Clinical and laboratory studies of a new micronized preparation of hamycin in systemic mycoses in man

Determination of fungicidal activities against yeasts and molds: lessons learned from bactericidal testing and the need for standardization

In certain unique clinical settings, the ability of the antimicrobial agent administered to kill the pathogen outright may be quite important. These situations invariably involve infection of a site not easily accessed by host defenses and/or of a structure with essential anatomic or physiologic function such as the heart (endocarditis), central nervous system (meningitis), or bone (osteomyelitis). Likewise, infections in immunosuppressed hosts, especially those who are neutropenic, are often thought to require microbicidal therapy. Proof of the cidal nature of an antimicrobial agent in vitro is tedious, complex, and fraught with error. Although several methods for assessing in vitro bactericidal activity have been standardized (NCCLS M26-A and M21-A), the clinical relevance of these determinations is questionable and the tests are performed infrequently in most laboratories. Most of the clinical data supporting the need for microbicidal therapy and testing have focused on bacterial infections. However, given the fact that most serious fungal infections occur in profoundly immunosuppressed individuals, it is generally assumed that a cidal regimen would be preferable in that setting as well. In view of this clinical concern and the perceived need to assess the fungicidal activity of a variety of agents, we considered that it would be useful to review what is known about the issues and problems in assessing bactericidal activity and the clinical utility of such measurements. Following this review, we discuss the issue of how one defines fungicidal activity in vitro and in vivo and how feasible it might be to determine the fungicidal activity of organism-drug combinations for purposes of both drug development and clinical care. Proposed methods for fungal time-kill determinations and minimal fungicidal concentration determinations are also discussed.

Influence of diminished susceptibility of Streptococcus pneumoniae to ciprofloxacin on the serum bactericidal activity of gemifloxacin and trovafloxacin after a single dose in healthy volunteers

The serum bactericidal activity against 2 Streptococcus pneumoniae strains (ciprofloxacin MIC 1 and 4 mg/l) was measured in 12 volunteers who received oral single doses of gemifloxacin 320 mg and trovafloxacin 200 mg in a crossover fashion. The 4-fold increase in ciprofloxacin MIC from the susceptible to the resistant strain resulted in a 2-fold increase in MIC (from 0.015 to 0.03 mg/l), a 2-fold decrease in C(max)/MIC (104 vs 52) and in AUC(0-24 h)/MIC (532 vs 266), but a 5.6-fold decrease in area under the bactericidal curve (AUBC: 168 vs 30) for gemifloxacin. Trovafloxacin showed a 4-fold higher MIC (0.25 vs 0.06 mg/l), a 4-fold lower C(max)/MIC (8.6 vs 36), a 4-fold lower AUC(0-24 h)/MIC (85 vs 356) and a 11-fold lower AUBCs (2 vs 22) against the resistant isolate compared with the susceptible one. Trovafloxacin serum bactericidal titres against the ciprofloxacin-resistant strain were measurable generally only at 1 h after dosing (median titre=2). Gemifloxacin showed similar ex vivo bactericidal activity against the ciprofloxacin-resistant strain to that of trovafloxacin against the ciprofloxacin-susceptible strain.

Ex vivo antibacterial properties of rufloxacin compared with those of norfloxacin in a study with healthy volunteers

Twelve adult males participated in a randomized crossover phase I clinical trial comparing serum bactericidal titers (SBTs), urine bactericidal titers (UBTs), and urine killing rates (UKRs) against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213, after the administration of single 400-mg doses of rufloxacin and norfloxacin at different times up to 72 h postdose. SBTs were significantly higher (P < 0.05) against E. coli from 8 to 48 h and against S. aureus from 4 to 24 h with rufloxacin. UBTs for E. coli were higher (P < 0.05) for norfloxacin at early sample times (0 to 8 h) but higher for rufloxacin (P < 0.05) at sample times from 16 h on for both E. coli and S. aureus. Similar UKRs were obtained for both quinolones for 0 to 2 h and 8 to 12 h, but the UKR was maintained for 72 h with rufloxacin. The high and sustained mean levels of rufloxacin in urine (> 35 micrograms/ml), median UBTs (> 32 for E. coli and 16 for S. aureus) and UKRs for E. coli suggest prolonged urine antibacterial activity (for at least 72 h) and its use as a single 400-mg dose in the treatment of uncomplicated cystitis.

Effects of supraphysiologic temperature and broth dilution on serum protein binding

Pooled human serum, unheated (UU) and heated at 56 degrees C for 30 (HU-30) and 60 (HU-60) min, and these media diluted 1:1 with broth (UD, HD-30, and HD-60) were used to assess the effects of supraphysiologic temperature and broth dilution on the serum protein binding of ceftriaxone. Protein binding was determined by ultrafiltration and subsequent high-performance liquid chromatography analysis. Significant differences in protein binding between UU and HU-60 (P less than 0.05), UD and HD-60 (P less than 0.01), HD-30 and HD-60 (P less than 0.01), and all undiluted and diluted media (P less than 0.01) were found. These alterations in protein binding may influence the in vitro microbiologic testing of highly protein-bound antibiotics.

Daptomycin (LY146032) treatment of experimental enterococcal endocarditis

This study compared daptomycin (LY146032) with penicillin G procaine and vancomycin without and with gentamicin for treatment of experimental enterococcal endocarditis. The strain of Streptococcus (Enterococcus) faecalis used in this study was killed by daptomycin in vitro in broth but not in serum. In rabbits treated for 3 days, daptomycin significantly reduced bacterial counts of vegetations compared with no therapy but was significantly less effective than penicillin G procaine or vancomycin. Daptomycin-gentamicin significantly reduced bacterial counts of vegetations compared with daptomycin alone but was significantly less effective than vancomycin plus gentamicin. The efficacy of daptomycin-gentamicin did not differ significantly from that of penicillin G procaine-gentamicin. The lack of enterococcal killing by daptomycin alone in serum and in experimental endocarditis is probably related to the high protein binding of the agent.

Serum bactericidal test

The serum bactericidal test represents one of the few in vitro tests performed in the clinical microbiology laboratory that combines the interaction of the pathogen, the antimicrobial agent, and the patient. Although the use of such a test antedates the antimicrobial era, its performance, results, and interpretation have been subject to question and controversy. Much of the confusion concerning the serum bactericidal test can be avoided by an understanding of the various factors which influence bactericidal testing. In addition, the methodologic aspects of the serum bactericidal test have recently been addressed and should place this test on firmer ground. New information on the clinical utility of this test is becoming available; additional data are needed to establish more clearly the usefulness of the serum bactericidal test in specific infections. Such clinical trials from multiple centers will enable firmer recommendations for the future use of the serum bactericidal test.

Influence of technical factor variations on serum inhibition and bactericidal titers

The influence of technical factor variations on serum bactericidal and serum inhibitory titers was studied by using Staphylococcus aureus clinical isolates versus oxacillin-spiked human serum. Parallel tests, both with and without the use of beta-lactamase in count plates to inactivate oxacillin carryover, were performed with a conventional macrodilution approach, a carefully controlled macrodilution procedure, and a standard microdilution method. Careful control of technical factor variations diminished the incidence of low serum bactericidal titers and decreased the dispersion of results, a finding corollary to the known influence of technical factor variations on the measurement of MBCs. The incorporation of beta-lactamase into count plates resulted in a shift of serum bactericidal titers to lower values. The microdilution method appeared to be least influenced by technical variations and, with the addition of beta-lactamase to count plates, provided the best results.

Technical aspects and clinical correlations of the serum bactericidal test

A review of the studies using 50% human serum as a diluent for the serum bactericidal test has shown correlations with patient outcome. Human serum used as diluent of the patient's serum appears to be essential because of high protein binding of some antibiotics. An inoculum of 10(5)-10(6) bacteria/ml and a bactericidal criteria of 99.9% killing are technical aspects that have gained popularity. Careful timing of serum collection for the assay is important. Neither the macrotube nor microtiter techniques are entirely satisfactory. The latter method, however, has the advantage of being more reproducible than the macrotube method, less cumbersome and requiring less serum. Preliminary guidelines for performing and interpreting the test are provided. Future research should be directed toward making the microtiter technique more sensitive for identifying antibiotic tolerance, developing effective methods to eliminate the need for human serum as a diluent and obtaining more clinical correlations.

The usefulness of the serum bactericidal test in orthopedic infections

The serum bactericidal test is proposed as a means to monitor the effectiveness of antibiotic therapy in orthopedic cases. Preliminary results of a multicenter study of the test in osteomyelitis suggest that trough titers yield the best indication of successful treatment.

Minimum inhibitory and bactericidal concentrations of 44 antimicrobial agents against three standard control strains in broth with and without human serum

Standard minimum inhibitory and bactericidal concentrations are not established for most antimicrobial agents against strains of bacteria commonly used for quality control in susceptibility testing. The effects of cation and human serum supplementation of broth on the values are also unknown. Therefore, we performed 10 minimum inhibitory and bactericidal concentration determinations for 44 antimicrobial agents against the standard control strains Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and Pseudomonas aeruginosa ATCC 27853 in Mueller-Hinton broth and in Mueller-Hinton broth supplemented with calcium, magnesium, and 50% pooled human serum. Agreement of replicates was within one twofold dilution 97% of the time. Supplemented Mueller-Hinton broth gave higher minimum inhibitory concentrations for 24 antibiotics against S. aureus, for 17 drugs against E. coli, and for 12 drugs against P. aeruginosa, whereas it gave lower minimum inhibitory concentrations for 1 antibiotic against S. aureus, for 5 against E. coli, and for 5 against P. aeruginosa. Results for minimum bactericidal concentrations were similar. Added serum did not further affect the increased resistance of P. Aeruginosa to aminoglycosides encountered with cation supplementation of broth. These results provide expected values for the quality control strains when minimum inhibitory and bactericidal concentrations are determined in these two Mueller-Hinton media.

Streptococcus equinus septicemia: report of two cases and review of the literature

Two cases of septicemia with Streptococcus equinus, a group D streptococcus, are reported, and the literature pertaining to infections with this organism is reviewed. Both of our patients presented with obvious signs of infection, had S equinus isolated from multiple blood cultures, and had a good clinical response to penicillin therapy, alone or in combination with streptomycin. In vitro testing of the isolates confirmed susceptibility to penicillin. S equinus should now be recognized as a human pathogen as are the other group D streptococci, S bovis and the enterococci.

Use of the serum bactericidal titer to assess the adequacy of oral antibiotic therapy in the treatment of acute hematogenous osteomyelitis

Serum bactericidal titers against Staphylococcus aureus were measured in 63 children who were receiving mafcillin or methicillin intravenously, or dicloxacillin, penicillin, or cephalexin orally. The SBTs obtained following unit does of 25 mg/kg of dicloxacillin, 35 mg/kg of penicillin, or 25 mg/kg of cephalexin with probenecid were comparable to those seen following intravenous doses of 40 mg/kg nafcillin or methicillin. Twenty-two children with acute hematogenous osteomyelitis proven or presumed to be due to S. aureus were treated intravenously until point tenderness and fever had resolved, and then with oral therapy. The mean duration of intravenous therapy was 14 days. Oral doses were adjusted so that a peak SBT of greater than or equal to 1:16 and a trough SBT of greater than or equal to 1:2 were obtained in most children. No recurrences occurred. The SBT proved to be a practical means of assessing the adequacy of oral therapy in children with infections due to S. aureus.

Comparison of a micromethod for performance of the serum bactericidal test with the standard tube dilution method

A micromethod for performance of the serum bactericidal test is described, and the results obtained with this method are compared with those obtained with the standard tube dilution macromethod. An agreement within +/- 1 dilution was achieved in 23 of 25 (92%) determinations of the serum bactericidal titer. The micromethod used approximately one-third of the amount of pooled normal human serum and of the technician's time required for performance of the macromethod. The micromethod offers an accurate and economical alternative to the macromethod for the performance of the serum bactericidal test and is particularly useful with infants and children since it minimizes blood loss.