The in-vitro activity of tobramycin compared with that of other aminoglycosides

The influence of medium composition, pH, serum, and magnesium on the action of tobramycin is compared to that on the action of gentamicin. The minimum inhibitory concentration of tobramycin, gentamicin, kanamycin, and streptomycin was determined for 472 strains including 19 species: tobramycin was found to be the most active against Ps. aeruginosa and kanamycin against Providence, but gentamicin was usually the most active against all other species. Ps. aeruginosa passaged on medium containing either gentamicin or tobramycin showed increased resistance to both. Sensitive strains of this species were shown to contain a small minority of cells resistant to these antibiotics, the presence of which is believed to account for the marked bactericidal synergy which was demonstrated between tobramycin and carbenicillin.

Incompatibility groups and the classification of fi - resistance factors

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.

The effect of osmolality on the response of Escherichia coli and Proteus mirabilis to penicillins

The response of broth cultures of Escherichia coli and Proteus mirabilis to ampicillin was continuously monitored turbidometrically. The rapid lytic response which follows a few minutes after addition of the antibiotic as well as the later slow lysis of spheroplasts could be manipulated by altering the osmolality of the medium. A higher osmolality was found to be necessary to protect Esch. coli than Pr. mirabilis and this explains the differential response of the 2 organisms that we have previously described.

R factors in hospital infection

In order to assess the clinical importance of R factors 524 "coliform" infections were studied in a general hospital. Of these, 95 were caused by Pseudomonas aeruginosa. Among the remaining 429, 43% were caused by drug-resistant enterobacteria; resistance was frequently multiple and determined by transmissible R factors. Choice of therapy was thus limited but in every case at least one antibiotic, effective in vitro, was still available.

Amoxycillin: a new semi-synthetic penicillin

Amoxycillin (alpha-amino-p-hydroxybenzylpenicillin) is a new semi-synthetic penicillin with a broad spectrum of antibacterial activity similar to that of ampicillin. Penicillin-sensitive strains of staphylococci, streptococci, and pneumococci were sensitive to concentrations of 0.1 mug or less of amoxycillin/ml. Strains of Haemophilus influenzae were inhibited by a level of 0.5 mug/ml, and most strains of Escherichia coli, Proteus mirabilis, Shigella sonnei, Salmonella species, and Streptococcus faecalis were sensitive to a concentration of 5 mug or less of amoxycillin/ml. Penicillinase-producing strains of Staphylococcus aureus and strains of Pseudomonas aeruginosa, indole-positive Proteus, Klebsiella, and Enterobacter were insensitive to amoxycillin. The new penicillin was bactericidal in activity, as with other penicillins, and its antibacterial activity was not reduced in the presence of serum. After oral administration to volunteer subjects amoxycillin produced serum concentrations twice as high as those obtained with similar doses of ampicillin, and the penicillin was recovered unchanged in high concentrations in the urine. The absorption of amoxycillin was not greatly influenced by food, and administration of probenecid resulted in increased and more prolonged concentrations of amoxycillin in serum.