Filamentous prophages in the genomes of Acinetobacter baumannii from egypt: impact on biofilm formation and the potential to induce enterotoxicity

Abstract

Filamentous phages (FPs) have been recently isolated from Acinetobacter baumannii. While FPs are known to modulate the virulence of some Gram-negative pathogens, their role in A. baumannii has not been fully explored. This study analyzed 18 clinical isolates of A. baumannii from global clones (GC), with draft genomes generated by Illumina sequencing. All isolates were screened for filamentous prophage (FPP) genomes using the Zonula occludens toxin (Zot)-coding gene as a marker. Nine out of the 18 isolates were found to carry zot genes. The complete sequences of four FPPs were predicted. FPPs were exclusively found within GC1, GC7, and GC9 strains. Among the A. baumannii genomes deposited in the NCBI genomic database, FPPs were found to be disseminated in 42 Pasteur STs spanning at least six GCs, most commonly GC1. The impact of FPs on biofilm formation in A. baumannii was investigated using crystal violet assay. None of the zot-negative isolates formed strong biofilms, while six (66.6%) zot-positive isolates did. The biofilm indices of zot-positive isolates were significantly higher compared to zot-negative isolates. The potential enterotoxicity of the zot-positive strains was also assessed using in silico and experimental methods. The cytotoxic effect of cell-free supernatants (CFSs) on Caco-2 cells was measured by the MTT assay. Cells treated with CFSs from zot-positive strains exhibited significantly higher cytotoxicity than those treated with CFSs from zot-negative strains. Upon injecting the CFS of a zot-positive strain intraperitoneally into BALB/c mice, severe diarrhea was observed within 6 h. Histological examination of the intestinal tissue 24 h post-injection revealed significant changes. In conclusion, this study suggests that FPPs are widely disseminated in A. baumannii GCs and may enhance biofilm formation and enterotoxicity, potentially contributing to the pathogen’s virulence.