Fig. 1
Effect of treatment with combinations of steroidal alkaloids and levofloxacin on survival of G. mellonella larvae infected with P. aeruginosa PAM1032 (a) and PAM1034 (b), or larval burden of the same strains PAM1032 (c) and PAM1034 (d). All larvae were inoculated with 2.5 × 103 cfu/mL P. aeruginosa and treated with each agent individually or in combination with three doses at 2, 4 and 6 h post-infection (indicated by the arrows). Treatments consisted of PBS, steroidal alkaloids (50, 100 or 200 mg/kg), levofloxacin (5 mg/kg), and a combination of steroidal alkaloids with levofloxacin. Larvae were incubated at 37 °C for 96 h and survival recorded every 24 h. The burden of P. aeruginosa was determined from five individual larvae every 24 h. For clarity, data for treatment with PBS alone is not shown because the data obtained was similar to that obtained for steroidal alkaloid treatment alone. * a) and b); combination treatment group with significantly enhanced survival compared with any of the constituent monotherapies (P < 0.05, log-rank test with Holm’s correction for multiple comparisons). n = 45 (pooled from triplicate experiments). Error bars indicate ±SEM. LVX, levofloxacin; ALKS, steroidal alkaloids. * c) and d); significant difference in larval burden between groups treated with the combination of steroidal alkaloids and levofloxacin compared with the constituent monotherapies; n = 5 (P < 0.05, the Mann–Whitney U-test compared the combination therapy with each monotherapy individually). The black bar represents the median value of larval burden per group