S. Panama¶

At a Glance


Antigenic Formula	`1,9,12:l,v:1,5`
Serogroup	O:9 (D1)
NCBI Pathogen Detection	View isolates

Background Information¶

Salmonella enterica subsp. enterica serovar Panama (antigenic formula 1,9,12:l,v:1,5) is a serovar of the O:9 (D₁) serogroup. Serovar Panama was first identified in 1931 after being isolated during a foodborne outbreak affecting US military personnel stationed in Panama. In Taiwan, a case of neonatal meningitis caused by serovar Panama was linked to consumption of contaminated breast milk. Other than meningitis, septicemia and osteomyelitis have also been associated with serovar Panama infections. In Latin America, serovar Panama contributes substantially to the regional salmonellosis burden, with surveillance data from the 2000s indicating a confirmed incidence rate of 3.5 culture-positive cases per 100,000 population. Despite ranking among the top 30 most common Salmonella serotypes—with 1,903 reported cases (∼173 annually) from 2003–2013—this serotype accounted for only 1% of total Salmonella isolation, though it showed higher proportional isolation from bloodstream infections. Serovar Panama has been found to be an invasive non-typhoidal Salmonella (iNTS) serovar. Serovar Panama exhibits exceptional clinical invasiveness than most Salmonella serovars, with geographically consistent evidence of disproportionate systemic infection rates. In Martinique, it caused invasive infections 11 times more frequently. In England, 7% of serovar Panama isolates were from extraintestinal sites (vs. 2-3% for Salmonella Typhimurium/Enteritidis). In Taiwan, 70% of serovar Panama isolates were obtained from invasive cases compared to 12% for serovar Enteritidis. Australian epidemiological studies have also identified serovar Panama among the predominant iNTS serovars, demonstrating high invasiveness risk (odds ratios: 13.9, 15.26). Data collected from 2003 to 2013 (where total isolates tested were > 100), showed that serovar Panama was the 3rd most likely non-typhoidal serotype to be isolated from extra-intestinal sources (15.1%), exceeded only by serotypes Schwarzengrund (15.3%) and Poona (15.1%) in US.

Genetic Characteristics¶

Serovar Panama has been found to be monophyletic. A recent study identified two distinct sub-lineages of serovar Panama, which fall under a known Asian lineage. Among the Australian isolates, 46 (51.7%) exhibited multi-drug resistance (resistance to three or more drug classes). A plasmid-borne colistin resistance gene, mcr1.1, was found in one Australian serovar Panama isolate, located on an IncI plasmid previously documented in Salmonella and Escherichia coli strains from poultry in Southeast Asia. Analysis of serovar Panama intracellular replication revealed diverse phenotypes. In THP-1 macrophages, despite limited uptake by host cells, serovar Panama replicated more efficiently over time compared to Salmonella Typhimurium.

Pulford et al. identified four monophyletic clades of serovar Panama, C1 (n = 338), C2 (n = 124), C3 (n = 131), and C4 (n = 104), with an additional 139 genomes being polyphyletic. Clade C1 was predominantly composed of Latin American & Caribbean isolates (n = 295/338), including the earliest serovar Panama isolate from 1931. Clade C2 primarily contained European isolates, with notable subclades overrepresented by isolate from France and the UK. Clade C4 was largely associated with Asia and Oceania. Among the 836 isolates in this study, 14.5% (n = 121) exhibited resistance to at least one antimicrobial class, while 85.5% (n = 715) were pan-susceptible. Most resistant isolates clustered in C2 (Europe) and C4 (Asia/Oceania) (n = 113/121). The predominant resistance profile (35.5%, n = 43/121) included streptomycin (aadA1, aadA2), ampicillin (bla_TEM-1B), chloramphenicol (cmlA1), trimethoprim (dfrA12), sulfisoxazole (sul3), and tetracycline (tetA). Plasmid analysis revealed that IncFIA(HI1) (n = 40/131) and IncFIB(K) (n = 35/131) were exclusive to C4, frequently carrying the aforementioned resistance genes (n = 27/35). In contrast, IncN plasmids were mainly found in C2 (n = 28/131), sharing a similar resistance profile but substituting chloramphenicol resistance with kanamycin resistance. The estimated most recent common ancestor of all serovar Panama isolates dated back to 1555 (95% highest probability density interval: 1458–1634). Additionally, serovar Panama exhibited a mean invasiveness index of 0.2294—slightly higher than broad-host-range serovars (e.g., Salmonella Enteritidis and Typhimurium) and significantly higher than host-restricted serovars (e.g., Salmonella Typhi and Gallinarum).

Animal Reservoir¶

Serovar Panama demonstrates a broad host range, including swine, cattle, reptiles, and amphibians.

Geographical Distribution¶

Serovar Panama has been widely distributed globally.

Human/Animal Outbreaks¶

Multiple human outbreaks linked to serovar Panama have been reported. Below are some example.

Year	Location	Associated source	Number of cases
2023	US: KY	Not reported	9
2017	Costa Rica	Not identified	5
2015-2016	Taiwan	Not identified	41
2011	US: multistate	Cantaloupes from Guatemala	20
2001	US: TX	Barbeque chicken	109
1931	Panama	Not identified	About 40

Border Rejections¶

Year	Exporting country	Importing country	Associated source	Product category
2020	Brazil	Germany	Black pepper¹	Herbs and spices

¹ Salmonella Infantis and Panama were found.

Recalls¶

Year	Location	Recalled product	Type
2011	US: multistate	Cantaloupes¹	Fruits and vegetables

¹ This recall was caused by a multistate outbreak described above. Del Monte issued a recall of nearly 60,000 cantaloupes that were grown and shipped from the Del Monte Fresh farm Asuncion Mita in Guatemala.