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PubMed2026

Mobile genetic elements-driven partitions of mega-plasmids resistome in Salmonella Infantis.

Salmonella enterica serovar Infantis (S. Infantis) becomes the primary pathogen among the top Salmonella serotypes, contributing to numerous cases of foodborne illness annually in the United States. S. Infantis infection has spread rapidly worldwide, especially the clones with pESI-like plasmids. However, the underlying mechanisms regarding the transmission of S. Infantis, particularly mobile genetic elements (MGEs), mediated horizontal gene transfer, are limited. The objective of this study was to evaluate the relationship, if any, among MGEs, antibiotic-resistant genes (ARGs), and virulence factors (VFs) within S. Infantis via genomic analysis. A total of 91 S. Infantis complete genomes with high sequencing quality were selected for downstream bioinformatic analysis. The results showed that the majority of VFs were located in the bacterial chromosomes, while most ARGs were carried by S. Infantis mega-plasmids in an MGE-favored manner. Integrons and transposons were closely associated with certain ARGs, but prophages within mega-plasmids displayed a diverse ARG profile. Collectively, MGE-mediated horizontal gene transfer might lead to ARG acquisition by mega-plasmids, subsequently contributing to the resistome of S. Infantis. Our findings provide insights into the development of MGE-associated resistome in S. Infantis that could inform more effective prevention and intervention strategies to control this pathogen, further ensuring public health and safety.IMPORTANCEThe rapid emergence and transmission of antibiotic-resistant foodborne pathogens pose a significant risk to public health, necessitating the discovery of underlying mechanisms to control multidrug-resistant pathogens. Salmonella enterica serovar Infantis (S. Infantis) has become a pathogen of clinical and epidemiological relevance in recent years, ranking as the top prevalent serovar associated with foodborne illnesses and exhibiting resistance to several antibiotics. The current investigation of multidrug resistance (MDR) S. Infantis strains primarily emphasized the presence of mega-plasmids. However, the question of how mega-plasmids contribute to the transmission of antibiotic-resistant genes (ARG) is unaddressed. Utilizing the genomic characterization of S. Infantis complete genomes with high quality, our study revealed that the resistome of S. Infantis mega-plasmids-the primary ARG reservoirs of S. Infantis-followed a specific pattern of mobile genetic elements (MGEs). Monitoring the spread of MGE-carried ARGs within mega-plasmids should be considered in future surveillance.

Interspersed Repetitive Sequences↗
PubMed2026

Molecular characterization of pESI-like megaplasmids in Salmonella Infantis from poultry in Lebanon.

UNLABELLED: Salmonella enterica serovar Infantis has emerged as a globally disseminated multidrug-resistant (MDR) pathogen, largely driven by the spread of the plasmid of emerging Salmonella Infantis (pESI)-like megaplasmid. In our study, we investigated the prevalence, antimicrobial resistance (AMR) phenotypes, and genomic features of S. Infantis isolates collected from poultry farms in Lebanon. A total of 72 isolates were recovered during a nationwide surveillance effort, among which 67 (93%) were MDR based on antimicrobial susceptibility testing (disk diffusion and broth microdilution) results, including resistance to critically important agents such as quinolones, and highly important classes such as tetracyclines and sulfonamides. Whole-genome sequencing was performed on 19 isolates selected through a stratified approach to encompass all identified AMR phenotypes; this analysis revealed a conserved pESI-like backbone together with MDR-associated determinants, including sul1, tet(A), and aadA. Plasmid marker analysis confirmed the presence of pESI in the majority of isolates, with plasmid-associated genes (ardA and trbA) and replicon markers (IncP and IncFIB(pN55391)) among the most prevalent. Comparative plasmid alignments with representative pESI sequences from Italy, Turkey, and the United States revealed strong conservation of the backbone alongside regional variation in AMR gene content. These findings highlight the role of poultry production systems in Lebanon as reservoirs for pESI-like megaplasmids and MDR S. Infantis, underscoring the zoonotic and public health risks posed at the human-animal-environment interface. Strengthened surveillance, antimicrobial stewardship, and biosecurity interventions are urgently needed to mitigate the spread of MDR S. Infantis within agriculture and beyond. IMPORTANCE: The emergence of plasmid of emerging Salmonella Infantis (pESI)-like megaplasmids has transformed Salmonella Infantis into a globally distributed multidrug-resistant (MDR) clone with the capacity to persist in livestock and disseminate resistance genes across ecological boundaries. Our study provides the first genomic characterization of pESI-positive S. Infantis from poultry farms in Lebanon, a region with high antimicrobial usage and limited stewardship frameworks. By integrating phenotypic susceptibility testing and whole-genome sequencing, we demonstrate that Lebanese isolates harbor conserved pESI-like backbone markers together with antimicrobial resistance determinants, aligning them with internationally circulating lineages. Comparative analysis with isolates from Italy, Turkey, and the United States highlights both the evolutionary stability and geographic diversity of pESI. These findings emphasize the urgent need for integrated surveillance and stewardship strategies to curb the spread of MDR S. Infantis and reduce the zoonotic risk at the human-animal-environment interface.

Animals↗
PubMed1979

Bacteriophage typing scheme for Salmonella infantis.

A bacteriophage typing system is described for Salmonella infantis. Nine phages were selected, of which three were isolated from sewage and six from human feces. All except 7 of the 546 strains collected between 1974 and 1978 could be classified into 23 different phage types. The five most common phage types comprised 26, 13, 9, 9, and 9% of all strains, respectively. Strains from humans, animals, food, and water isolated during nine episodes, or from given patients at different intervals of time, belonged to the same phage type.

Bacteriophage Typing↗
PubMed1979

Therapeutical trials with antimicrobial agents and cultured cecal microflora in Salmonella infantis infections in chickens.

The efficacy of short antimicrobial therapy was examined in chicks infected with S. infantis on the day of hatching. An attempt was made to prevent the reappearance of salmonellae by treating the chicks with a culture of cecal microflora to re-establish the normal intestinal flora. The following drugs were used: neomycin/polymyxin, oxytetracyline/neomycin, dihydrostreptomycin, furazolidone, and trimethoprim/sulphadiazine. The oxytetracycline/neomycin therapy was most effective, but reappearance of the infection was not avoided. Combined therapy with other antimicrobials and the culture reduced the number of infected chicks compared with the respective control groups. A slight reduction was also found when the culture was used alone without any preceding antimicrobial treatment.

Animals↗
PubMed1976

Isolation of salmonellae and other potential pathogens from the freshwater aquarium snail Ampullaria.

The freshwater aquarium snail (Ampullaria spp.) was demonstrated to carry as many as 10(8) viable mesophilic bacteria per g of meat plus shell. Some 16 genera of bacteria were identified, with gram negatives predominating. Enrichment culture techniques enabled the isolation of salmonellae from 24 to 42 lots of 200 g each. The salmonellae comprised eight different serotypes, including Salmonella newport, Salmonella saint-paul, and Salmonella infantis. This association of salmonellae with snails may contribute to cases of human salmonellosis, since other aquarium species have already been shown to contribute to many such cases. The snails were also found to commonly harbor Pseudomonas aeruginosa and, occasionally, Edwardsiella tarda.

Animals↗
PubMed1979

Evaluation of organic acids and other compounds as Salmonella antagonists in meat and bone meal.

Twelve compounds were evaluated as salmonella antagonists in commercial meat and bone meal. The test organism was a nalidixic acid-resistant strain of Salmonella infantis. Adequate moisture to support salmonella growth was assured by the addition of 40% water to each 50 g test sample. Compounds were tested at levels permitted for food additives except formalin which has not been approved. Salmonella counts were determined every few days by spread plates and the pH was recorded from the initial 1:10 dilution. Although the salmonella population initially declined in the presence of several additives, none of the compounds were effective in preventing salmonella multiplication in the MBM except formalin at levels greater than .1%.

Animal Feed↗
PubMedDate not supplied

Further studies on competitive exclusion for controlling Salmonellae in chickens.

A native intestinal microflora of chickens which is protective against salmonella readily transferred to penmates and apparently to birds in adjacent pens. The microflora not only minimized infection resulting from exposure following colonization of the gut with microflora, but significantly abbreviated the period of infection when introduced after a salmonella infection was established in chicks. A microflora with undiminished protective activity, sensitive to only a few commonly used antibacterials, was established in a SPF-Cofal/Marek-negative population. Intestinal microflora from mourning doves was at least partially effective in protecting chicks against a naladixic-acid-resistant strain of Salmonella infantis. In limited tests with 2 of 3 sources of protective microflora, the growth rate of chicks in the absence of salmonellae was significantly improved. A hypothesis involving specificity of attachment between the glycocalyces of the protective microflora and of the intestinal mucosa is offered as the likely mechanism of protection.

Animal Feed↗
PubMed1978

Frequency and duration of paratyphoid organism shedding by experimentally infected bobwhite quail (Colinus virginianus).

Four-week old bobwhite quail (Colinus virginianus) were experimentally infected with Salmonella urbana, S. infantis, S. newport, S. gaminara, S. braenderup, and S. litchfield. Rates of mortality varied from 0 to 50%. The rate of shedding of paratyphoid organisms varied from 14 to 100% for 18 or more days after infection. The maximum duration of shedding was 53 days by 12% of the quail infected with S. braenderup and the minimum duration was 18 days by 14% of the quail infected with S. litchfield.

Animals↗
PubMedDate not supplied

Evaluation of several methods of detecting salmonellae in groups of chickens.

Chickens exposed experimentally to Salmonella agona, S. blockley, S. enteritidis, S. infantis, and S. typhimurium were tested serologically by microagglutination and microantiglobulin procedures and culturally by cloacal swabs and environmental samples. Chicks infected at one day old yielded the highest level of positive cloacal swab cultures, whereas exposure of older birds gave maximal serologic titers. Recovery of salmonella from environmental samples is dependent on a number of factors, including excretion rate by the population and survival rate of salmonellae in the environment. Serologic titers persisted after salmonellae could no longer be isolated from cloacal swabs or environmental samples. The possibility of false-positive serologic reactions was explored in two groups of chickens, one exposed to other Enterobacteriaceae, and one composed of eight specific-pathogen-free flocks. Occasional serologic microantiglobulin titers were observed only in the latter group. Extensive culturing of the environment from these flocks had negative results.

Agglutination Tests↗
PubMed1978

Animal salmonellosis in peninsular Malaysia. II. Annual and zoological distribution of Salmonella serotypes over the 10-year period 1966-1975.

A total of 860 Salmonella isolations were made in Peninsular Malaysia from 15 animal species (domestic and wild), eggs, molluscs, flies, and animal feed. The isolations were distributed among 31 serotypes in eight groups. The most common serotype isolated was Salmonella pullorum, followed by S. choleraesuis and S. infantis. S. typhimurium had the widest zoological distribution. The importance of controlling animal salmonellosis is emphasized.

Animals↗
PubMed1976

Salmonella in effluent from sewage treatment plants, wastepipe of butcher's shops and surface water in Walcheren.

In the frame of the "Walcheren-project" in which the epidemiology of salmonellosis is studied in a certain area, effluent from sewage treatment plants, wastepipe's of butcher's shops and surface waters, which receive the effluent were studied for the presence of salmonellae. From 160 samples of effluent 150 (94%) contained salmonellae. The most common serotype was S. typhi murium (35%) followed by S. panama and S. infantis. 14 butcher's shops' wastepipes were sampled 54 times. 14 (26%) times salmonellae were found, but only twice was the type isolated from the butcher's shop the same as found in the effluent on the same day. With regard to the presence of salmonellae in surface waters receiving effluent it was shown that from the immediate vicinity of the plant to 250 m downstream from the site of drainage of effluent the number of salmonellae per 100 ml remains almost constant. After 1.5-4 kilometers Salmonella could not be isolated from any of the samples examined. The results underline the hypothesis that salmonellae multiply in the sewage system and/or plant. The spread of samonellae by effluent seems to be limited to the plant itself and of the nearest vicinity. Proposals are brought forward to interupt contamination cycles by decontamination measures.

Industrial Waste↗
PubMed1978

Prevalence and epizootiology of equine salmonellosis.

Feces from 1,451 horses entering a veterinary hospital over a 13-month period were cultured for salmonella. A total of 46 horses (3.2%) yielded 1 or more salmonella-positive fecal cultures. Twenty horses were found to be excreting salmonella in the feces on admission, and 5 of these later had severe diarrhea associated with enteric salmonellosis. Abdominal surgery and other severe stresses were associated with all cases of severe enteric salmonellosis. Serotypes of salmonella isolated included Salmonella agona (15), S anatum (14), S typhimurium (7), S typhimurium var copenhagen (4), S infantis (2), S montevideo (1), S meleagridis (1), S drypool (1), and an unnamed Salmonella serotype (1). Seven deaths were attributed to 4 serotypes (S typhimurium, 3; S anatum, 2; S typhimurium var copenhagen, 1; and S montevideo, 1). A marked seasonal incidence is isolations was found with isolations highest in later summer to early fall and lowest in the spring. It was also found that horses can shed salmonella intermittently, and a minimal of 5 consecutive negative fecal cultures is recommended before considering a horse not to be infected with salmonella.

Animals↗
PubMed2026

Draft genome sequences of 188 Salmonella isolates from no-antibiotics-ever and conventionally raised poultry samples from retail stores.

We describe the draft genomes of 188 Salmonella isolates from no-antibiotics-ever and conventionally raised chicken and turkey products. Top three isolated serotypes were S. Infantis, S. Kentucky, and S. Typhimurium. The genome sizes, contig numbers, and GC contents of 188 isolates range from 4.68 to 5.15 Mb, 31 to 168, and 51.6% to 52.2%, respectively.

No antibiotic ever↗
PubMed1978

[Incidence of salmonellosis in the Province of Trento in the past 3 years].

72 strains of Salmonella, belonging to 23 different serum types have been isolated during the last three years. These strains come from adult patients admitted to the Infective department of St. Chiara hospital in Trento and from three asymptomatic carriers found among the hospital staff, who have been regularly submitted to microbiological checks. Among the most frequent strains the AA. have found: S. enteritidis and S. typhi murium. Salmonellas, never isolated before, have spread, but they have shown poor adaptation to the environment: among these S. panama, S. infantis, S infantis, S. münchen. S. wien has not found, in the Province of Trento, environing conditions fit for its colonization. S. agona has shown a certain tendency to create a situation of asymptomatic carrier.

Age Factors↗
PubMed1979

Antimicrobial resistant Salmonella spp. isolated from double-crested cormorants (Phalacrocorax auritus) and common loons (Gavia immer) in Florida.

Antimicrobial resistant Salmonella spp. were found in double-crested cormorants and common loons in Florida. Single or multiple resistance occurred in all Salmonella agona isolates from cormorants, primarily to ampicillin, sulfonamids, streptomycin, neomycin, and kanamycin. Similar patterns of resistance were found in S. agona isolates from common loons. In addition, isolates of S. Saint paul from loons were found resistant to tetracycline and streptomycin, while 2 of 7 isolates of S. infantis were resistant to tetracycline only.

Ampicillin↗