The Impact of Overstocking and Negative Energy Balance on Quantitative Measurement of Non-typhoidal Salmonella in Periparturient Dairy Cattle

Dynamics of Salmonella Dublin infection and antimicrobial resistance in a dairy herd endemic to salmonellosis

Salmonella Dublin is a serovar that causes severe infections and cattle. Despite the importance of this agent, research on achieving its elimination from dairy farms is limited, which complicates risk mitigation and control efforts. This study thus aimed to assess the prevalence of S. Dublin on a farm with a history of outbreaks, to understand the dynamics of the infection, characterize the antimicrobial resistance of the isolates, and evaluate their genetic similarity. Multiparous cows in the postpartum phase are nearly five times more likely to shed Salmonella sp. A total of 39 cases of fatal septicemic salmonellosis caused by S. Dublin were confirmed in calves aged 3-5 months. Antimicrobial susceptibility was evaluated in 45 strains of S. Dublin, with 48.9% of the isolates classified as multidrug resistant, including resistance to penicillin (48.9%), tetracyclines (42.2%), and fluoroquinolones (33.3%). Seven multidrug-resistant isolates were selected for genomic sequencing. Among the resistance determinants identified, a mutation in the gyrA gene, present in all sequenced isolates, was notable. Analyses of cgMLST and SNPs revealed that the isolates from healthy animals were closely related to those found in animals with confirmed cases of S. Dublin, confirming that the agent was circulating among healthy animals across various categories. A high similarity was also found between the isolates in this study and strains causing salmonellosis in humans in Brazil, thus reinforcing the zoonotic nature and possible epidemiological link between cattle, and the occurrence of this disease in humans.

Molecular characterization of antibiotic resistant Salmonella enterica across the poultry production chain in Costa Rica: A cross-sectional study

Antibiotic resistant Salmonella enterica are on the increase, worldwide. Given the scarcity of data, this study aimed to investigate its occurrence, virulence, and antibiotic resistance in Costa Rica's food chain. In total, 65 chicken meat- and 171 chicken caecal samples were collected and examined for Salmonella. High frequencies of Salmonella were found in chicken meat (58.5 %, n/N = 38/65) and poultry farms (38.0 %, n/N = 65/171). The majority of Salmonella from chicken meat (89.5 %, n/N = 34/38) and caecum samples (93.6 %, n/N = 59/63) exhibited multidrug resistance (MDR). Serovar Infantis was the most prevalent (94 %, n/N = 67/71), followed by serovars Anatum and Kentucky (3 %, n/N = 2/71). A pESI-like plasmid (92 %, n/N = 65/71) containing virulence and resistance markers was found in S. Infantis. Given the high prevalence of MDR Salmonella, this study emphasizes the need to enhance surveillance systems for foodborne pathogens and antimicrobial resistance in Costa Rica's food production chain.

Prevalence and genetic characteristics of Salmonella enterica serovar Meleagridis from animals and humans

Salmonella enterica serovar Meleagridis (S. Meleagridis) is a non-typhoidal Salmonella serotype commonly found in food and humans. In this study, we investigated 61 Chinese S. Meleagridis isolates from various sources, predominantly from pigs and pig products. Additionally, the serotype was also identified in samples from human infections. Whole-genome sequencing analysis of these isolates, combined with 10 isolates from other countries, demonstrated that the Chinese isolates formed a distinct Cluster C, further divided into two subclusters (Cluster C-1 and Cluster C-2) based on cgMLST analysis. CRISPR typing divided the 61 isolates into three CRISPR types (MCT1, MCT2, MCT3), belonging to Cluster I (96.7%, 59/61) and Cluster II (3.3%, 2/61), which corresponded to Cluster C-2 and Cluster C-1, respectively. Among the 48 identified spacers, the spacer SoeB5 was the only target differentiating MCT1 and MCT2 isolates of Cluster I. MelB12 and MelB13, identified in US and Denmark isolates, were not found among the 61 Chinese isolates. Examination of antimicrobial resistance gene profiles and their genetic contexts uncovered the presence of IncR plasmids in 43 (70.5%, 43/61) isolates within Cluster C, conferring resistance to tetracycline and trimethoprim/sulfamethoxazole. Homology analysis of spacers showed that 12 spacers exhibited similarity to sequences in phages or plasmids. Additionally, five spacers showed homology to sequences in plasmids from other Salmonella serotypes, suggesting their potential role in helping S. Meleagridis resist against Salmonella isolates carrying similar plasmids. The comprehensive analysis of CRISPR, cgMLST, and antimicrobial resistance in S. Meleagridis highlights the pig reservoir as a crucial factor in the evolution and transmission of this serotype to humans.

Semi-Quantitative Biosecurity Assessment Framework Targeting Prevention of the Introduction and Establishment of Salmonella Dublin in Dairy Cattle Herds

An increasing average herd size and complexity in farm structures call for a higher level of biosecurity. It can reduce the risk of introducing and establishing pathogens with multiple-pathway and indirect spread mechanisms, such as Salmonella Dublin, a pathogen with an increasing occurrence in dairy cattle farms across different countries and continents. Therefore, this study aimed to use existing knowledge to develop a framework with a supporting tool allowing for a time-efficient, yet comprehensive, assessment of biosecurity measures that can help prevent the introduction and establishment of S. Dublin in dairy herds. Based on the literature review, a seven-step biosecurity assessment framework was developed and evaluated in collaboration with biosecurity experts. The resulting framework includes a weighted semi-quantitative assessment method with a scoring guide in an electronic supporting tool for 12 biosecurity sections assessed through on-farm observations and farmer interviews. The framework and tool provide a novel approach to comprehensively assess the overall (mainly external) on-farm biosecurity level by a trained biosecurity assessor. They can be used for systematic data collection in epidemiological studies on risk factors for the introduction and establishment of S. Dublin in dairy farms. Preliminary interrater reliability testing indicated moderate reliability between assessors with varying biosecurity skills.

Detection of Virulence and β-lactamase resistance genes of non-typhoidal Salmonella isolates from human and animal origin in Egypt "one health concern"

BACKGROUND

Non-typhoidal Salmonella (NTS) is a major foodborne zoonotic pathogen worldwide. In the current study, Various NTS strains were isolated from (cows, milk and dairy products in addition to humans) in New Valley and Assiut Governorate, Egypt. NTS were firstly serotyped and tested by antibiotic sensitivity test. Secondly, some virulence genes and Antibiotic resistance genes have been identified by using PCR. Finally, Phylogenesis was performed depending on the invA gene, for two S. typhimurium isolates (one of animal origin and the other of human origin for evaluating zoonotic potential).

RESULTS

Out of 800 examined samples, the total number of isolates was 87 (10.88%), which were classified into 13 serotypes, with the most prevalent being S. Typhimurium and S. enteritidis. Both bovine and human isolates showed the highest resistance to clindamycin and streptomycin, with 90.80% of the tested isolates exhibiting MDR. The occurrence of the invA gene was 100%, while 72.22%, 30.56%, and 94.44% of the examined strains were positive for stn, spvC, and hilA genes, respectively. Additionally, blaOXA-2 was detected in 16.67% (6/ 36) of the tested isolates, while blaCMY-1 was detected in 30.56% (11of 36) of the tested isolates. Phylogenesis revealed a high degree of similarity between the two isolates.

CONCLUSIONS

The high occurrence of MDR strains of NTS in both human and animal samples with high degree of genetic similarity, shows that cows, milk and milk product may be a valuable source of human infection with NTS and interfere with treatment procedures.