Showing papers by "Ian Chopra published in 1986"
TL;DR: Although polymyxin B and PMBN both caused release of periplasmic proteins, the individual proteins released by the compounds differed, and scanning electron microscopy showed that polymyXin B produced greater morphological changes than PMBN.
Abstract: The effects of polymyxin B and polymyxin B nonapeptide (PMBN) on cell envelope integrity in Escherichia coli were compared. Both compounds caused loss of proteins from E. coli K-12 3300(pBR322), although PMBN released less protein than did polymyxin B. The origin of the released protein was determined both by polyacrylamide gel electrophoresis and by using specific enzyme markers (beta-lactamase in periplasm, beta-galactosidase in cytoplasm). The proteins released by both compounds were derived principally from the periplasm, accompanied in the case of polymyxin B by a low level of cytoplasmic proteins. Although polymyxin B and PMBN both caused release of periplasmic proteins, the individual proteins released by the compounds differed. The periplasmic fraction contained six principal polypeptides with molecular weights between 62,000 (polypeptide 1) and 29,000 (polypeptide 6). Polypeptide 6 was identified as the pBR322-encoded beta-lactamase, but the other proteins were not specifically identified. Polymyxin B caused considerable release of polypeptides 1, 2, and 5 with some release of polypeptides 4 and 6. PMBN released polypeptide 1 (trace), 3, 4, and 6 (trace). Scanning electron microscopy showed that polymyxin B and PMBN both caused surface damage in E. coli. However, polymyxin B produced greater morphological changes than PMBN.
100 citations
TL;DR: It is suggested that the bactericidal activity of polymyxin B may be related to its previously reported ability to release cytoplasmic proteins from bacteria.
Abstract: The effects of polymyxin B and polymyxin B nonapeptide (PMBN) on the permeability of the Escherichia coli cytoplasmic membrane were investigated. Both compounds caused loss of free amino acids, uracil and K+ from E. coli. The rates of loss promoted by polymyxin B were one and a half to two-fold greater than those caused by PMBN. Although PMBN mediated loss of low molecular weight substances from E. coli, it was not bactericidal. In contrast, polymyxin B treated E. coli lysed and rapidly lost viability. We suggest that the bactericidal activity of polymyxin B may be related to its previously reported ability to release cytoplasmic proteins from bacteria.
88 citations
TL;DR: Despite gaps in the understanding of the molecular basis of the changes, data are accumulating showing that low-level, or single-dose, antibiotic administration can be used for the successful therapy of certain bacterial infections.
Abstract: Publisher Summary The effects of sublethal concentrations of antibiotics on bacteria are varied and for the most part uncharacterized at the molecular level. Low concentrations of antibiotics have antimicrobial activity and may also exhibit immunological side effects in the host by either directly inhibiting or stimulating immune-response mechanisms. Exposure of bacteria to low concentrations of β-lactam antibiotics usually leads to growth inhibition accompanied by the production of abnormal morphological forms. However, this is not always so as reports are now emerging to show that certain β-lactam antibiotics are capable either of inducing the synthesis of novel penicillin-binding proteins (PBPs), or altering the balance of existing PBPs to permit normal growth in the presence of β-lactam antibiotics. Despite gaps in the understanding of the molecular basis of the changes, data are accumulating showing that low-level, or single-dose, antibiotic administration can be used for the successful therapy of certain bacterial infections.
43 citations
TL;DR: The likely tetracycline binding site (a common dipeptide) in each effluxprotein was predicted and the presence of the common binding site is consistent with the ability of an efflux protein originating in Bacillus species to be expressed in Escherichia coli.
Abstract: Properties of several, well characterized, tetracycline resistance determinants were compared. The determinants in Tn1721 and Tn10 (both from Gram-negative bacteria) each contain two genes; one encodes a repressor that regulates both its own transcription and that of a membrane protein that confers resistance by promoting efflux of the drug. Determinants from Gram-positive bacteria also encode efflux proteins, but expression of resistance is probably regulated by translational attenuation. The likely tetracycline binding site (a common dipeptide) in each efflux protein was predicted. The presence of the common binding site is consistent with the ability of an efflux protein originating in Bacillus species to be expressed in Escherichia coli.
30 citations
TL;DR: The observations suggest that the ability of translational inhibitors to decrease K88ac mediated adhesion probably results from direct inhibition of synthesis of fimbrial protein itself, together with inhibition of 'helper' polypeptide synthesis.
Abstract: The ability of ten inhibitors of bacterial protein synthesis to decrease adhesion of Escherichia coli bearing K88ac fimbriae was examined. In the presence of the antibiotics at concentrations below the MIC values neomycin was the least effective inhibitor of adhesion and minocycline the most active. The effect of minocycline on the synthesis of individual polypeptides encoded by the K88ac determinant was examined in detail. The rate of synthesis of K88ac pilus protein in the presence of minocycline 0.75 mg/l (0.5 MIC) was less than that of total cell protein synthesis, suggesting that pilus protein becomes progressively 'diluted' in the outer membrane during exposure to this antibiotic concentration. Furthermore, the synthesis of two 'helper' polypeptides (molecular weights of 27.5 K and 27 K) which are probably involved in secretion of K88ac pilus protein through the cell envelope, was particularly sensitive to minocycline. Our observations suggest that the ability of translational inhibitors to decrease K88ac mediated adhesion probably results from direct inhibition of synthesis of fimbrial protein itself, together with inhibition of 'helper' polypeptide synthesis.
12 citations
TL;DR: Structural features of the tetracycline molecule required for transport into Escherichia coli were investigated by examining the uptake of various tetraciescline analogues and suggest that the carboxamide group at the C2 position of the Tn10 encoded resistance to tetrACYcline is required for Transport into bacteria.
Abstract: Structural features of the tetracycline molecule required for transport into Escherichia coli were investigated by examining the uptake of various tetracycline analogues. Uptake was assessed by determining the ability of analogues to induce Tn10 encoded resistance to tetracycline and by direct transport assays using tetracycline susceptible bacteria. Seven tetracyclines (including tetracycline itself) were studied. Two of these compounds, chlorotetracyclinonitrile and tetracyclinonitrile were not accumulated by E. coli, which suggests that the carboxamide group at the C2 position of the tetracycline molecule is required for transport into bacteria.
7 citations
1 citations