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Journal of Clinical Microbiology, September 2003, p. 4408-4410, Vol. 41, No. 9
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.9.4408-4410.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Chemically Defined Media for Growth of Haemophilus influenzae Strains
Hannah N. Coleman,
Dayle A. Daines, Justin Jarisch, and Arnold L. Smith*
Seattle Biomedical Research Institute, Seattle, Washington 98109
Received 16 February 2003/
Returned for modification 27 April 2003/
Accepted 9 June 2003

ABSTRACT
A chemically defined medium that supports the growth of both
encapsulated and nontypeable
Haemophilus influenzae strains
in broth to densities that are

10
9 CFU/ml or
on agar plates is described. The mean generation time of a panel
of clinical isolates was comparable to that in rich, chemically
undefined media (brain-heart infusion broth supplemented with
heme and ß-NAD).

TEXT
Haemophilus influenzae is a fastidious, gram-negative coccus
that inhabits the upper respiratory system of humans and has
an obligate requirement for heme and ß-NAD for aerobic
growth. Prior investigators studying
Haemophilus influenzae sought a chemically defined medium to facilitate genetic and
metabolic studies. Multiple defined media were devised for use
with Rd derivatives of
H. influenzae (
2,
3,
4,
5,
6,
8,
13,
15), but these media would not support the growth of many nontypeable
clinical isolates or encapsulated strains.
During the course of experiments studying the invasion of human cell lines by pathogenic H. influenzae, we found that RPMI medium-based tissue culture media appeared to support bacterial growth. Further studies led to the development of the chemically defined media described herein.
Table 1 describes the strains used in this study, which were stored at -70°C in 10% skim milk and were subcultured onto chocolate agar. One liter of chocolate agar was prepared by adding 36 g of GC base (catalog no. 228920; Difco, Detroit, Mich.) and 10 g of hemoglobin (catalog no. ZIZ392; BD Biosciences, Sparks, Md.) and autoclaving at 121°C at 15 lb/in2 for 20 min; after cooling to 55°C, 5,000 U of bacitracin and 10 ml of GCHI Rehydrating Solution (catalog no. 450411; Remel, Lenexa, Kans.) were added and the plates were poured. Supplemented brain-heart infusion (sBHI) agar was prepared by adding 37 g of BHI media (catalog no. 211059; BD Biosciences) and 15 g of BactoAgar (catalog no. 214530; BD Biosciences) to 1 liter of deionized water, autoclaving, cooling to 55°C, and adding 10 ml of ß-NAD and 10 ml of heme and L-histidine stock. The heme-histidine stock was prepared by dissolving 0.2 g of L-histidine (freebase; Sigma catalog no. H 8000) in 200 ml of deionized water and then adding 0.2 g of hemin HCl (catalog no. H 5533, bovine; Sigma) and 4 ml of 1 N NaOH and steaming over a boiling water bath for 5 to 10 min to solubilize the mixture. The solution was then cooled to room temperature, filter sterilized (0.2-µm pore size), and placed in a foil-covered bottle at 4°C. We found that the histidine decreased the rate at which the hemin precipitated from solution. ß-NAD+ stock was prepared by dissolving 100 mg of ß-NAD+ (catalog no. N 7004; Sigma) in 100 ml of deionized water, filter sterilizing (0.2-µm pore size), and storing at 4°C. sBHI broth was prepared without the agar.
Defined liquid medium was made with the following: 191 ml of
RPMI 1640 with
L-glutamine and 25 mM HEPES, pH 7.26 (catalog
no. 61870036; InVitrogen), 2 ml of a 100 mM MEM sodium pyruvate
solution (catalog no. 11360070; InVitrogen), 2 ml of ß-NAD
+ stock, 4 ml of heme-
L-histidine stock, 10 ml of a 2-mg/ml uracil
solution (catalog no. U 0750; Sigma) dissolved in 0.1 N NaOH,
and 20 ml of a 20-mg/ml inosine solution (catalog no. I 4125;
Sigma) dissolved in deionized water and filter sterilized (0.2-µm
pore size). The final pH of the liquid medium was 7.56. Where
specified, NaHCO
3 (2 g/liter) was added to the liquid medium.
Defined medium solidified with agar was made as follows: a package of RPMI 1640 powder containing L-glutamine and 25 mM HEPES (pH 7.26) (catalog no. 31800022; InVitrogen), which when reconstituted will make 1.0 liter of medium, was added to 334 ml of deionized H2O, 8.7 ml of 100 mM MEM sodium pyruvate solution (as described above), 8.7 ml of ß-NAD (1 mg/ml), 17.5 ml of heme-histidine stock, 44 ml of uracil (2 mg/ml), 87 ml of inosine (20 mg/ml), and 1 ml of bacitracin (5,000 U/ml). This 2x solution was adjusted to a pH of 7.18 to 7.2, filter sterilized (0.2-µm pore size), and warmed to 55°C. Fifteen grams of BactoAgar was added to 500 ml of deionized H2O, autoclaved for 20 min, and cooled to 55°C in a water bath. After the agar reached 55°C, the two solutions were mixed in a sterile fashion and were poured into 100-mm-diameter plates. Agar plates were incubated in either a 37°C Lab-Line Imperial II bacterial incubator or a NuAire 5% CO2, 37°C water-jacketed tissue culture incubator.
Growth curves were performed at 37°C by using 125-ml Erlenmeyer flasks with a starting volume of 15 ml of medium (sBHI broth or liquid defined medium) shaken at 200 rpm in room air or in 5% CO2. A 1-ml sample was taken from the flask at time zero and then at hourly intervals, and the A600 was measured in a Hitachi U2000 spectrophotometer. The flask contents were incubated in a New Brunswick floor shaker or on a platform shaker placed inside the tissue culture incubator. The defined media allowed growth of all 14 strains tested (Table 2). All strains grew to an A600 of >1.10 after 24 h of incubation, a turbidity equivalent to 107 to 109 CFU/ml. However, the final density of the Rd derivative R652 in defined media was about one-third that seen with sBHI broth: a mean of 3.5 x 109 versus 9.0 x 109 CFU/ml. Strains E1a and R2866 reached densities of 9.9 x 107 and 7.3 x 108 CFU/ml, respectively.
Representative
H. influenzae strains, R652 (a reference strain),
E1a (a prototypic type b), and R2866 (an invasive, unencapsulated
strain), were chosen for further study. To estimate mean generation
time, 0.1 ml was removed at the end of the lag phase and colony
counts were repeated in duplicate at a minimum of three time
points until the stationary phase was reached. With strains
E1a and R2866, the mean generation time was slightly shorter
in sBHI broth when the flasks were shaken in an environment
of 5% CO
2 than when they were shaken in room air (Table
3).
The mean generation time of the prototypic strain R652 grown
in defined medium and incubated in room air was 35.66 ±
9.43 min (
n = 7), while in the CO
2-enriched environment it was
31.36 ± 1.15 min (
n = 3), differences that were not statistically
significant.
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TABLE 3. Mean generation time of selected strains grown in sBHI broth or defined media when incubated in air or 5% CO2a
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We observed that, after 7 h of incubation, phenol red in the
defined medium changed from pink to yellow and that there was
a strain dependence and incubation environment effect on apparent
acidification. To more precisely define the apparent acidification,
we measured the pH of sBHI broth and defined media after 18
h of incubation in air and in a CO
2-enriched environment. In
general, there was acidification of sBHI broth in air and in
5% CO
2. The same trend was seen with defined media, but there
was less acidification in 5% CO
2 (Table
4). Since defined media
contain 23.8 mM NaHCO
3, we added the same concentration to sBHI
broth and measured the overnight growth and pH (Table
4). In
general there were less acidification and less growth. Doubling
the NaHCO
3 concentration in defined media increased the final
pH after incubation in room air but, as expected, had little
effect in the 5% CO
2 environment.
Since
H. influenzae is a facultative anaerobe, we examined the
growth of strains R652, E1a, and R2866 in liquid defined media
under anaerobic conditions. Anaerobic incubations were performed
by placing a 125-ml Erlenmeyer flask containing 15 ml of medium
and a sterile stirring bar inside a Becton Dickinson anaerobic
chamber by using the BBL GasPak
Plus anaerobic system envelopes
(catalog no. 271040; BD Biosciences) and BBL Dry Anaerobic Indicator
strips (catalog no. 271051; BD Biosciences). The chamber was
then placed on a magnetic stirrer inside a standard 37°C
bacteriological incubator. The chamber was insulated from the
surface of the stirrer by a 13-mm-thick styrofoam square. The
cell density after overnight incubation was comparable to that
observed in air; strain R652 reached 10
9 CFU/ml, E1a reached
9.9
x 10
7 CFU/ml, and R2866 reached 7.3
x 10
9 CFU/ml. Defined
media solidified with agar supported growth of all the strains
listed in Table
1 incubated in air or 5% CO
2.
We conclude that this medium will facilitate metabolic studies of a wide variety of H. influenzae.

ACKNOWLEDGMENTS
This work was supported in part by grants AI 44002 and DC 005833
from the National Institutes of Health.

FOOTNOTES
* Corresponding author. Mailing address: Seattle Biomedical Research Institute, 4 Nickerson St., Suite 200, Seattle, WA 98109. Phone: (206) 284-8846. Fax: (206) 284-0313. E-mail:
arnold.smith{at}sbri.org.

Present address: Department of Molecular Microbiology & Immunology, School of Medicine, University of MissouriColumbia, Columbia, MO 65212. 

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Journal of Clinical Microbiology, September 2003, p. 4408-4410, Vol. 41, No. 9
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.9.4408-4410.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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