Differentiation of Mycobacterium chelonei from M. fortuitum by ciprofloxacin susceptibility

Analysis of DNA gyrA Gene Mutation in Clinical and Environmental Ciprofloxacin-Resistant Isolates of Non-Tuberculous Mycobacteria Using Molecular Methods

Background

During the past several years, nontuberculous mycobacteria (NTM) have been reported as some of the most important agents of infection in immunocompromised patients.

Objectives

The aim of this study was to evaluate the ciprofloxacin susceptibility of clinical and environmental NTM species isolated from Isfahan province, Iran, using the agar dilution method, and to perform an analysis of gyrA gene-related ciprofloxacin resistance.

Materials and Methods

A total of 41 clinical and environmental isolates of NTM were identified by conventional and multiplex PCR techniques. The isolates were separated out of water, blood, abscess, and bronchial samples. The susceptibility of the isolates to 1 µg/mL, 2 µg/mL and 4 µg/mL of ciprofloxacin concentrations was determined by the agar dilution method according to CLSI guidelines. A 120-bp area of the gyrA gene was amplified, and PCR-SSCP templates were defined using polyacrylamide gel electrophoresis. The 120-bp of gyrA amplicons with different PCR-SSCP patterns were sequenced.

Results

The frequency of the identified isolates was as follows: Mycobacterium fortuitum, 27 cases; M. gordonae, 10 cases; M. smegmatis, one case; M. conceptionense, one case; and M. abscessus, two cases. All isolates except for M. abscessus were sensitive to all three concentrations of ciprofloxacin. The PCR-SSCP pattern of the gyrA gene of resistant M. abscessus isolates showed four different bands. The gyrA sequencing of resistant M. abscessus isolates showed 12 alterations in nucleotides compared to the M. abscessus ATCC 19977 resistant strain; however, the amino acid sequences were similar.

Conclusions

This study demonstrated the specificity and sensitivity of the PCR-SSCP method for finding mutations in the gyrA gene. Due to the sensitivity of most isolates to ciprofloxacin, this antibiotic should be considered an appropriate drug for the treatment of related diseases.

Clinical significance, biochemical features, and susceptibility patterns of sporadic isolates of the Mycobacterium chelonae-like organism

Mycobacterium chelonae-like organisms are nonpigmented rapidly growing mycobacteria whose clinical significance is unknown. We evaluated 87 sporadic isolates encountered in a clinical laboratory. Most isolates (62%) were respiratory; only 2 of 54 (4%) (both from patients with AIDS) were clinically significant. Among 33 nonrespiratory isolates, 20 of 33 (or 61%) were clinically significant. Clinical diseases included posttraumatic wound infections and catheter-related sepsis. Routine biochemical features included growth inhibition by 5% NaCl (100%), a smooth colony morphology (94%), positive 3-day arylsulfatase reaction (84%), no color or a light tan color on iron uptake (100%), and variable nitrate reduction (45%). Additional characteristics that helped to separate this group from M. chelonae and Mycobacterium abscessus were susceptibility to cephalothin (90%) and ciprofloxacin (100%), utilization of mannitol (94%) and citrate (83%) as carbon sources, and unique patterns of mycolic acid esters by high-performance liquid chromatography. This group was quite drug susceptible, with 100% of isolates inhibited by amikacin, imipenem, cefoxitin, cefmetazole, and the newer quinolones ciprofloxacin and ofloxacin. Three examples of this group, including a proposed type strain, have been deposited in the American Type Culture Collection.

Activities of ciprofloxacin and ofloxacin against rapidly growing mycobacteria with demonstration of acquired resistance following single-drug therapy

The susceptibility to ciprofloxacin of 548 clinical isolates of rapidly growing mycobacteria belonging to eight subgroups or species was determined. The 170 isolates of Mycobacterium fortuitum biovar.fortuitum were most susceptible; the MIC for 90% of the organisms was 0.125 micrograms/ml. The other biovariants of M. fortuitum, M. smegmatis, and the M. chelonae-like organisms were less susceptible; the modal MIC was 0.5 micrograms/ml, and the MIC for 90% of organisms was 1.0 micrograms/ml. The two subspecies of M. chelonae were generally resistant, with only 8% of 206 isolates falling in the moderately susceptible category (MIC, 2 micrograms/ml) and only 2% falling in the susceptible category (MIC, less than or equal to 1 micrograms/ml). MICs of ofloxacin averaged 1 to 2 dilutions higher than those of ciprofloxacin for all subgroups tested. Three patients with M. fortuitum cutaneous disease relapsed after an initial response to therapy with ciprofloxacin, and their isolate was shown to have acquired drug resistance. Mutational frequencies for M. fortuitum with ciprofloxacin were relatively high (10(-5) to 10(-7), and MICs for single-step mutants were similar to those for the clinically resistant strains. Thus, despite the excellent activity of ciprofloxacin against rapidly growing mycobacterial groups other than M. chelonae, single-drug therapy should be used with caution because of the risk of development of mutational resistance.

Ability of ciprofloxacin but not pipemidic acid to differentiate all three biovariants of Mycobacterium fortuitum from Mycobacterium chelonae

When tested against 312 clinical isolates of rapidly growing mycobacteria, the quinolone pipemidic acid correctly separated Mycobacterium chelonae (M. chelonei) from Mycobacterium fortuitum biovar fortuitum but not from biovar peregrinum or the third biovar complex. The new 4-quinolone ciprofloxacin correctly separated all three biovars of M. fortuitum from M. chelonae and appears to provide a better taxonomic test.