Characterization and susceptibility of streptococci and enterococci isolated from Nile tilapia (Oreochromis niloticus) showing septicaemia in aquaculture and wild sites in Egypt

Abstract

Background: The present investigation was an endeavor into the elucidation of the disease-causing pathogen of streptococcosis in Nile tilapia (Oreochromis niloticus) in Egypt affecting adult fish cultured and wild fish in the Nile river. Fish were obtained from commercial fishermen, collected as part of their routine fishing activities. The researchers observed the routine fishing process and selected fish for use in the study, at the point of purchase from the fisherman.

Results: Diseased fish showed exophthalmia with accumulation of purulent and haemorrhagic fluid around eyes, and ventral petechial haemorrhages. The Post mortem examination revealed, abdominal fat haemorrhage, pericarditis and enlargement of the liver, spleen and kidney. Gram-stained smears revealed the presence of Gram-positive cocci, β-hemolytic, oxidase and catalase negative. Analysis of the 16S rRNA gene confirmed that the 17 tilapia isolates studied were 6/17 Enterococcus faecalis, 2/17 Enterococcus gallinarum, 3/17 Streptococcus pluranimalium, 2/17 Aerococcus viridans, 1/17 isolate of each Streptococcus dysgalactiae, Streptococcus anginosus, Lactococcus garvieae and Granulicetella elegans/Leuconostoc mesenteroides cremoris. It should be noted that there was no mixed infection. Multiple resistance was observed and the most frequent antibiotic combination was penicillin, ampicillin, vancomycin, chloramphenicol, rifampicin, ofloxacin, clindamycin, erythromycin and tetracycline representing eight classes.

Conclusions: Consequently, we concluded that Streptococcus species are an emerging pathogen for Nile tilapia aquaculture in Egypt and to be considered as a new candidate in the warm water fish diseases in Egypt with special reference to L. garvieae, S. dysgalactiae in addition to L. mesenteroides cremoris which was not reported before from tilapia and taking into consideration their zoonotic implications for public health.

Keywords: Antibiotic resistance; L. Garvieae; L. Mesenteroides cremoris; Lancefield C; S. Dysgalactiae; Streptococcus species; Tilapia (Oreochromis spp.).

Fig. 1

a Body shape of Tilapia fish laterally compressed to oval. Lateral line interrupted with cycloid scales. Caudal fin has distinct vertical stripes and strong body vertical bands. Healthy transparently clear and spherical eye lenses. Normal glistening skin with no pathological lesions observed. b Tilapia fish showing externally eye redness, hemorrhage and ulcers on different parts of the body, hemorrhagic dorsal and tail fins, extensively detached scales and distended abdomen with signs of bleeding beneath the skin appearing as small dots the size of a pinprick or as a patch. c Shows normal appearance of Tilapia fish with normal liver, kidney, gall bladder and intestines with bright red gills. d Tilapia fish postmortum internal findings revealed tipical signs of septicemia in which severely congested gill, kidney, spleen, intestine and heart, dark gall bladder, in addition to hemorrhagic ascites, friable pale liver, muscle redness, and parts of the intestine were devoid of food

Fig. 2

Percentage resistance of the seven species of streptococci isolated from Nile tilapia (Oreochromis niloticus) to the 18 antibiotics tested