Spoiled meat niche
Description of Niche
Where located?
Physical Conditions?
What are the conditions in your niche? Temperature, pressure, pH, moisture, etc.
Influence by Adjacent Communities (if any)
Is your niche close to another niche or influenced by another community of organisms?
Conditions under which the environment changes
Do any of the physical conditions change? Are there chemicals, other organisms, nutrients, etc. that might change the community of your niche.
Who lives there?
Are there any non-microbes present?
Which microbes are present?
Brochotrix thermosphacta
Brochothrix Thermosphacta is a microorganism for which meat is considered an ecological niche. Its ability to grow under both aerobic and anaerobic conditions makes a significant meat colonizer. The genus Brochothrix is characterizes as gram-positive, nonsporeforming, nonmotile, catalase-postiive, facultatively anaerobic, reluglar, rod shaped bacteria.. The optimal temperature for growth is 20-25º C. The optimal pH for B. thermosphacta to grow is pH 7.0 but growth is seen within the ranges of pH 5-9. Brochothrix thermosphacta is more resistant to irradiation than common meat spoilage organism such as Pseudomonas but are affected by irradiation does of 0.5 to 2.0 kilogray. The species have often been isolated from irradiated meat and poultry. Although, they are an important spoilage organism found prepacked meats and in meat stored in chill temperature, they can also inhabit other niches such frozen foods, milk, and cream. Storage conditions often selectively favor its growth. Brochothrix ssp can grow at temperatures a low as 0º C and under conditions of low oxygen concentration and high C02 concentration. For metabolism, Brochothrix thermosphacta has enzymes for both the hexose-monophosphate and glycolysis pathways of glucose. Fermentative metabolism of glucose always results in the production of L+ lactic acid, but other end products depend on growth conditions [8]. Major end products of aerobic metabolism of glucose by B. Thermosphacta growing on meat are acetoin and acetic, isobutyric, isovaleric and 2 methylbutyric acis. In minimal medium, glucose is the source of all the end products; However, in complex medium such as meat, only acetoin and acetic acid are derived from glucose; Isobutyric, isovaleric, and 2-methylbutyric acids are produced from valine, leucine, and isoleucine, respectively[s4]. These compounds, or their derivatives, are responsible for the odor that often characterizes spoiled meat. Unlike proteolytic spoilage bacteria such as Pseudomonas, B. thermosphacta is usually found only on the meat surface. In prepacked meat, it grows in the area between the meat-plastic film [s8].
Carnobacterium
Clostridium [[1]]
Clostridium is a rod-shaped cell with a gram-positive membrane. These microbes are anaerobes and some are toxin-producing pathogens. Some of them produce acetone, butanol, ethanol, isopropanol, and organic acids. This bacterium can go through spore formation for survival. Clostridium produces large amounts of gas in packaged meat. It is usually coupled up with foul odors and causes the package to appear in a blown pack. [JT5] The toxin produced by this bacterium can do harm and help heal. So far this toxin has helped treat dystonias (neurologic diseases involved abnormal muscle posture and tension), urinary bladder muscle relaxation, esophageal sphincter muscle relaxation, and tics. However at the same time, the toxin released can cause botulism poisoning. Proteolytic strains of toxin is produced at around 35°C and for nonproteolytic strains, they can grow in environments of 26-28°C. Toxin produced from bacterium will cause botulism which is food poisoning that will lead to muscle paralysis. [JT6]
Enterobacterium
Lactobacillus [[2]]
Leuconostoc [[3]]
Leuconostoc is one of the lactic acid bacteria; it produces D-lactate and ethanol. This group of microbe is responsible for the discoloration, gas production, and buttery smell of spoiled meat. [JT2] The genus Leuconostoc is described as being spherical cells that is gram-positive and often lenticular on agar. This bacterium grows optimally in an environment of 20-30°C. However, they also require a rich and complex media for growth. A rich and complex media includes nicotinic acid, thiamin, biotin, and pantothenic acid. For energy, they are heterofermentatives, which means they use a combination of pentose phosphate and phosphoketolase pathways. This microbe cannot go through spore formation for survive. They fall under the facultative anaerobic category, which means they can live in an environment with or without oxygen. Leuconostoc was originally placed into Streptococcaceae bacteria family as mentioned in Bergey’s Manual of Determinative Bacteriology. However, in 1986, the Bergey’s Manual of Systematic Bacteriology moved Leuconostoc from the Streptococcaceae family into the Deinococcaceae family. [JT4]
Pseudomonas [[4]]
The predominant bacteria that are often associated with spoiled meat are Pseudomonas. They are polarly flagellated, gram –negative, rod shaped, aerobic bacteria. [a1]. A few microorganisms under the genus Pseudomonas are known to effectively use meat as a niche due to their ability to break down glucose and amino under aerobic conditions and at refrigerated temperature. Pseudomonades are able to break down the long peptide chains of proteins in meats into amino acids and foul-smelling compounds such as ammonia, amines, and hydrogen sulfide [a2]. Some strain of Pseudomonas produce esters, many produce sulfur-containing compounds, and a few produce methyl ketones, secondary alcohols, and unsaturated hydrocarbons [a3]. Florescent Pseudomonas strains represent one of the most important groups among Pseudomonas because of their ability to produce water-soluble yellow-green pigments, called pyoverdines (PVDs). These yellow-green pigments act as siderophores, allow Pseudomonas to uptake iron from their environment. The most common Pseudomonas species found in beef, pork, lamb and poultry meat appears to be Pseudomonas fragi. Perhaps Pseudomonas fragi strains are so dynamic because it is capable of using a wide range of carbon compounds including D-arabinose, creatine, and bile acids [a6]. Pseudomonas fragi growing on meat surface uses compounds such as glucose, free amino acids, and lactate. These carbon sources are enough support growth until spoilage has occurred. When the concentration of these compounds decrease in the uppermost layer, the compounds diffuse from below. Proteolytic activity and penetration of bacteria down in the tissue does not occur before the meat is already spoiled. In general, Pseudomonas shows preference for glucose. It is only when glucose is depleted that the Pseudomonas takes up the free amino acids (the amino acids are consumed before lactate). The order of preference from most to least is glucose> lactate>citrate>aspirate-glutamate>creatine-creatinine. It is at the point when amino acids are consumed that the meat gives off an offensive odor from the volatile by-products of amino acid catabolism. [a7].
Shewanella putrefaciens
Do the microbes that are present interact with each other?
Do the microbes change their environment?
Brochothrix thermosphacta, Carnobacterium spp., Enterobacteriaceae, Lactobacillus spp., Leuconostoc spp., Pseudomonas spp., Shewanella putrefaciens and Weissella spp. work together to create the spoiled meat profile: discoloration, gas production, slime production, decrease in pH, and sour off-flavor. [JT2]
Leuconostoc produces H2O2, which gives spoiled meat its green discoloration. [JT7]
Clostridium work with lactic acid bacteria [Lactobacillus and Leuconostoc] to produce large amounts of gas (H2 and CO2) which is accompanied by a foul odor. [JT2]
Do the microbes carry out any metabolism that affects their environment?
Do they ferment sugars to produce acid, break down large molecules, fix nitrogen, etc. etc.
Clostridium can perform nitrogen fixation. Clostridium can go through fermentation of carbon sources to produce acetone, butanol, ethanol, isopropanol, and organic acids. [JT5]
Leuconostoc produces ammonia by the use to bacterial deamination of amino acid and the production of ammonia will lead to a decrease in acidity. The process it takes to produce H2O2 involves the oxidation of nitrosohaemochrome to choleomyoglobin. [JT7]
Current Research
In lactic acid bacteria associated with vacuum-packed cooked meat product spoilage: population analysis by rDNA-based methods (2006), investigators aimed to research and find which lactic acid bacteria was involved in the spoilaged of vacuum packaged cooked meat products. They did this by studying different samples of bacteria within 4 meat products, some of which had spoilage symptons, some that did not. Colonies of these were then grown on yeast glucose lactose peptone and trypticase soy yeast plates, and where then identifived via internal spacer region. The study found that Leuc. Mesenteroides was the main spoilage agent within vacuum packaged meats. The significance of this study was to determine what organisms to look for to prevent the spoilage of vacuum packaged meats. [1]
Development of a Microbial Model for the Combined Effect of Temperature and pH on Spoilage of Ground Meat, and Validation of the Model under Dynamic Temperature Conditions (2005). The study aimed at using microbiological and sensory analysis to predict spoilage of aerobic stored ground meat. Under aerobic conditions, samples of ground meat (beef and pork) were analyzed for changes in their appearances, smells and microbes composition at certain ranges of pH (5.34-6.13) and temperature (0-20 Celcius). As observed, pseudomonads were the predominant bacteria isolated from these samples. In addition, it was also detected that the changes in pseudonomads populations is proportional to the sensory changes. Thus,it can be concluded that microbiological and sensory analysis can be used as a “good index for spoilage of aerobically stored ground meat”. Following this type of model, the meat industry can benefit from by running more “effective management systems, which will optimize the quality of meat products”. [3 JN]
References
[6] Vangelova, L. “Botulinum Toxin: A Poison That Can Heal”. FDA Consumer Magazine. 1995.
[8] Jorngen J. Leisner, B. G. Laursen, H. Prevost, D. Drider, and P. Dalgaard. 2007. Carnobacterium: Positive and Negative Effects in the Environment and in Foods. FEMS Microbiol Rev. 31: 592-613.
[9] Weigand I., H. K. Geiss, D. Mack, E. Sturenburg, and H. Seifert. 2007. Detection of Extended-Spectrum Beta-Lactamases among Enterobacteriaceae by Use of Semiautomated Microbiology Systems and Manual Detection Procedures. Journal of Clinical Microbiol. 45: 1167-1174.
Edited by [Steven Lee , Jade Nguyen , Ngoc-minh Nguyen , Sarah Paek , June Tse , Amy Vo], students of Rachel Larsen
