Affiliation:
1. Infectious Diseases Division and Medical Services, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
2. Department of Pediatrics, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
Abstract
ABSTRACT
Endogenous transporters protect
Staphylococcus aureus
against antibiotics and also contribute to bacterial defense from environmental toxins. We evaluated the effect of overexpression of four efflux pumps, NorA, NorB, NorC, and Tet38, on
S. aureus
survival following exposure to pyocyanin (PYO) of
Pseudomonas aeruginosa
, using a well diffusion assay. We measured the PYO-created inhibition zone and found that only an overexpression of NorA reduced
S. aureus
susceptibility to pyocyanin killing. The MIC
PYO
of the NorA overexpressor increased threefold compared to that of wild-type RN6390 and was reduced 2.5-fold with reserpine, suggesting that increased NorA efflux caused PYO resistance. The PYO-created inhibition zone of a
ΔnorA
mutant was consistently larger than that of a plasmid-borne NorA overexpressor. PYO also produced a modest increase in
norA
expression (1.8-fold at 0.25 µg/mL PYO) that gradually decreased with increasing PYO concentrations. Well diffusion assays carried out using
P. aeruginosa
showed that
ΔnorA
mutant was less susceptible to killing by PYO-deficient mutants PA14
phzM
and PA14
phzS
than to killing by PA14. NorA overexpression led to reduced killing by all tested
P. aeruginosa
. We evaluated the NorA–PYO interaction using a collection of 22 clinical isolates from adult and pediatric cystic fibrosis (CF) patients, which included both
S. aureus
(CF-SA) and
P. aeruginosa
(CF-PA). We found that when isolated alone, CF-PA and CF-SA expressed varying levels of PYO and
norA
transcripts, but all four CF-PA/CF-SA pairs isolated concurrently from CF patients produced a low level of PYO and low
norA
transcript levels, respectively, suggesting a partial adaptation of the two bacteria in circumstances of persistent co-colonization.
Funder
HHS | National Institutes of Health
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology