In December 2023, the study "Epidemiological cut-off values for non-O1/non-O139 Vibrio cholerae disc diffusion data generated by standardised methods" was published as part of a transnational scientific cooperation. AGES was involved in this project through Florian Heger and Sonja Pleininger (Public Health Division, Institute of Medical Microbiology and Hygiene).
Together with scientists from the Medical University of Vienna and the University of Krems, from Ireland, France and Germany, they investigated the growth of non-O1/non-O139 Vibriocholerae bacteria under the influence of different antibiotics.
Based on the bacterial growth, epidemiological cut-off values (ECOFFs) were defined for the sensitivity of the bacteria to 19 different antibiotics. These values are subsequently submitted to the Clinical Laboratory Standards Institute (CSLI) and the European Committee for Antimicrobial Susceptibility Testing (EUCAST). The data obtained will serve as a basis for further studies, so that they can make specific statements regarding the clinical therapeutic success of antibiotics for infections with non-cholera vibrios.
Non-cholera vibrios
Vibrio cholerae are gram-negative bacteria from the vibrio group that occur naturally in salt and fresh water. Serotypes O1 and O139 produce toxins and can therefore cause cholera in humans. Non-O1/non-O139 serotypes do not produce cholera toxin and therefore do not cause cholera, but can lead to other infections (wound infections, ear infections, etc.).
Antibiotic resistance
Bacteria can develop resistance to antibiotics, making them less sensitive to these substances. Pronounced resistance means that antibiotics can no longer be used against bacterial infections or can only be used to a limited extent. Until now, the testing of antibiotics against non-O1/non-O139 Vibriocholerae could only be based on non-species-specific threshold values.
The aim of the present study was therefore to determine species-specific epidemiological cut-off values (ECOFFs) for non-O1/non-O139 Vibriocholerae strains.
Although ECOFFs do not yet provide any information on the efficacy of antibiotics in the clinical treatment of infections, they do provide the basic possibility of distinguishing resistant strains from so-called wild-type strains (i.e. without acquired resistance).
Agar diffusion tests and epidemiological thresholds
Agar diffusion tests were used to create these ECOFFs. In agar diffusion tests, the growth of bacteria is observed in the presence of antibiotic-soaked filter paper discs. If there is no resistance, a zone forms around the antibiotic platelet in which no growth takes place. The size of this growth-free zone around the antibiotic platelet, known as the inhibition zone, can be used to determine the threshold value.
In the present study, 147 non-O1/non-O139 Vibriocholerae isolates from waters in France and Austria were used and 19 different antibiotics were tested. Four European laboratories, in France, Germany and Austria, including the Institute of Medical Microbiology and Hygiene of AGES, carried out the corresponding agar diffusion tests and measurements of the inhibition zones.
Finally, ECOFFs for the 19 antibiotics tested were calculated from the combined data of all laboratories. These minimum zone sizes serve as epidemiological threshold values: anything smaller than this zone size indicates resistance to the tested substance.
Outlook
The ECOFFs determined are submitted to the Clinical Laboratory Standards Institute (CSLI) and the European Committee for Antimicrobial Susceptibility Testing (EUCAST). With the inclusion of further data and parameters, clinical threshold values are to be defined from the ECOFFs, which will then enable specific statements to be made in future regarding the clinical therapeutic success of antibiotics in infections with non-cholera vibrios.
The study is available at: Epidemiological cut-off values for non-O1/ non-O139 Vibrio cholerae disc diffusion data generated by standardised methods - PubMed (nih.gov)