Evaluation of the Synergistic Haemolysis (CAMP-like) test in the Identification of Motile, Mesophilic Aeromonas Species

Abstract

Usefulness of the synergistic haemolysis (CAMP-like) test in the identification of Aeromonas hydrophila, Aeromonas sobria, and Aeromonas caviae was evaluated, using beta-toxin producing Staphylococcus aureus ATCC 25923 and alpha-toxin producing Clostridium perfringens ATCC 13124 as sphingomyelinase producing indicator strains. The tests were done on Columbia Blood Agar Base supplemented with 5% sheep blood (CBA; Difco Laboratories, Detroit, MI, USA). When cultured aerobically, 77% of A. hydrophila isolates, 75% of A. sobria isolates, and 23% of A. caviae isolates elicited synergistic haemolysis of sheep erythrocytes with the beta-toxin producing strain of S. aureus. Anaerobically, using the same indicator strain, synergistic haemolysis was given by 91%, 51% and 82% of A. hydrophila, A. sobria, and A. caviae, respectively. When alpha-toxin producing C. perfringens was used in the test instead of beta-toxin producing S. aureus, 100%, 86%, and 93% of A. hydrophila, A. sobria, and A. caviae isolates, respectively, showed synergistic haemolysis of sheep erythrocytes. Due to the high number of the tested isolates of A. hydrophila, A. sobria, and A. caviae giving a positive synergistic haemolysis reaction in both atmospheric conditions of culture, this test cannot be used to identify any of the three Aeromonas spp. The use of alpha-toxin producing C. perfringens did not improve discriminatory power of the test. Because the nature of the product of Aeromonas spp. responsible for the lytic phenomenon is not known, the use of Aeromonas factor and synergistic haemolysis terms was proposed rather than CAMP (reaction, test) or CAMP (-like) factor.