Synergistic activity between beta-lactams and igy antibodies against Pseudomonas aeruginosa in vitro

Multi-drug resistant Pseudomonas aeruginosa is a gram-negative bacillus responsible for nosocomial infections. Immunoglobulin Y (IgY) is a chicken immunoglobulin used for research, immunodiagnosis, and immunotherapy. IgY presents antimicrobial properties and it is under investigation for use as an adjunct to prophylactic therapies. The current study aimed to assess the synergistic action between anti-P aeruginosa IgY and the beta-lactams ceftazidime, imipenem, and meropenem. IgY antibodies were obtained from laying hens immunized with SPM-1 producing P. aeruginosa (Pa48_spm-1+) or VIM-2 producing P. aeruginosa (Pa23_{vim-2 +}). The antimicrobial activity of IgY antibodies was evaluated by the growth inhibition test, and the synergistic effect was assessed by determination of the fractional inhibitory concentration index. Anti-Pa48_spm-1+ IgY shows antimicrobial activity at 1.25 mg/ml and anti-Pa23_vim-2+ IgY shows antimicrobial activity at 2.5 mg/ml. The fractional inhibitory concentration indices of anti-Pa48_spm-1+ IgY and ceftazidime, or imipenem, or meropenem at 72 h of experiment were 0.189, 0.209, and 0.440, respectively. For anti-Pa23_vim-2+ IgY, the fractional inhibitory concentration indices were 0.440 with ceftazidime, 0.453 with imipenem, and 0.441 with meropenem at 72 h. We conclude that there is a synergistic action between anti-P. aeruginosa IgY and the antimicrobials tested. Further studies are necessary to investigate the mechanisms associated with this action.