G. Balasubramanian

Antibiotic resistance in bacteria isolated from Artemia nauplii and efficacy of formaldehyde to control bacterial load.

Abstract A study was carried out to determine the antibiotic resistance in bacteria isolated from Artemia nauplii and the efficiency of formaldehyde to control the bacteria associated with Artemia nauplii. The total aerobic heterotrophic bacteria of Artemia nauplii was determined on seawater nutrient agar and TCBS agar, and ranged from 3.8×10 3 to 8.1×10 3 and 9.4×10 2 to 4.3×10 3 colony forming units (CFU) per nauplius on seawater nutrient agar and TCBS agar plates, respectively. Among these bacteria, 336 isolates were tested for their resistance to five antibiotics. The minimum inhibiting concentrations of chloramphenicol, erythromycin, nitrofurazone, oxytetracycline, tetracycline, formaldehyde and sodium hypochlorite for 336 isolates were recorded. The LC50 values of oxytetracycline, formaldehyde and sodium hypochlorite for Artemia nauplii were determined as 540.5, 293.1 and 5.6 mg/l, respectively, after 24 h of exposure. The efficacy of formaldehyde was compared with that of antibiotics and formaldehyde was found to be very effective in controlling the bacteria of Artemia nauplii.

Studies on the immunomodulatory effect of extract of Cyanodon dactylon in shrimp, Penaeus monodon, and its efficacy to protect the shrimp from white spot syndrome virus (WSSV).

The present study investigates the protection of shrimp Penaeus monodon against white spot syndrome virus (WSSV) using antiviral plant extract derived from Cyanodon dactylon and the modulation of the shrimp non-specific immunity. To determine the antiviral activity, the shrimp were treated by both in vitro (intramuscular injection) and in vivo (orally with feed) methods at the concentration of 2mg per animal and 2% of the plant extract incorporated with commercially available artificial pellet feed, respectively. The antiviral activity of C. dactylon plant extract was confirmed by PCR, bioassay and Western blot analysis. In the present study, anti-WSSV activity of C. dactylon plant extract by in vivo and in vitro methods showed strong antiviral activity and the immunological parameters such as proPO, O(2)(-), NO, THC and clotting time were all significantly (P<0.05) higher in the WSSV-infected shrimp treated with plant extract when compared to control groups. These results strongly indicate that in vivo and in vitro administration of C. dactylon plant extract enhances immunity of the shrimp. Based on the present data and the advantages of plant extract available at low price, we believe that oral administration of C. dactylon plant extract along with the pellet feed is a potential prophylactic agent against WSSV infection of shrimp.

Artemia is not a vector for monodon baculovirus (MBV) transmission to Penaeus monodon.

Monodon baculovirus (MBV) of penaeid shrimp has been associated with high mortalities in hatchery-reared larval, post-larval and early juvenile stages of Penaeus monodon and is thought to have originated from Taiwan (Lightner, Redman & Bell 1983). MBV is pathogenic to several species of shrimp such as P. monodon Fabricius, P. penicillatus Alcock and Metapenaeus ensis De Haan (Chen, Chang, Kou & Lightner 1989). The principal clinical sign of MBV is the presence of single or multiple, generally spherical occlusion bodies in the hepatopancreas and midgut epithelial cells. In India, the prevalence of MBV and mortalities in hatcheries and farms associated with the virus has been reported (Ramasamy, Brennan & Jayakumar 1995; Karunasagar, Otta & Karunasagar 1998). The virus can be transmitted via horizontal transmission directly through the water column (Paynter, Vickers & Lester 1992), or through cannibalism and it is believed, but not proven, that transmission can also be vertical from brood stock to offspring. Infection can result in substantial economic loss due to poor growth and reduced survival of post-larvae of up to 90% at high densities. Furthermore, stress and overcrowding are predisposing factors that may increase the severity of MBV infection (Lightner et al. 1983). The MBV particles are rod shaped and replicate in the nucleus. They appear either free or within proteinaceous polyhedral occlusion bodies, and contain DNA. However, little is known about the mechanism of MBV production in the host cell (Lu, Tang, Kou & Chen 1995). Diagnosis of MBV depends upon the demonstration of MBV occlusion bodies in hypertrophied nuclei of the anterior midgut epithelium and hepatopancreatic cells by direct light microscopy or standard HE Muroga, Higashi & Keitiku 1989; Nicolas, Robic & Ansquer 1989) and viruses, such as infectious pancreatic necrosis virus (IPNV), Macrobrachium rosenbergii nodavirus and fish nodavirus (Mortensen, Evensen, Rodseth & Hjeltnes 1993; Skliris & Richards 1998; Sudhakaran, YogJournal of Fish Diseases 2008, 31, 631–636 doi:10.1111/j.1365-2761.2008.00926.x