Grampositive bacteria

Relatively few Gram-positive bacterial diseases have been described from bivalves; however, Nocardia sp. is a Gram-positive, acid-fast actinomycete,

*9

Fig. 20.10. (and Opposite) (a) Chlamydia-like inclusion bodies (arrows) in the digestive tubules of Crassostrea virginica. H & E, x 160. (b) Different developmental stages of a filamentous Chlamydia-like infection of the digestive tubules of Crassostrea virginica. Note rupture of the basal membrane, rather than the apical membrane, by one colony. H & E, x 630. (c) Heavy tubule epithelium infection by Rickettsia-like organisms (dense spheres) in Crassostrea virginica. Note massive hypertrophy of some infected cells (arrows). H & E, x 160. (d) Rickettsia-like colony in a tubule epithelial cell of the mussel Mytilus edulis. H & E, x 250.

Rickettsia Like Organism

Table 20.2. Summary of significant bacterial infections in shellfish.

Group

Common name or disease name

Host species

Rickettsia- like organisms

Placopecten magellanicus

Rickettsia- like organism (RLO)

Nuclear inclusion X (NIX)

Stained prawn disease

Pecten maximus

Siiiqua patuia

Pan da ius piatyceros

Penaeus +

merguiensis, Penaeus marginatus Penaeus ?+

monodon

Ol 00

Tissue

Shape

Reference

Gills

Gills

Gills

Fixed macrophages of the digestive gland Hepato-pancreas

Midgut, hepato-pancreas and caeaca

(microcolonies)

19.0-33.0 (microcolonies)

Ovoid

Globular (type I) Rod (type II) Ovoid n/a

Ovoid

Spherical

Gulka et al., 1983; Gulka and Chang, 1984a,b; Morrison and Shum, 1983 LeGall et al., 1988, 1991

Eiston, 1986a; Olson and Pierce, 1988 Bower et al., 1993

Lightner et al., 1992a

Anderson et al., 1987; Lightner et al., 1992a

Texas pond Penaeus +

mortality vannamei syndrome (TPMS), Texas necrotizing hepatopancreatitis (TNHP)

Carcinus +

mediterraneus (exptl)

Paralithodes platypus

Chlamydia-tike organisms

Rickettsiella

Cherax quadricarcinatus

Argopecten irradians

Mycoplasma-\\ke organisms (MLO)

Actinomycetales

Intracellular bacterium disease

Nocardia sp. Pacific oyster nocardiosis (PON)

Patinopecten yessoensis

Crassostrea gigas

Hepato- -ve 0.25x0.9 Pleomorphic Krol eta/., 1991;

pancreas ('primary form') ovoid Lightner et at.,

0.25x2.0-3.5 ('primary form') 1992c ('helical form')

Connective tissue of hepatopancreas, gill, gonads and intestine Hepatopancreas

Systemic

Digestive gland

Haemocytes in abscess lesions

Haemolymph, mantle, gill, adductor and cardiac muscle

(cells)

(microcolonies)

(cells)

(microcolonies)

(cells)

Ovoid

Pappalardo and Bonami, 1980

Johnson, 1984

Ketterer et ai, 1992

Leibovitz, 1989

(reticulate bodies) (reticulate bodies)

(intermediate bodies)

(elementary bodies)

Elongate (intermediate bodies) Ovoid

(elementary bodies)

Ovoid

Filamentous branching and beaded

Bower and Meyer, 1991

Imai etal., 1968; Eiston et al„ 1987; Friedman and Hedrick, 1991

Continued over

Table 20.2. Continued.

Common name or Host Dis.

Group disease name species sig.

Bacterial abscess disease

Streptococcaceae

Gaffkemia, red-tail disease, Aerococcus vir id ans var. homari Streptococcus faecalis var. liquefaciens

Homarus +

americanus and Homarus gammarus

C. mediterraneus +

Vibrionaceae

Penaeid bacterial septicaemia, penaeid vibriosis, red-leg disease, 'Sein dun', luminescent vibriosis, sindroma gaviota

Penaeid shrimps and

Macrobrachium rosenbergíí

Tissue

Shape

Reference

Adductor muscle abscesses and focal systemic aggregations Haemolymph and systemic n/a

Pleomorphic

Coccoid tetrads

Getchell, 1991; McGladdery, 1990

Stewart, 1980 (comprehensive research review)

Interstitial cells of the hepatopancreas

Hepatopancreas, lymphoid organ, appendages and oral cavity

(from Fig. 5, Pappalardo and Boemare, 1982)

Coccoid, diploccocic

Straight or curved rods

Pappalardo and Boemare, 1982

Anderson et al., 1988; Lightner et al., 1992a; Vera et al., 1992

Bacillary necrosis, larval necrosis, larval vibriosis Vibrio sp., Vibrio anguiiiarum, Vibrio aiginoiyticus and Vibrio tubiashi Vibrio P1 Brown-ring disease (BRD) Vibrio of T. phiiippinarum Juvenile oyster disease*

Most cultured bivalve and abalone larvae, juvenile lobsters

Tapes phiiippinarum phiiippinarum Crassostrea virginica

(larvae)

Bacterial ulceration V. aiginoiyticus, Vibrio damsela, Vibrio parahaemolyticus,

Aeromonas cavia

(+ Pseudomonas Stutzer!)

Octopus joubini, Octopus briareus

Systemic, especially surface ciliated epithelia, pericardial fluids and haemolymph

Periostracum

Soft tissues Mantle epithelium and shell

Muscle

Curved rod

Tubiash eta/., 1973; Elston and Lockwood, 1983; Hada et al., 1984; Rosemark and Fisher, 1988; Elston, 1989; Bower et al., 1994a

Straight rods Maes and

Paillard, 1990

? Vibrio- ? like agent proposed

As for other vibrios

Nicolas et al., 1992b Brice[j eta/., 1992

Hanlon eta/., 1984

Continued over

Table 20.2. Continued.

Group

Common name or disease name

Host species

Dis. sig-

Tissue

Gram -/+ve

Size (nm)

Shape

Reference

Vibrio

Octopus

+

Limb muscle

-ve

As for other

-

Han Ion and

carchariae

bimacuioides and

vibrios

Forsythe, 1990

Octopus maya

Vibrio harveyi,

Sepioteuthis

+

Eye

-ve

As for other

-

Han Ion and

V. carchariae

iessoniana

vibrios

Forsythe, 1990

Vibrio

Sepia

+

Dorsal

-ve

As for other

-

Han Ion and

spiendidus,

officinalis

blood-vessels

vibrios

Forsythe, 1990

Vibrio peiagius

(+ P. stutzeri)

Cytophagales

Hinge

Most cultured

+

Hinge

-ve

2.5->200

Rod

Dungan and Elston,

ligament

bivalve larvae

(also

ligament

1988; Dungan et

disease

enhances

ai., 1989; Elston,

Cytophaga- like

secondary

1989

bacteria (CLB)

infections)

Neisseriaceae and

Ulcerative

Octopus

?/+

Epidermis

-ve

0.9-1.6 x

Rod

Stoskopf etai., 1987

Pseudomonadaceae

disease

dofieini

1.5-2.5

(A. anitratus)

Acinetobacter

(A. anitratus)

anitratus and

Pseudomonas

Micrococcaceae

Ulcerative eye

Loiigo forbesi

+

Eye

+ve

1.0-2.0

Cocci

Han Ion and

disease

Forsythe, 1990

Micrococcus sp.

Cytophagales

Bacterial

Most

+

Surfaces of

-ve

?

Mainly

Fisher and

fouling,

crustaceans

(unhealthy

gills, eggs and

filamentous

Wickham, 1976;

filamentous

hosts)

appendages

Fisher, 1988b;

bacteria,

Lightner, 1988b;

epibionts,

Brock and

Fiexibacter spp.

Lightner, 1990

Dis. sig., disease significance; ¡cos., icosahedral.

'Aetiology under investigation. Lewis eta/. (1996) indicate possible protistan involvement.

Octopus Haemocyte

Fig. 20.11. (a) Encapsulated lesion of inflammatory haemocytes in the connective tissue of the digestive gland of Patinopecten yessoensis associated with infection by an intracellular bacterium. Photograph courtesy of S.M. Bower. H & E, scale bar = 25 mm. (b) Electron micrograph of a haemocyte of Patinopecten yessoensis containing bacteria-like organisms (arrows). Infected haemocytes occur on the periphery of encapsulated inflammatory lesions (Fig. 20.11a). Photograph courtesy of S.M. Bower. TEM, scale bar = 1 mm.

Fig. 20.11. (a) Encapsulated lesion of inflammatory haemocytes in the connective tissue of the digestive gland of Patinopecten yessoensis associated with infection by an intracellular bacterium. Photograph courtesy of S.M. Bower. H & E, scale bar = 25 mm. (b) Electron micrograph of a haemocyte of Patinopecten yessoensis containing bacteria-like organisms (arrows). Infected haemocytes occur on the periphery of encapsulated inflammatory lesions (Fig. 20.11a). Photograph courtesy of S.M. Bower. TEM, scale bar = 1 mm.

responsible for the disease Pacific oyster nocardiosis (PON) infecting C. gigas along the west coast of the USA, British Columbia and Japan (Imai et al., 1968; Elston et al., 1987; Friedman et al., 1988, 1991; Friedman and Hedrick, 1991). Mortalities of up to 35% occur in late summer and autumn. Yellow-green pustules, up to 1 cm in diameter, in the mantle, gills, adductor and cardiac muscle are caused by intense haemocyte infiltration around the branching mycelial colonies of Nocardia (which distinguishes them from other basophilic, periodic acid-Schiff (PAS)-positive, bacteria) (Friedman et al., 1991) (Fig. 20.12).

Gram-positive bacteria have also been isolated from abscess lesions in giant sea scallops (P. magellanicus) from Atlantic USA and Canada (Sherburne and Bean, 1986; Getchell, 1991; McGladdery et al., 1993). The lesions are visible as 'brown spots', up to 3 mm in diameter, on the adductor muscle, which render the meat unmarketable. 'Bacterial abscess disease' (or 'brown-spot disease') has a patchy distribution in lower-salinity, estuarine environments. Prevalences are generally less than 4%, although some foci may reach 25%. Larger scallops appear to be most severely affected, but there is no direct correlation to shell-fouling or population density. Histologically, the disease is similar to intracellular bacterium disease of Japanese scallops (Mycoplasma disease described above), with systemic focal lesions containing Gram-positive, pleomorphic, bacteria (Fig. 20.13). Attempts to culture and identify the 'brown-spot disease' bacteria have been unsuccessful to date (Getchell, 1991).

Fig. 20.12. Aggregations of Gram-positive actinomycete Nocardia bacteria in the connective tissue of Crassostrea gigas (arrows). Note infiltration of haemocytes around the bacteria. H & E, x 160.
Fig. 20.13. Bacterial abscess lesion in the adductor muscle of Placopecten magellanicus. Note focal aggregation of necrotic haemocytes and myodegeneration. H & E, x 25.

Gram-positive bacteria (Micrococcus sp.) have been observed in abscess lesions from Canada and the USA (Getchell, 1991), but Gram-negative species (Vibrio, Pseudomonas and Aeromonas) have also been cultured. All identified genera are ubiquitous, mainly aerobic, bacteria, while systemic infections suggest an anaerobe involvement. This may indicate a non-pathogen-specific aetiology or difficulty in preventing contamination by surface or secondary histolytic bacteria.

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