Determination of Florfenicol Dose Rate in Feed for Control of Mortality in Nile Tilapia Infected with Streptococcus iniae

Abstract

A dose titration study was conducted to determine the dosage of florfenicol (FFC) in feed to control Streptococcus iniae-associated mortality in Nile tilapia Oreochromis niloticus. Six tanks were assigned to each of five treatments: (1) not challenged with S. iniae and fed unmedicated feed; (2) challenged with S. iniae by injection and fed unmedicated feed; (3) challenged with S. iniae and given FFC at 5 mg/kg of body weight (bw) in medicated feed; (4) challenged with S. iniae and given 10 mg FFC/kg bw; and (5) challenged with S. iniae and given 15 mg FFC/kg bw. Treatment was initiated the day after inoculation, and feed was administered for 10 d. Cumulative mortality was 0% in the unchallenged, untreated group; 35.8 +/- 4.4% (mean +/- SE) in the challenged, unmedicated group; 19.2 +/- 2.7% in the 5-mg/kg treated group, 12.5 +/- 3.8% in the 10-mg/kg group, and 2.5 +/- 1.1% in the 15-mg/kg group. The cumulative mortality was significantly less in each challenged, FFC-treated group than in the challenged, unmedicated controls (5 mg/ kg: P = 0.0156; 10 mg/kg: P = 0.0007; 15 mg/kg: P < 0.0001). The efficacy of the 10- and 15-mg/kg FFC dosages was studied in a separate dose confirmation study. Fish in all tanks were injected with S. iniae. At 4 h postinoculation, 10 tanks were assigned to each of three feed treatments: (1) unmedicated feed; (2) 10 mg FFC/kg bw; and (3) 15 mg FFC/kg bw. Cumulative mortality was 20.5 +/- 2.0% in the challenged, unmedicated group; 11.0 +/- 2.1% in the 10-mg/kg group; and 5.5 +/- 2.4% in the 15-mg/kg group. Mortality was significantly less in the medicated groups than in the challenged, unmedicated control group (10 mg/kg: P = 0.0270; 15 mg/kg: P = 0.0007). Fish in both studies were necropsied, cultured for bacteria, and examined for gross lesions. The minimum inhibitory concentration of FFC against S. iniae in both studies ranged from 0.5 to 1.0 microg/mL. Florfenicol was palatable, safe, and efficacious for control of Nile tilapia mortality due to S. iniae infection.

Efficacy of florfenicol for control of mortality associated with Francisella noatunensis subsp. orientalis in Nile tilapia, Oreochromis niloticus (L.)

“…Commercial tilapia feed was ground and repelleted as previously described (Gaunt et al . ,b). For preparation of medicated feeds, FFC 50% premix (Aquaflor 50% Type A Medicated Article; Merck Animal Health) was mixed with the dry ground feed and then pelleted.…”

“…), Aeromonas salmonicida (Samuelsen, Hjeltnes & Glette ), Streptococcus iniae (Darwish ; Gaunt et al . ), Flavobacterium columnare (Gaunt, Gao & Endris ) and Edwardsiella ictaluri (Gaunt et al . ).…”

“…In the United States, FFC in salmonids and catfish is labelled for use at 10 mg kg −1 days −1 for 10 days; however, different dose rates [5, 15 or 20 mg FFC kg −1 body weight (bw) per days for 10 days] have been explored to treat several bacterial infections in tilapia (Gaunt et al . ,b; Soto et al . ).…”

“…Florfenicol (FFC) is a fluorinated derivative of thiamphenicol that blocks the peptidyltransferase at the 50S subunit of the 70S ribosome and acts against a wide variety of both Gram-positive and Gram-negative bacteria (Cannon, Jarford & Davies 1990). As a medicated feed, FFC has been used to treat a wide variety of bacterial diseases in various warm-and cold-water cultured fish species, such as Fno (Soto, Endris & Hawke 2010b), Vibrio anguillarum (Samuelsen & Bergh 2004;Seljestokken et al 2006), Aeromonas salmonicida (Samuelsen, Hjeltnes & Glette 1998), Streptococcus iniae (Darwish 2007;Gaunt et al 2010b), Flavobacterium columnare (Gaunt, Gao & Endris 2010a) and Edwardsiella ictaluri (Gaunt et al 2003). In the United States, FFC in salmonids and catfish is labelled for use at 10 mg kg À1 days À1 for 10 days; however, different dose rates [5, 15 or 20 mg FFC kg À1 body weight (bw) per days for 10 days] have been explored to treat several bacterial infections in tilapia (Gaunt et al 2010a,b;Soto et al 2010b).…”

Streptococcus agalactiae isolates from cultured fishes in Malaysia manifesting low resistance pattern towards selected antibiotics

“…Several studies revealed the efficacy of florfenicol in controlling S. iniae infection in Nile tilapia, O. niloticus (L.), blue tilapia and sunshine bass (Darwish , ; Gaunt et al . ). However, a study reported that in fish farming industries, the widespread use of antibiotics for treating bacterial diseases has been associated with the development of antibiotic resistance, such as in Aeromonas hydrophila , A. salmonicida, Edwardsiella tarda, E. ictaluri , Vibrio anguillarum, V. salmonicida, Pasteurella piscicida and Yersinia ruckeri (Serrano ).…”