Effects of iron depletion on antimicrobial activities against planktonic and biofilm Pseudomonas aeruginosa.
OBJECTIVE
Iron plays an important role in the development of Pseudomonas aeruginosa biofilm. Here we evaluated effects of iron depletion on the antimicrobial activity of ceftazidime, tobramycin and ciprofloxacin against planktonic and biofilm Pseudomonas aeruginosa.


METHODS
We tested the sensitivities of wild-type PAO1, type-IV pilus mutant PAO-DeltapilHIJK and the quorum-sensing mutant PAO-JP2 P. aeruginosa planktonic cultures and biofilms to antibiotics under iron-depleted conditions.


RESULTS
In planktonic bacteria, the minimum concentration that inhibited visible growth (MIC) of ciprofloxacin was increased slightly in an iron-depleted environment in all three strains, whereas the MIC of tobramycin was similar in iron-depleted and control environments. The MIC of ceftazidime increased in the PAO-JP2 strain when iron was depleted. Tobramycin achieved the best bactericidal effect in biofilms. Viable counts were reduced by one log under iron-depleted conditions in all three strains when tobramycin reached 4 MIC and when ceftazidime and ciprofloxacin reached 8 MIC.


CONCLUSIONS
This study suggests that once the biofilm is formed, iron depletion may only slightly promote the bactericidal effect of antibiotics on PAO1, PAO-DeltapilHIJK and PAO-JP2. Although these changes were relatively small, iron as one of the environmental factors should not be ignored when evaluating bactericidal effect of antibiotics. The combination of an iron chelator and antibiotics may have therapeutic value under certain bacterial growth conditions.
Cai
Yun
Y
Department of Clinical Pharmacology, the PLA General Hospital, Beijing 100853, PR China.
Yu
Xu-Hong
XH
Wang
Rui
R
An
Mao-Mao
MM
Liang
Bei-Bei
BB
D015082:2,2'-Dipyridyl / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D002442:Ceftazidime / Q000494:pharmacology; D002939:Ciprofloxacin / Q000494:pharmacology; D007501:Iron / Q000378:metabolism*; D009753:Nutritive Value; D010933:Plankton / Q000187:drug effects* / Q000254:growth & development; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D014031:Tobramycin / Q000494:pharmacology
D000890:Anti-Infective Agents; D015082:2,2'-Dipyridyl; D002939:Ciprofloxacin; D002442:Ceftazidime; D007501:Iron; D014031:Tobramycin