A national surveillance study was conducted to determine trends in antimicrobial resistance patterns among three common causes of community-acquired respiratory tract infections. Fifteen participating U.S. medical centers submitted clinically significant isolates of Haemophilus influenzae, MoraxeeUa (BranhameUla) isolates, 1 (0.2%) was penicillin resistant, while 3.8% were relatively resistant to penicillin, 4.5% were resistant to trimethoprim-sulfamethoxazole, 2.3% were resistant to tetracycline, 1.2% were resistant to chloramphenicol, and 0.2% were resistant to erythromycin. Overall, the lowest resistance rates for these common bacterial respiratory pathogens were noted with amoxicillin-clavulanate, cefuroxime, and cefaclor.Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella (Branhamella) catarrhalis are bacterial agents responsible for a number of upper and lower respiratory tract infections, including otitis media (3, 4, 6, 12), maxillary sinusitis (3,6,12,22), community-acquired pneumonia (6, 11), and in some cases, exacerbations of chronic bronchitis (6,12,29). These species may harbor resistance mechanisms which affect several antimicrobial agents commonly used to treat such infections (2,3,5,6,14,15,17,23,24,26,31

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...

The need for complex growth media has complicated routine susceptibility testing of Haemophilus influenzae because of antagonism of certain antimicrobial agents by the medium or because of difficulties in interpretation of growth endpoints. Haemophilus test medium (HTM) is a simple, transparent medium for brothor agar-based tests with H. influenzae. HTM incorporates Mueller-Hinton medium with additions of 15 ,ug of hematin per ml, 15 ,ug of NAD per ml, and 5 mg of yeast extract per ml as growth-promoting additives. Agar or broth microdilution MICs of 10 antimicrobial agents for a collection of 179 H. influenzae isolates determined by using HTM compared favorably with MICs determined by the conventional agar or broth dilution methods recommended by the National Committee for Clinical Laboratory Standards. Disk diffusion tests performed with HTM allowed accurate categorization of susceptible and resistant strains and were easier to interpret than tests performed with Mueller-Hinton chocolate agar. A particular advantage of HTM was the reliability of brothor agar-based test results with trimethoprim-sulfamethoxazole. The results of the study suggest modification of current National Committee for Clinical Laboratory Standards MIC-interpretive criteria for H. influenzae with amoxicillin-clavulanate, chloramphenicol, and trimethoprim-sulfamethoxazole. Error rate-bounded analysis of MICs and disk diffusion zone sizes also suggest modified zone-interpretive criteria for ampicillin, amoxicillin-clavulanate, chloramphenicol, and tetracycline with HTM or conventional media. Interpretive zone sizes are newly proposed for cefaclor and rifampin disk diffusion tests.

The in vitro activity of the new lipopeptide antibiotic LY146032 was generally four-fold greater (MIC 90 less than or equal to 0.5 microgram/ml) than that of vancomycin against methicillin-susceptible or methicillin-resistant Staphylococcus aureus and coagulase-negative species of Staphylococcus. Enterococci, Streptococcus bovis, group B and viridans streptococci, and Corynebacterium group J-K isolates were inhibited by less than or equal to 4 micrograms/ml of LY146032, which represented activity equivalent to or greater than that of vancomycin. Unlike vancomycin, LY146032 was bactericidal for Enterococcus faecalis, Enterococcus faecium and Listeria monocytogenes. Due to its bactericidal properties LY146032 appeared to represent an improvement over vancomycin and teicoplanin.

The capability of the Abbott Avantage system to identify 10 species of commonly isolated glucose nonfermentative or oxidase-positive gram-negative bacilli in a 5-h test period was evaluated in a collaborative study. The Avantage nonenteric data base uses 20 biochemical test reactions performed in an expanded Abbott bacterial identification cartridge plus the results of a manual oxidase test. The species included in the Avantage data base are Acinetobacter anitratus, Acinetobacter lwoffi, Aeromonas hydrophila, Flavobacterium meningosepticum-IIb group, Pseudomonas aeruginosa, Pseudomonas cepacia, Pseudomonas fluorescens-putida group, Pseudomonas maltophilia, Pasteurella multocida, and Plesiomonas shigelloides. The collaborative study included the testing of 200 coded challenge strains in all three laboratories and the subsequent testing of an additional group of 100 to 200 clinical isolates recovered independently by each laboratory. Reference identifications for all isolates were determined by conventional biochemical test reactions. The overall accuracy of identification of the coded challenge strains for the three laboratories was 97%, whereas 95% of 437 clinical isolates and selected stock cultures of clinical derivation were identified correctly.