Emergence of new Salmonella strains in Hungary

Medical-News: In a recent study conducted by researchers from the HUN-REN Veterinary Medical Research Institute and the National Food Chain Safety Office, a concerning development has been observed in Hungary. For the first time, the Salmonella serovar Ohio has been detected in brown rats and food-producing animals. This Medical News report delves into the findings of this study and its implications for public health and food safety.


Emergence of new Salmonella strains in Hungary

The Rise of Salmonella Ohio
Salmonella is a well-known pathogen, responsible for causing salmonellosis, a common foodborne illness. While many are familiar with the more prevalent serovars like Enteritidis and Typhimurium, the emergence of less common strains, such as Salmonella Ohio, poses new challenges. This study, for the first time, reports the presence of Salmonella Ohio in Hungary, detected in brown rats (Rattus norvegicus) and various food-producing animals.
 
The research team, led by Dr Ama Szmolka from the HUN-REN Veterinary Medical Research Institute, along with collaborators from the National Food Chain Safety Office, collected samples from 92 brown rats captured across different sites in Hungary. These rats are particularly significant from an epidemiological standpoint, as they are known reservoirs for numerous zoonotic pathogens, including various strains of Salmonella.
 
The Spread Among Brown Rats and Food-Producing Animals
The study revealed that Salmonella Ohio was present in 4.3% of the sampled brown rats. Notably, all these positive samples were obtained from rats captured at the same zoological garden. This low prevalence is similar to findings from other studies on urban rats, where Salmonella prevalence typically ranges from 0.5% to 1.4%. However, in environments like livestock farms and wet markets, where rats have close contact with animal feed and meat products, the prevalence can soar as high as 10% to 49%.
 
Interestingly, while Salmonella Ohio was found in brown rats, the researchers did not detect it in other animal species living in close proximity to the rat capture sites. This suggests that while rats may carry this pathogen, its transmission to other species may be limited by factors such as host genetics, microbiota composition, and bacterial diversity.
 
The presence of Salmonella Ohio was also confirmed in various food-producing animals, albeit at a low prevalence. The study found the pathogen in broiler chickens, fattening turkeys, geese, and swine. These findings are concerning as they suggest that Salmonella Ohio could potentially spread through the food chain, posing a risk to human health.
 
Unique Phenotypic Features
One of the significant findings of the study was the identification of unique phenotypic characteristics in the Salmonella Ohio strains isolated from rats. While typical Salmonella strains form black-centered colonies on selective XLD agar plates and crimson colonies on Rambach agar plates, the Salmonella Ohio strains from rats exhibited a pale pink colorat ion on Rambach agar. This atypical colony appearance could be due to mutations in the genes responsible for propylene glycol metabolism, which is used as a carbon source in Rambach agar. This deviation from the norm highlights the genetic diversity within the Salmonella Ohio strains and suggests potential adaptations to their hosts or environments.
 
Genomic Insights: Virulence and Antimicrobial Resistance
To gain a deeper understanding of the pathogenic potential and antibiotic resistance of these strains, the researchers conducted a comprehensive genomic analysis. Five representative strains from brown rats, broiler chickens, fattening turkeys, geese, and swine were selected for whole-genome sequencing.
 
The results revealed that 76.4% of the virulence and antimicrobial resistance genes identified were conserved across the Salmonella serovars Ohio, Infantis, Enteritidis, and Typhimurium. This suggests that these genes are widespread among different Salmonella serovars and may not be unique to Salmonella Ohio.
 
However, the study also found that certain virulence genes typically associated with Salmonella infection were absent in the Salmonella Ohio strains. These included genes involved in the Type III Secretion Systems (T3SS-1 and T3SS-2), which are crucial for Salmonella's ability to infect host cells.
 
Moreover, the study found that the Hungarian Salmonella Ohio strains lacked plasmid-encoded antibiotic resistance genes, making them susceptible to the antibiotics tested. This contrasts with reports from other countries where Salmonella Ohio strains have been found to carry multidrug-resistant plasmids. The absence of such resistance in the Hungarian strains suggests that this serovar may be relatively new to the region and has not yet acquired resistance through exposure to local farming practices and antibiotics.
 
Phylogenetic Analysis: A Closer Look at Strain Relationships
The researchers also conducted a phylogenetic analysis to determine the genetic relatedness of the Hungarian Salmonella Ohio strains with those from other regions. The analysis revealed that the strains from brown rats and poultry in Hungary were closely related and clustered together with Salmonella Ohio strains isolated from aquatic environments in other countries. This suggests that the strains found in Hungary may have originated from or been influenced by aquatic sources, potentially introduced into the environment through water contaminated with these pathogens.
 
The close genetic relationship between rat and poultry strains raises concerns about the potential for cross-species transmission and the role of rats in spreading this pathogen to food-producing animals. The study emphasizes the need for ongoing surveillance and monitoring of Salmonella in both wild and domestic animal populations to prevent the spread of this emerging pathogen.
 
Conclusion: A Call for Vigilance
The emergence of Salmonella Ohio in Hungary is a reminder of the dynamic nature of bacterial pathogens and the constant threat they pose to public health. While the prevalence of this serovar in Hungary is currently low, the study's findings highlight the importance of vigilant monitoring and control measures. The unique phenotypic features and genomic characteristics of the Hungarian Salmonella Ohio strains suggest that this pathogen is still adapting to its environment and hosts. Therefore, there is a window of opportunity to prevent its spread through targeted interventions.
 
The study findings were published in the peer-reviewed International Journal of Molecular Sciences.
https://www.mdpi.com/1422-0067/25/16/8820
 
For the latest on Salmonella research, keep on logging to Thailand Medical News.
 
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