Tetrahymena: An Alternative Model Host for Evaluating Virulence of Aeromonas Strains

Abstract

An easier assessment model would be helpful for high-throughput screening of Aeromonas virulence. The previous study indicated the potential of Tetrahymena as a permissive model to examine virulence of Aeromonas hydrophila. Here our aim was to assess virulence of Aeromonas spp. using two model hosts, a zebrafish assay and Tetrahymena-Aeromonas co-culture, and to examine whether data from the Tetrahymena thermophila model reflects infections in the well-established animal model. First, virulence of 39 Aeromonas strains was assessed by determining the 50% lethal dose (LD50) in zebrafish. LD50 values ranging from 1.3×102 to 3.0×107 indicated that these strains represent a high to moderate degree of virulence and could be useful to assess virulence in the Tetrahymena model. In Tetrahymena-Aeromonas co-culture, we evaluated the virulence of Aeromonas by detecting relative survival of Aeromonas and Tetrahymena. An Aeromonas isolate was considered virulent when its relative survival was greater than 60%, while the Aeromonas isolate was considered avirulent if its relative survival was below 40%. When relative survival of T. thermophila was lower than 40% after co-culture with an Aeromonas isolate, the bacterial strain was regarded as virulent. In contrast, the strain was classified as avirulent if relative survival of T. thermophila was greater than 50%. Encouragingly, data from the 39 Aeromonas strains showed good correlation in zebrafish and Tetrahymena-Aeromonas co-culture models. The results provide sufficient data to demonstrate that Tetrahymena can be a comparable alternative to zebrafish for determining the virulence of Aeromonas isolates.

Identification of Aeromonas hydrophila Genes Preferentially Expressed after Phagocytosis by Tetrahymena and Involvement of Methionine Sulfoxide Reductases

“…Seven virulent A. hydrophila strains (NJ-35, XY-16, NJ-34, CS-43, NJ-1, XX-14, and NJ-37), and five avirulent A. hydrophila strains (NJ-28, JH-19, NJ-3, CS-34, and JH-17; Pang et al, 2012), were used in this study (Table 1). The nucleotide sequence of the complete genome of NJ-35 has been deposited in GenBank (accession number CP006870).…”

“…Then, 5000:1 co-cultures of A. hydrophila and T. thermophila were used to investigate their interaction (Pang et al, 2012). Before co-culture, T. thermophila SB210 with an initial inoculum of 10 3 cells/mL was grown in 50 mL of SPP medium at 28°C for 36 h, when the cultures entered stationary phase.…”

“…This time point was selected on the basis of our previous study, which demonstrated that virulent A. hydrophila strains survived better than avirulent A. hydrophila strains when co-cultured with T. thermophila , particularly after co-culture for 12 h (Pang et al, 2012). In considering the MOI, our preliminary dose-response studies showed that, the number of A. hydrophila which was taken up by an average protis nearly reached saturation at the MOI of 5000 (data not shown).…”

“…We have previously demonstrated that the hypervirulence phenotype of A. hydrophila can survive efficiently within T. thermophila (Li et al, 2011; Pang et al, 2012). All of this evidence indicates an important link between Aeromonas and grazing protozoa.…”

Protective efficacy of recombinant hemolysin co-regulated protein (Hcp) of Aeromonas hydrophila in common carp (Cyprinus carpio)

“…Hcp secretion was found to be strongly induced by 30 low temperature in A. hydrophila. Immunoblot analysis demonstrated that Hcp is 31 conserved among A. hydrophila strains of different origins. The vaccination with 32 recombinant Hcp resulted in an increased survival (46.67%) in common carp during a 33 10-day challenge time compared to non-vaccinated fish (7.14%).…”