In vitro activities of 39 antimicrobial agents for Branhamella catarrhalis and comparison of results with different quantitative susceptibility test methods

Abstract

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...

Antimicrobial resistance among respiratory isolates of Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae in the United States

“…This high rate of P-lactamase production supports the notion that M. catarrhalis should be considered as predictably resistant to penicillin and ampicillin-amoxicillin. Results of this study also support the concept that, in the United States, M. catarrhalis is universally susceptible to a wide array of antimicrobial agents which might be chosen for therapy of respiratory infections (1,7,10). Although Brown and colleagues (2) recently reported one erythromycin-resistant and two tetracycline-resistant strains based on MIC testing, our findings support the recommendation of NCCLS (28) that, at present, only 3-lactamase determinations are necessary in the routine testing of M. catarrhalis for susceptibility to antimicrobial agents.…”

In vitro activity of cefpodoxime proxetil (U-76,252; CS-807) against clinical isolates of Branhamella catarrhalis

“…regard, it is acknowledged that j-lactamase instability may not always be reflected by MICs in the resistant range. Overall, our results with antimicrobial agents other than cefpodoxime are consistent with those of Doern and Tubert (5). With regard to the in vitro activity of cefpodoxime against B. catarrhalis, our data expand considerably upon the findings of Yagi and Zurenko (27th ICAAC) and others (3,8), who evaluated small numbers of B. catarrhalis isolates and in certain instances did not clarify the P-lactamase activity associated with the tested strains.…”

Evaluation of OPC-17116 against important pathogens that cause respiratory tract infections

“…This profile of OPC-17116 might be related to its potent activity against gram-positive bacteria, as reported previously (14). In general, the outer membranes of gram-negative bacteria act as a diffusion barrier against hydrophobic compounds (11), but it is known that some gram-negative bacteria such as Bacteroides fragilis (7,9), M. catarrhalis (2,4), and Neisseria gonorrhoeae (13) are susceptible to hydrophobic antibiotics. It seems that these bacteria have a hydrophobic cell surface compared with other general gram-negative bacteria such as E. coli, Salmonella spp., and P. aeruginosa.…”