Fluoroquinolones are increasingly used for the treatment of infections caused by multidrug-resistant Mycobacterium tuberculosis. Our study was designed to determine the frequency of the emergence of ciprofloxacin-resistant isolates in a university hospital (Rabta University Hospital Tunis, Tunisia) and to characterize the mutations responsible for the resistance phenotype. A total of 495 clinical M. tuberculosis isolates obtained from January 2005 to July 2008 were investigated for their susceptibility to ciprofloxacin, using the standard proportion method, PCR and DNA sequencing. Four resistant isolates (0.8%) were identified. Among these, only two carried point mutations in gyrA leading to amino acid changes other than the phenotypically silent S95T substitution. No gyrB missense mutations were found in any of the clinical isolates. Although fluoroquinolone resistance is still rare in Tunisia, accurate surveillance is needed in order to control the possible emergence of resistance to fluoroquinolones, which are essential for the successful treatment of multidrug-resistant tuberculosis.

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Analysis of the gene encoding the ␤-subunit of Mycobacterium tuberculosis RNA polymerase (rpoB) has demonstrated a small region that harbors the mutations most frequently associated with rifampin resistance. In this study, we determined the occurrence of rifampin resistance in 544 Tunisian clinical M. tuberculosis strains isolated in a university hospital between 2004 and 2006 by using the standard-proportion agar method, the INNO-LiPA Rif.TB assay, and DNA sequencing.One of the most alarming trends concerning tuberculosis (TB) is the emergence of drug-resistant Mycobacterium tuberculosis strains, which has become a worldwide health care problem (15). The early detection of resistance to primary anti-TB agents is essential for the efficient treatment and control of multidrug-resistant (MDR) strains. Rifampin (RMP) is one of the most potent anti-TB drugs; therefore, resistance to RMP often results in high clinical relapse rates, particularly if RMP resistance is associated with resistance to other anti-TB drugs (8).It has been established that RMP resistance in M. tuberculosis is mainly due to a group of mutations within a limited region of the rpoB gene that encodes the ␤-subunit of the RNA polymerase (28). These mutations can be characterized by PCR single-strand conformation polymorphism analysis (1, 23), heteroduplexing (21), dideoxy fingerprinting (6), the line probe assay (4,7,19), and automated DNA sequencing analysis (9, 24). However, few of these findings are associated with isolates from Tunisia, where the global incidence of TB infection was about 23.54 per 100,000 inhabitants (12). Therefore, the aim of our study was to determine the molecular basis of resistance in M. tuberculosis RMP-resistant strains by using the INNO-LiPA Rif.TB assay (Innogenetics, Ghent, Belgium) and DNA sequencing and to correlate these results with clinical and antibiotic sensitivity data.A total of 544 clinical M. tuberculosis strains from 475 patients were isolated in a university hospital in an urban setting, the Rabta center, Tunis, Tunisia, during a 2-year period (2004 to 2006). The culturing of mycobacterial isolates was performed on solid Löwenstein-Jensen (LJ) medium. All M. tuberculosis cultures were biochemically characterized and confirmed by the AccuProbe method (Gen-Probe Inc., San Diego, CA).Susceptibility testing for isoniazid (INH), RMP, ethambutol (EMB), streptomycin (SM), and ciprofloxacin (CIP) was carried out on LJ medium according to the standard procedure (2, 3). The critical concentrations of RMP, INH, EMB, SM, and CIP were 40, 0.2, 1, 10, and 10 g/ml, respectively. Resistance to RMP was defined as Ն1% growth on RMP-containing medium compared to the rate of growth on control medium. On final analysis of the 544 isolates, 10 (1.83%) were RMP-resistant and 534 were characterized as fully susceptible to RMP. These 10 clinical isolates recovered from six different patients were classified as MDR strains since they were also resistant to INH. Complete medical records were available for all of the six patients...

Forty three isoniazid (INH)-resistant Mycobacterium tuberculosis isolates were characterized on the basis of the most common INH associated mutations, katG315 and mabA -15C→T, and phenotypic properties (i.e. MIC of INH, resistance associated pattern, and catalase activity). Typing for resistance mutations was performed by Multiplex Allele-Specific PCR and sequencing reaction. Mutations at either codon were detected in 67.5% of isolates: katG315 in 37.2, mabA -15C→T in 27.9 and both of them in 2.4%, respectively. katG sequencing showed a G insertion at codon 325 detected in 2 strains and leading to amino acid change T326D which has not been previously reported. Distribution of each mutation, among the investigated strains, showed that katG S315T was associated with multiple-drug profile, high-level INH resistance and loss or decreased catalase activity; whereas the mabA -15C→T was more prevalent in mono-INH resistant isolates, but it was not only associated with a low-level INH resistance. It seems that determination of catalase activity aids in the detection of isolates for which MICs are high and could, in conjunction with molecular methods, provide rapid detection of most clinical INH-resistant strains.

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