How do pathogenic bacteria cause disease

Bacterial bowel disease

A multitude of different bacteria live in the human intestine, some of which we even need to digest our food. But every year thousands of people are attacked by pathogens that actually settle in the intestines of animals - sometimes with life-threatening consequences

Clinical picture


A multitude of different bacteria colonize the human intestine. Some are useful, for example aiding digestion by helping to break down the ingredients of the food. Others behave inconspicuously, so they live in peaceful coexistence with us, are of no use to us, but are also not harmful. But a third group can cause problems for the human organism under certain conditions. These pathogens infect the intestinal mucosa and cause, for example, diarrhea - and other potentially dangerous organ damage.
This infection can take place in two ways: On the one hand, foreign pathogens can be introduced that do not naturally occur in the healthy intestinal flora. These include pathogenic strains of the otherwise harmless E. coli bacteria such as EHEC (enterohaemorrhagic E. coli), EPEC (enteropathogenic E. coli), ETEC (enterotoxic E. coli) and EIEC (enteroinvasive E. coli). Pathogens of the Campylobacter strain C. jejuni and the germ Yersinia enterocolita do not actually occur in the human intestinal flora.

Clostridium difficile, on the other hand, lives peacefully in the intestines of many healthy people without causing complications. Only when the balance of the natural intestinal flora is disturbed - for example through treatment with antibiotics - this bacterium can become dangerous. The pathogenic effect of bacteria comes from their metabolism. Because they produce cell-damaging poisons that can cause serious complaints.



The symptoms that these different intestinal pathogens can trigger are similar in the first stage. However, with some germs there can be particularly dangerous complications. After an incubation period - that is the time between infection and the outbreak of the disease - of up to ten days, people who have become infected with a pathogenic E. coli strain, Yersinia enterocolita or Campylobacter jejuni suffer from "bloodless, often watery diarrhea, which can be accompanied by symptoms such as abdominal pain, nausea, vomiting and fever, "says Keikawus Arastéh, chief physician of gastroenterology and infectology at the Vivantes Auguste Viktoria Clinic. In severe disease, painful abdominal cramps and bloody diarrhea also occur. However, not every infection with one of the E. coli pathogens causes symptoms - it is not uncommon for the disease to be symptom-free and therefore go unnoticed.

Infections with the EHEC germ can also be particularly severe. The toxins secreted by the bacteria destroy the intestinal cells and therefore cause bloody excretions, just like the other germs. "However, they can also damage the blood cells and vessels of the kidneys and lead to kidney failure," says Keikawus Arastéh. Doctors like him then speak of the hemolytic uremic syndrome (HUS). Another, albeit less common, complication of an EHEC infection is the so-called thrombocytopenic purpura (TTP). Triggered by the destructive effect of the cell poison on the blood platelets, thrombosis occurs in the brain and kidneys.

Finally, Clostridium difficile causes intestinal inflammation with diarrhea as well as fever and abdominal cramps. In severe cases, the inflamed intestinal wall "sweats out" the protein fibrin. This protein combines with white blood cells and dead intestinal cells to form a white layer on the intestinal wall. Doctors call this process pseudomembranous colitis. The conglomerate formed can clog the digestive system and cause it to swell. In this ideal breeding site, the Clostridium difficile bacteria can multiply more intensely, as a result of which the intestinal walls are destroyed and ultimately sepsis - i.e. blood poisoning - threatens the entire organism.



In contrast to the harmless E. coli bacteria that live in the human intestine, the pathogenic E. coli strains, Campylobacter and Yersinia enterocolita occur in the intestines of ruminants such as cattle, goats and sheep, but also deer and deer. Without becoming ill themselves, the animals excrete the bacteria in their faeces. The pathogens are transmitted to healthy people through a smear infection of infected animals or sick people. However, food and drinking water contaminated with faeces can also lead to infection. Clostridium difficile also enters the organism faecal-orally - i.e. from the stool to the mouth. However, many people already carry the germ before the onset of the disease. A disease usually only occurs when the intestinal flora is disturbed by the use of antibiotics: The bacteria naturally living in the intestine are killed and make room for a toxin-forming subgroup of Clostridium difficile. That is why diarrhea is one of the typical side effects of antibiotic therapy.



In order to avoid infections with pathogens, the standards of hygiene should be observed: This includes washing your hands with soap after using the toilet and before preparing food. In order to avoid "smear infection of animals in the petting zoo", particular attention should be paid to the hygiene of children, says chief physician Arasteh. Raw foods can also be a source of infection. Raw milk products, uncooked meat and raw vegetables (raw fruits and vegetables) lead to illnesses again and again. In order to kill the heat-sensitive intestinal bacteria and to defuse the toxins they produce, food should be heated to a core temperature of 70 degrees Celsius for ten minutes. And fruit, vegetables and lettuce - Arastéh advises - "wash thoroughly!"



According to the Robert Koch Institute, around 34,000 Campylobacter jejuni diseases were reported to health authorities across Germany in 2010, 3008 of them in Berlin. The EHEC bacterium, which is also notifiable, was registered almost 1000 times across Germany last year, and the Berlin health authorities counted 31 cases. In the same period, around 3400 cases of Yersinia enterocolita were diagnosed, in the state of Berlin there were 81. Infectologists suspect that the number of unreported diseases is significantly higher, since a laboratory report is not requested for every diarrheal disease. Treatments in the hospital: Most diarrheal diseases are treated on an outpatient basis. However, if the disease progresses more seriously and has complications, patients have to go to hospital. In 2008, the Berlin hospitals counted over 1,600 patients with bacterial intestinal diseases.



Diagnostics In order to identify the pathogen, bacterial colonies grown from stool samples are analyzed in the laboratory using various test methods. Since the symptoms and treatment of these intestinal diseases are very similar, the exact identification of the pathogen is often not done.



Diarrheal diseases are usually treated by outpatient doctors. But if life-threatening complications such as hemolytic uremic syndrome (HUS) or thrombocytopenic purpura (TTP) occur, inpatient therapy in the hospital is unavoidable.
Diseases caused by aggressive E. coli bacteria can only be treated symptomatically, for example with drugs that lower the fever or relieve pain. But the fluid and electrolyte balance should also be supported. Yersinia enterocolitica and Campylobacter jejuni are also treated symptomatically; antibiotics are only given in exceptional cases. Although Clostridium difficile diseases are often only triggered by antibiotic therapy, the pathogen can be fought with a special, locally acting antibiotic.
Antibiotics usually have a counterproductive effect on the E. coli bacteria that excrete toxins: Doctors suspect that the drug not only kills the pathogens, but also releases the poison it contains suddenly, which increases the risk of life-threatening complications such as HUS or TTP is increased. The blood cleansing of patients whose kidney function is impaired as a result of HUS must be supported by dialysis. The basis of TTP therapy is plasmapheresis, i.e. the replacement of the patient's blood plasma with healthy donor plasma.

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