Time-dependent effects of inosine on competence development in Haemophilus influenzae

The effect of inosine on the development of competence is dependent upon the time at which it is added to the competence medium. Competence is inhibited if inosine is added within 15 min after the development begins, but is stimulated if the addition is made at later times. Protein synthesis is stimulated by the addition of inosine, but the effect is quantitatively similar regardless of the time at which inosine is added.

Tetracycline levels in bronchial secretions

The excretion of tetracycline HCl in sputum was studied in 42 hospital patients suffering from various respiratory disorders who were receiving oral tetracycline therapy of 1.0 gram daily in divided doses.The tetracycline levels were estimated biologically by a cup-plate agar diffusion method using B. cereus. Two separate methods of sputum homogenization are described: enzymic liquefaction with pronase, a powerful proteolytic enzyme, and ultracentrifugation at 103,000 g for three hours which sediments the viscous mucoids leaving 80-90% as a clear, non-viscous supernatant. The two methods allowed duplicate assays on sputum samples and generally showed close agreement. The ultracentrifugation technique is favoured for normal purposes because of its simplicity and the avoidance of any biochemical interference.A close correlation was shown between the tetracycline levels in sputum samples and the average serum level for each patient. Over the serum tetracycline range 1.0-5.0 mug/ml, the mean sputum tetracycline levels after centrifugation were 23-18%, and the average level was 0.50 mug/ml.The levels found in sputum were compared with the minimum inhibitory concentration of tetracycline for strains of H. influenzae and Strep. pneumoniae. Eighty-six percent of 29 H. influenzae strains tested and all Strep. pneumoniae strains tested were sensitive to 0.5 mug/ml tetracycline. The remaining H. influenzae strains had a minimum inhibitory concentration of 1.0 mug/ml or higher, a tetracycline level in sputum which appeared to be outside the mean range at the oral dosage of 1.0 gram daily. Hence it is suggested that a small proportion of patients with lower respiratory tract infections due to H. influenzae would be unresponsive, or only partially responsive, to this usual therapeutic range of tetracycline.

Ampicillin levels in sputum, serum, and saliva

The ampicillin levels in sputum, serum, and saliva from 40 patients receiving a dose of 250 mg., 26 patients receiving a dose of 500 mg., and 11 patients receiving a dose of 1 g. were estimated. The ampicillin was given orally four times daily.

The 1-2 hour and 2-3 hour sputum levels were similar in individual patients. There was no difference in the range or mean sputum or saliva levels between specimens from patients receiving 250 mg. and 500 mg., but the levels were significantly higher after the 1 g. dose. The mean serum level showed a small increase after 500 mg. ampicillin as compared with the 250 mg. dose and a big increase after the 1 g. dose: only the latter difference was significant. The sputum levels were approximately 30 to 40 times lower than the corresponding serum levels. There was considerable scatter in the sputum level for any level of ampicillin in the serum: in only two of the 1-2 hour sputum specimens was there no detectable ampicillin.

There was no correlation between the sputum levels and either the body weight or the dose in milligrams per kilogram. There was no evidence that corticosteroids or diuretics affected the sputum level.

It was not possible to demonstrate any relationship between the purulence of the sputum and the level of ampicillin after doses of 250 mg. or 500 mg., but higher levels were found in the more purulent specimens after 1 g. doses.

In-vitro comparison of erythromycin, lincomycin, and clindamycin

The in-vitro antibacterial activities of erythromycin, lincomycin, and clindamycin, a new derivative of lincomycin, were compared. Clindamycin was always more active than lincomycin, and was either as active as erythromycin or more so against betahaemolytic streptococci, Streptococcus viridans, Str. pneumoniae, and erythromycin-sensitive Staphylococcus aureus. It was also fully active against most erythromycin-resistant strains of Staph. aureus. On the other hand, it was somewhat less active than erythromycin against Haemophilus influenzae and considerably less active than erythromycin against Str. faecalis and Neisseria gonorrhoeae.Clinical trials seem to be justified in infections with sensitive organisms for which erythromycin might have been indicated.

The effect of carbon dioxide on the sensitivity of Bacteroides fragilis to certain antibiotics in vitro

The effect of 10% carbon dioxide on the sensitivity to four antibiotics of 10 strains of Bacteroides fragilis was studied. The minimum inhibitory concentrations of erythromycin and lincomycin hydrochloride for these strains were four to 32 times higher, when grown in hydrogen plus 10% carbon dioxide, than the values obtained when the strains were grown in pure hydrogen. A similar effect was obtained by growing the strains in hydrogen on an acid medium. Except for Haemophilus influenzae and Clostridium tertium the sensitivity to erythromycin and lincomycin hydrochloride of other species of bacteria examined was not affected by the atmosphere in which the tests were carried out. 7-Chlorolincomycin and rifamycin B diethylamide, to which the strains of B. fragilis were uniformly sensitive, were not significantly affected by additional carbon dioxide. The possible mechanisms underlying this phenomenon and its clinical implications are discussed, and a case report describing the successful use of erythromycin in the treatment of a cerebral abscess due to B. fragilis is presented. In a recent study in this laboratory of the sensitivity to antibiotics of B. fragilis the majority of strains were found to be inhibited by 0.15 mug/ml of erythromycin and by 0.55 mug/ml of lincomycin hydrochloride (Ingham, Selkon, Codd, and Hale, 1968). After this work had been completed hydrogen plus 10% carbon dioxide was substituted for pure hydrogen in the anaerobic technique. Strains of B. fragilis isolated on routine culture now appeared to be relatively resistant to erythromycin and lincomycin hydrochloride when their sensitivity was examined by the disc diffusion method. A more detailed investigation of this phenomenon was carried out, the results of which are reported here. The opportunity was also taken to examine the susceptibility of B. fragilis to two new antibiotics, namely, 7-chlorolincomycin and rifamycin B diethylamide.

Photodynamic action on native and denatured transforming deoxyribonucleic acid from Haemophilus influenzae

The photodynamic inactivation of native or denatured transforming deoxyribonucleic acid (DNA) from Haemophilus influenzae is described. The inactivation at the same pH was higher for denatured than native DNA. At acidic pH, the inactivation both for native and denatured DNA was faster than at alkaline pH. The guanine content of photoinactivated native DNA at neutral pH was less than untreated DNA. The inactivation of biological activity was more extensive than the alteration of guanine. The absorption spectrum of photoinactivated native or denatured DNA was only slightly different than the control DNA at the different experimental conditions.