Survival and growth of Listeria monocytogenes in broth as a function of temperature, pH, and potassium lactate and sodium diacetate concentrations

Potassium Lactate as a Strategy for Sodium Content Reduction without Compromising Salt-Associated Antimicrobial Activity in Salami

Reformulating recipes of ready-to-eat meat products such as salami to reduce salt content can mitigate the negative health impacts of a high salt diet. We evaluated the potential of potassium lactate (KL) as a sodium chloride (NaCl) replacer during salami production. NaCl and KL stress tolerance comparisons showed that four food-derived Listeria innocua isolates were suitable as biologically safe Listeria monocytogenes surrogates. Effects of the high salt (4% NaCl) concentration applied in standard salami recipes and a low salt (2.8% NaCl) plus KL (1.6%) combination on product characteristics and growth of contaminating Listeria and starter culture were compared. Simulated salami-ripening conditions applied in meat simulation broth and beef showed that the low salt plus KL combination retained similar to superior anti-Listeria activity compared to the high salt concentration treatment. Salami challenge tests showed that the low NaCl plus KL combination had comparable anti-Listeria activity as the high NaCl concentration during ripening and storage. No significant differences were detected in starter culture growth profiles and product characteristics between the high NaCl and low NaCl plus KL combination treated salami. In conclusion, KL replacement enabled a 30% NaCl reduction without compromising the product quality and antimicrobial benefits of high NaCl concentration inclusion.

Draft Genome Sequence of Listeria monocytogenes Serovar 1/2a Strain IZSAM_Lm_14-16064, Isolated from an Italian Cooked Ham in 2014

In this report, the draft genome sequence of Listeria monocytogenes serovar 1/2a strain IZSAM_Lm_14-16064, isolated in Italy from a cooked ham, is announced. The genome is similar to that of a clinical strain isolated in 2014.

In this report, the draft genome sequence of Listeria monocytogenes serovar 1/2a strain IZSAM_Lm_14-16064, isolated in Italy from a cooked ham, is announced. The genome is similar to that of a clinical strain isolated in 2014.

ISP1-Anchored Polarization of GCβ/CDC50A Complex Initiates Malaria Ookinete Gliding Motility

Ookinete gliding motility is essential for penetration of the mosquito midgut wall and transmission of malaria parasites. Cyclic guanosine monophosphate (cGMP) signaling has been implicated in ookinete gliding. However, the upstream mechanism of how the parasites activate cGMP signaling and thus initiate ookinete gliding remains unknown. Using real-time imaging to visualize Plasmodium yoelii guanylate cyclase β (GCβ), we show that cytoplasmic GCβ translocates and polarizes to the parasite plasma membrane at "ookinete extrados site" (OES) during zygote-to-ookinete differentiation. The polarization of enzymatic active GCβ at OES initiates gliding of matured ookinete. Both the P4-ATPase-like domain and guanylate cyclase domain are required for GCβ polarization and ookinete gliding. CDC50A, a co-factor of P4-ATPase, binds to and stabilizes GCβ during ookinete development. Screening of inner membrane complex proteins identifies ISP1 as a key molecule that anchors GCβ/CDC50A complex at the OES of mature ookinetes. This study defines a spatial-temporal mechanism for the initiation of ookinete gliding, where GCβ polarization likely elevates local cGMP levels and activates cGMP-dependent protein kinase signaling.

Effects of natural antimicrobials with modified atmosphere packaging on the growth kinetics of Listeria monocytogenes in ravioli at various temperatures

The objective of this study was to investigate the antimicrobial effects of cultured sugar/vinegar (CSV) blend and nisin to control the risk of Listeria monocytogenes in ready to cook (RTC) ravioli. Ravioli dough was prepared with 0.1, 0.3, 0.5, 1% CSV blend and 0.1, 0.2, and 0.3% nisin. Inoculated spinach or artichoke raviolis with 2.0 ± 0.5 log cfu/g of L. monocytogenes were packed aerobically or using modified atmosphere packaging (MAP), and then stored at 4, 10, 17, and 24 °C for 60 days. Growth kinetic parameters of the observed data fit well to the Baranyi equation. Ravioli with spinach filling materials yielded a higher risk than that with artichoke. L. monocytogenes was able to survive in ravioli with artichoke, but did not grow. The addition of 1% CSV blend or 0.3% nisin in spinach ravioli with the combination of MAP effectively controlled the growth of L. monocytogenes at the temperature below 10 °C. The organoleptic quality of spinach ravioli was not also affected by the application of 1% CSV blend. Therefore, the CSV blend can be recommended to improve the microbial safety and quality of natural RTC ravioli at retail market.

Practical applications

The risk of ravioli was affected by the filling materials of ravioli at retail market. Addition of 1% cultured sugar/vinegar blend in dough substantially contributes to the extension of shelf-life of MAP spinach raviolis. classification and regression tree analysis results indicate that refrigeration temperature is the main control factor to affect lag time and growth rate, while packaging method is critical for maximum population density.

Comparing listeriosis risks in at-risk populations using a user-friendly quantitative microbial risk assessment tool and epidemiological data

Although infection by the pathogenic bacterium Listeria monocytogenes is relatively rare, consequences can be severe, with a high case-fatality rate in vulnerable populations. A quantitative, probabilistic risk assessment tool was developed to compare estimates of the number of invasive listeriosis cases in vulnerable Canadian subpopulations given consumption of contaminated ready-to-eat delicatessen meats and hot dogs, under various user-defined scenarios. The model incorporates variability and uncertainty through Monte Carlo simulation. Processes considered within the model include cross-contamination, growth, risk factor prevalence, subpopulation susceptibilities, and thermal inactivation. Hypothetical contamination events were simulated. Results demonstrated varying risk depending on the consumer risk factors and implicated product (turkey delicatessen meat without growth inhibitors ranked highest for this scenario). The majority (80%) of listeriosis cases were predicted in at-risk subpopulations comprising only 20% of the total Canadian population, with the greatest number of predicted cases in the subpopulation with dialysis and/or liver disease. This tool can be used to simulate conditions and outcomes under different scenarios, such as a contamination event and/or outbreak, to inform public health interventions.

Phosphonoformic acid inhibits viral replication by trapping the closed form of the DNA polymerase

Phosphonoformic acid (PFA, foscarnet) belongs to a class of antiviral drugs that inhibit the human cytomegalovirus DNA polymerase (UL54) by mimicking the pyrophosphate leaving group of the nucleotide transfer reaction. Difficulties expressing UL54 have hampered investigation of the precise structural requirements rendering inhibition by this drug. However, a previously engineered chimeric DNA polymerase, constructed by mutating the homologous polymerase from bacteriophage RB69 (gp43) to express several variable elements from UL54, can bypass this obstacle because of its favorable expression and acquired sensitivity to PFA (Tchesnokov, E. P., Obikhod, A., Schinazi, R. F., and Götte, M. (2008) J. Biol. Chem. 283, 34218-34228). Here, we compare two crystal structures that depict the chimeric DNA polymerase with and without PFA bound. PFA is visualized for the first time in the active site of a DNA polymerase, where interactions are resolved between the PP(i) mimic and two basic residues absolutely conserved in the fingers domain of family B polymerases. PFA also chelates metal ion B, the cation that contacts the triphosphate tail of the incoming nucleotide. These DNA complexes utilize a primer-template pair enzymatically chain-terminated by incorporation of acyclo-GMP, the phosphorylated form of the anti-herpes drug acyclovir. We postulate that the V478W mutation present in the chimera is critical in that it pushes the fingers domain to more readily adopt the closed conformation whether or not the drug is bound. The closed state of the fingers domain traps the variant polymerase in the untranslocated state and increases affinity for PFA. This finding provides a model for the mechanism of UL54 stalling by PFA.

Antimicrobial activity of sodium citrate against Streptococcus pneumoniae and several oral bacteria

AIMS

The aim of this study is to assess the antibacterial activity of sodium citrate against Streptococcus pneumoniae and several oral bacteria.

METHODS AND RESULTS

The antibacterial activity was determined by broth microdilution method. The results showed that although Enterocuccus faecium OB7084 and Klebsiella pneumoniae OB7088 had high tolerance to sodium citrate, several oral bacteria including Fusobacterium nucleatum JCM8532(T) , Streptococcus mutans JCM5705(T) and Strep. pneumoniae NBRC102642(T) were susceptible. Furthermore, the bactericidal activity of sodium citrate against Strep. pneumoniae NBRC102642(T) was not influenced by pH in the range of 5·0-8·0, whereas that of sodium lactate was weakened at neutral or weak alkaline pH. When Strep. pneumoniae NBRC102642(T) was treated with sodium citrate for 2 h, many burst cells were observed. However, addition of MgCl(2) or CaCl(2) to an assay medium weakened the antimicrobial activity although ZnCl(2) or MnCl(2) did not influence.

CONCLUSIONS

Independent of pH, sodium citrate inhibited the growth of oral bacteria, which suggests that the mechanism is different from that of sodium lactate.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results presented in this study would be available for understanding the antimicrobial property of sodium citrate.

Development and validation of a predictive model for foodborne pathogens in ready-to-eat pork as a function of temperature and a mixture of potassium lactate and sodium diacetate

We developed and validated secondary models that can predict growth parameters of Salmonella Typhimurium and Staphylococcus aureus in cooked-pressed ready-to-eat (RTE) pork as a function of concentrations (0 to 3%) of a commercial potassium lactate and sodium diacetate mixture (PL+SDA) and temperature (10 to 30°C). The primary growth data were fitted to a Gompertz equation to determine the lag time (LT) and growth rate (GR). At 10°C, the growth of Salmonella Typhimurium and S. aureus in cooked-pressed RTE pork containing 2% and 3% PL+SDA was completely inhibited. The effects of temperature and concentration of PL+SDA on the growth kinetics of Salmonella Typhimurium and S. aureus in cooked-pressed RTE pork were modeled by response surface analysis using polynomial models of the natural logarithm transformation of both LT and GR. Model performance was also evaluated by use of the prediction bias (B(f)) and accuracy (A(f)) factors, median relative error, and mean absolute relative error, as well as the acceptable prediction zone method. The results showed that LT and GR models of Salmonella Typhimurium and S. aureus in cooked-pressed RTE pork are acceptable models. Thus, both the LT and GR growth models developed herein can be used for the development of tertiary models for Salmonella Typhimurium and S. aureus in cooked-pressed RTE pork in the matrix of conditions described in the present study.

The combination of lactate and diacetate synergistically reduces cold growth in brain heart infusion broth across Listeria monocytogenes lineages

Combinations of organic acids are often used in ready-to-eat foods to control the growth of Listeria monocytogenes during refrigerated storage. The purpose of this study was to quantitatively assess synergy between two organic acid growth inhibitors under conditions similar to those present in cold-smoked salmon, and to assess the effect of evolutionary lineage on response to those growth inhibitors. Thirteen strains of L. monocytogenes, representing lineages I and II, were grown at 7 degrees C in broth at pH 6.1 and 4.65% water-phase NaCl, which was supplemented with 2% potassium lactate, 0.14% sodium diacetate, or the combination of both at the same levels. Our data suggest that lineages adapt similarly to these inhibitors, as the only significant growth parameter difference between lineages was a minor effect (+/- 0.16 day, P = 0.0499) on lag phase (lambda). For all strains, lactate significantly extended lambda, from 2.6 +/- 0.4 to 3.8 +/- 0.5 days (P < 0.001), and lowered the maximum growth rate (mu(max)) from 0.54 +/- 0.06 to 0.49 +/- 0.04 log(CFU/ml)/day (P < 0.001), compared with the control. Diacetate was ineffective alone, but in combination with lactate, synergistically increased lambda to 6.6 +/- 1.6 days (P < 0.001) and decreased mu(max) to 0.34 +/- 0.05 log(CFU/ml)/day (P < 0.001). Monte Carlo simulations provided further evidence for synergy between diacetate and lactate by predicting signficantly slower growth to nominal endpoints for the combination of inhibitors. This study shows potassium lactate and sodium diacetate have significant synergistic effects on both lambda and mu(max) of L. monocytogenes at refrigeration temperature in broth, and justifies combining these inhibitors, at effective levels, in food product formulations.