Institute of Bacterial Infections and Zoonoses (IBIZ)

Antibiotic resistance is an increasing challenge due to the increasing limitation of treatment success of bacterial infections. Bacteria that are not killed by antibiotics can develop resistances (acquired or secondary antibiotic resistance). It can be assumed that any use of an antibiotic will encourage the development of resistance. However, there are also bacteria that are insensitive to certain antibiotics due to natural, pre-existing resistance mechanisms (so-called intrinsic or primary antibiotic resistance, e.g. ampicillin in Klebsiella pneumoniae, tetracycline in Proteus mirabilis). Multi-resistance is resistance of a germ to several classes of antibiotics simultaneously.

The laboratory for AMR at IBIZ is particularly active in achieving a high quality of test results. Testing for resistance is routinely performed using internationally recognized quantitative methods. The quality of the results is guaranteed by participation in national and international interlaboratory comparisons such as proficiency testing for MIC determination by the BVL and sensitivity testing to antibiotics by INSTAND e.V. A variety of modern molecular biological methods such as PCR and WGS are available for the targeted epidemiological investigation of resistance.

IBIZ is involved in numerous national and international studies on antibiotic resistance. IBIZ scientists also advise policy makers and public animal health services. The main focus of the work is the investigation of antibiotic resistance in zoonotic pathogens and other pathogens as far as they pose a threat to veterinary and public health. For this purpose, the laboratory performs resistance testing of isolates originating from animals, food and feed, and the environment.

The laboratory researches focuse on different aspects of antibiotic-resistant pathogens, their spread, control and prevention strategies under Animal Health Law (AHL) and Official Controls Regulation (OCR). The focus is on Campylobacter, Staphylococcus and Streptococcus.

• Phenotypic antibiotic resistance testing
• Molecular biology of antibiotic resistance
• Research and consulting
• The investigation of the molecular basis of increasing resistance of pathogens
• The development of diagnostic methods to determine the emergence of antimicrobial resistance
• Transfer and validation of these new developed methods in practice

In vitro susceptibility testing plays an important role in this process. Sensitivity testing can be performed qualitatively, semi-quantitatively or by using molecular biological methods.

The results of qualitative methods are usually indicated as one of the following: "sensitive (S)", "intermediate (I)" and "resistant (R)". The widely used classical agar diffusion method (Kirby-Bauer test) can be used for fast growing bacteria. Here, antibiotic-impregnated platelets are placed on agar media that have been inoculated with the pathogen to be tested.

Semiquantitative methods determine the minimum concentration of a substance necessary to inhibit the growth of a specific pathogen in vitro. This minimum inhibitory concentration (MIC) is expressed as a numerical value, which is then assigned to one of three categories (S), (I) or (R). The broth-dilution method is the gold standard in most reference laboratories worldwide.

An alternative method for detection MIC uses a polyester strip (E-test) impregnated with a concentration gradient along its entire length.

Sensitivity testing can be performed using an automated computerized system. The sample data are recorded electronically and the corresponding antibiotic test card is assigned. Nucleic acid-based methods involve molecular biology procedures similar to those used for pathogen identification and to detect known resistance genes or mutations by PCR and WGS. Although a number of such genes are known, their presence does not automatically imply in vivo resistance. Also, because new mutations or other resistance genes may be present, their absence does not guarantee antibiotic susceptibility. For these reasons, routine phenotypic susceptibility testing methods remain the standard approach to assess bacterial susceptibility to antimicrobial drugs.