Rickettsial and mollicute infections in hepatopancreatic cells of cultured Pacific white shrimp (Penaeus vannamei)

Abstract

Infections by multiple species of bacteria occurred in hepatopancreatic epithelial cells of cultured Pacific white shrimp (Penaeus vannamei). Grossly, hepatopancreases of moribund shrimp were pale white. Light microscopically, hepatopancreatic tubules appeared atrophied and were associated with granulomas. Examination by scanning and transmission electron microscopy revealed heavy cytoplasmic infections by three forms of microorganisms: (1) a rickettsia-like bacterium, (2) a helical form of a mollicute-like bacterium, and (3) a filamentous mollicute-like bacterium. The rod-shaped rickettsia (900 nm long by 300 nm wide) appeared to be free in the cytoplasm and had both a plasma membrane and a cell wall. Neither form of mollicute possessed a cell wall. The helical mollicute was blunt at its wide end (about 260 nm in diameter) where it contained electron-lucent bodies. Helical turns along its tapered axis resembled those of a spiroplasma (the only helical form of mycoplasma in the class Mollicutes) or a spirochete. The helical bacterium did not possess periplasmic flagella characteristic of spirochetes, which lends support to its being a type of spiroplasma. The filamentous mollicute consisted of masses of short, branched filaments 60 nm wide with intermittent spherical dilations and terminal blebs on the branches. The presumed mollicutes have not been reported previously in crustaceans. Each bacterium, or concurrent infections of the bacteria, are pathogenic to cultured shrimp, could impact culture operations and thus deserve more study.

Molecular detection methods developed for a systemic rickettsia-like bacterium (RLB) in Penaeus monodon (Decapoda: Crustacea)

“…To survive and reproduce, the rickettsia organism must enter the eucaryotic host cell, multiply within the cell, exit and reestablish this cycle in another cell (Winkler 1990). Rickettsia-like microorganisms infect a wide range of aquatic crustaceans including amphipods, crabs, freshwater crayfish and prawns (Federici et al 1974, Harshbarger et al 1977, Bonami & Pappalardo 1980, Larrson 1982, Johnson 1984, Brock et al 1986, Anderson et al 1987, Krol et al 1991, Frelier et al 1992, Fryer & Lan-nan 1994, Bower et al 1996, Jimenez & Romero 1997, Edgerton & Prior 1999, Wang & Gu 2002.…”

Antibacterial effect of biosynthesized silver nanoparticles in Pacific white shrimp Litopenaeus vannamei (Boone) infected with necrotizing hepatopancreatitis bacterium (NHP B)

“…The necrotizing hepatopancreatitis bacterium (NHP-B), a Gram-negative Rickettsia-like intracellular bacterium, has emerged as one of the major diseases impacting the shrimp farming industry (Krol et al, 1991). During the acute phase of the disease, the shrimp hepatopancreas is atrophied while during the chronic phase the hepatopancreas is melanized, the tubules are necrotized, among many other anomalies.…”

Bioinformatic analysis of the flagellar system of the rickettsia-like alphaproteobacteria Candidatus Hepatobacter penaei

“…Esta se ha identificado en el orden de las rickettsiales debido a que presenta características endosimbióticas al desarrollarse y multiplicarse dentro de las células epiteliales del hepatopáncreas en varias especies de camarones peneidos: Farfantepenaeus aztecus, F. californiensis, Litopenaeus vannamei, L. setiferus y L. stylirostris (Krol et al 1991, Frelier et al 1992, Lightner et al 1992, Lightner 1996. Es así, que estudios morfológicos han revelado su presencia en el citoplasma y en el epitelio tubular del hepatopáncreas de camarones peneidos (Frelier et al 1992, Lightner et al 1992.…”

“…La bacteria Candidatus Hepatobacter penaei presenta forma de cocobacilo, su tamaño oscila alrededor de 0,32 µm de diámetro mostrando una membrana trilaminar, sin flagelos; tiene una sección transversal constricta en la parte central, indicando replicación por fisión binaria (Krol et al 1991, Frelier et al 1992. Sin embargo, estudios posteriores a estos describen una bacteria helicoidal con dimensiones de 0,59 -1,18 µm de longitud y 0,36 µm de ancho (Loy et al 1996), posee una membrana trilaminar con 8 flagelos en el ápice basal 1 o 2 en la cresta de la hélice (Lightner et al 1992), considerándose dos diferentes etapas de vida.…”

“…Sin embargo, estudios posteriores a estos describen una bacteria helicoidal con dimensiones de 0,59 -1,18 µm de longitud y 0,36 µm de ancho (Loy et al 1996), posee una membrana trilaminar con 8 flagelos en el ápice basal 1 o 2 en la cresta de la hélice (Lightner et al 1992), considerándose dos diferentes etapas de vida. Krol et al (1991). También describen una tercera forma de vida, observada ocasionalmente en el hepatopáncreas infectado; esta forma presenta la morfología de las dos variantes, lo que sugiere el desarrollo de la forma replicativa de cocobacilo a la forma elíptica (Lightner et al 1992).…”