Antimicrobial susceptibility patterns of Nocardia asteroides

Ribotyping: a tool for taxonomy and identification of the Nocardia asteroides complex species

Ribotyping has been evaluated as a taxonomic tool for studying bacteria belonging to the Nocardia asteroides complex. The probe used was obtained by PCR from DNA extracted from the type strain Nocardia asteroides ATCC 19247, a sequence that codes partly for 16S rRNA. Interpretation of hybridization after EcoRI restriction of total DNA of 21 strains of the N. asteroides complex allowed for the identification of only four different ribotypes: two related to N. asteroides sensu stricto, one related to N. farcinica and one related to N. nova. These results confirm the classification established by Tsukamura in 1982 (M. Tsukamura, Microbiol. Immunol. 26:1101-1119, 1982) as well as the heterogeneity of N. asteroides sensu stricto species. Ribotyping may also provide a major identification technique for the species belonging to the N. asteroides complex.

Activities of the glycylcyclines N,N-dimethylglycylamido-minocycline and N,N-dimethylglycylamido-6-demethyl-6-deoxytetracycline against Nocardia spp. and tetracycline-resistant isolates of rapidly growing mycobacteria

Susceptibilities to the new semisynthetic tetracycline (Tet) compounds N,N-dimethylglycylamido-minocycline (DMG-MINO) and N,N-dimethylglycylamido-6-demethyl-6-deoxytetracycline (DMG-DMDOT) were compared with those to doxycycline, minocycline, and Tet for 198 Tet-resistant (Tetr) and 33 Tet-susceptible (Tets) clinical isolates of rapidly growing mycobacteria (RGM) including the Mycobacterium fortuitum group, Mycobacterium abscessus, Mycobacterium chelonae, and Mycobacterium mucogenicum and 68 isolates belonging to six taxa of Nocardia spp. All Tetr RGM were highly susceptible to the glycylcyclines. The MICs at which 50 and 90% of isolates are inhibited were < or = 0.125 and < or = 0.25 microgram/ml, respectively, for DMG-DMDOT and < or = 0.25 and 1 microgram/ml, respectively, for DMG-MINO. The MIC of DMG-DMDOT at which 50% of Tetr strains are inhibited was the same as that for Tets strains for each of the four taxa of RGM. The new agents were less active against Nocardia spp. MICs of DMG-DMDOT were comparable to those of minocycline except for the MICs for Nocardia brasiliensis sensu stricto, the new taxon Nocardia pseudobrasiliensis, and some isolates of Nocardia nova, against which they were four- to eightfold more active. The MICs of DMG-DMDOT were consistently lower than those of DMG-MINO for RGM. This class of drugs offers exciting therapeutic potential for RGM and for selected species of Nocardia.

DNA amplification and restriction endonuclease analysis for differentiation of 12 species and taxa of Nocardia, including recognition of four new taxa within the Nocardia asteroides complex

Nineteen reference and 156 clinical strains of the genus Nocardia belonging to 12 taxonomic groups were studied for restriction fragment length polymorphism (RFLP) by using an amplified 439-bp segment of the 65-kDa heat shock protein gene. Of 30 restriction endonucleases, digestion with MspI and then digestion with BsaHI produced RFLP band patterns which separated all 12 groups except N. asteroides type IV from 6 of 12 N. transvalensis isolates and N. carnea from the N. asteroides type VI isolates. Commonly encountered species such as N. nova, N. farcinica, N. brasiliensis sensu stricto, and N. otitidiscaviarum were easily separated. Each taxon resulted in a single RFLP band pattern that included > or = 96% of all biochemically grouped isolates for 9 of 12 taxa with MspI and for 8 of 12 taxa with BsaHI. With the use of both patterns, only 6 of 175 (3.4%) isolates failed to fit the biochemically defined group patterns. These studies provide the first evidence for the separate identities of four antibiogram-defined (but currently unnamed) groups within the N. asteroides complex (types I, II, IV, and VI) and the presence of two subgroups within N. transvalensis. They also provide genotypic evidence for the separate identities of N. nova and N. farcinica. The lack of BstEII recognition sites in amplicons obtained from nocardiae provides a simple and rapid method for the differentiation of nocardiae from mycobacteria. DNA amplification with RFLP analysis is the first rapid method that distinguishes all clinically significant taxa and recognized species within the genus Nocardia.

New Nocardia taxon among isolates of Nocardia brasiliensis associated with invasive disease

Nocardia brasiliensis, the second most frequently isolated aerobic actinomycete in the clinical laboratory, is usually associated with localized cutaneous infections. However, 22% of 238 N. brasiliensis isolates from the United States and 12% of 66 isolates from Queensland, Australia, which had been collected over a 17-year period, were associated with extracutaneous and/or disseminated diseases. Of the 62 invasive isolates, 37 (60%) were susceptible to ciprofloxacin and/or were susceptible to clarithromycin and resistant to minocycline, compared with only 6 (3%) of 242 localized cutaneous isolates. The 43 isolates with this susceptibility pattern appeared to define a new taxon. They were similar to Nocardia asteroides complex isolates clinically in proportions from persons with pulmonary (70%), central nervous system (23%), and/or disseminated diseases (37%) in the setting of corticosteroids (74%) or AIDS (14%). This putative new taxon differed from N. brasiliensis in the hydrolysis of adenine (92 versus 4%), beta-lactamase patterns on isoelectric focusing, and the presence of two early mycolic acid-ester peaks by high-performance liquid chromatography. Restriction analysis of a 439-bp fragment of the 65-kDa heat shock protein gene revealed that N. brasiliensis and the new taxon had different restriction patterns with 8 of the 11 enzymes tested. Screening of invasive isolates of N. brasiliensis for susceptibility to ciprofloxacin will identify most isolates of the new taxon, which likely represents a new Nocardia species.

Antimicrobial activity of cefotaxime tested against infrequently isolated pathogenic species (unusual pathogens)

The cefotaxime sodium spectrum of activity is very broad and includes many common species and a variety of less frequently isolated pathogens. We have reviewed the clinical microbiology literature (44 references) and the data base of the University of Iowa Hospitals and Clinics (Iowa City, IA) to collect data on the activity of cefotaxime against the less common species. Cefotaxime was consistently active against Actinobacillus actinomycetemcomitans, Capnocytophaga spp., Eikenella corrodens, Erysipelothrix rhusiopathiae, Pasteurella multocida, Plesiomonas shigelloides, and Fusobacterium nucleatum. The species Alcaligenes xylosoxidans, Flavobacterium spp., Stenotrophomonas (Xanthomonas) maltophilia, Bacillus cereus, Listeria monocytogenes, and Rhodococcus equi were uniformly cefotaxime resistant. For many other species there was considerable variation in reported minimum inhibitory concentrations. These data may be helpful in guiding therapy of unusual infections, particularly in the case of fastidious species, where the appropriate susceptibility testing methodology may not be immediately or routinely available.

Nocardiosis diagnosed by lung FNA: a case report

A 63-yr-old woman with systemic lupus erythematosus (SLE) diagnosed 12 mo previously and treated with prednisolone and cyclophosphamide presented with recent fever and dyspnoea. The etiology of a 3 cm diameter centrally cystic coin lesion in the lower lobe of the left lung was obscure. Blood cultures and sputum examination had been non-contributory, and the diagnosis of Nocardia asteroides infection was initially made by cytologic examination of material obtained by lung fine-needle aspiration (FNA). It is notoriously difficult to detect this organism by conventional sputum examination or with histologic sections, and it has rarely been detected by lung FNA. If this organism is demonstrated, appropriate microbiologic cultures for confirmation and susceptibility testing should be instituted. Long-term antimicrobial therapy is needed. In this case, complete resolution of the lung lesion followed 5 mo of therapy.

Nocardial brain abscess: treatment strategies and factors influencing outcome

The successful management of nocardial brain abscess remains problematic. The authors report 11 cases of nocardial brain abscess treated between 1971 and 1993 and review 120 cases reported since 1950. The clinical findings included focal deficits in 55 patients (42%), nonfocal findings in 36 (27%), and seizures in 39 (30%). Extraneural nocardiae were present in 66% of the cases; pulmonary (38%) and cutaneous/subcutaneous (20%) locations were the most frequent. The abscesses were single in 54% of the patients, multiple in 38%, and of unknown number in 8%. Forty-four of 131 patients (34%) were immunocompromised; since 1975, 18 of 40 immunocompromised patients (45%) were transplant recipients and six (15%) had human immunodeficiency virus. The mortality rate was 24% after initial craniotomy and excision (11/45), 50% after aspiration/drainage (17/34), and 30% after nonoperative therapy (7/23); 29 cases (22%) were diagnosed at autopsy. The mortality rate was 33% in patients with single abscesses and 66% in those with multiple abscesses (P < 0.0003). There was no difference in the mortality rates of immunocompromised and nonimmunocompromised patients treated before computed tomography (CT) was available; since the advent of CT, however, the mortality rate has been significantly higher in immunocompromised patients (55% vs. 20%, P < 0.05). Although the mortality rate for nocardial brain abscesses has dropped almost 50% since the advent of CT, it has remained virtually unchanged in immunocompromised patients and is three times higher than that of other bacterial brain abscesses (30% vs. 10%). The authors recommend image-directed stereotactic aspiration for diagnosis; however, craniotomy and total excision are necessary in most cases, because nocardial abscesses are usually multiloculated. Patients with minimal neurological deficits or small abscesses may be treated initially with antibiotics alone. Sulfonamides, alone or in combination with trimethoprim, are most effective and should be continued for at least 1 year. Minocycline, imipenem, or aminoglycoside in combination with a third-generation cephalosporin may be used with reasonably good success as second-line agents in cases of allergy or nonresponsiveness to sulfa agents.

Opacification of Middlebrook agar as an aid in distinguishing Nocardia farcinica within the Nocardia asteroides complex

Among 58 aerobic actinomycetes isolated from different sources and geographical locations, none of 23 Nocardia asteroides isolates, at 18 N. farcinica isolates, 1 of 5 N. otitidiscaviarum isolates, and 1 of 4 Rhodococcus species isolates opacified Middlebrook 7H10 medium. Within the N. asteroides complex, this characteristic, together with growth at 45 degrees C and resistance to each of erythromycin, cefotaxime, and tobramycin, provides a simple means of distinguishing N. farcinica from N. asteroides.

The medically important aerobic actinomycetes: epidemiology and microbiology

The aerobic actinomycetes are soil-inhabiting microorganisms that occur worldwide. In 1888, Nocard first recognized the pathogenic potential of this group of microorganisms. Since then, several aerobic actinomycetes have been a major source of interest for the commercial drug industry and have proved to be extremely useful microorganisms for producing novel antimicrobial agents. They have also been well known as potential veterinary pathogens affecting many different animal species. The medically important aerobic actinomycetes may cause significant morbidity and mortality, in particular in highly susceptible severely immunocompromised patients, including transplant recipients and patients infected with human immunodeficiency virus. However, the diagnosis of these infections may be difficult, and effective antimicrobial therapy may be complicated by antimicrobial resistance. The taxonomy of these microorganisms has been problematic. In recent revisions of their classification, new pathogenic species have been recognized. The development of additional and more reliable diagnostic tests and of a standardized method for antimicrobial susceptibility testing and the application of molecular techniques for the diagnosis and subtyping of these microorganisms are needed to better diagnose and treat infected patients and to identify effective control measures for these unusual pathogens. We review the epidemiology and microbiology of the major medically important aerobic actinomycetes.

Disseminated Nocardia farcinica infection in an AIDS patient

This report describes an AIDS patient presenting with disseminated Nocardia farcinica infection diagnosed by percutaneous kidney biopsy. The isolate was initially identified as Nocardia asteroides. Though Nocardia asteroides remains sensitive to most antimicrobial agents, Nocardia farcinica is resistant to gentamicin, tobramycin and cephalosporins and is indistinguishable from Nocardia asteroides by regular laboratory methods. In view of the rising incidence of infections with Nocardia farcinica, third-generation cephalosporins should not be used in the initial management of Nocardia infections, and all isolates should be submitted for antibiotic susceptibility testing.

Case report: Nocardia osteomyelitis

Osteomyelitis is an unusual manifestation of infection with Nocardia spp, and most cases result from direct extension from a primary lung or cutaneous lesion. The authors report what they believe to be the first case of Nocardia vertebral osteomyelitis occurring postoperatively, and review the literature on the 19 previously reported cases of Nocardia osteomyelitis due to hematogenous dissemination or direct inoculation, excluding those occurring from direct extension of a mycetoma or primary lung infection.

A case of testicular nocardiosis and literature review

A case of epididymo-orchitis due to Nocardia asteroides in a liver transplant recipient is reported. Nocardiosis is an extremely rare cause of epididymo-orchitis. Four other cases published in the English language medical literature are reviewed. All patients were immunocompromised, and other organs were affected simultaneously. Clinically the infection presented as a painful enlargement of the testicle with few inflammatory signs. Mortality was high (3/5), and in the two survivors long-term sulfonamide therapy was combined with orchiectomy. Nocardiosis should be considered in the diagnosis of epididymo-orchitis in the immunocompromised host.

Activity of antimicrobial drugs evaluated by agar dilution and radiometric methods against strains of Nocardia asteroides isolated in Italy from immunocompromised patients

Benzylpenicillin, amoxicillin, amoxicillin plus clavulanic acid, cephalothin, cephaloridine, cefotaxime, imipenem, erythromycin, clarithromycin, azithromycin, amikacin, ciprofloxacin and trimethoprim-sulfamethoxazole were tested in vitro by the agar dilution method against eleven strains of Nocardia asteroides isolated both from AIDS and other immunocompromised patients. Imipenem, amikacin and trimethoprim-sulfamethoxazole were shown to be the most active drugs with minimum inhibitory concentrations (MIC) values nearly always lower than concentrations achievable in blood. Ciprofloxacin, cephaloridine and cefotaxime were moderately active, while the remaining drugs were totally ineffective. When susceptibility was assessed by the radiometric method the MIC90 values were uniformly lower than those in the agar method, possibly due to lower inactivation of drugs during incubation. The two methods showed a good correlation only for imipenem, amikacin and ciprofloxacin. The results obtained by the radiometric method seem to indicate that, as for mycobacteria, this method may also give a more accurate evaluation of the antimicrobial susceptibility of Nocardiae.

Partial characterization of Nocardia farcinica beta-lactamases

The beta-lactamases obtained from culture supernatants and cell extracts of 26 clinical strains and 5 reference strains of Nocardia farcinica were partially characterized. The enzymes exhibited two patterns on isoelectric focusing (IEF). beta-Lactamases from the majority of the 31 strains (87%) including the 5 reference strains exhibited two major bands with pIs of 4.56 and 4.49. The remaining strains had two similar major bands but with slightly higher pIs. Culture supernatants and cell extracts exhibited identical patterns. The two sets of enzymes were functionally indistinguishable by substrate and inhibitor profiles and lack of inducibility. By disk testing, ampicillin, amoxicillin, ticarcillin, amoxicillin-clavulanic acid, and imipenem were highly synergistic with cefotaxime. The enzymes were primarily penicillinases and hydrolyzed cephalosporins at rates of < or = 12% of those for penicillins. N. farcinica beta-lactamases were susceptible to inhibition by clavulanic acid and BRL 42715, exhibiting 50% inhibitory concentrations of 0.025 to 0.045 micrograms/ml (0.12 to 0.22 microM) and 0.05 to 0.1 micrograms/ml (0.31 to 0.63 microM), respectively, less susceptible to tazobactam, and least susceptible to sulbactam, cloxacillin, and imipenem. The beta-lactamases of N. farcinica are believed to mediate penicillin resistance and may play a secondary role in extended-spectrum cephalosporin resistance. The close similarity among N. farcinica beta-lactamases and their distinct differences from beta-lactamases of other Nocardia species support the taxonomic identity of this species.

Mouse pathogenicity studies of Nocardia asteroides complex species and clinical correlation with human isolates

Nocardia asteroides complex organisms derived from human specimens between 1979 and 1992 were identified to the species level. Of 117 N. asteroides complex organisms, 34 (29%) were N. farcinica, 28 (24%) were N. nova, and 55 (47%) were N. asteroides sensu stricto. An analysis of the specimen sites from which the organisms were derived showed that isolates derived from blood, brain, or bone marrow were more likely to be N. farcinica than the other two species. A study of the virulence of ten strains of each species was undertaken, using a mouse model with intravenous inoculation. The 50% lethal doses (LD50) for N. farcinica were significantly lower than those of the other two species. LD50 values for N. nova and N. asteroides were not significantly different. The above data confirming the greater virulence of N. farcinica support the identification of species within the N. asteroides complex.

In vitro antimicrobial susceptibilities of Nocardia species

The in vitro activities of various quinolones, two new aminoglycosides, a new cephamycin analog (cefmetazole) and a new spectinomycin analog (trospectomycin), imipenem, and trimethoprim-sulfamethoxazole against 26 isolates of Nocardia asteroides, 7 isolates of N. brasiliensis, and 6 isolates of N. caviae were determined by a broth microdilution method. The three new quinolones, PD 117558, PD 117596 and PD 112739, inhibited 90% of N. asteroides at 1 to 2 micrograms/ml, and two new aminoglycosides, SCH 21420 and SCH 22591, inhibited 90% of N. asteroides at 2 to 4 micrograms/ml. Among the beta-lactams, cefmetazole was more active than imipenem. N. brasiliensis and N. caviae isolates were also very susceptible to the three quinolones (MICs for 50% of the isolates, 0.25 to 1 microgram/ml) and the two aminoglycosides (MICs for 50% of the isolates, 1 to 2 micrograms/ml). Cefmetazole was moderately active against N. brasiliensis, whereas imipenem showed poor activity against both of these species.

Pneumonia caused by Nocardia nova and Aspergillus fumigatus after cardiac transplantation

Nocardia nova, a newly established species of the Nocardia asteroides complex, has recently been characterized as a human pathogen. This report of a case of pneumonia caused by Nocardia nova and Aspergillus fumigatus in a patient after cardiac transplantation is the first reported infection caused by Nocardia nova following its detailed description. Accurate identification and susceptibility testing of the Nocardia nova isolate allowed successful oral therapy with clarithromycin when therapy with sulfisoxazole was not tolerated.

Pleurocerebral Nocardia in a patient with human immunodeficiency virus

OBJECTIVE

To report a case of Nocardia asteroides pneumonia and subsequent brain abscess in an immunocompromised host.

SETTING

Private, community, teaching hospital.

PATIENT

A man readmitted to the hospital for a third time with a fatal brain abscess, after responding to (misdirected) therapy in previous admissions.

INTERVENTIONS

Treatment with cefuroxime, erythromycin, trimethoprim/sulfamethoxazole at different times.

RESULTS

Patient's condition deteriorated and he died after one month of intravenous trimethoprim/sulfamethoxazole therapy.

CONCLUSIONS

Because it is an infection of the immunocompromised host, it may be considered an AIDS-defining illness. Several other similar cases have been reported in the literature.

Corneal ulceration due to Nocardia asteroides

A case of corneal ulceration due to infection with Nocardia asteroides is described. Microbiological examination of corneal scrapings permitted accurate diagnosis and suggested appropriate therapy. Nineteen other cases that have been described in the world literature are reviewed.

Clinical and laboratory features of Nocardia nova

Recent studies have shown that Nocardia asteroides isolates have five major antibiotic resistance patterns; one of these patterns identifies isolates of Nocardia farcinica. In the current study, we investigated a second pattern characterized by susceptibility to ampicillin and erythromycin. This pattern was seen in 17% of 223 clinical isolates identified by standard techniques as N. asteroides and associated with diseases typical for nocardiae. Biochemically, isolates with this drug pattern were relatively homogeneous and identical to the type strain and previous descriptions of Nocardia nova. The strains studied were unique among nocardiae in having both alpha- and beta-esterase activity (85 and 95%, respectively). However, the arylsulfatase activity at 14 days (75%) and antimicrobial susceptibility patterns, including susceptibility to erythromycin (100%), were the only routinely available methods that would separate N. nova strains from other members of N. asteroides. N. asteroides should be considered a complex because current clinical identification schemes include isolates of N. farcinica and N. nova and may well include additional species. This is the first detailed description of N. nova as a pathogen in humans.

Two cases of Nocardia asteroides sternotomy infection treated with ofloxacin and a review of other active antimicrobial agents

Two patients who developed post-operative sternotomy infections due to Nocardia asteroides were treated successfully with ofloxacin, in vitro susceptibility of the organisms being used as a guide to dosage. The place of this drug in the treatment of infection due to Nocardia asteroides merits further investigation.

The aminoglycosides

Despite the introduction of newer, less toxic antimicrobial agents, the aminoglycosides continue to serve a useful role in the treatment of serious enterococcal and gram-negative bacillary infections. Gentamicin, because of its low cost, remains the aminoglycoside of choice in hospitals with low levels of resistance among Enterobacteriaceae and Pseudomonas aeruginosa. Amikacin is useful against gentamicin-resistant gram-negative bacilli and also in the treatment of infections caused by susceptible Nocardia and nontuberculous mycobacteria. An alarming increase in resistance to aminoglycosides among enterococci has been noted, despite little change in susceptibility patterns among gram-negative bacilli. Future efforts will need to be directed toward a better understanding of mechanisms of antimicrobial resistance and toward the prevention of aminoglycoside-induced toxicity.

Intracerebral Nocardia asteroides abscess treated by neurosurgical aspiration and combined therapy with sulfadiazine and cefotaxime

We present a patient with a Nocardia brain abscess who failed to respond to repeated neurosurgical aspiration in combination with sulfadiazine therapy but improved after additional treatment with cefotaxime.

Cefotaxime-resistant Nocardia asteroides strains are isolates of the controversial species Nocardia farcinica

A recent study of Nocardia asteroides revealed that 95% of clinical strains had one of five antibiotic resistance patterns. We found the pattern of resistance to cefotaxime and cefamandole in 19% of 200 clinical N. asteroides isolates. Isolates with this drug resistance pattern were from numerous geographic sources and were associated with significant clinical disease (56% of patients had disseminated infections). Phenotypic studies revealed that these isolates were relatively homogeneous and matched previous descriptions and reference strains of the controversial species N. farcinica. Growth at 45 degrees C, acid production from rhamnose, ability to utilize acetamide as a nitrogen and carbon source, and resistance to tobramycin and cefamandole were features of N. farcinica that could be tested in the clinical laboratory and allowed their distinction from N. asteroides. The serious nature of disease due to N. farcinica and its resistance to the newer cephalosporins suggest a clinical need for laboratory identification of this species. (Current tests used in clinical laboratories do not distinguish N. farcinica from N. asteroides.) This is the first recognition that N. farcinica has a specific drug resistance pattern and confirms the previously described concept that drug resistance patterns of N. asteroides may be associated with specific taxonomic groups.

Therapy of pulmonary nocardiosis in immunocompromised mice

We compared the bactericidal efficacies of various antimicrobial agents and combinations thereof in experimentally induced Nocardia asteroides pneumonia in immunocompromised mice. Cortisone acetate treatment, which produced impaired cell-mediated immune function, was followed by nasal inoculation of 5 x 10(4) CFU of N. asteroides into each mouse. Therapy was begun 24 h after inoculation and continued for the next 96 h. Dosages of antimicrobial agents resulted in concentrations approximating levels in human serum. Animals from each of nine treatment groups were sacrificed every 24 h. The pulmonary tissue obtained was homogenized and quantitatively cultured. Results were calculated to indicate the number of CFU per gram of lung tissue. Amikacin and imipenem were the two most effective single agents studied. Sulfadiazine and ciprofloxacin were ineffective, and ceftriaxone reduced bacterial counts modestly. Combination therapy did not enhance the bactericidal activities of the agents tested. We conclude that amikacin and imipenem, as well as select broad-spectrum cephalosporins, represent therapy superior to the sulfonamides in this experimental model and may represent alternative treatment for patients who cannot tolerate sulfa agents (e.g., human immunodeficiency virus-infected patients) or who fail primary treatment.

DNA probes for the identification of Nocardia asteroides

DNA probes for the rapid identification of Nocardia asteroides were obtained by constructing a genomic library of strain GUH-2 in the lambda cloning vector EMBL3. Of 50 recombinant clones tested, 2 were identified that hybridized with 31% of the N. asteroides strains in a reference collection without cross-hybridization with related members of the Actinomycetales. Additional libraries were then generated from selected strains of N. asteroides that had failed to hybridize with any of the GUH-2 clones. Four additional clones were obtained from these strains which, when pooled, provided DNA probes specific for all of the N. asteroides strains tested.

Aminoglycoside therapy. Current use and future prospects

The microbiological, pharmacokinetic, toxicological and clinical aspects of aminoglycosides are reviewed. Aminoglycosides still have an important place in serious infections in neutropenic patients, endocarditis and Pseudomonas aeruginosa infections, all in combination with beta-lactams. Monotherapy (with streptomycin) is indicated in less common diseases like tularemia and bubonic plague. Several experimental studies support a once-daily dosing regimen for aminoglycosides (comparable or better efficacy with less ototoxicity and nephrotoxicity). Only a very limited number of prospective comparative studies have been performed, and much more data on efficacy, development of resistance and toxicity is needed before once-daily administration can be recommended. The choice of an aminoglycoside should be based primarily on the local sensitivity patterns and cost. Differences in ototoxicity and nephrotoxicity are usually minor. If the acquisition costs of amikacin decline, it is to be expected that amikacin will be the aminoglycoside of choice.