The microbiota of the intestinal tract of chickens plays an important role in inhibiting the establishment of intestinal pathogens. Earlier culturing and microscopic examinations indicated that only a fraction of the bacteria in the cecum of chickens could be grown in the laboratory. Therefore, a survey of cecal bacteria was done by retrieval of 16S rRNA gene sequences from DNA isolated from the cecal content and the cecal mucosa. The ribosomal gene sequences were amplified with universal primers and cloned or subjected to temporal temperature gradient gel electrophoresis (TTGE). Partial 16S rRNA gene sequences were determined from the clones and from the major bands in TTGE gels. A total of 1,656 partial 16S rRNA gene sequences were obtained and compared to sequences in the GenBank. The comparison indicated that 243 different sequences were present in the samples. Overall, sequences representing 50 phylogenetic groups or subgroups of bacteria were found, but approximately 89% of the sequences represented just four phylogenetic groups (Clostridium leptum, Sporomusa sp., Clostridium coccoides, and enterics). Sequences of members of the Bacteroides group, the Bifidobacterium infantis subgroup, and of Pseudomonas sp. each accounted for less than 2% of the total. Sequences related to those from the Escherichia sp. subgroup and from Lactobacillus, Pseudomonas, and Bifidobacterium spp. were generally between 98 and 100% identical to sequences already deposited in the GenBank. Sequences most closely related to those of the other bacteria were generally 97% or less identical to those in the databases and therefore might be from currently unknown species. TTGE and random cloning indicated that certain phylogenetic subgroups were common to all birds analyzed, but sequence data from random cloning also provided evidence for qualitative and quantitative differences among the cecal microbiota of individual birds reared under very similar conditions.

No abstract

A tremendous effort has been made over the last decade to develop and test films with antimicrobial properties to improve food safety and shelf life. This review catalogues and analyses the outcome of these research efforts. The bacteriocin nisin was the antimicrobial most commonly incorporated into films, followed by foodgrade acids and salts, chitosan, plant extracts, and the enzymes lysozyme and lactoperoxidase. The methodologies for measuring antimicrobial activity of both edible and inedible films varied considerably among the studies. Results, defined as the difference in the log 10 colony-forming unit (CFU) of a test organism exposed to a control film and the log 10 CFU of the organism exposed to the antimicrobial film, ranged from 0 to 9 for many of the antimicrobials tested. Even for antimicrobials such as nisin, chitosan or antimicrobial acids with a 'long' history of studying their incorporation into antimicrobial films, the majority of results centred around 2 log 10 reductions. The results suggest that antimicrobial films still face limitations and are perhaps still best viewed as part of a hurdle strategy to provide safe foods. SCOPE AND LIMITATIONS OF THE REVIEWThe development and testing of antimicrobial films for wrapping or coating foods has become a worldwide endeavour over the last decades, and this effort has produced a diverse range of film types utilizing an assortment of antimicrobial compounds. A number of review articles have described the nature of these films and their antimicrobial constituents, their construction and general effectiveness, 1-9 but what appears to be absent from the literature is a comparative analysis of how well the different types of films have performed overall towards the goal of eliminating or reducing foodborne pathogens or of extending shelf life. Therefore, this review aims to summarize and, as much as possible, analyse quantitative results of microbiological assays conducted over the last decade involving antimicrobial films intended for use in foods.An even very cursory glance at the literature of antimicrobial film studies reveals a field that uses multiple methodological approaches to the common goal of measuring the efficacy of newly created films. The literature is not only diverse with respect to the way experiments were carried out, but also the way the results were reported.

The nucleotide sequence of a region of the Azotobacter vinelandii genome exhibiting sequence similarity to nifH has been determined. The order of open reading frames within this 6.1-kilobase-pair region was found to be anfH (alternative nitrogen fixation, nifH-like gene), anfD (nifD-like gene), anfG (potentially encoding a protein similar to the product of vnfG from Azotobacter chroococcum), anfK (nifK-like gene), followed by two additional open reading frames. The 5'-flanking region of anfH contains a nif promoter similar to that found in the A. vinelandii nifHDK gene cluster. The presumed products of anfH, anfD, and anfK are similar in predicted Mr and pI to the previously described subunits of nitrogenase 3. Deletion plus insertion mutations introduced into the anfHDGK region of wild-type strain A. vinelandii CA resulted in mutant strains that were unable to grow in Mo-deficient, N-free medium but grew in the presence of 1 microM Na2MoO4 or V2O5. Introduction of the same mutations into the nifHDK deletion strain CA11 resulted in strains that grew under diazotrophic conditions only in the presence of vanadium. The lack of nitrogenase 3 subunits in these mutant strains was demonstrated through two-dimensional gel analysis of protein extracts from cells derepressed for nitrogenase under Mo and V deficiency. These results indicate that anfH, anfD, and anfK encode structural proteins for nitrogenase 3.

The nucleotide sequence (6,559 base pairs) of the genomic region containing the structural genes for nitrogenase 2 (V nitrogenase) from Azotobacter vinelandii was determined. The open reading frames present in this region are organized into two transcriptional units. One contains vnJH (encoding dinitrogenase reductase 2) and a ferredoxinlike open reading frame (Fd). The second one includes vnJf) (encoding the a subunit of dinitrogenase 2), vnfG (encoding a product similar to the 8 subunit of dinitrogenase 2 from A. chroococcum), and vnfK (encoding the 3 subunit of dinitrogenase 2). The 5'-flanking regions of vnfH and vnJf) contain sequences similar to ntrA-dependent promoters. This gene arrangement allows independent expression of vn.f-Fd and vnfDGK. Mutant strains (CA80 and CA11.80) carrying an insertion in vnjf are still able to synthesize the a and 1 subunits of dinitrogenase 2 when grown in N-free, Mo-deficient, V-containing medium.A strain (RP1.1l) carrying a deletion-plus-insertion mutation in the vnfDGK region produced only dinitrogenase reductase 2.