23
as the sole reason for diagnosing botulism, in view of its possible widespread presence in this habitat (see Trust et al. 1979 ). Alternatively, diagnosis may be achieved
using bioassays to detect the presence of the neurotoxin in serum, which are especially useful if culturing is not achieved (Gaunt et al. 2007 ; Khoo et al 2011 ).
Characteristics of the Pathogen
Descriptions of fi sh pathogenic clostridia have tended towards extreme brevity.
However, it is clear that the outbreaks of botulism in fi sh have been caused by predominantly Cl. botulinum type E.
Diagnosis
Diagnosis of botulism has been accomplished by isolation of Cl. botulinum from
diseased tissues, and more importantly, by demonstrating the presence of circulating toxin (particularly to Cl. botulinum type E) in the blood of moribund fi sh (Cann
and Taylor 1982 ).
Box 2.1: Clostridium botulinum
Cultures comprise anaerobic, chemo-organotrophic, Gram-positive, nonacid- fast rods, of 3.4–7.5 × 0.3–0.7 μm in size, which are motile by means of
peritrichous fl agella. It is important to note that care should be taken in interpreting Gram-stained smears, because cells may appear Gram-negative with
age. Oval, sub-terminally positioned endospores are formed, which have
characteristics appendages and exosporia. The cell wall contains diaminopimelic acid. Surface colonies are 1–3 mm in diameter, slightly irregular with
lobate margins and raised centres, and translucent to semi-opaque with a matt
appearance. Poor to moderate growth occurs in cooked meat broth, but abundant growth occurs in broth containing fermentable carbohydrates at the optimum temperature of 25–30 °C. Lecithinase, lipase, neurotoxins and
haemolysins, but not catalase, caseinase, H 2 S, indole or urease, are produced.
Gelatinase is not usually produced by Cl. botulinum type E. Nitrates are not
reduced, nor is the Voges Proskauer reaction positive. Some carbohydrates,
such as fructose and glucose, but not aesculin, cellobiose, dulcitol, glycogen,
inulin, mannitol, melezitose, melibiose, raffi nose, rhamnose, salicin, sorbose,
starch, sucrose and xylose, are fermented to acetic and butyric acids. The
G + C ratio of the DNA is in the range of 26–28 moles % (Cato et al. 1986 ).
Clostridiaceae Representative
as the sole reason for diagnosing botulism, in view of its possible widespread presence in this habitat (see Trust et al. 1979 ). Alternatively, diagnosis may be achieved
using bioassays to detect the presence of the neurotoxin in serum, which are especially useful if culturing is not achieved (Gaunt et al. 2007 ; Khoo et al 2011 ).
Characteristics of the Pathogen
Descriptions of fi sh pathogenic clostridia have tended towards extreme brevity.
However, it is clear that the outbreaks of botulism in fi sh have been caused by predominantly Cl. botulinum type E.
Diagnosis
Diagnosis of botulism has been accomplished by isolation of Cl. botulinum from
diseased tissues, and more importantly, by demonstrating the presence of circulating toxin (particularly to Cl. botulinum type E) in the blood of moribund fi sh (Cann
and Taylor 1982 ).
Box 2.1: Clostridium botulinum
Cultures comprise anaerobic, chemo-organotrophic, Gram-positive, nonacid- fast rods, of 3.4–7.5 × 0.3–0.7 μm in size, which are motile by means of
peritrichous fl agella. It is important to note that care should be taken in interpreting Gram-stained smears, because cells may appear Gram-negative with
age. Oval, sub-terminally positioned endospores are formed, which have
characteristics appendages and exosporia. The cell wall contains diaminopimelic acid. Surface colonies are 1–3 mm in diameter, slightly irregular with
lobate margins and raised centres, and translucent to semi-opaque with a matt
appearance. Poor to moderate growth occurs in cooked meat broth, but abundant growth occurs in broth containing fermentable carbohydrates at the optimum temperature of 25–30 °C. Lecithinase, lipase, neurotoxins and
haemolysins, but not catalase, caseinase, H 2 S, indole or urease, are produced.
Gelatinase is not usually produced by Cl. botulinum type E. Nitrates are not
reduced, nor is the Voges Proskauer reaction positive. Some carbohydrates,
such as fructose and glucose, but not aesculin, cellobiose, dulcitol, glycogen,
inulin, mannitol, melezitose, melibiose, raffi nose, rhamnose, salicin, sorbose,
starch, sucrose and xylose, are fermented to acetic and butyric acids. The
G + C ratio of the DNA is in the range of 26–28 moles % (Cato et al. 1986 ).
Clostridiaceae Representative