Cephalexin: human studies of absorption and excretion of a new cephalosporin antibiotic

1. Serum levels, half-lives and urine concentrations of cephalexin, an oral cephalosporin antibiotic which is unique in its absorption and excretion, are reported in human volunteers, fasting, non-fasting and non-fasting plus probenecid. Accumulation does not seem to occur.2. Cephalexin clearance was 376 ml./min and the ratio of cephalexin/creatinine clearances was 2.6 in one volunteer.3. Cephalexin had no effect on the urinary excretion of leucocytes, red cells or protein.4. The very high rate of absorption giving high serum levels and urine concentrations suggest cephalexin will be a useful antibiotic in susceptible bacterial infections in man.

Inhibition of Aerobacter cephalosporin beta-lactamase by penicillins

Cephalosporinase (beta-lactamase) was obtained from cell washings of Aerobacter (Enterobacter) cloacae as a highly active preparation. An alkalimetric method was used to determine the enzyme activity and to estimate its inhibition by 6-amino-penicillanic acid derivatives. Their order of decreasing inhibitory effect was as follows: cloxacillin, oxacillin, methicillin, ampicillin, and penicillin G. We found that 2 to 3 ng of cloxacillin per ml was sufficient to decrease the enzyme activity by 50% in the presence of 400 mug of cephalosporin C per ml. Cloxacillin exerted a potentiating effect on the inhibition of the E. cloacae organisms by cephalosporin C.

Formation of desacetylcephalosporin C in cephalosporin C fermentation

The origin of desacetylcephalosporin C in cephalosporin C fermentation broths was investigated. Esterase activity was detected in cell-free extracts of Cephalosporium acremonium, but these extracts failed to deesterify cephalosporin C. When cephalosporin C was added to sterile and inoculated fermentation media, the antibiotic decayed at nearly identical rates. The formation of desacetylcephalosporin C during the fermentation was measured by quantitative chromatography and by the incorporation of valine-1-(14)C into the molecule. The rate constants obtained from the results of these experiments were equivalent to those for the decay of cephalosporin C in sterile and inoculated media. The data demonstrate that desacetylcephalosporin C is produced by nonenzymatic hydrolysis of cephalosporin C.

Thiol-group binding of zinc to a beta-lactamase of Bacillus cereus: differential effects on enzyme activity with penicillin and cephalosporins as substrates

Zinc, which is required for the hydrolysis of cephalosporins by a crude enzyme from Bacillus cereus 569, also increased the stability of this activity during storage. A loss in activity of the zinc-activated enzyme which occurred on prolonged hydrolysis of cephalosporin C was not restored by further addition of zinc. The thiol reagents N-ethyl maleimide (NEM), iodoacetic acid (IAA), CdCl(2), and p-chloromercuribenzoate, all at 10(-3)m, and iodine at 1.6 x 10(-3)n prevent zinc activation of the "cephalosporinase" activity. However, NEM and IAA have minimal or no demonstrable inhibitory effect if the enzyme is first treated with zinc. This suggests that zinc is linked to the apoenzyme by a thiol group. Activation by zinc is only partially prevented by NEM if the crude enzyme is pretreated with nickel, which alone causes negligible activation of the apoenzyme. The order of affinities of these metals for the apparent thiol group is thus Hg(++), Cd(++) > Zn(++) > Ni(++). The "cephalosporinase" inhibition by Hg(++) was reversible with dithiothreitol. These metals and thiol reagents do not decrease the ability of the crude enzyme to hydrolyze benzylpenicillin, which is consistent with the report that purified "penicillinase" from B. cereus contains no cysteine residue. This suggests that the beta-lactamases of B. cereus that hydrolyze penicillin and cephalosporins differ from each other by at least one amino acid (cysteine).

Examination of various gram-negative bacteria for beta-lactamase activity

The beta-lactamase activity in 10 bacterial species from different genera were evaluated where direct evidence and quantitative data were lacking. A quantitative iodometric method and infrared spectrophotometry were used for the determination of the beta-lactamase activity. The organisms tested were shown to have enzyme activity directed against the beta-lactam ring, and on the basis of the activity on two members of the beta-lactam group of antibiotics, penicillin G and cephalosporin C, a particular ratio was obtained for each species. This report supports the fact of the widespread distribution of beta-lactamase and reopens the question of its significance.

Beta-lactamase activity of Escherichia intermedia

Escherichia intermedia was found to produce a β-lactamase that hydrolyzed several penicillin and cephalosporin C derivatives. Culture conditions affecting production of the enzyme were studied. The enzyme was non-inducible and cell-bound. Growth temperature, medium, and physiological age had a marked effect on production of the enzyme. Properties of the enzyme were studied with intact cells and with a cell-free preparation. Although the β-lactamase of E. intermedia was different in some respects to that produced by gram-positive organisms, it was found to have properties similar to the β-lactamases of gram-negative organisms. 6-Aminopenicillanic acid was cleaved by the enzyme, but 7-aminocephalosporanic acid was resistant to cleavage. The rate of hydrolysis by intact cells and the purified preparation was influenced by the type of N-acyl sidechain of 7-aminocephalosporanic acid and 6-aminopenicillanic acid. The desacetoxy derivatives of cephalosporin C and cephalothin were hydrolyzed less rapidly than the parent compounds. The specific activity of the intact cells on cephalonium and methicillin was substantially less than that of the purified preparation.

Characteristics of Aerobacter beta-lactamase

In this investigation, Aerobacter cloacae is shown to inactivate cephalosporin by hydrolysis of its beta-lactam ring. This was demonstrated by iodine absorption and infrared absorption spectra.The values of the Michaelis constant obtained with cephalosporin C and deacetyl cephalosporin C indicate a great affinity of the Aerobacter's beta-lactamase for its substrate. The enzyme was most active at pH 7.0 and 37 C. Aqueous washings of the Aerobacter cells were a potent source of enzyme.The beta-lactamase of A. cloacae was active on both cephalosporin and penicillin. A higher rate of hydrolysis was observed with cephalosporin C and deacetyl cephalosporin C than with cephalothin and cephaloridine. The ratio of reaction rates on cephalosporin C to that on penicillin G was consistently of the order of 100 to 1. The activity on V, N, and especially the semisynthetic penicillins was also low.The A. cloacae enzyme was easily demonstrable in large amount without added inducer. By contrast, the activity of the beta-lactamase from Pseudomonas pyocyanea cannot be detected unless high concentrations of inducer are used.

Cephalexin, a new orally absorbed cephalosporin antibiotic

A new antibiotic, structurally related to cephaloglycin, has been assigned the generic name cephalexin, 7-(D-alpha-amino-alpha-phenylacetamido)-3-methyl-3-cephem-5-carboxylic acid. In vitro antimicrobial activity of cephalexin does not equal that of cephaloglycin. However, excellent oral absorption and lack of serum binding of cephalexin compensates significantly for the lower in vitro activity. Exceptional efficacy against experimental bacterial infections in mice was obtained with cephalexin therapy as compared with cephaloglycin, tetracycline, and chloramphenicol. The data suggest that cephalexin merits clinical trial.

Steroid transformations by species of Cephalosporium and other fungi

A total of 58 cultures, tentatively identified as species of the genus Cephalosporium, were screened in flask fermentations for their ability to effect conversions of progesterone (Delta(4)-pregnene-3,20-dione) and Reichstein's Substance S (Delta(4)-pregnene-17alpha,21-diol-3,20-dione). A large number of transformations were observed by means of a series of five paper chromatography systems rated for analysis of steroid compounds ranging in polarity from progesterone to polyhydroxylated steroids. Five different transformation products were selected for isolation and identification. For purposes of recovery, conversions were conducted under submerged conditions in either 4- or 200-liter fermentors in which the broth was agitated and aerated. The steroid substrate was dissolved in acetone and added aseptically to the growing culture in a final concentration of 0.025%. After the conversions were effected, the whole broth was extracted with chloroform, and the transformation products were recovered, either by direct crystallization from solvents or through the use of silica gel columns. It was determined that C. ciferrii 21C converted progesterone to Delta(4)-androstene-3,17-dione. Kendall's Compound F (Delta(4)-pregnene-11beta,17alpha,21-triol-3,20-dione) was converted to its 20beta-ol analogue by Geotrichum sp. 51C (during these studies, a number of cultures were taxonomically reclassified). Cephalosporium sp. 27C formed the Delta(1)-analogue of Reichstein's Substance S, and Cephalosporium sclerotigenum 31C and Verticillium aphidum both converted Substance S to the 6beta-hydroxy derivative. Paecilomyces persicinus 22C converted Substance S to a product believed to be a dihydroxylated derivative.

The purification and properties of a penicillinase whose synthesis is mediated by an R-factor in Escherichia coli

1. The penicillinase (beta-lactamase) from Escherichia coli strain TEM has been purified and its activity against a range of penicillin and cephalosporin derivatives measured. 2. The enzyme shows little resemblance to penicillinases from Bacillus cereus, Bacillus licheniformis and Staphylococcus aureus. 3. The molecular weight of the enzyme is 16700+/-5%, which is about half the value obtained for other penicillinases. 4. The enzyme is most similar in properties to a crude preparation of a penicillinase from Klebsiella (Aerobacter) aerogenes, but clearly different from crude enzyme preparations from other strains of E. coli. 5. Since penicillinase synthesis in E. coli strain TEM is mediated by an R-factor known to infect many other species of Enterobacteriaceae, the appearance of similar enzymes in other Gramnegative species is not surprising.

Cephalosporinase and penicillinase activities of a beta-lactamase from Pseudomonas pyocyanea

1. Pseudomonas pyocyanea N.C.T.C. 8203 produces a beta-lactamase that is inducible by high concentrations of benzylpenicillin or cephalosporin C. Methicillin appeared to be a relatively poor inducer, but this could be attributed in part to its ability to mask the enzyme produced. Much of the enzyme is normally cell-bound. 2. No evidence was obtained that the crude enzyme preparation consisted of more than one beta-lactamase and the preparation appeared to contain no significant amount of benzylpenicillin amidase or of an acetyl esterase. 3. The maximum rate of hydrolysis of cephalosporin C and several other derivatives of 7-aminocephalosporanic acid by the crude enzyme was more than five times that of benzylpenicillin. Methicillin, cloxacillin, 6-aminopenicillanic acid and 7-aminocephalosporanic acid were resistant to hydrolysis, and methicillin and cloxacillin were powerful competitive inhibitors of the action of the enzyme on easily hydrolysable substrates. 4. Cephalosporin C, cephalothin and cephaloridine yielded 2 equiv. of acid/mole on enzymic hydrolysis, and deacetylcephalorsporin C yielded 1 equiv./mole. Evidence was obtained that the opening of the beta-lactam ring of cephalosporin C and cephalothin is accompanied by the spontaneous expulsion of an acetoxy group and that of cephaloridine by the expulsion of pyridine. 5. A marked decrease in the minimum inhibitory concentration of benzylpenicillin and several hydrolysable derivatives of 7-aminocephalosporanic acid was observed when the size of the inoculum was decreased. This suggested that the production of a beta-lactamase contributed to the factors responsible for the very high resistance of Ps. pyocyanea to these substances. It was therefore concluded that the latter might show synergism with the enzyme inhibitors, methicillin and cloxacillin, against this organism.