Isolation and characterization of Mycoplasmas from some moribund Egyptian fishes

Mycoplasma is associated with fatal diseases in human, animals, and fish. Mycoplasma of aquatic origin has not been thoroughly studied. The current study has shed the light on isolation and characterization of unique piscine Mycoplasma isolates retrieved from diverse geographical locations across the Egyptian state. Mycoplasma spp. was isolated using specific culture media. Mycoplasma was identified using the morphochemical tests and then confirmed molecularly by PCR of the 16S rRNA gene. The results indicated that the incidence of Mycoplasma from Cyprinus carpio, Oreochromis niloticus, Aulopiformes synodontida, and Clarias gariepinus were 33.33%, 16.36%, 8.108%, and 6.45%, respectively, while Mugil cephalus were negative for Mycoplasma isolation. Mycoplasma was detected only from gills and swim bladder of affected fish. Biochemically, the isolated Mycoplasmas were grouped into two clusters. Mycoplasma cluster 1 (35 isolates) and Mycolplasma cluster 2 (7 isolates). Mycoplasma cluster 1 was positive for tetrazolium reduction while Mycoplasma cluster 2 was negative. The phylogenetic tree of partial sequences of 16S rRNA showed that both clusters were grouped in one branch and separated from other Mycoplasma spp., suggesting that both clusters are belonging to one species. Interestingly, all fish Mycoplasma isolates were PCR negative for both Mycoplasma mobile and Mycoplasma monodon using specific species primers. This result confirmed that these two clusters belonged to unspecified Mycoplasma species, for which the temporary names Mycoplasma cluster 1 and Mycoplasma cluster 2 were designated. Pathogenicity trials of both Mycoplasmas clusters revealed that all inoculated Nile tilapias were susceptible to the unspecified Mycoplasmas.