Option Explicit
Sub test()
Dim t As String, x As Range
t = Range("P18").Value
With ActiveSheet.Columns(1)
Set x = .Find("PRISSAL", , xlValues, xlPart, , , False)
If Not x Is Nothing Then
Do
x.Replace "PRISSAL", t
x.Characters(InStr(x, t), Len(t)).Font.Bold = True
Set x = .FindNext
Loop While Not x Is Nothing
End If
End With
End Sub