A newly published scientific study in the U.S. (Siceloff et al., 2021) demonstrated the effectiveness of new assay technologies, based on CRISPR, to detect certain antibiotic-resistant subpopulations of Salmonella in animals. While highlighting the unsuitability, in this regard, of conventional systems.
Indeed, new molecular identification techniques allow for more accurate screening than classical culture methods, better characterizing precisely those groups that may contribute to the spread of antimicrobial resistance (AMR). (1)
Salmonella and antibiotic resistance
Salmonella
is one of the most prevalent pathogenic bacteria-even in Europe, as shown by the recent ECDC and EFSA report on zoonoses (2020)-among farm and companion animals, wild animals and cold-blooded animals as well. Some of its strains, in addition to causing disease outbreaks even in humans, are vectors of antimicrobial resistance. (2)
Antimicrobial resistance is increasingly prevalent, in Salmonella as in Campylobacter, with increasing difficulties in using classical drug treatments. (3) The misuse of antibiotics in medicine and veterinary medicine has led to a general increase in the phenomenon on a global scale, although European authorities (ECDC, EFSA, EMA, 2021) have recently observed a slight reduction in the trend.
Salmonella serotypes
A serotype (or serovar) is a microbial subspecies that is characterized by a specific antigen, to which a specific antibody will be able to respond. The species Salmonella enterica is known for its many serotypes and the various diseases that can develop in humans. (4)
Reading serotype is prevalent in livestock farms, especially among cattle and turkeys. On cattle, in particular, this serotype develops antimicrobial resistance with high frequency-due in part to recent widespread outbreaks in North America-and it is even more necessary to find systems that facilitate its identification. (5)
Salmonella, CRISPR-SeroSeq Technology.
Surveillance and isolation of Salmonella generally depend on the culture method used. This approach currently allows for the identification of a few serotypes-primarily, those most abundant within the population analyzed-and often does not consider minority ones, which nevertheless operate as reservoirs of AMR. (6)
CRISPR(Clustered Regularly Interspaced Short Palindromic Repeats, also used for genomicediting, as noted)-specifically, CRISPR-SeroSeq-is a technology that instead allows the identification of frequencies related to multiple serotypes in a single sample. And it has therefore also been tested to identify Salmonella serotypes. (7)
CRISPR-SeroSeq, study results
Analysis of populations isolated from bovine matrices identified that two-thirds of the Salmonella-positive samples tested contained numerous serotypes including Reading (although present in the minority, probably because it was uncompetitive).
CRISPR-SeroSeq technology was indeed found to be able to more accurately and precisely classify the Salmonella populations present and to detect numerous serotypes, even those that are difficult to detect such as the Reading serotype, especially with traditional isolation methods and related AMR strains.
Treatment with antibiotics has shown variation in the development and behavior of isolated populations, which is particularly useful in identifying the most sensitive serotypes and strains and those most resistant to various treatments.
Interim conclusions
The functionality of the new technology for classifying Salmonella species in animal matrices is certainly a useful new tool for more effective and accurate screening not only of the microorganism, but of all antimicrobial resistance carriers.
The system will also need to be tested in other contexts with a view to its validation. Its use combined with other technologies (e.g., qPCR) could further improve the efficiency of the system to thus identify resistance traits of all serotypes in a population.
Dario Dongo and Andrea Adelmo Della Penna
Notes
(1) Siceloff et al. (2021). Antimicrobial resistance hidden within multiserovar Salmonella populations. Antimicrobials Agents and Chemotherapy 65(6):e00048-21, https://doi.org/10.1128/AAC.00048-21
(2) Silvia Bonardi. Salmonella and antibiotic resistance. GIFT(Great Italian Food Trade) 29.12.18, https://www.greatitalianfoodtrade.it/salute/salmonella-e-antibiotico-resistenza
(3) Marta Strinati. Salmonella and Campylobacter increasingly resistant to antibiotics. GIFT(Great Italian Food Trade) 09.4.21, https://www.greatitalianfoodtrade.it/sicurezza/salmonella-e-campylobacter-sempre-più-resistenti-agli-antibiotici
(4) Hannemann et al. (2017). Salmonella enterica serovar-specific transcriptional reprogramming of infected cells. PLoS Pathogens 13(7): e1006532, https://doi.org/10.1371/journal.ppat.1006532
(5) Miller et al. (2020). Emergence of a Novel Salmonella enterica Serotype Reading Clonal Group Is Linked to Its Expansion in Commercial Turkey Production, Resulting in Unanticipated Human Illness in North America. Clinical Science and Epidemiology 5(2):e00056-20, https://doi.org/10.1128/mSphere.00056-20
(6) Shah et al. (2017). Population dynamics and antimicrobial resistance of the most prevalent poultry-associated Salmonella serotypes. Poultry Science 96:687-702, https://doi.org/10.3382/ps/pew342
(7) Thompson et al. (2018). High-resolution identification of multiple Salmonella serovars in a single sample by using CRISPR-SeroSeq. Appl Environ Microbiol 84:e01859-18, https://doi.org/10.1128/AEM.01859-18
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
Graduated in Food Technologies and Biotechnologies, qualified food technologist, he follows the research and development area. With particular regard to European research projects (in Horizon 2020, PRIMA) where the FARE division of WIISE Srl, a benefit company, participates.
