Emergence of resistance to beta-lactam and aminoglycoside antibiotics during moxalactam therapy of Pseudomonas aeruginosa infections

Resistance of Pseudomonas aeruginosa to new beta-lactamase-resistant beta-lactams

An isogenic set of mutants of Pseudomonas aeruginosa, altered in permeability or permeability plus constitutive production of beta-lactamase, was examined for susceptibility to newer beta-lactam antibiotics. Kinetic data on the chromosomal beta-lactamase and susceptibility studies for the test beta-lactams indicate that permeability was the major mechanism of resistance to the poorly hydrolyzed and nonhydrolyzed antibiotics, e.g., carbenicillin, moxalactam, and cefsulodin. An exception was cefotaxime, with a low Km and a low Vmax, which had reduced efficacy in the permeability mutant and was further affected by the constitutive beta-lactamase. In this case, since the Vmax was low, a nonhydrolytic barrier may provide the additional reduction in susceptibility.

Antimicrobial agent susceptibility patterns of bacteria in hospitals from 1971 to 1982

Bacterial susceptibility to 16 commonly used antibiotics was analyzed for a 12-year period (from 1971 to 1982, inclusive). Susceptibilities of 5,828,243 strains isolated from a mean of 242 hospitals nationwide and of 194,575 strains isolated at the Massachusetts General Hospital, Boston, Mass., and the Bronx Lebanon Hospital Center, New York, N.Y., were compared. Strains of Escherichia coli, Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa showed virtually the same susceptibilities to antibiotics throughout the 12-year period, whereas Streptococcus faecalis and Staphylococcus epidermidis showed significant increases in resistance to most antibiotics. The close similarity between antibiotic susceptibilities shown at both the 242 hospitals and the 2 individual hospitals suggests that this analysis accurately reflects trends of bacterial resistance to antibiotics in U.S. hospitals. Since most of the species analyzed produce serious disease and high mortality, their susceptibility to antibiotics is relevant both to physicians treating infectious diseases and to epidemiologists.

Cephalosporin antibiotic agents

The cephalosporins are a group of antibiotic agents that have been available now for 20 years. Three classes, or generations, of cephalosporins are recognized. The newer third-generation drugs have wider spectra of antibacterial activity; because of this attribute and their ability to achieve high bactericidal titres in CSF these newer compounds constitute an advance in antibiotic therapy by providing safe and effective treatment for Gram-negative bacillary meningitis. The earlier cephalosporins provide cheap, useful and convenient prophylaxis for vascular and orthopaedic operations near the inguinal area. Comparative trials with other broad-spectrum agents need to be performed before the true place of the third-generation agents in anti-infective therapy and prophylaxis is finally determined.

Surgical antimicrobial prophylaxis: principles and guidelines

Antimicrobial prophylaxis for surgical procedures is an area that is recognized as being subject to individual clinical variations. This review gives practitioners some basic principles of rational prophylaxis as defined by the medical literature. In addition, this literature is evaluated and condensed to provide clinicians with guidelines for particular procedures: obstetric, gynecologic, gastric, biliary, colonic, urologic, cardiac, thoracic, vascular, orthopedic and head and neck. Each section concludes with recommendations for the clinically most accepted prophylactic regimens. Antibiotics discussed include not only the older agents, but where good information exists, the newer cephalosporins. The suggested regimens consider efficacy, safety and cost as determinants in rational prescribing. Although research into even shorter, and perhaps more cost-effective, regimens continues, this compilation lists state-of-the-art recommendations.

Failure of the disk diffusion test to detect tobramycin resistance in kanamycin-resistant Escherichia coli strains

Approximately 40% of Escherichia coli strains isolated from clinical specimens at the Institute of Medical Microbiology of the University of Zurich were resistant to kanamycin but susceptible to tobramycin in disk diffusion tests. Whereas 50% of these strains required a MIC of 7 micrograms of tobramycin per ml to inhibit 1 x 10(5) to 4 x 10(5) cells, 20% of them required a concentration of 8 micrograms or more of the drug per ml. The disk diffusion test, therefore, failed to detect resistance to tobramycin in kanamycin-resistant E. coli strains. Cell extracts from two representative strains phosphorylated and inactivated kanamycin, amikacin, gentamicin, tobramycin, 3',4'-dideoxykanamycin B (dibekacin), butirosin, lividomycin,and ribostamycin, which together constituted a novel spectrum of substrates for the enzymatic activity.

In vitro activity of HR 810, a new cephalosporin

The in vitro susceptibility of 409 clinical isolates to HR 810, a new cephalosporin, was evaluated and compared with their susceptibility to aztreonam, cefazolin, ceftazidime, imipenem, moxalactam, piperacillin, and gentamicin. On a weight basis, the activity of HR 810 against gram-negative bacilli was equivalent or superior to that of the other beta-lactam agents except imipenem.

Changing patterns of resistance to new beta-lactam antibiotics. In vitro efficacy of cefoperazone against bacterial pathogens

No evidence for significant increase in resistance to cefoperazone was detected in susceptibility test surveillance programs or in the literature through 1983, but rare endemic resistance to cefoperazone and some other newer beta-lactams was found. Medical centers contemplating the use of a third-generation drug for cost-containment should be aware of the susceptibility of isolates in their hospitals, and the drug's ability to withstand beta-lactamase hydrolysis by local pathogens. The possible dangers of inducible cephalosporins in certain Enterobacteriaceae and strains of Pseudomonas aeruginosa are discussed in the light of the physical and chemical characteristics of the newer antimicrobial agents. Criteria for judging the values of investigational beta-lactams are presented. These focus on the interaction of antimicrobial agents with host defense mechanisms and circulating blood elements.

Empiric therapy with moxalactam alone in patients with bacteremia

Moxalactam was administered (20 mg/kg intravenously every 8 hours) as single-drug empiric antimicrobial therapy to 63 patients with bacteremia who were neither neutropenic nor immunosuppressed. Six patients (10%) had microorganisms that were susceptible to moxalactam and resistant to all other antimicrobial agents tested; two patients (3%) had microorganisms that were resistant to moxalactam and other agents tested. Of these 63 patients, 47 (75%) were cured with moxalactam therapy. Nine patients (14%) had breakthrough bacteremia while receiving other antimicrobial therapy and were cured subsequently with moxalactam therapy alone. The two major risk factors for failure of moxalactam therapy were polymicrobial bacteremia and an extrahepatic intra-abdominal source of infection; these two conditions frequently coexisted. Six of nine patients with polymicrobial bacteremia died. Superinfection (one pseudomonal, five enterococcal) was responsible for 6 of the 16 treatment failures. Enterococcal superinfection occurred exclusively among patients who had received relatively prolonged therapy with moxalactam for extrahepatic intra-abdominal infection, especially intraabdominal abscess. These five patients died, and postmortem examination showed that enterococcal superinfection was the major cause of death in all. Mild, reversible adverse reactions associated with use of moxalactam occurred in 14 of the 63 patients (22%). None had clinically overt bleeding. The use of moxalactam alone seems to be safe and effective and a cost-effective alternative empiric antimicrobial therapy for most patients with bacteremia who are not immunosuppressed or neutropenic and who are not at high risk of having Pseudomonas or polymicrobial bacteremia.

In vitro synergistic activities of aminoglycosides and new beta-lactams against multiresistant Pseudomonas aeruginosa

The in vitro interactions between amikacin, netilmicin, tobramycin, gentamicin, and various antipseudomonal beta-lactams were studied by the agar dilution checkerboard technique against 30 Pseudomonas aeruginosa strains resistant to all tested antibiotics. Amikacin produced more frequent synergy both at the total and clinically applicable level. Among the beta-lactams, clinically relevant synergistic interactions were obtained in the following order: ceftazidime and ceftriaxone greater than moxalactam greater than aztreonam greater than cefotaxime greater than azlocillin greater than cefoperazone greater than cefsulodin greater than carbenicillin.

In vitro comparison of Pseudomonas aeruginosa isolates with various susceptibilities to aminoglycosides and ten beta-lactam antibiotics

Susceptibilities of 98 clinical isolates of Pseudomonas aeruginosa, including 33 strains with known mechanisms of amikacin resistance, were tested by the agar dilution method against 10 beta-lactam drugs. Ceftazidime, imipenem, and cefsulodin had the greatest activity, regardless of the aminoglycoside susceptibilities. The strains which were highly resistant to amikacin appeared to be less susceptible to some beta-lactam drugs, especially if their resistance was related to amikacin-inactivating enzymes; statistical significance, however, was observed for aztreonam only.

The use of moxalactam in the treatment of serious infections due to multi-resistant organisms

Moxalactam was evaluated as the sole therapy of 45 episodes of infection in 41 patients due primarily to bacteria resistant to older antibiotics. Infections included bacteremias, pulmonary, skin and soft tissue infections, osteomyelitis, and meningitis. Clinical and bacteriological cure was achieved in 69% of infections. Cure was achieved with moxalactam in patients infected with cefazolin-resistant, carbenicillin-resistant, chloramphenicol and gentamicin-resistant organisms. Although adverse reactions were generally mild, diarrhea developed in five patients, a major increase in prothrombin time and bleeding in three patients and a disulfiram reaction in two patients.

Comparison of moxalactam and gentamicin in the treatment of complicated urinary tract infections

Moxalactam and gentamicin were compared in a prospective, randomized study of 49 hospitalized patients with complicated urinary tract infections. Patients received parenteral moxalactam, 250 mg every 12 h, or gentamicin, 1 mg/kg every 8 h. The average duration of therapy (moxalactam, 7.5 days; gentamicin, 8.6 days) was similar for both groups. Sixty-two percent of patients treated with moxalactam and 57% of those receiving gentamicin were cured of their infection, as defined by a negative culture after therapy. No side effects required discontinuation of either drug. An enterococcus caused two superinfections and three reinfections in patients treated with moxalactam. Moxalactam resistance developed in Pseudomonas aeruginosa isolates from three patients treated with moxalactam. Moreover, two of these isolates showed decreased susceptibility to gentamicin, tobramycin, and amikacin. An additional 10 patients with gentamicin-resistant but moxalactam-susceptible isolates were treated with moxalactam. Forty percent of these patients were cured of their infections. Moxalactam appears to be a safe, effective drug for complicated urinary tract infections caused by susceptible bacteria, including those resistant to gentamicin. However, patients receiving moxalactam should be carefully monitored to detect enterococcal superinfections or development of resistance to moxalactam in isolates of P. aeruginosa.

Moxalactam (latamoxef). A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Moxalactam (latamoxef) is a new synthetic oxa-beta-lactam antibiotic administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria, is particularly active against Enterobacteriaceae and is resistant to hydrolysis by beta-lactamases. Moxalactam has moderate activity against Pseudomonas aeruginosa, but on the basis of present evidence can not be recommended as sole antibiotic treatment of known or suspected pseudomonal infections. Like the related compounds, the cephalosporins, moxalactam is effective in the treatment of complicated urinary tract infections and lower respiratory tract infections caused by Gram-negative bacilli. As moxalactam is also active against Bacteroides fragilis it has considerable potential in the treatment of intra-abdominal infections in patients with normal immunological mechanisms, as well as in immunocompromised patients, when used alone or in combination with other antibiotics. Likewise, its ready penetration into the diseased central nervous system, its high level of activity against Gram-negative bacilli, and the lack of necessity to monitor drug plasma concentrations, indicate its potential value in the treatment of neonatal Gram-negative bacillary meningitis. Further clinical experience is needed before it can be determined whether moxalactam alone can be used in the treatment of conditions for which the aminoglycosides are drugs of choice, but if established as equally effective, moxalactam has the advantage of being devoid of nephrotoxicity. Bleeding is a potentially serious problem, however, particularly in the elderly, malnourished and in the presence of renal impairment.

In vitro activity of HR 810, a new broad-spectrum cephalosporin

HR 810, 3-[(2,3-cyclopenteno-1-pyridinium)methyl]-7-[2-syn-methoximino-2-(2-aminothiazole-4-yl)-acetamido] ceph-3-em-4-carboxylate, is a new semisynthetic cephalosporin derivative. The in vitro activity of HR 810 was compared with that of cefotaxime, ceftazidime, piperacillin and gentamicin using 368 strains of gram-negative and gram-positive bacteria. HR 810 was highly active against Enterobacteriaceae, being the most active of the cephalosporins against Enterobacter, Serratia and Citrobacter spp.; the MICs ranged from much less than 0.06 to 8 mg/l. The activity of HR 810 against Pseudomonas aeruginosa and Acinetobacter spp. was almost as good as that of ceftazidime. The new compound was superior to the other cephalosporins against Staphylococcus aureus and inhibited all Streptococcus faecalis strains at a concentration of 16 mg/l.

Influence of clindamycin on derepression of beta-lactamases in Enterobacter spp. and Pseudomonas aeruginosa

Previous studies in this and other laboratories have shown that derepression of beta-lactamases in strains of Enterobacter and Pseudomonas spp. is responsible for the rapid development of resistance to a variety of beta-lactam antibiotics. The purpose of the current study was to evaluate the effects of clindamycin on derepression of beta-lactamases in these two genera. In tests with four strains of each genus, clindamycin diminished derepression in one isolate of each genus and completely prevented derepression in a second Enterobacter isolate (strain 55). Additional tests with strain 55 revealed that other inhibitors of macromolecular synthesis did not completely prevent derepression of beta-lactamase when tested at concentrations that did not inhibit replication. However, clindamycin did not affect synthesis of beta-lactamase that was constitutively produced in a mutant of this strain (55M). It also did not inhibit derepression of beta-galactosidase in either strain 55 or 55M. Clindamycin did not diminish the bactericidal effects of beta-lactam antibiotics against Enterobacter or Pseudomonas spp. However, it enhanced the bactericidal activity of cefamandole against strain 55. These in vitro effects of clindamycin on strain 55 that were related to prevention of derepression of beta-lactamase were confirmed in vivo with an animal model of infection. These results indicate that in some strains, clindamycin can specifically prevent derepression of beta-lactamases without inhibiting growth. Such a selective effect may provide a new approach for the enhancement of the antibacterial activity of certain beta-lactam antibiotics.

Characterization of beta-lactamase induction in Enterobacter cloacae

The induction of beta-lactamase was studied in a strain of Enterobacter cloacae. A wide variety of beta-lactam compounds were found to induce beta-lactamase in this organism, and the degree of induction was directly related to the stability of the inducer to degradation by the enzyme. The kinetics of the induction process were consistent with a system normally under repressor control, suggesting a direct interaction of the beta-lactam compound with a repressor protein in the E. cloacae cells. Although these characteristics are common to many inducible systems in gram-negative organisms, the induction of beta-lactamase in this strain was not subject to catabolite repression with glucose and remained unaffected by exogenous cyclic AMP in the culture medium. This suggests that the organization and function of the beta-lactamase regulatory genes in E. cloacae are unlike those of other inducible gene systems, such as those composing the well-characterized lactose operon in Escherichia coli.