Campylobacter jejuni: a study on environmental conditions affecting culturability and in vitro adhesion/invasion

Aims:  Nongrowing cultures of Campylobacter jejuni lose their culturability. It is unclear whether this loss in culturability also affects their ability to interact with host cells. The purpose of this study was to determine the relevance of the number of culturable cells to the ability to adhere/invade in Caco-2 cells.
Methods and Results:  For C. jejuni C356, culturability and adhesion/invasion were monitored in time (days) under different storage conditions (temperature, medium, atmosphere). Decrease rates of both culturability and adhesion/invasion were dependent on the conditions used, but the number of adhering/invading cells per culturable cell was not affected by the environmental conditions. Furthermore five strains were monitored at one condition. The culturability and adhesion/invasion decrease rates did not significantly differ per strain; however the number of adhering/invading cells per culturable cell was strain dependent.
Conclusions:  Culturability and adhesion/invasion of C. jejuni are linearly related. The number of adhering/invading cells per culturable C. jejuni cell is strain dependent, but is not affected by environmental conditions.
Significance and Impact of the Study:  It was shown that the number of culturable cells is a good measure for the in vitro adhesion/invasion of. C. jejuni.     

Identification and molecular cloning of a gene encoding a fibronectin-binding protein (CadF) from Campylobacter jejuni

Campylobacter jejuni , a Gram-negative bacterium, is a common cause of gastrointestinal disease. By analogy with other enteric pathogens such as Salmonella and Shigella , the ability of C. jejuni to bind to host cells is thought to be essential in the pathogenesis of enteritis. Scanning electron microscopy of infected INT407 cells suggested that C. jejuni bound to a component of the extracellular matrix. Binding assays using immobilized extracellular matrix proteins and soluble fibronectin showed specific and saturable binding of fibronectin to C. jejuni . Ligand immunoblot assays using ¹²⁵I-labelled fibronectin revealed specific binding to an outer membrane protein with an apparent molecular mass of 37 kDa. A rabbit antiserum, raised against the gel-purified protein, reacted with a 37 kDa protein in all C. jejuni isolates ( n  = 15) as tested by immunoblot analysis. Antibodies present in convalescent serum from C. jejuni -infected individuals also recognized a 37 kDa protein. The gene encoding the immunoreactive 37 kDa protein was cloned and sequenced. Sequencing of overlapping DNA fragments revealed an open reading frame (ORF) that encodes a protein of 326 amino acids with a calculated molecular mass of 36 872 Da. The deduced amino acid sequence of the ORF exhibited 52% similarity and 28% identity to the root adhesin protein from Pseudomonas fluorescens . Isogenic C. jejuni mutants which lack the 37 kDa outer membrane protein, which we have termed CadF, displayed significantly reduced binding to fibronectin. Biotinylated fibronectin bound to a protein with an apparent molecular mass of 37 kDa in the outer membrane protein extracts from wild-type C. jejuni as judged by ligand-binding blots. These results indicate that the binding of C. jejuni to fibronectin is mediated by the 37 kDa outer membrane protein which is conserved among C. jejuni isolates.     

Direct real-time PCR quantification of Campylobacter jejuni in chicken fecal and cecal samples by integrated cell concentration and DNA purification

Campylobacter jejuni is a major cause of diarrheal disease and food-borne gastroenteritis. The main reservoir of C. jejuni in poultry is the cecum, with an estimated content of 6 to 8 log10 CFU/g. If a flock is infected with C. jejuni, the majority of the birds in that flock will harbor the bacterium. Diagnostics at the flock level could thus be an important control point. The aim of the work presented here was to develop a complete quantitative PCR-based detection assay for C. jejuni obtained directly from cecal contents and fecal samples. We applied an approach in which the same paramagnetic beads were used both for cell isolation and for DNA purification. This integrated approach enabled both fully automated and quantitative sample preparation and a DNA extraction method. We developed a complete quantitative diagnostic assay through the combination of the sample preparation approach and real-time 5'-nuclease PCR. The assay was evaluated both by spiking the samples with C. jejuni and through the detection of C. jejuni in naturally colonized chickens. Detection limits between 2 and 25 CFU per PCR and a quantitative range of >4 log10 were obtained for spiked fecal and cecal samples. Thirty-one different poultry flocks were screened for naturally colonized chickens. A total of 262 (204 fecal and 58 cecal) samples were analyzed. Nineteen of the flocks were Campylobacter positive, whereas 12 were negative. Two of the flocks contained Campylobacter species other than C. jejuni. There was a large difference in the C. jejuni content, ranging from 4 to 8 log10 CFU/g of fecal or cecal material, for the different flocks tested. Some issues that have not yet promoted much attention are the prequantitative differences in the ability of C. jejuni to colonize poultry and the importance of these differences for causing human disease through food contamination. Understanding the colonization kinetics in poultry is therefore of great importance for controlling human infections by this bacterium.     

Application of real-time PCR for quantitative detection of Campylobacter jejuni in poultry, milk and environmental water

Campylobacter jejuni is a leading human food-borne pathogen. The rapid and sensitive detection of C. jejuni is necessary for the maintenance of a safe food/water supply. In this article, we present a real-time polymerase chain reaction (PCR) assay for quantitative detection of C. jejuni in naturally contaminated poultry, milk and environmental samples without an enrichment step. The whole assay can be completed in 60 min with a detection limit of approximately 1 CFU. The standard curve correlation coefficient for the threshold cycle versus the copy number of initial C. jejuni cells was 0.988. To test the PCR system, a set of 300 frozen chicken meat samples, 300 milk samples and 300 water samples were screened for the presence of C. jejuni. 30.6% (92/300) of chicken meat samples, 27.3% (82/300) of milk samples, and 13.6% (41/300) of water samples tested positive for C. jejuni. This result indicated that the real-time PCR assay provides a specific, sensitive and rapid method for quantitative detection of C. jejuni. Moreover, it is concluded that retail chicken meat, raw milk and environmental water are commonly contaminated with C. jejuni and could serve as a potential risk for consumers in eastern China, especially if proper hygienic and cooking conditions are not maintained.     

Detection and genotyping of Arcobacter and Campylobacter isolates from retail chicken samples by use of DNA oligonucleotide arrays

To explore the use of DNA microarrays for pathogen detection in food, we produced DNA oligonucleotide arrays to simultaneously determine the presence of Arcobacter and the presence of Campylobacter in retail chicken samples. Probes were selected that target housekeeping and virulence-associated genes in both Arcobacter butzleri and thermotolerant Campylobacter jejuni and Campylobacter coli. These microarrays showed a high level of probe specificity; the signal intensities detected for A. butzleri, C. coli, or C. jejuni probes were at least 10-fold higher than the background levels. Specific identification of A. butzleri, C. coli, and C. jejuni was achieved without the need for a PCR amplification step. By adapting an isolation method that employed membrane filtration and selective media, C. jejuni isolates were recovered from package liquid from whole chicken carcasses prior to enrichment. Increasing the time of enrichment resulted in the isolation of A. butzleri and increased the recovery of C. jejuni. C. jejuni isolates were further classified by using an additional subset of probes targeting the lipooligosaccharide (LOS) biosynthesis locus. Our results demonstrated that most of the C. jejuni isolates likely possess class B, C, or H LOS. Validation experiments demonstrated that the DNA microarray had a detection sensitivity threshold of approximately 10,000 C. jejuni cells. Interestingly, the use of C. jejuni sequence-specific primers to label genomic DNA improved the sensitivity of this DNA microarray for detection of C. jejuni in whole chicken carcass samples. C. jejuni was efficiently detected directly both in package liquid from whole chicken carcasses and in enrichment broths.     

PCR-ELISAs for the detection of Campylobacter jejuni and Campylobacter coli in poultry samples

Campylobacter species, primarily Campylobacter jejuni and Campylobacter coli, are regarded as a major cause of human gastrointestinal disease, commonly acquired by eating undercooked chicken. We describe a PCR-ELISA for the detection of Campylobacter species and the discrimination of C. jejuni and C. coli in poultry samples. The PCR assay targets the 16S/23S ribosomal RNA intergenic spacer region of Campylobacter species with DNA oligonucleotide probes designed for the specific detection of C. jejuni, C. coli, and Campylobacter species immobilized on Nucleo-Link wells and hybridized to PCR products modified with a 5' biotin moiety. The limit of detection of the PCR-ELISA was 100-300 fg (40-120 bacterial cells) for C. jejuni and C. coli with their respective species-specific oligonucleotide probes and 10 fg (4 bacterial cells) with the Campylobacter genus-specific probe. Testing of poultry samples, which were presumptive positive for Campylobacter following culture on the Malthus V analyzer, with the PCR-ELISA determined Campylobacter to be present in 100% of samples (n = 40) with mixed cultures of C. jejuni/C. coli in 55%. The PCR-ELISA when combined with culture pre-enrichment is able to detect the presence of Campylobacter and definitively identify C. jejuni and C. coli in culture-enriched poultry meat samples.     

DNA-DNA hybridization and analysis of restriction endonuclease and rRNA gene patterns of atypical (catalase-weak/negative) Campylobacter jejuni from paediatric blood and faecal cultures

Sixteen strains of atypical (catalase-weak or negative), hippurate-hydrolysing campylobacters from paediatric blood and faecal cultures were identified by DNA–DNA slot hybridization. All were closely related ( 67%) to Campylobacter jejuni and representative strains had G + C contents of 30 ± 1 mol%. Numerical analysis of chromosomal DNA Hae III digest patterns revealed two clusters of strains at the 55%S level corresponding to C. jejuni subsp. jejuni and C. jejuni subsp. doylei ; most strains belonged to the latter subspecies. No two strains had identical patterns but within each subspecies two subgroups were identifiable, corresponding to Lior biotypes I and II. Southern blot hybridization analysis with a 16 + 23S rRNA cistron probe from Escherichia coli also showed differences between the various strains, and in a numerical analysis three groupings were formed at 70%S corresponding to C. jejuni subsp. jejuni Lior biotypes I and II, and C. jejuni subsp. doylei . Four of the subspecies doylei strains contained a 3·4-MDa plasmid. These analyses showed that catalase-negative C. jejuni subsp. jejuni were genomically distinguishable from C. jejuni subsp. doylei as were Lior biotypes within subsp. jejuni . Ability to produce catalase is not a feature common to all C. jejuni strains, and our results confirm that some strains of subspecies jejuni may be negative in that character although typical in other respects. DNA pattern heterogeneity was consistent with serological differences between strains.     

Characterization of mono- and mixed-culture Campylobacter jejuni biofilms

Campylobacter jejuni, one of the most common causes of human gastroenteritis, is a thermophilic and microaerophilic bacterium. These characteristics make it a fastidious organism, which limits its ability to survive outside animal hosts. Nevertheless, C. jejuni can be transmitted to both humans and animals via environmental pathways, especially through contaminated water. Biofilms may play a crucial role in the survival of the bacterium under unfavorable environmental conditions. The goal of this study was to investigate survival strategies of C. jejuni in mono- and mixed-culture biofilms. We grew monoculture biofilms of C. jejuni and mixed-culture biofilms of C. jejuni with Pseudomonas aeruginosa. We found that mono- and mixed-culture biofilms had significantly different structures and activities. Monoculture C. jejuni biofilms did not consume a measurable quantity of oxygen. Using a confocal laser scanning microscope (CLSM), we found that cells from monoculture biofilms were alive according to live/dead staining but that these cells were not culturable. In contrast, in mixed-culture biofilms, C. jejuni remained in a culturable physiological state. Monoculture C. jejuni biofilms could persist under lower flow rates (0.75 ml/min) but were unable to persist at higher flow rates (1 to 2.5 ml/min). In sharp contrast, mixed-culture biofilms were more robust and were unaffected by higher flow rates (2.5 ml/min). Our results indicate that biofilms provide an environmental refuge that is conducive to the survival of C. jejuni.     

Latex agglutination for the detection of Campylobacter species in water

A commercially available sensitized latex suspension could detect viable (10²organisms/ml) or heat-killed Campylobacter jejuni. Cross-reactions with other Campylobacter spp. and Helicobacter pylori were only seen with suspensions > 10⁵organisms/ml. In laboratory microcosms, C. jejuni remained viable for 16 d at 4°C but latex detected antigen for at least 6 months. In water from a sewagecontaminated lake, the latex gave results comparable with culture for C. jejuni but much more rapidly. Culture-negative water supplies in chicken sheds containing campylobacter-colonized birds were shown to be sometimes latex-positive.     

Response of Campylobacter jejuni to combinations of ferrous sulphate and cadmium chloride

On Mueller Hinton (MH) agar, Campylobacter jejuni showed 20.0 and 30.9 mm zones of inhibition surrounding discs impregnated with 2.5 and 20 micrograms CdCl2 respectively. The minimal inhibitory concentration (MIC) ranged from 0.64 to 3.2 micrograms CdCl2/ml of MH agar for four C. jejuni strains. In the presence of 23 micrograms FeSO4/ml of MH the MIC increased to a range of 1.5-5.4 micrograms CdCl2/ml of MH. Moreover, the numbers of colonies present on MH supplemented with FeSO4 were greater than on MH without iron. The growth response of C. jejuni in the presence of 0.025% (w/v) FeSO4 in MH broth was increased about 10,000 fold in three of four strains when compared with the growth in unsupplemented MH broth. Zones of inhibition surrounding 20 micrograms discs of CdCl, were 50.6 and 24.4 mm on MH and Campy-BAP media respectively, with cells grown on MH. These results suggest that the blood-containing medium 'neutralized' the biocidal influence of the CdCl2. In comparison, C. jejuni inoculum from fluid thioglycollate (FT) medium showed smaller zones of inhibition. These decreased from 34.9 mm on MH agar to 19.6 mm on Campy-BAP agar, suggesting that components in the FT growth medium ameliorated the toxic influence of CdCl2. Atomic absorption spectroscopy analysis indicated mean values (mg/100 g dry weight) of selected metals bound by C. jejuni as: Cu, 10.4; Mg, 146; Na, 2385; Fe, 45.1; Zn, 13.0; and K, 172.     

The detection of genetic variation in Leptospira interrogans serogroup ICTEROHAMORRHAGIAE by ribosomal RNA gene restriction fragment patterns

Twenty-eight isolates of catalase-negative/weak (CNW) thermophilic campylobacters from human blood and faecal cultures were characterized by one-dimensional (1-D) high-resolution SDS-PAGE of cellular proteins. A further 11 Campylobacter strains were included for reference purposes. Partial protein patterns were used as the basis for numerical analysis, which showed that all of the hippurate-positive strains had a high similarity to C. jejuni. Two subclusters were formed within C. jejuni corresponding to C. jejuni subsp. doylei (15 strains) and C. jejuni subsp. jejuni (4 strains). Most of the paediatric strains from South Africa were members of C. jejuni subsp. doylei. Hippurate-negative CNW thermophilic strains were identified as "C. upsaliensis". The analysis demonstrated that the catalase-negative C. jejuni strains were quite distinct from "C. upsaliensis" and that electrophoretic protein patterns provide an excellent criterion for the identification of subspecies within C. jejuni.     

Enzyme-linked immunosorbent assay in the diagnosis of campylobacteriosis

Campylobacter jejuni and Campylobacter coli are the bacterial cause of human gastroenteritis commonly reported worldwide. The serodiagnosis of Campylobacter infections is not routinely done in Poland so the aim of this study was to evaluation of ELISA in the diagnosis ofcampylobacteriosis. Serum samples obtained from 145 patients with gastroenteritis were tested by ELISA with 7 different heat-stable antigens of C. jejuni and one of C. coli and by the commercial Virion/Serion ELISA with purified 45 kDa outer membrane protein of C. jejuni. Antibodies for heat-stable antigens of C. jejuni were detected statistically more often than antibodies for heat-stable antigens of C. coli and for purifled protein of C. jejuni. We found significant differences in the frequency of detection of antibodies to different heat-stable antigens, ranged from 18.6% to 68.9% of positive results, what indicate for serological heterogenicity of C. jejuni strains isolated in Poland. The results of our study showed usefulness of ELISA in serological diagnosis of campylobacteriosis. However it is necessary to serotype the C. jejuni strains isolated in Poland to find the appropriate C. jejuni serotype for using in ELISA.     

A murine intraperitoneal infection model reveals that host resistance to Campylobacter jejuni is Nramp1 dependent

We tested the hypothesis that host resistance to Campylobacter jejuni is Nramp1 dependent. Following intraperitoneal (IP) inoculation of Nramp1+/+ and isogenic Nramp1-deficient (Nramp1-/-) mice C. jejuni primarily associated with mac1-positive cells in liver tissue. A significant reduction of C. jejuni was observed in Nramp1+/+ mice 4 days post-infection (PI) (liver) and 8 days PI cecum-colon. In contrast, Nramp1-/- mice showed no significant reduction of C. jejuni and instead had a chronic inflammatory response and significant histopathological lesions 30 days PI. Differential cytokine profiles were observed in C. jejuni infected Nramp1+/+ and Nramp1-/- primary dendritic cells. Taken together these data indicate that Nramp1 is critical for host resistance to C. jejuni.     

Response of Campylobacter jejuni to combinations of ferrous sulphate and cadmium chloride

On Mueller Hinton (MH) agar, Campylobacter jejuni showed 20.0 and 30.9mm zones of inhibition surrounding discs impregnated with 2.5 and 20 μg CdCl₂ respectively. The minimal inhibitory concentration (MIC) ranged from 0.64 to 3.2 μg CdCl₂/ml of MH agar for four C. jejuni strains. In the presence of 23 μg FeSO₄/ml of MH the MIC increased to a range of 1.5–5.4 μg CdCl₂/ml of MH. Moreover, the numbers of colonies present on MH supplemented with FeSO₄ were greater than on MH without iron. The growth response of C. jejuni in the presence of 0.025% (w/v) FeSO₄ in MH broth was increased about 10000 fold in three of four strains when compared with the growth in unsupplemented MH broth. Zones of inhibition surrounding 20 μg discs of CdCl₂ were 50.6 and 24.4 mm on MH and Campy-BAP media respectively, with cells grown on MH. These results suggest that the blood-containing medium 'neutralized' the biocidal influence of the CdCl₂. In comparison, C. jejuni inoculum from fluid thioglycollate (FT) medium showed smaller zones of inhibition. These decreased from 34.9 mm on MH agar to 19.6 mm on Campy-BAP agar, suggesting that components in the FT growth medium ameliorated the toxic influence of CdCl₂. Atomic absorption spectroscopy analysis indicated mean values (mg/100 g dry weight) of selected metals bound by C. jejuni as: Cu, 10.4; Mg, 146; Na, 2385; Fe, 45.1; Zn, 13.0; and K, 172.     

空肠弯曲菌生物学特性上的一些歧异

对195例不同年龄腹泻患者的粪便、690只健康和腹泻畜禽的直肠和泄殖腔拭子及108份腹泻死亡畜禽的脏器材料进行了空肠弯曲菌培养,共分离鉴定458株弯曲菌(其中空肠弯曲菌445株、结肠弯曲菌13株),就其一些生物学特性进行了观察,采用Lior生物学分型法进行了354株弯曲菌(空肠弯曲菌352株、结肠弯曲菌2株)的分型。虽然表明绝大多数生物学性状符合已有文献描述,但也发现在形态、培养和生理生化特性及抗菌药抗性上存有一些歧异,其中最为主要的是483%(215/445)的空肠弯曲菌和231%(3/13)的结肠弯曲菌有萘啶酮酸抗性,11%(5/445)的空肠弯曲菌和76%(1/13)的结肠弯曲菌有噻孢霉素抗性,抗菌药抗性与菌株来源有关(P<0005)。352株空肠弯曲菌生物学分型结果表明在这些动物体内生物型Ⅰ(409%)和Ⅱ(582%)占优势,同一动物体内可有该菌的2个生物型分布。     

DNA-DNA hybridization and analysis of restriction endonuclease and rRNA gene patterns of atypical (catalase-weak/negative) Campylobacter jejuni from paediatric blood and faecal cultures.

Sixteen strains of atypical (catalase-weak or negative), hippurate-hydrolysing campylobacters from paediatric blood and faecal cultures were identified by DNA-DNA slot hybridization. All were closely related (greater than or equal to 67%) to Campylobacter jejuni and representative strains had G + C contents of 30 +/- 1 mol%. Numerical analysis of chromosomal DNA HaeIII digest patterns revealed two clusters of strains at the 55%S level corresponding to C. jejuni subsp. jejuni and C. jejuni subsp. doylei; most strains belonged to the latter subspecies. No two strains had identical patterns but within each subspecies two subgroups were identifiable, corresponding to Lior biotypes I and II. Southern blot hybridization analysis with a 16 + 23S rRNA cistron probe from Escherichia coli also showed differences between the various strains, and in a numerical analysis three groupings were formed at 70%S corresponding to C. jejuni subsp. jejuni Lior biotypes I and II, and C. jejuni subsp. doylei. Four of the subspecies doylei strains contained a 3.4-MDa plasmid. These analyses showed that catalase-negative C. jejuni subsp. jejuni were genomically distinguishable from C. jejuni subsp. doylei as were Lior biotypes within subsp. jejuni. Ability to produce catalase is not a feature common to all C. jejuni strains, and our results confirm that some strains of subspecies jejuni may be negative in that character although typical in other respects. DNA pattern heterogeneity was consistent with serological differences between strains.     

The Campylobacter jejuni stringent response controls specific stress survival and virulence-associated phenotypes

Campylobacter jejuni is a highly prevalent food-borne pathogen that causes diarrhoeal disease in humans. A natural zoonotic, it must overcome significant stresses both in vivo and during transmission despite the absence of several traditional stress response genes. Although relatively little is understood about its mechanisms of pathogenesis, its ability to interact with and invade human intestinal epithelial cells closely correlates with virulence. A C. jejuni microarray-based screen revealed that several known virulence genes and several uncharacterized genes, including spoT, were rapidly upregulated during infection of human epithelial cells. spoT and its homologue relA have been shown in other bacteria to regulate the stringent response, an important stress response that to date had not been demonstrated for C. jejuni or any other epsilon-proteobacteria. We have found that C. jejuni mounts a stringent response that is regulated by spoT. Detailed analyses of a C. jejuni delta spoT mutant revealed that the stringent response is required for several specific stress, transmission and antibiotic resistance-related phenotypes. These include stationary phase survival, growth and survival under low CO2/high O2 conditions, and rifampicin resistance. A secondary suppressor strain that specifically rescues the low CO2 growth defect of the delta spoT mutant was also isolated. The stringent response additionally proved to be required for the virulence-related phenotypes of adherence, invasion, and intracellular survival in two human epithelial cell culture models of infection; spoT is the first C. jejuni gene shown to participate in longer term survival in epithelial cells. Microarray analyses comparing wild-type to the delta spoT mutant also revealed a strong correlation between gene expression profiles and phenotype differences observed. Together, these data demonstrate a critical role for the C. jejuni stringent response in multiple aspects of C. jejuni biology and pathogenesis and, further, may lend novel insight into unexplored features of the stringent response in other prokaryotic organisms.     

Campylobacter jejuni infection in patient with Guillain-Barré syndrome: a case report

The Guillain-Barré syndrome is an acute inflammatory polineuropathy; it's frequency is established at the level of 1,3 cases/ 100 000 persons/ year. The main etiological factors concerned with the GBS occurrence are: Campylobacter jejuni, cytomegalovirus, Epstein-Barre virus, Mycoplasma pneumoniae. The authors present a case of the 15 years old boy with the clinical features of acute motor axonal polineuropathy and confirmed C. jejuni infection. Identification of C. jejuni isolate was based on colony morphology on CCDA plate (OXOID), characteristic motility, catalase, oxidase, hippurate hydrolysis and acetate hydrolysis. The identity of C. jejuni was also confirmed by a specific PCR. According to the authors' knowledge this is the first case of a patient with GBS with confirmed C. jejuni infection reported from Poland.     

Colonization of Syrian hamsters with streptomycin resistant Campylobacter jejuni

A streptomycin resistant Campylobacter jejuni inoculated per os into two populations of Syrian hamsters (one endemically harboring C. jejuni, the other free of C. jejuni) established chronic colonization of the organism in both groups. Diet, steroid administration, age of hamsters or prior exposure to C. jejuni did not appreciably alter incidence of diarrhea or colonization of C. jejuni. The majority of hamsters sampled during the course of the experiment (1 to 22 weeks) shed streptomycin resistant C. jejuni in the feces. In four hamsters sampled at 14, 17, 19, and 22 weeks, post inoculation, streptomycin resistant C. jejuni were recovered in ileal, cecal, jejunal, duodenal and colonic contents (10(4) to 10(7) colony forming units/gram of intestinal content). The hamster appears to be a potentially useful model for the study of intestinal colonization of enteropathogenic C. jejuni. Hamsters shedding C. jejuni in their feces for extended periods of time should be considered a zoonotic threat to both pet owners and laboratory personnel.     

Yoghurt: an unlikely source of Campylobacter jejuni/coli

Knowledge of the relative insensitivity of Campylobacter jejuni to moderately acid environments prompted us to study its survival in different batches of yoghurt of pH range 4.2–5.3 and the role of organic or inorganic acid in the die-off of this pathogen. None of the 11 strains of C. jejuni or C. coli survived more than 25 min in yoghurt. Suspecting that this rapid die-off cannot be accounted for by the pH of the yoghurt we compared the survival rates of C. jejuni in milk, whose pH had been adjusted by lactic, propionic and hydrochloric acid respectively, with that of yoghurt. Even for an inoculum of 10⁵–10⁸ cfu/ml propionic acid was bactericidal in minutes. Lactic acid reduced the bacterial populations by 3–5 logs in 30 min. Strong inorganic acid HC1, by contrast, had little or no effect on the populations. Although lactic acid is quite bactericidal for C. jejuni , it is apparently not the only factor to which the prompt elimination of this pathogen from yoghurt could be attributed.