INVASION OF CACO-2 CELLS BY SALMONELLA-TYPHIMURIUM (COPENHAGEN) ISOLATES FROM HEALTHY AND SICK CHICKENS

In a previous study, Salmonella isolates of sick birds were distinguis hed from those of apparently healthy birds by their high degree of inv asion of tissue culture cells. In this study, a single pair of Salmone lla isolates was examined to determine the source of this observed dif ference in invasion. When isolates were allowed to invade Caco-2 cells for 8 hours, the isolate from the sick bird (S) appeared to invade in greater numbers than did the isolate from the healthy bird (H). Howev er, when invasion was distinguished from Intracellular growth/survival , it was found that H invaded in greater numbers than S, but once insi de the cell, H declined in number, and S increased. Inhibition of RNA, protein, and DNA syntheses lessened the degree to which both invaded. The presence of mannose inhibited invasion by S but did not appear to inhibit invasion by H. Trypsin treatment of monolayers affected invas ion of S and H, whereas neuraminidase treatment did not. There was no significant difference noted between S and H in ability to adhere to f ixed monolayers. Therefore, the two isolates tested differ in their me chanisms of entry into Caco-2 cells, the efficiency with which they in vade, and their ability to survive within Caco-2 cells.