Effect of adherent Lactobacillus spp. on in vitro adherence of salmonellae to the intestinal epithelial cells of chicken

Single strains of Lactobacillus acidophilus and Lact. fermentum, isolated from chicken intestine, were used to study in vitro interactions with Salmonella enteritidis, Salm. pullorum or Salm. typhimurium in an ileal epithelial cell (IEC) radioactive assay. Exclusion, competition and displacement phenomena were investigated by respectively incubating (a) lactobacilli and IEC together, prior to addition of salmonellae, (b) lactobacilli, IEC and salmonellae together, and (c) salmonellae and IEC, followed by the lactobacilli. Lactobacilli were selected for study because of their strong ability to adhere to IEC and poor aggregation with salmonellae. The results demonstrated that Lact. acidophilus significantly reduced ( P < 0.05) the attachment of Salm. pullorum to IEC in the tests for exclusion and competition, but not in the displacement tests. Lactobacillus fermentum was found to have some ability to reduce the attachment of Salm. typhimurium to IEC under the conditions of exclusion ( P < 0.08), competition ( P < 0.09), but not displacement. However, both Lact. acidophilus and Lact. fermentum were unable to reduce the adherence of Salm. enteritidis to IEC under any of the conditions.     

The effect of Lactobacillus spp. on the attachment of enterotoxigenic Escherichia coli to isolated porcine enterocytes

A total of 43 strains of lactobacilli were isolated from the gastrointestinal tract of piglets at the time of weaning. Isolates, grown on solid media, were allocated to strongly adherent or non/weakly adherent groups on the basis of numbers attaching to isolated porcine enterocytes. Strains of Lactobacillus fermentum were disproportionally represented amongst the strongly-adherent strains and Lact.acidophilus and Lact. salivarius amongst the non/weakly-adherent group. Lactobacilli showed significantly better attachment ability when grown on agar than when grown in broth culture. Strongly adherent strains were not found to effect the attachment of enterotoxigenic Escherichia coli to porcine enterocytes, tested under the conditions of exclusion (lactobacilli added to the enterocytes before E. coli ), competition (lactobacilli and E. coli added simultaneously) and displacement ( E. coli added before lactobacilli). Tests were made with [¹⁴C]-labelled E. coli. Suspensions of bacteria and enterocytes were passed through a filter selected to retain enterocytes but pass free bacterial cells. Counts (dpm) obtained from filters after solubilization were taken as a measure of E. coli attachment. Some strains of lactobacilli coaggregated with enterotoxigenic E. coli with K88 fimbriae, but not with a K88-negative mutant strain. These were excluded from the competitive exclusion experiments. In the apparent absence of a direct effect on the association of E. coli with host tissue, removal of potential gut pathogens by aggregation could contribute to the probiotic properties ascribed to lactic acid bacteria.     

The adherence of lactic acid bacteria to the columnar epithelial cells of pigs and calves

The adhesion of various lactobacilli and streptococci to columnar epithelial cells of pigs and calves were studied, by in vitro methods. The porcine strains isolated most frequently were Lactobacillus delbrueckii, Lact. acidophilus and Lact. fermentum. Thirteen of the 22 lactobacilli were adhesive. All the streptococci isolated belonged to Lancefield's D-group; none of them adhered to pig epithelial cells. The adhesive strains (9 of 22) of calves were identified as Lact. fermentum. Adherence was variable even between strains of the same species. Isolates from plant material, cultured milk and cheese did not adhere to the columnar epithelial cells in vitro. The adhesive porcine strains tolerated low pH and bile acids, which is important for their survival under conditions in the stomach and intestine.     

Enzyme production by lactobacilli and the potential link with infective endocarditis

H.J. OAKEY, D.W.S. HARTY AND K.W. KNOX. 1995. Fifty-six strains of lactobacilli were examined for the production of glycosidases and proteases (arylamidases) that could be associated with the ability to grow in vivo and/or be a factor in the pathogenesis of endocarditis. The strains were from seven species, with an emphasis on Lactobacillus rhamnosus and Lact. paracasei subsp. paracasei , both of which have been associated with endocarditis and provided 12 of the 13 strains isolated from cases of the disease. Other species were Lact. acidophilus, Lact. plantarum, Lact. salivarius, Lact. fermentum and Lact. oris.
Commonly expressed glycosidase activities were α-D-galactosidase and β- N -acetyl-D-glucosaminidase followed by β-D-glucosidase and α-L-fucosidase. The combined production of β- N -acetyl-D-glucosaminidase and α-D-galactosidase was a feature of the endocarditis isolates. In contrast, β-D-galactosidase was produced by very few of the strains within species implicated in endocarditis but most of the strains of Lact. salivarius, Lact. fermentum and Lact. oris.
The most commonly produced arylamidases active against substrates employed for testing human blood clotting cascade were activated protein C(Ca)-like, activated factor X(Xa)-like and Hageman factor-like followed by kallikrein-like and chymotrypsin-like enzymes. Kallikrein-like enzyme activity was shown more frequently by strains from species commonly isolated from cases of endocarditis ( Lact. rhamnosus and Lact. paracasei subsp. paracasei ) than from other oral species ( Lact. plantarum, Lact. salivarius, Lact. fermentum and Lact. oris ).
The data indicate that some lactobacilli can produce enzymes that would enable the breakdown of human glycoproteins and the synthesis and lysis of human fibrin clots, characteristics which aid the colonization and survival of bacteria infecting an endocarditis vegetation.     

Metabolism and some characteristics of lactobacilli isolated from the rumen of young calves

Fourteen strains of lactobacilli isolated from the rumen of young calves were studied to determine their biochemical characteristics, growth parameters, metabolism on lactose and sensitivity to 28 antimicrobial agents. Thirteen homofermentative strains belonged to Lactobacillus acidophilus and one heterofermentative strain resembled Lact. fermentum. The relevance of rumen lactobacilli to the nutrition of calves is discussed.     

Metabolism and some characteristics of lactobacilli isolated from the rumen of young calves

Fourteen strains of lactobacilli isolated from the rumen of young calves were studied to determine their biochemical characteristics, growth parameters, metabolism on lactose and sensitivity to 28 antimicrobial agents. Thirteen homofermentative strains belonged to Lactobacillus acidophilus and one heterofermentative strain resembled Lact. fermentum. The relevance of rumen lactobacilli to the nutrition of calves is discussed.     

Inhibition of Escherichia coli O157:H7 attachment by interactions between lactic acid bacteria and intestinal epithelial cells

The intestinal epithelial cell (IEC) layer of the intestinal tract makes direct contact with a number of microbiota communities, including bacteria known to have deleterious health effects. IECs possess innate protective strategies against pathogenic challenge, which primarily involve the formation of a physicochemical barrier. Intestinal tract mucins are principal components of the mucus layer on epithelial surfaces, and perform a protective function against microbial damage. However, little is currently known regarding the interactions between probiotics/pathogens and epithelial cell mucins. The principal objective of this study was to determine the effects of Lactobacillus on the upregulation of MUC2 mucin and the subsequent inhibition of E. coli O157:H7 attachment to epithelial cells. In the current study, the attachment of E. coli O157:H7 to HT-29 intestinal epithelial cells was inhibited significantly by L. acidophilus A4 and its cell extracts. It is also important to note that the expression of MUC2 mucin was increased as the result of the addition of L. acidophilus A4 cell extracts (10.0 mg/ml), which also induced a significant reduction in the degree to which E. coli O157:H7 attached to epithelial cells. In addition, the mRNA levels of IL-8, IL-1beta, and TNF-alpha in HT-29 cells were significantly induced by treatment with L. acidophilus A4 extracts. These results indicate that MUC2 mucin and cytokines are important regulatory factors in the immune systems of the gut, and that selected lactobacilli may be able to induce the upregulation of MUC2 mucin and specific cytokines, thereby inhibiting the attachment of E. coli O157:H7.     

Differentiation of Lactobacillus isolates from infant faeces by SDS-PAGE and rRNA-targeted oligonucleotide probes

Isolates of lactobacilli from infant faeces phenotypically characterized as Lactobacillus paracasei subsp. paracasei (six strains), Lact. rhamnosus (six strains), Lact. gasseri (three strains), Lact. acidophilus (one strain) and Lact. fermentum/reuteri (three strains) according to recent classification systems were subjected to SDS-PAGE of whole cell proteins and rRNA-targeted oligonucleotide probe hybridization, in order to confirm the phenotypic characterization and elucidate the exact taxonomic position of the three strains that had properties between fermentum and reuteri. Results suggested a good agreement between the phenotypic characterization, SDS-PAGE and rRNA-targeted oligonucleotide probe hybridization for strains of all species except for the Lact. fermentum/reuteri strains. Results obtained by rRNA probes suggested a possible phylogenetic relatedness of the strains to Lact. reuteri. Isolates from infant faeces with interesting probiotic properties could be used as components of fermented milk products.     

Effect of Lactobacillus isolates on the adhesion of pathogens to chicken intestinal mucus in vitro

AIMS: The aims of this study were to investigate in vitro the effects of Lactobacillus isolates from a chicken on adhesion of pathogenic Salmonella and Escherichia coli to chicken intestinal mucus obtained from different intestinal regions. METHODS AND RESULTS: Bacteria were labelled by using methyl-1,2-[(3)H]-thymidine. The bacterial adhesion was assessed by measuring the radioactivity of bacteria adhered to the mucus. The results showed that the abilities of Lactobacillus spp. to bind to the same intestinal mucus were higher than those of pathogenic Salmonella and E. coli. Pretreatment of intestinal mucus with Lactobacillus fermentum and Lactobacillus acidophilus, alone or in combination, reduced the adhesion of the tested pathogens, but the reductive extent of pathogenic adhesion by Lactobacillus spp. in combination was relatively high. CONCLUSIONS: The tested bacteria had different adhesions to mucus glycoproteins isolated from different intestinal regions of chicken. Lactobacillus acidophilus and Lact. fermentum in combination revealed a better ability to inhibit attachments of Salmonella and E. coli to chicken intestinal mucus than Lactobacillus sp. alone. SIGNIFICANCE AND IMPACT OF THE STUDY: A mixture of intestinal Lactobacillus spp. from a chicken may play a protective role in excluding pathogenic Salmonella and E. coli from the intestine of chicken.     

Antagonistic activity of probiotic lactobacilli and bifidobacteria against entero- and uropathogens

AIM: To develop in vitro assays for comparing the antagonistic properties and anti-oxidative activity of probiotic Lactobacillus and Bifidobacterium strains against various entero- and urinary pathogens. METHODS AND RESULTS: The antagonistic activity of five probiotic lactobacilli (Lactobacillus rhamnosus GG, Lactobacillus fermentum ME-3, Lactobacillus acidophilus La5, Lactobacillus plantarum 299v and Lactobacillus paracasei 8700:2) and two bifidobacteria (Bifidobacterium lactis Bb12, Bifidobacterium longum 46) against six target pathogens was estimated using different assays (solid and liquid media, anaerobic and microaerobic cultivation) and ranked (low, intermediate and high). Bacterial fermentation products were determined by gas chromatography, and the total anti-oxidative activity of probiotics was measured using linolenic acid test. Pyelonephritic Escherichia coli was highly suppressed by GG and both bifidobacteria strains. Lactobacilli strains 8700:2, 299v and ME-3 were the most effective against Salmonella enterica ssp. enterica in microaerobic while ME-3 and both bifidobacteria expressed high activity against Shigella sonnei in anaerobic milieu. Lact. paracasei, Lact. rhamnosus and Lact. plantarum strains showed intermediate antagonistic activity against Helicobacter pylori under microaerobic conditions on solid media. The highest anti-oxidative activity was characteristic for Lact. fermentum ME-3 (P < 0.05). No efficient antagonist against Clostridium difficile was found. The positive correlations between the pH, lactic acid production and anti-microbial activity for all tested probiotics were assessed. CONCLUSIONS: Developed experimental assays enable to compare the anti-microbial and -oxidative activity of Lactobacillus and/or Bifidobacterium probiotics, which have been claimed to possess the ability of suppressing the growth of various enteric and urinary pathogens. SIGNIFICANCE AND IMPACT OF THE STUDY: Screening Lactobacillus and Bifidobacterium sp. strains according to their activity in various environmental conditions could precede the clinical efficacy studies for adjunct treatment with probiotics in cure of different gastrointestinal and urinary tract infections.     

Variable response to exogenous Lactobacillus acidophilus NCFM consumed in different delivery vehicles

AIMS: To study the effects of the delivery vehicle for Lactobacillus acidophilus on the human faecal microbiota. Our hypotheses were that (i) the delivery vehicle would influence faecal lactobacilli numbers and (ii) consumption of Lact. acidophilus would influence the populations of Bifidobacterium and hydrogen sulphide-producing bacteria. METHODS AND RESULTS: Ten subjects each received Lact. acidophilus with skim milk or water. Lactobacillus, Bifidobacterium and hydrogen sulphide-producing bacterial populations were analysed before, during and after each treatment. Regardless of the vehicle, faecal lactobacilli populations changed during treatment. Bifidobacteria and the hydrogen sulphide-producing bacteria underwent no statistically significant population changes. Intra- and intersubject variability was observed. CONCLUSIONS: The vehicle in which Lact. acidophilus was delivered did not influence faecal lactobacilli numbers. Consumption of Lact. acidophilus did not influence the populations of Bifidobacterium and hydrogen sulphide-producing bacteria. The lactobacilli populations of subjects were variable. The fed lactobacilli did not appear to colonize the gastrointestinal tract. SIGNIFICANCE AND IMPACT OF THE STUDY: We provide evidence that (i) there was no collective advantage to using skim milk as a delivery vehicle vs water; (ii) exogenous Lact. acidophilus did not affect endogenous bifidobacteria or hydrogen sulphide-producing bacteria; (iii) data should be carefully examined before pooling for analysis and (iv) continuous feeding was required to maintain an elevated lactobacilli population.     

Growth studies of potentially probiotic lactic acid bacteria in cereal-based substrates

AIMS: The overall growth kinetics of four potentially probiotic strains (Lactobacillus fermentum, Lact. reuteri, Lact. acidophilus and Lact. plantarum) cultured in malt, barley and wheat media were investigated. The objectives were to identify the main factors influencing the growth and metabolic activity of each strain in association with the cereal substrate. METHODS AND RESULTS: All fermentations were performed without pH control. A logistic-type equation, which included a growth inhibition term, was used to describe the experimental data. In the malt medium, all strains attained high maximum cell populations (8.10-10.11 log10 cfu ml(-1), depending on the strain), probably due to the availability of maltose, sucrose, glucose, fructose (approx. 15 g l(-1) total fermentable sugars) and free amino nitrogen (approx. 80 mg l(-1)). The consumption of sugars during the exponential phase (10-12 h) resulted in the accumulation of lactic acid (1.06-1.99 g l(-1)) and acetic acid (0.29-0.59 g l(-1)), which progressively decreased the pH of the medium. Each strain demonstrated a specific preference for one or more sugars. Since small amounts of sugars were consumed by the end of the exponential phase (17-43%), the decisive growth-limiting factor was probably the pH, which at that time ranged between 3.40 and 3.77 for all of the strains. Analysis of the metabolic products confirmed the heterofermentative or homofermentative nature of the strains used, except in the case of Lact. acidophilus which demonstrated a shift towards the heterofermentative pathway. All strains produced acetic acid during the exponential phase, which could be attributed to the presence of oxygen. Lactobacillus plantarum, Lact. reuteri and Lact. fermentum continued to consume the remaining sugars and accumulate metabolic products in the medium, probably due to energy requirements for cell viability, while Lact. acidophilus entered directly into the decline phase. In the barley and wheat media all strains, especially Lact. acidophilus and Lact. reuteri, attained lower maximum cell populations (7.20-9.43 log10 cfu ml(-1)) than in the malt medium. This could be attributed to the low sugar content (3-4 g l(-1) total fermentable sugar for each medium) and the low free amino nitrogen concentration (15.3-26.6 mg l(-1)). In all fermentations, the microbial growth ceased at pH values (3.73-4.88, depending on the strain) lower than those observed for malt fermentations, which suggests that substrate deficiency in sugars and free amino nitrogen contributed to growth limitation. CONCLUSIONS: The malt medium supported the growth of all strains more than barley and wheat media due to its chemical composition, while Lact. plantarum and Lact. fermentum appeared to be less fastidious and more resistant to acidic conditions than Lact. acidophilus and Lact. reuteri. SIGNIFICANCE AND IMPACT OF THE STUDY: Cereals are suitable substrates for the growth of potentially probiotic lactic acid bacteria.     

Species composition of intestinal lactoflora of healthy rhesus monkeys

The results of the study of the species composition of the fecal microflora of 15 healthy rhesus macaques, from whom 204 strains of lactobacilli have been isolated and identified, are presented. The intestinal microflora has been shown to include different species, subspecies and biovars of homo- and heterofermentative lactobacilli and to possess definite individual properties. L. acidophilus, mannose-negative biovar I, and L. fermentum, mannose-negative biovars I and II, occur most frequently in feces. Certain differences in the species composition of lactoflora in monkeys and humans have been revealed: in the former, L. fermentum, mannitose-positive biovar III, and L. casei occur considerably more seldom. The inclusion of L. acidophilus strain I L. fermentum strains I and II isolated from rhesus macaques into eubiotics for these monkeys has been suggested.     

Evaluation of numerical analyses of RAPD and API 50 CH patterns to differentiate Lactobacillus plantarum, Lact. fermentum, Lact. rhamnosus, Lact. sake, Lact. parabuchneri, Lact. gallinarum, Lact. casei, Weissella minor and related taxa isolated from kocho and tef

AIM: The study was carried out to assess the agreement of API 50 CH fermentation data of food lactobacilli with their RAPD profiles to determine whether the system could be used alone as a reliable taxonomic tool for this genus. METHODS AND RESULTS: API 50 CH, RAPD and DNA:DNA reassociation data for 42 lactobacilli from tef and kocho were compared with 30 type strains. Discrepancies were observed between the three methods in assigning strains of Lactobacillus plantarum, Lact. fermentum, Weissella minor and Lact. gallinarum, and Lact. fermentum, Lact. amylophilus, Lact. casei subsp. pseudoplantarum and Lact. rhamnosus. DNA reassociation data agreed well with RAPD results. CONCLUSIONS: API 50 CH profiles should be complemented with molecular genetic results for effective identification in Lactobacillus. SIGNIFICANCE AND IMPACT OF THE STUDY: The study suggested less dependability of metabolic data alone as an identification tool.     

16S ribosomal DNA analysis of the faecal lactobacilli composition of human subjects consuming a probiotic strain Lactobacillus acidophilus NCFM

AIMS: The aims of this study were to evaluate the ability of exogenous Lactobacillus acidophilus strain NCFM to survive through the human gastro-intestinal (GI) tract, and to evaluate the selectivity of Rogosa SL medium for faecal lactobacilli. METHODS AND RESULTS: The composition of the faecal lactobacilli of 10 healthy subjects was monitored for two weeks prior to, two weeks during and two weeks after the administration of the Lact. acidophilus strain NCFM consumed with skim milk (daily dose 10(10) viable cells). Fresh faecal samples were collected, processed and cultured on Rogosa SL selective medium for lactobacilli enumeration. Colonies demonstrating various morphologies were identified and purified for 16S ribosomal DNA sequence analysis for speciation of colonial genotype. The species composition of cultivable faecal lactobacilli changed considerably during consumption of the strain NCFM. CONCLUSIONS: The probiotic Lact. acidophilus strain NCFM can survive through the human GI tract, but cannot colonize itself during the two-week consumption. Rogosa SL medium is selective for faecal lactobacilli. However, genetic analysis is required for colony speciation. SIGNIFICANCE AND IMPACT OF THE STUDY: It is demonstrated that continuous consumption is necessary to maintain a high population of the probiotic strain, and that the Rogosa SL medium is reliable.     

Characterization of cell envelope-associated proteinases of thermophilic lactobacilli

D. FIRA, M. KOJIC, A. BANINA, I. SPASOJEVIC, I. STRAHINIC AND L. TOPISIROVIC. 2001 . The proteolytic activities of two natural isolates of thermophilic lactobacilli, Lactobacillus acidophilus BGRA43 and Lact. delbrueckii BGPF1, and Lact. acidophilus CH2 (Chr. Hansen's strain) and Lact. acidophilus V74 (Visby's strain), were compared. Results revealed that optimal pH for all four proteinases is 6·5, whereas temperature optimum varied among proteinases. Determination of caseinolytic activity done under optimal conditions for each strain revealed that the CH2 and V74 proteinases completely hydrolysed both α_S1-casein and β-casein, showing very low activity towards κ-casein. The BGPF1 proteinase completely hydrolysed only β-casein. The BGRA43 proteinase completely hydrolysed all three casein fractions. The proteolytic activities of whole cells were inhibited by serine proteinase inhibitors, suggesting that all four strains produce serine proteinases. DNA–DNA hybridization and PCR analysis showed that BGPF1 contains the prtB -like proteinase gene. Characterized thermophilic strains BGPF1 and BGRA43 were successfully used as starter cultures for production of yoghurt and acidophilus milk, respectively.     

Use of folic acid casei medium reveals trimethoprim susceptibility of Lactobacillus species

AIM: Lactobacilli have been reported to have intrinsic resistance to trimethoprim. The susceptibility of lactobacilli to trimethoprim on different media was investigated in order to search for a phenotypic test method that could indicate the presence of acquired resistance genes. METHODS AND RESULTS: Strains of Lactobacillus acidophilus, Lact. paracasei, Lact. rhamnosus and Lact. plantarum were susceptibility tested with E-tests on folic acid casei medium (FACM), MRS and defined medium 1. The effects of addition or removal of nucleosides and thymidine phosphorylase were investigated. E-tests on FACM yielded reproducible minimal inhibitory concentrations (MICs) for trimethoprim but addition of nucleosides was necessary for growth of Lact. acidophilus. MICs for the tested strains were 0.125-0.19, 0.25-3 and 0.064-0.19 microg ml(-1) for Lact. paracasei, Lact. rhamnosus and Lact. plantarum, respectively. With the addition of deoxyuridine and deoxyadenosine to FACM the MICs of Lact. acidophilus were 0.064-1 microg ml(-1). CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: Lactobacilli do not have intrinsic resistance to trimethoprim. The results show that trimethoprim susceptibility testing of the tested Lactobacillus species is possible and indicate that transferable resistance genes are absent in all the tested strains.     

Probiotic properties of human lactobacilli strains to be used in the gastrointestinal tract

AIMS: The study of two human strains of Lactobacillus to be used as probiotics in the gastrointestinal tract. METHODS AND RESULTS: The Lactobacillus acidophilus UO 001 and Lact. gasseri UO 002, were resistant to the gastrointestinal conditions (pH 2 and 3, presence of pepsin, pancreatin or bile salts), the resistance was enhanced in the presence of skimmed milk. Additionally, adhered to Caco-2 cells through glycoproteins in Lact. gasseri and carbohydrates in the case of Lact. acidophilus. These strains are able to inhibit the growth of certain enteropathogens: Salmonella, Listeria and Campylobacter without interfering with the normal microbiota of the gastrointestinal tract, as stated by using the mixed culture and the spot agar test. Finally, strongly adherent Lact. gasseri were found to inhibit the attachment of Escherichia coli O111 to intestinal Caco-2 cells under the condition of exclusion. CONCLUSIONS: These results indicate that the two strains of Lactobacillus from human origin present important properties for survival in, and colonization of, the gastrointestinal tract, that give them potential probiotic. SIGNIFICANCE AND IMPACT OF THE STUDY: Two strains of Lactobacillus isolated from human vagina of healthy premenopausal women could be promising candidates to be used in the preparation of probiotic products and for their use as health-promoting bacteria.     

Characterization of Escherichia coli serogroups causing meningitis, sepsis and enteritis. I. Serological properties and animal pathogenicity of O18, O78 and O83 isolates.

Escherichia coli O78: K80 strains isolated from an outbreak among premature and newborn infants with meningitis, sepsis and enteritis, from sporadic cases of enteritis and from healthy carriers were compared with one another and with different E. coli serogroups. The O78: K80 cultures uniformly failed to give the rabbit intestinal loop test and the guinea pig eye reaction and none of them contained L1 antigen. After intraperitoneal injection into mice, the organisms multiplied in the peritoneal cavity and caused bacteriaemia lasting at least 2 weeks. E. coli strains originating from septicaemia (O78: K80, O18a,c: K?, O83: K?) showed significantly lower LD50 values for mice (9 x 10(3)--7 x 10(5)) than did E. coli serogroups associated with infantile enteritis only (3 x 10(8)--7 x 10(8)). It is assumed that the isolates differ in pathogenicity not only from E. coli strains associated with "cholera-like" disease and with "dysenteriform" infection, but also from L1 antigen-containing cultures described in neonatal meningitis, and constitute a separate group characterized by an ability to cause meningitis, sepsis and enteritis within the same outbreak.     

COMPARING ATTACHMENT, HEAT TOLERANCE AND ALKALI RESISTANCE OF PATHOGENIC AND NONPATHOGENIC BACTERIAL CULTURES ON ORANGE SURFACES

Trials were conducted to compare surrogate organisms (PSO) to human pathogens (Salmonella spp. and Escherichia coli O157:H7) on the surface of orange fruit. Among the six evaluated PSO, E. coli ATCC 8739 and E. coli ATCC 35218 showed a significantly lower attachment (S_R) on fruit in comparison to Salmonella spp. In thermal tolerance studies, the D_70C values of the evaluated PSO were either no different from or greater than those of the pathogens. However, the D_80C ofE. coli ATCC 25922 was significantly lower than that of the E. coli O157:H7. In general, E. coli ATCC 11229 exhibited a higher level of alkali sensitivity than both pathogens; whereas Lactobacillus plantarum ATCC 14917 and, to a lesser extent, Lactobacillus fermentum ATCC 538 showed a significantly greater tolerance to the alkali treatments. The results suggest that nonpathogenic cultures ofE. coli ATCC 11229, L. fermentum ATCC 538, and L. plantarum ATCC 14917 may be utilized in fresh fruit research as surrogates for pathogens to evaluate the efficacy of thermal decontamination. In addition, E. coli ATCC 25922, L. fermentum ATCC 538, and L. plantarum ATCC 14917 cultures may be used to represent pertinent pathogens for validating fruit decontamination by alkaline cleaners.