ABSTRACT
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.
Subject(s)
Antiporters/genetics , Bacterial Proteins/genetics , DNA, Bacterial/genetics , Drug Resistance, Multiple, Bacterial , Membrane Transport Proteins/genetics , Mycobacterium Infections/microbiology , Mycobacterium/genetics , Anti-Bacterial Agents/pharmacology , Ciprofloxacin/pharmacology , DNA Primers/genetics , Doxycycline/pharmacology , Humans , Microbial Sensitivity Tests , Minocycline/analogs & derivatives , Minocycline/pharmacology , Mycobacterium/isolation & purification , Polymerase Chain Reaction/methods , Spain , TigecyclineABSTRACT
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.
