Of 103 strains of Haemophilus ducreyi isolated in Johannesburg, 96 produced ,Blactamase and were resistant to penicillin and ampicillin. Most strains showed resistance to tetracycline, sulfisoxazole, and sulfamethoxazole. All isolates were susceptible to rifampin, erythromycin, and cefoxitin, moderately susceptible to trimethoprim-sulfamethoxazole (1:19) and minocycline, and somewhat less susceptible to doxycycline.

One hundred and thirty seven patients presenting with genital ulcerations from which Haemophilus ducreyi was isolated were treated with erythromycin stearate 500 mg every six hours for seven days. Of these, 91 (66%) had associated inguinal lymphadenopathy. Only two of the 100 patients who returned after one week showed no clinical improvement. Despite decrease in size H ducreyi was reisolated from the ulcers of three patients, two of whom had not complied with treatment. The patients were treated for a further week either with erythromycin or with a placebo preparation and on day 14 no discernible difference in clinical response was evident. H ducreyi was not reisolated from any lesion. In contrast, the natural course of development of associated lymphadenopathy was not modified by treatment. H ducreyi was not, however, isolated from any gland after the start of treatment. Side effects attributable to erythromycin were minimal and treatment had to be discontinued in only two patients. This study clearly indicates that treatment with erythromycin for one week results in rapid healing of lesions and the elimination of H ducreyi from both ulcers and associated lymph glands.

Seven of the 96 ampicillin-resistant isolates of Haemophilus ducreyi reported in the preceding article (Bilgeri et al., Antimicrob. Agents Chemother. 22:686-688, 1982) were investigated and found to harbor plasmids of 3.95, 5.2, 5.8, and 6.4 megadaltons. All except the 5.8-megadalton plasmid have been shown to code for P-lactamase. The 6.4-and 5.2-megadalton plasmids of three isolates were conjugally transferable to a streptomycin-resistant mutant of H. ducreyi at high frequencies, perhaps due to the presence in these strains of a high-molecularweight plasmid.Hammond et al. (7) found that 3 of 19 strains of Haemophilus ducreyi isolated in an outbreak of chancroid in Winnipeg, Manitoba, Canada, produced , and Brunton et al. (3) found that all three harbored a 6.0 x 106-dalton plasmid which coded for 1-lactamase but was not conjugally transferable to Haemophilus influenzae. In a later study, Handsfield et al. (8) found that seven ampicillin-resistant (Apr) H. ducreyi isolates from the United States and abroad carried plasmids of 3.6, 5.7, and 7.3 megadaltons (Mdal) coding for P-lactamase.Plasmid molecular weights were identical for isolates from epidemiologically linked cases and differed according to the geographic origin of the strains. Handsfield and co-workers did not investigate the transmissibility of these plasmids.In a recent study, Bilgeri et al. (1) found that 96 of 103 strains of H. ducreyi isolated from patients suffering from chancroid in the Johannesburg area were Apr. We wondered, therefore, whether these resistant strains carried plasmids coding for P-lactamase and, if so, whether they were conjugally transferable, as this could possibly account for the extremely high percentage (93%) of Apr H. ducreyi strains isolated from patients suffering from chancroid. We report here the demonstration that all of the Apr H. ducreyi isolates studied carried plasmids coding for 3-lactamase, ranging in size from 3.95 to 6.4Mdal. Two of these plasmids are conjugally transferable at high frequencies to a streptomycin-resistant mutant of H. ducreyi, perhaps due to the presence in these donor stains of a highmolecular-weight plasmid.H. ducreyi isolates were obtained from patients with clinical chancroid in the Johannesburg environs and were isolated at 350C on MHIC medium (1) with 3 ,zg of vancomycin per ml to inhibit the growth of contaminating microorganisms. The Apr local isolates, GU 10, GU 36, GU 55, GU 68, GU 71, GU 75, and GU 80, were of low passage numbers to mitigate possible plasmid segregation. The H. ducreyi reference strain, ATCC 27722, was obtained from the American Type Culture Collection, Rockville, Md., and GU 74 was a local Aps isolate. Escherichia coli HB1O1(pBR322) was used as a control as it carries a 2.6-Mdal plasmid coding for ampicillin and tetracycline resistance (2). Minimum inhibitory concentrations of antibiotics were determined, and 3-lactamase production was analyzed as described (1).All of the Apr isolates were shown to produce TEM-type P-lactamase, and analysis of the minimu...