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Drug resistance of Haemophilus ducreyi
A Rutanarugsa1, M Vorachit, N Polnikorn
1Department of Pathology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.
Insights
Chancroid diagnosis in Thailand relies on clinical signs, but increasing antimicrobial resistance in *Haemophilus ducreyi* necessitates laboratory testing. This study found MBV medium effective for isolation and identified widespread resistance to ampicillin, tetracycline, and sulfonamides.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Chancroid, caused by *Haemophilus ducreyi*, is a prevalent sexually transmitted disease (STD) in tropical regions like Thailand.
- Current diagnosis in Thailand relies on clinical presentation, often leading to confusion with other genital ulcer diseases.
- Emerging antimicrobial resistance in *H. ducreyi* highlights the critical need for accurate cultivation and susceptibility testing.
Purpose of the Study:
- To evaluate the efficacy of different culture media for *H. ducreyi* isolation.
- To determine the antimicrobial susceptibility patterns of *H. ducreyi* strains in Thailand.
- To characterize the beta-lactamase enzymes produced by *H. ducreyi* isolates.
Main Methods:
- Isolation of *H. ducreyi* using various culture media, with Mueller-Hinton agar supplemented with vancomycin, bacitracin, and polymyxin B (MBV) identified as optimal.
- Antimicrobial susceptibility testing of isolates against a panel of antibiotics.
- Determination of the isoelectric point (pI) of beta-lactamase enzymes from *H. ducreyi* strains.
Main Results:
- MBV medium demonstrated the highest isolation success rate at 48%.
- All tested strains were resistant to ampicillin due to beta-lactamase production.
- High resistance rates were observed for tetracycline (99%), sulfamethoxazole (92%), and trimethoprim (32%).
- All isolates remained susceptible to chloramphenicol, ceftriaxone, erythromycin, and fluoroquinolones (ciprofloxacin, norfloxacin, ofloxacin, pefloxacin).
- Beta-lactamase analysis revealed a consistent isoelectric point of 5.4, characteristic of plasmid-mediated TEM-1 type.
Conclusions:
- MBV medium is recommended for improved *H. ducreyi* isolation in clinical settings.
- Significant antimicrobial resistance necessitates updated treatment guidelines for chancroid in Thailand.
- The prevalence of TEM-1 beta-lactamase indicates a specific resistance mechanism that warrants monitoring.
Abstract:
Chancroid, the disease caused by H. ducreyi is one of the common sexually transmitted diseases (STD) in Thailand and other tropical countries. In Thailand, the diagnosis of chancroid is still based on clinical appearance which may be confused with other STD manifested by genital ulcers. In recent years the increasing resistance strains of H. ducreyi to these antimicrobial agents has been reported so that cultivation and antimicrobial susceptibility tests of this organism have become more important. This study showed that MBV is the best medium for isolation with a success rate of 48%. All strains tested from isolates of this study were resistant to ampicillin, due to production of beta-lactamase. Approximately 99% of the strains were resistant to tetracycline 92% of strains were resistant to sulfamethoxazole and 32% were resistant to trimethoprim. All isolates were susceptible to chloramphenicol, ceftriaxone, erythromycin and the fluorinated quinolones ciprofloxacin, norfloxacin, ofloxacin and pefloxacin. Beta-lactamase enzymes produced by 37 strains of H. ducreyi were determined for their isoelectric point (pI). All had pI of 5.4, indicative of plasmid-mediated beta-lactamase type TEM-1.