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PubMedDate not supplied

Comparison of purified 12 kDa and recombinant 15 kDa Fasciola hepatica antigens related to a Schistosoma mansoni fatty acid binding protein.

Vaccines in schistosomiasis using homologous antigens have been studied extensively in experimentally infected mammalian hosts. Vaccines using heterologous antigens have received comparatively less attention. This review summarizes recent work on a heterologous 12 kDa Fasciola hepatica antigenic polypeptide which cross reacts with Schistosoma mansoni. A cDNA has been cloned and sequenced, and the predicted amino acid sequence of the recombinant protein has been shown to have significant (44%) identity with a 14 kDa S. mansoni fatty acid binding protein. Thus in the parasitic trematodes fatty acid binding proteins may be potential vaccine candidates. The F. hepatica recombinant protein has been overexpressed and purified and denoted rFh15. Preliminary rFh15 migrates more slowly (i.e. may be slightly larger) than nFh12 on SDS-PAGE and has a predicted pI of 6.01 vs. observed pI of 5.45. Mice infected with F. hepatica develop antibodies to nFh12 by 2 weeks of infection vs. 6 weeks of infection to rFh15; on the other hand, mice with schistosomiasis mansoni develop antibodies to both nFh12 and rFh15 by 6 weeks of infection. Both the F. hepatica and S. mansoni cross-reactive antigens may be cross-protective antigens with the protection inducing capability against both species.

Amino Acid Sequence↗

PubMedDate not supplied

Genetic and antigenic characterization of a poxvirus isolate from ostriches.

Avian poxvirus was isolated from nodules on the heads and conjunctiva of two 3-to-4-wk-old ostrich chicks. The ostriches from which poxvirus was isolated had been placed on premises where turkeys that had shown evidence of poxvirus infection had been raised earlier. Microscopically, the nodules from the ostriches were composed of proliferating and hypertrophic epithelial cells that formed large fronds. Most of the hypertrophic epithelial cells contained large eosinophilic intracytoplasmic inclusion bodies characteristic of poxvirus. Characterization of the avian poxvirus isolated from the cutaneous lesions in ostriches was based on western blotting of virus antigen, restriction fragment length polymorphism of genomic DNA, pathogenesis, and cross-protection studies in chickens. Antigenic and genetic studies did not reveal any significant difference between the poxvirus isolated from ostriches (PVO) and fowl poxvirus (FPV). Further, susceptible chickens immunized with the PVO were protected when challenged with a virulent strain of FPV. Thus, the poxvirus isolated from ostriches had similar antigenic, genetic, and biological properties to FPV.

Animals↗

PubMed2005

Interference between mild and pathogenic strains of infectious bursal disease virus in chickens.

Infectious bursal disease virus is a contagious, immunosuppressive disease of young chickens that is controlled by vaccination. Cross-protection occurs between different strains of the virus as a result of shared neutralizing epitopes. However, interactions between two antigenically similar strains (a mild and a pathogenic) coinfecting the same host have not been investigated. Groups of specific-pathogen-free chickens were inoculated with a mild strain followed by a pathogenic strain at 0, 16, 24, or 48 hr postinoculation (PI) with a mild strain. Virus persistence and the predominant strain of the virus were determined by reverse transcriptase-polymerase chain reaction and restriction fragment length polymorphism analysis, respectively, in bursas at 2, 4, 8, 14, and 21 days PI with the pathogenic strain. Severity of infection was assessed by the bursa/body weight ratios and histopathologic lesion scores. The mild virus interfered with replication of the pathogenic virus. The greatest interference was observed when the pathogenic strain was inoculated 24 hr PI with the mild strain. The interference phenomenon observed might be due to competition for host receptor sites or production of cytokine(s). This interference phenomenon could have practical implications for vaccine usage and protection.

Animals↗

PubMed2001

Identification of fatty acid molecules in a Fasciola hepatica immunoprophylactic fatty acid-binding protein.

Fasciola hepatica adult flukes have a native protein complex denoted nFh12 and consisting of fatty acid binding proteins that comprise at least 8 isoforms. It is a potent immunogen because in several animal hosts it induces an early antibody response to F. hepatica infection. It is also a potent cross-protective immunogen because it induces a protective immune response in mice to challenge infection with Schistosoma mansoni cercariae. The gene encoding this protein has been cloned and sequenced. It produces a polypeptide of 132 amino acids with a predicted molecular mass of 14.7 kDa and is denoted rFh15. It also has a significant homology to a 14-kDa S. mansoni fatty acid binding protein (Sm14). In the present study, nFh12 was delipidated with charcoal treatment and then studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Additionally, a lipid analysis of nFh12 was undertaken using gas chromatography-mass spectrometry to demonstrate that the nFh12 protein complex is, in fact, a complex of fatty acid binding proteins. Five long-chain saturated and unsaturated fatty acids were detected. The most abundant were palmitic acid (38%), stearic acid (24%), and oleic acid (13%). These fatty acid molecules do not have covalent bonds attached to the protein molecule. Because both nFh12 and Sm14 protect mice against challenge infection with F. hepatica and S. mansoni, it is possible that they have common protective epitopes in which fatty acids could be involved. Further studies are in progress to determine the chemical nature of these potential common epitopes.

Animals↗

PubMed1990

Theileria parva: the nature of the immune response and its significance for immunoprophylaxis.

Theileria parva is a tick-borne haemoprotozoan parasite of cattle and buffalo which is responsible for considerable economic losses to cattle farming in Eastern, Central and Southern Africa. Infection with the parasite results in an acute lymphoproliferative disorder with high mortality, but animals which survive infection are solidly immune to homologous challenge. Such immunity can be reproduced by infecting cattle with the parasite and treating them with tetracyclines or theilericidal drugs, but the widespread use of this technique as a method of control is hindered by its dependence on live parasites which require cryopreservation for maintenance and can give rise to carrier states. In addition, cross-protection between different strains of the parasite is not absolute. These problems have prompted a search for methods of immunisation based on the use of inactivated parasites or their derivatives. Such efforts have met with consistent failure, however, and in recent years scientists have adopted the more rational approach of defining the immune responses of cattle to the parasite with a view to identifying the parasite components which provoke them. These studies have revealed that protection is likely to be mediated by parasite-specific cytotoxic T cells which are restricted by class I major histocompatibility complex (MHC) products. The significance of this observation to the development of an effective subunit vaccine is discussed in the light of current knowledge of the inductive requirements of cytotoxic T cells.

Animals↗

PubMed2004

HIV-1 superinfection: evidence and impact.

Superinfection is defined as infection by a second virus during an immunologic steady state, following infection by a primary virus. It is now well established that superinfection with HIV-1 occurs in humans. Detection of an increasing number of circulating recombinant forms, which result from infection of a cell by two or more clades, suggests that superinfection occurs more frequently than previously thought. The second virus (from a different clade or the same clade as the primary virus) can superinfect some time after the first and this is associated with rapid viral rebound and immune decline. Primary infection with a specific clade appears not to provide cross-protection against superinfection with a different clade or the same clade. Estimating the overall impact of HIV-1 superinfection on pathogenesis and attempts to create a broadly protective prophylactic HIV-1 vaccine is complicated by our inability to quantify the true incidence and prevalence.

Animals↗

PubMed1996

In vivo anti-influenza virus activity of Kampo (Japanese herbal) medicine "Sho-seiryu-to"--effects on aged mice, against subtypes of a viruses and B virus, and therapeutic effect.

When aged BALB/c mice (approximately 6 months old) were treated with a Kampo (Japanese herbal) medicine "Sho-seiryu-to (SST)" (1 g/kg, 10 times) orally from 7 days before to 4 days after the infection and infected with mouse-adapted influenza virus A/PR/8/34 (H1N1 subtype) by nasal site-restricted infection, replication of the virus in the broncho-alveolar cavity was efficiently inhibited at 5 days after infection in comparison with water-treated mice. The antiviral IgA antibody in the broncho-alveolar wash of the SST treated aged mice increased significantly. When mice (7 weeks old) were administered orally with SST (1 and 2 g/kg, 7 times) from 4 days before to 3 days after the infection and infected with mouse-adapted influenza virus A/Guizhou/54/89 (H3N2 subtype) or B/Ibaraki/2/85, replication of the viruses in the nasal cavity and lung were significantly inhibited at 4 days after infection in comparison with control mice. When mice infected with influenza virus A/Fukuoka/C29/85 (H3N2) before 14 days were secondary infected with A/PR/8 virus and administered orally with SST (1 g/kg, 5 times) from 2 h to 5 days after the secondary infection, replication of the virus in both nasal and broncho-alveolar cavities were significantly inhibited at 5 days after the secondary infection in comparison with water-treated control. Oral administration of SST (1 g/kg, 18 times) from 7 days before to 14 days after vaccination followed by secondary nasal inoculation of influenza HA vaccine (5 micrograms/mouse) at 14 days after the first vaccination significantly augmented nasal antiviral IgA antibody and broncho-alveolar and serum antiviral IgG antibodies. These results suggest that SST is useful for influenza virus infection on aged persons and for cross-protection of subtypes of influenza A viruses and influenza B virus. SST is also useful for the treatment of influenza virus infection on human which has a history of influenza virus infection and/or influenza vaccination.

Aging↗

PubMed1994

Effect of Re-17 mutant Salmonella typhimurium bacterin toxoid on clinical coliform mastitis.

The objective of this study was to test the hypothesis that the incidence and severity of clinical coliform mastitis could be decreased by Re-17 mutant Salmonella typhimurium bacterin toxoid. Holstein-Friesian cows from two Arizona dairies were selected for this study based on July through November projected calving dates; peak lactation occurred during the period of highest rainfall and peak environmental stress. The cows were randomly assigned to either a vaccinate or a control group, and 1292 cows were paired by herd, parity, calving date, and milk yield. The 646 vaccinates were injected twice during the third trimester of pregnancy with an Re-17 mutant S. typhimurium bacterin toxoid, and the 646 controls were not vaccinated. Vaccinated cows had significantly fewer clinical cases of coliform mastitis with positive coliform cultures and had lower culling rate from coliform mastitis than control cows during the first 5 mo of lactation. During the same period, the mortality rate from clinical coliform mastitis was 75% less in the vaccinated clinical coliform mastitic group than in the control group. Incidence of mastitis increased with advancing parity. The Re-17 mutant Salmonella typhimurium bacterin toxoid provided cross-protection against coliform mastitis; incidence and severity of clinical coliform mastitis were significantly lowered during the first 5 mo of lactation.

Animals↗

PubMed2006

Making better influenza virus vaccines?

Killed and live influenza virus vaccines are effective in preventing and curbing the spread of disease, but new technologies such as reverse genetics could be used to improve them and to shorten the lengthy process of preparing vaccine seed viruses. By taking advantage of these new technologies, we could develop live vaccines that would be safe, cross-protective against variant strains, and require less virus per dose than conventional vaccines. Furthermore, pandemic vaccines against highly virulent strains such as the H5N1 virus can only be generated by reverse genetics techniques. Other technologic breakthroughs should result in effective adjuvants for use with killed and live vaccines, increasing the number of available doses. Finally, universal influenza virus vaccines seem to be within reach. These new strategies will be successful if they are supported by regulatory agencies and if a robust market for influenza virus vaccines against inter-pandemic and pandemic threats is made and sustained.

Adjuvants, Immunologic↗

PubMed2006

Influenza surveillance in Victoria, 2005.

Influenza activity remained within normal seasonal activity with a well-defined peak at week 29 (beginning 18 July) during the Victorian influenza season from May to September 2005. Surveillance was based on sentinel general practice influenza-like illness (ILI) notifications with laboratory confirmation, medical locum service ILI notifications and laboratory notification of influenza detections. One thousand and eighty-seven consultations for ILI were reported from 38 general practices, while medical practitioners from the locum service reported 317 consultations for ILI. The average weekly rate of ILI from sentinel surveillance was 7.3 per 1,000 consultations. Similar numbers of influenza A subtypes H1N1 and H3N2 were detected; 45 per cent of which were A/California/7/2004-like (H3), 44 per cent were A/New Caledonia/20/99-like (H1) and 11 per cent were A/Wellington/1/2004 (H3). Of the influenza B samples, 67 per cent were B/Hong Kong/330/2001-like and 33 per cent were B/Shanghai/361/2002-like. The influenza vaccine for 2005 contained: A/New Caledonia/20/99(H1N1)-like virus, A/Wellington/ 1/2004(H3N2)-like virus, and B/Shanghai/361/2002-like virus. Although the predominant H3 and B circulating strains were not included in the vaccine, there was reasonable serological cross protection between vaccine and circulating strains.

Adolescent↗

PubMed2026

Chimeric vaccine based on Iraqi HLA alleles against a predominant local Escherichia coli phylogroup.

INTRODUCTION: Escherichia coli remains amongst the most globally important pathogens implicated in severe clinical manifestations. The progressive rise in multidrug-resistant strains highlights the urgent need for new vaccines. Therefore, this study was designed to develop a new multi-epitope vaccine containing the most conserved epitopes across E. coli pathotypes. Consequently, the study aimed to investigate the immunoadjuvant role of faecal microbiota transplantation in enhancing vaccine efficacy. METHODS: Eighteen of the most conserved B-cell and T-cell epitopes of FimH, LptD, and BamA proteins were selected and included in a single construct. During the epitope selection process, HLA alleles predominant in the Iraqi population, as reported in previous studies, were used as criteria for selecting T-cell epitopes. The chimeric protein was expressed in BL21 E. coli and purified using affinity chromatography. Vaccine cross-protective immunity and protection were tested in in vivo experiments. Different formulations were used in the experimental evaluation: three doses of 100 μg of purified chimeric protein, injected intraperitoneally alone or encapsulated in PLGA nanoparticles, after faecal microbiota transplantation with and without gut microbiota modulation mediated by a cocktail of antibiotics. IgG1, IL-4, INF-γ, and NLRP3 levels were measured at 30 and 75 days after the first immunisation dose. Immunised mice were challenged with the local B2 UPEC phylogroup, and protection efficacy was considered 48 h later. Finally, the histological effects of the different chimeric protein formulations on the liver were assessed. RESULTS: All vaccine formulations except those after faecal microbiota transplantation without gut microbiota modulation induce significant increases in IgG1, IL-4, and INF-γ levels at different times. Only vaccination after faecal microbiota transplantation with gut microbiota modulation elicited robust NLRP3 levels at 30 and 75 days after, and this was linked to the highest reduction in bladder bacterial load by 813-fold compared to the other formulations, as well as the mildest effect on liver histological changes. DISCUSSION: These results demonstrated that the chimeric vaccine provides preliminary protection against a local B2 UPEC isolate. Furthermore, modulating gut microbiota via faecal transplantation markedly enhances the immunogenicity and protective efficacy of vaccination, suggesting its adjuvanticity.

Animals↗

PubMed2001

Heterosubtypic immunity to influenza A virus in mice lacking IgA, all Ig, NKT cells, or gamma delta T cells.

The mechanisms of broad cross-protection to influenza viruses of different subtypes, termed heterosubtypic immunity, remain incompletely understood. We used knockout mouse strains to examine the potential for heterosubtypic immunity in mice lacking IgA, all Ig and B cells, NKT cells (CD1 knockout mice), or gamma(delta) T cells. Mice were immunized with live influenza A virus and compared with controls immunized with unrelated influenza B virus. IgA(-/-) mice survived full respiratory tract challenge with heterosubtypic virus that was lethal to controls. IgA(-/-) mice also cleared virus from the nasopharynx and lungs following heterosubtypic challenge limited to the upper respiratory tract, where IgA has been shown to play an important role. Ig(-/-) mice controlled the replication of heterosubtypic challenge virus in the lungs. Acute depletion of CD4+ or CD8+ T cell subsets abrogated this clearance of virus, thus indicating that both CD4+ and CD8+ T cells are required for protection in the absence of Ig. These results in Ig(-/-) mice indicate that CD4+ T cells can function by mechanisms other than providing help to B cells for the generation of Abs. Like wild-type mice, CD1(-/-) mice and gamma(delta) (-/-) mice survived lethal heterosubtypic challenge. Acute depletion of CD4+ and CD8+ cells abrogated heterosubtypic protection in gamma(delta) (-/-) mice, but not B6 controls, suggesting a contribution of gamma(delta) T cells. Our results demonstrate that the Ab and cellular subsets deficient in these knockout mice are not required for heterosubtypic protection, but each may play a role in a multifaceted response that as a whole is more effective than any of its parts.

Administration, Intranasal↗

PubMed2003

Greater CD8+ TCR heterogeneity and functional flexibility in HIV-2 compared to HIV-1 infection.

Virus-specific CD8(+) T cells are known to play an important role in the control of HIV infection. In this study we investigated whether there may be qualitative differences in the CD8(+) T cell response in HIV-1- and HIV-2-infected individuals that contribute to the relatively efficient control of the latter infection. A molecular comparison of global TCR heterogeneity showed a more oligoclonal pattern of CD8 cells in HIV-1- than HIV-2-infected patients. This was reflected in restricted and conserved TCR usage by CD8(+) T cells recognizing individual HLA-A2- and HLA-B57-restricted viral epitopes in HIV-1, with limited plasticity in their response to amino acid substitutions within these epitopes. The more diverse TCR usage observed for HIV-2-specific CD8(+) T cells was associated with an enhanced potential for CD8 expansion and IFN-gamma production on cross-recognition of variant epitopes. Our data suggest a mechanism that could account for any possible cross-protection that may be mediated by HIV-2-specific CD8(+) T cells against HIV-1 infection. Furthermore, they have implications for HIV vaccine development, demonstrating an association between a polyclonal, virus-specific CD8(+) T cell response and an enhanced capacity to tolerate substitutions within T cell epitopes.

Amino Acid Sequence↗

PubMed1998

Epidemiologic, genetic, and clinical associations among phenotypically distinct populations of Leishmania (Viannia) in Colombia.

Phenotypic characterization of 511 strains of Leishmania, subgenus Viannia, isolated from Colombian patients was conducted based on electrophoretic polymorphisms of 13 isoenzymes. Ninety-one Colombian strains of L. braziliensis were the most heterogeneous, constituting seven zymodemes while 397 L. panamensis and 22 L. guyanensis strains yielded five and three zymodemes, respectively. Phosphogluconate dehydrogenase, nucleoside hydrolase, and superoxide dismutase were the most polymorphic enzymes in this collection of strains, and together with glucose-6-phosphate dehydrogenase, allowed the discrimination of the three aforementioned species. Hierarchical cluster analysis of the zymodemes using Jaccard's coefficient of similarities revealed two clusters, one constituted by L. braziliensis zymodemes, and another by three subgroups consisting of zymodemes of L. panamensis closely related to the species reference strain, another consisting of L. guyanensis zymodemes, and a third group distinguished by new electromorphs of proline iminopeptidase and aspartate aminotransferase that reacted with the L. panamensis-specific monoclonal antibody B-11. Multiple zymodemes of L. panamensis and L. guyanensis were found to be sympatrically transmitted in foci along the Pacific coast. Leishmania braziliensis variants were ubiquitous throughout the territory of Colombia; L. panamensis was prevalent in the western region and L. guyanensis was prevalent in the Orinoco and Amazon river basins in the eastern half of the country. Distinct zymodemes of L. panamensis predominated in the northern and southern regions of the Pacific coast. Nine zymodemes of all three species were isolated from mucosal lesions. Zymodeme 1.1 of L. braziliensis had the highest frequency of mucosal involvement (10% of the cases), and disease caused by this zymodeme had the longest mean time of evolution (31 months; P = 0.002). In addition to being useful in describing epidemiologic relationships, the intraspecific heterogeneity of strains of the Viannia subgenus within and among foci can be used to understand such fundamental questions as the pathogenicity of different populations of parasites, and the induction of cross-protection against related parasites.

Animals↗

PubMed1999

Effects of pH and acid resistance on the radiation resistance of enterohemorrhagic Escherichia coli.

The effects of pH and the induction of pH-dependent stationary-phase acid resistance on the radiation resistance of Escherichia coli were determined for seven enterohemorrhagic strains and one nonenterohemorrhagic strain. The isolates were grown in acidogenic or nonacidogenic media to pH levels of approximately 4.7 and 7.2, respectively. The cells were then transferred to brain heart infusion (BHI) broth adjusted to pH 4.0, 4.5, 5.0, and 5.5 (with HCl) that was preequilibrated to 2 degrees C, and cultures were then irradiated using a 137Cs source. Surviving cells and the extent of injury were determined by plating on BHI and MacConkey agars both immediately after irradiation and after subsequent storage at 2 degrees C for 7 days. Decreasing the pH of the BHI in which E. coli was irradiated had relatively little effect on the microorganism's radiation resistance. Substantial differences in radiation resistance were noted among strains, and induction of acid resistance consistently increased radiation resistance. Comparison of E. coli levels immediately after irradiation and after 7 days of refrigerated storage suggested that irradiation enhanced pH-mediated inactivation of the pathogen. These results demonstrate that prior growth under conditions that induce a pH-dependent stationary phase cross-protects E. coli against radiation inactivation and must be taken into account when determining the microorganism's irradiation D value.

Acids, Acyclic↗

PubMed2000

Effect of pH on survival, thermotolerance, and verotoxin production of Escherichia coli O157:H7 during simulated fermentation and storage.

Heat treatment is increasingly being introduced to fermented meat processing, since the acid tolerance properties of Escherichia coli O157:H7 can permit this organism to survive traditional processing procedures. This study investigated the effect of growth pH and fermentation on the thermotolerance at 55 degrees C of E. coli O157:H7 in a model fermented meat system. E. coli O157:H7 (strain 380-94) was grown at pH 5.6 or 7.4 (18 h at 37 degrees C), fermented to pH 4.8 or 4.4 in brain heart infusion broth, and stored for 96 h. Cells grown at pH 5.6 had higher D values at 55 degrees C (D55 degrees C) than cells grown at pH 7.4 (P < 0.001). Cells fermented to pH 4.8 had higher D55 degrees C than those fermented to pH 4.4 (P < 0.001). Cells fermented to pH 4.8 demonstrated an increase in D55 degrees C during storage (P < 0.001), whereas cells fermented to pH 4.4 showed a decrease in D55 degrees C during the same period (P < 0.001). The effect of growth pH on verotoxin production by E. coli O157:H7 was assessed using the verotoxin assay. Cells grown at pH 5.6 had lower verotoxin production then cells grown at pH 7.4. This effect was not sustained over storage. These results indicate that a lower growth pH can confer cross-protection against heat. This has implications for the production of acidic foods, such as fermented meat, during which a heating step may be used to improve product safety.

Animals↗

PubMed2004

Survival and growth of Escherichia coli O157:H7 in roast beef and salami after exposure to an alkaline cleaner.

Survival and growth of wild-type (EDL 933) and rpoS-deficient (FRIK 816-3) strains of Escherichia coli O157:H7 after exposure to an alkaline cleaner for 2 min and inoculating into roast beef (pH 6.3) and hard salami (pH 4.9) at low (0.003 to 0.52 CFU/g) and high (0.69 to 31.5 CFU/g) populations were determined. Roast beef was stored at 4 and 12 degrees C; salami was stored at 4, 12, and 20 degrees C. At 4 degrees C, untreated cells of both strains showed greater reductions in populations in salami than in roast beef during a 21-day storage period. Populations of treated and untreated cells recovered from roast beef and salami stored at 4 degrees C on tryptic soy agar were significantly (P < or = 0.05) higher than on sorbitol MacConkey agar, indicating that a portion of the cells was injured. Treated and untreated cells grew in roast beef at 12 degrees C. Growth of treated cells of the FRIK 816-3 strain in roast beef at 12 degrees C was significantly slower than that of the EDL 933 strain. Populations of both strains decreased at different rates in salami stored at different temperatures (20 degrees C > 12 degrees C > 4 degrees C). E. coli O157:H7 strain EDL 933 grew more rapidly at 20 degrees C in a slurry (pH 5.97) prepared from stored salami (17 days at 20 degrees C) on which Penicillium chrysogenum had grown than in a slurry (5.23) prepared from salami showing no mold growth. Within 2 to 3 days, populations were ca. 3 log CFU/ml higher in slurry made from infected salami than in control salami. Results indicate that treatment of E. coli O157: H7 with an alkaline cleaner for 2 min does not impair resuscitation and growth of surviving cells in roast beef at 12 degrees C. Cross protection of cells exposed to an alkaline cleaner against subsequent stress conditions imposed by roast beef and salami stored at 4 degrees C was not evident in either of the test strains.

Adaptation, Physiological↗

PubMed2004

Changes in heat resistance resulting from pH and nutritional shifts of acid-adapted and non-acid-adapted Listeria monocytogenes Scott A.

Stationary-phase Listeria monocytogenes cells that were either pH dependent acid adapted or not acid adapted were heat challenged at 60 degrees C in a two-level full factorial design for three variables. The three variables and the levels consisted of tryptic soy broth (TSB) and sterile cell-free culture supernatant (sterile TSB), the presence and absence of 1% added glucose, and pH 4.8 and pH 7. Non-acid-adapted cells were most heat resistant when challenged in TSB (mean decimal reduction times at 60 degrees C: D60 = 1.16 min). In the absence of added glucose, non-acid-adapted cells had similar D60-values for inactivations at pH 4.8 and pH 7; however, the presence of glucose caused non-acid-adapted cells challenged at pH 4.8 to be more heat sensitive (D60 = 0.65 min) than those inactivated at pH 7 (D60 = 1.03 min), indicating an interaction between glucose and pH. Overall, the significantly decreased heat resistance of the acid-adapted cells was due to the presence of glucose (D60 = 0.78 min without glucose, D60 = 0.59 min with glucose). Acid-adapted cells heat challenged in TSB had similar D60-values for inactivations at pH 4.8 and pH 7; however, acid-adapted cells in sterile TSB challenged at pH 4.8 (D60 = 0.52 min) had significantly lower heat resistance than did cells challenged at pH 7 (D60 = 0.76 min), indicating an interaction between the medium and pH. The L. monocytogenes survivor data were modeled to extract information on the frequency distribution of heat resistance within heat-challenged populations, and the frequency distribution characteristics of mean, mode, and variance were compared among treatment conditions. Significant differences in the frequency distribution data were compared with the D60-values. These data indicated that the presence and level of cross-protection is highly dependent on the physiological state of the cells and nutrient availability at the time of heat challenge. Such conditions should be considered to ensure that stressed pathogens in foods are destroyed or inactivated.

Adaptation, Physiological↗