Cephalexin and Cephaloglycin Activity In Vitro and Absorption and Urinary Excretion of Single Oral Doses in Normal Young Adults

A large number of recently isolated bacterial pathogens were tested for susceptibility to cephalexin and cephaloglycin by the replica inoculating method. Strains of group A hemolytic streptococci, viridans (alpha and gamma) streptococci, pneumococci, gonococci, meningococci, and penicillin G-sensitive Staphylococcus aureus were all moderately to highly susceptible to both of these cephalosporin analogues, nearly all of the strains being two to eight (median four) times more susceptible to cephaloglycin than to cephalexin. The penicillin G-resistant, penicillinase-producing strains of S. aureus varied in their susceptibility; many were moderately resistant to both analogues, particularly to cephalexin. Strains of enterococci, Haemophilus influenzae, and most of the common gram-negative bacilli were moderately to highly resistant. Reducing the size of the inoculum had variable effects on inhibition by these drugs, depending on the species or strain. The activity of cephalexin was very little affected by pH of the medium within the clinical range or by incubation at 37 C in broth for up to 24 hr. In contrast, cephaloglycin in broth deteriorated rapidly at 37 C, and its activity was markedly reduced in alkaline medium. Both cephalexin and cephaloglycin were rapidly absorbed and excreted into the urine after single oral doses of 500 mg. Much higher levels were achieved and sustained with the former. Absorption of both analogues was delayed when taken with food, and the levels in the serum were significantly higher and better sustained when probenecid was also given. Very high concentrations of cephalexin were excreted into the urine during the first 4 hr, and the levels were still high in the 4- to 8-hr collection. The concentrations of cephaloglycin in the urine at these times were much lower. An average of 80 to 93% of the dose of cephalexin and 25 to 30% of the cephaloglycin were accounted for as active drug in the urine collected in 8 hr. Both analogues were well tolerated.     

Analysis of sequential stages in serum bactericidal reactions

Michael, J. Gabriel (House of the Good Samaritan, Children's Hospital Medical Center, Boston, Mass.), and Werner Braun. Analysis of sequential stages in serum bactericidal reaction. J. Bacteriol. 87:1067-1072. 1964.-The bactericidal reaction of "normal" human serum against Escherichia coli was found to be separable into two distinctive stages. The early (first) stage of the reaction lasts for a relatively short period of time, and involves factors that are present in sufficient amounts only in slightly diluted serum. The later (second) stage needs more time and requires factors present in highly diluted serum. The first stage depends on the presence of Ca(++) and Mg(++) and on the activity of all components of complement; the second stage does not require divalent cations and C'1, C'2, and C'4, but requires factors that can be removed by zymosan. Under our conditions, removal of lysozyme did not influence either stage of the reaction. Bacteria exposed to concentrated serum for a short time, during the first stage, are essentially unaffected as far as their potential for subsequent multiplication is concerned; the actual damage to cellular integrity occurs only during the second stage of the reaction. In the absence of cell division, the "sensitization" produced during the first stage can be preserved for prolonged periods, and the bactericidal reaction can be completed later by exposure to antibody-free, highly diluted serum (second stage). Cell multiplication abolishes the sensitizing effects of the first stage.     

Integration of the Serratia marcescens haemolysin into human erythrocyte membranes

The haemolytic activity of Serratia marcescens is determined by two proteins, ShlA and ShlB. ShlA integrates into the erythrocyte membrane and causes osmotic lysis through channel formation. The conformation of ShlA and its interaction with erythrocyte membranes were studied by determining the cleavage of ShlA by added trypsin. Our results suggest that the conformation of inactive ShlA (from an ShlB- strain) differs from the active ShlA, and that in a hydrophobic environment (detergent or membrane) active ShlA assumes a conformation distinct from that in buffer. Only active haemolysin adsorbed to erythrocytes. ShlA was firmly integrated into the erythrocyte membrane since it was only released under conditions which also dissolved the integral erythrocyte membrane proteins. Moreover, ShlA integrated into 'ghosts' remained there and was not haemolytic when incubated with erythrocytes. From the trypsin cleavage pattern obtained with haemolysin and C-terminally truncated, but still active, haemolysin derivatives integrated into erythrocytes, and sealed and unsealed erythrocyte 'ghosts', we conclude that ShlA is preferentially cleaved by trypsin at a few sites but only from the inside of the erythrocyte. Haemolysin in the erythrocyte membrane forms a water-filled channel and is resistant to trypsin and other proteases.