The Pathogenic Bacteria Affect - Essay Example

www.academia-research.com Sumanta Sanyal d: 22/11/06 Food-Poisoning Bacteria: Combinational Effect of Temperature at Storage and Chemical Composition of Food on Growth Abstract The paper studies how particular strains of pathogenic bacteria affect particular groups of foodstuff and finds that this is entirely dependent upon the molecular mechanism of the micro-organisms. Special genomic/proteomic traits (Fratamico, P., 2006) enable the micro-organisms to generate certain chemicals (Beuchat and Worthington, 1976; Kort, R., 2005) that are helpful in allowing them to gain access and survive in particular sets of food. Thus, careful study of both the chemical composition of food and the micro-organisms, together with the genetics involved, can enable much more efficient sterilization of foodstuff through temperature control or combination strategies that is the main objective of study. Interestingly, it has been proved that lysozyme action against thermophilic bacterial strains (all tabulated strains are noticeably thermophilic and inclusive) is available within a range of C (Hughey and Johnson, 1987). This is especially true for thermophilic spore-formers and it is reported that the enzyme can be used post-thermal sterilisation to enhance shelf longevity (Hughey and Johnson, 1987). It has also been proved that pathogenic bacteria can be inhibited in food by a combination of hydrostatic pressure and heat at lower temperatures than heat alone (Alpas, H., et al, 1999;). It is noted here that many foodborne pathogenic bacteria that are both gram-negative and positive have an enzyme DegP protease (C Hal, J., et al, 2001) that ensures their thermal stability. Targeting this enzyme or the gene that initiates it by either thermal or any other process would much increase death rates in these bacteria easily. It is also necessary to effectively assess the time required to initiate or complete phases other than the death phase to do this (McMeekin, T.A., et al, 1997). It is also noted at first that some of the literature is dated but care has been taken to incorporate only information that is still germane and effective today. In this some original research papers that are still quoted today as legitimate sources have been utilised. The paper finds, primarily, that foods that cannot be heated should be stored at such low temperatures that both psychrophilic and thermophilic bacteria cannot regenerate. Foods that can be heated should be heated to such a temperature that at least all possible vegetative cells of possible pathogenic bacteria be killed and should either be eaten immediately or stored at cold temperatures such that spores, if present, cannot regenerate upon longer periods of storage. Introduction A U.S. Department of Agriculture report - the Agricultural Economic Report No. 741, 1996 - reported that microbial pathogens in food cause 6.5-33 million cases of human illnesses and 9,000 deaths in America. The report, though slightly backdated, is utilised here because it is one of a kind and one as comprehensive as it is not available for more recent times. It estimates that over 40 such foodbourne microbial agents - viruses, bacteria, fungi and parasites - are responsible for these illnesses. The medical and productivity costs of both acute short-term and chronic long-term illness conditions are considerable. For just six bacterial pathogens, the costs are $9.3-$12.9 billion annually of which $2.9-$6.7 billion annually is attributed to foodbourne bacteria (Report No. 741, 1996). Though the figures are of 1996 recent literature on the subject concede that the problem remains extensive enough and provides impetus to the purpose of this paper. Nature of Bacteria To better understand how bacterial growth is influenced by the combination of temperature and food composition it is somewhat necessary to first study the true nature of some of the different bacterial strains that induce pathogenic conditions in food. Bacteria, like other such micro-organisms, can be broadly classified by the optimal temperature range they need for growth. These are: Psychrophiles (cold-loving) - (C, upper limit C); Mesophiles (middle range) - (C); Thermophiles (heat-loving) - (C - C, C optimal) and hyperthermophiles (extremely heat-loving) - (C and above) (Deacon, J., Undated. All temperatures are approximate). Bacteria grow at phenomenal rates through a four-phase growth cycle. They do so by binary fission, dividing every 20-30 minutes under optimal conditions (Michigan DA, 2006). The four growth phases are: 1) Lag Phase - This is the phase when the bacteria adjust their metabolism to any drastic change in environment. The numbers remain constant. 2) Logarithmic Growth Phase - This is the growth phase when the bacteria divide through fission exponentially. The time taken for one cell to divide into two is called the 'generation time' or 'doubling time'. 3) Stationary Phase - this is the phase when numbers are constant and growth and death rates are equable. Nutrients are fast being depleted and waste is accumulating. 4) Death Phase - In this phase the numbers continue to decrease as nutrients decrease and toxic metabolic by-products increase. (Adapted: Michigan Department of Agriculture, 2006) In the death phase, when conditions become unfavourable, bacteria begin to form spores, with tough coats, to help them tide over the unfavourable conditions and, upon finding favourable ones, the bacteria become active again and go into lag phase to start a new growth cycle. Not all bacteria form spores though. Nature of Food It is also considered necessary to know a little about the composition of various foodstuff that promote bacterial growth and are thus considered hazardous. The Australia-New Zealand Food Standard, 2002, has been consulted to identify a set of such foodstuff because it is the most comprehensive available. Hazardous foods are as follows. Food items containing raw or cooked meat (including poultry and game) such as casseroles, curries, lasagne, etc. and meatloaf products. Dairy Products such as milk, custard and dairy-based desserts. Seafood (excluding live seafood) such as seafood salads, fish balls, stews with seafood and fish stock, etc. Processed fruits and vegetables such as salads and cut melons. Cooked rice and pasta. Other protein-rich foods such as eggs, beans including soybean, quiche, fresh pasta, nuts, etc. It is noticeable that hazardous foods derived from animals, rich in protein and fat, are most susceptible to pathogenic bacterial attack while plant derived foods, mostly rich in carbohydrates, become quickly susceptible only after cooking or processing. Pathogenic Effects Table 1 of the Appendix contains data on some foodbourne bacteria. All strains have important pathogenic implications in the US. With the exception of Bacillus cereus (European Commission, 2002), which thrives in carbohydrate-rich items derived from plants, all the other tabulated strains cause pathogenic conditions in animal-derived foodstuff. The most economically important pathogenic (foodbourne) bacteria in the USA are Campylobacter, Salmonella, E. coli and Listeria (Callaway, T.R., et al, 2003). All these are tabulated except the E.coli strains. It is noticeable that three principal environmental factors affect bacterial growth rates. These are temperature, pH value and water activity. The last is the amount of water that is available at a certain temperature for bacterial use. While the food may contain significant quantities of water, at a particular temperature, all of it may not be available for the bacteria to use. The factor is expressed in decimals where 1 is signified as the total water in the food. For spore-forming and toxin producing bacteria like C.botulinum (Type E), death rates for spores can be initiated only at very high temperatures - C and toxicity can be averted at even higher temperatures - C. This is relatively low for bacteria. Type A and the proteolytic B strains of C.botulinum have even higher death rate temperatures for spores and for averting toxicity. So it is for B. cereus when a high temperature of C is necessary for cessation of the emetic toxin. Particular Strains: Temperature Ranges For some of the tabulated pathogenic bacteria two temperature figures are posted and it is observed that the time function for the death rate is lower for the higher temperature than for the lower one. This is effective in the sense that when temperature control is being used to render the food safe for consumption it is necessary to heat it for a longer time at the lower temperature and vice versa (Angelotti, R., et al, 1960). It is also noteworthy that when temperatures that kill only vegetative cells of spore-formers are being used as safeguard it is necessary to caution for a very short shelf-life as any spores present can possibly go into lag phase give longer shelf-life if enough spores are formed before complete cauterisation. Otherwise, the storage temperature can be kept at such a low level that bacterial growth cannot be regenerated from possible spores. It is advised that foods that cannot be heated for reasons of conserving aesthetic, organoleptic and nutritional properties should be treated and stored at low temperatures that can inhibit both psychrotropic and thermophilic bacterial strains (McMeekin, T.A., et al, 1997). Conclusion While combination strategies may enhance food safety it is opined that thermal treatment of selected foods that retain their desired characteristics through the treatment is still a useful option though non-thermal treatment is a focus area because thermal treatment often degrades food quality attributes (FAO, 2001). Also, it is concluded that though much can be reported about the mechanisms of how chemical components of specific bacteria access chemical components of specific foods (the entire mechanism mediated by specific genes in the bacteria) the paper has adopted a more general approach to conserve brevity. Nevertheless, the rendering is believed to be thorough enough to be of utility as a base for more research, possibly in the direction of combinational strategies as the paper notes that the current research trend is in that direction though cooking needs that home have to be guided exclusively by such simple treatment methods as the thermal one. Reference 1. Alpas, H., et al, Variation in Resistance to Hydrostatic Pressure among Strains of Foodborne Pathogens, Appl Environ Microbiol. 1999 September; (65)9: 4248-4251. Extracted on 12th November, 2006, from: http://aem.asm.org/cgi/content/full/65/9/4248 2. Angelotti, R., et al, Time-Temperature Effects on Salmonellae and Staphylococci in Foods, 1960. Extracted on 11th November, 2006, from: http://www.pubmedcentral.nih.gov/articlerender.fcgiartid=1057731 3. Beuchat, L.R., and Worthington, R.E., Relationships between heat resistance and phospholipid fatty acid composition of Vibrio parahaemolyticus, Appl Environ Microbiol. 1976 March; 31(3): 389-394. Extracted on 11th November, 2006, from: http://www.pubmedcentral.nih.gov/botrender.fcgiblobtype=html&artid=239702 4. Callaway, T.R., et al, Preslaughter intervention strategies to reduce food-borne pathogens in food animals, J. Anim. Sci. 2003. 81:E17-E23. Extracted on 12th November, 2006, from: http://www.animal-science.org/cgi/content/full/81/14_suppl_2/E17 5. Hal Jones, C., et al, Conserved DegP Protease in Gram-Positive Bacteria is Essential for Thermal and Oxidative Tolerance and Full Virulence in Streptococcus pyogenes, Infect Immun, 2001 Spetember; (69)9: 5538-5545. Extracted on 14th November, 2006, from: http://www.pubmedcentral.nih.gov/botrender.fcgiblobtype=html&artid=98667 6. Deacon, Jim, Undated, The Microbial World: Thermophilic Bacteria. Extracted on 14th November, 2006, from: http://serc.carleton.edu/resources/2520.html 7. European Commission, Risk assessment of food borne bacterial pathogens: Quantitative methodology relevant for human exposure assessment, 2002. Extracted 11th November, 2006, from: http://ec.europa.eu/food/fs/sc/ssc/out308_en.pdf 8. FAO, 2001, Technical Elements of New and Emerging Non-Thermal Food Technologies. Extracted on 14th November, 2006, from: http://www.fao.org/ag/ags/agsi/Nonthermal/nonthermal_1.htm 9. Food Standards Australia New Zealand, 2002. Extracted on 14th November, 2006, from: 10. Fratamico, Pina, 2006, Improving Food Safety Through a Better Understanding of Bacterial Responses to Environmental Factors. Extracted on 12th November, 2006, from: http://www.ars.usda.gov/Research/docs.htmdocid=6732 11. Hughey, V.L. and Johnson, E.A., Antimicrobial Activity of Lysozyme against Bacteria Involved in Food Spoilage and Food-Borne Disease, Appl. And Environ Biol. Sept. 1987, p. 2165-2170. Extracted on 14th November, 2006, from: http://www.pubmedcentral.nih.gov/articlerender.fcgiartid=204075 12. Meekin, T.A., et al, Quantitative Microbiology: A Basis for Food Safety, Emerging Infectious Diseases, Vol. 3, No. 4, 1997. Extracted on 12th November, 2006, from: http://www.cdc.gov/ncidod/eid/vol3no4/mcmeekin.htm 13. Module 6: Foodborne Microbiological Control, Michigan Department of Agriculture, 2006. Extracted on 12th November, 2006, from: http://www.michigan.gov/documents/MDA_mod_06_21260_7.html 14. Price, Bob, 1995, Environmental Conditions for Pathogenic Bacterial Growth. Extracted on 12th November, 2006, from: http://seafood.ucdavis.edu/Pubs/pathogen.htm 15. U.S. FDA, The Safe Food Chart: Meat, Poultry and Seafood, 2001. Extracted on 12th November, 2006, from: http://vm.cfsan.fda.gov/dms/fttright.html 16. US FDA, Bacterial Foodborne Diseases: Medical Costs and Productivity Losses, Agricultural Economic Report No. 741, 1996. Appendix Table 1: Bacterial Strains and their Growth Factors Bacteria and Foodstuff Temp. Range for Growth pH Range for Growth Min. Water Activity for Growth Growth (Doubling Time) Death Rate (90% Reduction Time) Infectious Bacteria Listeria monocytogenes (pork, poultry, and seafood) C 4.5-9.5 4.83 min @ C 2.85 min @ C Yersinia enterocolitica (meat and seafood) C 4.6-9 7.5 days @ C 41 min @ C 0.24-0.96 min @ C Vibrio (except V. cholerae) (seafood) C 4.8-11 0.937 .08-48.2 min @ C 1.7 min @ C Salmonella (beef, pork, poultry and seafood) C 4.1-9 0.92 5.3-48.3 min @ C Campylobacter jejuni (beef and poultry) C 4.9-8 50 min @ C 12-21 sec @ C Toxin producers and spore formers Clostridium perfringens (meat) C 5-8.3 0.95 7.2 min @ C 7.2 min @ C (vegetative cells) 26-31.4 min @ C Clostridium botulinum (Type E) (seafood) C 5-9 0.97 .49-.74 min @ C (cessation of spore formation) 5 min @ C (cessation of toxin formation) Staphylococcus aureus (beef, pork and poultry) C 4.5-9.3 0.83 5.25-7.82 min @ C (death rate for vegetative cells) 134.2 min @ C (cessation of toxin production) Bacillus cereus C 4.35-9.3 0.912 29 min @ C 1 min @ C (death rate for vegetative cells) 2.7-3.1 min @ C (cessation of spore formation) 5 min @ C (cessation of diarrhoeal toxin production) Stable 90 min @ C (cessation of emetic toxin production) (Table prepared with combined reference from: Price, Bob, 1995, Environmental Conditions for Pathogenic Bacterial Growth, and U.S. FDA, The Safe Food Chart: Meat, Poultry and Seafood, 2001) Note: Care has been taken that all temperatures correlate with findings from more recent research. 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