How do multidrug-resistant organisms (MDRO) arise?

Each human being is constantly in contact with a huge variety of bacteria with which their body’s immune system has to cope. Bacteria are not necessarily damaging to health. However a few of them – those known as pathogenic bacteria – can cause infections which constitute a health risk. Certain strains of streptococci, staphylococci, legionellae and salmonellae are known to be capable of causing severe infections especially in immunocompromised people. Such bacterial infectious diseases are usually treated with antibiotics.

Killing bacteria with the help of antibiotics

The discovery of antibiotics is among the most important developments in the history of medicine. In 1928 the bacteriologist Alexander Fleming discovered by coincidence that a mould fungus produced a substance that was deadly to several types of bacteria. He called the substance penicillin. Since then numerous other antibiotics have been developed with different active agent classes. A distinction is made between antibiotics which are only effective against certain pathogens and so-called broad spectrum antibiotics which act against several pathogens. For a long time it was assumed that, because of this effective treatment option, bacterial infections were no longer a problem. Now, however, some types of bacteria are demonstrating resistance to certain antibiotics. That means these antibiotics are not an effective treatment and the infection can continue to spread within the patient’s body.

Mechanisms of resistance development

Bacteria multiply by dividing into two.  Some species double their population size in 20 minutes. In this process mutations happen repeatedly by chance. These mutations can include genes that make the bacterium resistant to antibiotics. If antibiotics are used again, only the resistant bacteria survive to reproduce. This leads to selection and after a while the entire population consists of resistant bacteria. When the bacteria are resistant to several different types of antibiotic they are said to be multidrug-resistant (MDR). The genetic mutation can happen within a person’s body. Alternatively it can happen somewhere else, such as in water or on foods, which means the resistant bacteria are transferred from outside.


Multidrug-resistant pathogens are leading to more nosocomial infections

Antibiotic resistant pathogens now represent a major health problem. In hospitals and care homes, in particular, they spread ever further in spite of improved hygiene measures. The fatal problem is that these are places where many immunocompromised people live close together and where antibiotics are used regularly, encouraging more resistance to develop. It is thought that about 400,000 - 600,000 nosocomial infections occur in Germany every year leading to 10,000 – 15,000 deaths. According to data from the antibiotic resistance surveillance (ARS) database at the Robert Koch Institute, about 30,000 of these infections are due to multidrug-resistant pathogens – and this number is on the increase.1

The occurrence of antibiotic resistance has been recorded systematically for a number of years. This means it is now known which multidrug-resistant pathogens are most common and which antibiotics are no longer effective against them. One well-known multidrug-resistant bacterium is MRSA (methicillin-resistant Staphylococcus aureus). It often colonises the skin or mucous membranes. Many strains are now resistant not only to beta lactam antibiotics but also to other antibiotic classes. The result is that sepsis (an infection of the bloodstream) caused by the resistant strain of Staphylococcus aureus is twice as likely to be deadly as sepsis caused by sensitive strains.²

And there are more pathogens that are less well-known. Severe life-threatening infections can result not only from MRSA but also from such pathogens as klebsiellae, pseudomonads (Pseudomonas aeruginosa), enterococci (vancomycin-resistant Enterococcus faecium and Enterococcus faecalis (VRE)) and certain clostridiae.

There are various ways to combat this disturbing development. In recent years, people have worked successfully to improve hygiene in hospitals and care homes. KRINKO, the commission for hospital hygiene and infection prevention at the Robert Koch Institute, makes recommendations on preventing nosocomial infections. These include organisational and structural ways to comply with hygiene standards such as water filters, instructions on the reprocessing of medical devices, etc.

In addition, efforts are in progress at national level to use antibiotics in a more targeted and sparing way – in other words, using antibiotics only when they are really indicated and then paying increased attention to correct usage.

1Gastmeier P, Fätkenheuer G. Dtsch Ärztebl 2015; 112(15): A-674 / B-576 / C-559. ( infektionskrankheiten/mrsa.html