Abstract
Several Acinetobacter strains have utility for biotechnology applications, yet some are opportunistic pathogens. We compared strains of seven Acinetobacter species (baumannii, Ab; calcoaceticus, Ac; guillouiae, Ag; haemolyticus, Ah; lwoffii, Al; junii, Aj; and venetianus, Av-RAG-1) for their potential virulence attributes, including proliferation in mammalian cell conditions, haemolytic/cytolytic activity, ability to elicit inflammatory signals, and antibiotic susceptibility. Only Ah grew at 102 and 104 bacteria/well in mammalian cell culture medium at 37°C. However, co-culture with colonic epithelial cells (HT29) improved growth of all bacterial strains, except Av-RAG-1. Cytotoxicity of Ab and Ah toward HT29 was at least double that of other test bacteria. These effects included bacterial adherence, loss of metabolism, substrate detachment, and cytolysis. Only Ab and Ah exhibited resistance to killing by macrophage-like J774A.1 cells. Haemolytic activity of Ah and Av-RAG-1 was strong, but undetectable for other strains. When killed with an antibiotic, Ab, Ah, Aj and Av-RAG-1 induced 3 to 9-fold elevated HT29 interleukin (IL)-8 levels. However, none of the strains altered levels of J774A.1 pro-inflammatory cytokines (IL-1β, IL-6 and tumor necrosis factor-α). Antibiotic susceptibility profiling showed that Ab, Ag and Aj were viable at low concentrations of some antibiotics. All strains were positive for virulence factor genes ompA and epsA, and negative for mutations in gyrA and parC genes that convey fluoroquinolone resistance. The data demonstrate that Av-RAG-1, Ag and Al lack some potentially harmful characteristics compared to other Acinetobacter strains tested, but the biotechnology candidate Av-RAG-1 should be scrutinized further prior to widespread use.
Highlights
The genus Acinetobacter comprises 27 known species and several unnamed provisional species of gram-negative, ubiquitous, nonmotile, non-fermentative, coccobacilli [1,2]
Microbial Growth and Influence of Mammalian Cells The proliferation capacity of the different Acinetobacter strains was compared in a bacterial medium (LB) and mammalian cell culture medium at 37uC
The exception was Av-RAG-1, which was highly bioreductive compared to all other strains in LB, but showed the lowest bioreduction in mammalian cell culture medium and no bioreduction in the presence of HT29 cells
Summary
The genus Acinetobacter comprises 27 known species and several unnamed provisional species of gram-negative, ubiquitous, nonmotile, non-fermentative, coccobacilli [1,2]. One promising example is the RAG-1 strain of A. venetianus, which has been shown to produce several oil-modifying substances such as emulsans, esterases, lipases and surfactants [9,10,11]. This strain was previously assigned to other species groups (A.calcoaceticus and A.lwoffi) [12] which are recognized as opportunistic pathogens. Further advancement of the Acinetobacter genus for beneficial applications requires a rigorous clarification concerning threats to drinking water [13,14] and linkages to nosocomial infections [15,16,17,18,19,20]
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