Detection of lfrA and tap efflux pump genes among clinical isolates of non-pigmented rapidly growing mycobacteria.

This study was performed to detect LfrA and Tap efflux pumps among clinical isolates of non-pigmented rapidly growing mycobacteria (NPRGM). Gene detection was performed using polymerase chain reaction (PCR) with specific primers designed for each gene. Susceptibility of the strains to doxycycline, tigecycline and ciprofloxacin was analysed using the broth microdilution reference technique. In total, 166 clinical isolates were included in the study. The lfrA gene was detected in four strains (2.4%), comprising two strains of Mycobacterium chelonae (6.7% of this species), one Mycobacterium fortuitum (1.1%) and one Mycobacterium mucogenicum (14.3%). The tap gene was detected in 109 strains (65.7%), comprising 3 Mycobacterium abscessus (33.3%), 12 M. chelonae (40%), 75 M. fortuitum (84.3%), 2 Mycobacterium mageritense (40%), 15 Mycobacterium peregrinum (68.2%), 1 Mycobacterium alvei and 1 Mycobacterium porcinum; no strains of M. mucogenicum were tap-positive. No differences between tap-positive and -negative strains were observed for resistance to doxycycline (Fisher's exact test, P=0.055). lfrA is rare among clinical isolates of NPRGM, whilst tap is found more commonly. No correlation was detected between the presence of the efflux pumps and resistance to quinolones or tetracyclines.

Biofilm development by clinical strains of non-pigmented rapidly growing mycobacteria.

The relationship between clinical significance of non-pigmented, rapidly growing mycobacteria (NPRGM), in vitro biofilm development and sliding motility was evaluated in this study. One hundred and sixty-eight clinical strains of NPRGM were included. Forty-one of these were clinically significant isolates. Biofilm was formed by 123 strains. Seventy-six biofilm-positive and 25 biofilm-negative strains showed sliding motility. There was a relationship between clinical significance and biofilm development (p <0.000,001), sliding motility (p 0.0037) and species (p <0.000,001). No relationship was found between motility and biofilm development. The ability to develop biofilm is a characteristic that can have importance in the development of infections caused by NPRGM.

Prevalence of erm methylase genes in clinical isolates of non-pigmented, rapidly growing mycobacteria.

The aim of this study was to determine the frequency of erm genes coding for macrolide resistance among clinical isolates of non-pigmented rapidly growing mycobacteria (NPRGM) and to evaluate their importance in phenotypic resistance. Broth microdilution susceptibility testing was performed for all NPRGM tested. A PCR assay with consensus primers was used to evaluate the presence of erm genes among the 167 clinical isolates studied, which belonged to nine species of NPRGM; erm genes were detected in all nine species and 109 strains were erm-positive. The highest percentage of erm-positive isolates was found among Mycobacterium mageritense (100%) and the lowest among Mycobacterium mucogenicum (14%). The MICs of macrolides were found to be lower for erm-negative isolates (MIC(90): 2 mg/L) than for erm-positive isolates (MIC(90): 16 mg/L), although in some cases high MICs were found for erm-negative isolates. The finding that erm methylases are present in the majority of the species of NPRGM analysed in this study is not in agreement with conventional susceptibility studies. It therefore appears necessary to use a combination therapy to treat infections caused by NPRGM.

In vitro activity of tigecycline and 10 other antimicrobials against clinical isolates of the genus Corynebacterium.

We studied the in vitro activity of tigecycline and 10 other commonly used antibiotics against 135 clinical isolates of non-diphtheria Corynebacterium spp. using the Etest system. Tigecycline minimum inhibitory concentrations for 50% and 90% of the organisms (MIC(50) and MIC(90) values, respectively, in mg/L) were: Corynebacterium urealyticum, 0.094 and 0.125; Corynebacterium amycolatum, 0.125 and 2; Corynebacterium jeikeium, 0.094 and 0.75; Corynebacterium coyleae, 0.064 and 0.064; Corynebacterium striatum, 0.064 and 1; Corynebacterium aurimucosum, 0.094 and 0.125; and Corynebacterium afermentans, 0.064 and 0.094. The activities of all other antimicrobials were variable, with good activity of glycopeptides, linezolid, quinupristin/dalfopristin and daptomycin and with resistance to macrolides in a high number of isolates. Tigecycline is a good alternative for the therapy of infections caused by non-diphtheria corynebacteria.

In vitro activities of tigecycline and 10 other antimicrobials against nonpigmented rapidly growing mycobacteria.

We evaluated the in vitro activities of tigecycline and 10 other antibiotics against clinical isolates of nonpigmented rapidly growing mycobacteria. Fifteen collection strains and 165 clinical isolates were included in the study. Tigecycline showed the highest activity among all antibiotics studied: all the strains were inhibited by 1 mg/liter.

Epidemiology of infections due to nonpigmented rapidly growing mycobacteria diagnosed in an urban area.

The objective was to determine the incidence, clinical significance, and epidemiology of the isolates of nonpigmented, rapidly growing mycobacteria (NPRGM) in Madrid, Spain. Patients with new isolates of NPRGM during 2005 were selected prospectively for review of clinical charts. Clinical significance was analyzed according internationally accepted criteria. Randomly amplified polymorphic DNA (RAPD) was used for the genotyping of the isolates. NPRGM were identified in 70 patients (1.51 cases/100,000 inhabitants). The species were M. abscessus (in 5 patients), M. chelonae (in 9), M. fortuitum (in 40), M. peregrinum (in 9), M. mageritense (in 5), M. mucogenicum (in 2), and M. alvei (in 1 patient). The isolates were clinically significant in 17 cases (24.3%, 0.39 cases/100,000 inhabitants): in 4 cases of M. abscessus, in 5 of M. chelonae, and in 9 of M. fortuitum. Only 10.7% of the respiratory isolates were significant, whereas 75% of the nonrespiratory ones were significant (p < 0.001). RAPD analysis showed no relationship among the 74 strains available for the study. No characteristic resistance pattern could be found, although 4 strains appeared to be resistant to amikacin. Significant isolates were mainly nonrespiratory ones. The most significant species was M. abscessus. No relationship between the various isolates was detected, ruling out interhuman transmission between these cases.