Antimicrobial combinations in the therapy of infections due to gram-negative bacilli

The antimicrobial efficacy of copper, cobalt, zinc and silver nanoparticles: alone and in combination

With the advent of nanotechnology, there has been an extensive interest in the antimicrobial potential of metals. The rapid and widespread development of antimicrobial-resistant and multidrug-resistant bacteria has prompted recent research into developing novel or alternative antimicrobial agents. In this study, the antimicrobial efficacy of metallic copper, cobalt, silver and zinc nanoparticles was assessed againstEscherichia coli(NCTC 10538),S. aureus(ATCC 6538) along with three clinical isolates ofStaphylococcus epidermidis(A37, A57 and A91) and three clinical isolates ofE. coli(Strains 1, 2 and 3) recovered from bone marrow transplant patients and patients with cystitis respectively. Antimicrobial sensitivity assays, including agar diffusion and broth macro-dilution to determine minimum inhibitory and bactericidal concentrations (MIC/MBC) and time-kill/synergy assays, were used to assess the antimicrobial efficacy of the agents. The panel of test microorganisms, including antibiotic-resistant strains, demonstrated a broad range of sensitivity to the metals investigated. MICs of the type culture strains were in the range of 0.625-5.0 mg ml^-1. While copper and cobalt exhibited no difference in sensitivity between Gram-positive and Gram-negative microorganisms, silver and zinc showed strain specificity. A significant decrease (p< 0.001) in the bacterial density ofE. coliandS. aureuswas demonstrated by silver, copper and zinc in as little as two hours. Furthermore, combining metal nanoparticles reduced the time required to achieve a complete kill.

Optimizing empirical antimicrobial therapy for infection due to gram-negative pathogens in the intensive care unit: utility of a combination antibiogram

OBJECTIVE

To determine whether the use of dual antimicrobial therapy based on the results of a combination antibiotic susceptibility report (antibiogram) increases the likelihood of selecting adequate empirical coverage in critically ill patients with infection due to potentially resistant gram-negative pathogens.

DESIGN

Retrospective data analysis.

SETTING

Urban academic medical center.

METHODS

An analysis of culture results and susceptibility data from intensive care unit patients determined by the clinical microbiology laboratory was performed. The proportion of 5 common gram-negative pathogens susceptible to monotherapy with 1 of 3 antipseudomonal antibiotics (piperacillin-tazobactam, ceftazidime, or imipenem) was compared with the proportion susceptible to each of these 3 "backbone" agents plus 1 of 4 additional antimicrobial agents used in combination.

RESULTS

More than 5,000 clinical isolates were examined. When all isolates recovered during the entire study period were included, the addition of any of the second antibiotics studied to each of the 3 backbone agents significantly increased the likelihood of covering the causative pathogen (P < .01 for each). The benefit of combination therapy was variable when results for each of the 5 organisms were examined individually. When temporal trends in susceptibility were examined, the decrease in the proportion of organisms susceptible to monotherapy was statistically significant for both imipenem and ceftazidime (P < .01).

CONCLUSIONS

Reporting antibiotic susceptibility data in the form of a combination antibiogram may be useful to clinicians who are considering empirical antimicrobial therapy in the intensive care unit.

In vitro antimicrobial effects of various combinations of penicillin and clindamycin against four strains of Streptococcus pyogenes

Previous studies using mouse models of Streptococcus pyogenes necrotizing fasciitis demonstrated that clindamycin had greater efficacy than penicillin. Frequently both agents are used concurrently in the treatment of severe S. pyogenes infections. This study investigated interactions between penicillin and clindamycin. E-test and broth microdilution assays suggested additivity or indifference, while timed-killing assays demonstrated concentration-dependent variable effects. Timed-kill studies utilizing clinical concentrations suggest that there is no antagonism with the combination of drugs but that the combination does not have a bactericidal advantage over either penicillin or clindamycin alone.

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

Sultamicillin is the tosylate salt of the double ester of sulbactam plus ampicillin. Sulbactam is a semisynthetic beta-lactamase inhibitor which, in combination with ampicillin, extends the antibacterial activity of the latter to include some beta-lactamase-producing strains of bacteria that would otherwise be resistant. The combination of sulbactam plus ampicillin for parenteral use has previously been shown to be clinically and bacteriologically effective in a variety of infections. The chemical linkage of sulbactam and ampicillin has now produced an orally effective compound, sultamicillin, with antibacterial activity and clinical efficacy which are similar to those of the parenteral formulation. Sultamicillin has been shown to be clinically effective in non-comparative trials in patients with infections of the respiratory tract, ears, nose and throat, urinary tract, skin and soft tissues, as well as in obstetric and gynaecological infections, and in the treatment of gonorrhoea. In a small number of controlled trials, sultamicillin has shown comparable clinical efficacy to phenoxymethyl penicillin (penicillin V) and to amoxycillin (alone and in combination with clavulanic acid) in the treatment of paediatric streptococcal pharyngitis and acute otitis media, respectively; to cefaclor in the treatment of acute otitis media in adults; and to bacampicillin, cloxacillin and flucloxacillin plus ampicillin in skin and soft tissue infections in adults, children and adult diabetic patients, respectively. Sultamicillin was superior in efficacy to bacampicillin in the treatment of chronic respiratory infections, to cefaclor in the treatment of acute otitis media in adults, and to cefadroxil in the treatment of patients with complicated urinary tract infections. However, in single-dose treatment of uncomplicated gonorrhoea, sultamicillin (1500mg plus probenecid 1g) was inferior to a 2g intramuscular dose of spectinomycin. While in several studies the incidence of diarrhoea associated with sultamicillin was greater than that with comparative antibacterials, sultamicillin-associated diarrhoea was generally mild and transitory, although occasionally severe enough to necessitate discontinuation of treatment. Further studies in larger groups of patients are needed to clarify the therapeutic efficacy and safety of sultamicillin in comparison with other antibacterial regimens, and to determine the optimum single dosage for the treatment of gonorrhoea. Nonetheless, sultamicillin appears to provide a similar pharmacodynamic and pharmacokinetic profile to that of parenteral sulbactam plus ampicillin and, as such, will extend the therapeutic efficacy of ampicillin, with the further advantage of allowing treatment of patients with an oral formulation, thus avoiding the potentially adverse clinical and financial effects of prolonged parenteral therapy.

Aminoglycosides plus beta-lactams against gram-negative organisms. Evaluation of in vitro synergy and chemical interactions

Combination antibiotic therapy has been used mainly to broaden the antibacterial spectrum and prevent the development of resistance. Antibiotic combinations proven to be synergistic in vitro are associated with a significantly better in vivo response, particularly in the compromised host in whom traditional treatment combines an antipseudomonal penicillin plus an aminoglycoside. Several investigators have examined combining new agents, such as the third-generation cephalosporins (cefotaxime, ceftriaxone, ceftizoxime, ceftazidime, cefoperazone, and moxalactam), aztreonam, or the ureidopenicillins, with amikacin. When compared with combinations of an older cephalosporin, carbenicillin or ticarcillin, plus gentamicin or tobramycin, these newer combinations produce higher rates of clinically meaningful synergy and rapid enhancement of in vitro bactericidal activity against the difficult-to-treat Enterobacteriaceae (i.e., Serratia, Citrobacter, Enterobacter, Providencia, and indole-positive Proteus species). This effect, without any evidence of antagonism, has been reported even for strains moderately or completely resistant to the former antibiotics. Unsatisfactory and unpredictable synergistic interactions against both resistant and susceptible strains of Pseudomonas aeruginosa--the most difficult nosocomial pathogen to treat--have been noted with combinations of tobramycin or gentamicin plus cefotaxime, moxalactam, or cefoperazone. Conversely, the use of amikacin plus various beta-lactams against multi-resistant strains is more frequently synergistic. Agents have been observed to exhibit such synergy in the following order of activity, from most to least synergistic: ceftazidime, ceftriaxone, moxalactam, aztreonam, cefotaxime, azlocillin, cefoperazone, cefsulodin, and carbenicillin. The combination of amikacin plus imipenem or ciprofloxacin against strains of P. aeruginosa resistant to the former and moderately resistant to the latter was recently reported to have a low probability of synergy; the combination of two of the newer beta-lactams had mostly an unpredictable or even antagonistic result. In vitro studies have also demonstrated that high concentrations of the antipseudomonal penicillins can inactivate the aminoglycosides. Among the latter compounds, the inactivation order, from most to least inactivated, was as follows: tobramycin, gentamicin, netilmicin, and amikacin. To date, the reports of aminoglycoside inactivation by the newer cephalosporins have been rather contradictory; only moxalactam has been shown produce a significant decrease in activity.

Have the new beta-lactams rendered the aminoglycosides obsolete for the treatment of serious nosocomial infections?

Hospital-acquired infections are often due to multi-resistant gram-negative bacilli. When treating these infections, the physician must use potent antibiotics that have broad spectrums of activity. Aminoglycosidic aminocyclitols and the newer beta-lactam antibiotics are particularly valuable in the management of hospital-acquired infections. This article discusses the role of both classes of antibiotics in this setting.

Selected overview of nongynecologic surgical intra-abdominal infections. Prophylaxis and therapy

True prophylaxis of intra-abdominal nongynecologic infections is limited to elective, nonemergency surgery and is best shown in three clean-contaminated surgical procedures. All of these have an infection rate of approximately 10 to 20 percent and include all colon resection surgery, most gastric surgery, and about one third of the cholecystectomies for chronic calculous cholecystitis. Each of these three surgical procedures has a somewhat different pattern of bacterial pathogens. The most useful comparative studies of early preoperative therapy have been performed in cases of suspected appendicitis (50 percent of which usually show perforation or gangrene at the time of surgery) and penetrating abdominal wounds (80 percent of which usually enter some part of the bowel and theoretically soil the peritoneum). These procedures are usually classified as contaminated, with a 20 to 30 percent infection rate, or dirty, with a more than 30 percent infection rate, depending upon several factors. Comparative investigations of intraoperative and postoperative antibiotic therapy of established intra-abdominal infections are more difficult to obtain because of the heterogeneity of the sites, organisms, and medical and surgical therapy. The initial pathogens causing secondary peritonitis and hepatic, perirectal, diverticular, and most other types of intraperitoneal abscesses are mixed coliforms and anaerobes, with emphasis on the anaerobes. Retroperitoneal abscesses, pancreatic abscesses, and biliary tract infections are predominantly caused by coliforms. The organisms responsible for these early infections are usually community-acquired rather than more antibiotic-resistant hospital-acquired bacteria. Considering the availability of a large number of effective broad-spectrum antibacterial agents and therapeutic combinations, it has become increasingly difficult to assess the rightful place of any new prospective antimicrobial regimen unless it has quite unique characteristics. Most empiric therapy in established intra-abdominal infection studies have compared gentamicin and clindamycin, the most popular regimen in the United States over the past 15 years, with a cephalosporin, broad-spectrum penicillin, or aminoglycoside, either alone or together with clindamycin or metronidazole. Results have usually been considered similar in most studies, although in some studies, agents with limited Bacteroides fragilis activity, such as cefamandole or cefaperazone, have been considered inferior. Most new prophylactic regimens have been compared with the first-generation cephalosporins and, again, similar results have been obtained between the groups with two exceptions. Cepha