[Effects of Aeromonas hydrophila biofilm on the drug resistance].

Aeromonas hydrophila (Ah) biofilm (BF) model in vitro was established and antibiotic effects of 11 antimicrobials on BF and free-cell(FC) bacteria were tested. After the Ah J-1 on the surfaces of the silicon pieces was incubated for 7 days in TSB, the intact BF was formed by detection of AgNO3 solution staining. The FC bacteria were resistant to Penicillin but susceptible to Enrofloxacin and Fulgram. Their minimum bactericidal concentrations (MBCs) were 256 microg/mL, 0.03 microg/mL and 0.25 microg/mL respectively. Florfenicol had a strong antibacterial effect on BF bacteria and the ratio of MBC between BF and FC bacteria was 2 to 1, but more than 32 to 1 occurred for Kanamycin, Penicillin and Neomycin. Morphology and structure of BFs with/without the treatment of Enrofloxacin were observed under scanning electron microscope, while the bactericidal curve was detected. Enrofloxacin could eradicate the FC bacteria completely but not the BF bacteria at a concentration of 4 fold MBC. The 32 fold MBC Enrofloxacin could entirely kill the FC bacteria in 4h, but in 24h for BF bacteria. The result suggested that BF enabled Ah to have strong resistance to antimicrobials and the potential influence of BF should be highly considered.