Since July 2005, recurrent outbreaks of vibriosis have occurred in shrimp farms in northwestern Mexico. Moribund Litopenaeus vannamei associated with mass mortalities were lethargic and displayed red discoloration spots on their abdomen, and hence were called 'bright-reds' by farmers. Shrimp submitted for diagnosis were examined using wet tissue mounts, bacteriological assays and their respective minimum inhibitory concentration (MIC), and histology. A dominant yellow bacterial colony was isolated in thiosulphate citrate bile salts-sucrose (TCBS) agar and identified by molecular methods as Vibrio harveyi strain CAIM 1792. Pathogenicity of the V. harveyi strain was demonstrated in L. vannamei. The lowest MIC against Vibrio isolates from bright-red shrimp was obtained with enrofloxacine (3.01, SD = 5.96 µg ml
Vibriosis is one of the most widespread infectious diseases of cultured shrimp in Mexico; as a result, the Research Centre for Food and Development (CIAD, for the Spanish wording) offers a diagnostic service to the shrimp farmers where they bring samples of diseased shrimp as judged by themselves. Hemolymph (HL) and hepatopancreas (HP) of diseased Litopenaeus vannamei were analyzed from five regions of Northwestern Mexico (from 2001 to 2006) in tiosulphate citrate bile sacharose (TCBS) agar; a total of 5912 shrimp were examined. The results showed a mean vibrios density of 6.45 × 103, SD = 6.90 × 104 CFU/mL for HL and 1.40 × 105, SD = 3.20 × 105 CFU/g for HP (n = 5912). HL samples had 12% (SD = 26%) of green colonies (GCs) in TCBS, and 23% (SD = 34%) of GCs in HP samples. Of the total shrimp analyzed, 46% were not found to possess vibrios in HL, whereas 60% of the shrimp examined contained more than 105 CFU/g of HP. More than 60 and 40% of the shrimp did not have GC in HL and HP, respectively. The highest Pearson coefficient correlation was observed between vibrios HL and GCs in HL for 2006 (r = 0.611, n = 712, P < 0.001).
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