Tag: microbiology

Dear Dr. B: What is a bacterium? What are the common bacteria which cause illnesses in humans?

Answer: A bacterium (bacteria is the plural of bacterium) is a very small, single-celled microorganism that can reproduce rapidly. A bacterium has no nucleus. Bacteria come in many shapes including spheres, rods and spirals. They are the most abundant living organisms on earth, and are found in all living things and in all of the earth’s environments.

Bacteria usually live off other organisms. A bacterium is a completely self-contained and self-reproducing unit. A virus, on the other hand, cannot reproduce without a living host.

Most bacteria are considered harmless. Many are beneficial to humans. A small percentage of bacteria, which are harmful, feed on the tissues of the human body and excrete toxins and acids afterwards which causes bacterial infection. Most viruses, on the other hand, serve no beneficial purpose. Their mission in life is to create more viruses in order to assure survival of the strain

Here are some examples of common illnesses caused by bacteria.

The most important human pathogens among the Gram-positive cocci are Staphylococcus aureus which causes skin and soft tissue infections and toxic shock syndrome. Pharyngitis is caused by Streptococcus pyogenes, neonatal meningitis is caused by Streptococcus agalactiae, pneumonia is caused by Streptococci pneumoniae and Enterococcus faecalis causes urinary tract infection.

Meningitis and gonorrhea is caused by the Gram-negative cocci called Neisseria. Gram-positive bacilli cause meningitis, pneumonia, soft tissue infections, brain abscess and diphtheria. There are many other groups of bacteria including the Gram-negative bacilli, the Enterobacteriaceae and others which cause variety of illnesses in humans.

The dawn of bacteriology started with Louis Pasteur (1822-1895). He was interested in the process of fermentation. He proved that fermentation was caused by bacteria or fungi. According to Illustrated History of Surgery, Pasteur studied fermentation of wine and beer and invented the process of pasteurization, which became very important in the dairy industry. He also found a vaccine against anthrax (an illness caused by bacteria).

Pasteur was not a doctor. He was a chemist and became professor of chemistry at the Sorborne in Paris. He also discovered bacteria called staphylococci and streptococci and explained their toxic effects. Pasteur also produced a vaccine against rabies (a viral disease), at that time thought to be incurable disease.

Robert Koch (1843-1910) along with Pasteur is credited with launching the first “golden age” of bacteriology. Koch was one of the first professors of hygiene and bacteriology in Berlin. Koch had developed an apparatus for keeping bacteria alive under the microscope. He discovered the bacteria which causes tuberculosis and cholera. Koch won the Nobel Prize in 1905.

Diseases caused by bacteria are many. We continue to fight the battle against the continuous onslaught from bacteria by developing different varieties of vaccines, medications and antibiotics. But bacteria have ability to change in order to survive treatment. This is called antibiotic resistance and this phenomenon is a growing concern among the health care providers. Overuse and inappropriate use of antibiotics result in bacteria developing resistance.

Our battle against bacteria will never be over. Just like viruses, they keep one step ahead of the game. We should continue to be vigilant in washing our hands and keeping our bodies and environment clean and healthy.

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Dear Dr. B: What is a virus? What are the common viruses which cause illnesses in humans?

Answer: A virus is a minute organism that consists of a core of nucleic acid surrounded by protein. Viruses can grow and reproduce only inside living cells such as bacteria, plants and animals. They are composed of RNA or DNA. Viruses are very small. A special kind of microscope is required to see them.

There are many, perhaps hundreds of different viruses causing all kinds of diseases in animals and plants. Some examples of common human diseases caused by viruses are: AIDS, measles, mumps, smallpox, yellow fever, rabies, poliomyelitis, influenza, the common cold, hepatitis and certain types of cancers. Viruses also cause gastroenteritis.

In the last few months many institutions have fallen victim to viral gastroenteritis, also known as “stomach flu,” although influenza virus has nothing to do with gastroenteritis. Getting a flu shot will not prevent viral gastroenteritis. Many different viruses can cause gastroenteritis, including rotaviruses, adenoviruses, caliciviruses, astroviruses, Norwalk virus and a group of Norwalk-like viruses, now known as noroviruses.

The main symptoms of viral gastroenteritis are watery diarrhea and vomiting. The affected person may also have headache, fever and abdominal cramps (stomachache). In general, the symptoms begin one to two days following infection with a virus that causes gastroenteritis and may last for one to 10 days, depending on which virus causes the illness.

Normally the prognosis is good. Most people recover completely without any long-term effects. But in children and old patients the disease can be fatal if fluid and electrolyte balance of the body is not maintained.

Viral gastroenteritis is contagious. The virus spreads through close contact with infected persons by sharing food and water. Food may be contaminated by people who cook or handle food who have viral gastroenteritis, especially if they do not wash their hands regularly after using the bathroom or changing diapers.

Viral gastroenteritis can affect people in all parts of the world. Some viruses have seasonal activity and occur during cooler months of October to April. Quite often the outbreaks occur in institutional settings such as schools, hospitals and nursing homes and group settings such as cruise ships. Transmission of Norwalk virus is through the fecal-oral route.

Studies have shown water is the most common source of outbreaks. Shellfish and salad ingredients are the foods most often implicated in Norwalk outbreaks. Ingestion of raw or insufficiently steamed clams and oysters poses a high risk for infection with Norwalk virus. Rotavirus and the Norwalk family of viruses are the leading causes of viral gastroenteritis.

Wash your hands, clean and cook your food well and maintain good hygiene. That’s the best way to prevent gastroenteritis. If you like to eat out then pick your restaurants carefully.

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Helicobacter pylori (H pylori) is an organism found in stomach. It is estimated that more than half the world’s population is infected with this bacteria. That includes 20 to 40 percent of Canadians.

Usually, infected individuals have no symptoms and develop no problems as a result of this. Only 15 percent of infected individuals develop clinically significant H pylori related disease in their lifetime – stomach ulcers, gastritis and cancer.

Is this bacteria a normal inhabitant of stomach since so many people seem to carry it? Or people are infected from others? The answer is not very clear.

Since the bacteria have potential to cause illness, should we screen everybody for this bug?

Here is what a review article in the Canadian Journal of Gastroenterology says:

-Consensus conference of the Canadian Helicobacter Study Group does not recommend screening in asymptomatic individuals.

-Recommendation is to screen and treat all patients with gastric or duodenal ulcer whether they are symptomatic or asymptomatic.

-There is controversy as to whether patients with dyspepsia (indigestion) benefit from H pylori eradication. It seems that a small number (up to 15 percent) of such patients benefit from treatment.

How can we test for H pylori infection?

A blood test can tell us whether one has been exposed to the infection. If this test is negative then there is 90 percent chance that there is no infection. A positive blood test does not mean that you are currently infected. Under the age of 50, this test should be good enough depending on patient’s symptoms.

Urea breath test is superior to the blood test and is another simple way to check for infection. It has less than 10 percent false negative and false positive results. But in Medicine Hat, most patients end up getting the most expensive invasive test called gastroscopy. Why? Because the other two tests are not readily available.

What to do if infection with H pylori is detected?

The review article says that testing should not be performed to detect the presence of H pylori without an intention to treat if the test result is positive. Recently published guidelines recommend treatment of asymptomatic patients whose infection becomes known. In patients with peptic ulcer disease, eradication of H pylori infection is cost effective.

Treatment is with an acid suppressant (proton pump inhibitor) and two antibiotics for seven days. This is called triple therapy. It is almost always curative, and the infection almost never recurs in Canadian adults, but research says that eradicating the bacteria in the absence of peptic ulcer rarely fixes the problem of indigestion.

Are we smarter today than 17 years ago when the bacterium was first discovered?

In many ways, yes! Now we can cure peptic ulcer without surgery. But new studies suggest that treating this bacterium may increase the risk of esophageal ulcers and cancer. If you don’t treat it then there may be a risk of getting stomach cancer! Go figure!

Who said doctors know everything? In the last 20 years, this is one of the most important discoveries in medical science. But there are many unanswered questions.

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