- Volume 68, Issue 3, 1971

The rates of hydrolysis of carbenicillin and of other penicillins and cephalosporins by nine different β-lactamase preparations obtained from Gram-negative bacteria were compared. Enzymes produced by Klebsiella strains, most active against penicillins, as well as β-lactamases synthesized by Escherichia coli and Proteus mirabilis strains hydrolysed carbenicillin, although at relatively lower rates than ampicillin or cephaloridine. In contrast, carbenicillin was extremely resistant to β-lactamases with a predominant cephalosporinase activity as produced by Pseudomonas aeruginosa, Proteus vulgaris and Enterobacter strains. The cephalosporin β-lactamases activity of these enzymes was inhibited by carbenicillin. A considerably increased enzymic activity observed in one strain of Pseudomonas aeruginosa when grown in the presence of carbenicillin or other β-lactam antibiotics was unable to destroy carbenicillin to any measurable extent. A possible permeability barrier to carbenicillin has been demonstrated in some strains.

Polymyxin B and the non-ionic surfactant polysorbate 80 acted synergistically against Pseudomonas aeruginosa with respect to leakage, death and lysis. Polysorbate 80 alone was non-toxic. The enhancement of polymyxin occurred throughout the polysorbate concentration range (0·0001 to 0#x00B7;250%, v/v). No sudden change in the pattern of enhancement occurred near the critical micelle concentration of polysorbate. The onset of action of polysorbate was prompt, implying a direct physical effect on the bacteria. Exposure of bacteria to this surfactant did not cause an increase in uptake of polymyxin. It is proposed that polysorbate 80 alters the outer lipid structure of the envelope of P. aeruginosa allowing easier access of polymyxin to the underlying membrane.

Summary: The sorption of two marine bacteria to surfaces involved an instantaneous reversible phase, and a time-dependent irreversible phase. Reversible sorption of the non-motile Achromobacter strain r 8 decreased to zero as the electrolyte concentration decreased, or as the thickness of the electrical double-layer increased.

The electrolyte concentration at which all bacteria were repelled from the glass surface depended on the valency of the cation. The reversible phase is interpreted in terms of the balance between the electrical double-layer repulsion energies at different electrolyte concentrations and the van der Waals attractive energies. Even at the electrolyte concentration of seawater, the bacteria probably are held at a small distance from the glass surface by a repulsion barrier. Reversible sorption often led to rotational motion of the motile Pseudomonas sp. strain R3 at a liquid-glass interface.

Pseudomonas R3 produced polymeric fibrils in artificial seawater; these may be concerned in the irreversible sorption of the bacteria to surfaces. Sorption and polymer production were stimulated by 7 mg./l. glucose but higher levels inhibited irreversible sorption. Omission of Ca2+ and Mg2+ from the artificial seawater prevented growth, polymer production, and sorption to surfaces by Pseudomonas R3.

Summary: Paramecia belonging to certain strains of Paramecium aurelia (syngens 1, 2 and 8) were transferred from dual culture with bacteria to axenic media, where the growth of some stocks continued, with weekly subculturing. The only axenically grown stock found to be capable of supporting growth of mu particles indefinitely was stock 138 (syngen 8).

Lambda and mu particles from axenically grown Paramecium aurelia were cultivated in vitro in a highly complex medium at 27° under aerobic conditions. The particles retained their characteristic killing action on certain P. aurelia stocks but could not infect sensitive paramecia. The particles divided at approximately one fission per day and achieved a maximum density of only 16–20 × 103/ml. The implications of these studies for the interaction of the nuclear genes and the killer particles are discussed.

Clostridium acetobutylicum has been studied during batch cultivation at pH 7 and 35° in a glucose + casein hydrolysate + vitamins and salts medium kept (i) anaerobic (E h, −400 to −370 mV), (ii) aerated (E h, −50 to o mV; dissolved 02, < 1 μ m), and (iii) aerobic (E h, + 100 mV; dissolved O2, 40 to 50 μ m). Shortterm (4 to 6 h.) exposure to oxygen was not lethal, though at sufficiently high concentrations oxygen decreased the rate of glucose consumption, halted growth and prevented net synthesis of DNA, RNA and protein. Under these aerobic conditions the organism was drained of‘reducing power’ and starved of energy - as evidenced by cessation of butyrate formation (but not of acetate production), and by a marked fall in intracellular ATP. These consequences of oxygenation were swiftly reversed when anaerobic conditions were re-established; ‘ normal ’ growth and glucose metabolism then resumed. There was no evidence of H202 production, nor could the effects of oxygenation be attributed merely to its elevation of the culture E h. Thus oxygen (40 μ m) inhibited growth even in a medium poised with dithiothreitol at − 50 mV, while growth and glucose metabolism continued unchecked when the E h of an anaerobic culture was maintained at + 370 mV by addition of potassium ferricyanide.

SUMMARY: An electron microscopic study of strains of many serological groups of streptococci substantiates a previous suggestion that an intracellular structure, termed ‘core’, is a presumptive taxonomic indicator for group D streptococci.