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Lambda prophage decreases Escherichia coli sensitivity to human serum bactericidal effect
S Vaca-Pacheco1, E Piedra-Ibarra, D Arenas-Aranda
1Escuela Nacional de Estudios Profesionales Iztacala, Universidad Nacional Autónoma de México, Mexico.
Revista Latinoamericana De Microbiologia
|January 1, 1993
Summary
Bacteriophage lambda protects Escherichia coli from human serum's bactericidal action via the alternative complement pathway. Lysogenized bacteria exhibit significantly reduced susceptibility to serum-mediated killing.
Area of Science:
- Microbiology
- Immunology
- Bacteriology
Background:
- The human complement system, particularly the alternative pathway, plays a crucial role in innate immunity against bacterial infections.
- Escherichia coli is a common bacterium that can cause various infections, and its susceptibility to host immune mechanisms is a key factor in pathogenesis.
- Bacteriophages, viruses that infect bacteria, can integrate their genetic material into the host genome (lysogeny), potentially altering bacterial characteristics.
Purpose of the Study:
- To investigate the effect of lambda (λ) bacteriophage lysogeny on the susceptibility of Escherichia coli C600 to the bactericidal activity of normal human serum.
- To determine which complement pathway is responsible for the serum-mediated killing of E. coli C600.
- To elucidate the mechanism by which lambda phage might confer serum resistance to its E. coli host.
Main Methods:
- Susceptibility testing of E. coli C600 and C600(λ) strains to normal human serum.
- Inactivation of the alternative complement pathway by heating serum.
- Selective inhibition of the classical complement pathway using EGTA and MgCl2.
- Quantification of bacterial survival over time.
Main Results:
- E. coli C600 showed significant killing by normal human serum, with survival reduced to 16% after 180 minutes.
- E. coli C600(λ) exhibited markedly reduced susceptibility, with survival rates of 199%, 109%, and 65% at the same time points.
- The alternative complement pathway was identified as the primary mediator of bactericidal activity, with C600 being 4-14 times more susceptible than C600(λ).
Conclusions:
- Lambda bacteriophage lysogeny significantly enhances the resistance of Escherichia coli C600 to serum-mediated killing, primarily through the alternative complement pathway.
- The protective effect is likely due to alterations in the bacterial surface, potentially involving phage-encoded proteins, which interfere with the complement membrane attack complex.
- These findings suggest a novel mechanism by which bacteriophages can influence bacterial-host interactions and immune evasion.