Providencia rettgeri: an unexpected case of Gram-negative cellulitis

Abstract

Providencia (P.) rettgeri is a rare facultative anaerobic Gram-negative organism most often isolated from genitourinary and gastrointestinal sources, causing diarrhea and urogenital symptoms. The authors present a case of P. rettgeri causing cellulitis in a patient lacking the typical risk factors normally associated with the bacterium. There was limited clinical improvement with empirical antimicrobial therapy. Blood cultures identified P. rettgeri responsive to adjusted Gram-negative therapy. Poor personal hygiene and living in a retirement home may have been potential risk factors for the infection

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Case reports
Wilson Kwong, Internal Medicine,
University of Toronto, Canada
Mohammad Shaee is Assistant
Professor, Department of Medicine,
University of Toronto and Toronto
General Hospital, Canada
Maan Hasso is Postgraduate
Medical Microbiology Resident,
University of Toronto, Canada
Umar Sharif is Research Fellow,
Internal Medicine, Toronto General
Hospital, Canada
30 Wounds International 2015 | Vol 6 Issue 4 | ©Wounds International 2015 | www.woundsinternational.com
Gram-positive bacteria are considered
the most common group of organisms
isolated in cellulitis, in large part
because of their ability to survive and thrive on
oxygen-rich skin surfaces[1]. However, Gram-
negative and anaerobic bacteria are often
implicated as a source of cellulitis[2].
Environmental factors favouring Gram-
negative and anaerobic bacterial growth include
areas with poor vascular and oxygen supply,
ulcerations involving the mucous membrane,
or injuries of the lower extremities. These risk
factors are most common in patients with
diabetes and vascular diseases[2].
Current guidelines emphasise the importance
of immediate identication and tailoring
of antibiotic coverage in people where
Gram-negative bacterial growth is suspected[3].
The genus Providencia
Providencia (P.) rettgeri is a rare Gram-negative,
facultative anaerobe belonging to the
Providencia genus, which was initially isolated
in 1904[4]. The genus consists of ve species:
P. alcalifaciens, P. heimbachae, P. rettgeri,
P. rustigianii and P. stuartii. In Canada, Providencia
was documented to be isolated in 3.4/100,000/
year and has a higher prevalence rate in
nursing homes[5].
Human isolates of Providencia species have
been recovered from urine, throat, perineum,
axilla, stool, blood and wound specimens. The
organism is usually isolated from genitourinary
and gastrointestinal sources (urine, faeces
and perineum), causing diarrhoea and
urogenital symptoms with a high degree of
antibiotic resistance[6].
The authors present a novel case report
of P. rettgeri causing cellulitis in a patient
with atypical risk factors for Gram-negative
infection. Their ndings may help guide
clinicians in identifying P. rettgeri as a source
of Gram-negative cellulitis in predisposed
patient populations.
Case presentation
An 88-year-old man from a care home
presented to hospital with a ve-day history
of worsening leg swelling and pain. His vital
signs were stable. Physical examination
revealed extensive cellulitis involving most
of his lower left leg with contralateral leg
showing mild venous insuciency. He had no
fever, chills, palpitations or gastrointestinal/
urinary symptoms. The patient’s medical
history included chronic kidney disease (stage
IV), rhabdomyolysis, atrial brillation and
stable angina. His home medications included
bisoprolol, amlodipine, furosemide, warfarin
and acetylsalicylic acid.
Before this hospital visit, he was treated by
his family physician with a three-day course of
cephalexin without any clinical improvement.
He was, therefore, admitted to hospital where he
was treated with vancomycin and cefazolin.
On admission, the laboratory ndings
revealed a moderate leukocytosis and
hyperkalemia. The wound appeared on the
lower part of the patient’s left leg. It was
erythematous all around the aected area,
with serosanguinous secretions on palpation.
The wound was distributed with areas of skin
breakdown throughout, without areas of
bone exposure.
Providencia rettgeri: an unexpected
case of Gram-negative cellulitis
Providencia (P.) rettgeri is a rare facultative anaerobic Gram-negative organism
most often isolated from genitourinary and gastrointestinal sources, causing
diarrhoea and urogenital symptoms. The authors present a case of P. rettgeri
causing cellulitis in a patient lacking the typical risk factors normally associated
with the bacterium. There was limited clinical improvement with empirical
antimicrobial therapy. Blood cultures identied P. rettgeri responsive to
adjusted Gram-negative therapy. Poor personal hygiene and living in a
retirement home may have been potential risk factors for the infection.
Authors:
Wilson Kwong,
Mohammad Shaee,
Maan Hasso,
Umar Sharif

Wounds International 2015 | Vol 6 Issue 4 | ©Wounds International 2015 | www.woundsinternational.com 31
A deep wound swab from the cellulitis site
showed a few pus cells, predominantly Gram-
negative bacilli, and a few Gram-positive
cocci. Cultures from the wound site grew a
heavy amount of commensal flora, including
Gram-negative bacilli and Staphylococcus (S.)
aureus strain (MSSA) sensitive to cefazolin and
cloxacillin. The antimicrobial treatment was,
therefore, changed to cefazolin monotherapy
(to provide coverage for S. aureus) and
vancomycin was discontinued. However,
the patient did not experience any clinical
improvement with respect to the infection
site, and the redness and swelling spread
down to involve his left ankle as well.
Following the change in antimicrobial
therapy, blood culture from one peripheral
site grew P. rettgeri that appeared to be an
extended-spectrum beta-lactamase strain
[Table 1]. The infectious disease service was
consulted and the antimicrobial regimen was
changed to meropenem.
A marker was used to map the outer areas
of the wound at presentation. Throughout the
course of the patient’s stay in hospital, the
cellulitis receded and did not extend beyond
this bordered area.
A number of investigations were performed
during his hospital stay to try and identify a
potential source of the P. rettgeri infection.
Urine cultures were negative on admission,
while a CT scan of the abdomen revealed no
significant abdominal or visceral dilatation.
An abdominal ultrasound was subsequently
performed, but did not reveal any abscess
or fluid collection that would suggest an
infectious source.
The patient’s cellulitis improved
significantly over his stay in hospital, and he
was stepped down to oral ciprofloxacin and
cephalexin before discharge.
The patient was seen in clinic one week
after being discharged from hospital,
with substantial improvement in his
left leg cellulitis.
Discussion
The authors present a case of cellulitis in
a non-diabetic patient that was caused
by P. rettgeri, a rare anaerobic Gram-
negative bacterium that is usually isolated
in genitourinary infections. Predisposing
factors in this case were the patient’s poor
hygiene, skin breakdown and possibly venous
insufficiency. To the authors’ knowledge,
this is only the second reported case of
a Providencia species causing cellulitis in
a human.
Previously, P. stuartii was implicated in
causing cellulitis and osteomyelitis in a
patient who worked as a pool technician,
with exposure to commercial pool water
and animal urine as the most likely source
of infection[7]. The patient had no indwelling
catheter and urine cultures were also
negative, as was the case with the patient in
this report. The only other case of cellulitis
the authors have been able to identify
was in a dog, where P. stuartii was thought
to have originated through a urinary
tract infection[8].
Species within this genus play a role
as nosocomial pathogens with other
opportunistic organisms to cause bacteremia
and urinary tract infections. With plasmid
mediated resistance, they are capable
of causing a high degree of morbidity
and mortality[4]. P. rettgeri can be isolated
from other non-lactose fermenters using
a polymyxin-mannitol-xylitol medium for
Providencia (PMXMP), where it forms red to
pink colonies of motile, non-H2S producers
that metabolise manitol [Figure 1][6].
There are currently no reported cases of
P. rettgeri causing cellulitis, with previous
case reports documenting it only as a
source of urinary tract infections, sepsis,
implantable cardioverter defibrillator (ICD)
pocket infection and meningitis infection and
meningitis[4,6,9,10,11]. This current report is novel
both in terms of the rarity of the infectious
organism and uncharacteristic presentation
for Gram-negative cellulitis.
Gram-positive bacteria are generally
the most commonly isolated organisms in
cellulitis because of their ability to survive
Table 1. Resistance prole of organism
isolated from blood culture.
Blood culture and
sensitivity
Providencia rettgeri
Amoxicillin/clavulin Resistant
Ampicillin Resistant
Ceftazidime Resistant
Ceftriaxone Resistant
Ciprooxacin Susceptible
Gentamicin Susceptible
Pipracillin/tazobactam Resistant
Tobramycin Susceptible
Trimethoprim/
sulfamethoxazole
Susceptible

32 Wounds International 2015 | Vol 6 Issue 4 | ©Wounds International 2015 | www.woundsinternational.com
covering Gram-positive organisms[3], the
authors recommend consideration of
anaerobic Gram-negative coverage after
2–3 days of treatment failure in patients
with poor hygiene and signs of venous
insufficiency. This is particularly important
given that only a small percentage of
patients with cellulitis yield positive
blood cultures, and organism-specific
treatment regimens are not always
possible. This is particularly important
given the severity and resistance profile of
Providencia infections. Wint
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and thrive on oxygen-rich skin surfaces[1].
However, anaerobic Gram-negative bacteria
should be considered in patients with
poor oxygen supply (tissue ischaemia,
vascular disease, diabetes), venous stasis
(venous insuciency, persistent oedema),
concomitant isolation of facultative anaerobes
and penetration of mucosal barriers
(recent surgery, gastrointestinal injury and
infections)[2,11]. The patient did not present with
these typical factors favouring Gram-negative
and anaerobic bacterial growth, with the
possible exception of venous insuciency.
His medical history included chronic kidney
disease, atrial brillation and stable angina.
The authors believe that the patient’s poor
hygiene most likely resulted in exposure to
the Providencia species from water in the
bathroom. This is substantiated by the fact
that the patient lives in a care home (where
Providencia is generally more common)[5] and
had visible signs of skin breakdown that likely
served as the port of entry. The only risk factor
to Gram-negative anaerobic bacterial growth
may have been venous insuciency, as noted
by vascular changes to the patient’s lower
extremities on physical examination.
Contrary to other reported cases of
Providencia infections, the patient did not
have an indwelling catheter and the authors
were not able to identify a urinary source
of infection.
Even though most guidelines recommend
empiric treatment of cellulitis with antibiotics
Case reports
Figure 1. Typical morphology of P. rettgeri.
[Used with permission from bacteriainphotos.com, courtesy of Hans Newman]