Acid resistance of attached organisms and its implications for the pathogenicity of plasmid-bearing Escherichia coli

Organisms of Escherichia coli attached to glass beads in a model attachment system were more resistant to acid than were unattached organisms and this applied to cultures exposed to either pH 2·5 or 3·5. Attached organisms of both Col^- and Col V, I-K94⁺ strains showed the effect but with prolonged exposure to pH 2·5, the attached Col V⁺ organisms appeared more resistant than the attached Col^- ones, possibly because they formed a thicker surface layer. It is proposed that the increased resistance of attached organisms to pH 2·5 might allow the survival, in gastric acid, of organisms attached to food particles. This would be more significant for the Col V⁺ strains because the plasmid enhances enterobacterial attachment properties. The increased resistance of attached organisms to pH 3·5 might be significant for survival of particle- or surface-bound organisms in the acidic environment of the phagocyte especially since lactate (which occurs in phagocytes) enhanced the effect of exposure to pH 3·5.     

Alkali sensitivity in plasmid-bearing strains of Escherichia coli

Introduction of the ColV,I-K94 plasmid into any of four strains of Escherichia coli gave derivatives which grew less well than the parent at alkaline pH. The alkali sensitivity of the 1829 derivative resulted from the presence of the plasmid rather than from its introduction into a less alkali tolerant variant. Of two other ColV plasmids tested, one (ColV-K30) conferred substantial alkali sensitivity whereas the other (ColV-41) had little effect. Of several other plasmids examined, R124-F2 (which confers derepressed transfer properties) resembled ColV,I-K94 in its effect on alkali sensitivity and ColV-K98 produced a marked effect. The other plasmids (F lac , R124 itself, R1 and R483ColIa) had only a small effect. For ColV plasmids, it appears to be the presence of transfer and colicin components together which leads to the reduced tolerance to alkaline pHs.     

Mercury resistance in a plasmid-bearing strain of Escherichia coli

A strain of Escherichia coli carrying genes determining mercury resistance on a naturally occurring resistance transfer factor (RTF) converts 95% of 10(-5)m Hg(2+) (chloride) to metallic mercury at a rate of 4 to 5 nmoles of Hg(2+) per min per 10(8) cells. The metallic mercury is rapidly eliminated from the culture medium as mercury vapor. The volatilizing activity has a temperature dependence and heat sensitivity characteristic of enzymatic catalysis and is inducible by mercuric chloride. Ag(+) and Au(3+) are markedly inhibitory of mercury volatilization.     

Colonization of R plasmid-bearing Escherichia coli strains in the mouse alimentary tract.

In order to examine the ability of R plasmid-bearing Escherichia coli strains to colonize in the mouse alimentary tract, an R plasmid-positive (R(+)) E. coli strain and its R plasmid-negative (R(-)) counterpart were together inoculated into the streptomycin-treated mouse alimentary tract, and the numbers of fecal E. coli strains were enumerated. The numbers of R(+) strains were always at the level similar to or lower than those of their counterparts and rapidly decreased in the fecal population. However, when R plasmids, which were originated from a cryptic plasmid of the host E. coli strain, were utilized, an R(+) strain dominated over its R(-) counterpart during the experimental period. These experimental results indicated that the relationship between the host strain and R plasmids affected the ability of the host strain to colonize in the alimentary tract.     

Bacteriophage Mu repressor as a target for the Escherichia coli ATP-dependent Clp Protease.

Bacteriophage Mu repressor, which is stable in its wildtype form, can mutate to become sensitive to its Escherichia coli host ATP-dependent ClpXP protease. We further investigated the determinants of the mutant repressor's sensitivity to Clp. We show the crucial importance of a C-terminal, seven amino acid long sequence in which a single change is sufficient to decrease the rate of degradation of the protein. The sequence was fused at the C-terminal end of the CcdB and CcdA proteins encoded by plasmid F. CcdB, which is naturally stable, was unaffected, while CcdA, which is normally degraded by the Lon protease, became a substrate for ClpXP while remaining a substrate for Lon. In agreement with the current hypothesis on the mechanism of recognition of their substrates by energy- dependent proteases, these results support the existence, on the substrate polypeptides, of separate motifs responsible for recognition and cleavage by the protease.     

Bacteriophage Typing as an Epidemiological Tool for Urinary Escherichia coli

Phage typing was used to identify strains of Escherichia coli isolated from urinary and nonurinary sources. When eight phages isolated in Pennsylvania were used to type 717 cultures from Missouri, 50.3% of 624 urinary isolates and 34.4% of 93 nonurinary isolates were typable. Strains from nonurinary sources were not found commonly in urine. When five additional phages isolated in Missouri were added to the original set of eight phages, 80.4% of 331 urinary isolates were typable. When this set of phages was used to type 552 urinary cultures isolated in California, Minnesota, Ohio, Pennsylvania, Virginia, and West Virginia, 82.0% of the cultures were typable. Some common phage types were found in high incidence among cultures from the different regions. No correlation was found between phage type and the pattern of resistance to antibiotics. Phage typing data were presented also on the number of strains in individual urine specimens and the recurrences of strains in patients with chronic bacteriuria. Of 97 fecal isolates, 75.2% of the cultures were typable, and the most common phage type was observed in high incidence among the urinary isolates from this region. When 75 cultures from nine other genera of enteric bacteria were typed, only the shigellae were lysed. In view of the information obtained by phage typing and the ease and speed with which it can be done, it is suggested that phage typing be considered a new tool in epidemiological studies of urinary tract infections by E. coli.     

Volatilization of mercuric chloride by mercury-resistant plasmid-bearing strains of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa

Several bacterial strains carrying genes determining mercury resistance on naturally occurring plasmids will convert 10(-5)m Hg(2+) (chloride) to a form of mercury which is volatile and soluble in organic solvents. The volatilization activity is induced by exposure to HgCl(2).     

Pasteurella Bacteriophage Sex Specific in Escherichia coli

Phage H, thought to be specific for Pasteurella pestis, was shown to plate efficiently on F⁻ strains of Escherichia coli but not on F⁺, F′, or Hfr strains. The phage was adsorbed rapidly to F⁻ strains but was not adsorbed to strains carrying F. Comparison with seven other reported female-specific phages showed that, although phage H was similar to the other phages in some characteristics, the exceptionally low efficiency of plating (<10⁻⁹) on F-containing cells makes phage H a particularly useful female-specific phage.     

Bacteriophage T4 multiplication in a glucose-limited Escherichia coli biofilm

An Escherichia coli K-12 biofilm was grown at a dilution rate of 0.028 h(-1) for 48 h in a glucose-limited chemostat coupled to a modified Robbins' device to determine its susceptibility to infection by bacteriophage T4. Bacteriophage T4 at a multiplicity of infection (MOI) of 10 caused a log reduction in biofilm density (expressed as colony forming units (CFU) per cm2) at 90 min postinfection. After 6 h, a net decrease and equilibrium in viral titer was seen. When biofilms were exposed to T4 phage at a MOI of 100, viral titer doubled after 90 min. After 6 h, viral titers (expressed as plaque forming units (PFU) per cm2) stabilized at levels approximately one order of magnitude higher than seen at a MOI of 10. Scanning confocal laser microscopy images also indicated disruption of biofilm morphology following T4 infection with the effects being more pronounced at a MOI of 100 than at a MOI of 10. These results imply that biofilms under carbon limitation can act as natural reservoirs for bacteriophage and that bacteriophage can have some influence on biofilm morphology.     

Oxidative stress resistance of Escherichia coli strains deficient in glutathione biosynthesis

Sensitivity to various oxidants was determined for Escherichia coli strains JTG10 and 821 deficient in biosynthesis of glutathione (gsh-) and their common parental strain AB1157 (gsh+). The three strains showed identical sensitivity to H2O2. E. coli 821 was more resistant than AB1157 and JTG10 to menadione, cumene hydroperoxide, and N-ethylmaleimide. This resistance was not related to the gsh mutation because the other gsh- mutant and the parental strain showed similar sensitivity to these oxidants. The measured activities of NADPH:menadione diaphorase and glucose-6-phosphate dehydrogenase and the extracellular level of menadione suggested that the enhanced resistance of E. coli 821 to menadione might be due to decreased diaphorase activity, but not to a lowered rate of menadione uptake.     

Transmissible antibiotic resistance in strains of Escherichia coli isolated from the ovine rumen

Transmissible multiple resistance to tetracycline, ampicillin and streptomycin was found to be associated with transfer of the larger of the two plasmids (˜ 80 and ˜ 45 kbp) present in a group of tetracycline-resistant Escherichia coli strains isolated from the rumen of sheep. A second group of rumen tet^R strains, which differed in the ability to utilize several sugars, showed non-transmissible resistances to tetracycline and streptomycin.     

Isolation of the Bacteriophage Lambda Receptor from Escherichia coli

A factor which inactivates the phage lambda can be extracted from Escherichia coli. This factor is a protein and is located in the outer membrane of the bacterial envelope. It is found in extracts of strains which are sensitive to phage lambda, but not in extracts of strains specifically resistant to this phage. We conclude that this factor is the lambda receptor, responsible for the specific adsorption of the phage lambda to E. coli cells. A partial purification of the lambda receptor is described. Inactivation of the phage by purified receptor is shown to be accompanied by the release of deoxyribonucleic acid from the phage.