Background Bacterial virulence is a key factor determining the outcome of each bacterial infection and virulent bacteria are often associated to high-risk infections. Extraintestinal pathogenic Escherichia coli (ExPEC) is the most implicated bacterium in human bacterial infections and its virulence factors are classified into five categories: adhesins, toxins, iron capture systems, protectins and invasins. Furthermore, bacterial biofilms are the main cause of hospital-acquired infections like urinary catheter-associated infections, valve endocarditis, Otitis and cystic fibrosis.Results For the sixteen virulence genes sought by standard polymerase chain reaction (PCR), all the 78 ExPECs isolates carried at least four virulence genes. Following prevalences of virulence genes were reported: adhesins genes fimH (98.7%), mrkD (98.7%), papC (46.2%), afaC (9%), sfa / focDE (1.3%); iron acquisition systems genes entB (98.7%), fepA (98.7%), ybtS (93.6%), fyuA (91%), iucA (91%), iucB (91%), iutA (34.6), iroB (6.4%), iroN (6.4%) and toxins genes hlyA (10.3%), cnf (1 & 2) (10.3%). Seventy-five out of 78 isolates (96.2%) carried at least the combination of two adhesins genes and two iron capture systems genes whereas 8 out of 78 (10.3%) harbored the combination of (adhesins genes + iron acquisition systems genes + toxins genes). Among the 78 strains studied, one hospital-acquired strain isolated from urine harbored 15 virulence genes out of 16 sought. The evaluation of biofilm-formation capacity revealed that all (29/29) hospital-acquired isolates were biofilm producers with (6/29; 20.7%) strong biofilm producers, (15/29; 51.7%) moderate biofilm producers and (8/29; 27.6%) weak biofilm producers. Isolates carrying papC had greater biofilm formation capacity than those not carrying papC (p < 0.001).Conclusions Most of our strains had moderate biofilm-formation capacity and carried an average of 9 virulence genes out of 16 sought. These eight strains carrying a combination of genes (adhesins + iron acquisition systems genes + toxins genes) may be hypervirulent isolates. Additional studies may confirm this. The deepening of this kind of study on bacterial virulence and hospital bacterial biofilms could lead to the improvement of infections investigation, prevention and therapeutic protocols.

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