No description available.

No description available.

Mikroorganizmų gebėjimą prisitaikyti ir išlikti nuolat besikeičiančioje aplinkoje sąlygoja molekuliniai ir genetiniai mechanizmai, kurių dėka yra užtikrinamas savitasis atsakas į vieną ar kitą stresinį poveikį, pasireiškia adaptacinės organizmo savybės. Neatsitiktinai didžiąją dalį bakterijų genomo sudaro genai, koduojantys atsako ir adaptacijos į įvairius aplinkos veiksnius komponentus. Žemas aplinkos pH yra dažnai neutrofilinių mikroorganizmų gamtoje sutinkamas veiksnys jiems įsitvirtinant įvairiose ekologinėse nišose, tarp jų ir šeimininko organizme (Foster, 2004). E. coli molekuliniai mechanizmai, kuriuos ši bakterija naudoja apsaugai nuo rūgštinio streso, yra stebėtinai įvairūs ir pasireiškia esant skirtingoms augimo sąlygoms (Foster, 2004). Vienomis ar kitomis rūgštinio streso aplinkybėmis atsakui pasirenkamas efektyviausias mechanizmas. Tikėtina, kad molekuliniai komponentai, dalyvaujantys rūgštinio streso atsake, funkcionuoja visuose ląstelės erdvės skyriuose nuo išorinės membranos iki bakterijos nukleoido. Tiriant atsako į rūgštinį aplinkos stresą molekulinius mechanizmus bei jų reguliaciją, iškelta prielaida, kad bakterijų apvalkalėlio struktūrinių ir funkcinių savybių pokyčiai yra svarbus bakterijų rūgštinio streso fiziologijos aspektas (Canet ir kt., 2003, Booth ir kt., 2002). Būtent jis yra pirmoji bakterijų ląstelės struktūra, susidurianti su žemu aplinkos pH ir kartu pirmasis barjeras saugantis bakterijas nuo protonų ir silpnų organinių rūgščių, mažinančių... [toliau žr. visą tekstą] / Enteric bacteria often encounter acid stress conditions in a variety of pathogenic and natural situations. Bacteria that are able to survive under such conditions have to endure a pH difference of 4-5 pH units either by secreting the excess of protons or blocking extracellular protons from the cytoplasm. As a result bacteria have evolved complex strategies designed to detect, adapt and minimize acid induced damages. It is thought that cell envelope is one of the main structures determining protection from the acid stress, though its structural and functional components involved in the protection and the maintenance of homeostasis are not known. The aim of this study was to analyze changes of the cell envelope permeability to protons and the buffering power of bacterial suspensions during acid adaptation. We also investigated hypothetical acid stress protein Asr for its chaperone like activity. E. coli mutants of structural membrane components (ompC and phoE) and a periplasmic acid stress protein (Asr) were used in the studies. We showed, that envelope permeability to protons and cells buffering capacity increase during acid adaptation and the level of changes depends on the external pH. OmpC porin is essential for increasing E. coli cells buffering capacity while anion-specific PhoE porin has no influence on cell envelope interaction with protons. In vitro studies with periplasmic protein aggregation led to a conclusion that periplasmic protein Asr is not an acid stress... [to full text]

No description available.

No description available.

No description available.

No description available.

Numerous outbreaks of foodborne illness have been attributed to non-intact beef (e.g., tenderized, marinated, and enhanced) products contaminated with Escherichia coli O157:H7. Organic acids are commonly utilized in the beef industry as antimicrobial interventions, which must be validated to eliminate or reduce E. coli O157:H7 to an undetectable level. Rifampicin-resistant Biotype I E. coli O157:H7 surrogate microorganisms (ATCC BAA-1427, BAA-1428, and BAA-1430) were applied as a cocktail (7.8 log10 CFU/ml) to three beef products (boneless strip loins, top sirloin butts, and bottom sirloin flaps) prior to treatment with an antimicrobial intervention (2.5% Beefxide or 2.9% lactic acid). Products were then subjected to a single or multiple pass tenderization and/or marination process. Beefxide and lactic acid treatments resulted in statistically significant log reductions of the microorganisms (P < 0.05) on the surfaces for all three products. Surrogate microorganisms were recovered from interior samples of all three products after mechanical tenderization. Additionally, surrogate concentrations recovered from flap surface and internal samples taken post-tumbling and marination were statistically similar (P < 0.05). These data indicate that tenderization and marination processes can transfer microorganisms into the interior of whole-muscle cuts, and suggest Beefxide and lactic acid may be similar in their efficacy as an antimicrobial applied as an intervention in the production of non-intact beef products.

Bacterial biofilms are microbial communities that adhere to abiotic or biotic surfaces. Biofilm formation (BF) studies in E. coli have primarily concentrated on uropathogenic E. coli, commensal K-12 and enterohemorrhagic E. coli O157:H7. This does not include the vast diversity of environmental strains. Quorum sensing (QS) is a means by which bacteria can communication with one another through the production of signalling molecules. The autoinducer 2 (AI-2) QS system is utilized by E. coli and several other bacterial species for controlling gene expression. The role of AI-2 in E. coli BF varies among different strains. For example in the K-12 strain, AI-2 regulates motility, and thus can affect BF; whereas in O157:H7, AI-2 has a more metabolic role. Interestingly, in strain O157:H7, motility is controlled by a newly discovered QS system regulated by the autoinducer 3 (AI-3) molecule plus the mammalian hormones epinephrine (Epi) and norepinephrine (Ne). The purpose of this study was to investigate the ability of a panel of environmental E. coli strains to form biofilms and to determine whether QS is involved in the process. A new pathotype of E. coli, adherent invasive E. coli (AIEC) which is associated with Crohn’s disease was included in the investigation. Study 1 sought to determine whether BF under different media conditions correlated with the presence of genes involved in the AI-2 QS system or adhesin factors. Media conditions were the principal variable affecting the BF. Study 2 examined the role of the AI-2 and AI-3/Epi/Ne QS systems in motility and BF by the AIEC strain. It was discovered that the AI-3 system is involved in motility; whereas the AI-2 system had no effect on BF or motility. In Study 3, microarray gene expression analysis and invasion assays were performed using qseB or qseC mutants. These genes encode the two-component regulatory system recognizing AI-3 or its cognate, epinephrine. Our findings indicate that alternative pathways likely account for the BF observed for the qseB and qseC mutants. It was concluded that the AI-3/Epi/Ne QS system partially controls AIEC motility and the invasion of epithelial cells.

No description available.