Rifampin-Resistant Mycobacterium kansasii

Abstract

We identified 36 rifampin-resistant Mycobacterium kansasii isolates, including 17 (4%) of 464 isolates recovered in Texas between 1989 and 1992. Of 29 patients infected with rifampin-resistant M. kansasii whose history of medication was known, 90% had previously received rifampin, and 58% of these patients had been treated with one or two effective drugs. Thirty-two percent of rifampin-resistant isolates recovered since 1989 were from patients who were seropositive for human immunodeficiency virus (HIV) infection. Twenty courses of therapy with a four-drug regimen determined on the basis of in vitro susceptibilities were administered to 16 patients from whom rifampin-resistant isolates were recovered; the therapy did not include surgery. Sputum cultures converted to negative as the result of 90% of treatments (time to conversion: mean, 11 weeks; range, 4-20 weeks). Bacteriologic relapses occurred in four of five patients who withdrew from therapy after being culture negative for < or = 6 months of therapy and in one of 12 patients who were culture negative for at least 12 months of therapy (mean, 16.3 months). This study suggests that the prognosis for cure of infection due to rifampin-resistant M. kansasii with chemotherapy alone is excellent, although the number of cases appears to be increasing, in part because of the HIV disease epidemic.

Molecular Analysis of Mycobacterium kansasii Isolates from the United States

“…Most had detailed histories that have previously been published (22) and that clearly established them as definite pathogens. Such a selection factor could have biased the molecular genotypes observed if one genotype more than another tends to be associated with rifampin resistance.…”

Antimicrobial Susceptibility Testing, Drug Resistance Mechanisms, and Therapy of Infections with Nontuberculous Mycobacteria

“…Despite the laboratory issues with INH, treatment with the above-described regimens is usually successful (132,451). However, treatment failure can occur (418). When treatment failure occurs, the isolate is almost always resistant in vitro to rifampin and occasionally one or more of the companion drugs as well.…”

“…Because treatment failure is always associated with rifampin and/or clarithromycin resistance, the current CLSI recommendation is to test all initial isolates of M. kansasii against rifampin and clarithromycin only (140,418,451,452). For isolates found to be rifampin resistant (MIC Ͼ 1 g/ml), secondary antimicrobials, including amikacin, ciprofloxacin, ethambutol, linezolid, moxi-floxacin, rifabutin, and trimethoprim-sulfamethoxazole, should be tested (451).…”

Management of Infection With Nontuberculosis Mycobacteria

“…Thus, in vitro test results based on a breakpoint for tuberculosis will produce false resistance for an isolate of NTM (21,22). The use of methods that provide minimum inhibitory concentration (MIC) data will enable regimens to be constructed specifically for NTM that take into account the achievable concentrations of antibiotics (26,27).…”

“…Although rifampicin is the most important drug in the treatment of M. kansasii infection if patients are treated with a regimen that includes three drugs to which the infecting organism is susceptible a good outcome is likely. Many of these regimens include clarithromycin and ciprofloxacin (26). …”