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Background: Salmonella enterica subsp. enterica serovar Saintpaul (antigenic formula 1,4,[5],12:e,h:1,2) is a serovar of the O:4 (B) serogroup. In 1940, serovar Saintpaul was first isolated from turkey in US. In the U.S. it ranks among the top 15 serovars causing human salmonellosis. In Oceania, this serovar is the fourth most common serovar in humans. In addition, S. Saintpaul is commonly reported in Europe and outbreaks have been linked to internationally imported food (e.g., from Mexico) Enter-Net surveillance data from European national reference centers revealed serovar Saintpaul as the fourth most prevalent Salmonella serovar (1.6%) in human isolates during Q4 2006, marking a notable increase in its role as a cause of human salmonellosis compared to previous years. Subsequent surveillance showed declining prevalence, with the serovar accounting for 1.2% and 0.6% of human Salmonella infections in Q1 2007 and Q1 2008, respectively. Salmonella Saintpaul was frequently listed as top 20 Salmonella serovars in humans in Oceania and North America. A case of testicular seminoma complicated by serovar Saintpaul-induced testicular abscess has been reported.

NCBI PD link for serovar Saintpaul: https://www.ncbi.nlm.nih.gov/pathogens/isolates/#(taxgroup_name:%22Salmonella%20enterica%22)%20AND%20computed_types:(%22serotype=Saintpaul%22)

Genetic characteristics: Chen et al. found that serovar Saintpaul appeared to be polyphyletic with four distinct phylogenetic groups identified. Within serovar Saintpaul, the comparative genomic analysis revealed 384 and 619 genes enriched in isolates from 5 human-associated (HA) and 4 non-human-associated (NHA) SNP clusters, respectively, that showed the strongest association with their isolation sources. This included five known HA-linked virulence genes located on Gifsy-1/Gifsy-2 prophages. Additionally, premature stop codons were more prevalent in 3 HA and 7 NHA genes. Cell culture experiments with representative strains from 4 HA and 3 NHA clusters found no increased invasion or intracellular survival capability in HA SNP clusters. However, the presence of sodCI (encoding a superoxide dismutase)—detected in 4 HA and 1 NHA clusters—correlated with enhanced survival in macrophage-like cells. In the study of worldwide population dynamics of serovar Saintpaul, Panzenhagen et al. found a total of 49 sequence types (STs), with ST-50 (787 genomes) and ST-27 (634 genomes) being the most common. All clinical isolates from South America, including PP_BR059 (isolated from a hospitalized patient in Ceará, Brazil), belonged to ST-50. Antimicrobial resistance (AMR) analysis indicated that 60% of Salmonella Saintpaul genomes had no resistance, while ST-27 contained the highest number of AMR strains. More specifically, among the 1,954 serovar Saintpaul isolates analyzed, 391 (20%) exhibited resistance genes associated with a multidrug-resistant phenotype. Additionally, seven isolates harbored the mcr-1 gene, while 17 isolates carried the CTX-M gene. They also identified separate evolutionary lineages within ST-50 and ST-27. PP_BR059 showed reduced macrophage invasion (3.82%) but notably higher survival rates inside cells at both 2 hours (68.72%) and 20 hours (25.68%) post-infection. Similarly, serovar Saintpaul carrying both bla_CTX-M-2 and mcr-9.1 isolated in chicken carcass was reported.

In Germany, a clonal line of Salmonella Saintpaul with a multidrug resistant phenotype was found in turkeys and human feces. These isolates exhibited resistance (either complete or intermediate) to ampicillin, amoxicillin-clavulanic acid, gentamicin, kanamycin, nalidixic acid, streptomycin, spectinomycin, and sulfamethoxazole, along with intermediate resistance or reduced susceptibility to ciprofloxacin and multiple third-generation cephalosporins (including ceftiofur and cefoxitin). Genotypic analysis revealed a conserved resistance pattern, featuring bla_TEM-1, aadB, aadA2, sul1, and a Ser83→Glu83 mutation in the gyrA gene. Additionally, all isolates carried a chromosomal class 1 integron harboring the aadB-aadA2 gene cassette. In an Ethiopian study, among all tested isolates (n=28), only 17.9% were pan-susceptible, while 82.1% exhibited resistance to one to three antimicrobials. All isolates remained susceptible to gentamicin, trimethoprim-sulfamethoxazole, and trimethoprim. The highest resistance was observed against oxytetracycline (82.2%), followed by chloramphenicol, neomycin, and polymyxin B (3.6% each).

Zwe and Yuk found that pre-treatment of serovar Saintpaul with ceftiofur resulted in enhanced phenotypic resistance to ceftriaxone. However, this exposure paradoxically reduced the bacterium's ability to transfer cephalosporin resistance via conjugative transfer of the bla_CTX-M-65 gene.

Animal reservoir: Unknown, but turkey and swine are likely to be reservoirs for serovar Saintpaul.

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