Uropathogenic Escherichia coli and tolerance to nitric oxide: the role of flavohemoglobin.
OBJECTIVE
NO has an important role as part of the innate host response against bacterial infections. Flavohemoglobin, which is encoded by the hmp gene, protects Escherichia coli against nitrosative stress. We compared the NO tolerance of UPEC and nonpathogenic strains, and examined the involvement of flavohemoglobin.


METHODS
The E. coli K12 derivates HB101 and DH5alpha represent nonpathogenic strains, while J96 and IA2 represent UPEC strains. HB101 was used as the host for a pBR322 plasmid carrying the hmp gene. Bacterial tolerance to NO was evaluated by determining cfu. Flavohemoglobin expression was examined using Northern and Western blot analysis.


RESULTS
In the stationary growth phase, J96 was significantly more tolerant to DETA/NO (Alexis Biochemical, Lausen, Switzerland) (1 mM) compared to HB101 (47% +/- 11% vs 6.4% +/- 3.1% cfu). In the exponential growth phase DETA/NO exposure resulted in 98% +/- 4.6% cfu for J96 and 74% +/- 7.6% cfu for IA2 compared to 15% +/- 5.9% for HB101 and 21% +/- 12% for DH5alpha. HB101 over expressing hmp showed increased tolerance to DETA/NO (0.5 mM) compared to WT HB101 (106% +/- 5.6% vs 67 +/- 6.2%, p <0.01). Northern and Western blot analysis demonstrated increased flavohemoglobin expression after DETA/NO exposure and the strongest expression in HB101 carrying hmp on a multicopy plasmid.


CONCLUSIONS
UPEC strains were significantly more tolerant to DETA/NO than nonpathogenic strains, which suggests a correlation between virulence and NO tolerance. Flavohemoglobin expression increased after DETA/NO exposure in UPEC and in nonpathogenic strains.
Svensson
Lovisa
L
Department of Chemistry and Biomedical Sciences, University of Kalmar, Kalmar, Sweden.
Marklund
Britt-Inger
BI
Poljakovic
Mirjana
M
Persson
Katarina
K
D004093:Dihydropteridine Reductase / Q000502:physiology*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000472:pathogenicity / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000502:physiology*; D006420:Hemeproteins / Q000502:physiology*; D009247:NADH, NADPH Oxidoreductases / Q000502:physiology*; D009569:Nitric Oxide / Q000494:pharmacology*; D014552:Urinary Tract Infections / Q000382:microbiology
D029968:Escherichia coli Proteins; D006420:Hemeproteins; D009569:Nitric Oxide; D004093:Dihydropteridine Reductase; C076538:hmp protein, E coli; D009247:NADH, NADPH Oxidoreductases