Antacid increases survival of Vibrio vulnificus and Vibrio vulnificus phage in a gastrointestinal model

Bioactive chitosan-citral Schiff base zinc complex: A pH-responsive platform for potential therapeutic applications

The application of CO2 supercritical fluid (SCF) technology has developed rapidly because of its non-toxic, environmentally friendly, mild reaction conditions and safety. The SCF technology can effectively speed up the reaction process of nano-material synthesis, and maintains a high degree of controllability and repeatability. This study mainly included carboxymethyl chitosan sodium salt (CCS), citral (CT), p-coumaric acid (CA), and ZnSO4 as raw materials to prepare CCS-CT-CA-Zn complex as a pH-responsive agent and was investigated using supercritical fluid technique. The coordination structure of Bridge-CCS-CT-CH3COO-CA-Zn-Schiff base/OH and the morphology of the complex agents were verified. The prepared CCS-CT-CA-Zn complex showed good dispersion and uniformity (mean size: 852 ± 202 nm, PdI: 0.301, and mean zeta potential: -31 ± 6 mV). Also, it has a good pH responsive release in an acid environment. Besides, both of CCS-CT-CA-Zn complex (DS-B) and its decomposed mixture in acid (DS-A) demonstrated significant antioxidant and anti-vibrio activity. Moreover, both DS-B complex and DS-A mixture inhibited biofilm formation, swimming, and swarming motilities of V. parahaemolyticus in a dose-dependent manner. This work will provide a scientific basis for the further design and development of natural products derived antibacterial-antioxidant complex agents, food additives and feed additives.

In Vivo Recovery of Bacteriophages and Their Effects on Clostridium perfringens-Infected Broiler Chickens

The objectives of this study were to recover bacteriophages (BPs) from the intestinal digesta of BP-fed broilers and to evaluate the antibacterial effects of encapsulated or powdered BPs in broiler chickens challenged with Clostridium perfringens. Day-old broiler chicks (n = 320/experiment) were randomly assigned to 32 pens (n = 10 broilers/pen) and allocated to one of four dietary groups: (1) unchallenged group (NEG); (2) C. perfringens-challenged group (POS); (3) POS group fed a diet supplemented with powdered BPs; and (4) POS group fed a diet supplemented with encapsulated BPs. On days 21, 22, and 23 post-hatch, all chickens except NEG were orally inoculated twice a day with 2 mL C. perfringens (1.0 × 10⁸ cfu/mL). Varying BP levels were detected in gut digesta at all ages and were numerically or significantly higher in the encapsulated BP group than in the powdered BP group. Dietary powder or encapsulated BPs reversed the C. perfringens-mediated increase in crypt depth. In addition, villus height to crypt depth ratio was elevated in the NEG and BP-treated/challenged groups compared with that in the POS group. C. perfringens counts in the cecum were significantly lower in the BP-fed chickens than in the POS group. The encapsulated BP-supplemented diet-fed chickens had the highest serum IgA levels. Collectively, our results suggest that dietary BP remains viable in intestinal digesta upon ingestion and can inhibit cecal C. perfringens counts.

On the feasibility of spray-dried eudragit-trehalose microparticles for enteric drug delivery

Enteric infections have long constituted a silent epidemic responsible for hundreds of thousands of deaths around the world every year. Because of the global rise in antibiotic-resistant bacteria and the slow development of new small-molecule antibiotics, alternatives such as bacteriophage therapy have become a much sought-after option in the treatment of enteric infections. However, the administration of therapeutics through the oral route to target gastrointestinal infections poses challenges to dosage formulation because these active ingredients, particularly relatively fragile biological entities, require protection from the stomach's harsh acids. Encapsulation of the therapeutics within a pH-responsive coating capable of surviving low pH conditions has the potential to provide such protection. In this study, we developed a spray-dried powder vehicle capable of withstanding low pH comparable to stomach conditions, using Eudragit® S100 as a protective particle coating and trehalose as a stabilizing excipient for a possible active component. A particle formation model and a monodisperse droplet chain technique were initially used to study the formation process of Eudragit-trehalose composite microparticles at different ratios and in different ratios of water-ethanol solvent, which showed formation of particles with Eudragit shells varying in thickness from 0.13 μm to 0.75 μm. Promising Eudragit-trehalose formulations were subsequently spray-dried and their survival in acidic and alkaline environments studied using a new shadowgraphic imaging method. The results demonstrated that Eudragit was capable of creating a protective shell in the particles irrespective of the type of solvent used to prepare the formulations. The trehalose cores of particles with higher than 5% w/w of Eudragit remained protected after one hour of exposure at pH 2, indicating the potential of Eudragit-trehalose formulations for enteric delivery of drugs.

In Vitro and In Vivo Gastrointestinal Survival of Non-Encapsulated and Microencapsulated Salmonella Bacteriophages: Implications for Bacteriophage Therapy in Poultry

The therapeutic use of bacteriophages is recognized as a viable method to control Salmonella. Microencapsulation of phages in oral dosage forms may protect phages from inherent challenges of the gastrointestinal tract in chickens. Therefore, the main objective of this study was to assess the survival of Salmonella BP FGS011 (non-encapsulated and microencapsulated) through the gastrointestinal tract under in vitro as well as in vivo conditions after oral administration to 1-day-old chicks. To this end, the phage FGS011 was encapsulated in two different pH-responsive formulations with polymers Eudragit^® L100, and Eudragit^® S100 using the process of spray drying. Phages encapsulated in either of the two formulations were able to survive exposure to the proventriculus-gizzard in vitro conditions whereas free phages did not. Moreover, phages formulated in polymer Eudragit^® S100 would be better suited to deliver phage to the caeca in chickens. In the in vivo assay, no statistically significant differences were observed in the phage concentrations across the gastrointestinal tract for either the free phage or the encapsulated phage given to chicks. This suggested that the pH of the proventriculus/gizzard in young chicks is not sufficiently acidic to cause differential phage titre reductions, thereby allowing free phage survival in vivo.

Vibriosis and Aeromonas infection in shrimp: Isolation, sequencing, and control

Background and Aim: Shrimp is one of the most commonly consumed types of seafood. It is a very nutritious healthy food. Shrimp is low in calories and rich in protein and healthy fats. It also contains a treasure trove of vitamins and minerals. On the negative side, it may be affected by many bacterial diseases which affect its health. Furthermore, it may be incriminated as a vector of foodborne illnesses that range from mild gastrointestinal upset to life-threatening diseases. This study was designed to assess the clinical picture and zoonotic importance of vibriosis and Aeromonas infection in live shrimp and to study the antibacterial effect of citric acid (lemon juice) and acetic acid (vinegar) on these pathogens. Materials and Methods: A total of 170 live shrimp (Metapenaeus monoceros) samples were collected from Suez City, Egypt. The samples were examined clinically, and then, they were enriched into alkaline peptone water and cultivated on thiosulfate-citrate-bile salts-sucrose agar and ampicillin MacConkey agar for the isolation of Vibrio and Aeromonas species, respectively. The recovered isolates were confirmed biochemically and genotypically using duplex polymerase chain reaction (PCR) and sequencing. The germicidal effects of vinegar and lemon on artificially contaminated shrimp samples with Aeromonas hydrophila and Vibrio parahaemolyticus at different times (0.25, 1, 1.5, and 24 h) and temperatures (5° and 30°C) were studied. Results: The results revealed that some of the infected shrimp were hypoxic, lethargic with abnormal swimming behavior. In most cases, body appendages, telsons, uropods, and gills took black coloration. In addition, the hepatopancreas appeared soft, swollen, and congested. The prevalence rates of vibriosis in each of the musculature and hepatopancreas were 4.7%, while the prevalence rates of Aeromonas infection in the musculature and hepatopancreas were 11.8% and 11.2%, respectively. Duplex PCR showed that Aeromonas isolates gave double bands: 237 bp specific for gcat and 500 bp specific for 16S rRNA, while Vibrio spp. and Plesiomonas shigelloides isolates gave single band at 500 bp. The effect of organic acid treatment showed that acetic acid (vinegar 5%) had increasing reduction rates that reached its maximum level after 24 h; where it caused (100% inhibition) for A. hydrophila at both temperatures and (33.63% and 60% inhibition) for V. parahaemolyticus at refrigerator and room temperatures, respectively. Moreover, acetic acid was more effective at room temperature than at refrigerator temperature. Concerning the effect of lemon juice (citric acid), it was more effective than acetic acid at short marination (0.25 and 1 h) at both temperatures for the two pathogens. Moreover, lemon was more effective at refrigerator temperature than at room temperature at the same aforementioned time. The difference between the reduction effects of the two acids on both pathogens was statistically significant (p<0.0001). Conclusion: Overall, the examined shrimp samples were found to be vectors for Vibrio and Aeromonas spp. Application of hygienic measures during handling and cooking of shrimp should be esteemed. The organic acid treatment trial showed that vinegar and lemon juice can be used as a safe and economic method to limit the microbial contamination in seafood.

Cholera Outbreak due to Raw Seafood Consumption in South Korea, 2016

Three cases of cholera occurred in South Korea during a period of three weeks in August 2016. All the cases were associated with the consumption of raw seafood in southern coastal area of South Korea. Epidemiologic investigations were performed to track the spread of cholera, including persons in contact with the cholera patients, seafood, and seawater from the fish tank and marine environments. A microbiological investigation demonstrated that cholera isolated from the three patients and a seawater sample at the Korea Strait showed identical serotype (O1 Ogawa), biotype (El tor), and toxin (ctx-positive). Pulsed-field gel electrophoresis analysis showed that the three clinical strains are identical (100%) and shared 97% identity with the seawater sample.

A minireview on the in vitro and in vivo experiments with anti-Escherichia coli O157:H7 phages as potential biocontrol and phage therapy agents

Phage therapy is an old method of combating bacterial pathogens that has recently been taken into consideration due to the alarming spread of antibiotic resistance. Escherichia coli O157:H7 is a foodborne pathogen that causes hemorrhagic colitis and life-threatening Hemolytic Uremic Syndrome (HUS). There are several studies on isolation of specific phages against E. coli O157:H7 and more than 60 specific phages have been published so far. Although in vitro experiments have been successful in elimination or reduction of E. coli O157:H7numbers, in vivo experiments have not been as promising. This may be due to escape of bacteria to locations where phages have difficulties to enter or due to the adverse conditions in the gastrointestinal tract that affect phage viability and proliferation. To get around the latter obstacle, an alternative phage delivery method such as polymer microencapsulation should be tried. While the present time results are not very encouraging the work should be continued as more efficient phage treatment regimens might be found in future.

Complete genome sequence of Vibrio vulnificus bacteriophage SSP002

Vibrio vulnificus phages are abundant in coastal marine environments, shellfish, clams, and oysters. SSP002, a V. vulnificus-specific bacteriophage, was isolated from oysters from the west coast of South Korea. In this study, the complete genome of SSP002 was sequenced and analyzed for the first time among the V. vulnificus-specific bacteriophages.

Genomic, proteomic and physiological characterization of a T5-like bacteriophage for control of Shiga toxin-producing Escherichia coli O157:H7

Despite multiple control measures, Escherichia coli O157:H7 (STEC O157:H7) continues to be responsible for many food borne outbreaks in North America and elsewhere. Bacteriophage therapy may prove useful for controlling this pathogen in the host, their environment and food. Bacteriophage vB_EcoS_AKFV33 (AKFV33), a T5-like phage of Siphoviridae lysed common phage types of STEC O157:H7 and not non-O157 E. coli. Moreover, STEC O157:H7 isolated from the same feedlot pen from which the phage was obtained, were highly susceptible to AKFV33. Adsorption rate constant and burst size were estimated to be 9.31 × 10(-9) ml/min and 350 PFU/infected cell, respectively. The genome of AKVF33 was 108,853 bp (38.95% G+C), containing 160 open reading frames (ORFs), 22 tRNA genes and 32 strong promoters recognized by host RNA polymerase. Of 12 ORFs without homologues to T5-like phages, 7 predicted novel proteins while others exhibited low identity (<60%) to proteins in the National Centre for Biotechnology Information database. AKVF33 also lacked the L-shaped tail fiber protein typical of T5, but was predicted to have tail fibers comprised of 2 novel proteins with low identity (37-41%) to tail fibers of E. coli phage phiEco32 of Podoviridae, a putative side tail fiber protein of a prophage from E. coli IAI39 and a conserved domain protein of E. coli MS196-1. The receptor-binding tail protein (pb5) shared an overall identify of 29-72% to that of other T5-like phages, with no region coding for more than 6 amino acids in common. Proteomic analysis identified 4 structural proteins corresponding to the capsid, major tail, tail fiber and pore-forming tail tip (pb2). The genome of AKFV33 lacked regions coding for known virulence factors, integration-related proteins or antibiotic resistance determinants. Phage AKFV33 is a unique, highly lytic STEC O157:H7-specific T5-like phage that may have considerable potential as a pre- and post-harvest biocontrol agent.

Campylobacter bacteriophages and bacteriophage therapy

Members of the genus Campylobacter are frequently responsible for human enteric disease with occasionally very serious outcomes. Much of this disease burden is thought to arise from consumption of contaminated poultry products. More than 80% of poultry in the UK harbour Campylobacter as a part of their intestinal flora. To address this unacceptably high prevalence, various interventions have been suggested and evaluated. Among these is the novel approach of using Campylobacter-specific bacteriophages, which are natural predators of the pathogen. To optimize their use as therapeutic agents, it is important to have a comprehensive understanding of the bacteriophages that infect Campylobacter, and how they can affect their host bacteria. This review will focus on many aspects of Campylobacter-specific bacteriophages including: their first isolation in the 1960s, their use in bacteriophage typing schemes, their isolation from the different biological sources and genomic characterization. As well as their use as therapeutic agents to reduce Campylobacter in poultry their future potential, including their use in bio-sanitization of food, will be explored. The evolutionary consequences of naturally occurring bacteriophage infection that have come to light through investigations of bacteriophages in the poultry ecosystem will also be discussed.

Lactic acid as a potential decontaminant of selected foodborne pathogenic bacteria in shrimp (Penaeus merguiensis de Man)

Fresh raw shrimps were dipped for 10, 20, and 30 min at room temperature (25°C ± 1°C) in lactic acid (LA; 1.5%, 3.0%, v/v) to evaluate their antipathogenic effects against Vibrio cholerae, Vibrio parahaemolyticus, Salmonella entreitidis, and Escherichia coli O157:H7 inoculated at a level of 10(5) CFU/g. Significant reductions in the population of all these pathogenic bacteria were recorded after dipping treatments, which were correlated to the corresponding LA concentrations and treatment time. With respect to the microbial quality, 3.0% LA treatment for 10 min was acceptable in reducing the pathogenic bacteria. Additionally, sensory evaluation results revealed a 10-min dip in 3.0% LA to be more acceptable organoleptically compared with 20 and 30 min of treatments. Results of the present study are envisaged to be useful for commercial applications for effective decontamination of shrimp.

Survival of Listeria monocytogenes in a simulated dynamic gastrointestinal model during storage of inoculated bologna and salami slices in vacuum packages

Listeria monocytogenes counts were determined during storage (82 days, 4 degrees C) in vacuum packages of inoculated bologna and salami slices and after exposure to a simulated dynamic model of the stomach and small intestine. Variables controlled in the model included gastric emptying and gastrointestinal fluid secretion rates, gradual gastric acidification, and intestinal pH maintenance. L. monocytogenes populations increased on bologna and decreased on salami, reaching 8.7 and 1.4 log CFU/g, respectively, on day 82. Inactivation rates (IR) during gastric exposure of bologna and salami ranged from 0.079 (day 14) to 0.158 (day 57) log CFU/g/min and from 0.013 (day 42) to 0.051 (day 1) log CFU/g/min, respectively. On corresponding days, gastric IR for cells on salami were lower than on bologna, suggesting potential protective effects of the former product. However, it is also possible that the low initial L. monocytogenes levels reached with storage of salami (< or = 2.5 log CFU/g after day 27) may have resulted in slower reductions than in the high levels on bologna. Gradual decline of gastric pH allowed survival in the gastric compartment during the initial stages, which resulted in a large fraction of the cells being delivered into the intestinal compartment. Intestinal IR ranged from 0.003 to 0.048 (bologna) and from 0.002 to 0.056 (salami) log CFU/g/min throughout storage. Although findings indicated potential effects of salami against gastric killing of L. monocytogenes, any effects of the food matrix per se on the gastrointestinal survival of the pathogen were overwhelmed by the high and low contamination levels reached on bologna and salami, respectively, during storage.

Differences in survival among 13 Listeria monocytogenes strains in a dynamic model of the stomach and small intestine

Thirteen Listeria monocytogenes strains were compared for the ability to survive in a dynamic gastrointestinal model. Strains displayed various degrees of susceptibility to gastric acidity; however, strain-to-strain variations became evident mainly after 90 min of exposure (pH 2.0). Cell levels transferred to the intestine depended on initial populations, while reductions during intestinal exposure were relatively small for all strains.

Adaptation of Salmonella spp. in juice stored under refrigerated and room temperature enhances acid resistance to simulated gastric fluid

The objective of this study was to evaluate the acid resistance of Salmonella spp. adapted in juices stored under refrigeration and room temperatures to simulated gastric fluid (SGF, pH 1.5). Five Salmonella serovars, Agona, Gaminara, Michigan, Montevideo, and Poona were used in this study. Apple, orange, and tomato juices inoculated with five serovars were stored at refrigeration (7 degrees C) and room temperature (20 degrees C) for 24 h for adaptation. Acid resistances of serovars adapted in juice were determined in SGF at 37 degrees C. All acid-adapted Salmonella serovars in juices displayed enhanced survival time compared to non-adapted controls. Among serovars, S. Poona adapted in apple at 20 degrees C and orange juices at 7 and 20 degrees C showed >2.0 log cfu/ml survivors, while the other serovars decreased to non-detectable level or <2.0 log cfu/ml for 100 s in SGF. Unlike apple and orange juices, all serovars adapted in tomato juice survived with >2.0 log cfu/ml for 100 s. For D-values, all Salmonella serovars adapted in apple and tomato juice enhanced their acid resistances compared to orange juices. S. Agona adapted in tomato juice at 7 degrees C and S. Poona in apple juice at 20 degrees C had the highest D-values with 82.9 and 82.5s, respectively. Results showed that the adaptation in juice increased acid resistance in SGF and varied by serovar, juice type, and adaptation temperature. Therefore, this study indicates that the introduction of Salmonella spp. to an acidic juice environment during processing can enhance their ability to survive in a human stomach, possibly increasing the risk of a Salmonella outbreak by juice.

Post-Hurricane Katrina challenge: Vibrio vulnificus

PURPOSE

To describe the epidemiology, pathophysiology, diagnosis, treatment, and prevention of Vibrio vulnificus, a rare organism that surfaced following Huricane Katrina and caused serious problems for many victims.

DATA SOURCES

Selected scientific literature supplemented with case presentations of patients seen following Katrina.

CONCLUSIONS

After Hurricane Katrina and as a result of extensive flooding of below-sea-level New Orleans, toxic waters contaminated many areas of the city. As a result of this extensive flooding of toxic waters, people were exposed to V. vulnificus.

IMPLICATIONS FOR PRACTICE

Consider V. vulnificus in the differential diagnosis and culture all wounds for this organism in any patients exposed to contaminated seawater. Prompt initiation of antibiotic treatment, especially before the onset of septic shock, provides the best outcomes.

Effect of trisodium phosphate adaptation on changes in membrane lipid composition, verotoxin secretion, and acid resistance of Escherichia coli O157:H7 in simulated gastric fluid

Escherichia coli O157:H7 (HEC), E. coli O157:H7 rpoS mutant (HEC-RM), and nonpathogenic E. coli (NPEC) were step-wise adapted to trisodium phosphate (TSP) by incubation in broths of increasing concentration, from 0% to 0.6%, at 37 degrees C for 24 h. After incubation at each concentration, each population was examined for acid resistance (D value) in simulated gastric fluid of pH 1.5, cell envelope membrane lipid composition, and intracellular and extracellular verotoxin concentrations. The ratio of cis-vaccenic acid (18:1omega7c) to palmitic acid (16:0) increased, indicating increased membrane fluidity with increasing TSP concentration up to 0.4%, but decreased at 0.6%. HEC and HEC-RM adapted at 0.4% TSP had the highest verotoxin concentrations of 1805 and 1879 ng/ml, respectively. In addition, with HEC the ratio of extracellular to intracellular verotoxin concentration decreased at higher TSP concentrations. In contrast, the ratio for HEC-RM increased at 0.4% TSP. HEC adapted to 0.4% TSP had the greatest survival in gastric fluid (58 min D value) among all treatments. For HEC, the increase in membrane fluidity was associated with increased acid resistance and extracellular verotoxin concentration for cells adapted to 0.4% TSP. In contrast, the increase in membrane fluidity was associated with decreased acid resistance of TSP adapted HEC-RM although the extracellular verotoxin concentration increased. Therefore, the deletion of the rpoS gene appeared to affect the changes in verotoxin concentration and acid resistance of TSP adapted E. coli O157:H7.

The coexistence of Escherichia coli serotype O157:H7 and its specific bacteriophage in continuous culture

For the development of phage therapy, systematic understanding mechanisms of bacteriophage resistance will be required. We describe a new strain of Escherichia coli O157:H7, named Mu(L), which stably co-exists with the O157:H7-specific lytic bacteriophage PP01. Chemostat cultures of E. coli O157:H7 infected with PP01 showed unchanging cell concentration, but phage concentrations which increased by approximately 10(8) PFU mL(-1). However, the latent period, burst size, and growth rate of Mu(L) were the same as in a PP01-susceptible strain. The binding rate of PP01 to the cell surface was diminished 8.5-fold in Mu(L). By observation of the binding of fluorescently labeled O157:H7-specific phage to individual Mu(L) cells, we found that clonal Mu(L) cultures were heterogeneous in their ability to bind bacteriophage. 15% of the Mu(L) population was completely resistant to PP01 infection. Mu(L) also co-existed with bacteriophages unrelated to PP01. Broad-range phage resistance by clonal heterogeneity represents a new class of bacteria-phage interactions.

Influence of acetic, citric, and lactic acids on Escherichia coli O157:H7 membrane lipid composition, verotoxin secretion, and acid resistance in simulated gastric fluid

The effect of organic acid (acetic, citric, and lactic acids) adaptation at equivalent initial pH values (6.4 and 5.4) on changes in membrane lipid composition, verotoxin concentration, and acid resistance in simulated gastric fluid (pH 1.5, 37 degrees C) was determined for Escherichia coli O157:H7 ATCC 43895 (HEC) and an rpoS mutant of E. coli O157:H7 ATCC 43895 (RM, FRIK 816-3). For HEC, lactic acid-adapted (pH 5.4) cells had the greatest D-value (32.2 min) and acetic acid-adapted (pH 5.4) cells had the smallest D-value (16.6 min) in simulated gastric fluid. For RM, D-values of citric and acetic acid-adapted cells were similar to those for nonadapted cells grown at pH 7.3, but D-values increased from 13.1 to 27.9 min in lactic acid-adapted cells (from pH 7.3 to pH 5.4). For both strains, the ratio of cis-vaccenic to palmitic acids decreased for citric and lactic acid-adapted cells, but the ratio increased for acetic acid-adapted cells at pH 5.4. Organic acid-adapted cells produced less total verotoxin than did nonadapted cells at approximately 10(8) CFU/ml. Extracellular verotoxin concentration proportionally decreased with decreasing pH for both HEC and RM. Changes in membrane lipid composition, verotoxin concentration, and acid resistance in HEC and RM were dependent on both pH and organic acid. Deletion of the rpoS gene did not affect these changes but did decrease acid resistance in citric acid-adapted cells. Results indicate that decreased membrane fluidity may have caused increased acid resistance and decreased verotoxin secretion.

Effects of acid stress on Vibrio parahaemolyticus survival and cytotoxicity

For several foodborne bacterial pathogens, an acid tolerance response appears to be an important strategy for counteracting acid stress imposed either during food processing or by the human host. The acid tolerance response enhances bacterial survival of lethal acid challenge following prior exposure to sublethal acidic conditions. Previous studies have revealed relationships between a foodborne pathogen's ability to survive acid challenge and its infectious dose. Vibrio parahaemolyticus is capable of causing gastroenteritis when sufficient cells of pathogenic strains are consumed. This study was designed to characterize acid sensitivities and to compare the effects of sublethal acid exposure (adaptation) on survival capabilities and cytotoxicities of different V. parahaemolyticus strains. Survival of acid challenge by stationary-phase cells differed by up to 3 log CFU/ml among the 25 isolates tested. No differences in acid resistance were found between strains when they were grouped by source (clinical isolates versus those obtained from food). Survival at pH 3.6 for log-phase cells that had been previously exposed to sublethal acidic conditions (pH 5.5) was enhanced compared with that for cells not previously exposed to pH 5.5. However, for stationary-phase cells, exposure to pH 5.5 impaired both subsequent survival at pH 3.6 and cytotoxicity to human epithelial cells. Relative cytotoxicities of nonadapted stationary-phase cells were 1.2- to 4.8-fold higher than those of adapted cells. Sublethal acid exposure appears to impose measurable growth phase-dependent effects on subsequent lethal acid challenge survival and cytotoxicity of V. parahaemolyticus.

Adaptation of Escherichia coli O157:H7 to pH alters membrane lipid composition, verotoxin secretion, and resistance to simulated gastric fluid acid

The influence of adaptation to pH (from pH 5.0 to 9.0) on membrane lipid composition, verotoxin concentration, and resistance to acidic conditions in simulated gastric fluid (SGF) (pH 1.5, 37 degrees C) was determined for Escherichia coli O157:H7 (HEC, ATCC 43895), an rpoS-deficient mutant of ATCC 43895 (HEC-RM, FRIK 816-3), and nonpathogenic E. coli (NPEC, ATCC 25922). Regardless of the strain, D values (in SGF) of acid-adapted cells were higher than those of non-acid-adapted cells, with HEC adapted at pH 5.0 having the greatest D value, i.e., 25.6 min. Acid adaptation increased the amounts of palmitic acid (C16:0) and decreased cis-vaccenic acid (C18:1 omega 7c) in the membrane lipids of all strains. The ratio of cis-vaccenic acid to palmitic acid increased at acidic pH, causing a decrease in membrane fluidity. HEC adapted to pH 8.3 and HEC-RM adapted to pH 7.3 exhibited the greatest verotoxin concentrations (2,470 and 1,460 ng/ml, respectively) at approximately 10(8) CFU/ml. In addition, the ratio of extracellular to intracellular verotoxin concentration decreased at acidic pH, possibly due to the decrease of membrane fluidity. These results suggest that while the rpoS gene does not influence acid resistance in acid-adapted cells it does confer decreased membrane fluidity, which may increase acid resistance and decrease verotoxin secretion.

Coevolution of bacteriophage PP01 and Escherichia coli O157:H7 in continuous culture

The interaction between Escherichia coli O157:H7 and its specific bacteriophage PP01 was investigated in chemostat continuous culture. Following the addition of bacteriophage PP01, E. coli O157:H7 cell lysis was observed by over 4 orders of magnitude at a dilution rate of 0.876 h(-1) and by 3 orders of magnitude at a lower dilution rate (0.327 h(-1)). However, the appearance of a series of phage-resistant E. coli isolates, which showed a low efficiency of plating against bacteriophage PP01, led to an increase in the cell concentration in the culture. The colony shape, outer membrane protein expression, and lipopolysaccharide production of each escape mutant were compared. Cessation of major outer membrane protein OmpC production and alteration of lipopolysaccharide composition enabled E. coli O157:H7 to escape PP01 infection. One of the escape mutants of E. coli O157:H7 which formed a mucoid colony (Mu) on Luria-Bertani agar appeared 56 h postincubation at a dilution rate of 0.867 h(-1) and persisted until the end of the experiment (approximately 200 h). Mu mutant cells could coexist with bacteriophage PP01 in batch culture. Concentrations of the Mu cells and bacteriophage PP01 increased together. The appearance of mutant phage, which showed a different host range among the O157:H7 escape mutants than wild-type PP01, was also detected in the chemostat culture. Thus, coevolution of phage and E. coli O157:H7 proceeded as a mutual arms race in chemostat continuous culture.