Effect of neonatal malnutrition on expression of nitric oxide synthase enzyme, production of free radicals and in vitro viability of alveolar macrophages infected with methicillin-sensitive and methicillin-resistant Staphylococcus aureus.

OBJECTIVE

Evaluate the effects of neonatal malnutrition on the microbicidal response and viability of in vitro macrophages infected with Staphylococcus aureus sensitive/resistant to methicillin.

METHODS

Male Wistar rats (n = 24) were divided into two distinct groups: nourished (rats breast-fed by mothers undergoing diet with 17% casein) and malnourished (rats breast-fed by mothers undergoing diet with 8% casein). Macrophages were recovered after surgical tracheostomy procedure by collecting bronchoalveolar lavage. Four systems were established: negative control, composed only by phagocytes; positive control, macrophages plus lipopolysaccharide; and two test systems, macrophages plus Staphylococcus aureus sensitive and resistant to methicillin. Plates were incubated at 37 °C for 24 h. After this period, tests for the analysis of cell viability and microbicidal response were performed. In the statistical analysis, the Student's t and ANOVA tests were used, accepting p < 0.05.

RESULTS

The neonatal malnutrition impaired the animals' body weight. There was a lower expression of the inducible nitric oxide enzyme (iNOS), nitric oxide production, and viability of macrophages infected with methicillin-resistant Staphylococcus aureus. However, increased production of superoxide anion in the malnourished group was detected.

CONCLUSION

Neonatal malnutrition focusing on critical periods of development promoted lower expression of iNOS, nitric oxide production, cell viability, and exacerbated reactive oxygen species production. The high levels of reactive oxygen species may favor the onset of serious and systemic infections with fatal outcome if associated with methicillin-resistant Staphylococcus aureus.