Surfactant proteins A and D inhibit the growth of Gram-negative bacteria by increasing membrane permeability
Huixing Wu, … , Kwang Sik Kim, Francis X. McCormack
Huixing Wu, … , Kwang Sik Kim, Francis X. McCormack
Published May 15, 2003
Citation Information: J Clin Invest. 2003;111(10):1589-1602. https://doi.org/10.1172/JCI16889.
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Article Pulmonology

Surfactant proteins A and D inhibit the growth of Gram-negative bacteria by increasing membrane permeability

Abstract

The pulmonary collectins, surfactant proteins A (SP-A) and D (SP-D), have been reported to bind lipopolysaccharide (LPS), opsonize microorganisms, and enhance the clearance of lung pathogens. In this study, we examined the effect of SP-A and SP-D on the growth and viability of Gram-negative bacteria. The pulmonary clearance of Escherichia coli K12 was reduced in SP-A–null mice and was increased in SP-D–overexpressing mice, compared with strain-matched wild-type controls. Purified SP-A and SP-D inhibited bacterial synthetic functions of several, but not all, strains of E. coli, Klebsiella pneumoniae, and Enterobacter aerogenes. In general, rough E. coli strains were more susceptible than smooth strains, and collectin-mediated growth inhibition was partially blocked by coincubation with rough LPS vesicles. Although both SP-A and SP-D agglutinated E. coli K12 in a calcium-dependent manner, microbial growth inhibition was independent of bacterial aggregation. At least part of the antimicrobial activity of SP-A and SP-D was localized to their C-terminal domains using truncated recombinant proteins. Incubation of E. coli K12 with SP-A or SP-D increased bacterial permeability. Deletion of the E. coli OmpA gene from a collectin-resistant smooth E. coli strain enhanced SP-A and SP-D–mediated growth inhibition. These data indicate that SP-A and SP-D are antimicrobial proteins that directly inhibit the proliferation of Gram-negative bacteria in a macrophage- and aggregation-independent manner by increasing the permeability of the microbial cell membrane.

Authors

Huixing Wu, Alexander Kuzmenko, Sijue Wan, Lyndsay Schaffer, Alison Weiss, James H. Fisher, Kwang Sik Kim, Francis X. McCormack

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Deletion of OmpA enhances the susceptibility of smooth E. coli variant E...
Deletion of OmpA enhances the susceptibility of smooth E. coli variant E98 to growth inhibition by SP-A and SP-D. (a) Silver-stained SDS-PAGE of E. coli strain E98. (b) A clinical isolate of E98 (parental), an isogenic OmpA-negative (ΔOmpA) mutant, and ΔOmpA bacteria containing either an empty vector (ΔOmpAv) or a plasmid directing overexpression of OmpA in the OmpA-negative background (ΔOmpA+) were embedded in agar and incubated overnight with albumin, lysozyme, rSP-A, rSP-D, rrSP-A, a C-terminal fragment of rrSP-A (ΔSP-A), hSP-A, and rrSP-D at 0.5 μg/well or 5.0 μg/well, as indicated.