Correlation between in vitro antimicrobial susceptibilities and beta-lactamase plasmid contents of isolates of Haemophilus ducreyi from the United States

Abstract

We determined the susceptibilities of 94 strains of Haemophilus ducreyi isolated in various municipalities in the United States between 1982 and 1989 to the following antimicrobial agents: amoxicillin-clavulanic acid, ceftriaxone, erythromycin, azithromycin, ciprofloxacin, ofloxacin, trimethoprim, and spectinomycin. Ceftriaxone (MIC, .0.008 ,g/ml), azithromycin (MIC, <0.125 ,Lg/ml), erythromycin (MIC, .0.125 ,ug/ml), ciprofloxacin (MIC, <0.25 ,ug/ml), and ofloxacin (MIC, .0.25 ,ug/ml) were highly active against all isolates. Amoxicillin-clavulanic acid (MICs, 0.25 to 8.0 ,ug/ml), trimethoprim (MICs, 0.06 to 16.0 ,ug/ml), and spectinomycin (MICs, 2.0 to .32.0 jLg/ml) were less active against these isolates. Isolates possessing the 5.7-MDa 1-lactamase plasmid were less susceptible to erythromycin, trimethoprim, and spectinomycin than were isolates possessing the 3.2-MDa I5-lactamase plasmid. The susceptibilities of plasmidless isolates to erythromycin, trimethoprim, and spectinomycin were distributed bimodally; the median MIC for the more susceptible plasmidless isolates corresponded to that for isolates with the 3.2-MDa plasmid, and the median MIC for the less susceptible plasmidless isolates corresponded to that for isolates with the 5.7-MDa plasmid. Thus, plasmid profiles may be valuable markers for geographical variations in antimicrobial susceptibilities of H. ducreyi strains that may indicate the relative efficacy of regimens for the treatment of chancroid. Of the regimens recommended by the U.S. Public Health Service for the treatment of chancroid, our results support the use of erythromycin, ceftriaxone, and ciprofloxacin, and perhaps ofloxacin, but suggest that amoxicillinclavulanic acid and sulfamethoxazole-trimethoprim should be used with caution.

In vitro susceptibilities of isolates of Haemophilus ducreyi from Thailand and the United States to currently recommended and newer agents for treatment of chancroid

“…Our data showed that isolates that possessed the 4. quinolones for the treatment of chancroid, unless the susceptibilities of clinical isolates are routinely monitored for resistance. In the present study, as in another recent study (10), we identified the resistance phenotypes of H. ducreyi. These resistance phenotypes can be used to screen currently recommended therapeutic agents and newer agents for the treatment of chancroid.…”

“…In the present study, we compared the in vitro activities of currently recommended and newer antimicrobial agents against H. ducreyi isolates from Thailand that possessed novel plasmids (13) The activities reported for A-C, ceftriaxone, erythromycin, azithromycin, ciprofloxacin, and ofloxacin against the isolates tested in the present study are similar to those reported previously for U.S. isolates with similar plasmid profiles (10) and to the susceptibilities of isolates reported elsewhere (1, 5-9, 12, 16). Agents were less active against isolates that possessed the 5.7-MDa plasmid than against isolates that possessed no plasmid or those that possessed the 3.2-MDa plasmid.…”

“…Previously, we determined the susceptibilities of selected H. ducreyi strains isolated in the United States to selected antimicrobial agents and demonstrated that most antimicrobial agents were less active against strains that possessed a 5.7-MDa 1-lactamase plasmid than against strains that possessed a 3.2-MDa ,-lactamase plasmid (10). In the present study, we compared the in vitro activities of currently recommended and newer antimicrobial agents against H. ducreyi isolates from Thailand that possessed novel plasmids (13) The activities reported for A-C, ceftriaxone, erythromycin, azithromycin, ciprofloxacin, and ofloxacin against the isolates tested in the present study are similar to those reported previously for U.S. isolates with similar plasmid profiles (10) and to the susceptibilities of isolates reported elsewhere (1, 5-9, 12, 16).…”

Chancroid and Haemophilus ducreyi: an update.

“…Geographical and temporal differences in antimicrobial susceptibilities have been observed. Many of the differences are due to the presence or absence of resistance plasmids (10,100,136,137). Plasmids which encode resistance, either separately or in combination, to sulfonamides (6,169), aminoglycosides (135,169), tetracyclines (8,92,(126)(127)(128), chloramphenicol (128), and ␤-lactam antibiotics (25,89,90,124,154) have been identified in H. ducreyi (Table 5).…”

“…Very little information concerning the development of chromosomally mediated antimicrobial agent resistance in H. ducreyi is available. Approximately 30% of strains isolated in the United States between 1982 and 1990 were shown to lack resistance plasmids (100,137). Some of these strains exhibited decreased susceptibilities to TMP, ciprofloxacin, and ofloxacin, suggesting the presence of chromosomally mediated resistance to these antimicrobial agents.…”