Pseudomonas bacteria are a genus of bacteria which exist widely in the environment. They are gram negative, rod shaped, non spore forming, motile, flagellated aerobes. Pseudomonas aeruginosea, probably the most well know of all pseudomonas strains, is an opportunistic pathogen that has the capability of adapting to many niches. It can infect animals and humans alike and can cross the species barrier and for this reason it is considered a potentially zoonotic pathogen. This type of bacteria is immune to many types of bacteria because it has within it’s cell wall a mechanism known as an efflux pump which pumps antibiotics back out of the cell before they have had time to take effect. It is the second most common bacterial contaminant in hospitals and it is known to be paticularly malicious in burn units where it prevents the regeneration of healthy tissue. Bacteria of the pseudomonas family are grown on blood agar which turns from a blood red color to a marine blue/green hue. It also gives off a quite pleasant slightly minty smell.
One form of Pseudomonas pathogen causes a highly contageous disease in horses which is also highly infectious to humans. The disease in horses is know as glanders because it affects the glands in and around the throat and jaws of the horse. This disease was common when colonial forces shipped large quantities of horses to places like Africa, the Middle East and the Far East. Now, this disease is more rarer. The scientific name of this pathogen is Pseudomonas Mallei and it is registered as one of the possible bacterial strains that could be used in bacterial warefare together with Clostridium Botolinum and Anthrax.
Other forms of Pseudonas bacteria are known to cause spoilage in food at low temperatures. These psicrophilic Pseudomonas strains include: P. fragi which causes spoilage of dairy products , P. taetrolens which causes mustiness in eggs and P. mudicolens, and P. lundensis, which causes spoilage of milk, cheese, meat, and fish.
The term spoilage is used in food hygiene for a condition by which the food takes on an unpleasant texture, color change smell taste. This does not mean that the food has necessarily become a serious health risk in the same way as if meat were infected with e.coli or salmonella, for instance, but at the same time it is definitely not advisable to eat spoiled food. It means that the food has been infected with bacteria which cause the physical nature of the food to change. For instance, meat may become slimy to the feel or the outer lawyer of certain foods may become pulpy, it may also smell slightly sour and change color. This happens to food which has been stored in refrigerated conditions for long periods of time in places which have not been properly cleaned with anti bacterial disinfectants. I often see this condition in places such as deli counters where meat is sliced in front of the customer.
However a little slime on meat, such as with cured pastrami in particular and with other types of processed meats is not always a sign of spoilage. It may well be due to a reaction between the protein of the meat, the curing chemicals and the air. Many manufacturers now use preservatives to prevent such spoilage. In addition, the reaction of the preservative with the air and other factors within the meat can cause the color of the product to change slightly as well. The color of the may become slightly irridescent or take on a greenish hue. If the meat smells even the slightest bit sour, feels or looks slimy or has a bad color refuse to accept it.
Spoiled food such as cured meats meat can cause stomach discomfort, diarrhea, vomiting or mild allergic symptoms in some people and may even become more serious in people whose immune system is compromised. Remember this central rule of food hygiene, “When in doubt throw it out”.
Fish products are particularly susceptible to spoilage and it can be very difficult to guess from a casual inspection if the deterioration of the fish is due to spoilage bacteria such as the psicrophilic pseudonmonas species stated above or if the cause is due to more dangerous, pathogenic forms of bacteria. If fish looks even slightly slimy, discolored or smells in the least sour don’t buy it or if it has turned bad in your fridge throw it out and clean you fridge thoroughly with disinfectant. (A tactic used by many fresh fish mungers to hide the tell tale smell of fish which has started to show signs of going off is to constantly pour sea water over it. Watch out for this trick. If you are not sure if you are smelling the actual fish or sea water, don’t buy the fish). Most importantly, keep all fish products in closed containers to avoid cross contamination with of by other food products in your fridge.
The same goes for eggs milk and cheese, if you distinguish any changes in color texture or smell, don’t take any risks, better to throw out and buy fresh. To lower the risk being sold spoiled or food which is about to spoil, buy only from supermarkets and stores which are very busy and have a high turnover of merchandise, particularly in the deli sections. Don’t be embarrassed to inspect what you buy, you are paying for fresh and healthy food and the decision to take what is on offer or not is entirely your own. The customer is always right. If you notice that the food you buy goes off quickly and you know that a). your fridge is clean and b). the temperature of the fridge is as it should be then take the food back to the store with your receipt and demand a refund or a fresh replacement. If the problem continues report your findings to your local authority for food hygiene.