IN VITRO BIOLOGICAL ACTIVITY OF CEPHALOTHIN

Cephalosporin resistance, tolerance, and approaches to improve their activities

Cephalosporins comprise a β-lactam antibiotic class whose first members were discovered in 1945 from the fungus Cephalosporium acremonium. Their clinical use for Gram-negative bacterial infections is widespread due to their ability to traverse outer membranes through porins to gain access to the periplasm and disrupt peptidoglycan synthesis. More recent members of the cephalosporin class are administered as last resort treatments for complicated urinary tract infections, MRSA, and other multi-drug resistant pathogens, such as Neisseria gonorrhoeae. Unfortunately, there has been a global increase in cephalosporin-resistant strains, heteroresistance to this drug class has been a topic of increasing concern, and tolerance and persistence are recognized as potential causes of cephalosporin treatment failure. In this review, we summarize the cephalosporin antibiotic class from discovery to their mechanisms of action, and discuss the causes of cephalosporin treatment failure, which include resistance, tolerance, and phenomena when those qualities are exhibited by only small subpopulations of bacterial cultures (heteroresistance and persistence). Further, we discuss how recent efforts with cephalosporin conjugates and combination treatments aim to reinvigorate this antibiotic class.

SENSITIVITY OF COCCAL AND L FORMS OF STAPHYLOCOCCUS AUREUS TO FIVE ANTIBIOTICS

Kagan, B. M. (Cedars of Lebanon Hospital, Los Angeles, Calif.), Susan Zolla, R. Busser, and Silvija Liepnieks. Sensitivity of coccal and L forms of Staphylococcus aureus to five antibiotics. J. Bacteriol. 88:630-632. 1964.-Antibiotics whose primary site of action is in the cell wall (penicillin and cephalothin) do not inhibit growth of L-phase organisms. In this study, kanamycin, neomycin, polymyxin B, lincomycin, and gentamycin were found to be more active against L-phase growth of Staphylococcus aureus in vitro than against the coccal forms. Therefore, their primary site of antimicrobial activity appears to be other than that involved in the synthesis or integrity of the cell wall.

MORPHOLOGICAL CHANGES IN GRAM-NEGATIVE BACILLI EXPOSED TO CEPHALOTHIN

Chang, Te-Wen (Tufts University School of Medicine, Boston, Mass.), and Louis Weinstein. Morphological changes in gram-negative bacilli exposed to cephalothin. J. Bacteriol. 88:1790-1797. 1964.-Exposure of gram-negative bacteria to cephalothin (7-[thiophene-2-acetamido]-cephalosporanic acid) revealed the formation of long filaments and large bodies, which were capable of reverting to normal cells when removed from contact with the drug. The degree of morphological change was found to be related to the concentration of antibiotic in which the organisms were suspended. The large bodies were altered by contact with solutions of varying osmolarity. Different species showed variation in the ability to develop large bodies. A relationship between antibiotic sensitivity and the capacity to resist morphological alteration was observed. Though most sensitive gram-negative bacilli were strikingly changed by exposure to cephalothin, naturally resistant ones were unaffected. Organisms made drug-resistant in vitro underwent changes in cellular form which were qualitatively the same but less intense than those which developed in parent strains originally sensitive to cephalothin.

INDUCTION BY ANTIBIOTICS AND COMPARATIVE SENSITIVITY OF L-PHASE VARIANTS OF STAPHYLOCOCCUS AUREUS

Molander, C. W. (Cedars of Lebanon-Mount Sinai Hospitals, Los Angeles, Calif.), B. M. Kagan, H. J. Weinberger, E. M. Heimlich, and R. J. Busser. Induction by antibiotics and comparative sensitivity of L-phase variants of Staphylococcus aureus. J. Bacteriol. 88:591-594. 1964.-The penicillins, cephalothin, vancomycin, and bacitracin were found to be less inhibitory to the L-phase variants than to their respective parent bacteria. Those antibiotics not considered to be primarily inhibitors of cell-wall synthesis were, in general, somewhat more inhibitory to the L form than to their parent bacteria. Only the penicillins and cephalothin readily induced L-phase variation. Novobiocin induced pleomorphic growth resembling the earliest stages of L-phase transformation. Failure of observable induction by bacitracin and vancomycin suggests that these two antibiotics affect cell-wall synthesis in a manner different from the penicillins, or that L-phase transformation may require more than "penicillin-like" interference with cell-wall synthesis.

The cephalosporins: activity and clinical use

The cephalosporin antibiotics have been employed with increasing frequency since their introduction into clinical practice in the early 1960s. With the exception of cephaloridine, cephalosporin compounds are not associated with the production of significant untoward effects. The availability of newer cephalosporins, both oral and parenteral, with enhanced antibacterial activity, has expanded the clinical indications for administration of these antibiotics.

In vitro activity of BL-s640 against gram-negative bacilli and Staphylococcus aureus compared with activity of four other semisynthetic cephalosporins

The in vitro activity of BL-S640 (cefatrizine) was determined against 674 recent clinical isolates of Staphylococcus aureus and Enterobacteriaceae. Activity against S. aureus was less than that of cephapirin, cephalothin, and cefazolin, but greater than that of cephalexin. Activity against gram-negative isolates was variable: BL-S640 was slightly less potent than cefazolin against Escherichia coli and Klebsiella, but more active than the other compounds. As for the more resistant gram-negative genera, BL-S640 was significantly superior to the control cephalosporins. The effect of inoculum size on the antibacterial activity was moderate for most organisms except Enterobacter, Providencia stuartii, and indole-positive Proteus, the median minimal inhibitory concentrations of which were 6 to 27 times lower when determined with a 10(-4)-diluted culture compared with the undiluted one. The stability in aqueous solution at 37 C was remarkably high at the lower pH values, but low at the neutral point.

Cephapirin: in vitro antibacterial spectrum

Cephapirin, a new semisynthetic cephalosporin derivative, was found to have an antibacterial spectrum similar to that of cephalothin. Staphylococcus aureus was inhibited by cephapirin concentrations of 0.09 to 12.5 mug/ml. S. epidermidis, S. viridans, S. pyogenes, and Diplococcus pneumonia isolates were inhibited by less than 1 mug/ml. The Enterococcus required a concentration of 25 mug of antibiotic per ml for inhibition. Approximately 65% of Escherichia coli, and all Klebsiella, indole-negative Proteus, and Salmonella strains tested were inhibited by the drug. Serratia, Pseudomonas, indole-positive Proteus, and Erwinia strains were highly resistant. Inoculum size was not an important factor in determining the level of sensitivity of S. aureus to cephapirin. The antibiotic does not appear to be significantly bound to serum protein. In vitro development of resistance to the drug was demonstrated with two isolates of S. aureus.