Alternative antimicrobial compounds to control potential Lactobacillus contamination in bioethanol fermentations.

Antibiotics are commonly used to control microbial contaminants in yeast-based bioethanol fermentation. Given the increase in antibiotic-resistant bacteria, alternative natural antimicrobials were evaluated against the potential contaminant, Lactobacillus. The effects of nisin, ϵ-polylysine, chitosan (CS) and lysozyme were screened against 5 Lactobacillus strains. A standard broth- microdilution method was used in 96-well plates to assess the minimal inhibitory concentration (MIC). L. delbrueckii subsp lactis ATCC479 exhibited maximal MICs with CS, ϵ-polylysine and nisin (1.87, 0.3125 and 0.05 mg/mL, respectively). Nisin reduced most Lactobacillus strains by 6 log CFU/mL after 48 hours with the exception of L. casei. Synergism occurred when ethylenediaminetetraacetic acid (EDTA) was added with nisin. An MIC of 0.4 mg/mL of nisin combined with the EDTA at an MIC of 1 mg/ml markedly suppressed L .casei by 6 log CFU/mL. In conclusion, alternative antimicrobials proved to be a potential candidate for controlling bacterial contamination in the fermentation process. Synergistic effect of nisin with EDTA successfully inhibited the nisin-resistant contaminant, L. casei.

Population dynamics of Salmonella enterica serotypes in commercial egg and poultry production.

Fresh and processed poultry have been frequently implicated in cases of human salmonellosis. Furthermore, increased consumption of meat and poultry has increased the potential for exposure to Salmonella enterica. While advances have been made in reducing the prevalence and frequency of Salmonella contamination in processed poultry, there is mounting pressure on commercial growers to prevent and/or eliminate these human pathogens in preharvest production facilities. Several factors contribute to Salmonella colonization in commercial poultry, including the serovar and the infectious dose. In the early 1900s, Salmonella enterica serovars Pullorum and Gallinarum caused widespread diseases in poultry, but vaccination and other voluntary programs helped eradicate pullorum disease and fowl typhoid from commercial flocks. However, the niche created by the eradication of these serovars was likely filled by S. Enteritidis, which proliferated in the bird populations. While this pathogen remains a significant problem in commercial egg and poultry production, its prevalence among poultry has been declining since the 1990s. Coinciding with the decrease of S. Enteritidis, S. Heidelberg and S. Kentucky have emerged as the predominant serovars in commercial broilers. In this review, we have highlighted bacterial genetic and host-related factors that may contribute to such shifts in Salmonella populations in commercial poultry and intervention strategies that could limit their colonization.

Prescreening of microbial populations for the assessment of sequencing potential.

Next-generation sequencing (NGS) is a powerful tool that can be utilized to profile and compare microbial populations. By amplifying a target gene present in all bacteria and subsequently sequencing amplicons, the bacteria genera present in the populations can be identified and compared. In some scenarios, little to no difference may exist among microbial populations being compared in which case a prescreening method would be practical to determine which microbial populations would be suitable for further analysis by NGS. Denaturing density-gradient electrophoresis (DGGE) is relatively cheaper than NGS and the data comparing microbial populations are ready to be viewed immediately after electrophoresis. DGGE follows essentially the same initial methodology as NGS by targeting and amplifying the 16S rRNA gene. However, as opposed to sequencing amplicons, DGGE amplicons are analyzed by electrophoresis. By prescreening microbial populations with DGGE, more efficient use of NGS methods can be accomplished. In this chapter, we outline the protocol for DGGE targeting the same gene (16S rRNA) that would be targeted for NGS to compare and determine differences in microbial populations from a wide range of ecosystems.

Presence of arsenic resistance in Salmonella enterica serovar Kentucky and other serovars isolated from poultry.

A collection of 125 Salmonella enterica poultry isolates (71 serovar Kentucky isolates, and the remainder belonging to serovars Alachua, Enteritidis, Hadar, Heidelberg, Montevideo, Mbandaka, Senftenberg, Typhimurium, and Worthington) were tested for the ability to grow on tryptic soy agar containing sodium arsenite [As(III)] or arsenate [As(V)]. All serovar Kentucky isolates and 18 of the non-Kentucky isolates were able to grow in the presence of 0.1 mM As(III), and 69 grew in the presence of 1 mM As(V). Thirty of the non-Kentucky isolates did not grow at these As(III) and As(V) concentrations, but seven grew at 1 mM As(III) and 10 mM As(V). PCR-based analysis demonstrated the presence of arsB and arsD sequences in all Kentucky isolates, whereas one or both of these sequences were present in only 30 of the other isolates. It remains to be determined if these arsenic-resistance determinants benefit Salmonella exposed to man-made arsenic-containing compounds in poultry environments.

Salmonellosis outbreaks in the United States due to fresh produce: sources and potential intervention measures.

Foodborne Salmonella spp. is a leading cause of foodborne illness in the United States each year. Traditionally, most cases of salmonellosis were thought to originate from meat and poultry products. However, an increasing number of salmonellosis outbreaks are occurring as a result of contaminated produce. Several produce items specifically have been identified in outbreaks, and the ability of Salmonella to attach or internalize into vegetables and fruits may be factors that make these produce items more likely to be sources of Salmonella. In addition, environmental factors including contaminated water sources used to irrigate and wash produce crops have been implicated in a large number of outbreaks. Salmonella is carried by both domesticated and wild animals and can contaminate freshwater by direct or indirect contact. In some cases, direct contact of produce or seeds with contaminated manure or animal wastes can lead to contaminated crops. This review examines outbreaks of Salmonella due to contaminated produce, the potential sources of Salmonella, and possible control measures to prevent contamination of produce.

Precut prepackaged lettuce: a risk for listeriosis?

The most recent outbreaks of listeriosis have been traced back to contaminated ready-to-eat (RTE) poultry and meat products. However, Listeria monocytogenes can be isolated from every food group, including fresh vegetables. This review is focused on one of the most popular RTE vegetable products, precut prepackaged lettuce. The available literature concerning Listeria contamination of vegetables is reviewed, and possible reasons why no recent outbreaks or sporadic cases of listeriosis due to contaminated precut prepackaged lettuce are explored.