DISCUSSION
To place our case in context, we searched the MEDLINE database on 27
September 2022 to determine the spectrum of pathologies caused byPantoea and associated risk factors. We used the search term
‘Pantoea ’ with no restriction on publication date, and applying
the ‘human’ and ‘English language’ filters. This search yielded 278
results, from which 69 case reports, case series, and outbreak reports
were selected for data extraction. Patients included in these
publications were stratified by immune status and age, with children
defined as those <18 years old. We also extracted data on
clinical syndromes of sporadic cases, as well as sources of outbreaks.
The literature review is summarized in the flowchart shown in Figure 5.
As is evident from the flowchart, Pantoea infections are rare,
with only 248 cases reported worldwide between 1991 and 2022, 53 of
which were outbreak cases stemming from various contaminated
environmental sources.(7-11) Sporadic adult and paediatric cases were
seen in equal proportions, with immunocompetent patients greatly
outnumbering their immunocompromised counterparts. Bacteraemia,(14-36)
followed by skin and soft tissue infections (SSTI),(31, 32, 37-42) were
the commonest manifestations of Pantoea infection, but the range
of syndromes was wide, including peritonitis,(32, 43-52) bone and joint
infection,(32, 53-60) intra-abdominal abscess,(61-63) pneumonia,(31, 64)
urinary tract infection,(31, 32) ocular infection,(65-71) and
rhinosinusitis.(72) One case each of endocarditis,(15) prosthetic joint
infection,(55) and post-neurosurgical meningitis (73) was also reported,
as were four cases of neonatal sepsis.(74, 75) Only in 19 patients, all
of whom had either SSTI,(37, 41, 42) septic arthritis,(53, 56, 58, 59)
or ocular infection (66, 69) was there a history of penetrating plant
trauma, indicating that this risk factor is less important than
previously assumed. The vast majority (84%) of infections were caused
by P. agglomerans , with only four other culprit species reported:P. dispersa ,(16, 17, 25, 27, 28, 72) P. ananatis ,(19, 21,
68) P. calida ,(24, 73) and P. stewartii .(18) In four other
cases, identification to species level was unable to be performed,(39,
66, 67, 71) like in ours. However, the diversity of Pantoeaspecies is not adequately differentiated by many laboratory
identification methods and, as such, many cases attributed to P.
agglomerans may, in fact, have been cause by other species.(76-78)
Our patient, therefore, exhibited a very atypical manifestation of aPantoea SSTI mimicking malignancy, to the extent that both
clinical and radiological findings raised concerns for sarcoma. Sarcoma
is highly unlikely in our case, given the repeated pure growth ofPantoea spp., the long intervening period without death or
deterioration, and the expert opinion provided by the specialist sarcoma
multi-disciplinary meeting. While he denied any penetrating trauma,
whether plant-related or otherwise, it is possible that micro-abrasions
may have occurred when he fell, providing a portal of entry.
Furthermore, given his rural residence, it is likely that plant or
animal material was present on the ground, and his poor diabetic control
likely contributed to the development and progression of infection.
Only one other case of Pantoea pseudotumour has been reported,
although this patient from India provided a clear history of penetrating
plant trauma due to his work in agriculture.(42) Like our case, this
patient also reported a distant history of a fall four years prior to
presentation. Regardless, both cases, despite the different management
approaches taken, resulted in good outcomes. While surgical drainage of
the lesion is ideal, as in the latter case, it is interesting that in
our patient the infection was successfully contained with him remaining
well ten years after symptom onset, even without surgical management. An
important clinical lesson, therefore, is that foreign bodies, especially
of plant origin which are not well-visualised on plain radiographs, may
be retained following such trauma and act as foci of chronic
inflammation leading to pseudotumour formation.
Our case raises some interesting questions. The first is whether the
patient’s HTLV-1 infection further predisposes to the establishment of a
chronic bacterial infection. HTLV-1, unlike HIV, does not result in
overt immunodeficiency, but associations between HTLV-1 and
non-bacterial infections, such as scabies and strongylodiasis, are
well-described.(79) However, little is known about how HTLV-1 mediates
concurrent bacterial infections,(80) making this an important research
question of clinical significance for the many infected Indigenous
Central Australians in whom rates of bacterial infection far exceed
those of their non-Indigenous countrymen,(79) as well as people living
with this neglected tropical disease worldwide.
The second question arises from the ability of Pantoea to secrete
products with bioremediative and immunogenic potential, facilitating its
adaptation to diverse ecological niches, including in hostile
environments.(1) It may well be that this has aided the establishment of
a well-contained infective focus in our patient, given that macrophage
activation and epithelial-mesenchymal transformation due to inflammatory
mediators released by P. agglomerans leading to fibrosis has been
recently reported.(81) Such a process may have succeeded in walling off
the abscess, thus preventing cell-mediated immunity from eradicating the
infection but also preventing the development of sepsis. Unfortunately,
our laboratory was unable to speciate the causative organism, but other
species may also have this capability. As such, research to elucidate
the mechanisms of action of pathogen mediators released duringPantoea infections may be clinically useful.