A chemical agent obtainable from a plant of the Euphorbiaceae family or a pharmaceutically compatible salt thereof which chemical agent is a macrocyclic diterpene selected from compounds of the ingenane family represented by the general formula:- wherein: R 24, R 25 and R 26 are independently selected from hydrogen, OH, R 27, R 28, F, Cl, Br, I, CN, OR 27, SR 27, NR 27 R 28, N(=O) 2, NR 27 OR 28, ONR 27 R 28, SOR 27, SO 2 R 27, SO 3 R 27, SONR 27 R 28, SO 2 NR 27 R 28, SO 3 NR 27 R 28, P(R 27) 3, P(=O)(R 27) 3, Si(R 27) 3, B(R 27) 2, (C=X)R 29 or X(C=X)R 29 where X is selected from sulfur, oxygen and nitrogen; R 27 and R 28 are each independently selected from C 1 -C 20 alkyl (branched or straight chained), C 1 -C 20 arylalkyl, C 3 -C 8 cycloalkyl, C 6 -C 14 aryl, C 1 -C 14 heteroaryl, C 1 -C 14 heterocycle, C 2 -C 10 alkenyl (branched or straight chained), C 2 -C 10 alkynyl (branched or straight chained), C 1 -C 10 heteroarylalkyl, C 1 -C 10 alkoxyalkyl, C 1 -C 10 haloalkyl, dihaloalkyl, trihaloalkyl, haloalkoxy, C 1 -C 10 alkyl which is substituted by CN, OR 27', SR 27 ', NR 27' R 28', N(=O) 2, NR27'OR 28', ONR 27' R 28', SOR 27', SO 2 R 27', SO 3 R 27, SONR 27' R 28', SO 2 NR 27' R 28', SO 3 NR 27' R 28', P(R 27') 3, P(=O)(R27 ') 3, Si(R 27') 3, B(R 27') 2; R 27 ' and R 28' are each independently selected from C 1 -C 20 alkyl (branched or straight chained), C 1 -C 20 arylalkyl, C 3 -C 8 cycloalkyl, C 6 -C 14 aryl, C 1 -C 14 heteroaryl, C 1 -C l4 heterocycle, C 2 -C 10 alkenyl (branched or straight chained), C 2 -C 10 alkynyl (branched or straight chained), C 1 -C 10 heteroarylalkyl, C 1 -C 10 alkoxyalkyl, C 1 -C 10 haloalkyl, dihaloalkyl, trihaloalkyl, haloalkoxy; R 29 is selected from R 27, R 28, CN, COR 27, CO 2 R 27, OR 27, SR 27, NR 27 R 28, N(=O) 2, NR 27 OR 28, ONR 27 R 28, SOR 27, SO 2 R 27, SO 3 R 27, SONR 27 R 28, SO 2 NR 27 R 28, SO 3 NR 27 R 28, P(R 27) 3) P(=O)(R 27) 3, Si(R 27) 3, B(R 27) 2 and which chemical agent or pharmaceutically compatible salt thereof is capable of modulating PKC activity, PKC-dependent gene expression or PKC enzyme turnover for use in the treatment or prophylaxis of infection by a pathogenic organism or a potentially pathogenic organism in a subject and wherein said chemical agent or pharmaceutically compatible salt thereof is for administration for a time and under conditions sufficient to ameliorate one or more symptoms associated with infection by said pathogenic organism or potentially pathogenic organism. R 24, R 25 and R 26 are independently selected from hydrogen, OH, R 27, R 28, F, Cl, Br, I, CN, OR 27, SR 27, NR 27 R 28, N(=O) 2, NR 27 OR 28, ONR 27 R 28, SOR 27, SO 2 R 27, SO 3 R 27, SONR 27 R 28, SO 2 NR 27 R 28, SO 3 NR 27 R 28, P(R 27) 3, P(=O)(R 27) 3, Si(R 27) 3, B(R 27) 2, (C=X)R 29 or X(C=X)R 29 where X is selected from sulfur, oxygen and nitrogen; R 27 and R 28 are each independently selected from C 1 -C 20 alkyl (branched or straight chained), C 1 -C 20 arylalkyl, C 3 -C 8 cycloalkyl, C 6 -C 14 aryl, C 1 -C 14 heteroaryl, C 1 -C 14 heterocycle, C 2 -C 10 alkenyl (branched or straight chained), C 2 -C 10 alkynyl (branched or straight chained), C 1 -C 10 heteroarylalkyl, C 1 -C 10 alkoxyalkyl, C 1 -C 10 haloalkyl, dihaloalkyl, trihaloalkyl, haloalkoxy, C 1 -C 10 alkyl which is substituted by CN, OR 27', SR 27 ', NR 27' R 28', N(=O) 2, NR27'OR 28', ONR 27' R 28', SOR 27', SO 2 R 27', SO 3 R 27, SONR 27' R 28', SO 2 NR 27' R 28', SO 3 NR 27' R 28', P(R 27') 3, P(=O)(R27 ') 3, Si(R 27') 3, B(R 27') 2; R 27 ' and R 28' are each independently selected from C 1 -C 20 alkyl (branched or straight chained), C 1 -C 20 arylalkyl, C 3 -C 8 cycloalkyl, C 6 -C 14 aryl, C 1 -C 14 heteroaryl, C 1 -C l4 heterocycle, C 2 -C 10 alkenyl (branched or straight chained), C 2 -C 10 alkynyl (branched or straight chained), C 1 -C 10 heteroarylalkyl, C 1 -C 10 alkoxyalkyl, C 1 -C 10 haloalkyl, dihaloalkyl, trihaloalkyl, haloalkoxy; R 29 is selected from R 27, R 28, CN, COR 27, CO 2 R 27, OR 27, SR 27, NR 27 R 28, N(=O) 2, NR 27 OR 28, ONR 27 R 28, SOR 27, SO 2 R 27, SO 3 R 27, SONR 27 R 28, SO 2 NR 27 R 28, SO 3 NR 27 R 28, P(R 27) 3) P(=O)(R 27) 3, Si(R 27) 3, B(R 27) 2 and which chemical agent or pharmaceutically compatible salt thereof is capable of modulating PKC activity, PKC-dependent gene expression or PKC enzyme turnover for use in the treatment or prophylaxis of infection by a pathogenic organism or a potentially pathogenic organism in a subject and wherein said chemical agent or pharmaceutically compatible salt thereof is for administration for a time and under conditions sufficient to ameliorate one or more symptoms associated with infection by said pathogenic organism or potentially pathogenic organism.