Analysis of the protein profiles of the antibiotic-resistant Salmonella typhimurium definitive phage type (dt) 104

The emergent Salmonella typhimurium definitive phage type (DT) 104 is of particular global concern due to its frequent isolation and multiple antibiotic resistances. There is thus a need to know the kind of proteins expressed by S. typhimurium DT104 so as to provide a basis for developing an intervention. This study examined the protein profiles of a few isolates of S. typhimurium DT104 and a non-DT104 strain S. typhimurium L1388 (ST). Crude SDS-soluble whole cell and outer membrane protein (OMP) extracts revealed similar protein profiles for both phage types. A single major protein band (28.4 kDa) was observed in periplasmic fractions from both phage types. However, proteins released into growth medium was variable; one of the DT104 isolates had common proteins with the non-DT104 strain ST. Similar SDS-soluble whole cell protein profiles were observed for both phage types grown in a low-iron Medium A at 37 degree C; but a 38.5 kDa protein (observed in TSB-grown cells) was observed only in the temperature-tolerant DT104 isolate. The protein contents of cell-free ultracentrifuge supernatants of sonically disrupted cells of each of the DT104 isolates were significantly (P < 0.05) more than that from ST L1388, but the latter expressed a 51-kDa protein absent in the supernatants of all DT104 isolates. The higher protein content of DT104s provides possible indication of increased production of protein-like metabolites. Although the N-terminal sequence of the first twenty amino acids of the 51-kDa protein (Ala-Gln-Val-Ile-Asn-Thr-Asn-Ser-Leu-Ser-Leu-Leu- Thr-Gln-Trp-Ala-Ala-Ala-Ala-Ala) showed 14-amino acid overlap and resemblance with the flagillin, FLIC, only fourteen of its 104 trypsin digests were homologous with those of FLIC. Further work is being done to characterize this protein and to investigate its potential for use as vaccine target through antigenicity tests.