Extremely High Frequency Electromagnetic Irradiation in Combination with Antibiotics Enhances Antibacterial Effects on Escherichia coli

Antibacterial effects of the electromagnetic irradiation (EMI) of 51.8 and 53 GHz frequencies with low intensity (the flux capacity of 0.06 mW/cm(2)) and non-thermal action were investigated upon direct irradiation of E. coli K12. Significant decrease in bacterial growth rate and in the number of viable cells, marked change in H(+) and K(+) transport across membrane were shown. Subsequent addition of kanamycin or ceftriaxone (15 or 0.4 μM, respectively) enhanced the effects of irradiation. This was maximally achieved at the frequency of 53 GHz. These all might reveal membrane as probable target for antibacterial effects. Apparently, the action of EMI on bacteria might lead to changed membrane properties and to antibiotic resistance. The results should improve using extremely high frequency EMI in combination with antibiotics in biotechnology, therapeutic practice, and food industry.     

R Factors Improving Survival of Escherichia coli K-12 After Ultraviolet Irradiation

Two R factors which have the capacity to improve survival of some strains of Escherichia coli K-12 by approximately 60% after ultraviolet light have been identified and characterized. Both are fi(-), but neither produce colicins. The ability to enhance survival can be separated from all other identified R-factor functions. Improved survival does not result from improved excisional capacity, but does require an intact host capacity for genetic recombination. No effects on host cell growth or postirradiation lag were observed. A proposed mechanism of action is described.     

Influence of Electromagnetic Signal of Antibiotics Excited by Low-Frequency Pulsed Electromagnetic Fields on Growth of Escherichia coli

Energy medicine (EM) provides a new medical choice for patients, and its advantages are the noninvasive detection and nondrug treatment. An electromagnetic signal, a kind of EM, induced from antibiotic coupling with weak, extremely low-frequency pulsed electromagnetic fields (PEMFs) is utilized for investigating the growth speed of Escherichia coli (E. coli). PEMFs are produced by solenoidal coils for coupling the electromagnetic signal of antibiotics (penicillin). The growth retardation rate (GRR) of E. coli is used to investigate the efficacy of the electromagnetic signal of antibiotics. The E. coli is cultivated in the exposure of PEMFs coupling with the electromagnetic signal of antibiotics. The maximum GRR of PEMFs with and without the electromagnetic signal of antibiotics on the growth of E. coli cells in the logarithmic is 17.4 and 9.08 %, respectively. The electromagnetic signal of antibiotics is successfully coupled by the electromagnetic signal coupling instrument to affect the growth of E. coli. In addition, the retardation effect on E. coli growth can be improved of by changing the carrier frequency of PEMFs coupling with the electromagnetic signal of antibiotics. GRR caused by the electromagnetic signal of antibiotics can be fixed by a different carrier frequency in a different phase of E. coli growth.     

Origins of Escherichia coli Growth Rate and Cell Shape Changes at High External Osmolality

In Escherichia coli, a sudden increase in external concentration causes a pressure drop across the cell envelope, followed by an active recovery. After recovery, and if the external osmolality remains high, cells have been shown to grow more slowly, smaller, and at reduced turgor pressure. Despite the fact that the active recovery is a key stress response, the nature of these changes and how they relate to each other is not understood. Here, we use fluorescence imaging of single cells during hyperosmotic shocks, combined with custom made microfluidic devices, to show that cells fully recover their volume to the initial, preshock value and continue to grow at a slower rate immediately after the recovery. We show that the cell envelope material properties do not change after hyperosmotic shock, and that cell shape recovers along with cell volume. Taken together, these observations indicate that the turgor pressure recovers to its initial value so that reduced turgor is not responsible for the reduced growth rate observed immediately after recovery. To determine the point at which the reduction in cell size and turgor pressure occurs after shock, we measured the volume of E. coli cells at different stages of growth in bulk cultures. We show that cell volume reaches the same maximal level irrespective of the osmolality of the media. Based on these measurements, we propose that turgor pressure is used as a feedback variable for osmoregulatory pumps instead of being directly responsible for the reduction in growth rates. Reestablishment of turgor to its initial value might ensure correct attachment of the inner membrane and cell wall needed for cell wall biosynthesis.     

Extremely High Frequency Electromagnetic Radiation Enforces Bacterial Effects of Inhibitors and Antibiotics

The coherent electromagnetic radiation (EMR) of the frequency of 51.8 and 53 GHz with low intensity (the power flux density of 0.06 mW/cm(2)) affected the growth of Escherichia coli K12(lambda) under fermentation conditions: the lowering of the growth specific rate was considerably (approximately 2-fold) increased with exposure duration of 30-60 min; a significant decrease in the number of viable cells was also shown. Moreover, the enforced effects of the N,N'-dicyclohexylcarbodiimide (DCCD), inhibitor of H(+)-transporting F(0)F(1)-ATPase, on energy-dependent H(+) efflux by whole cells and of antibiotics like tetracycline and chloramphenicol on the following bacterial growth and survival were also determined after radiation. In addition, the lowering in DCCD-inhibited ATPase activity of membrane vesicles from exposed cells was defined. The results confirmed the input of membranous changes in bacterial action of low intensity extremely high frequency EMR, when the F(0)F(1)-ATPase is probably playing a key role. The radiation of bacteria might lead to changed metabolic pathways and to antibiotic resistance. It may also give bacteria with a specific role in biosphere.     

Evolution of Escherichia coli for Growth at High Temperatures

Evolution depends on the acquisition of genomic mutations that increase cellular fitness. Here, we evolved Escherichia coli MG1655 cells to grow at extreme temperatures. We obtained a maximum growth temperature of 48.5 °C, which was not increased further upon continuous cultivation at this temperature for >600 generations. Despite a permanently induced heat shock response in thermoresistant cells, only exquisitely high GroEL/GroES levels are essential for growth at 48.5 °C. They depend on the presence of lysyl-tRNA-synthetase, LysU, because deletion of lysU rendered thermoresistant cells thermosensitive. Our data suggest that GroEL/GroES are especially required for the folding of mutated proteins generated during evolution. GroEL/GroES therefore appear as mediators of evolution of extremely heat-resistant E. coli cells.     

Effects of Acridine Orange on the Growth of Escherichia coli

Exposure of Escherichia coli to critical acridine orange (AO) concentrations did not result in loss of viability. However, the deoxyribonucleic acid (DNA) of cells exposed to such agents was rapidly degraded and repolymerized. On the other hand, a bacterium deficient in DNA repair (pol A₁⁻, lacking DNA polymerase) was sensitive to the action of AO. The DNA of such cells was also degraded but it was not repaired.     

Variant of Penicillinase Mediated by an R Factor in Escherichia coli

The penicillinase from an Escherichia coli strain harboring an R factor R(GN823) was purified and its properties were compared with those of a known type I penicillinase mediated by R factors. The molecular weight and S(20,w) of the enzyme were 22,600 and 2.42S, respectively. The isoelectric point of the enzyme was 6.9. These values are clearly different from those of type I penicillinase. The specific activity of the enzyme was 84,700 units per mg of the purified enzyme protein, which is about 20 times higher than that of the type I penicillinase. However, similarities were observed between the enzyme and the type I-penicillinase at optimal pH (6.5 to 7.0), optimal temperature (40 to 45C), substrate specificity, Michaelis constants for penicillins and cephaloridine, and effect of inhibitors. Furthermore, antiserum against type I penicillinase showed cross-reaction against this enzyme. The enzyme was named type Ib penicillinase, and the original type I penicillinase was renamed type Ia-penicillinase.     

Interaction of Ribosomes and the Cell Envelope of Escherichia coli Mediated by Lysozyme

Evidence is presented suggesting the existence of a natural ribosome-membrane complex. A reconstruction system is described wherein free ribosomes form a complex which appears to involve cell fragments. The reconstructed complex is similar in stability to the inferred natural complex. The reconstructed complex is generated by lysozyme, and it is concluded that at least part of the inferred natural complex is also generated by lysozyme. These results are discussed with reference to existing data concerning certain membrane-associated systems in bacteria.     

Changes in the Ultraviolet Sensitivity of Escherichia coli During Growth in Batch Cultures

The ultraviolet (UV) sensitivity of Escherichia coli B/r harvested at various times during growth in batch cultures was measured. The results showed a period of increased UV sensitivity in late log phase, just before the cultures entered stationary phase. This increase in sensitivity was associated with a decreased shoulder in the UV survival curves. The postirradiation division delay of survivors was shortest for cells harvested during the period of maximal sensitivity. This period of increased UV sensitivity during late log phase was not found in the radiation-sensitive, repair-deficient mutant B(s-1) (a strain which is unable to excise pyrimidine dimers from UV-damaged deoxyribonucleic acid). These results suggest that the variation in UV sensitivity of E. coli B/r as a function of time of harvesting of the cells from batch cultures is related to the varying capacities of these populations to repair UV-damaged deoxyribonucleic acid. Further experiments designed to elucidate the mechanism underlying this variation in UV sensitivity indicated that it arises from the partial depletion of nutrients in the medium during late log phase. We suggest that growth in such depleted media leads to a depression in the intercellular concentration or activity of one or more of the repair enzymes concerned with the repair of damaged deoxyribonucleic acid.     

Mutants of Escherichia coli with High Minimal Temperatures of Growth.

O'Donovan, Gerard A. (University of California, Davis), Catherine L. Kearney, and John L. Ingraham. Mutants of Escherichia coli with high minimal temperatures of growth. J. Bacteriol. 90:611-616. 1965.-Three general classes of mutants showing increased minimal temperatures of growth have been isolated from Escherichia coli. These mutants do not grow at temperatures below 20 C, although their parents can grow at temperatures as low as 8 C. The first class of mutants (K-I) cannot grow below 20 C in either complex or minimal medium, but grows at nearly normal rates at 37 C on both types of media. Normal growth rate at 20 C can be conferred on these mutants by infection at a low multiplicity with a transducing phage grown on the parent. The second class of mutants (K-II) fails to grow only in minimal medium at 20 C. These mutants are characterized by their singular response to specific nutrients in minimal medium at 20 C. The third class of mutants (K-III) grows normally in minimal medium at all temperatures with either glucose or glycerol as the carbon source, but does not grow at 20 C with lactose as the carbon source.     

Effect of Nalidixic Acid on Semiconservative Replication and Repair Synthesis After Ultraviolet Irradiation in Escherichia coli

Both semiconservative deoxyribonucleic acid replication and "extensive repair" synthesis, after ultraviolet irradiation, appear to be blocked by nalidixic acid. These findings suggest that the agent(s) responsible for both of these modes of replication, or some necessary common process or structure, is affected by this drug.     

Structure of Escherichia coli After Freeze-Etching

Survival of Escherichia coli, quick-frozen under conditions similar to those employed for freeze-etching, is close to 100%. For determination of cell shrinkage, the diameters of freeze-etched E. coli cells (average, 0.99 mum) were compared with those of preparations after negative staining and after ultrathin sectioning. Negatively stained cells measured from 0.65 to 1.0 mum in diameter, and ultrathin sections showed average cell diameters of 0.70 mum. Freeze-etched replicas of logarithmically growing, as well as stationary, E. coli B cells revealed a smooth, finely pitted cell surface in contrast to cell surfaces seen with other preparative methods. The frozen cell wall may cleave in two planes, exposing (i) a smooth fracture face within the lipid layer and (ii) in rare instances an ill-defined particulate layer. Most frequently, however, cleavage of the envelope occurred between wall and protoplasmic membrane; large areas of the membrane were then exposed and showed a surface studded with predominantly spherical particles, an appearance which did not significantly change when the cells were fixed in formaldehyde and osmium tetroxide before freeze-etching. The distribution of these particles differed between logarithmically growing cells and stationary cells.     

Improved Laboratory Enrichment for Enterohemorrhagic Escherichia coli by Exposure to Extremely Acidic Conditions

Analysis of food samples for E. coli O157:H7 using the standard U.S. Food and Drug Administration procedure is frequently complicated by overgrowth of nontarget microorganisms. A new procedure was developed for enrichment of enterohemorrhagic E. coli (EHEC) which utilizes exposure to pH 2.00 for 2 h. This procedure yielded larger populations of EHEC than the standard method by factors ranging from 2.7 to 7.7 and, when age-stressed cultures were used, by factors ranging from 2.7 to 11.5. Cultures of competing enterics were more effectively inhibited by the new enrichment protocol as well.     

Growth stasis by accumulated L-alpha-glycerophosphate in Escherichia coli

Cozzarelli, N. R. (Harvard Medical School, Boston, Mass.), J. P. Koch, S. Hayashi, and E. C. C. Lin. Growth stasis by accumulated l-alpha-glycerophosphate in Escherichia coli. J. Bacteriol. 90:1325-1329.1965.-Cells of Escherichia coli K-12 can grow on either glycerol or l-alpha-glycerophosphate as the sole source of carbon and energy. The first step in the dissimilation of glycerol requires a kinase, and the initial process of utilization of l-alpha-glycerophosphate involves an active transport system. In either case, intracellular l-alpha-glycerophosphate is an intermediate whose further metabolism depends upon a dehydrogenase. When this enzyme is lost by mutation, the cells not only fail to grow on glycerol or l-alpha-glycerophosphate, but are subject to growth inhibition in the presence of either compound. Resistance to inhibition by glycerol can be achieved by the loss of glycerol kinase. Such cells are still susceptible to growth inhibition by l-alpha-glycerophosphate. Similarly, in dehydrogenase-deficient cells, immunity to exogenous l-alpha-glycerophosphate can be achieved by genetic blocking of the active transport system. Such cells are still sensitive to free glycerol in the growth medium. Reversal of inhibition by glycerol or l-alpha-glycerophosphate in cells lacking the dehydrogenase can also be brought about by the addition of glucose. Glucose achieves this effect without recourse to catabolite repression. Our results suggest that growth stasis associated with the over-accumulation of l-alpha-glycerophosphate is due to interference with other cellular processes by competition with physiological substrates rather than to depletion of cellular stores of adenosine triphosphate or inorganic phosphate.     

Sister Chromatid Exchange Frequencies in Escherichia coli Analyzed by Recombination at the dif Resolvase Site

Sister chromatid exchange (SCE) in Escherichia coli results in the formation of circular dimer chromosomes, which are converted back to monomers by a compensating exchange at the dif resolvase site. Recombination at dif is site specific and can be monitored by utilizing a density label assay that we recently described. To characterize factors affecting SCE frequency, we analyzed dimer resolution at the dif site in a variety of genetic backgrounds and conditions. Recombination at dif was increased by known hyperrecombinogenic mutations such as polA, dut, and uvrD. It was also increased by a fur mutation, which increased oxidative DNA damage. Recombination at dif was eliminated by a recA mutation, reflecting the role of RecA in SCE and virtually all homologous recombination in E. coli. Interestingly, recombination at dif was reduced to approximately half of the wild-type levels by single mutations in either recB or recF, and it was virtually eliminated when both mutations were present. This result demonstrates the importance of both RecBCD and RecF to chromosomal recombination events in wild-type cells.