Activity of 16 antimicrobial agents against drug-resistant strains of Mycobacterium tuberculosis

Lanfranco Fattorini, Elisabetta Iona, Maria Luisa Ricci, Ove Fredrik Thoresen, Germano Orrù, Marco Rinaldo Oggioni, Enrico Tortoli, Claudio Piersimoni, Patrizia Chiaradonna, Mirella Tronci, Gianni Pozzi, Graziella Orefici

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The in vitro activity of 16 antimicrobial agents against 46 drug- resistant strains of Mycobacterium tuberculosis recently isolated from Italian patients was determined. As for first-line antituberculosis drugs, while isoniazid was ineffective against all the strains tested, resistance to streptomycin, rifampicin, pyrazinamide, and ethambutol was 80.4%, 71.7%, 39.1%, and 8.7%, respectively. Among second-line antituberculous drugs, resistance to ciprofloxacin, ofloxacin, and sparfloxacin and to amikacin and kanamycin was around 20%. About 10% of the strains were resistant to capreomycin and cycloserine and 4.3% were resistant to ethionamide; no strain was found to be resistant to thiacetazone, para-aminosalicylic acid, and viomycin. Although all strains displayed a rather continuous distribution of minimal inhibitory concentrations (MICs), a bimodal distribution was observed for rifampicin, amikacin, and kanamicin, with very high MIC values for resistant strains; relatively low MICs were found for fluoroquinolone- resistant strains. Among the small number of strains resistant to second-line agents, low resistant levels were observed. Restriction fragment length polymorphism analysis showed few strain clusters with resistance to first- line antituberculous drugs and aminoglycosides, fluoroquinolones, or both. Altogether, these results showed that second-line agents were still active against the isoniazid-resistant and multiply first-line resistant strains tested, with none or low resistance levels; these observations can be of importance for the treatment of multidrug-resistant tuberculosis in Italy.

Original languageEnglish
Pages (from-to)265-270
Number of pages6
JournalMicrobial Drug Resistance
Issue number4
Publication statusPublished - 1999

ASJC Scopus subject areas

  • Microbiology (medical)
  • Pharmacology
  • Immunology
  • Microbiology


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