Efflux Pump Lde Is Associated with Fluoroquinolone Resistance in Listeria monocytogenes

Abstract

Five Listeria monocytogenes isolates (CLIP 21369, CLIP 73298, CLIP 74811, CLIP 75679, and CLIP 79372) were found to be resistant to fluoroquinolones during the screening for antibiotic resistance of 488 L. monocytogenes isolates from human cases of listeriosis in France. On the basis of a fourfold or greater decrease in the ciprofloxacin MIC in the presence of reserpine, fluoroquinolone resistance was attributed to active efflux of the drugs. The lde gene (Listeria drug efflux; formerly lmo2741) encodes a 12-transmembrane-segment putative efflux pump belonging to the major facilitator superfamily of secondary transporters that displayed 44% identity with PmrA from Streptococcus pneumoniae. Insertional inactivation of the lde gene in CLIP 21369 indicated that the corresponding protein was responsible for fluoroquinolone resistance and was involved in the level of susceptibility to dyes such as ethidium bromide and acridine orange.Listeria monocytogenes is widely distributed in the environment and can cause serious human infections, such as bacteremia and central nervous system infections, primarily in neonates and immunocompromised adults, and abortions (22). Food-borne transmission is recognized as the main route of acquisition of the infection during epidemic and sporadic listerioses (3, 18). Listeriosis differs from most food-borne diseases by its high fatality rate (20 to 30% of cases), despite the administration of appropriate antibiotics (3, 9). L. monocytogenes is generally susceptible to a wide range of antibiotics but is not susceptible to cephalosporins and fosfomycin (8). However, during the last few years, increasing numbers of strains resistant to one or more antibiotics have been reported (1,2,8,11,19,20).Although indications for the use of fluoroquinolones do not include listeriosis, they can, due to their increasing use for other pathologies such as respiratory tract infections, select resistant Listeria. In gram-positive bacteria, resistance usually results from mutational alterations in the so-called quinolone resistance-determining regions (QRDRs) of the intracellular targets of fluoroquinolones, the type II DNA topoisomerases gyrase and topoisomerase IV, or active export of the drugs via efflux pumps (12). We have detected ciprofloxacin-resistant L. monocytogenes clinical isolates and characterized the efflux pump involved in resistance.(An initial report of this work was presented at the 41st Interscience Conference on Antimicrobial Agents and Chemotherapy [S. Godreuil, M. Galimand, G. Gerbaud, and P. Courvalin, Abstr. 41st Intersci. Conf. Antimicrob. Agents Chemother., abstr. UL-11, 2001].) MATERIALS AND METHODSStrains, plasmids, and growth conditions. Screening of 488 L. monocytogenes isolates responsible for human listeriosis in France for resistance to fluoroquinolones was carried out on brain heart infusion agar (Difco Laboratories, Detroit, Mich.) containing 4 g of ciprofloxacin per ml. Strains that were found to be resistant and susceptible L. monocytogenes EGD were studied ( Table 1)....

Characterization of antibiotic resistance in Listeria spp. isolated from slaughterhouse environments, pork and human infections

“…The gyrA and parC genes, which encode subunits of DNA gyrase topoisomerase II and topoisomerase IV, and the lde gene, which encodes an efflux pump associated with fluoroquinolone resistance, were amplified using primer sequences from Godreuil et al [19] and Romanova et al [20], respectively. The isolates were also screened for clindamycin resistance.…”

Identification of the mechanisms of resistance and potential cross resistance of Listeria monocytogenes upon adaptation to different antimicrobials

“…were not enhanced in the mutants were similar to earlier observations with ciprofloxacinresistant clinical isolates (86). Taken together, these data suggest that MDR efflux system mutations are likely responsible for the phenotype of the mutants in the current study.…”

“…A broad host range conjugative transposon Tn916 with tetM tetracycline resistance gene, and Tn916-related transposon, Tn1545 both found in E. faecalis (35,77,177) (86,144).…”

“…Ethidium bromide (EthBr) (Fisher Scientific) resistance was determined using agar dilutions on MHA as previously described (86 The efflux inhibitor reserpine (Sigma) was used at 10µg/ml as described (86). When MICs were determined in the presence of the efflux inhibitor reserpine, MICs in the absence of reserpine were always determined as control.…”

Antibacterial and Resistance Modifying Activities of Nigella sativa Essential Oil and its Active Compounds Against Listeria monocytogenes

“…The efflux pumps are proteins of bacterial membranes which extrude and limit the intracellular accumulation of antibiotics and other antimicrobial agents (5). It was previously identified that the increased resistance to ciprofloxacin (a fluoroquinolone) confers also increased resistance to EtBr, and an increased expression of the Lde transporter (11). Our data showed the potential of N. sativa essential oil, thymoquinone, carvacrol, and p-cymene to decrease the MIC of ciprofloxacin at least two-fold and up to eight-fold.…”