The Inhibition of Growth of Escherichia coli Spheroplasts by Antibacterial Agents

Abstract

Escherichia coli NCTC 86 organisms with impaired walls were prepared by three methods and the effect of antibacterial agents on their growth studied. The growth of penicillin spheroplasts was masked by the overgrowth of unaltered cells in the culture ; the EDTA-lysozyme spheroplasts themselves were non-viable. The growth of penicillin spheroplasts was not affected by cell-wall inhibitors and ampicillin suppressed the overgrowth of unaltered cells. The sensitivity of penicillin spheroplasts and parent cells to inhibition by a range of agents was similar. EDTA treatment enhanced the susceptibility of E. coli N C T C~~ and other strains of Gramnegative species to several antibiotics, particularly erythromycin. Polyacetic acid chelating agents related to EDTA and some new amides derived from glycine, alanine, phenylalanine or methionine also potentiated erythromycin in vitro. Erythromycin showed some activity in protecting mice against infection by EDTAtreated E. coli N C T C~~. The antibiotic did not protect against infection by the untreated bacteria and its activity was not greatly enhanced by simultaneous administration of EDTA or the amide derivatives.

Increased Antibiotic Sensitivity in Pseudomonas aeruginosa Following Passage in Carbenicillin‐containing Media

“…Our demonstration that some strains at least of P. aeruginosa can be converted by extended contact with a cell-wall inhibitor into forms possessing greatly increased sensitivity to several antibiotics is evidence that P. aeruginosa resembles other Gram negative bacteria (Weiser et al, 1968;Teuber, 1969;Spicer & Spooner, 1974) in its intrinsic sensitivity to a number of antibacterial agents which act at intracellular sites. Such agents may be excluded from the cells of normal organisms by the presence of a permeability barrier which is absent or at least impaired in the L-form.…”

Bactericidal Action of Ascorbic Acid on <i>Pseudomonas aeruginosa</i>: Alteration of Cell Surface as a Possible Mechanism

“…This action is comparable with that of EDTA which alters the cell wall permeabili ty of the Pseudomonads [6]. However, un like EDTA, ascorbic acid does not chelate magnesium to form a detectable complex as measured by the potentiometric method [unpubl.…”

Enhancement of the Sensitivity of the Limulus Assay for the Detection of Gram Negative Bacteria

“…For all Gram negative organisms tested the Limulus assay is able to detect 500 cells or less in saline + lop5 M-EDTA after incubation for one hour. This concentration of EDTA is lower than that normally used for rendering bacteria permeable to antibacterial agents (Spicer & Spooner 1974;Haque & Russell 1976) but it may be 'unmasking' or solubilizing endotoxin. Preliminary results indicate that the effect of EDTA could be due to the chelation of divalent cations necessary for membrane integrity (Leive 1974).…”