1) What is this test called and why?
CAMP test, after the people who were involved in developing it (Christie, Atkins & Munch-Peterson.)
2) Given that the horizontal streak is Staphylococcus aureus, what organism is likely to be represented by the “arrow” pointing towards it?
It is likely to be Streptococcus agalactiae (Group B streptococcus). There is synergistic haemolysis between the Streptococcus agalactiae and the Staphylococcus aureus producing an arrowhead effect. The bottom left hand streak is likely to be a negative control such as Streptococcus pyogenes.
3) Another bacteria can cause a similar phenomenen. What is it?
Listeria monocytogenes also causes a positive CAMP test, although it is usually slightly weaker. A Gram stain can easily discriminate between Group B streptococcus and Listeria monocytogenes.
4) How useful is this test likely to be in the future?
Maldi-TOF and other rapid ID methodologies will likely make the CAMP test obsolete in the future. It may be a method consigned to those antique textbooks!
See this ASM article for a little more detail on CAMP (and reverse CAMP) testing.