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Effect of different surfactants on pulmonary group B streptococcal infection in premature rabbits
M P Sherman1, L A Campbell, T A Merritt
1Department of Pediatrics, University of California, Los Angeles, Medical Center.
Insights
Clinical surfactants do not accelerate group B streptococci (GBS) lung infections in premature rabbits. Some surfactants actually inhibit GBS growth, with effects not linked to macrophage function.
Area of Science:
- Neonatal research
- Pulmonary medicine
- Microbiology
Background:
- Premature infants are susceptible to pulmonary infections, including those caused by group B streptococci (GBS).
- Surfactants are crucial for lung function and are administered to premature infants, but their impact on GBS infection is not fully understood.
Purpose of the Study:
- To assess how different surfactants affect pulmonary GBS infection in premature rabbits.
- To investigate the influence of various surfactants on newborn rabbit pulmonary alveolar macrophage function.
Main Methods:
- Preterm and term rabbit pups were infected with GBS aerosols.
- Intratracheal administration of various surfactants (calf lung extract, Curosurf, Exosurf Neonatal, Survanta, human amniotic fluid-derived, rabbit surfactant) or saline vehicle was performed.
- Intrapulmonary GBS clearance, phagocytosis, and in vitro bacterial growth were evaluated.
Main Results:
- Premature rabbits showed increased GBS pulmonary growth compared to term rabbits.
- Exosurf Neonatal demonstrated the lowest GBS proliferation in premature rabbits, while Curosurf and human amniotic fluid-derived surfactant showed the highest.
- No surfactant accelerated GBS growth in vivo; some inhibited it. Macrophage function in term rabbits remained unaffected.
Conclusions:
- Surfactants used clinically do not exacerbate GBS lung infections in preterm rabbits.
- Certain surfactants may inhibit streptococcal proliferation within the lungs.
- The observed effects of surfactants on GBS are not attributable to alterations in macrophage function.
Objectives:
To evaluate the effects of different surfactants on pulmonary infection with group B streptococci in premature rabbits and to examine the effects of different surfactants on pulmonary alveolar macrophage function of newborn rabbits.
Model:
Preterm and term rabbit pups.
Methods:
Rabbit pups were infected with GBS aerosols followed by intratracheal administration of either calf lung surfactant extract, minced porcine lung surfactant (Curosurf), synthetic surfactant (Exosurf Neonatal), minced bovine lung surfactant (Survanta), human amniotic fluid-derived surfactant, rabbit surfactant, saline vehicle, or no treatment. Intrapulmonary clearance of GBS was determined by comparing bacterial counts in left lungs cultured immediately after aerosol infection with similarly infected lungs analyzed 4 hours after surfactant therapy. Phagocytosis of streptococci was ascertained by microscopic examination of the right lungs fixed in situ at 4 hours. For comparison, an in vitro method was used to measure growth of GBS in the different surfactants.
Results:
Preterm animals had a sixfold increase in pulmonary bacterial growth compared with a slight decrease in intrapulmonary GBS in term animals when all were delivered by cesarean section (p < 0.05). In premature rabbits, GBS proliferation was lowest in animals treated with Exosurf Neonatal and highest in animals receiving Curosurf and human amniotic fluid-derived surfactant (p < 0.05). None of the surfactants promoted accelerated growth of GBS in comparison with control animals. Similar growth of GBS was seen in in vitro cultures. Intrapulmonary phagocytosis of GBS in premature pups was not altered by any of the surfactants. In term rabbit pups, the following measures of macrophage population kinetics remained normal at 1 and 24 hours after surfactant administration: viability, cell numbers based on lung lavage, and in vivo incorporation of thymidine.
Conclusions:
Surfactants used in clinical practice do not accelerate the in vivo growth of group B streptococci in the lungs of preterm rabbits. Some surfactants inhibit streptococcal proliferation. The effects of different surfactants are not explained by changes in macrophage function.