Effect of S. marcescens on growth of L. mexicana in vitro . (A) In vitro 24 h incubation of Serratia bacterial cells (107 CFU mL-1) or (B) filtered spent medium from Serratia culture with L. mexicana (3 × 106 promastigotes mL-1). Results are based on triplicate samples repeated three times and bar charts represent mean ± SEM. *P ≤ 0.009. **P ≤ 0.0001 (Mann-Whitney U test).