In vitro activity of amphotericin B in combination with imipenem/colistin against mixed cultures of Candida spp. and Gram-negative bacteria

A new direction of research was established due to biofilms' infections caused by a mixture of fungal and bacterial species. Diagnosis of these infections becomes more difficult and high doses of drugs are used in treatment, especially in critically ill patients. The aim of the current study was to examine the effects of amphotericin B, in combination with imipenem or colistin against Candida albicans - Acinetobacter baumannii- Proteus mirabilis and Candida tropicalis - Acinetobacter baumannii -Proteus mirabilis polymicrobial biofilms. According to the microdilution method of the Clinical Laboratory Standards Institute (CLSI) published in documents M27-A3 (2008) and M07-A10 (2015) respectively, the susceptibility of the clinical isolates Candida yeasts to amphotericin B and Gram-negative bacteria to imipenem and colistin was determined. A Checkerboard assay was employed to evaluate the efficacy of drugs combinations. The 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyl tetrazolium bromide (MTT) reduction assay was used to quantify the biofilms. The combination amphotericin B/colistin and amphotericin B/imipenem did not produce obvious effects against the polymicrobial biofilms formed for 48 hours. Whereas colistin alone produced strong effects against Candida albicans-Acinetobacter baumannii and Candida albicans - Acinetobacter baumannii -Proteus mirabilis compared to Candida tropicalis - Acinetobacter baumannii and Candida tropicalis - Acinetobacter baumannii - Proteus mirabilis polymicrobial biofilms. For mixed Candida spp. bacterial biofilms, these results point to the difficulties in eradicating these biofilms, as well as in preventing their development.