Factors promoting survival of bacteria in chlorinated water supplies

Results of our experiments showed that the attachment of bacteria to surfaces provided the greatest increase in disinfection resistance. Attachment of unencapsulated Klebsiella pneumoniae grown in medium with high levels of nutrients to glass microscope slides afforded the microorganisms as much as a 150-fold increase in disinfection resistance. Other mechanisms which increased disinfection resistance included the age of the biofilm, bacterial encapsulation, and previous growth conditions (e.g., growth medium and growth temperature). These factors increased resistance to chlorine from 2- to 10-fold. The choice of disinfectant residual was shown to influence the type of resistance mechanism observed. Disinfection by free chlorine was affected by surfaces, age of the biofilm, encapsulation, and nutrient effects. Disinfection by monochloramine, however, was only affected by surfaces. Importantly, results showed that these resistance mechanisms were multiplicative (i.e., the resistance provided by one mechanism could be multiplied by the resistance provided by a second mechanism).     

Factors promoting survival of bacteria in chlorinated water supplies.

Results of our experiments showed that the attachment of bacteria to surfaces provided the greatest increase in disinfection resistance. Attachment of unencapsulated Klebsiella pneumoniae grown in medium with high levels of nutrients to glass microscope slides afforded the microorganisms as much as a 150-fold increase in disinfection resistance. Other mechanisms which increased disinfection resistance included the age of the biofilm, bacterial encapsulation, and previous growth conditions (e.g., growth medium and growth temperature). These factors increased resistance to chlorine from 2- to 10-fold. The choice of disinfectant residual was shown to influence the type of resistance mechanism observed. Disinfection by free chlorine was affected by surfaces, age of the biofilm, encapsulation, and nutrient effects. Disinfection by monochloramine, however, was only affected by surfaces. Importantly, results showed that these resistance mechanisms were multiplicative (i.e., the resistance provided by one mechanism could be multiplied by the resistance provided by a second mechanism).     

Factors affecting survival of test bacteria in sea water: marine bacteria,test bacteria and solid surfaces

Summary 1. The antibacterial activity of raw sea water varied considerably during incubation of successive inocula ofEscherichia coli, Staphylococcus aureus, andSerratia marinorubra. In most cases inactivation of second inocula was stronger than that of first ones. However, withS. aureus, contradictory results were obtained also.2. The bactericidal effect of filter-sterilized sea water was strengthened by inactivated cells ofEscherichia coli andStaphylococcus aureus. Contradictory findings were obtained from autoclaved sea water.3. Inactivation of test bacteria was greatly influenced by solid surfaces. In most cases, the kill ofEscherichia coli andStaphylococcus aureus in raw and sterile-filtered sea water was stronger at increased surface/volume ratios than under standard conditions. More rapid inactivation of these test strains in sterile-filtered, than in raw, sea water occurred more often at enlarged ratios of solid surface per unit volume. The survival ofSerratia marinorubra was positively affected by solid surfaces.4. It is concluded that changes in nutritive conditions occurring during the experiments are more important in regard to antibacterial activity of sea water than production of harmful matter by marine bacteria.

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Faktoren, welche das Überleben von Testbakterien in Meerwasser beeinflussen: Meeresbakterien, Testbakterien und feste Oberflächen

Kurzfassung Der Einfluß der vorstehend genannten Faktoren wurde auf die Überlebensfähigkeit vonEscherichia coli, Staphylococcus aureus undSerratia marinorubra in Meerwasser untersucht. Aktivitäten mariner Bakterien führten nicht generell zu verstärkter antibakterieller Wirkung rohen Meerwassers. Häufig waren sie für das Überleben vonE. coli undS. aureus förderlich. Inaktivierte Zellen vonE. coli undS. aureus erhöhten die bakterizide Wirkung rohen und filtersterilisierten Meerwassers gegenüber sekundär inokulierten, gleichartigen Testbakterien, während sie die inaktivierende Potenz autoklavierten Meerwassers verminderten. Durch erhöhtes Angebot an Glasoberfläche/Volumeneinheit, welches die adsorptive Anreicherung organischer Substanzen verstärkt, wurde die Inaktivation vonE. coli undS. aureus meistens beschleunigt, während sich diejenige vonS. marinorubra um so stärker verminderte, je größer das Verhältnis Oberfläche/Volumen war. Raschere Abtötung vonE. coli undS. aureus in Sterilfiltraten als in rohem Meerwasser trat bei erhöhtem Oberfläche/Volumen-Verhältnis häufiger auf als unter Standardbedingungen. Aus den Ergebnissen wird geschlossen, daß die während der Versuche eintretenden Veränderungen des Nährstoffangebotes, hervorgerufen durch Nährstoffverbrauch sowie durch Lysis inaktivierter Testbakterien, bezüglich der bakteriziden Wirkung von Meerwasser generell von größerer Bedeutung sind als bakterizide Stoffwechselprodukte mariner Bakterien.

     

Classification and mode of action of membrane-active bacteriocins produced by gram-positive bacteria

Bacteriocins are ribosomally synthesized antimicrobial peptides produced by microorganisms belonging to different eubacterial taxonomic branches. Most of them are small cationic membrane-active compounds that form pores in the target cells, disrupting membrane potentials and causing cell death. The production of small cationic peptides with antibacterial activity is a defense strategy found not only in bacteria, but also in plants and animals. Bacteriocins are classified according to different criteria by different authors; in this review, we will summarize the principal bacteriocin classifications, highlight their main physical and chemical characteristics, and describe the mechanism of some selected bacteriocins that act at the membrane level.     

eFGF and its mode of action in the community effect during Xenopus myogenesis

The community effect is an interaction among a group of many nearby precursor cells, necessary for them to maintain tissue-specific gene expression and differentiate co-ordinately. During Xenopus myogenesis, the muscle precursor cells must be in group contact throughout gastrulation in order to develop into terminally differentiated muscle. The molecular basis of this community interaction has not to date been elucidated. We have developed an assay for testing potential community factors, in which isolated muscle precursor cells are treated with a candidate protein and cultured in dispersion. We have tested a number of candidate factors and we find that only eFGF protein is able to mediate a community effect, stimulating stable muscle-specific gene expression in demonstrably single muscle precursor cells. In contrast, Xwnt8, bFGF, BMP4 and TGF(&bgr;)2 do not show this capacity. We show that eFGF is expressed in the muscle precursor cells at the right time to mediate the community effect. Moreover, the time when the muscle precursor cells are sensitive to eFGF corresponds to the period of the endogenous community effect. Finally, we demonstrate that FGF signalling is essential for endogenous community interactions. We conclude that eFGF is likely to mediate the community effect in Xenopus myogenesis.     

182 Investigating the mode of action of an essential OBG GTPase,CgtA in bacteria

CgtA is an essential OBG GTPase (Trach & Hoch, 1989) highly conserved from bacteria to eukaryotes. It is a multifunctional protein, involved in DNA replication, chromosome partitioning (Slominska et al., 2002), nutritional stress response, initiation of sporulation, ribosome maturation, etc. Despite being a multifunctional essential protein, its mode of action is not well- characterized and key question remains: how does this protein work in wide varieties of cellular function? The expression of cgtA-mRNA increases on the onset of nutritional stress. Purified CgtA protein shows increased GTPase activity in the presence of ribosome. Our experiment with thiostrepton reveals that, although ribosome is able to trigger the GTPase activity of CgtA, its probable site of GTPase inducing activity is different from other regular translation factors like EF-G, that uses GTP. For structure function study we have generated an energy minimized homology model of the Vibrio cholerae CgtA protein, which reveals two large domains, an OBG-fold and a GTP– hydrolysis domain, with an extended C-terminal part. We compared the amino acid sequence of CgtA across various species in the database, and found that its Glycine98 and the Tyrosine195 residues are 100% conserved in prokaryotes. These amino acids are highly conserved in eukaryotes as well. Gly98 and Tyr195 are located on the hinge region of CgtA comprising of portions of the OBG and the GTP–hydrolysis domains, respectively. To decipher the mode of actions of CgtA and the role of the conserved Gly98 residue, we have replaced the Gly with a relatively larger amino acid, i.e. Asp. Our study reveals that the mutant CgtA(G98D) shows a reduced GTPase activity in presence of ribosome compared to the wild type. This indicates a restricted inter-domain movement of CgtA due to the above point mutation. To understand this phenomenon we are using MD simulations. We will discuss results from MD simulations and other mutation studies as well. Our results indicate that ribosome acts as a modulator for increasing the GTPase activity of CgtA. The perfect conservation of G98 residue is important for the proper functionality of CgtA.     

Comparative survival of antibiotic-resistant and -sensitive fecal indicator bacteria in estuarine water.

The survival of antibiotic-resistant and -sensitive strains of Escherichia coli, Enterococcus faecalis, Enterococcus faecium, Streptococcus equinus, and two environmental isolates, AP17 and AQ62, was examined in estuarine water. Each strain was rendered resistant to a combination of two antibiotics by serial passage in increasing concentrations of antibiotics. Cultures were incubated in filter-sterilized estuarine water for up to 7 days. Recovery was assessed by examining colony-forming ability on media with and without antibiotics. None of the antibiotic-resistant forms survived longer than its antibiotic-sensitive counterpart in estuarine water. Three of the resistant strains died off more rapidly than the antibiotic-sensitive wild type. Survival of the test bacteria in estuarine water was as follows: sensitive and resistant AQ62, resistant Escherichia coli less than sensitive Escherichia coli less than resistant AP17 less than resistant Enterococcus faecium less than sensitive AP17, sensitive and resistant S. equinus less than sensitive and resistant Enterococcus faecalis, sensitive Enterococcus faecium. The results supported the suggestion that fecal entercocci may serve as better indicators of fecal pollution than Escherichia coli in marine ecosystems. Moreover, the results indicated that the use of antibiotic-resistant mutants to follow the fate of bacteria in the environment is inappropriate without adequate studies to ensure that resistant and wild-type strains react similarly to environmental stressors.     

Factors affecting the survival and growth of bacteria introduced into lake water

The populations of Pseudomonas sp. B4, Escherichia coli, Klebsiella pneumoniae, Micrococcus flavus, and Rhizobium leguminosarum biovar phaseoli declined rapidly in lake water. The initially rapid decline of the two pseudomonads and R. phaseoli was followed by a period of slow loss of viability, but viable cells of the other species were not found after 10 days. The rapid initial phase of decline was not a result of Bdellovibrio spp., bacteriophages, or toxins in the water since Bdellovibrio spp. were not present and passage of the lake water through filters that should not have removed bacteriophages or soluble toxins led to the elimination of the rapid phase of decline. The addition of 250 g of cycloheximide and 30 g of nystatin per ml eliminated viable protozoa form the lake water, and the population of Pseudomonas sp. B4 did not fall and the decline of E. coli and K. pneumoniae was delayed or slowed under these conditions. Pseudomonas sp. L2 proliferated rapidly in lake water amended with glucose, phosphate, and NH₄NO₃, but its numbers subsequently fell abruptly; however, in water amended with cycloheximide and nystatin, which killed indigenous protozoa, the population density was higher and the fall in numbers was delayed. Of the nutrients, the chief response was to carbon, but when glucose was added, phosphorus and nitrogen stimulated growth further. Removing other bacteria by filtering the lake water before inoculation with Pseudomonas sp. L2 suggested that competition reduced the extent of response of the pseudomonad to added nutrients. We suggest that the decline in lake water of bacteria that are resistant to starvation may be a result of protozoan grazing and that the extent of growth of introduced species may be limited by the supply of available carbon and sometimes of nitrogen and phosphorus, and by predation by indigenous protozoa.     

Cytokinin action in response to abiotic and biotic stresses in plants

The phytohormone cytokinin was originally discovered as a regulator of cell division. Later, it was described to be involved in regulating numerous processes in plant growth and development including meristem activity, tissue patterning, and organ size. More recently, diverse functions for cytokinin in the response to abiotic and biotic stresses have been reported. Cytokinin is required for the defence against high light stress and to protect plants from a novel type of abiotic stress caused by an altered photoperiod. Additionally, cytokinin has a role in the response to temperature, drought, osmotic, salt, and nutrient stress. Similarly, the full response to certain plant pathogens and herbivores requires a functional cytokinin signalling pathway. Conversely, different types of stress impact cytokinin homeostasis. The diverse functions of cytokinin in responses to stress and crosstalk with other hormones are described. Its emerging roles as a priming agent and as a regulator of growth‐defence trade‐offs are discussed.     

Alcohol dehydrogenase of acetic acid bacteria: structure, mode of action, and applications in biotechnology

Pyrroquinoline quinone-dependent alcohol dehydrogenase (PQQ-ADH) of acetic acid bacteria is a membrane-bound enzyme involved in the acetic acid fermentation by oxidizing ethanol to acetaldehyde coupling with reduction of membranous ubiquinone (Q), which is, in turn, re-oxidized by ubiquinol oxidase, reducing oxygen to water. PQQ-ADHs seem to have co-evolved with the organisms fitting to their own habitats. The enzyme consists of three subunits and has a pyrroloquinoline quinone, 4 heme c moieties, and a tightly bound Q as the electron transfer mediators. Biochemical, genetic, and electrochemical studies have revealed the unique properties of PQQ-ADH since it was purified in 1978. The enzyme is unique to have ubiquinol oxidation activity in addition to Q reduction. This mini-review focuses on the molecular properties of PQQ-ADH, such as the roles of the subunits and the cofactors, particularly in intramolecular electron transport of the enzyme from ethanol to Q. Also, we summarize biotechnological applications of PQQ-ADH as to enantiospecific oxidations for production of the valuable chemicals and bioelectrocatalysis for sensors and fuel cells using indirect and direct electron transfer technologies and discuss unsolved issues and future prospects related to this elaborate enzyme.     

Triketones active against antibiotic-resistant bacteria: synthesis, structure-activity relationships, and mode of action

A series of acylated phloroglucinols and triketones was synthesized and tested for activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VRE) and multi-drug-resistant Mycobacterium tuberculosis (MDR-TB). A tetra-methylated triketone with a C₁₂ side chain was the most active compound (MIC of around 1.0 μg/ml against MRSA) and was shown to stimulate oxygen consumption by resting cell suspensions, suggesting that the primary target was the cytoplasmic membrane.