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Applied and Environmental Microbiology, August 2008, p. 5224-5227, Vol. 74, No. 16
0099-2240/08/$08.00+0 doi:10.1128/AEM.00621-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Analysis of a Novel Insect Cell Culture Medium-Based Growth Medium for Bartonella Species
Tanja Riess,1,
Florian Dietrich,1,
Katja V. Schmidt,1
Patrick O. Kaiser,1
Heinz Schwarz,2
Andrea Schäfer,1 and
Volkhard A. J. Kempf1*
Institut für Medizinische Mikrobiologie und Hygiene, Eberhard-Karls-Universität, Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany,1
Max-Planck-Institut für Entwicklungsbiologie, Elektronenmikroskopie, Spemannstr. 35, 72076 Tübingen, Germany2
Received 14 March 2008/
Accepted 10 June 2008

ABSTRACT
Human- and animal-pathogenic
Bartonella species are fastidious
and slow-growing bacteria difficult to isolate and cultivate.
We describe a novel, easy-to-prepare liquid medium for the fast
and reliable growth of several
Bartonella spp. that does not
affect bacterial protein expression patterns or interactions
with host cells.

INTRODUCTION
Bartonella spp. are important pathogens in human and veterinary
medicine, of which
B. henselae and
B. quintana are considered
to represent the most-relevant human-pathogenic
Bartonella species
(
8). New members of the genus with unclear epidemiology (e.g.,
"
B. rochalimae") were recently described (
10).
Bartonella spp.
are present in a broad spectrum of mammals (
4,
14), which either
suffer from these infections (
11) or serve as asymptomatic reservoir
hosts (
8).
Usually, Bartonella spp. are cultivated using highly supplemented blood agars, which still results in long incubation periods. To date, the slow growth of Bartonella spp. on solid media has limited diagnostic (e.g., primary isolation) and experimental (e.g., analyses of B. henselae pathogenicity) approaches. In light of these problems, a laboratory diagnosis of a Bartonella infection is generally made by serology (5) or molecular approaches (7).
Here, we describe the discovery, characterization, and optimization of a liquid growth medium for Bartonella spp. This inexpensive and easy-to-prepare medium allows for relatively fast planktonic growth of the fastidious bacteria. It facilitates approaches for analyzing, e.g., B. henselae pathogenicity and might also be evaluated for its use in the primary cultivation of Bartonella spp. from human or veterinary samples in the future.

Development of a liquid growth medium for Bartonella henselae.
While analyzing the interaction of
B. henselae Marseille (
9)
with Schneider cells from
Drosophila melanogaster (
19), we noticed
the growth of
B. henselae in the insect cell culture medium
(Schneider's drosophila powder medium, revised [Serva, Heidelberg,
Germany], supplemented with 10% fetal calf serum [FCS] and 2
mM glutamine [data not shown]). As no easy-to-prepare liquid
growth medium for
Bartonella spp. has been described before,
we further evaluated Schneider's medium for its use as a growth
medium. For all of the following experiments,
Bartonella spp.
were grown either in liquid media in cell culture flasks with
constant, slow shaking (60 rpm/min) or on Columbia blood agar
(CBA) in a humidified atmosphere at 37°C with 5% CO
2.
First, Schneider's medium supplemented with 10% FCS was inoculated with B. henselae (1.0 x 106 CFU/ml) and incubated for 9 days. Bacterial growth was determined by measuring the optical densities at 600 nm (OD600) at 24-h intervals, revealing a typical growth curve with a lag phase, a logarithmic growth phase, and a stationary phase (Fig. 1A). At the same time points, viable bacteria were quantified by plating serial dilutions on CBA (Fig. 1B). As described previously (6, 13), the number of viable bacteria decreased rapidly after the exponential growth phase (death phase), with no detectable stationary phase. We speculate that this early death phase might be caused by a lack of nutrients in the culture medium and not by lytic phage induction as described earlier (6), as the OD does not decrease during the death phase. Our observation has direct consequences when, e.g., infection experiments are performed with such liquid-grown Bartonella spp.; here, for each bacterial strain, the time point of entering the death phase needs to be evaluated to avoid an excess of dead bacteria.
Interestingly, no growth of
B. henselae was observed in Schneider's
medium without FCS or in Luria-Bertani broth, in brain heart
medium, or in endothelial cell growth medium, all supplemented
with 10% FCS (data not shown). Cultivation of
B. henselae in
Bartonella Alphaproteobacteria growth medium (BAPGM [
13]; provided
by Ricardo Maggi, Chapel Hill, NC) supplemented with 10% FCS
(instead of 5% sheep blood) revealed growth curves similar to
those of the cultures in Schneider's medium with 10% FCS. Remarkably,
the maximum bacterial numbers were higher in Schneider's medium
(1.9
x 10
8 CFU/ml) than in BAPGM (1.2
x 10
8 CFU/ml). In contrast
to BAPGM, our medium is not hampered by turbidity due to the
addition of blood, thus allowing the detection of bacterial
growth by visual inspection or by measurement of OD. Furthermore,
it does not contain hemin (a necessary component of other liquid
Bartonella media [
17,
20,
21]), of which various concentrations
were shown to be essential for the growth of different
Bartonella species (
20).
While evaluating different methods for the genetic manipulation of B. henselae, we realized that the addition of 5% (wt/vol) sucrose to Schneider's medium with 10% FCS resulted in even faster bacterial growth. Schneider's medium with 10% FCS and 5% sucrose was inoculated with B. henselae (1.0 x 106 CFU/ml), and the OD and numbers of CFU/ml were determined at 24-h intervals. In accordance with the OD, the maximum bacterial number was
3.3-fold higher when sucrose was added, and again, we observed an early death phase after the exponential growth phase (Fig. 1C and D). The maximum growth rate between days 1 and 2 allowed us to calculate a generation time of
5.6 h [to calculate the generation time, we used the equation 1 x lg2(t – t0)/lgN – lgN0, where t is time, t0 is time zero, N is the bacterial number, and N0 is the bacterial number at time zero].
To analyze the influence of further carbohydrates on the growth of B. henselae, Schneider's medium containing 10% FCS was supplemented with 5% (wt/vol) fructose, glucose, mannose, or galactose. While the addition of fructose showed no significant effect, the addition of glucose lowered bacterial growth rates, and remarkably, the addition of mannose or galactose suppressed the growth of B. henselae completely (data not shown). Right now, it is unclear why sucrose improves the growth of B. henselae but other carbohydrates do not influence, reduce, or even inhibit bacterial growth. Several ABC transporters (including a sugar ABC transporter) are present in the genome of B. henselae (1) and might facilitate the use of sucrose as a carbon source, whereas mannose and galactose could be toxic for B. henselae. For example, mannose might be taken up in an energy-consuming process by a phosphoenolpyruvate-dependent sugar phosphotransferase system (2), causing phosphoenolpyruvate starvation and killing of B. henselae.

Growth of different Bartonella spp. in Schneider's medium containing 10% FCS.
Next, the growth of medically and veterinarily important
Bartonella spp. (
B. henselae Marseille,
B. henselae Houston-1 [ATCC 49882],
B. quintana Toulouse [Collection de l'Institut Pasteur, Paris,
France],
B. quintana JK31 [
22], and
B. vinsonii subsp.
berkhoffii [ATCC 51672]) was analyzed (inoculum, 1.0
x 10
5 bacteria/ml;
OD determination at 24-h intervals [Fig.
2]). All five strains
grew, but the amount of time needed to reach the respective
exponential phase and the maximum OD differed from strain to
strain. The best-growing strain was
B. quintana JK31 (OD
600,
1.37 at day 7), and the slowest-growing strains were
B. henselae Marseille (OD
600, 0.76 at day 9) and
B. vinsonii (OD
600, 0.95
at day 10), demonstrating that even within a certain species,
generation times and maximum growth rates deviate significantly
(e.g., for
B. henselae strains Houston-1 and Marseille).

Functional analysis of B. henselae grown in Schneider's medium-based Bartonella growth medium.
Expression of
Bartonella adhesin A (BadA) depends on the cultivation
procedures used (
3,
16). Therefore, we analyzed
B. henselae Marseille grown in our liquid medium for BadA expression. Immunofluorescence
using specific antibodies and electron microscopy (done as described
previously [
15]) demonstrated a strong surface expression of
BadA (Fig.
3A). BadA was also present in trichloroacetic acid-precipitated
culture supernatants (inoculum,
B. henselae [1.0
x 10
7 CFU/ml];
incubation period, 10 days) and detectable by the appearance
of the typical ladder-like pattern of BadA bands (
15,
16) in
immunoblotting (Fig.
3B). No eminent differences were detected
in the total protein compositions and immunoreactivities of
B. henselae Marseille grown on CBA and in liquid medium (exponential
growth phase), compared by sodium dodecyl sulfate-polyacrylamide
gel electrophoresis and immunoblotting using the sera of a rabbit
infected with
B. henselae Marseille (
15) and of a patient suspected
of having a
B. henselae infection (indirect immunofluorescence
assay titer, 1:400). Finally, no difference was observed in
the levels of expression of Pap31 (detected by immunoblotting
using the monoclonal antibody VKS29 [
23]) (Fig.
3C).
B. henselae adheres to and invades endothelial cells (
12). We
next analyzed the interaction of liquid-grown
B. henselae with
human umbilical vein endothelial cells (HUVEC) which were infected
with
B. henselae Marseille grown either on CBA or in Schneider's
medium containing 10% FCS and 5% sucrose for 6 days. Adhesion
and invasion were analyzed 30 min, 2 h, and 24 h after infection
by confocal laser scanning microscopy as described previously
(
12), revealing no differences in the amounts of adherent and
intracellular
B. henselae (data not shown). Moreover, experiments
investigating the secretion of vascular endothelial growth factor
(VEGF) from HeLa cells (
15) or of interleukin-8 (IL-8) from
HUVEC (
18) demonstrated that using our liquid medium to grow
B. henselae (exponential growth phase) does not affect bacterium-triggered
cytokine secretion (Fig.
4).
Taken together, we describe the development of an inexpensive
and easy-to-prepare liquid medium for the cultivation of
Bartonella spp. that uses only three widely used ingredients (Schneider's
medium, FCS, and sucrose). This medium allows relatively fast
planktonic growth and does not affect host-cell interaction
in vitro. The use of Schneider's medium-based growth medium
for microbiological diagnostics of
Bartonella infections in
veterinary or human medicine and for the cultivation of other
fastidious bacteria will be evaluated in the future.

ACKNOWLEDGMENTS
We thank Ricardo Maggi (Chapel Hill, NC) for providing the BAPGM
and Silke Dorner (Max Planck Institute for Developmental Biology,
Tübingen, Germany) for providing the Schneider cells.
This work was supported by grants from the Deutsche Forschungsgemeinschaft (grant DFG-SFB 766) and from the University of Tübingen (Center for Interdisciplinary Clinical Research, junior group program) to V.A.J.K.

FOOTNOTES
* Corresponding author. Mailing address: Institut für Medizinische Mikrobiologie und Hygiene, Elfriede-Aulhorn-Str. 6, D-72076 Tübingen, Germany. Phone: 49-7071-2982352. Fax: 49-7071-295440. E-mail:
volkhard.kempf{at}med.uni-tuebingen.de 
Published ahead of print on 20 June 2008. 
T.R. and F.D. contributed equally to this work. 

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Applied and Environmental Microbiology, August 2008, p. 5224-5227, Vol. 74, No. 16
0099-2240/08/$08.00+0 doi:10.1128/AEM.00621-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.