Comparative antibacterial activities of 7 alpha-methoxy cephalosporins and 7 beta-methoxyiminoacetamido cephalosporins against Bacteroides fragilis

Interactions of hydrolyzed β-lactams with the L1 metallo-β-lactamase: Crystallography supports stereoselective binding of cephem/carbapenem products

L1 is a dizinc subclass B3 metallo-β-lactamase (MBL) that hydrolyzes most β-lactam antibiotics and is a key resistance determinant in the Gram-negative pathogen Stenotrophomonas maltophilia, an important cause of nosocomial infections in immunocompromised patients. L1 is not usefully inhibited by MBL inhibitors in clinical trials, underlying the need for further studies on L1 structure and mechanism. We describe kinetic studies and crystal structures of L1 in complex with hydrolyzed β-lactams from the penam (mecillinam), cephem (cefoxitin/cefmetazole) and carbapenem (tebipenem, doripenem and panipenem) classes. Despite differences in their structures, all the β-lactam-derived products hydrogen bond to Tyr33, Ser221 and Ser225 and are stabilized by interactions with a conserved hydrophobic pocket. The carbapenem products were modelled as Δ¹-imines, with (2S)-stereochemistry. Their binding mode is determined by the presence of a 1β-methyl substituent: the Zn-bridging hydroxide either interacts with the C-6 hydroxyethyl group (1β-hydrogen-containing carbapenems), or is displaced by the C-6 carboxylate (1β-methyl-containing carbapenems). Unexpectedly, the mecillinam product is a rearranged N-formyl amide rather than penicilloic acid, with the N-formyl oxygen interacting with the Zn-bridging hydroxide. NMR studies imply mecillinam rearrangement can occur non-enzymatically in solution. Cephem-derived imine products are bound with (3R)-stereochemistry and retain their 3' leaving groups, likely representing stable endpoints, rather than intermediates, in MBL-catalyzed hydrolysis. Our structures show preferential complex formation by carbapenem- and cephem-derived species protonated on the equivalent (β) faces, and so identify interactions that stabilize diverse hydrolyzed antibiotics. These results may be exploited in developing antibiotics, and β-lactamase inhibitors, that form long-lasting complexes with dizinc MBLs.

Cefmetazole (CS-1170), a "new" cephamycin with a decade of clinical experience

In vitro and in vivo study results were reviewed from cefmetazole, a "new" parenteral cephamycin. Cefmetazole's spectrum of activity was comparable to that of second-generation cephalosporins, which includes clinical coverage of many Enterobacteriaceae, Staphylococcus spp., streptococci, Haemophilus spp., pathogenic Neisseria, Branhamella catarrhalis, and anaerobic bacteria. Cefmetazole was generally more potent (two- to eightfold) than cefoxitin against organisms within their spectrums and was particularly active for staphylococci (MIC90, 2.0 micrograms/ml). Methicillin-resistant S. aureus strains were more susceptible to cefmetazole alone or in combination (fosfomycin) than any other cephamycin. Cefmetazole has demonstrated excellent stability to aerobic and anaerobic organism-produced beta-lactamases. It also inhibits Type I cephalosporinases and, uniquely, some other cephalosporinases produced by the Bacteroides. This superior stability, enzyme interaction, and better penetration into bacterial cells results in a sustained bactericidal effect and a capacity for more infrequent dosing. The cefmetazole serum elimination half-life was 1.5 hr, also justifying use at greater than or equal to 8-hr intervals. Clinical trials in the United States and Japan demonstrated an acceptably high cefmetazole infection cure rate (88% to 100%), especially in direct comparative studies with cefoxitin. Cefmetazole was also proven very effective in minimizing infectious wound morbidity (prophylaxis) using 2 g single- or multidose regimens. Adverse drug reactions were usually minor; in the Japanese surveillance trial (118,318 patients) the rate was only 2.2% (8.8% in United States). Cefmetazole has been extensively and safely used in Japan since 1980.

Macrolide accumulation by Bacteroides fragilis ATCC 25285

The accumulation of macrolide antibiotics in Bacteroides fragilis ATCC 25285 was increased in the order erythromycin, josamycin, and rokitamycin, depending on hydrophobicity. The half-times of efflux were also prolonged in the same order. Furthermore, MICs of the antibiotics were correlated with the extent of hydrophobicity. These findings suggest that the macrolide antibiotics are accumulated in B. fragilis by means of their hydrophobic properties, and the efficient accumulation of the drugs may explain the susceptibility of this gram-negative bacterium to macrolides.

Cefotetan: a review of the microbiologic properties and antimicrobial spectrum

Cefotetan (formerly ICI 156834 and YM09330) is a 7-methoxy cephalosporin possessing some advantageous antimicrobial spectrum, safety, and pharmacokinetic characteristics compared with other so-called second-generation cephalosporins. The published literature was reviewed and the cefotetan quantitative susceptibility testing data from nearly 31,000 isolates was tabulated. Against 15,769 enteric bacilli, cefotetan was observed to have a potency and spectrum more closely resembling a third-generation cephalosporin and markedly superior to cefoxitin. The mean of all MIC 90s reported for the Enterobacteriaceae ranged from 0.06 to 13 micrograms/ml except for citrobacter species, E. cloacae, Enterobacter species, and C. freundii. The mean MIC 50 for all 22 recorded species was in the susceptible range. Cefotetan was very effective against B. catarrhalis, H. influenzae, and pathogenic Neisseria species. However, cefotetan and cefoxitin were not active against Pseudomonas species, Acinetobacter species, and some rarely isolated species. Cefotetan was moderately active against the staphylococci (mean MIC 50, 7.6 to 26 micrograms/ml) and streptococci (mean MIC 50, 0.9 to 6.6 micrograms/ml). The coagulase-negative staphylococcus species generally had higher cefotetan and cefoxitin minimum inhibitory concentrations compared with the S. aureus isolates. Oxacillin-resistant staphylococci were resistant to cefotetan. The enterococci, JK group diphtheroids, Corynebacterium species, and L. monocytogenes isolates were resistant. A review of 4,751 strict anaerobes showed cefotetan to have a very comparable activity and spectrum to cefoxitin. The 1,291 B. fragilis strains had a mean MIC 50 and MIC 90 of 5.4 and 23 micrograms/ml, respectively. These values were slightly superior to cefoxitin when tested in parallel. More elevated minimum inhibitory concentrations were observed for other B. fragilis group species for cefoxitin and cefotetan. The mean cefotetan MIC 90 for all other anaerobic bacteria except the Eubacterium species and Lactobacillus species predict favorable clinical efficacy. The beta-lactamase stability of cefotetan is very similar to that of other 7-methoxy cephalosporins. Cefotetan also inhibits Type Ia cephalosporinases with high enzyme affinity and is an inducer of these beta-lactamases, although cefotetan is not rapidly hydrolyzed. Synergy between cefotetan and numerous other antibiotics has been reported, but antagonism has also been occasionally observed.

National Committee for Clinical Laboratory Standards agar dilution susceptibility testing of anaerobic gram-negative bacteria

One hundred nine recent clinical isolates of anaerobic gram-negative bacteria were tested in triplicate by the National Committee for Clinical Laboratory Standards agar dilution procedure for their susceptibility to 32 antimicrobial agents. All isolates were inhibited by imipenem, but there were significant numbers of strains resistant to other beta-lactam drugs, and therefore the in vitro response to these antimicrobial agents cannot be predicted. This was particularly true for the bile-resistant or Bacteroides fragilis group. beta-Lactamase production was detected in 82% of the bacteroides with the nitrocefin test. Clavulanic acid combined with amoxicillin and ticarcillin and sulbactam combined with ampicillin resulted in synergistic activity against all beta-lactamase-positive organisms. Ceftizoxime was the most active of the cephalosporins. Two percent of the isolates were resistant to chloramphenicol and metronidazole. Clindamycin resistance was detected in 38% of the B. fragilis group, which is a marked increase from the 4% detected 10 years ago at this institution.

Activity of cefmetazole against anaerobic bacteria

The in vitro activity of cefmetazole versus that of other antimicrobial drugs was assessed against 374 clinical isolates of Bacteroides spp., Clostridium spp., and anaerobic gram-positive cocci. Compared with cefoxitin, cefmetazole showed good activity against Bacteroides fragilis, other Bacteroides species, and anaerobic cocci. It was somewhat less active than cefoxitin against Bacteroides thetaiotaomicron, B. ovatus, B. distasonis, and B. vulgatus and somewhat more active against Clostridium spp.

Cefmenoxime. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Cefmenoxime is an aminothiazolyl cephalosporin administered intravenously or intramuscularly. Like other 'third-generation' cephalosporins it is active in vitro against most common Gram-positive and Gram-negative pathogens, is a potent inhibitor of Enterobacteriaceae (including beta-lactamase-producing strains), and is resistant to hydrolysis by beta-lactamases. Cefmenoxime has a high rate of clinical efficacy in many types of infection and is at least equal in clinical and bacteriological efficacy to several other cephalosporins in urinary tract infections, respiratory tract infections, postoperative infections and gonorrhoea. Cefmenoxime, like latamoxef, cefoperazone and cefamandole, has an N-methyltetrazole side chain at the 3-position of the cephalosporin nucleus and thus possesses the potential for producing hypoprothrombinaemic bleeding and disulfiram-like reactions. However, these reactions have been reported very rarely and the antibacterial is generally well tolerated. It is likely that cefmenoxime will most closely resemble cefotaxime and ceftizoxime in therapeutic profile and usefulness.

Cephalosporins in surgery. Prophylaxis and therapy

Prophylactic antibiotics in surgery are intended to prevent morbidity and mortality, as well as to reduce the duration and cost of hospitalisation. The indications for prophylaxis, and its effectiveness, should be evaluated with these criteria in mind. The basis for antibiotic prophylaxis in surgery is either provision of an effective concentration of antibiotic in the tissue site at the time of potential contamination, or (primarily in the case of colorectal surgery) to reduce the inoculum of potentially contaminating bacteria. Cephalosporins are the antibiotics most widely used for prophylaxis in surgery, and have clearly been shown to reduce postoperative morbidity in vaginal hysterectomy, resection of head and neck cancers, vascular grafting, total joint replacement, repair of hip fractures, and high risk gastroduodenal surgery. They are probably also useful in cardiac surgery, abdominal hysterectomy, caesarean section, and colorectal surgery. For orthopaedic, cardiac, gynaecological, and gastroduodenal procedures it is important to select an antibiotic with proven clinical activity against Gram-positive organisms. For head and neck surgery, the spectrum of activity should also include oral anaerobes and Enterobacteriaceae. For biliary surgery an antibiotic effective against both Gram-positive and Gram-negative organisms may offer at least theoretical advantages, while for appendicectomy a cephamycin represents the most appropriate choice. In colorectal procedures, activity against B. fragilis is the major consideration in selecting an antibiotic for systemic prophylaxis. When intra-abdominal sepsis occurs following surgery, a potentially wide range of bacteria may be implicated, but in practice such infections are due to a small number of species, with B. fragilis most commonly implicated. The most useful cephalosporins in this setting are those active against both aerobic Gram-negative bacteria and anaerobes, especially B. fragilis. In practice, an aminoglycoside is often administered concomitantly. Importantly, prompt surgical treatment is the cornerstone of management of abdominal sepsis, and empirical antibiotic therapy should be adjusted as needed when culture and sensitivity tests become available.

Activity of cefotetan against anaerobic bacteria

The in vitro activity of cefotetan, a new cephamycin, was compared with that of cefoxitin, cefotaxime, moxalactam, and piperacillin against 368 strains of anaerobic bacteria. Cefotetan was similar to cefoxitin, moxalactam, and piperacillin in its activity against B. fragilis, B. vulgatus, Bacteroides species, anaerobic gram-positive cocci, Fusobacterium and Clostridium species. High resistance rates for cefotetan, however, were demonstrated among B. thetaiotaomicron-ovatus group and B. distasonis. Increasing inoculum concentrations had little effect on the activity of cefotetan.

Cefotetan. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Cefotetan is a new semisynthetic cephamycin antibiotic administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-negative aerobic and most clinically important Gram-positive and anaerobic bacteria, and is generally more active against Gram-negative bacteria than the 'first and second generation' agents. Cefotetan is particularly active against Enterobacteriaceae but has little activity against Pseudomonas aeruginosa. An extended plasma elimination half-life of about 3.5 hours, and relatively high achievable serum and tissue levels, enables cefotetan to be administered on a twice daily basis in the treatment of mild to severe infections. Cefotetan has shown good clinical efficacy in intra-abdominal, obstetric and gynaecological infections, postoperative wound infections, and infections in immunocompromised patients - all of which are often complicated due to their polymicrobial nature or by the presence of anaerobic pathogens. A satisfactory clinical response is achieved in over 90% of paediatric patients with acute otorhinolaryngological infections, whereas in the treatment of chronic disease, as with other agents, the efficacy is dramatically reduced. Like other cephalosporins, cefotetan is effective in treating patients with complicated urinary tract infections and lower respiratory tract infections. Its efficacy in urinary tract infections is at least as good as cefoxitin, although in this and some other clinical areas its activity relative to that of other cephamycins and cephalosporins remains to be assessed. Thus, with its convenient twice daily dosage schedule, cefotetan would appear to be a useful addition to a rapidly expanding group of antibacterial agents.

In vitro activity of cefbuperazone against Bacteroides spp

The activity of cefbuperazone was tested in vitro against 287 clinical isolates of Bacteroides spp. Cefbuperazone showed good activity against B. fragilis, B. vulgatus, and other Bacteroides species, comparable to that of cefoxitin. It was relatively ineffective against B. distasonis and the B. thetaiotaomicron-ovatus group and was not active against cefoxitin-resistant Bacteroides spp.

In vitro activity of cefbuperazone compared with that of other new beta-lactam agents against anaerobic gram-negative bacilli and contribution of beta-lactamase to resistance

Cefbuperazone was compared with other currently available and investigational antibiotics against 278 clinical isolates of anaerobic gram-negative bacilli by an agar dilution method. Cefbuperazone and cefotetan were equally active against Bacteroides fragilis, with 8% of the organisms tested found to be resistant to 32 micrograms of either drug per ml. Cefoperazone, cefotaxime, ceftriaxone, and cefmetazole were less active against these strains; cefoxitin, moxalactam, piperacillin, clindamycin, and metronidazole were more active. None of the agents were consistently active against any of the other anaerobic gram-negative bacilli except imipenem, for which the minimum concentration required to inhibit 90% of all strains tested was 4 micrograms/ml. A 10,000-fold increase in inoculum size caused an increase in the MIC of ceftriaxone, cefotaxime, and cefoperazone but not of cefbuperazone, cefotetan, or cefoxitin. Investigation of the mechanism of resistance to cephalosporin-like agents demonstrated a correlation between the level of resistance and beta-lactamase activity. Cefbuperazone, cefotetan, and cefoxitin were not hydrolyzed, had lower MICs, and were less affected by changes in inoculum size than were cefotaxime, ceftriaxone, and cefoperazone.

Ceftizoxime. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Ceftizoxime is a 'third generation' cephalosporin administered intravenously or intramuscularly. Like other third generation cephalosporins it has a wide spectrum of in vitro activity against Gram-positive and Gram-negative bacteria, is particularly active against Enterobacteriaceae (including beta-lactamase-positive strains), and is resistant to hydrolysis by beta-lactamases. However, the third generation cephalosporins are less active than earlier cephalosporins against staphylococci and so could not be considered the drugs of choice. Like many currently available third generation cephalosporins, ceftizoxime has limited activity against Pseudomonas aeruginosa, and thus cannot be recommended as sole treatment of known or suspected non-urinary tract pseudomonal infections. Similarly, although favourable clinical results have been obtained in patients treated with ceftizoxime for infections caused by mixed aerobic/anaerobic organisms (such as intra-abdominal, and obstetric and gynaecological infections), the relatively low in vitro activity of ceftizoxime (in common with most other third generation cephalosporins) against Bacteroides fragilis and enterococci may restrict its usage in situations where these organisms are the suspected or proven pathogens. Ceftizoxime appears to be similar in efficacy to several other cephalosporins in lower respiratory tract infections in elderly and/or debilitated patients, and in chronic and/or complicated urinary tract infections, 2 clinical situations in which third generation cephalosporins may have a major role. Ceftizoxime is also effective clinically and bacteriologically in skin, soft tissue, bone and joint infections, septicaemia/bacteraemia, meningitis and neonatal infections. However, a few large, well designed clinical comparisons of efficacy with aminoglycosides are needed before ceftizoxime can be recommended as an alternative in patients in whom potential aminoglycoside toxicity is a concern. Single intramuscular doses of ceftizoxime appear similar in efficacy to aqueous procaine penicillin G in gonorrhoeae due to nonpenicillinase-producing Neisseria gonorrhoea, and ceftizoxime is also highly effective against penicillinase-producing strains. Although only a few infections have been treated to date, ceftizoxime may be useful in the treatment of gonorrhoea in places where penicillinase-producing strains are common. Thus, ceftizoxime appears to be an effective addition to the growing number of third generation cephalosporins. However, further studies are needed to confirm its relative efficacy compared with other new cephalosporins, in particular cefotaxime.(ABSTRACT TRUNCATED AT 400 WORDS)

The cephalosporin antibiotic agents--III. Third-generation cephalosporins

The third-“generation” cephalosporin antibiotics (Table 1) represent a class of agents with an expanded gram-negative spectrum of activity beyond that of the first- and second-“generation” cephalosporins. Greater stability to beta-lactamases produced by gram-negative organisms confers to these agents a greater bactericidal action against the Enterobacteriaceae. Large bacterial inocula (105/ml) in vitro significantly increase the minimum inhibitory and bactericidal concentrations (MIC and MBC) explaining treatment failures with these agents in infections associated with large numbers of organisms. The pharmacokinetic features of some of the agents allow prolongation of dosing intervals, and enhanced tissue penetration amplifies their clinical utility in infections distant from the bloodstream (eg, meningitis).