Induction of complement sensitivity in Escherichia coli by citric acid and low pH.
OBJECTIVE
The lytic functions of the complement system play an important role in the control of Gram-negative infections. Complement-resistant Escherichia coli LP1395 (O18) grown under normal conditions can survive the bactericidal action of complement present in human serum. Towards elucidating the mechanisms of complement resistance, the resistance of E. coli LP1395 grown under conditions of low pH and in the presence of citric acid was tested.


RESULTS
E. coli LP1395 becomes sensitive to complement after growth in the presence of citric acid at pH 5. Complement resistance could be restored when the cells were transferred to pH 7 media. However, this recovery was greatly impaired when the cells were transferred to pH 7 media with chloramphenicol. This implies that protein synthesis may be involved in complement resistance. The cells exposed to citric acid at pH 5 showed no indication of a generalized outer membrane (OM) permeability when compared with those grown under normal conditions in terms of sensitivity to lysozyme, uptake of lipophilic dye, or sensitivity to a number of antibiotics.


CONCLUSIONS
Complement-resistant LP1395 may acquire a sensitivity to complement due not to a generalized disruption of the OM barrier, but possibly to the alteration of the activity of one or more normal complement resistance factors.


CONCLUSIONS
The elucidation of the mechanisms of complement resistance of Gram-negative pathogens would bring important information about bacterial infections. Complement resistance factors could also be potential targets in antimicrobial therapies.
Ocaña-Morgner
C
C
Department of Biology, University of Louisiana at Lafayette, LA 70504-2451, USA.
Dankert
J R
JR
D015057:1-Naphthylamine / Q000031:analogs & derivatives; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001770:Blood Bactericidal Activity / Q000187:drug effects; D002701:Chloramphenicol / Q000494:pharmacology; D019343:Citric Acid; D003165:Complement System Proteins / Q000276:immunology*; D003470:Culture Media; D004926:Escherichia coli / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D005456:Fluorescent Dyes; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009113:Muramidase / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D003470:Culture Media; D005456:Fluorescent Dyes; D019343:Citric Acid; D002701:Chloramphenicol; C005444:N-phenyl-1-naphthylamine; D003165:Complement System Proteins; D015057:1-Naphthylamine; D009113:Muramidase