Comparison of the activities of penicillin G and new beta-lactam antibiotics against clinical isolates of Bacteroides species

Synthesis, Pharmacological and Toxicological Screening of Penicillin-Triazole Conjugates (PNTCs)

A series of hybrid antimicrobial compounds were prepared by carboxylic acid protection of 6-aminopenicillanic acid using benzyl alcohol and thionyl chloride succeeded by azide displacement using trifluoromethanesulfonyl azide in dichloromethane. The azide thus formed was reacted with substituted alkynes to furnish benzyl-protected penicillin-triazole conjugates. Benzyl deprotection of the conjugates resulted in furnishing PNTCs under water methanol mixture using Pd/C as a catalyst. The PNTCs (7a-j) formed were screened for in vitro antibacterial potency against pathogenic strains of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes and antifungal potency against Candida albicans, Aspergillus niger, and Aspergillus clavatus. Further antimicrobial evaluation revealed compounds 7c, 7d, 7e, 7g, and 7i to be the most compounds of the series with minimum inhibitory concentration value for antibacterial in the range 0.5-50 μg/mL and for antifungal in the range 9-300 μg/mL. Toxicological analysis documented for compounds 7c, 7d, 7e, 7g, and 7i revealed compound 7i to be the most promising member of the series with 1000 and 500 mg/kg LD₅₀, and no-observed-adverse-effect level to facilitate future clinical studies of the same.

Evolution of anaerobe susceptibility testing in the United States

Susceptibility testing of anaerobes has been described for approximately 45 years, some 15 years fewer than descriptions for aerobic organisms. During that time period, >16 methods, >16 media, and a host of other variables have been described in the United States literature, culminating in the most recent standards published by the National Committee for Clinical Laboratory Standards (NCCLS) in 2001. These new guidelines include a single agar dilution reference method as well as an alternative minimal inhibitory concentration method validated by extensive multilaboratory collaborative trials. In addition, the Food and Drug Administration-approved E-test has proved valuable as a user-friendly alternative to NCCLS methods. Highlights of the "evolution" of various methods, their variations and their failures, factors that affected the development of the current standards, and the rationale for susceptibility testing of anaerobes are discussed herein.

Ureidopenicillins and beta-lactam/beta-lactamase inhibitor combinations

Although research and development of new penicillins have declined, penicillins continue to be essential antibiotics for the treatment and prophylaxis of infectious diseases. The most recent additions are the ureidopenicillins and beta-lactam/beta-lactamase inhibitor combinations. This article reviews the spectrum of activity, toxicity, pharmacokinetics, and clinical uses of the ureidopenicillins, and the beta-lactam/beta-lactamase inhibitor combination agents.

Major methodology-dependent discordant susceptibility results for Bacteroides fragilis group isolates but not other anaerobes

Two standardized susceptibility test methods, a broth microdilution (BMD) and agar dilution (AD) method were performed on a total of 441 clinical isolates of anaerobes with ceftizoxime, cefotaxime, ceftriaxone, cefoxitin, piperacillin, and metronidazole. Against the 339 strains of the Bacteroides fragilis group BMD minimum inhibitory concentration (MIC) values were lower than those from AD testing for all the beta-lactams. Overall for the B. fragilis group and the beta-lactams, the mode MIC values were two- to 64-fold lower, and the MIC50 values two- to eightfold lower. Resistance rates were 11%-28% higher overall with AD results and were higher especially for non-B. fragilis species. For non-Bacteroides anaerobes no major discrepancies were noted for Prevotella species, Peptostreptococcus species, and Viellonella parvula. With Clostridium species and Eubacterium species, some differences were noted with ceftizoxime because of differences in cut-off points. These data illustrate the magnitude of differences in results produced by the two methods using essentially the same test medium for the B. fragilis group. Fortunately, such major discordant results were not widely noted with other groups of anaerobes.

A five-year multicenter study of the susceptibility of the Bacteroides fragilis group isolates to cephalosporins, cephamins, penicillins, clindamycin, and metronidazole in the United States

Over 2800 clinical strains of the Bacteroides fragilis group were collected during a 5-year period from ten geographically separate sites and tested for their susceptibility to various antimicrobial agents using a broth microdilution method. Among the cephalosporins, ceftizoxime was the most active (13% resistance) and importantly exhibited relatively equal activity against both B. fragilis species and non-B. fragilis species. Cefotaxime exhibited similar activity with an overall resistance rate of 18%. Both ceftriaxone and cefoperazone were appreciably less active cephalosporins especially against non-B. fragilis species. With regard to cephamycins, cefoxitin (MIC90, 32 micrograms/ml) was more active than cefotetan (MIC90, > or = 256 micrograms/ml) and cefmetazole (MIC90, 64 micrograms/ml). Non-B. fragilis species were highly resistant to cefotetan and cefmetazole. Imipenem was highly active against all strains with the exception of four strains of B. fragilis. Ampicillin-sulbactam, amoxicillin-clavulanate, piperacillin-tazobactam, and cefoperazone-sulbactam were all highly active with resistance rates < 2%. No resistance was detected to metronidazole, whereas 14% of isolates were resistant to clindamycin. When compared with other studies, these findings underscore the wide variability in susceptibility patterns reported nationwide and the need to continue monitoring these patterns to aid in choosing the most active compounds for therapy.

Cross-resistance to beta-lactam-beta-lactamase inhibitor combinations and clindamycin among cefoxitin-resistant and cefoxitin-susceptible strains of the Bacteroides fragilis group

In the present study the cross-resistance rates of cefoxitin-resistant and cefoxitin-susceptible strains of the Bacteroides fragilis group were compared with regard to beta-lactam-beta-lactamase inhibitor combinations and clindamycin. Piperacillin-tazobactam was the most active agent tested with an overall resistance rate of 0.2% and no resistance among cefoxitin-resistant strains. Ticarcillin-clavulanate was the least active combination with an overall resistance rate of 1.6% but a resistance rate of 13.1% among cefoxitin-resistant strains. For ampicillin-sulbactam, amoxicillin-clavulanate, and clindamycin resistance, rates of cefoxitin-resistant versus cefoxitin-susceptible strains were 9.1% and 0.4%, 8.3% and 0.9%, and 28% and 12.9%, respectively.

Use of cephalosporins for prophylaxis and therapy of polymicrobial infection in mice

Cefoxitin, cefotetan, and cefmetazole were compared in 10-day therapy of intra-abdominal and subcutaneous infections caused by three organisms: Bacteroides fragilis and Bacteroides thetaiotaomicron combined with either Escherichia coli or Staphylococcus aureus. Intra-abdominal infection was caused by B. fragilis plus B. thetaiotaomicron plus E. coli. Therapy was initiated immediately before inoculation or was delayed for 8 h. Mortality was 14 of 30 (47%) for saline-treated mice, and all survivors developed abscesses. Immediate therapy reduced mortality and the percentage of mice with abscesses (in survivors), respectively, to 17 and 20% with cefoxitin, 0 and 13% with cefotetan, and 0 and 17% with cefmetazole, and the numbers of all bacteria were reduced by all the cephalosporins. Delayed therapy reduced mortality and abscess formation, respectively, to 20 and 8% of mice with cefoxitin, 10 and 93% with cefotetan, and 7 and 96% with cefmetazole. B. thetaiotaomicron survived in all abscesses treated with cefotetan and cefmetazole. Subcutaneous abscesses were caused by each organism alone or in combinations of one aerobe (S. aureus or E. coli) and one or two Bacteroides species. Early therapy reduced the numbers of all bacteria independent of their in vitro susceptibility. All agents reduced the number of each Bacteroides species with either E. coli or S. aureus. However, when therapy was delayed, cefotetan and cefmetazole were less effective than cefoxitin against B. thetaiotaomicron. Cefotetan was the most active agent against E. coli, and cefmetazole was the most effective against S. aureus. These data illustrate the efficacy of all tested cephalosporins in the prophylaxis of polymicrobial infections.

Current antimicrobial therapy of anaerobic infections

The treatment of many anaerobic infections involves antimicrobial therapy, appropriate surgical drainage of abscesses, and debridement of devitalized tissue. Most anaerobic infections are polymicrobial and require treatment with agents active against an array of aerobic and anaerobic bacteria. Bacterial resistance, especially to penicillins and tetracyclines, but also to newer agents of other classes, continues to increase. As a result, treatment with more than one drug is often required. Combination therapy is often necessary in serious infection, and is indicated for empiric treatment before receiving culture results. In the past combination therapy has been the mainstay of antimicrobial therapy, but more recent studies suggest that monotherapy for anaerobic infections may dominate the future. Selection of an agent requires consideration of the site of infection and the most likely etiologic agents. In vitro susceptibility is important, but it is not the only determinant of antimicrobial effectiveness. The pharmacology of the drug--absorption, distribution, concentrations in body fluids and tissues, excretion and metabolism--also plays an important role. The nature and severity of the underlying illness are important factors in selecting empiric therapy. Although it is a clinical judgement, in patients considered to have mild to moderate infections, several factors in selecting antimicrobial agents may be considered, including cost, whereas in patients judged to have severe or life-threatening infections, the most potent agents should be chosen as initial therapy, regardless of cost. Finally, the toxicities of the agent must also be considered.

Susceptibility testing of anaerobic bacteria: myth, magic, or method?

The demand for susceptibility testing of anaerobes has increased, yet consensus as to procedure and interpretation in this area has not been achieved. While routine testing of anaerobic isolates is not needed, certain isolates in specific clinical settings should be tested. Also, laboratories may monitor their local antibiograms by doing periodic surveillance batch testing. The National Committee for Clinical Laboratory Standards has published a protocol of methods approved for susceptibility testing of anaerobic bacteria. Both agar and broth microdilution are included; however, the broth disk elution method is no longer approved by the National Committee for Clinical Laboratory Standards because of method-related interpretive errors. A number of newer methods are undergoing evaluation and seem promising. Clinicians and microbiologists reviewing susceptibility reports should be aware of sources of variability in the test results. Variables in susceptibility testing of anaerobes include the media and methods used, organisms chosen for testing, breakpoints chosen for interpretation, antibiotic, and determination of endpoint. Clustering of MICs around the breakpoint may lead to significant variability in test results. Adherence of testing laboratories to approved methods and careful descriptions of the method and the breakpoints used for interpretation would facilitate interlaboratory comparisons and allow problems of emerging resistance to be noted. A variety of resistance mechanisms occurs in anaerobic bacteria, including the production of beta-lactamase and other drug-inactivating enzymes, alteration of target proteins, and inability of the drug to penetrate the bacterial wall. Antimicrobial resistance patterns in the United States and abroad are described.

Effect of beta-lactamase inhibitors on the activities of various beta-lactam agents against anaerobic bacteria

The in vitro activities of several new beta-lactam-beta-lactamase inhibitor combinations (piperacillin plus tazobactam, ceftizoxime and cefonicid with sulbactam and clavulanic acid, and ampicillin plus 8 micrograms of sulbactam per ml) were tested with anaerobic bacteria and compared with known beta-lactam-beta-lactamase inhibitor combinations and other potent antianaerobe agents. All the combinations tested (except for the cefonicid-inhibitor combinations) were active against almost all strains of the Bacteroides fragilis group. This report indicates that beta-lactamase inhibitors may improve the activity of beta-lactam agents with marginal activity against the B. fragilis group.

Growth of Bacteroides fragilis group in agar and broth media

The rate of bacterial growth of four Bacteroides fragilis group organisms was determined in agar and broth media. Exponential bacterial growth occurred in agar media within 4 to 8 h, while such growth was delayed in broth media and occurred within 12-24 h after inoculation. This phenomenon may explain why antimicrobials which manifest an 'inoculum effect' may show increased resistance to antimicrobials when tested in agar media.

Intra-abdominal abscess in children: a 13-year experience

The microbiology of intra-abdominal abscess in children is similar to that of adults--a mixture of aerobes and anaerobes. In abscess specimens taken from 36 children, predominant pathogens were Bacteroides fragilis group species, Peptostreptococcus species, and Escherichia coli.

Short prereduced anaerobically sterilized (PRAS) biochemical scheme for identification of clinical isolates of bile-resistant Bacteroides species

The rapid identification of isolates of bile-resistant Bacteroides species has clinical and therapeutic relevance because of differences in their patterns of susceptibility and virulence. Five hundred twenty-one strains of bile-resistant Bacteroides species that were previously identified by conventional biochemical methods were reexamined to determine the minimum essential parameters necessary for correct identification. Rapid tests for bile resistance, indole production, and catalase were combined with a novel scheme for biochemical determination of saccharolytic activity on arabinose, trehalose, rhamnose, and/or xylan that included the postincubation addition of bromthymol blue for visual pH determination. Organisms were inoculated into prereduced anaerobically sterilized (PRAS) carbohydrates directly from plates, and identification was complete within 24 h of obtaining a pure culture. Ninety-three percent of bile-resistant Bacteroides species from routine clinical specimens were identified correctly by this scheme; a small number of other indole-positive strains, B. splanchnicus, B. eggerthii, and B. stercoris, were misidentified as B. uniformis.

Differences in the in vitro inhibitory and bactericidal activity of ceftizoxime, cefoxitin, cefotetan, and penicillin G against Bacteroides fragilis group isolates. Comparison of time-kill kinetic studies with MIC values

Nineteen strains of the Bacteroides fragilis group were used to determine the bactericidal activity of ceftizoxime, cefoxitin, cefotetan, and penicillin G with time-kill kinetics studies. Each antimicrobial agent was tested at subinhibitory (1/2 X MIC), inhibitory (1 X MIC), and suprainhibitory (4 X MIC) concentrations. Penicillin G exhibited virtually no sustained bactericidal activity at any of the antimicrobial concentrations tested. At subinhibitory concentrations, ceftizoxime was considerably more bactericidal than cefoxitin or cefotetan: At 12 hr, ceftizoxime killed 89% of the inoculum, whereas cefoxitin and cefotetan killed 35% and 33% of the inoculum, respectively. At inhibitory concentrations, ceftizoxime was again more bactericidal than cefoxitin and cefotetan: At 12 hr, ceftizoxime killed 90% of the inoculum, whereas cefoxitin and cefotetan killed 78% and 73%, respectively. At suprainhibitory concentrations, all three antimicrobial agents showed comparable bactericidal activity at 12 and 24 hr. Ceftizoxime and cefoxitin had somewhat lower killing rates overall against test strains with high MICs (greater than or equal to 32) versus low MICs (less than or equal to 16). However, at subinhibitory concentrations, ceftizoxime killed the B. fragilis group strains with high or low MIC values more effectively than cefotetan killed strains with low MICs. At the highest antibiotic concentrations tested (4 X MIC), only slight differences were seen in the bactericidal activity of the three compounds, regardless of MICs.

Pathophysiologic basis for the use of third-generation cephalosporins

After 10 years of use, the third-generation cephalosporins remain excellent antibiotics. They have superior activity against selected streptococcal species compared with other cephalosporins, and superior activity against Haemophilus, Neisseria, Branhamella, and other less common oral gram-negative aerobic species. Despite a very broad spectrum of activity, the third-generation cephalosporins, like all other cephalosporins, have only poor activity against enterococci, Listeria, Corynebacterium jekeium, and methicillin-resistant staphylococci. Over the past 10 years, the activity of the third-generation cephalosporins against Escherichia coli, Klebsiella, Proteus, Providencia, Serratia, Haemophilus, and Neisseria has remained excellent. Equally as important, though perhaps less well recognized, is the activity of some of these agents against mouth anaerobic species and the anaerobic Bacteroides and Clostridium spp. of the pelvic area. At present, there are two main threats to the continued use of the third-generation cephalosporins. These are the increasing number of infections due to Enterobacter spp., which constitutively produce large amounts of a beta-lactamase that hydrolyzes cephalosporins, and the recent appearance of Klebsiella spp. in many parts of the world that possess new plasmid-mediated beta-lactamases that destroy cefotaxime, ceftazidime, and related third-generation parenteral cephalosporins. Correlation of pharmacologic properties with in vitro activity provides information as to reasonable dosage regimens for the third-generation cephalosporins. For most serious infections cefotaxime, ceftizoxime, and ceftazidime should be given three times a day provided that the patient has relatively normal renal function. Ceftriaxone can be administered once daily in less severe infections. The use of lower doses or less frequent dosing with cefotaxime, ceftizoxime, or ceftazidime is recommended in aged patients whose renal function is impaired. The unique interaction of cefotaxime with its active metabolite, desacetylcefotaxime, allows cefotaxime to be administered less frequently than three times a day in selected anaerobic infections. Correlation of the antibacterial activity and pharmacology of cephalosporins will help us to tailor their use more appropriately, so that the third-generation cephalosporins will remain useful antimicrobial agents for a further decade.

Efficacy of sulbactam in an in vitro model of mixed aerobic/anaerobic infections

Bacterial interactions in mixed infections may interfere with antimicrobial therapy. The in-vitro efficacy of ampicillin alone, combination sulbactam/ampicillin, and metronidazole was studied. Strains of Bacteroides fragilis, Escherichia coli, and Enterococcus faecalis, alone and in association, were tested by means of a broth dilution method. Minimal bactericidal concentrations (MBC) of ampicillin for B. fragilis 74 in association with E. coli 68 were up to 16-fold higher than for B. fragilis 74 alone (256 compared to 16 mg/l), but only 2-fold higher for sulbactam (5 mg/l)/ampicillin (0.5 and 0.25 g/l). Association of B. fragilis 45 and E. faecalis 186 increased ampicillin MBC of E. faecalis 186 from 2 to 16 mg/l, but the combination sulbactam/ampicillin restored activity of ampicillin. In association with E. faecalis, metronidazole MBCs of B. fragilis increased up to 64-fold. Strains of E. faecalis and E. coli were able to destroy 10 mg/l metronidazole within 8 to 20 h. The present experiments demonstrated effectiveness of sulbactam/ampicillin to inhibit beta-lactamases of associated pathogens. Destruction of metronidazole by E. faecalis lends additional support to the use of the combination in aerobic/anaerobic infections including E. faecalis.

Comparison of in vitro antibiograms of Bacteroides fragilis group isolates: differences in resistance rates in two institutions because of differences in susceptibility testing methodology

With 120 clinical isolates of the Bacteroides fragilis group, a comparison of rates of resistance to selected antimicrobial agents by using two susceptibility tests was performed in two medical institutions. The broth microdilution method produced MICs significantly lower than those determined by the agar dilution method. With ceftizoxime and cefoxitin, 88 and 18%, respectively, of the MICs were greater than or equal to 2 twofold dilutions apart. These differences in MIC results produced major interpretive discrepancies for ceftizoxime and cefoxitin, whereas no significant differences in resistance rates were noted for clindamycin and metronidazole.

Antibiotics in the treatment of wounds

In selecting an antibiotic, considerations include the sensitivity of the pathogen, drug distribution to the site of infection, bacteriostatic or bactericidal action under the existing tissue conditions, safety, and cost. Ideally, in vitro susceptibility of the pathogen can be obtained. In addition, cytologic evaluation, including a Gram stain, may be helpful in directing the initial course of therapy. Antibiotic sensitivity does not by itself guarantee satisfactory results. The terms "sensitive" and "resistant" are relative terms based on achievable blood levels of antimicrobial agents. The term "sensitive" implies that the level necessary to inhibit bacterial growth is achieved when an adequate dose is given at appropriate intervals. The distribution of the drug and, in turn, the level achieved at the site of infection depends on a number of factors, including molecular size, protein binding, and lipid solubility. Because, in most cases, specific tissue concentrations are not known, serum concentrations are used to represent the levels in the extracellular fluid space, which is the site of most bacterial infections. The local environment can further enhance or hinder antimicrobial penetration and activity. The antibiotic concentration achieved in the blood affects the concentration at the site of infection because simple passive diffusion appears to be the method of transport for most antibiotics. The antibiotic activity after reaching the site of infection is influenced by environmental conditions. Local production of enzymes, purulent and fibrinous exudate, and pH changes can adversely affect drug action. With many of these variables being difficult to predict, knowledge of etiologic agents is the cornerstone of rational use of the antimicrobial drugs. A reasonable suspicion based on clinical signs and knowledge of likely pathogens can guide the initial choice of antimicrobial therapy. Since both aerobic and anaerobic organisms may be involved in wound infections, and because antibiotic sensitivity of many of these pathogens is unpredictable, broad-spectrum antimicrobial therapy is often warranted initially.

A multicenter international study on the activity of sulbactam/ampicillin, ampicillin, and cefoxitin against anaerobic bacteria and introduction of a new model of susceptibility testing in mixed infections

Susceptibility of anaerobic clinical isolates from the United States, Canada, and Germany to sulbactam/ampicillin (1 + 2) (SBT/AMP), ampicillin alone (AMP), and cefoxitin (CFX) was determined with a standard agar dilution test. The isolates included 192 strains of Bacteroides fragilis, 132 strains of other Bacteroides spp., and 19 strains of Clostridium spp. Against all species tested, SBT/AMP was more active than AMP or CFX. Results obtained by a new model of associative susceptibility testing indicated that susceptibility testing of single pathogens from polymicrobial infections is not necessarily reflective of the susceptibility of the pathogens at the site of infection. The results suggest that sulbactam is effective in associations of pathogens producing beta-lactamases of Richmond-Sykes types II-V and beta-lactamases of anaerobic bacteria.

Annual incidence, epidemiology, and comparative in vitro susceptibilities to cefoxitin, cefotetan, cefmetazole, and ceftizoxime of recent community-acquired isolates of the Bacteroides fragilis group

The six species of the Bacteroides fragilis group are potent pathogens and commonly have different susceptibility patterns. We determined the relative annual isolation rate of anaerobic bacteria and the susceptibility of B. fragilis group species isolated during 1987 at two community hospitals. The relative frequencies of isolation of 261 strains were as follows: B. fragilis, 61%; B. thetaiotaomicron, 17%; B. distasonis, 7%; B. vulgatus, 6%; B. ovatus, 5%; and B. uniformis, 4%. A total of 234 recent clinical isolates were tested against cefmetazole, cefotetan, cefoxitin, ceftizoxime, clindamycin, imipenem, and piperacillin by a brucella agar dilution method. Imipenem was the most active agent tested with all but three isolates (two B. vulgatus and one B. distasonis) susceptible to less than 2 micrograms/ml. Of the cephalosporins tested, cefoxitin, cefotetan, and cefmetazole were relatively equal against B. fragilis, with 93 to 98% of strains susceptible to 32 micrograms/ml. Ceftizoxime was less active, with an MIC for 90% of strains tested of 128 micrograms/ml and only 75% of isolates susceptible to 32 micrograms/ml. Against B. ovatus, B. vulgatus, B. thetaiotaomicron, and B. uniformis, cefoxitin showed a two- to threefold-superior activity compared with that of cefotetan and cefmetazole. In general, ceftizoxime was much less active, except against B. distasonis, for which 78% of isolates were susceptible to 32 micrograms/ml compared with 68% for cefoxitin, 19% for cefmetazole, and 16% for cefotetan. Clindamycin and piperacillin showed activity similar to that of cefoxitin, except piperacillin was less active versus B. vulgatus and B. distasonis. We therefore suggest that clinical laboratories determine the species of B. fragilis group isolates as well as perform susceptibility studies on the isolates. Clinicians should be aware that while B. fragilis is the most frequent isolate, 38% of isolates are from other, more resistant B. fragilis group species.

Steady-state cord and amniotic fluid ceftizoxime levels continuously surpass maternal levels

As part of our management protocol for preterm premature rupture of membranes, ceftizoxime and tocolysis were used to prolong the latent period and prevent or treat concomitant infection. Ceftizoxime was selected for this protocol based on its physiochemical properties, which favor placental transfer of the drug. Patients achieving steady-state pharmacodynamics (more than three doses of the drug) were considered eligible for study. Ceftizoxime levels were determined by reverse-phase high-pressure liquid chromatography. All levels measured after the first hour of treatment were indicative of the relative concentration of ceftizoxime in the fetal and amniotic fluid compartments when compared with the maternal compartment. Mean (+/- SEM) ceftizoxime levels were 11.96 + 2.35 micrograms/ml in maternal serum, 24.54 +/- 4.78 micrograms/ml in cord serum, and 43.45 +/- 4.97 micrograms/ml in amniotic fluid. Based on its broad antibacterial activity and its high concentration in fetal blood and amniotic fluid, ceftizoxime appears to be an ideal agent for treatment of the intrauterine environment.

Recovery of anaerobic bacteria from clinical specimens in 12 years at two military hospitals

Examination of 15,844 clinical specimens submitted over 12 years (1973 to 1985) to the anaerobic microbiology laboratories in two military hospitals demonstrated the recovery of anaerobic bacteria in 4,458 (28.1%) specimens. The specimens yielded 6,557 anaerobic isolates (1.47 isolates per specimen). Bacteroides spp. accounted for 43% of all isolates; anaerobic gram-positive cocci, 26%; Clostridium spp., 7%; and Fusobacterium spp., 4%. Bacteroides spp. predominated in abscesses, obstetrical and gynecological (OBG) infections, abdominal infections, cysts, wounds, and tumors. Members of the Bacteroides fragilis group accounted for 44% of all Bacteroides spp., and of them, B. fragilis was mostly isolated in abscesses, wounds, abdomen, and blood. Pigmented Bacteroides spp. accounted for 21% of all Bacteroides sp. isolates and were mostly isolated in sinus, eye, chest, bone, and ear infections. Bacteroides melaninogenicus accounted for 42% of this group's isolates. Bacteroides bivius accounted for 9% of Bacteroides spp., and most isolates were found in OBG infections. Anaerobic gram-positive cocci were mostly isolated in OBG infections, abscesses, and wounds. The predominant anaerobic gram-positive cocci were Peptostreptococcus magnus (18%), Peptostreptococcus asaccharolyticus (17%), Peptostreptococcus anaerobius (16%), and Peptostreptococcus prevotii (13%). Clostridium spp. were mostly isolated from wounds, abscesses, abdominal infections, and blood. The predominant strain was Clostridium perfringens (48%). Fusobacterium spp. were recovered in abscesses and abdominal and OBG infections. The predominant isolate was Fusobacterium nucleatum (47%). These data illustrate the relative frequency of the different anaerobic bacteria in a variety of infections and demonstrate the predominance of certain isolates at different sites.

Management of infection following intra-abdominal trauma

Intra-abdominal infections following abdominal trauma often involve the gastrointestinal aerobic and anaerobic bacterial flora. These organisms possess various virulence factors and exhibit potential synergy between them. The intra-abdominal infection is biphasic, with the Enterobacteriaceae as the major pathogens in the peritonitis stage, and the Bacteroides fragilis group predominant in the abscess stage. Experiments with animals and experience in human beings support the need to use single or combined antimicrobial agent therapy that is effective against both Enterobacteriaceae and the B fragilis group.

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.

Criteria for in vitro susceptibility testing of cefotetan. Correlations with clinical and bacteriologic responses

Standardized in vitro susceptibility testing criteria and quality-control guidelines for cefotetan have been well documented in the scientific literature. Cefotetan and cefoxitin differ in their in vitro spectrums of activity and cannot be used interchangeably for in vitro tests. In vitro susceptibility information failed to correlate with clinical or bacteriologic responses of treated patients when 314 anaerobic bacteria from 145 patients were evaluated. All cefotetan-resistant anaerobic bacteria were eradicated by cefotetan therapy, and 93 percent of patients with resistant strains were clinically curved. Most members of the Bacteroides distasonis-ovatus-thetaiotaomicron group of pathogens were resistant in vitro, but only one strain persisted after cefotetan therapy for a 96.6 percent cure rate. There was better correlation when 2,336 aerobic bacteria from 1,630 infected body sites were considered. Microorganisms susceptible or moderately susceptible by in vitro tests were equally responsive to therapy (95 percent of patients clinically cured and 94 percent of isolates eradicated). However, strains that were resistant by in vitro test criteria were less likely to respond clinically. Development of resistance during therapy or superinfections (1.7 percent) were not found to be clinically important problems with cefotetan chemotherapy.

A multicenter study of the in vitro antianaerobic activity of cefotetan compared with other antimicrobial agents

The in vitro antianaerobic activity of cefotetan was compared with that of chloramphenicol, clindamycin, cefoxitin, and penicillin in a multicenter study. Both agar dilution and broth microdilution testing procedures, as described by the National Committee for Clinical Laboratory Standards (NCCLS), were employed; a total of 1,377 strains were examined. Results were interpreted using the U.S. Food and Drug Administration- and NCCLS-recommended criteria. This study indicates that Bacteroides fragilis, Clostridium difficile, and most other clinically significant anaerobic bacteria are susceptible to cefotetan.

Cost-effectiveness study of cefotetan versus cefoxitin and cefotetan versus combination antibiotic regimens

The clinical efficacy, adverse effects, cost of therapy, and administration time required to treat 141 patients were compared for cefotetan versus cefoxitin (Study A) and cefotetan versus combination antibiotic therapy (Study B). No major differences were observed in clinical efficacy or adverse effects in any of the treatment groups. Cefotetan was more cost-effective than cefoxitin, even though cefoxitin was given for shorter periods. Cefotetan was also more cost-effective than a combination of ampicillin, an aminoglycoside, and clindamycin. Although the ampicillin, aminoglycoside, and metronidazole combination appeared to be the most cost-effective regimen, this combination required the longest administration time (240 percent longer than cefotetan). Cefotetan appears to be comparably efficacious and more cost-effective than other currently used antianaerobic regimens in our institution.

In vitro activity of cefotetan compared with that of other antimicrobial agents against anaerobic bacteria

The activity of cefotetan against 430 strains of anaerobic bacteria was compared with that of cefoxitin, ceftizoxime, clindamycin, metronidazole, and chloramphenicol. Percent susceptible values for the Bacteroides fragilis group were 60, 80, 29, 86, 100, and 100%, respectively. Percent susceptible values for the B. fragilis species were 91, 92, 46, 98, 100, and 100%, respectively. Non-B. fragilis-group Bacteroides species were inhibited very well (90 to 100%) by all drugs except ceftizoxime (80%). Cefotetan and metronidazole were the most active agents against Clostridium difficile. Percent susceptible values for all strains were 72, 79, 44, 82, 93, and 98%, respectively.

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.

Comparative in vitro beta-lactam activity against aerobic and anaerobic surgical isolates

The comparative in vitro activity of cefoxitin, piperacillin, cefotetan, and ceftizoxime was compared against 843 surgical microbial isolates. All compounds exhibited excellent activity against the streptococcal isolates. Antimicrobial activity was poor for Staphylococcus aureus and S. epidermidis. Cefotetan activity against the Enterobacteriaceae was comparable to ceftizoxime (greater than 95% susceptible). Resistance rates of 0, 1, 5, and 2% were observed with cefoxitin, piperacillin, cefotetan, and ceftizoxime against the anaerobic cocci and anaerobic gram-positive non-spore-forming rods. Ninety-six and ninety-nine percent of the clostridial strains were susceptible to cefotetan and piperacillin, respectively. Piperacillin, cefotetan, and ceftizoxime exhibited similar activity against Bacteroides fragilis (resistance less than 10%). Cefotetan and cefoxitin exhibited poor activity against Bacteroides distasonis, B. ovatus, and B. thetaiotaomicron. Antimicrobial activities were comparable for the four drugs against other Bacteroides and Fusobacterium species. The results demonstrate that all four compounds exhibited broad antimicrobial activity against facultative and obligate anaerobic surgical isolates from intraabdominal and soft tissue infections.

Use of new beta-lactam antibiotics for surgical infections

The availability of beta-lactam antibiotics with extended spectra of activity against organisms commonly seen in surgical infections suggests that aminoglycoside-based therapy is no longer needed for most such community-acquired infections. The primary problems with specific beta-lactams are lack of activity against Bacteroides species and variable activity against Pseudomonas aeruginosa and enterococci. The pharmacokinetic properties of the newer beta-lactams vary considerably. This variation suggests specific settings in which these properties may be taken advantage of to improve clinical outcome.

A comparison of mezlocillin versus clindamycin/gentamicin for the treatment of postcesarean endomyometritis

In a prospective, randomized study of 96 patients after cesarean section who had endomyometritis, there was a therapeutic cure in 35 of 47 (74.5%) patients who received mezlocillin, in comparison with 42 of 49 (85.7%) patients who received clindamycin and gentamicin (p = 0.17). Only wound infections in the study population were predictive for therapeutic outcome. Four of the five patients who received mezlocillin and none of the three patients who received clindamycin and gentamicin with wound infections were associated with therapeutic failures. This suggests mezlocillin may not be as effective as clindamycin and gentamicin in successfully treating wound infections. The number of vaginal examinations in patients sectioned for cephalopelvic disproportion was associated with increased febrile morbidity, suggesting that an excessive number of vaginal examinations should be avoided in the laboring patient.

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.

Comparative antimicrobial activity of aminothiazolyl methoxyimino cephalosporins against anaerobic bacteria, including 100 cefoxitin-resistant isolates

Three aminothiazolyl methoxyimino cephalosporins (ceftizoxime, ceftriaxone, and cefotaxime with and without its metabolite) were tested against 500 strains of anaerobic bacteria using the NCCLS reference agar dilution procedure. Eighty-seven percent of all strains tested were from the Bacteroides fragilis group. When tested against a collection of 100 cefoxitin-resistant isolates, ceftizoxime and the cefotaxime/desacetyl-cefotaxime combination were the most active in vitro, inhibiting 32-38% of strains. Ceftriaxone inhibited the greatest number (87%) of cefoxitin-susceptible anaerobes at less than or equal to 32 micrograms/ml. A regional variation in the activity of these drugs was confirmed when an additional 300 isolates were examined from three medical centers. Cefotaxime, ceftizoxime, and ceftriaxone were essentially equal in overall antimicrobial activity, although each drug was judged the best at one of the three locations. Cefoxitin resistance (MIC greater than or equal to 32 micrograms/ml) was consistent among the institutions at a 25% incidence for all organisms tested, and 28% cefoxitin resistance among the B. fragilis group strains. Cefoxitin resistance was not determined to be associated with a beta-lactamase mechanism, but ceftriaxone and other aminothiazolyl cephems were hydrolyzed, thus elevating their MICs. Regional variation in anaerobic organism susceptibility to cephamycins and cephalosporins in company with the variable beta-lactam resistance mechanisms seems to require periodic, epidemiologic monitoring of in vitro drug activity by appropriate methods to assure continued antimicrobial efficacy.

Ceftizoxime and cefoxitin susceptibility testing against anaerobic bacteria: comparison of results from three NCCLS methods and quality control recommendations for the reference agar dilution procedure

Ceftizoxime and cefoxitin (control) were tested against 99 anaerobic bacteria using three commonly used susceptibility testing methods. The cefoxitin MIC results with the National Committee for Clinical Laboratory Standards (NCCLS) reference agar dilution (RAD) method and the broth microdilution (BMD) method did not differ by more than one log2 dilution step. However, the ceftizoxime BMD MIC results were 2- to 4-fold lower than those produced by the RAD procedure. Broth disk elution (BDE) tests for both cephalosporins (ceftizoxime and cefoxitin) had very high rates of false-susceptible and false-resistant error when compared to the RAD MICs: the BDE tests are not recommended for either cephalosporin. Findings indicate that because of method and possible medium or technical variability, ceftizoxime MICs should be determined only by the NCCLS RAD method. Also, cefoxitin susceptibility should be assessed primarily by RAD or BMD procedures. This should minimize confusion related to ceftizoxime's spectrum and activity against anaerobic bacteria compared to similar beta-lactam drugs. Ceftizoxime quality control guidelines were established for Bacteroides fragilis (ATCC 25285): mode, 64 micrograms/ml, range 32-128 micrograms/ml. Other control strains were not reliable.

Imipenem/cilastatin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic efficacy

Imipenem is the first available semisynthetic thienamycin and is administered intravenously in combination with cilastatin, a renal dipeptidase inhibitor that increases urinary excretion of active drug. In vitro studies have demonstrated that imipenem has an extremely wide spectrum of antibacterial activity against Gram-negative and Gram-positive aerobic and anaerobic bacteria, even against many multiresistant strains of bacteria. It is very potent against species which elaborate beta-lactamases. Imipenem in combination with equal doses of cilastatin has been shown to be generally well tolerated and an effective antimicrobial for the treatment of infections of various body systems. It is likely to be most valuable as empirical treatment of mixed aerobic and anaerobic infections, bacteraemia in non-neutropenic patients and serious hospital-acquired infections.

In vitro susceptibility of the Bacteroides fragilis group in community hospitals

The antimicrobial susceptibility of clinical isolates of the Bacteroides fragilis group was determined at six community hospitals (one large, greater than 600 beds; and five smaller, 96-325 beds). Imipenem was the most active beta-lactam with 100% of isolates being sensitive at 4 micrograms/ml. The percentage of isolates inhibited at 16 micrograms/ml (and 32 micrograms/ml) for the 7-alpha-methoxy antibiotics was: cefoxitin 66 (90); moxalactam 73 (85); cefotetan 68 (72); cefmetazole 40 (61). Metronidazole, chloramphenicol, and clindamycin were active against 100%, 100%, and 89% at breakpoints of 8 micrograms/ml, 8 micrograms/ml, and 4 micrograms/ml, respectively. The activity of several beta-lactams in our report differed slightly from that reported from university teaching hospitals. There were differences at many of the breakpoints for activity of some of the beta-lactam antibiotics for isolates from the large community hospital as compared with the combined isolates from the smaller community hospitals. Interestingly, the pattern was one of more resistance at the smaller community hospitals.

Effect of medium, pH, and inoculum size on activity of ceftizoxime and Sch-34343 against anaerobic bacteria

The effect of two media, three pH values, and three inoculum densities on the activity of ceftizoxime and Sch-34343 against anaerobic bacteria was evaluated. The activities of both antimicrobial agents were affected by medium composition, especially against Bacteroides fragilis. Changes in pH and inoculum size affected only the activity of ceftizoxime against anaerobic bacteria.

Comparative activity of SCH 34343 against anaerobic bacteria

The in vitro activity of SCH 34343 was compared with that of imipenem, clindamycin, cefoxitin, and metronidazole against 78 strains of anaerobic bacteria in the presence and absence of blood. Wilkins-Chalgren agar was used. SCH 34343 and imipenem were the most active agents, inhibiting all strains at less than or equal to 8 micrograms/ml. The addition of blood had little effect on the activity of any of the agents. Seven strains were unable to grow on Wilkins-Chalgren agar. Even with the addition of blood, one strain each of Bacteroides asaccharolyticus and Bacteroides bivius and two strains of Fusobacterium were unable to grow. Sixty-eight of the strains were tested against SCH 34343 and imipenem on Brucella lysed blood agar. Minimal inhibitory concentrations tended to be somewhat higher on Brucella lysed blood agar than on Wilkins-Chalgren agar, and all strains were able to grow on Brucella lysed blood agar.