The Problem Of Botulism

Botulism is thankfully one of those rare food poisoning events but it is still a fatal condition. Clostridium botulinum is the causative agent which releases toxins that are thought to be some of the most powerful known. Ironically, botulinum toxin injections are now a cosmetic must for those wanting to remove lies from around the eyes.

The toxins attack the nervous system such as the brain, spinal chord and nerves generally. The result is muscle paralysis, spasms and eventually death. Most particularly characteristic  is blurred or double vision with difficulty in swallowing (dysphagia), speaking (dysarthria) and strangely drooping eyelids and mouth. Death is usually by respiratory failure.

Food borne botulism occurs when food is contaminated with the bacteria. It can be borne in soil which is present on unwashed fruit and vegetables or when it has not been canned, processed or cooked properly. One of the most infamous cases was due to contaminated canned salmon and seafoods including the cocktails are particularly prone to Clostridium growth.

The NHS report that since 2000, there have been 147 cases of wound botulism with 8 deaths and only seven cases of food borne botulism with one death.

There are many types of C. botulinum. Perhaps the most significant is type E. Types A & B grow and produce the toxins at pHs below 4.6 which is significant because acidification is one of the major hurdles to reducing this bacteria’s growth (Tanaka, 1982).

Type E has been isolated from raw seafoods such as salmon, whitefish, cod and others but rarely if at all in processed fish foods (Craig et al., 1968). Crab and shrimp meat are excellent growth medium too for type E (Lerke, 1973). Although commercially washed eggs are also generally safe, if the washing methods are not scrupulous or there is improper cleaning and sanitising of equipment, then raw eggs are easily contaminated too (Moats, 1981). Salmonella is then not the issue here.

Reducing The Incidence of Botulism

The generally accepted limiting pH of 4.6 is considered to provide an ample margin of safety against the hazards of botulism in acidified food products and such products are normally then only given mild heat treatment (Gardner, 1976).

A number of studies over the years have looked at how to prevent the growth of Clostridium botulinum in foods. Canned meats especially those such as canned luncheon meat, canned pork foods and salmon as we mentioned earlier are especially prone to the growth of this bacteria if they are not processed properly. 

Generally the application of a rigorous form of heat processing if the conditions for processing are not met. Other steps include the addition of salt and nitrites. It’s also possible to alter the pH of the meat product using  phosphates for example.

The role of nitrite in preserving canned meats is peculiar because it is reckoned that even if nitrite as an entity disappears there is a legacy effect. Another type of inhibitor is formed called the Perigo-type factor (PTF) which prevents spores of C. botulinum from developing into full grown bacterial populations (Chang et al. 1974).

Since the early days of studies on botulism, much more is known about the role of nitrite and another preservative sorbate in preserving cured meats (Sofos et al., 1979). Reducing agents can also be added to enhance the antimicrobial effect of nitrite. Johnston and Loynes in 1971 added ascorbate (vitamin C) or cysteine to what they defined as under-processed meat slurry to which had been added nitrite. In that case the amount of nitrite needed to inhibit botulinum growth was severely inhibited.

References

Chang, P. C., Akhtar, S. M., Burke, T., & Pivnick, H. (1974). Effect of sodium nitrite on Clostridium botulinum in canned luncheon meat: Evidence for a Perigo-type factor in the absence of nitrite. Canadian Institute of Food Science and Technology Journal, 7(3), pp. 209-212 (Article).

Craig. J.M., Hayes. S., PiIcher, K.S. (1968) Incidence of Clostridium botulinurn type E in Salmon and other marine fish in the Pacific Northwest. Anal. Microbial. 16 pp.  553.

Gardner, J. (1976) Pickled, fermented and acidified foods. Proposed good manufacturing practices. Federal Register 41 pp. 30442.

Insalata. N.F., Fredericks, G.J.. Berman, J.H.. Barker, E. (1967) Clostridium botulinum type E in frozen vacuum-packed fish. Food Technol. 21 pp. 296.

Johnston, M.A. and Loynes, R. (1971). Inhibition of Clostridium  botulinum by sodium nitrite as affected by bacteriological media and meat suspensions. Can. Inst. Food Technol. J. 4: pp. 179

Lerke, P. (1973) Evaluation of potential risk of botulism from seafood cocktails. Appl. Microbial. 25 pp. 807.

Moats, W.A. (1981) Factors affecting bacterial loads on shells of commercially washed eggs. Poultry Sci. 60  pp.  2084.

Sofos, J. N., Busta, F. F., & Allen, C. E. (1979). Botulism control by nitrite and sorbate in cured meats: A review. Journal of Food Protection, 42(9), pp. 739-770 (Article)

Tanaka, N. (1982) Toxin production by Clostridium botulinum in media at pH lower than 4.6. J. Food Protect. 45  pp. 234.