Antibiotic prophylaxis for the prevention of late infections of prosthetic joints.

Late infection of prosthetic joints as a result of the haematogenous spread of an organism from a remote site with the seeding of that organism on the bone-implanted prosthesis interface is a well-documented but rare complication of prosthetic joint surgery. However, the use of antibiotic prophylaxis is such cases is controversial. The details of 67 previously reported cases of late infection have been reviewed in conjunction with the details of a series of 43 patients, and observations and recommendations regarding antibiotic prophylaxis are made upon the basis of these accumulated data.

A comparison of aztreonam and imipenem induction of class I beta-lactamase in Enterobacter cloacae ATCC 13047.

Aztreonam and imipenem were shown to induce Class I beta-lactamase in Enterobacter cloacae ATCC 13047 to a similar extent. Quantitatively, however, aztreonam was far less efficient as an inducer than imipenem. Optimum induction by aztreonam required a concentration of 200 mg/l, which was 800-fold greater than the concentration of 0.25 mg/l of imipenem which resulted in the optimum induction. The differences in the concentrations of aztreonam and imipenem that gave optimum induction were related to the inherent antibacterial activities of the antibiotics when these were determined under the conditions of broth culture. The beta-lactamase activity of sonicated cell samples following induction was inhibited by the presence of aztreonam but not by imipenem. The inhibition was overcome by first washing the cell samples from induced cultures and then incubating the sonicates for a prolonged period at 4 degrees C. It is proposed that the phenomena of an optimum inducing concentration and the interference with the assay of beta-lactamase by the presence of residual antibiotic demonstrated in this study with aztreonam and imipenem would be of relevance when applied more broadly to studies of beta-lactamase induction. In particular these would have a profound effect on the results of studies which attempt to compare the efficacy of beta-lactams as inducers of Class I beta-lactamase.

The penicillins.

The penicillins are among the most useful antibiotics despite the increasing problem of bacterial resistance. The authors review the various penicillins available in Australia and emphasise the rationale for their use and the mechanisms of bacterial resistance to these agents.

Comparison of glycine enhancement with cefoxitin induction of class 1 beta-lactamase production in Enterobacter cloacae ATCC 13047.

The presence of either glycine or cefoxitin in the growth medium resulted in an increase in the beta-lactamase activity of cultures of Enterobacter cloacae ATCC 13047. Although the beta-lactamases produced as a result of either glycine enhancement or cefoxitin induction were identical there were striking differences in the kinetics of beta-lactamase production. The increased production of beta-lactamase which resulted from enhancement by glycine occurred late in the growth cycle whereas, with cefoxitin induction, the maximum production of beta-lactamase occurred early in logarithmic-phase growth. After the peak activity was reached the beta-lactamase activity appeared to decline with both processes. However, the mechanism of the apparent fall in the intracellular beta-lactamase activity was different with glycine enhancement and cefoxitin induction. In glycine enhanced cultures the fall presumably was due to leakage of intracellular beta-lactamase into the culture medium whereas with cefoxitin induced cultures there was dilution of beta-lactamase activity by bacterial protein derived from an increase in cell numbers after the cessation of induction. High extra-cellular levels of beta-lactamase activity were observed in cultures enhanced by glycine, whereas little beta-lactamase activity was detected in the medium when the cultures were induced by cefoxitin. The findings demonstrate that there are considerable differences between glycine enhancement and cefoxitin induction, but a final mechanism common to both processes exists which results in the production of identical beta-lactamases by E. cloacae ATCC 13047.

The effect of casein derivatives on glycine enhancement of beta-lactamase production in Enterobacter cloacae ATCC.13047.

Our earlier work showed that glycine enhancement of class I beta-lactamase production in Enterobacter cloacae ATCC.13047 was greater on Isosensitest Agar than on other laboratory media. In the present study it was demonstrated that Casein Hydrolysate was the constituent of Isosensitest Agar which was necessary for glycine enhancement of beta-lactamase production. Also, a comparison of the effect of casein and casein derivatives on glycine enhancement of beta-lactamase production showed that acid hydrolysis of casein was a prerequisite for glycine enhancement of beta-lactamase production. Enterobacter cloacae ATCC.13047 failed to grow on a medium containing casein, and glycine enhancement of beta-lactamase production did not occur on a medium containing tryptic hydrolysate of casein. The effect on beta-lactamase production of variations in the concentrations of both Casein Hydrolysate and glycine was examined by titration of both components in a chequerboard fashion. Beta-lactamase production was influenced by the concentrations of both Casein Hydrolysate and glycine. This inter-relationship indicated that there was a balance between the concentrations of Casein Hydrolysate and glycine and that alterations in this balance modified beta-lactamase production. The significance of the observations is discussed in relation to the factors which influence glycine enhancement of beta-lactamase production in Enterobacter cloacae ATCC.13047.

Enhancement of beta-lactamase production by glycine in Enterobacter cloacae ATCC.13047.

Beta-lactamase production in Enterobacter cloacae ATCC.13047 was enhanced by glycine, and the degree of enhancement was dependent on the concentration of glycine and the medium used. Maximum enhancement occurred with a concentration of 0.05 moles/l of glycine, and of 4 media examined enhancement was greatest on Isosensitest Agar. Enhanced beta-lactamase production evoked by glycine was compared with that following induction by various concentrations of cefoxitin. The amount of beta-lactamase produced under conditions of maximum glycine enhancement was higher than that produced by cultures fully induced by cefoxitin. Other differences in the characteristics of the enhancement of beta-lactamase production by glycine and beta-lactamase induced by cefoxitin suggested that the mechanisms of the 2 phenomena were different. The significance of this finding in terms of the interpretation of in vitro antimicrobial sensitivity tests with beta-lactam antibiotics is discussed.

A case of Japanese B encephalitis imported into the United Kingdom.

A case of acute encephalomyelitis, serologically proven to be due to Japanese B encephalitis virus, is reported. The patient, a 35-year-old woman, contracted the disease whilst in Hong Kong but presented in the United Kingdom. She required ventilatory support and was given high-dose steroids. She recovered from the illness but died after a period of four months from respiratory/cardiac arrest.