Abstract
Acinetobacter baumannii is a common pathogen of nosocomial infection, and its ability to form biofilms further contributes to its virulence and multidrug resistance, posing a great threat to global public health. In this study, we investigated the inhibitory effects of five biofilm inhibitors (BFIs) (zinc lactate, stannous fluoride, furanone, azithromycin, and rifampicin) on biofilm formation of nine extensively drug-resistant A. baumannii (XDRAB), and assessed the synergistic antibacterial effects of these BFIs when combined with one of four conventional anti-A. baumannii antibiotics (imipenem, meropenem, tigecycline, and polymyxin B). Each of the five BFIs tested was found to be able to significantly inhibit biofilm formation of all the clinical isolates tested under sub-minimal inhibitory concentrations. Then, we observed synergistic effects (in 22%, 56% and 11% of the isolates) and additive effects (56%, 44% and 44%) when zinc lactate, stannous fluoride and furanone were combined with tigecycline, respectively. When zinc lactate and stannous fluoride were each used with a carbapenem (imipenem or meropenem), in 33% and 56–67% of the isolates, they showed synergistic and additive effects, respectively. Additivity in > 50% of the isolates was detected when rifampicin was combined with imipenem, meropenem, tigecycline, or polymyxin B; and a 100% additivity was noted with azithromycin-polymyxin B combination. However, antagonism and indifference were noted for polymyxin B in its combination with zinc lactate and stannous fluoride, respectively. In conclusion, five BFIs in combination with four antibacterial drugs showed different degrees of in vitro synergistic and additive antibacterial effects against XDRAB.
Highlights
Acinetobacter baumannii is a common pathogen of nosocomial infection, and its ability to form biofilms further contributes to its virulence and multidrug resistance, posing a great threat to global public health
According to the interpretive categories established by the Clinical and Laboratory Standards Institute (CLSI)[18], these isolates were either susceptible or non-susceptible to tigecycline and/or polymyxin B, but were resistant to other 13 antibacterial drugs (Table 1), and such drug resistance profiles placed these isolates as XDRAB19
The five biofilm inhibitors (BFIs) selected for this study, zinc lactate, stannous fluoride, furanone, azithromycin, and rifampicin, displayed different degrees of antibacterial effects on these XDRAB, with identical minimal inhibitory concentrations (MICs) values of 512, 512, 256, 1024, and 1 μg/ml, respectively, for all nine isolates tested
Summary
Acinetobacter baumannii is a common pathogen of nosocomial infection, and its ability to form biofilms further contributes to its virulence and multidrug resistance, posing a great threat to global public health. We investigated the inhibitory effects of five biofilm inhibitors (BFIs) (zinc lactate, stannous fluoride, furanone, azithromycin, and rifampicin) on biofilm formation of nine extensively drug-resistant A. baumannii (XDRAB), and assessed the synergistic antibacterial effects of these BFIs when combined with one of four conventional anti-A. baumannii antibiotics (imipenem, meropenem, tigecycline, and polymyxin B). It has been reported that three chemical substances, zinc lactate, stannous fluoride and furanone, and two antibiotics, azithromycin and rifampicin, can inhibit bacterial biofilm formation, but cannot effectively control the infection caused by biofilm-forming b acteria[12,13,14,15,16,17].
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