Clinical significance of overexpression of multiple RND-family efflux pumps in Bacteroides fragilis isolates.
OBJECTIVE
The aim of the present study was to determine correlation between bmeB efflux pump overexpression and resistance to fluoroquinolones and beta-lactams in Bacteroides fragilis clinical isolates (n = 51) and the effects of broad-spectrum efflux pump inhibitors (EPIs) on the MICs of the test antibiotics.


METHODS
Susceptibility to garenoxacin, levofloxacin, moxifloxacin, cefoxitin and faropenem +/- EPIs (CCCP, MC-207,110, reserpine and verapamil) was determined. Expression of bmeB efflux pumps was measured, topoisomerase genes were sequenced and beta-lactamase production was determined.


RESULTS
Isolates were grouped into categories based on susceptibility patterns, topoisomerase sequence and efflux pump expression. Panel I isolates (19/51, 37.3%) were highly resistant to fluoroquinolones and cefoxitin (resistance to all agents was significantly reduced by EPIs, P < 0.05), had a point mutation in gyrA (C-->T) causing a Ser-82-->Phe substitution, and overexpressed bmeB4 and bmeB15. Panel II isolates (7/51; 13.7%) had intermediate-level resistance to fluoroquinolones and cefoxitin and a GyrA substitution. Panel IIIA isolates (21/51; 41.2%) had intermediate-level fluoroquinolone resistance and high-level cefoxitin resistance [resistance to all agents was significantly reduced by EPIs (P < 0.05)] and overexpressed bmeB4 and bmeB15. Panel IIIB isolates (4/51; 7.8%) had low-level fluoroquinolone resistance and high-level resistance to cefoxitin [cefoxitin resistance was significantly reduced by EPIs (P < 0.05)] and overexpressed bmeB4, bmeB6, bmeB10 and bmeB14. All isolates were beta-lactamase-positive.


CONCLUSIONS
These data suggest that bmeB efflux pump overexpression can (i) cause low- to intermediate-level clinically relevant fluoroquinolone resistance; (ii) be coupled with GyrA substitutions to cause high-level fluoroquinolone resistance; (iii) contribute to high-level clinically relevant resistance to beta-lactams.
Pumbwe
Lilian
L
Greater Los Angeles Veterans Administration Healthcare Systems 691/151J, Los Angeles, CA 90073, USA.
Chang
Abraham
A
Smith
Rachel L
RL
Wexler
Hannah M
HM
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D001442:Bacteroides Infections / Q000382:microbiology; D001441:Bacteroides fragilis / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification; D024901:Drug Resistance, Multiple, Bacterial; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D006801:Humans; D050576:Membrane Fusion Proteins / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009154:Mutation
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D050576:Membrane Fusion Proteins; D026901:Membrane Transport Proteins