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Aminosides are antibiotics essential in the treatment of gram negative bacilli infections. Phenomena of resistance related to them are amongst the best documented. For enterobacteria encountered in clinical practice, the process is usually a plasmid mediated inactivation mechanism, the dispersion of which in a hospital context may be appreciated. Precise knowledge of the modes of inactivation and the molecular sites involved has led to the production of semi-synthetic aminosides which escape the action of these enzymes. A classification of hospital bacteria according to their type of resistance is possible by virtue of the study of phenotypes and may make it possible to define the true need of these new substances.

During a 10-yr period, 40 cases of severe Listeria monocytogenes meningitis were observed. All patients showed consciousness disturbances and 27 of them (68%) focal neurologic signs. Cranial nerve palsies were common (57%). Early general seizures (13 patients) and presence of underlying disease (12 patients) were associated with a high mortality rate. Although the management of antibiotic therapy is open for discussion, chloramphenicol (used in 7 patients) seems to be more effective than other drugs.

The high potency of Moxalactam on three major groups of bacteria, i.e. Enterobacteriae, Haemophilus and Bacteroïdes, predicted by previous studies, has been confirmed by the study of hospital strains in this multicenter investigation. Among these groups, the proportion of resistant strains is very low. However, Moxalactam is not superior to older agents on staphylococci, Streptococci and Listeria, and is less active than certain new agents on Pseudomonas. Moxalactam is one of the best "third generation" cephalosporins. It is remarkable by its potency against Bacteroides fragilis and its weak activity on Streptococci and Pneumococci. The unanswered question concerns the future of resistant strains: will they remain exceptional or will they multiply?

Meningitis caused by Gram-negative bacilli creates difficult problems since most strains are multiresistant. The purpose of this study was to evaluate the effectiveness of lamoxactam administered intravenously. Eleven patients admitted to an intensive care unit with meningitis due to Gram-negative bacilli were treated with this antibiotic, administered alone in 9 cases. Three patients had ventriculitis. Eight survived. The MICs ranged from 0.06 to 0.5 microgram/ml in 10 cases. The CSF was sterilized and rapidly became normal. Meningeal concentrations varied from 1-5 to 62 micrograms/ml and the CSF was bactericidal. In one female patient the CSF was sterile on the 5th day of treatment but remained abnormal; the meningeal concentration of lamoxactam (35 micrograms/ml) was much higher than the MIC (2 micrograms/ml) but below the MBC (128 micrograms/ml), which was consistent with the absence of bactericidal effect of the CSF. Owing to its very low CMIs and satisfactory passage through the blood-brain barrier, lamoxactam administered alone can be successful in the treatment of Gram-negative meningitis and ventriculitis. However, the bactericidal effect of the CSF should be rapidly assessed.

Gram-negative aerobic bacilli (Enterobacteria, Pseudomonas, Acinetobacter) isolated in clinical circumstances at the microbiology of the Claude Bernard Hospital, Paris, are classified according to their resistance to the usual beta-lactam antibiotics routinely tested: ampicillin, carbenicillin, cefalotin. The MICs of mezlocillin were measured on 204 strains and compared to the results obtained with older drugs in each group.

Gram-negative bacilli isolated from clinical specimens submitted for culture in two Paris hospitals during 1974 were studied for susceptibility to six currently used aminoglycosides: kanamycin, neomycin, paromomycin, lividomycin, gentamicin, and tobramycin. Resistance patterns of strains of various species including those of Enterobacteriaceae, Pseudomonas, and Moraxella were determined, and the strains were grouped into eight resistance "phenotypes." In comparative studies of 807 strains belonging to different phenotypes, amikacin was markedly more active than any of the six other antibiotics; at concentrations of less than or equal to 4 mug/ml, it inhibited about 88% of the strains, including those resistant to gentamicin and tobramycin. Some amikacin-resistant strains were found among different species. The mechanism of resistance to amikacin of strains of Serratia and Moraxella group II was related to an N-acetylating enzyme. Amikacin can be expected to be useful as an alternative treatment of infections due to gram-negative bacilli sensitive to aminoglycosides and also, more particularly, for the treatment of patients infected with multiresistant strains.

Incompatibility between R factors has been reported by several authors, and four incompatibility groups have already been described by Datta and Hedges among Rfi(-) factors. The stability of 12 plasmids in pairs was studied after 116 crosses, and five new groups were found, designated 5, 6, 7, 8, and 9. Each plasmid studied belongs to one single group. Incompatibility between plasmids in pairs is a clear-cut phenomenon, is easy to observe, and can provide a reliable method for recognizing and classifying resistance factors, and for tracing their spread among bacterial species.