistimethate parenterally, serum cidal levels at 1:8 or greater were achieved in five of six patients. Clinical improvement or microbiological cure was effected in four of six patients. STP may be potentially useful for selected Serratia infections for which single agents are unavailable or ineffective.

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

Sulfamethoxazole-Trimethoprim-Polymyxin Therapy of Serious Multiply Drug-Resistant Serratia Infections

Thomas

Leonard

Alford

1976

“…Recently, trimethoprim has been found to act synergistically when combined with rifampin and polymyxin (2,3,6). The combination of an aminoglycoside with trimethoprim alone has been evaluated in only a few previous studies (1,5), and none has assessed the interaction of sulfamethoxazole-trimethoprin, the currently available trimethoprim preparation in the United States, with an aminoglycoside.…”

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confidence: 99%

Synergistic Activity of Gentamicin with Trimethoprim or Sulfamethoxazole-Trimethoprim Against Escherichia coli and Klebsiella pneumoniae

Paisley

Washington

1978

The effect of combinations of gentamicin with trimethoprim or sulfamethoxazole-trimethoprim against clinical isolates of Escherichia coli (11 strains) and Klebsiella pneumoniae (12 strains) was examined by using a microdilution checkerboard technique. All isolates were susceptible to each antimicrobial agent. Synergism, defined as at least a 2-log2-dilution lowering of the minimal inhibitory concentration of either antibiotic in the combination compared with the minimal inhibitory concentration of the antibiotic alone, was observed with 15 of 23 (65%) isolates tested against trimethoprim and gentamicin and 14 of 23 (61%) isolates tested against sulfamethoxazole-trimethoprim and gentamicin. A 3-log2-dilution lowering of the minimnal inhibitory concentration of either antibiotic was observed in 7 of 23 (30%) trimethoprim and gentamicin trials and 3 of 23 (13%) sulfamethoxazole-trimethoprim and gentamicin trials. Antagonism was observed in 3 of 46 combination trials and only with strains of K. pneumoniae.The synergism of trimethoprim and sulfamethoxazole against a variety of gram-negative bacilli has been well documented. Recently, trimethoprim has been found to act synergistically when combined with rifampin and polymyxin (2, 3, 6). The combination of an aminoglycoside with trimethoprim alone has been evaluated in only a few previous studies (1, 5), and none has assessed the interaction of sulfamethoxazole-trimethoprin, the currently available trimethoprim preparation in the United States, with an aminoglycoside. The present study examines the interaction of trimethoprim alone and sulfamethoxazole-trimethoprim with gentamicin against strains of Escherichia coli and Klebsiella pneumoniae. MATERIALS AND METHODSStudy organisms were isolated by the Section of Clinical Microbiology from clinical specimens. They were stored on nutrient agar slants and subcultured to sheep blood agar 1 day before testing. The antibiotics included trimethoprim and sulfamethoxazole (Burroughs Weilcome, Research Triangle Park, N.C.) and gentamicin sulfate (Schering Corp., Kenilworth, N.J.). Stock solutions of the antimicrobial agents were stored at -20°C and diluted on the day of use. The sulfamethoxazole-trimethoprim combination consisted of a 20:1 (wt/wt) activity ratio of the respective drugs.Determination of minimal inhibitory concentrations (MICs) and checkerboard synergism testing were done simultaneously on eacn strain by using a microdilution technique. Mueller-Hinton broth was used for all procedures. For tests involving trimethoprim, thymidine phosphorylase (courtesy of S. M. Bushby, Burroughs Weilcome) was added in a final concentration of 0.1 U/ml. Testing for synergism was performed in microtiter plates (Cooke Engineering Co., Alexandria, Va.).The appropriate wells were loaded with 0.05 ml of broth. To one row of wells was added 0.05 ml of the first antibiotic, which was then serially diluted. Finally, 0.05 ml of the second antibiotic was added to one column of wells and serially diluted. Plates were stored in sealed plastic ...

“…Agar dilution can be applied to this technique (11). Several agar diffusion methods are also described (7,9,12).…”

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confidence: 99%

Microdilution Transfer Plate Technique for Determining In Vitro Synergy of Antimicrobial Agents

Dougherty¹,

Yotter²,

Matthews³

1977

A microdilution transfer plate technique for determining in vitro synergy of antimicrobial agents is described. Combinations of gentamicin-nalidixic acid against Proteus mirabilis and rifampin-amphotericin B against Candida albicans are used as examples to demonstrate the technique. Results correlate with published data obtained by conventional methods. The technique is effective for evaluating the in vitro effects of antimicrobial agent combinations against both bacteria and fungi. The technique enables one to produce a checkerboard gradient in a fast, convenient, and reproducible way; results are easily visualized.In vitro synergy of antimicrobial agents is traditionally accomplished using a tube broth dilution "checkerboard" in which several concentrations of one drug are each combined with concentrations of a second drug (4,14). Agar dilution can be applied to this technique (11). Several agar diffusion methods are also described (7,9,12). Microdilution methods have been described for determining synergy (3, 5, 6, 15, 16). Two methods (15, 16) involve dilution of both drugs before pipetting each into the microdilution plate. The method of Kluge et al. (6) requires diluting one drug in the microdilution plate, then adding the second drug (already diluted) to the wells containing the first drug. In two other methods described (3,5) Cultures and growth media. P. mirabilis (ICN 40) was used for the nalidixic acid-gentamicin combination; brain heart infusion (Difco) was the medium used for this example. C. albicans (ICN 80) was used for the amphotericin B-rifampin combination; a medium containing a yeast-nitrogen base (Difco), Lasparagine, and dextrose was used (13).All incubations were for 18 to 24 h at 35°C. Synergy assay. The test for synergy was performed using a 96-well, flat-bottom microdilution plate (Microtest II, Falcon, Div. of Becton, Dickinson & Co., Oxnard, Calif.) and 50-Al microdiluters (Cooke) to dilute drug I. Drug II was diluted in a transfer plate (Cooke) using 25-,l microdiluters (Cooke). Wells in the transfer plate have a calibrated orifice designed to retain the material in the well by surface tension until contact is made with the fluid in the flat-bottom plate. This contact breaks the surface tension and allows all wells ofthe transfer plate to drain. The system includes a transfer plate holder and carrier, which were autoclaved before use. Pipetting into plates was accomplished using precision pipettes with sterile, disposable tips (Medical Laboratory Automation Inc., Mt. Vernon, N. Y.).The flat-bottom plate was prepared by first pipetting 50 ,l of growth media into each well. Next, 50 ,ul of drug I was pipetted into all wells of row B (12 wells across). Twofold serial dilutions were then made from row B through row G using 50-/l microdiluters.The transfer plate was prepared by first pipetting 25 ,ul of growth media into each well. Next, 25 Al of drug II was pipetted into all wells of column 2 (8 wells across). Twofold serial dilutions were made from column 2 through column 11 using 2...