An in vitro study to evaluate the antimicrobial activity of a shunt catheter against Propionibacterium acnes
Authors: Litza Vera, Roger Bayston, Waheed Ashraf
Background
Infection is the major complication of shunt placement for
hydrocephalus. Propioni-bacterium acnes is an
anaerobic Gram positive rod -shaped skin bacterium, and a
recognised cause of shunt infections. The clinical presentation in
P. acnes shunt infections is delayed, and is
under-diagnosed due to lack of anaerobic culture conditions and the
need for laboratory incubation periods of at least 14 days. As the
evidence supporting antimicrobial prophylaxis for shunt infections
is weak, antimicrobial catheters have been developed. This
project aimed to evaluate the protective effect of an antimicrobial
shunt catheter, Bactiseal® (Johnson & Johnson Professional
Inc., Raynham, USA), against P. acnes and to monitor the
development of resistance by this bacterium.
Materials and Methods
Bactiseal® shunt catheters were supplied by Codman. Three
methods were used to evaluate the antimicrobial activity of the
catheter. The Serial Plate Transfer Test (SPTT) is a screening test
for the duration of antimicrobial activity and to monitor
resistance. Catheter segments were placed onto agar plates
seeded with P. acnes and incubated anaerobically. Every 7
days, segments were removed and placed on fresh plates and
reincubated. The inhibition zone was measured across the short
axis. This was repeated until no inhibition zones were seen.
In the second method, time taken to kill 100% of P. acnes
attached to catheter segments (tK100) was determined by allowing
P. acnes to adhere to plain and antimicrobial catheter
segments and incubating them. Three samples were retrieved daily,
sonicated to remove the adherent bacteria, and the sonicate
cultured quantitatively to detect P. acnes growth.
Thirdly, a simulated in vitro model was used to determine
the ability of the antimicrobial shunt catheters to resist
successive P. acnes challenges every 14 days under
constant perfusion, designed to mimic the CSF flow.
Results
The SPTT showed duration of antimicrobial activity for 70 days.
The tK100 showed that it takes 96 hours to kill all the P.
acnes attached to the catheter. The in vitro model
showed that the catheters protected against P. acnes
colonization after 5 successive challenges (ie up to 70
days). Also, no resistance was found.
Conclusions
This is the first in vitro study to evaluate the antimicrobial
activity of Bactiseal® against P. acnes. The findings of
this study indicate that the antimicrobial catheter is likely to
reduce shunt infections caused by P. acnes.
References:
Bayston R, Ashraf W, Barker-Davies Rt, Tucker E, Clement R,
Clayton J, Freeman BJ, Nuradeen B: Biofilm formation by
Propionibacterium acnes on biomaterials in vitro
and in vivo: Impact on diagnosis and treatment . J
Biomed Mater Res 2007, 81: 705-709.
Thompson TP Albright AL: Propionibacterium acnes
infections of cerebrospinal fluid shunts. Child's Nerv
Syst 1998, 14:378-380.
BRIG, Division of Orthopaedic and Accident
Surgery,Nottingham University Hospitals QMC, Nottingham,
NG7 2UH, United Kingdom
Presenting Author: Mr Waheed Ashraf
Contact Number: 0115 8231113
Email address: waheed.ashraf@nottingham.ac.uk
