Development of a sequence-based subtyping method for Bacillus cereus dairy isolates.

More About This Textbook


Recent research has suggested Gram-positive spore-forming microorganisms including Bacillus cereus are the predominant microorganisms in pasteurized milk during refrigerated storage. The presence of B. cereus in pasteurized milk is of concern to the dairy industry because this microorganism can influence the quality and safety of the product.;The objectives of the first portion of this work were to evaluate the microbiological quality of commercial milk from four manufacturers and to determine the level and incidence of B. cereus.;On the sell-by-date, milks stored at 4 and 7°C, yielded aerobic plate counts ranging from ≤1.0 to 8.5 log10 CFU/mL and ≤1.0 to 8.6 log10 CFU/mL, respectively. The growth of B. cereus during refrigerated storage appeared to be influenced by storage temperature. On the sell-by date, B. cereus was detected in 2 of 28 (7%) cartons stored at 4°C, and counts of milks ranged from ≤1.0 to 4.2 log10 CFU/mL. However, B. cereus was detected in 16 (57%) milk samples at 7°C, and counts ranged from ≤1.0 to 8.9 log10 CFU/mL. On the sell-by date, 9 (32%) of the milk samples stored at 7°C yielded B. cereus counts exceeding the minimum infectious dose for the diarrheal illness.;The second objective of this work was to develop a sequence-based subtyping method for B. cereus dairy isolates. Currently, the RAPD-PCR method developed by Nilsson et al. (1998) is the subtyping method used most extensively for tracking B. cereus in milk production and in the processing environment. This method is well-suited for large-scale typing studies because it is highly discriminatory and is relatively simple and inexpensive compared to other subtyping methods; however, this method has several disadvantages associated with fragment-based methods including difficulties in standardization and interpretation of the results and low portability of the data.;The focus of the second portion of this work was to develop a two- or three-gene MLST scheme for tracking B. cereus dairy isolates using housekeeping and virulence gene sequences. Bacillus cereus possesses a number of virulence genes that could potentially be included in a MLST scheme, but in order for these genes to be included in a MLST scheme, the genes would need to be widely distributed among B. cereus isolates. The incidence of nine virulence genes was evaluated among 13 B. cereus reference strains and milk isolates, and two virulence genes, entFM and nheC were detected in all of the strains.;The next part of the work involved comparison of the number of allelic types obtained with housekeeping gene sequences in the MLST scheme of Helgason et al. (2004) with sequences of virulence genes, entFM and nheC. It was expected that the virulence gene sequences would have a greater number of polymorphic sites and yield a greater number of allelic types than the housekeeping genes.;The number of allelic types obtained with sequences of housekeeping genes in the MLST scheme of Helgason et al. (2004) ranged from four (adk, recF, and sucC) to seven (ftsA and glpT). The percentage of polymorphic sites among these genes ranged from 1.7% (ftsA) to 7.3% (glpT). Virulence genes entFM and nheC yielded seven and six allelic types, respectively, and these genes exhibited a higher percentage of polymorphic sites (10.2 and 12.1%) than the housekeeping genes.;Finally, various combinations of housekeeping and virulence gene ( entFM and nheC) sequences were evaluated in the development of a two- or three-gene MLST scheme for B. cereus. The number of sequence types obtained with the two-gene MLST schemes ranged from five (ccpA and pyrE, adk or recF and sucC) to eight (any housekeeping gene and nheC, or entFM and nheC). The addition of a third gene to the MLST scheme did not increase the number of sequence types. The seven-gene MLST scheme described by Helgason et al. (2004) yielded seven sequence types, and the combination of the seven housekeeping genes and two virulence genes yielded eight sequence types.;The two-gene MLST schemes could be used for large-scale tracking studies to identify sources of B. cereus contamination. Such tracking studies could lead to a reduction in the level and incidence of B. cereus in pasteurized milk and result in improvements in the quality and shelf life of the product. (Abstract shortened by UMI.)
Read More Show Less

Product Details

  • ISBN-13: 9781109014785
  • Publisher: ProQuest LLC
  • Sold by: Barnes & Noble
  • Format: eTextbook
  • Pages: 103
  • File size: 878 KB

Customer Reviews

Be the first to write a review
( 0 )
Rating Distribution

5 Star


4 Star


3 Star


2 Star


1 Star


Your Rating:

Your Name: Create a Pen Name or

Barnes & Review Rules

Our reader reviews allow you to share your comments on titles you liked, or didn't, with others. By submitting an online review, you are representing to Barnes & that all information contained in your review is original and accurate in all respects, and that the submission of such content by you and the posting of such content by Barnes & does not and will not violate the rights of any third party. Please follow the rules below to help ensure that your review can be posted.

Reviews by Our Customers Under the Age of 13

We highly value and respect everyone's opinion concerning the titles we offer. However, we cannot allow persons under the age of 13 to have accounts at or to post customer reviews. Please see our Terms of Use for more details.

What to exclude from your review:

Please do not write about reviews, commentary, or information posted on the product page. If you see any errors in the information on the product page, please send us an email.

Reviews should not contain any of the following:

  • - HTML tags, profanity, obscenities, vulgarities, or comments that defame anyone
  • - Time-sensitive information such as tour dates, signings, lectures, etc.
  • - Single-word reviews. Other people will read your review to discover why you liked or didn't like the title. Be descriptive.
  • - Comments focusing on the author or that may ruin the ending for others
  • - Phone numbers, addresses, URLs
  • - Pricing and availability information or alternative ordering information
  • - Advertisements or commercial solicitation


  • - By submitting a review, you grant to Barnes & and its sublicensees the royalty-free, perpetual, irrevocable right and license to use the review in accordance with the Barnes & Terms of Use.
  • - Barnes & reserves the right not to post any review -- particularly those that do not follow the terms and conditions of these Rules. Barnes & also reserves the right to remove any review at any time without notice.
  • - See Terms of Use for other conditions and disclaimers.
Search for Products You'd Like to Recommend

Recommend other products that relate to your review. Just search for them below and share!

Create a Pen Name

Your Pen Name is your unique identity on It will appear on the reviews you write and other website activities. Your Pen Name cannot be edited, changed or deleted once submitted.

Your Pen Name can be any combination of alphanumeric characters (plus - and _), and must be at least two characters long.

Continue Anonymously

    If you find inappropriate content, please report it to Barnes & Noble
    Why is this product inappropriate?
    Comments (optional)