Sensitivity of Nocardia to trimethoprim and sulphonamides in vitro

Treatment and outcome of nocardia keratitis

OBJECTIVE

To report our experience in treatment and outcome ofNocardia keratitis.

METHODS

Medical and microbiology records of seven cases of culture-provenNocardia keratitis seen between January 1997 and March 1999 were reviewed retrospectively. In all patients, corneal scrapings were obtained for direct microscopic evaluation and culture. Drug sensitivity was determined by the Kirby-Bauer disk-diffusion method. The minimum inhibitory concentration of ciprofloxacin and amikacin for these isolates was determined by agar dilution method. Response to medical therapy and the end result were analyzed.

RESULTS

By the in vitro Kirby-Bauer disk-diffusion techniques, all isolates were sensitive to amikacin; six of these isolates were sensitive to gentamicin and four were sensitive to ciprofloxacin. The minimum inhibitory concentration (MIC) of amikacin for all isolates by the agar-dilution technique was well below the MIC breakpoint forNocardia resistance, whereas the MIC of ciprofloxacin was above the MIC breakpoint forNocardia resistance. All patients responded to medical therapy. The corneal infection resolved in three patients after treatment with ciprofloxacin, in one patient after fortified gentamicin, and in three patients after fortified amikacin. Outcome details were available for six patients. There was good visual recovery in four patients, with visual acuity of 20/25 or better in three. The cornea of two patients developed nonvascularized scars, and in four patients in whom the infiltrates were peripheral, vascularization was seen.

CONCLUSIONS

Although patients ofNocardia keratitis may respond to other antibiotics, amikacin appears to be a drug of choice. In this small series, when appropriate therapy was initiated,Nocardia keratitis resolved promptly with good visual recovery.

Ocular nocardia infections with special emphasis on the cornea

Nocardia are aerobic, gram-positive, nonmotile and branching filamentous bacteria. Corneal infection by Nocardia is rare. Trauma is the most common predisposing factor. Isolated case reports of nocardial infection associated with contact lens wear and laser in situ keratomileusis (LASIK) have been reported. The clinical picture usually consists of superficial patchy infiltrates, which may be arranged in a wreath pattern. Presence of gram-positive, branching, beaded filaments that stain with 1% acid-fast stain (using 1% sulfuric acid, modified Kinyoun's method) in smears of corneal scrapings is suggestive of nocardial infection. Nocardia grow on commonly used media as tiny, white, dry colonies. Available knowledge and clinical experience suggest that although sulfacetamide eyedrops can be tried as the initial drug, trimethoprim-sulfamethoxazole and amikacin are effective drugs. Once therapy is initiated, the infiltrate responds promptly and resolves, forming a corneal scar with or without vascularization, and good visual recovery can be expected.

An improved screening technique for isolation of Nocardia species from sputum specimens

Three selective isolation media and the paraffin baiting technique were compared with conventional culture (Sabouraud dextrose agar without antibiotic supplement) for the ability to grow and detect nocardiae from simulated sputum specimens. Modified Thayer-Martin medium, incorporating vancomycin, colistin, nystatin and trimethoprim as selective agents, produced the highest recovery rate and with the greatest suppression of normal respiratory tract flora. A clinical evaluation using a screening programme devised for a busy diagnostic microbiology laboratory was performed on 1600 sputum specimens. Inoculating sputum on modified Thayer-Martin medium and extending the initial incubation period of 3 days at 35 degrees C under 10% carbon dioxide to a further 3 weeks at room temperature in a candle jar, led to the diagnoses, which otherwise would have been missed, of pulmonary nocardiosis in 3 patients and pulmonary infections due to Neisseria meningitidis, Pseudomonas cepacia, and Serratia marcescens in a further 22 patients.

In vitro studies of antibiotic sensitivities of Streptomyces somaliensis--a cause of human actinomycetoma

Ten Streptomyces somaliensis strains isolated from mycetoma patients were tested in vitro against 13 antibacterial agents. Rifampicin was the most effective antibiotic in terms of low minimum inhibitory concentration (MIC) followed by erythromycin, tobramycin, fusidic acid and streptomycin sulphate. The S. somaliensis strains were all resistant to trimethoprim, even though the combination of sulphamethoxazole and trimethoprim is commonly used as treatment.

Cutaneous nocardiosis. Case reports and review

Two cases of cutaneous nocardial infection are reported. The Nocardia species are gram-positive, partially acid-fast bacteria. Cutaneous involvement may develop as one of four types: (1) mycetoma, (2) lymphocutaneous (sporotrichoid) infection, (3) superficial skin infection, or (4) systemic disease with cutaneous involvement. A review of each of these types of infection is included, as well as potential clues that may suggest the diagnosis of nocardiosis.

Synergistic action of trimethoprim and sulfamethoxazole for Nocardia asteroides: efficacious therapy in five patients

Eighteen isolates of Nocardia asteroides were tested for in vitro susceptibility to trimethoprim (TMP) and sulfamethoxazole (SMZ) alone and in various combinations using disc and paper strip diffusion tests. TMP-SMZ showed synergistic action for two-thirds of teh nocardia isolates tested. Five patients with Nocardia pneumonia were treated with TMP-SMZ and all were cured. Four of the patients' isolates were tested and all showed synergistic patterns of inhibition with the spaced disc and paper strip methods. The agar diffusion disc and synergy tests of TMP-SMZ appear to correlate with clinical usefulness when the Nocardia are susceptible with large zones of inhibition around the combination TMP-SMZ disc.

Endogenous ocular nocardiosis: a clinical and experimental study

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Growth inhibition of Candida albicans by folate pathway inhibitors. Their potential in the selection of auxotrophs

Growth studies were conducted on C. albicans in a glucose - salts - biotin (GSB) medium in the presence of folate inhibitors. Sulfanilamide inhibited growth which was restored by PABA or tetrahydrofolate (THF). Aminopterin inhibited growth to about the same level as did sulfanilamide, but this inhibition was not reversed with PABA nor THF, singly or in combination. Inhibition by combined sulfanilamide and aminopterin was synergistic, reducing growth by more than 90% for 48 h. The sulfanilamide component of the combined inhibition was reversed by PABA or THF to the level of that of aminopterin alone. Cytochrome synthesis was not affected by the inhibitors, but marked increases occurred in alpha-ketoglutarate, malate, isocitrate, and pyruvate dehydrogenases, especially in the presence of both inhibitors. The pyrimidines in combination with sulfanilamide were as inhibitory as was the combination of aminopterin and sulfanilamide, but they had no effect when added alone or in combination with aminopterin. Unlike the pyrimidines, the purines stimulated about a 50% recovery from inhibition by either of the inhibitors. Growth inhibition by combined sulfanilamide and aminopterin was overcome by about 50% by the addition of the THF-mediated end-produits: deoxythymidylate, adenine, histidine and methionine. The use of GSB medium containing adenine, histidine, methionine and the folate inhibitors but without deoxythymidylate resulted in thymineless death of prototrophic cells providing a method for the selection of auxotrophic mutants.

Factors influencing susceptibility of Nocardia species to trimethoprim-sulfamethoxazole

Demonstration of synergism between trimethoprim and sulfamethoxazole against 10 Nocardia isolates was found to be critically dependent upon the isolate, the duration of incubation, and the trimethoprim-sulfamethoxazole ratio. Inoculum effect was not significant. The trimethoprim-sulfamethoxazole ratio in the commercial, fixed-dose combination was found to contain too little trimethoprim to be optimal for Nocardia.

Nocardia asteroides primary cerebral abscess and secondary meningitis

A rare case of primary cerebral abscess due to Nocardia asteroides, and its surgical removal, are described. Postoperative meningitis caused by the same fungi was succesfully cured with sulphadiazine and cycloserine. The nocardial disease, its neurological complications, and therapy are reviewed.

Antimicrobial susceptibility of Nocardia species

Variations of inoculum, pH, and composition of the agar assay media each influenced the in vitro susceptibility of Nocardia organisms (30 strains of N. asteroides and 6 strains of N. brasiliensis) to one or more antimicrobial agents incorporated in solid agar and incubated at 37 C for 48 h. Among newer antimicrobial agents, doxycycline, minocycline, and 7-halogenated lincomycin analogues exhibited the most consistent in vitro inhibitory activity; among older agents, viomycin, erythromycin, and streptomycin exhibited more selective in vitro inhibitory activity, but against a significant percentage of strains tested. N. brasiliensis was conspicuously more susceptible to erythromycin and gentamicin and more resistant to viomycin and capreomycin than was N. asteroides. Cycloserine demonstrated no significant in vitro inhibitory activity when assayed in appropriately augmented alanine-free medium. The outstanding feature of this in vitro survey was the marked variation in susceptibility among individual strains of N. asteroides, which variation deserves more careful consideration in future clinical or experimental therapeutic trials.

Susceptibility of Nocardia asteroides to 45 antimicrobial agents in vitro

A method for preparing uniformly dispersed cultures of Nocardia asteroides for use in tests for susceptibility to antimicrobial agents is described. The minimal inhibiting concentration (MIC) of 45 agents for cultures thus prepared was determined with the use of a replica-inoculating apparatus. Minocycline at a concentration of 3.1 mug or less/ml inhibited 90% of the strains tested, and all were inhibited by 6.3 mug/ml. An erythromycin concentration of 0.8 mug or less/ml inhibited 40% of the strains, but the MIC for most of the others was > 100 mug/ml. The other agents were generally less active. Chemically related analogues varied in activity to different degrees. Also, the MIC of each antibiotic against different strains generally varied over a wide range. Sulfonamides and trimethoprim were not active against most strains in the method used. The size of the inoculum markedly affected the MIC of sulfonamides and had variable effects on other agents. Marked synergy of erythromycin with ampicillin was demonstrated for nearly all strains tested.

In vitro studies of the combined effect of ampicillin and sulfonamides on Nocardia asteroides and results of therapy in four patients

The minimal inhibiting concentrations (MIC) of ampicillin, trisulfapyrimidines, and various combinations of these drugs were determined for four clinical isolates of Nocardia asteroides on Mueller-Hinton agar. The combination of ampicillin and sulfonamides was found to be synergistic for three of the four isolates when an inoculum of 10(3) to 10(4) organisms per ml was used. (Synergism was defined as occurring when the MIC of each of the drugs in combination was one-quarter or less of the MIC of each drug alone.) All four isolates were inhibited by concentrations of the drugs in combination that were clinically achievable. Combined therapy with ampicillin and sulfonamides was used in four immunologically suppressed renal transplant patients who had pulmonary infection with N. asteroides. Clinical improvement was noted within 2 weeks in all patients, and the pulmonary infiltrates cleared by 6 months in three patients. One patient died from an unrelated illness 10 days after starting therapy. The disease was arrested in two patients who were maintained on full immunosuppressive therapy.