Surfactant proteins A and D inhibit the growth of Gram-negative bacteria by increasing membrane permeability.
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.
Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Cincinnati, Cincinnati, Ohio, USA.
Huixing
H
Wu
Alexander
A
Kuzmenko
Sijue
S
Wan
Lyndsay
L
Schaffer
Alison
A
Weiss
James H
JH
Fisher
Kwang Sik
KS
Kim
Francis X
FX
McCormack
D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000382:microbiology; D002455:Cell Division / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects*; D037222:Collectins / Q000494:pharmacology; D003609:Dactinomycin / Q000493:pharmacokinetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004927:Escherichia coli Infections / Q000188:drug therapy / Q000378:metabolism; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D020022:Genetic Predisposition to Disease; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D008809:Mice, Inbred C3H; D018345:Mice, Knockout; D008826:Microbial Sensitivity Tests; D037662:Pulmonary Surfactant-Associated Protein A / Q000172:deficiency / Q000235:genetics / Q000494:pharmacology*; D037663:Pulmonary Surfactant-Associated Protein D / Q000096:biosynthesis / Q000235:genetics / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012141:Respiratory Tract Infections / Q000188:drug therapy / Q000378:metabolism
D001425:Bacterial Outer Membrane Proteins; D037222:Collectins; D005456:Fluorescent Dyes; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; C078167:OMPA outer membrane proteins; D003609:Dactinomycin