Towards discrimination of mammary pathogenic Escherichia coli (MPEC) in cattle based on possession of different iron acquisition systems

Most efforts to elucidate virulence mechanisms of mammary pathogenic Escherichia coli (MPEC), causative agent of bovine clinical mastitis, have been failed but some recent studies introduced iron acquisition systems as major role players in pathogenicity. Here, we investigated the different iron uptake systems genotypes and assessed how they relate to virulence potential of MPEC. In total, 217 E. coli isolates (MPEC= 157, fecal isolates= 60) were screened for the presence of nine genes related to iron acquisition (iroN, iutA, fecA, fyuA, sitA, irp2, iucD, chuA and tonB) and phylogenetic groups were also determined. Next, bacterial growth potential and survival in raw and UHT milk which are representative for crucial steps in mastitis development were evaluated. In addition, the mineral consumption of E. coli cultured in milk were measured. The results showed that MPEC strains considerably tend to possess fecA (93%, p= 0.000) and belong to phylogenetic group A (42%, p= 0.042). The fecA+ strains from both mastitis and fecal E. coli had a significant (p= 0.000) growth potential in raw and UHT milk. Interestingly, for the first time, it was shown that fecA+ isolates consumed less amounts of iron and other metal ions. Overall, it seems that the uptake systems related to fecA contributes to overcoming harsh conditions of milk and genetic lineages could also affect pathogenicity of MPEC. These findings could lead us to define MPEC with more clarity based on genotypes or growth potential in milk and possibly promote novel solutions to control mastitis more effectively in future. ImportanceMastitis is one of the most costly concerns in bovine medicine and the main cause of antibiotic use in dairy herds worldwide. As a rule of thumb, it was believed that extraintestinal pathogenic E. coli expands iron acquisition virulence arsenal to enhance pathogenic potential in the environments of the host outside the intestines. The present study indicated that the long believed idea of possession of diverse mineral acquisition systems and siderophores in all ExPEC groups could be a fairy tale. Along with recent studies, the present research showed that the fec operon could be the minimal necessary factor to overcome the harsh conditions of milk with limiting mineral concentrations. Obviously, the fecA+ isolates were fast-growing and consumed less amounts of minerals. It seems that the fec locus and its related metabolic pathways could be the potential targets for diagnostic, preventive, and therapeutic purposes.