Previous Article | Next Article ![]()
Applied and Environmental Microbiology, March 2007, p. 1908-1913, Vol. 73, No. 6
0099-2240/07/$08.00+0 doi:10.1128/AEM.00740-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Robert T. Medler,
Stephen J. Billington,
B. Helen Jost, and
Lynn A. Joens*
Department of Veterinary Science and Microbiology, University of Arizona, Tucson, Arizona 85721
Received 30 March 2006/ Accepted 21 December 2006
|
|
|---|
|
|
|---|
Symptomatic infections of campylobacteriosis may consist of an acute onset of watery diarrhea, abdominal pain, fever, and the presence of blood and leukocytes in the stools. The disease is usually self-limiting, lasting from 2 to 11 days (5, 7, 20). Long-term secondary effects of infection may include reactive arthritis, Reiter's syndrome, and Guillain-Barré syndrome (19, 23).
Campylobacter spp. are considered normal flora of the gastrointestinal tract of a number of domestic animals and birds, such as commercial broiler chickens (1, 2, 6, 9, 38). Campylobacter spp. shed by these birds can enter waterways, which in turn can act as a source of contamination for other animals. Campylobacter infections occur through oral routes, including ingestion of contaminated water, unpasteurized milk, and undercooked or raw foods, such as poultry (6, 9, 38). However, consumption of raw milk and undercooked poultry is considered the major source of Campylobacter infections.
In most settings, natural, industrial, or clinical, bacteria are usually found in biofilms rather than in the planktonic state seen in the laboratory (7, 24). Current theories suggest that transition to a biofilm state is dependent on the nutritional content of the surrounding medium. Previous research has demonstrated that biofilm formation takes place via multiple steps, and upon completion, a mature, dynamic, three-dimensional structure is formed (11, 16, 24, 26). Some of the current biofilm models indicate that the participation of flagella and pili is important in the growth of the microcolony, especially during the early stages of biofilm formation (3, 13, 16, 17, 24, 27, 31).
C. jejuni has the ability to form biofilms in the watering supplies and plumbing systems of animal husbandry facilities and animal-processing plants, and these biofilms may provide a continual inoculum for domesticated animals and lead to human infections (9, 38). However, this possibility is supported by a very limited number of studies showing that C. jejuni can form biofilms on abiotic surfaces.
In this study, a biofilm assay was used to investigate the mechanisms required for C. jejuni biofilm formation on abiotic surfaces. Various environmental factors, including temperature, oxygen tension, and various nutritional factors of the bathing media, can influence the ability of C. jejuni to form biofilms on abiotic surfaces. In addition, both flagella and quorum sensing appear to affect biofilm formation in this organism.
|
|
|---|
|
View this table: [in a new window] |
TABLE 1. C. jejuni isolates used in this study
|
2.5 x 107 CFU). Plates were incubated at 37°C or 25°C in a 10% CO2 atmosphere or aerobically for 24, 48, or 72 h. Following incubation, the medium was removed, the wells were dried for 30 min at 55°C, and 1 ml 0.1% crystal violet (CV) was added for 5 min at room temperature. The unbound CV was removed, and the wells were washed twice with H2O. The wells were dried at 55°C for 15 min, and bound CV was decolorized with 80% ethanol-20% acetone. One hundred microliters of this solution was removed from the wells and placed in a 96-well plate, and the absorbance at 570 nm (A570) was determined using a microplate reader (Bio-Tek) to determine biofilm formation. In order to determine the effects of osmolytes, they were added to MHB prior to the biofilm assay. Plates were incubated at 37°C in a 10% CO2 atmosphere for 24 h.
C. jejuni biofilm formation on abiotic surfaces.
Sterile,
1- by 4-cm coupons of acrylonitrile butadiene styrene plastic (ABS), polyvinyl chloride plastic (PVC), polystyrene, or copper were placed in 15-ml polypropylene tubes with 5 ml MHB such that the coupon was completely submerged. The tubes were inoculated with C. jejuni to an OD600 of 0.025 and incubated for 24 h at 37°C and 10% CO2. The coupons were aseptically removed and placed in sterile 15-ml tubes with 2 ml of 0.1 M phosphate-buffered saline, pH 7.3, and 20- by 4-mm sterile glass beads. The bacteria were detached by vortex mixing on full speed for 1 min, which did not affect cell viability (data not shown). Viable bacteria were enumerated by dilution plating on Mueller-Hinton agar supplemented with 5% blood.
Inhibition of protein synthesis.
Overnight cultures of C. jejuni in MHB were treated with 0.5 µg/ml chloramphenicol (Cm) for 15 min at room temperature prior to being assayed for biofilm formation in the absence of antibiotic. At this concentration of Cm, protein synthesis was inhibited, but the viability of the C. jejuni isolates was not impaired (data not shown). Biofilm formation of Cm-treated C. jejuni isolates was assayed as described above.
Culture supernatant fluid.
Bacterial culture supernatant fluids (CSFs) were collected after 24 h of growth in the appropriate culture medium (Table 2). Cells were removed by centrifugation at 5,000 x g, and the CSF was filtered through a 0.22-µm filter. CSF or uninoculated culture medium was mixed 1:1 with MHB, and the biofilm formation of C. jejuni isolates was assayed in these media as described above.
|
View this table: [in a new window] |
TABLE 2. Bacterial and culture conditions used for production of CSF
|
The C. jejuni luxS mutant was constructed similarly, by cloning PCR products derived from the 5' end of the C. jejuni M129 luxS gene, which was amplified with the primers 5'-CTTCTTGTAACTCGAGTTGTCGTATC-3' and 5'-AATCAAATAAGCTTATATCATCACCC-3', and those from the 3' end of luxS, which was amplified with primers 5'-GAACTTAAGAATTCCCAATGCGGAAC-3' and 5'-ATCTTTATGGGATCCTACGCCTTGAG-3', into pSJB21. The resulting plasmid was then used for allelic exchange as described above.
|
|
|---|
![]() View larger version (15K): [in a new window] |
FIG. 1. Effects of growth medium, temperature, and oxygen tension on C. jejuni biofilm formation. (A) C. jejuni M129 biofilm formation in MHB and brucella and Bolton broths at 37°C and 10% CO2. (B) C. jejuni M129 biofilm formation in MHB in 10% CO2 or under aerobic conditions at either 37°C or 25°C. Biofilm formation was assessed by CV staining. Experiments were performed in triplicate on three separate occasions, and error bars represent one standard deviation from the mean.
|
![]() View larger version (29K): [in a new window] |
FIG. 2. Effect of NaCl (A) or sucrose or glucose (B) on the ability of C. jejuni M129 to form biofilms, as measured by CV staining. (B) White bars represent sucrose, and gray bars represent glucose. Experiments were performed three times in triplicate, and error bars represent one standard deviation from the mean.
|
![]() View larger version (14K): [in a new window] |
FIG. 3. Biofilm formation of C. jejuni M129 on coupons of polystyrene (PS), ABS, PVC, or copper was measured by a viable count following 24 h of incubation at 37°C in 10% CO2. Experiments were performed three times in triplicate, and the graph depicts data from a representative experiment.
|
![]() View larger version (21K): [in a new window] |
FIG. 4. Cm inhibits biofilm formation of C. jejuni. C. jejuni strains M129 and F38011 were treated with 0.5 µg/ml Cm for 15 min or left untreated prior to a standard biofilm assay in medium without antibiotic. Experiments were performed three times in triplicate, and error bars represent one standard deviation from the mean.
|
![]() View larger version (25K): [in a new window] |
FIG. 5. Flagella and quorum sensing positively influence biofilm formation in C. jejuni. C. jejuni M129, M129::flaAB, and M129::luxS strains were subjected to a standard biofilm assay. (A) Biofilm formation at 24, 48, and 72 h postinoculation was measured by CV staining. White bars represent M129, gray bars represent the M129::flaAB mutant, and hatched bars represent the M129::luxS mutant. (B) Representative wells at 24, 48, and 72 h postinoculation showing CV staining prior to decolorization. (C) CSF from wild-type M129 rescued biofilm formation in the M129::luxS mutant. Wild-type M129 CSF was mixed 1:1 with MHB and was used as the growth medium in a standard biofilm assay. Experiments were performed three times in triplicate, and error bars represent one standard deviation from the mean.
|
Few environmental biofilms contain a single bacterial species, and the structure of a biofilm, with cells in close proximity to one another, lends itself to interspecies signaling (13, 36). During this study, CSFs were prepared from various gram-negative and gram-positive bacteria grown under conditions favorable for the expression of quorum-sensing molecules. C. jejuni isolate M129 was grown in the presence of these CSFs mixed 1:1 with MHB, which was required to support the growth of C. jejuni (data not shown). In the presence of Pseudomonas and Arcanobacterium pyogenes BBR1 CSFs, an increase in biofilm development was observed, while CSFs from Clostridium perfringens and Chromobacterium violaceum had no apparent effect on biofilm development (Fig. 6).
![]() View larger version (16K): [in a new window] |
FIG. 6. CSFs from Pseudomonas spp. and A. pyogenes promote C. jejuni biofilm formation. Biofilm assays were performed with C. jejuni M129 in a growth medium consisting of 1:1 mixtures of MHB and CSF from Pseudomonas aeruginosa 9027, Pseudomonas fluorescens PF-5, Chromobacterium violaceum CV206, A. pyogenes BBR1, or C. perfringens strain 13. Trypticase soy broth (TSB) supplemented with 5% newborn calf serum (TSB-5%) and TSB supplemented with 0.5% yeast extract and 0.05% cysteine (TSBYC) were used as controls for A. pyogenes and C. perfringens CSFs, respectively. The source of the CSF or the type of control medium is shown on the x axis. Experiments were performed three times in triplicate, and error bars represent the standard deviation from the mean.
|
![]() View larger version (18K): [in a new window] |
FIG. 7. Biofilm formation by C. jejuni isolates does not correlate with isolate virulence. Biofilm assays were performed with the C. jejuni type strain NCTC11168, human clinical isolates M129, F38011, and UMC3, and strain S2B. Experiments were performed three times in triplicate, and error bars represent the standard deviation from the mean.
|
|
|
|---|
In their natural environments, bacteria are often challenged by environmental stresses, including nutrient starvation, osmotic changes, temperature variation, and various oxygen tensions (13, 16, 17, 24, 25, 31, 32). Bacteria are thought to form biofilms when they sense environmental changes, which trigger the transition to a sessile lifestyle (17, 18, 24, 27, 30, 34). Other factors affecting biofilm formation include substratum properties, hydrodynamics, conditioning of the substratum, and characteristics of the bathing medium (3, 13, 24, 33). In some biofilm models, changes in ionic strengths and nutrient concentrations influenced the rate at which bacteria attached to and formed biofilms on a surface (13, 16, 17). Since environmental factors and the content of the medium can affect biofilm formation, we tested various bathing medium conditions for their effect on C. jejuni biofilms. More nutrient-rich media did not support optimal biofilm formation, suggesting that nutrient-poor environments, such as those found in watering systems, may promote C. jejuni biofilm formation. We also examined the responses of C. jejuni biofilm formation to various concentrations of the osmolytes, glucose, sucrose, and NaCl. Increasing levels of each of these osmolytes resulted in a significant decrease in C. jejuni biofilm formation. This decrease may be the result of the morphological transformation from rod- or spiral-shaped cells to those which are more coccoid. Coccoid forms may represent a degenerate cell form in which damage to the cell membrane and degradation of cellular components may take place during periods when osmoadaptation may be required (22).
Incubation temperature and oxygen tension can also influence biofilm formation. However, few studies have been conducted on the direct effect of aerobiosis on C. jejuni survival and biofilm formation. In marine environments, dissolved oxygen concentrations may be decreased by lower water flow rates, increased temperature, competing organic matter, and reduced turbulence (7). In keeping with the microaerophilic and thermophilic growth preferences of C. jejuni, lower oxygen tensions and higher temperatures increased biofilm formation, whereas high ambient temperatures under aerobic conditions inhibited biofilm formation. These results indicate that environmental conditions and the nutritional state of the medium can influence the ability of C. jejuni to form biofilms.
Physicochemical properties of the abiotic surface can also affect C. jejuni attachment. C. jejuni was able to attach to hydrophobic and hydrophilic surfaces to various degrees, with good biofilm formation being observed on hydrophobic surfaces, such as plastics found in watering systems. Bacterial cell surfaces are usually negatively charged, but hydrophobic surface components such as flagella and exopolysaccharides can help overcome the repulsive forces (13, 15, 17, 18, 30).
Other studies have shown that the treatment of bacteria with protein synthesis inhibitors can markedly decrease biofilm formation and cause the release of attached bacteria (3, 13, 26), suggesting the requirement for de novo protein synthesis. Preincubation of C. jejuni cells with Cm inhibited biofilm formation, suggesting that C. jejuni synthesizes proteins required for attachment and biofilm formation in response to appropriate signals and growth conditions.
The flagella of a number of bacterial species play a significant role in the rate of attachment to a surface and subsequent biofilm formation (13, 18, 26, 27). In this study, a C. jejuni flagellum-deficient mutant (M129::flaAB) showed reduced biofilm formation compared with the wild-type strain at later time points. These findings may suggest that C. jejuni flagella may be required for biofilm development and maturation rather than, or in addition to, attachment to a surface. The results are consistent with reports that aflagellate C. jejuni mutants are defective in pellicle formation and attachment to glass at the air-liquid interface (18).
Quorum sensing or cell-to-cell signaling has been documented to play a role in cell attachment to and detachment from a biofilm (13, 14, 36). C. jejuni M129 was grown in the presence of CSFs from other bacteria. The CSFs from Pseudomonas spp. and A. pyogenes increased C. jejuni biofilm formation. While Pseudomonas spp. produce homoserine lactone signals, A. pyogenes has a luxS homologue responsible for the production of AI-2 (S. J. Billington and B. H. Jost, unpublished data). However, the exact content of the CSFs is unknown, as is the component responsible for promoting biofilm formation. In C. jejuni, the production of AI-2 was recently described. This system is highly conserved in both gram-positive and gram-negative bacteria and is thought to be used for interspecies communication (14). The luxS gene encodes the final enzyme in the biosynthetic pathway for AI-2 production (14). To assess the role of the AI-2 quorum-sensing system in C. jejuni biofilm formation, a C. jejuni luxS mutant deficient in the production of AI-2 was constructed. Our studies suggest the possibility that C. jejuni biofilm development may be dependent on AI-2 since a reduction in biofilm formation was observed in the luxS mutant compared to that in the wild type. We observed an increase in the luxS mutant biofilm when grown in the presence of wild-type M129 CSF. While the exact nature of gene regulation during C. jejuni biofilm formation is not understood, clearly cell-to-cell communication via AI-2 plays a role in the induction of the expression of genes required for these functions. Pseudomonas spp., commonly found in the environment, and A. pyogenes, a common inhabitant of domestic and wild animals, may have a common signal that C. jejuni recognizes and uses to activate the gene transcription necessary for attachment and biofilm formation.
Biofilm formation in C. jejuni does not appear to correlate with the pathogenesis of the isolate. The ability of C. jejuni to form biofilms on an abiotic surface may help explain its ability to survive outside its normal host and act as a source of contamination for animals and humans. Consistent with this interpretation, C. jejuni aggregates, which may at least mimic biofilm growth, confer increased survival compared to cells grown in the planktonic state (18).
Despite the environmental limitations of C. jejuni isolates, their survival in biofilms may play an important role in the transmission of the pathogen to animals and carcasses in husbandry and food processing plants, thus affecting humans. Biofilm variability among isolates could contribute to certain strains being of particular concern for human infections. Our studies should therefore be extended to determine the influence of watering distribution systems at these facilities and the correlation of C. jejuni isolates found in biofilms with those that colonize animals and cause human outbreaks.
Published ahead of print on 26 January 2007. ![]()
Current address: Ventana Medical Systems, 1910 E. Innovation Park Drive, Tucson, AZ 85737. ![]()
|
|
|---|
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»