The population of fluoroquinolone-resistant S. pneumoniae in the United States has increased but remains genetically diverse. However, 35% of LNSP were related to widespread pneumococcal clones, increasing the potential for the rapid spread of quinolone resistance in this species.

A total of 556 unique blood culture isolates of nonfastidious aerobic and facultatively anaerobic bacteria were examined by direct and standardized disk susceptibility test methods (4,234 antibiotic-organism comparisons). When discrepancies which could be accounted for by the variability inherent in disk diffusion susceptibility tests were excluded, the direct method demonstrated 96.8% overall agreement with the standardized method. A total of 1.6% minor, 1.5% major, and 0.1% very major discrepancies were noted.

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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.

One hundred forty-seven isolates of Streptococcus pneumoniae with high-level penicillin resistance collected during a national surveillance program in the United States were characterized by serotyping, pulsed-field restriction analysis, ribotyping, and repetitive-sequence (BOX element) PCR. The results generated by each method were compared by frequency of association to examine whether relationships existed between the various typing methods and statistically to determine association with the geographic source of the isolate or the age of the patient from whom the isolate was obtained. When the data were examined by pairwise analysis of individual strain classifications produced by each typing method, no statistically significant relationships between strain type, geographic location, or patient age were identified, suggesting that distinct clones of penicillin-resistant S. pneumoniae have been widely distributed throughout the United States. However, we did observed shared expression of two or three typing markers at a high frequency (>50%) among clusters of strains, indicating a certain level of concordance between the various typing methods used to classify penicillinresistant S. pneumoniae.Thirty years ago, the recovery of penicillin-resistant Streptococcus pneumoniae (PRSP) strains from patients residing in the United States was considered an anomaly. Over the past decade, however, there has been a dramatic rise in the rate of isolation of PRSP. At present, it is estimated that nearly one-third of all clinical isolates of S. pneumoniae from the United States demonstrate intermediate or high levels of resistance to penicillin (3). In essence, the isolation of penicillin-susceptible phenotypes of pneumococci in this country is rapidly approaching the point at which it will be the exception rather than the rule.In a recent study, Doern and colleagues (4) found that 103 (70.1%) of 147 PRSP isolates with high-level resistance collected from 30 surveillance centers across the United States during 1994 and 1995 clustered within 9 of 38 possible pulsedfield gel electrophoresis (PFGE) types. Four of the PFGE types accounted for 76 (51.7%) of the 147 PRSP isolates, while only six serotypes were represented among the entire collection. Collectively, these results suggest that the majority of PRSP isolates in the United States are represented by a relatively limited number of clonal groups. However, that study found no relationship between PFGE type, patient age, and the geographic location of the isolate.During the course of the discussion, the authors raised a number of provocative questions regarding the molecular typing of PRSP, not the least of which emphasizes that the use of a single typing method to establish the genetic relatedness of PRSP strains is completely arbitrary. Indeed, a variety of genotypic and phenotypic markers have been employed in previous studies to examine the epidemiological relationship of pneumococcal isolates (1,4,5,8,12,14,15). Clearly, the discriminatory power of any typing method (th...