Complement is one of the most important parts of the innate immune system. Some bacteria can gain resistance against the bactericidal action of complement by decorating their outer cell surface with lipopolysaccharides (LPSs) containing a very long O-antigen or with specific outer membrane proteins. Additionally, the presence of sialic acid in the LPS molecules can provide a level of protection for bacteria, likening them to human cells, a phenomenon known as molecular mimicry. Salmonella O48, which contains sialic acid in the O-antigen, is the major cause of reptile-associated salmonellosis, a worldwide public health problem. In this study, we tested the effect of prolonged exposure to human serum on strains from Salmonella serogroup O48, specifically on the O-antigen length. After multiple passages in serum, three out of four tested strains became resistant to serum action. The gas-liquid chromatography/tandem mass spectrometry analysis showed that, for most of the strains, the average length of the LPS O-antigen increased. Thus, we have discovered a link between the resistance of bacterial cells to serum and the elongation of the LPS O-antigen.

Non-typhoidal Salmonella (NTS) are globally distributed zoonotic pathogens of major concern within the One Health–One Biofilm framework. Fluoroquinolone-resistant Salmonella strains are included by the World Health Organization (WHO) in the Bacterial Priority Pathogens List as high-risk agents. A key virulence determinant of Salmonella is its ability to form biofilms, which may display multidrug-resistant (MDR) characteristics and contribute to bacterial persistence and treatment failure. Animals, particularly poultry and reptiles, represent important reservoirs of Salmonella, and reptile-associated salmonellosis (RAS) may manifest as extraintestinal infections in humans. In the post-antibiotic era, there is an urgent need to identify effective alternatives to conventional therapies. This review summarizes current knowledge on Salmonella biofilms, with particular attention to their MDR potential, and discusses possible strategies for their prevention and eradication, including specific immunoprophylaxis, bacteriophage therapy, and alternative antimicrobials. The promising antimicrobials include plant-based compounds/extracts, bacteriocins, fatty acids, and synthetic/semi-synthetic substances. The integration of vaccination, phage therapy, and novel anti-biofilm compounds may provide a sustainable alternative to antibiotics in controlling Salmonella infections and aligns with the principles of the One Health approach.

Of food poisoning. One of the reservoirs of Salmonella are reptiles, which are increasingly kept as pets. Most reptiles are asymptomatic carriers of Salmonella. These strains, isolated from reptiles, can cause serious infections, especially in infants, young children and people with immunodeficiencies. The disease called reptile-associated salmonellosis (RAS) may manifest with bloody diarrhea, meningitis, and arthritis, and consequently can cause bacteremia and sepsis. Among the strains described in the literature, Salmonella strains possessing the O48 antigen are an important group. Lipopolysaccharide (LPS) of Salmonella O48 contains sialic acid (NeuAc) in an O-specific-chain. LPS containing NeuAc exhibits antigenic similarity to antigens found in the human body, including blood serum, and therefore is correlated with the occurrence of the dangerous phenomenon of molecular mimicry. Bacteria containing NeuAc in their outer structures can evade the immunological response of the host, which significantly increases their virulence. Most data about RAS come from the USA, but in recent years cases from European countries are more frequent in the literature. Unfortunately, the occurrence of RAS in Poland has not been monitored so far. There is also no campaign to inform the public about the health risks connected with contact of people with reptiles.

Salmonellosis associated with reptiles is a well‐researched topic, particularly in China and the United States, but it occurs less frequently in Europe. The growth of the human population and changes in the environment could potentially increase the interaction between humans and free‐living reptiles, which are an unidentified source of Salmonella species. In this study, we sought to explore this issue by comparing the microbiota of free‐living European grass snakes, scientifically known as Natrix natrix , with that of captive banded water snakes, or Nerodia fasciata . We were able to isolate 27 strains of Salmonella species from cloacal swabs of 59 N. natrix and 3 strains from 10 N. fasciata . Our findings revealed that free‐living snakes can carry strains of Salmonella species that are resistant to normal human serum (NHS). In contrast, all the Salmonella species strains isolated from N. fasciata were sensitive to the action of the NHS, further supporting our findings. We identified two serovars from N. natrix : Salmonella enterica subspecies diarizonae and S. enterica subspecies houtenae . Additionally, we identified three different virulotypes (VT) with invA , sipB , prgH , orgA , tolC , iroN , sitC , sifA , sopB , spiA , cdtB and msgA genes, and β‐galactosidase synthesised by 23 serovars. The identification of Salmonella species in terms of their VT is a relatively unknown aspect of their pathology. This can be specific to the serovar and pathovar and could be a result of adaptation to a new host or environment.

The One Health approach emphasizes the importance of zoonoses due to their pandemic potential, highlighting the need to characterize emerging bacterial pathogens across animal reservoirs. Non-typhoidal Salmonella (NTS) species are among the most common zoonotic agents and can be transmitted by various reservoirs, including reptiles. Both direct and indirect contact with reptiles may result in Reptile-Associated Salmonellosis (RAS), which mainly affects children, immunocompromised individuals, pregnant women, and the elderly. This study aimed to isolate and characterize the Gram-negative intestinal microbiota from free-living snakes in Poland (Natrix natrix, Natrix tessellata, Coronella austriaca, Zamenis longissimus, and Elaphe dione) and to determine the prevalence and virulence potential of Salmonella. Using MALDI-TOF Mass Spectrometry, 432 isolates were identified. Serological analysis of 62 Salmonella isolates revealed 10 distinct O-antigen groups, and rare serovars O:38, O:48, O:57 and others were confirmed. Salmonella isolates were tested for antibiotic susceptibility and resistance to Human Serum; most isolates survived exposure to serum while remaining susceptible to antibiotics. One isolate was classified as multidrug-resistant (MDR), showing resistance to amoxicillin/clavulanic acid, ampicillin, cefuroxime, cephalexin, tigecycline, and fosfomycin. These findings demonstrate that wild snakes in Poland can act as reservoirs of pathogenic and zoonotic Salmonella, emphasizing their epidemiological significance in natural ecosystems.

Salmonella is a globally important pathogen and one of the World Health Organization and One Health priority organisms. Reptiles represent environmental reservoirs of Salmonella serovars that can cause reptile-associated salmonellosis (RAS) in humans. Due to distinct biochemical features and uncommon O and H antigen variants, reptile-associated isolates may be difficult to identify using standard microbiological diagnostics. This study analyzed 62 Salmonella isolates obtained from wild and kept snakes in Poland. Samples originated from Natrix natrix, N. tessellata, Coronella austriaca, Zamenis longissimus, Elaphe dione and Nerodia fasciata species. Serovar prediction using SeqSero1.2 was compared with classical slide agglutination. Seventeen serovars were confirmed, with S. enterica subsp. diarizonae (IIIb) 38:r:z being the most frequent. For seven isolates, molecular and serological results were inconsistent. Among three isolates from Coronella austriaca predicted as IIIb 38:z₁₀:z₅₀, three distinct second-phase flagellar phenotypes were detected. Slide agglutination confirmed the presence of serovar 38:z₁₀:z₆, which has not been previously listed in the White–Kauffmann–Le Minor scheme or described in the scientific literature. The findings highlight the utility of genetic serovar prediction while emphasizing the need for continuous validation, particularly for the identification of rare or atypical Salmonella serovars associated with reptiles.