A total of 2,811 clinical isolates of Haemopbilus influenzae were obtained during 1986 from 30 medical centers and one nationwide private independent laboratory in the United States. Among these, 757 (26.9%) were type b strains. The overall rate of 3-lactamase-mediated ampicillin resistance was 20.0%. Type b strains were approximately twice as likely as non-type b strains to produce (-lactamase Antimicrobial resistance among clinical isolates of Haemophilus influenzae has become an increasingly prevalent problem (G. V. Doern, Antimicrob. Newsl. 5: [28][29][30][31][32][33][34] 1986). In a national collaborative study conducted in 1984, 15.2% of a large number of strains of H. influenzae produced Ilactamase (6). The problem of ampicillin resistance is complicated by recent descriptions of clinical isolates of H. influenzae that are resistant to ampicillin by mechanisms other than the production of a TEM-type P-lactamase (10,11,14). In addition, chloramphenicol resistance has now been reported (2,15), as has resistance to a variety of alternative agents commonly used to treat Haemophilus infections (Doern, Antimicrob. Newsl. 5:28-34). The intent of this investigation was to define systematically the prevalence of antimicrobial resistance among clinical isolates of H. influenzae in the United States. Rates of P-lactamase production and the activities of 12 antimicrobial agents were assessed. These agents included ampicillin, chloramphenicol, cefamandole, cefaclor, cephalothin, cephalexin, tetracycline, rifampin, erythromycin, sulfisoxazole, and the combinations erythromycin-sulfisoxazole and trimethoprim-sulfamethoxazole (TMP-SMX). MATERIALS AND METHODSStudy centers. A total of 30 hospital-based microbiology laboratories and 1 national, private, independent laboratory participated in the study (Table 1) by the laboratories listed in Table 1. All isolates were recovered from different patients and were randomly selected for inclusion in the study. After being characterized in study center laboratories, isolates were subcultured to chocolate agar slants (GIBCO Diagnostics, Madison, Wis.), which were incubated overnight in a CO2 atmosphere and then mailed, with selected patient demographic information, to one of two coordinating study centers for further characterization. The coordinating study centers were the Department of Clinical Microbiology, University of Massachusetts Medical Center, Worcester, and the Department of Pathology, University of Texas Health Science Center, San Antonio. Upon receipt in the coordinating study centers, growth from slants was transferred into 10% sterile skim milk and frozen at -70°C in 1-dram (ca. 3.7-ml) plastic freezer vials.Isolate characterization. Frozen stock suspensions were thawed, and aliquots were subcultured to chocolate agar plates (GIBCO) which were incubated overnight at 35°C in 5 to 7% CO2. Individual isolated colonies were then subcultured to a second chocolate agar plate which was incubated under identical conditions. Growth from the second plate was used for the fol...

A total of 62 different clinical yeast isolates were examined for susceptibility to four antifungal agents, amphotericin B, 5-fluorocytosine (5-FC), ketoconazole, and miconazole, using synthetic amino acid mediumfungi (SAAM-F), buffered yeast nitrogen broth (BYNB), Kimmig broth, casein-yeast-glucose broth (CYG), antibiotic medium 3-FDA (ANTI-3), and tryptic soy broth (TSB). A macrobroth dilution format was used with MICs determined after incubation for 24 and 48 h. All analyses were performed in duplicate. In general, MICs were more reproducible after 48 h of incubation. Furthermore, with certain medium-antifungal agent combinations, MICs determined after incubation for 48 h were significantly higher than those determined after 24 h. For instance, with 5-FC irrespective of the medium used, >25% of all 48-h MICs were more than one twofold dilution higher than the corresponding MICs determined after incubation for 24 h. Similar observations were made with amphotericin B when tested with BYNB and CYG and with the imidazoles when tested in all of the media except CYG. The actual MICs obtained with the different antifungal agents were clearly influenced by the test medium used. The rank order of amphotericin B MICs according to test medium was as follows: BYNB > SAAM-F = Kimmig = CYG = ANTI-3 = TSB. With 5-FC, the following pattern was observed: Kimmig = ANTI-3 > SAAM-F = CYG = TSB > BYNB. For both imidazoles, ketoconazole and miconazole, the rank order of MICs according to test medium was BYNB = Kimmig = CYG = ANTI-3 = TSB > SAAM-F. The results of this investigation suggested that broth dilution susceptibility testing of yeasts is best performed with an incubation period of 48 h. Furthermore, medium composition can significantly influence the results of such testing.

The in vitro activities of 39 antimicrobial agents were assessed versus 74 clinical isolates of Branhamella catarrhalis. Resistance was observed only with penicillin and ampicillin and then only with I-lactamaseproducing strains. The results of in vitro susceptibility tests with agar dilution and broth microdilution procedures were found to be comparable. The results of broth tube macrodilution tests were, in general, one twofold-concentration increment higher.Branhamella catarrhalis is recognized as an etiologic agent of a variety of infectious diseases in humans (3). In terms of incidence and perhaps morbidity, the most important of these are acute otitis media, maxillary sinusitis, and bronchopulmonary infections. Numerous different oral and parenteral antimicrobial agents may be used to treat these diseases. The intent of this investigation was to compare the in vitro activities of selected antimicrobial agents that are of potential value in the treatment of Branhamella infections. In addition, the effect of susceptibility test format on MICs obtained with B. catarrhalis was assessed.A total of 39 agents (Table 1) were examined versus 74 recent clinical isolates of B. catarrhalis. Among these 74 strains, 58 (78.4%) produced ,-lactamase when tested with a conventional tube nitrocefin P-lactamase assay (7, 10). MICs for each organism-antimicrobial combination were determined by use of an agar dilution procedure which employed unsupplemented Mueller-Hinton agar (pH 7.2) with an inoculum size of 104 CFU per spot. Antimicrobial agents, obtained from manufacturers as laboratory-grade powders, were tested over a range of twofold-concentration increments from 0.004 to 128 ug/mnl. A growth control plate containing no antimicrobial agent was included with each test. Plates were incubated at 356C in ambient air for 20 to 24 h and examined for the presence of growth. The MIC was defined as the lowest concentration of antimicrobial agent tested which yielded no macroscopic evidence of growth of the test organism. Each determination was done twice on separate days, and the results were averaged to obtain an estimate of the MIC for each organism-antimicrobial combination. In 2,848 of the 2,885 paired determinations (98.7%), replicate MICs were the same. In no case did the results of replicate MICs vary by more than fourfold. In cases in which replicate MICs varied by one twofold-concentration increment, the higher value was assigned as the MIC. Depending on the antimicrobial agent being tested, Staphylococcus aureus ATCC 29213 or Escherichia coli ATCC 25922 was used as the daily test control.A total of 33 strains (20 of them ,B-lactamase positive) were selected from among the original 74 clinical isolates of B. catarrhalis for additional testing with both a broth tube macrodilution and a microdilution procedure. Eight antimi-* Corresponding author. crobial agents were tested (Tables 2 and 3). Cation-supplemented Mueller-Hinton broth and a final inoculum concentration of 1 x 105 to 2 x 105 CFU/ml were used with both procedu...

A total of 74

A total of 114 strains of Haemophilus influenza were characterized with respect to beta-lactamase production and ampicillin MIC. Of this total, 41 strains produced a TEM-type beta-lactamase, and ampicillin MICs for these strains were-2.0 ,ig/ml. It was found that 54 strains lacked TEM-type beta-lactamase activity, and ampicillin MICs for them were c0.5 ,ug/ml. The remaining 19 strains were beta-lactamase negative, but ampicillin MICs were .2.0 ,ug/ml. Disk diffusion susceptibility tests were performed with two media, i.e., Mueller-Hinton agar containing 1.0% hemoglobin and 1.0% IsoVitaleX supplement (CHOC-MHA) and enriched chocolate agar (CHOC), by using disks containing 10 and 2 ,ug of ampicillin. If strains of H. influenzae for which ampicillin MICs were .2.0 ,ug/ml were considered resistant, while strains for which MICs were c0.5 ,ug/ml were considered susceptible, the following zone diameter interpretive criteria were identified as