Persistence of hormonal and metabolic rhythms during fasting in 7- to 9-day-old rabbits entrained by nursing during the night

Rabbit does nurse their litter once every 24 h during the night. We hypothesized that corticosterone, ghrelin, leptin, and metabolites such as glucose, liver glycogen, and free fatty acids could be affected in the pups by the time at which does nurse them. Therefore, we measured these parameters in pups nursed at 02:00 h (nighttime for the doe) to compare them with results from a previous study where does nursed at 10:00 h, during daytime. From postnatal day 7, pups were sacrificed either just before their scheduled time of nursing or at 4, 8, 12, 16, or 20 h after nursing (n = 6 at each time point); additional pups were sacrificed at 4 h intervals between 48 and 72 h after nursing to study the persistence of oscillations during fasting. All pups developed locomotor anticipatory activity to nursing. Corticosterone, ghrelin, and free fatty acids exhibited a rhythm that persisted in fasted pups. Glucose concentrations were lower in fasted than in nursed pups, and glycogen was only detected in nursed subjects. Leptin values were stable and low in nursed subjects but increased significantly in fasted subjects up to 72 h after the expected nursing time. The rhythm of ghrelin persisted during fasting, contrary to our previous findings in pups nursed during daytime (i.e., outside the natural time of nursing for this species). Therefore, in 7-day-old rabbit pups, night nursing is a strong zeitgeber for corticosterone, ghrelin, free fatty acids, and energy metabolites but not for leptin.     

Occurrence of bifidobacteria in faeces of calves fed milk or a combined diet

The development of faecal bacteria composition in calves fed milk or a combined diet was investigated from 4 to 21 days of age. On day 7, bifidobacteria in faeces of milk-fed calves already increased from about 7.6 to 9.2 log CFU/g and did not change until the end of the study, whereas in calves fed the combined diet bifidobacteria only moderately increased to 7.9 log CFU/g and decreased slowly until day 21. The counts of bifidobacteria in calves on a combined diet were significantly (p < 0.01) lower compared to those in milk-fed calves. Bifidobacterial counts determined by cultivation or by fluorescence in situ hybridisation (FISH) did not differ significantly. Our results showed that the occurrence of bifidobacteria in calf faeces is highly dependent on the diet composition. Faecal bacteria flora of calves fed exclusively by milk is rich in bifidobacteria, but in calves on a combined diet coliforms dominated.     

Quantification of Bifidobacterium spp., Escherichia coli and Clostridium difficile in faecal samples of breast-fed and formula-fed infants by real-time PCR

To determine the influence of either exclusive breast-feeding or formula feeding on both composition and quantity of the gut microbiota in infants, we have developed real-time, quantitative PCR assays for the detection of Bifidobacterium spp. and Clostridium difficile. Furthermore, we have monitored the prevalence and counts of Escherichia coli by applying a previously described real-time PCR assay. We found all 100 infants tested to be colonized by Bifidobacterium spp. The bifidobacterial counts were comparable between the 50 breast-fed and 50 formula-fed infants with median values of 10.56 log10 and 10.24 log10 CFU g(-1) wet weight faeces, respectively. C. difficile was detected in 14% of the breast-fed and 30% of the formula-fed infants. In addition, the C. difficile counts were significantly lower in breast-fed infants than in the formula-fed group (median values of 3.28 log10 and 7.43 log10 CFU g(-1), respectively; p=0.03). The prevalence of E. coli in the breast-fed and formula-fed group was 80% and 94%, respectively. Also, the E. coli counts in colonized infants was significantly lower in the breast-fed infants than in the formula-fed group (median values of 9.11 log10 and 9.57 log10 CFU g(-1), respectively; p=0.004). We conclude that the prevalence and counts of C. difficile as well as E. coli are significantly lower in the gut microbiota of breast-fed infants than in that of formula-fed infants, whereas the prevalence and counts of Bifidobacterium spp. is similar among both groups.     

Inactivation of Staphylococcus aureus in raw milk cheese by combinations of high-pressure treatments and bacteriocin-producing lactic acid bacteria

AIMS: To investigate the combined effect of high-pressure treatments (HPT) and milk inoculation with bacteriocin-producing lactic acid bacteria (BP-LAB) on the survival of Staphylococcus aureus during ripening of raw milk cheese. METHODS AND RESULTS: Cheeses were manufactured from raw milk artificially contaminated with S. aureus at ca 5 log CFU ml(-1), a commercial starter culture and one of seven strains of BP-LAB, added as adjuncts at 0.1%. HPT of cheeses were performed on days 2 or 50 at 300 MPa (10 degrees C, 10 min) or 500 MPa (10 degrees C, 5 min). On day 3, S. aureus counts were 6.46 log CFU g(-1) in control cheese. Milk inoculation with different BP-LAB lowered S. aureus counts on day 3 when compared with control cheese by up to 0.46 log CFU g(-1), HPT at 300 MPa on day 2 by 0.45 log CFU g(-1) and HPT at 500 MPa on day 2 by 2.43 log CFU g(-1). Combinations of BP-LAB with HPT at 300 and 500 MPa on day 2 lowered S. aureus counts on day 3 by up to 1.02 and 4.00 log CFU g(-1) respectively. CONCLUSIONS: The combined effect of milk inoculation with some of the BP-LAB tested and HPT of cheese on S. aureus inactivation was synergistic. SIGNIFICANCE AND IMPACT OF THE STUDY: The combination of HPT at lower pressures with BP-LAB inoculation is a feasible system to improve cheese safety in case of deleterious effects on cheese quality caused by HPT at higher pressures.     

Rapid detection of Salmonella in field samples by nested polymerase chain reaction

A simple and universal protocol for the rapid detection of Salmonella spp. in various samples using nested polymerase chain reaction (PCR) was developed. The protocol takes advantage of the rapid purification and concentration of Salmonella by centrifugation onto a layer of 60% sucrose solution. DNA was released by treatment with proteinase K and Triton X-100. Even without pre-enrichment, the detection limit for the nested PCR was 10(5) CFU g-1 of faeces. After pre-enrichment, it was possible to detect Salmonella in faeces where their original concentration was approximately 10(2) CFU g-1 of faeces and in meat samples, it was possible to detect Salmonella in samples where their original concentration was less than 10 cells g-1 of minced meat.     

The effect of lactating rabbit does on the development of the caecal microbial community in the pups they nurture

AIMS: To study the effect of microbial community of the rabbit does as influenced by dietary factors, on the development of the gut microbiota of their litters. METHODS AND RESULTS: Twenty-four lactating does were given a diet unsupplemented (NAB) or with 100 ppm of bacitracin (BAC) or tiamulin (TIA) to modify their digestive microbiota. Litters were adjusted to six pups. In Trial 1, four does per diet milked their own six pups. In Trial 2, two does per diet nursed three of their pups and three fostered from the doe given the same diet. In Trial 3, two does on each diet nursed three of their pups and three fostered from another doe fed on another diet. Denaturing gradient gel electrophoresis (DGGE) analyses of the litter microbiota showed that the effect of the milking mother was greater than the influence of the biological mother. TIA had a strong effect on the bacterial profile even prevailing over that of the milking mother, in contrast to BAC. CONCLUSIONS: Nursing mother microbiota plays an important role over that of the litter. Caecal colonization that occurs during the lactation process prevailed over that during the partum. SIGNIFICANCE AND IMPACT OF THE STUDY: Manipulation of the mother's microbiota may help for adaptation of the litter microbial community against pathologic digestive processes.     

Comparison of bacterial flora and enzymatic activity in faeces of infants and calves

Sixty-four breast-fed infants and 23 calves were investigated for bacteria and enzymatic activity in their faecal samples. The bacteria were measured using cultivation and fluorescence in situ hybridization. Enzymatic activity was also examined. Forty-seven (64%) infants and all the calves had high numbers of bifidobacteria (usually >9 log CFU g-1) in their faeces, but 17 infants (36%) did not have a detectable amount of the bacteria. Most of the bifidobacteria-negative infants had significant quantities of clostridia in their faecal flora. While the infants did not have significantly higher counts of bifidobacteria, the samples from calves contained significantly (P<0.05) more coliform bacteria and lactobacilli. There were also significant differences in their enzymatic activities. Bifidobacteria-positive samples had a greater alpha-glucosidase activity, while bifidobacteria-negative samples had a lower activity of alpha-galactosidase, and calf samples had the highest beta-glucuronidase activity. A significant increase in bifidobacteria in calf faeces between days 3 and 7 was accompanied by a decrease in Escherichia coli. Our results show that the faecal flora of calves is similar to that of infants with regard to the occurrence of bifidobacteria as a dominant bacterial group.     

Comparison of the "nursing" and other parental behaviors of nulliparous and lactating female rats

Virgin female rats display maternal behaviors after continuous exposure to pups (sensitization) that are in some respects similar to those of postpartum females. We herein provide a detailed comparison of the "nursing" and other parental behaviors of maternally sensitized virgin females and postpartum lactating dams. Ovariectomized and intact virgin females were exposed to pups until displaying maternal behavior. On the females' fourth day of maternal responsiveness, the pups were removed for 3 h and then returned, and subject-litter interactions were observed for 45 min. Behavior of maternal virgins was compared with that of lactating dams observed on day 4 postpartum interacting with either suckling pups or pups unable to suckle due to perioral anesthesia. Ovariectomy had no effect on behavior of virgins. Retrieval and licking of pups were deficient in virgins compared with lactating dams. Suckled dams showed prolonged kyphosis (upright crouched nursing), whereas nonsuckled dams displayed little kyphosis but rather were often in a hunched position over pups. Some aspects of quiescent "nursing" behaviors of virgins were surprisingly similar to those of suckled dams, including the latency to and duration of quiescence. Nonsuckling pup stimulation elicited more kyphosis in virgins than in lactating dams, which was still much less than in suckled dams. Virgins also "nursed" pups in hunched and prone postures. Differences between sensitized and postpartum females in their maternal behaviors likely reflect differences in motivation as well as sensory inputs they receive from pups. In particular, sensory regulation of "nursing" behaviors is influenced by reproductive state because nonsuckling pups elicit different postural responses in sensitized and lactating mothers.     

Development and application of a spiral plating method for the enumeration of Escherichia coli O157 in bovine faeces

AIM: To develop and validate a direct plating method applicable to epidemiological studies for enumerating Escherichia coli O157 in cattle faeces. METHODS AND RESULTS: The spiral plate count method was used to enumerate E. coli O157 in faecal samples. The accuracy and variation of counts was then assessed using faecal samples inoculated with E. coli O157. There was good agreement between inoculated levels of E. coli O157 and those recovered from faeces, particularly when counts were > 10(2) CFU g(-1) of faeces. The method was applied to a small study assessing short-term survival of E. coli O157 in naturally infected cattle faeces. E. coli O157 was found to survive in faeces for over 10 days at concentrations above 10(3) CFU g(-1) of faeces. Populations of E. coli O157 were also found to increase 100-fold in the first few hours after defecation. CONCLUSIONS: The enumeration method is easy to implement and enables a quick throughput of large numbers of samples. The method is accurate and reliable and enables the inherent variation in count data to be explored but needs to be used in combination with a more sensitive method for samples containing < 10(2) CFU g(-1) of faeces. SIGNIFICANCE AND IMPACT OF THE STUDY: The method described is appropriate for enumeration of E. coli O157 in cattle faeces in large-scale epidemiological studies.     

Influence of Litter Gender Composition on Subsequent Maternal Behaviour and Maternal Aggression in Female House Mice

It has been suggested that the sex-dependent pattern of mother-pup interaction that occurs early in infancy can affect some aspects of the animal's behaviour repertoire in adulthood. The aim of this study was to investigate the effects of litter gender composition (LGC) on subsequent maternal behaviour and aggression in the female house mouse. Albino mouse litters were reduced at birth to six pups according to two conditions: FM (3 females and 3 males) and FF (all females). At weaning (day 21), all mice were rehoused in unisexual groups. At adulthood (70–90 days) the females were mated and litters culled at birth to 6 pups (3 females and 3 males). On days 2, 4, and 6 after delivery the females were tested for maternal behaviour (10 min) and retrieval of pups. On day 6, at the end of the recording of maternal behaviour, the females were also tested for maternal aggression towards a strange adult male conspecific (5-min exposure). In absence of differences in maternal behaviour scores, FM females showed shorter latencies for retrieval of the first pup on postnatal days 2 and 4. Maternal aggression was also significantly affected by the two conditions. FM females showed higher scores of both duration and frequency of aggressive grooming, defensive upright postures, fleeing and of the number of attacks. FF females spent more time self-grooming, crouching, and on nest. These results support the hypothesis that a series of factors, such as olfactory, tactile, and acoustic stimulation provided by the pups, the variation of maternal behaviour depending upon LGC, and the qualitative and/or quantitative variation in social interaction with the opposite sex in infancy, contribute to the broad interindividual plasticity to cope in different environmental situations.     

Effect of lactobacilli onE. coli adhesion to caco-2 cellsin Vitro

Inhibitory effect of various lactobacilli against pathogenic strains of E. coli in model system Caco2 cells was determined by enumerating the number of adhering E. coli after pre-incubation (exclusion), post-incubation (displacement) or co-incubation (competition) with lactobacilli. Porcine E. coli strain F107 (F18ab, Stx2v) in the competition assay with porcine lactobacillus strain P10 gave bacterial counts 7.25 (log CFU per well); in the exclusion test it was only 7.05 while in displacement test it reached 7.29. The lowest E. coli counts adhering to Caco-2 cells were in exclusion assay (pre-incubation, Lactobacillus inoculated as the first). Pre-treatment of E. coli with our lactobacilli strains reduced the cultivable E. coli numbers.     

The survival characteristics of a non-toxigenic strain of Escherichia coli O157:H7

The survival characteristics of a non-toxigenic, antibiotic-resistant strain of Escherichia coli O157:H7 in bovine faeces were investigated. Faecal samples were inoculated with 10(8-9) cfu g-1 of the organism and (i) stored in closed plastic containers at 10 degrees C, (ii) stored in closed plastic containers placed outside or (iii) decanted onto the surface of grazing land. Recovery and enumeration on Sorbitol MacConkey Agar (SMAC) and Tryptic Soya Agar (TSA) revealed that the E. coli O157:H7 numbers in both enclosed samples (i and ii) had decreased by 4.5-5.5 log10 cfu g-1 within 99 d. Numbers in samples decanted onto grassland (iii) decreased by 4.0-5.0 log10 cfu g-1 within 50 d but the organism was still detectable in the surrounding soil for up to 99 d. Persistence of E. coli O157:H7 in bovine faeces and contaminated pastures may therefore be an important factor in the initial infection and re-infection of cattle.     

Evaluation and remediation of bulk soap dispensers for biofilm

Recent studies evaluating bulk soap in public restroom soap dispensers have demonstrated up to 25% of open refillable bulk-soap dispensers were contaminated with ~ 6 log(10)(CFU ml(-1)) heterotrophic bacteria. In this study, plastic counter-mounted, plastic wall-mounted and stainless steel wall-mounted dispensers were analyzed for suspended and biofilm bacteria using total cell and viable plate counts. Independent of dispenser type or construction material, the bulk soap was contaminated with 4-7 log(10)(CFU ml(-1)) bacteria, while 4-6 log(10)(CFU cm(-2)) biofilm bacteria were isolated from the inside surfaces of the dispensers (n = 6). Dispenser remediation studies, including a 10 min soak with 5000 mg l(-1) sodium hypochlorite, were then conducted to determine the efficacy of cleaning and disinfectant procedures against established biofilms. The testing showed that contamination of the bulk soap returned to pre-test levels within 7-14 days. These results demonstrate biofilm is present in contaminated bulk-soap dispensers and remediation studies to clean and sanitize the dispensers are temporary.     

Endogenous clock gene expression in the suprachiasmatic nuclei of previsual newborn rabbits is entrained by nursing

The rabbit is particularly suitable for investigating the development of mammalian circadian function. Blind at birth, the pups are only visited by the mother to be nursed once every 24 h for about 3 min and so can be studied largely without maternal interference. They anticipate the mother's visit with increased behavioral arousal and with a rise in body temperature, both of which represent endogenous circadian rhythms. We now report that in newborn pups the suprachiasmatic nuclei of the hypothalamus (SCN; the main circadian pacemaker in mammals) show endogenous 24‐h rhythmicity in the expression of the clock genes Per1, Per2, and Bmal1. Pups nursed from postnatal days 1 to 7 and fasted to day 9 showed the same rhythms of clock gene expression as normally nursed controls. We also report that these rhythms are entrained by nursing. Pups killed on postnatal days 3–4 showed the same rhythms in gene expression as pups in the previous experiment, whereas littermates subsequently nursed from postnatal days 4 to 7 with nursing delayed 6 h showed a corresponding shift in the diurnal pattern of clock gene expression. Consistent with this, two groups of pups implanted with telemetric thermal sensors and nursed 6 h apart had daily patterns in body temperature synchronized with the two different nursing times. We conclude that the expression of clock genes associated with the newborn rabbit's circadian system is entrained by nonphotic cues accompanying nursing, the exact nature of which now needs to be clarified. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2009     

Detection and recovery rates achieved using direct plate and enrichment/immunomagnetic separation methods for Escherichia coli O157:H7 in minced beef and on bovine hide

AIMS: To assess the detection and recovery rates achieved with commonly used cultural methods for the enumeration and recovery of Escherichia coli O157:H7 from minced beef and bovine hide. METHODS AND RESULTS: Minced beef and bovine hide were inoculated with varying concentrations (log(10) 1.58-2.58 CFU g(-1) and log(10) 2.42-4.49 CFU 100 cm(2) respectively) of E. coli O157:H7 and recovered using a direct plate method or an enrichment/immunomagnetic separation (IMS) method and then plated onto SMAC or SMAC-CT in both cases. The direct plate method detected the pathogen consistently from minced beef samples with an average recovery of 69.2-91.2%. From faecal material on the bovine hide the recovery of the pathogen ranged from 1.80 to 64.5% with fresh faeces depending on the inocula while from dried faeces on hide the results ranged from no recovery at all to 25.1%. Enrichment/IMS recovered E. coli O157:H7 at all inocula levels tested in minced beef while the pathogen was only detected consistently at an average inocula level of log(10) 2.73 CFU 100 cm(2) from fresh faeces and log(10) 4.49 CFU 100 cm(2) from dried faeces on bovine hide. CONCLUSIONS: The direct count enumeration method for E. coli O157:H7 underestimated the numbers of pathogens present. The enrichment/IMS procedure consistently detected the pathogen from minced beef but did not always detect E. coli O157:H7 from faeces on bovine hide. SIGNIFICANCE AND IMPACT OF THE STUDY: Overall this study highlights that any microbial data, used in either predictive microbiology or risk assessment, must take account of the sensitivity and associated performance of the methods employed, in order to make an accurate reflection of the true microbiology of the examined sample.     

Enumeration of Escherichia coli O157 in cattle faeces using most probable number technique and automated immunomagnetic separation

AIMS: To determine the numbers of Escherichia coli O157 present in the faeces of naturally infected cattle. METHODS AND RESULTS: A combination of the most probable number (MPN) technique and automated immunomagnetic separation (AIMS) was used to enumerate E. coli O157 in cattle faeces from both pasture-fed and grain-fed animals. A total of 22 E. coli O157 positive faecal samples were enumerated for E. coli O157 (10 from pasture-fed and 12 from grain-fed animals). The numbers of E. coli O157 in cattle faeces varied from undetectable (<3 MPN g-1 of faeces) to 2.4 x 104 MPN g-1. There was no significant difference (P = 0.06) between the numbers of E. coli O157 in pasture-fed or grain-fed cattle faeces, although the geometric mean (antilog of the mean of log10 transformed MPN values) was higher in grain-fed (130 MPN g-1) than in pasture-fed (13 MPN g-1). CONCLUSIONS: Although the number of samples tested is small, the results indicate that E. coli O157 make up a small proportion of the total E. coli population present in cattle faeces. SIGNIFICANCE AND IMPACT OF THE STUDY: Information on the numbers of E. coli O157 present in cattle will assist in developing more robust quantitative risk assessments and formulating intervention strategies.     

Intestinal microflora and obesity in rats

The relationship was evaluated between early nutritional experiences, the intestinal microflora and the small intestinal functions in the mechanism of predisposition to obesity development. Male Sprague-Dawley rats were used in which the quantity of nutrition was manipulated from birth to weaning (day 30) by adjusting the number of pups in the nest to 4 small litters (SL) and 10 normal litters (NL) and fed a standard diet from days 30 to 40 of age. After 40 d, the postnatally overfed SL pups became heavier, displayed significantly enhanced adiposity, body mass gain and food intake as well as a significantly higher jejunal alkaline phosphatase and maltase activity than in rats nursed in NL nests. The effect of different early nutrition was also accompanied by the appearance of significantly decreased Bacteroides and significantly increased enterococci and lactobacilli of obese rats than in lean NL rats. The amounts of Bacteroides were negatively correlated with fat pad mass, body mass, body-mass gain and food intake whereas enterococci and lactobacilli were correlated positively with the same parameters. Our results demonstrate that postnatal nutritional experience may represent a predisposing factor influencing ontogeny of small intestine function and development of intestinal microbial communities. The acquired changes and associated alterations in food digestion could be a component of regulatory mechanisms contributing to the development of obesity and its maintenance in later life.     

Circadian thermoregulation in suckling rabbit pups

The rabbit pup is well suited to track the age-dependent development of periodic thermoregulation during the suckling period. Since the litters are regularly nursed once per day for a total of 3 to 4 min, an exogenous, metabolic, nonphotic periodic variable is supposed to have an impact on the 24-h rhythm of body temperature. The authors monitored the course of core body temperature during the suckling period of 20 pups by means of a transmitter implanted intraperitoneally on day 3 postpartum. The 24-h mean rose from an average of 37.8+/-0.3 degrees C on day 4 of life to 39.5+/-0.2 degrees C at weaning on day 27, for 2 out of 20 pups, and day 28, for 18 out of 20 pups. In constant dim illumination, the pups exhibited a 24-h rhythm even on postnatal day 4, which consolidated around days 5 to 7. The rhythm consisted of a significant anticipatory rise of 0.4 to 0.6 degrees C above the respective 24-h mean commencing 2.5 to 3.5 h prior to nursing. Milk intake was followed by a further increase of temperature for an additional 0.3 to 0.6 degrees C. Then the temperature dropped for 1.2 to 1.5 degrees C within 1 to 3 h and returned to average 3 to 5 h later. During a 48-h fast, the rhythm continued to exist, though in a modified shape: the anticipatory component persisted almost unchanged; a further elevation of temperature, however, did not occur. Thus, the anticipatory component apparently is generated endogenously and the second surge represents an exogenous suckling-induced, thermogenic peak. When maternal nursing was advanced for 15 min/day for a total of 5 h, the temperature rhythm of the pups followed the shift of the zeitgeber in parallel. These data confirm the assumption that a circadian rhythm exists during the first postnatal days of the rabbit and that this rhythm is entrained by the 24-h nursing rhythm. The authors suggest that the biological significance of a feeding entrainable oscillator (FEO) in the rabbit might be to activate the pups prior to the periodic nursing visit of the rabbit doe. Thus, the pups are prepared to quantitatively use the one and only short nursing episode per day for maximal milk ingestion.     

Identification and quantification of viable Bifidobacterium breve strain Yakult in human faeces by using strain-specific primers and propidium monoazide

Aims: To develop a quick and accurate PCR‐based method to evaluate viable Bifidobacterium breve strain Yakult (BbrY) in human faeces. Methods and Results: The number of BbrY in faeces was detected by using strain‐specific quantitative real‐time PCR (qPCR) derived from a randomly amplified polymorphic DNA analysis. And using propidium monoazide (PMA) treatment, which combined a DNA‐intercalating dye for covalently linking DNA in dead cells and photoactivation, only viable BbrY in the faeces highly and significantly correlated with the number of viable BbrY added to faecal samples within the range of 10⁵–10⁹ cells per g of faeces was enumerated. After 11 healthy subjects ingested 10·7 log CFU of BbrY daily for 10 days, 6·9 (±1·5) log CFU g^?1 [mean (±SD)] of BbrY was detected in faeces by using strain‐specific transgalactosylated oligosaccharide–carbenicillin (T‐CBPC) selective agar medium. Viable BbrY detected by qPCR with PMA treatment was 7·5 (±1·0) log cells per g and the total number (viable and dead) of BbrY detected by qPCR without PMA treatment was 8·1 (±0·8) log cells per g. Conclusions: Strain‐specific qPCR with PMA treatment evaluated viable BbrY in faeces quickly and accurately. Significance and Impact of the Study: Combination of strain‐specific qPCR and PMA treatment is useful for evaluating viable probiotics and its availability in humans.     

Growth and persistence of pathogens on granular activated carbon filters.

Three enteric pathogens Yersinia enterocolitica O:8, Salmonella typhimurium, and enterotoxigenic Escherichia coli, were examined for their ability to colonize granular activated carbon (GAC) in pure cultures and in the presence of autochthonous river water organisms. All three organisms readily colonized sterile GAC and maintained populations of ca. 10(5) to 10(7) CFU g-1 for 14 days when suspended in sterile river water. Exposure of pathogen biofilms on GAC to unsterile river water resulted in a gradual decline in pathogens on the carbon (0.08 to 0.14 log day-1). When pathogens were introduced to sterile GAC in the presence of heterotrophic plate count organisms, they attached at levels similar to those in the pure cultures and then decreased (0.10 to 0.22 log day-1). When added with heterotrophic plate count bacteria to GAC supporting a mature biofilm of native river water bacteria, they attached at a lower level (1.0 X 10(4) to 4.6 X 10(4) CFU g-1) and decreased at a more rapid rate (0.11 to 0.70 log day-1).