Effect of high ß-palmitate content in infant formula on the intestinal microbiota of term infants.

OBJECTIVES: Palmitic acid (PA) constitutes 17% to 25% of the human milk fatty acids, and ~70% is esterified in the sn-2 position of triglycerides (ß-palmitate). In the sn-2 position, PA is not hydrolyzed and thus is efficiently absorbed. The PA in palm oils, commonly used in infant formulas, is esterified in the sn-1 and sn-3 positions. In these positions, PA is hydrolyzed and forms poorly absorbed calcium complexes. The present study assessed whether high ß-palmitate in infant formulas affects the intestinal flora. METHODS: Thirty-six term infants were enrolled: 14 breast-fed (BF group) and 22 formula-fed infants who were randomly assigned to receive formula containing high ß-palmitate (HBP group, n=14), or low ß-palmitate (LBP group, n=8), where 44% and 14% of the PA was ß-palmitate, respectively. The total amount of PA in the formulas was 19% and 22% in the LBP and HBP groups, respectively. Neither formula contained pre- or probiotics. Stool samples were collected at enrollment and at 6 weeks for the quantification of bacteria. RESULTS: At 6 weeks, the HBP and BF groups had higher Lactobacillus and bifidobacteria counts than the LBP group (P<0.01). The Lactobacillus counts at 6 weeks were not significantly different between the HBP and BF groups. Lactobacillus counts were 1.2×10¹°, 1.2×10¹¹, and 5.6×10¹° CFU/g for LBP, HBP, and BF groups, respectively. Bifidobacteria counts were 5.1×109, 1.2×10¹¹, and 3.9×10¹° CFU/g for LBP, HBP, and BF groups, respectively. CONCLUSIONS: HBP formula beneficially affected infant gut microbiota by increasing the Lactobacillus and bifidobacteria counts in fecal stools.

The activity of BcsZ of Salmonella Typhimurium and its role in Salmonella-plants interactions.

Salmonella enterica is one of the most common human pathogens associated with fresh produce outbreaks. The present study suggests that expression of BcsZ, one of the proteins in the bcs complex, enhances the survival of Salmonella Typhimurium on parsley. BcsZ demonstrated glucanase activity with the substrates carboxymethylcellulose and crystalline cellulose, and was responsible for a major part of the S. Typhimurium CMCase activity. Moreover, there was constitutive expression of BcsZ, which was also manifested after exposure to plant polysaccharides and parsley-leaf extract. In an in-planta model, overexpression of BcsZ significantly improved the epiphytic and endophytic survival of S. Typhimurium on/in parsley leaves compared with the wild-type strain and bcsZ null mutant. Interestingly, necrotic lesions appeared on the parsley leaf after infiltration of Salmonella overexpressing BcsZ, while infiltration of the wild-type S. Typhimurium did not cause any visible symptoms. Infiltration of purified BcsZ enzyme, or its degradation products also caused symptoms on parsley leaves. We suggest that the BcsZ degradation products trigger the plant's defense response, causing local necrotic symptoms. These results indicate that BcsZ plays an important role in the Salmonella-plant interactions, and imply that injured bacteria may take part in these interactions.

Draft Genome Sequence of Salmonella enterica Serovar Senftenberg 070885 and Its Linalool-Adapted Mutant.

Here we report the genome sequences of both Salmonella Senftenberg 070885, a clinical isolate from the 2007 outbreak linked to basil, and its mutant linalool-adapted S Senftenberg (LASS). These draft genomes of S Senftenberg may enable the identification of bacterial genes responsible for resistance to basil oil.

Heat tolerance of Salmonella enterica serovars Agona, Enteritidis, and Typhimurium in peanut butter.

Recent large foodborne outbreaks caused by Salmonella enterica serovars have been associated with consumption of foods with high fat content and reduced water activity, even though their ingredients usually undergo pasteurization. The present study was focused on the heat tolerance of Salmonella enterica serovars Agona, Enteritidis, and Typhimurium in peanut butter. The Salmonella serovars in the peanut butter were resistant to heat, and even at a temperature as high as 90 degrees C only 3.2-log reduction in CFU was observed. The obtained thermal inactivation curves were upwardly concave, indicating rapid death at the beginning (10 min) followed by lower death rates and an asymptotic tail. The curves fitted the nonlinear Weibull model with beta parameters < 1, indicating that the remaining cells have a lower probability of dying. beta at 70 degrees C (0.40 +/- 0.04) was significantly lower than beta at 80 degrees C (0.73 +/- 0.19) and 90 degrees C (0.69 +/- 0.17). Very little decrease in the viable population (less than 2-log decrease) was noted in cultures that were exposed to a second thermal treatment. Peanut butter is a highly concentrated colloidal suspension of lipid and water in a peanut meal phase. We hypothesized that differences in the local environments of the bacteria, with respect to fat content or water activity, explained the observed distribution and high portion of surviving cells (0.1%, independent of the initial cell number). These results demonstrate that thermal treatments are inadequate to consistently destroy Salmonella in highly contaminated peanut butter and that the pasteurization process cannot be improved significantly by longer treatment or higher temperatures.

Biofilm formation ability of Salmonella enterica serovar Typhimurium acrAB mutants.

Recent studies offer contradictory findings about the role of multidrug efflux pumps in bacterial biofilm development. Thus, the aim of this study was to investigate the involvement of the AcrAB efflux pump in biofilm formation by investigating the ability of AcrB and AcrAB null mutants of Salmonella enterica serovar Typhimurium to produce biofilms. Three models were used to compare the ability of S. Typhimurium wild-type and its mutants to form biofilms: formation of biofilm on polystyrene surfaces; production of biofilm (mat model) on the air/liquid interface; and expression of curli and cellulose on Congo red-supplemented agar plates. All three investigated genotypes formed biofilms with similar characteristics. However, upon exposure to chloramphenicol, formation of biofilms on solid surfaces as well as the production of curli were either reduced or were delayed more significantly in both mutants, whilst there was no visible effect on pellicle formation. It can be concluded that when no selective pressure is applied, S. Typhimurium is able to produce biofilms even when the AcrAB efflux pumps are inactivated, implying that the use of efflux pump inhibitors to prevent biofilm formation is not a general solution and that combined treatments might be more efficient. Other factors that affect the ability to produce biofilms depending on efflux pump activity are yet to be identified.

Activity of dermaseptin K4-S4 against foodborne pathogens.

Dermaseptin S4 and its substituted derivative K(4)-S4 were investigated against various food-related pathogenic bacteria in culture media. K(4)-S4, but not the native peptide displayed significant growth inhibitory activity against all bacteria tested. Next, activity of K(4)-S4 against Escherichia coli O157:H7 was defined in terms of milieu dependencies. Salt-dependent kinetic studies in growth medium indicated that the peptide's antibacterial activity is maintained at fairly high (up to 600mM) NaCl concentrations but inhibited at higher concentrations. Similarly, antibacterial activity was reduced at high but not low pH conditions. Importantly, antibacterial activity was significantly maintained at temperatures lower than 37 degrees C and significantly enhanced at 42 degrees C. With respect to bactericidal kinetics, negative cultures were obtained in LB as well as in commercial apple juice, respectively, within 1 and 2h treatment, at twice the minimal inhibitory concentration (MIC) value. Overall, the data collected is indicative of a certain interest for dermaseptin derivatives as potential food preservatives.

Regulation of marA, soxS, rob, acrAB and micF in Salmonella enterica serovar Typhimurium.

Importance of the overexpression of AcrAB efflux pumps in the low-level resistance of pathogens to antimicrobials requires a better understanding of the AcrAB regulation. The goal of the present research was to study the transcription of acrAB, as well as the genes that play a role in its regulation in Salmonella enterica serovar Typhimurium. We monitored the transcription of these genes during growth at 30 degrees C and 37 degrees C, and thoroughly studied the effect of salicylate, paraquat and decanoate. The strengths of the promoters' activities were ordered from strong to weak as micF > rob > acrAB > soxS, marRAB. At both temperatures, marRAB was mainly upregulated by salicylate and decanoate, soxS by paraquat and acrAB and micF by all three compounds. rob was always downregulated. Transcription rates of all promoters were at the greatest level at the beginning of the stationary phase and, except for soxS, levels of transcription and induction were greater at 37 degrees C. Results show that despite the promoters' similar activity and the sequence homology between Escherichia coli and S. typhimurium, regulation of the investigated genes of both strains differed in the response to temperature. This difference was found to be dependent on the promoters' sequence, as the marRAB and acrAB promoters maintained their original dependence on temperature when they were analyzed in the other strain. Hence, it is most likely that the nutrient-limited environment at 37 degrees C in the human body will lead to increased transcription of marA, acrAB and micF in Salmonella, enhancing the resistance properties of the bacteria.

Quinolone resistance of Salmonella enterica serovar Virchow isolates from humans and poultry in Israel: evidence for clonal expansion.

Salmonella enterica serovar Virchow is highly prevalent in humans and farm animals in Israel. In addition to high rates of resistance to multiple antibiotics, this serovar exhibits a high incidence of resistance to nalidixic acid. More than 90% of Salmonella serovar Virchow isolates of human and poultry origin obtained from 1997 to 2004 were resistant to nalidixic acid (MIC > or = 128 microg/ml), with reduced susceptibility to ciprofloxacin (MIC between 0.125 and 0.250 microg/ml). Most isolates belonged to two predominant, closely related pulsed-field gel electrophoresis image types. Investigation of the mechanisms of quinolone resistance revealed that this pathogen probably emerged from a parental clone that overproduced the AcrAB efflux pump and had a single point mutation in gyrA leading to the Asp87Tyr substitution. The close resemblance between human and poultry isolates points to poultry as a likely source of Salmonella serovar Virchow in the food chain.

Branched aminoglycosides: biochemical studies and antibacterial activity of neomycin B derivatives.

The C5''-OH group in neomycin B was glycosylated with a variety of mono- and di-saccharides to probe the effect of introduction of additional binding elements on antibacterial activity and interaction with the aminoglycosides modifying enzyme APH(3')-IIIa. The designed structures show antibacterial activity superior to that of neomycin B against pathogenic and resistant strains, while in parallel they demonstrate poor substrate activity with APH(3')-IIIa.