Activity of ticarcillin/clavulanate and piperacillin/tazobactam (YTR 830; CL-298,741) against clinical isolates and against mutants derepressed for class I beta-lactamase

Piperacillin/tazobactam (YTR 830; CL-298,741) was tested against fresh and stock clinical isolates of Gram-negative bacilli, as well as against Gram-negative bacilli that had stably derepressed Class I beta-lactamases or that were hyperproductive of non-Class I beta-lactamases. Of 63 clinical isolates of the Enterobacteriaceae with ticarcillin (plus clavulanate) minimum inhibitory concentrations (MICs) of greater than or equal to 128 micrograms/ml, 16 had piperacillin/tazobactam MICs of less than or equal to 16/2 micrograms/ml. Of 48 clinical isolates of Pseudomonas spp. with ticarcillin (plus clavulanate) MICs of greater than or equal to 128 micrograms/ml, 35 had piperacillin/tazobactam MICs of less than or equal to 64/8 micrograms/ml. Tazobactam generally reduced piperacillin MICs by two- to greater than or equal to eightfold against stably derepressed mutants for Class I beta-lactamases.

In vitro testing of antimicrobial agents

Antimicrobial susceptibility tests provide information that may be helpful in the initial selection of antimicrobials to be used in therapy, may prompt a change in an existing regimen to one including a more active antimicrobial agent, or may allow substitution of one antimicrobial agent with another equally effective but less expensive antimicrobial agent. The clinical value of bactericidal testing is less clear-cut due, at least in part, to methodologic variations and biological and technical variables. Standardization of methods provides both intralaboratory and interlaboratory reproducibility, as well as interpretability of results.

Incidence, distribution, and outcome of episodes of infection in 100 orthotopic liver transplantations

Of 83 patients who underwent 100 orthotopic liver transplantations, 53 had a single transplant procedure and at least 6 months of follow-up. In this main study group of 53 patients, major infections developed in 28 (53%) (a mean of 1.8 major episodes per infected patient). Of 51 major infections, 27 were bacterial, 19 were viral, 3 were protozoan, and 2 were fungal. Of the 27 bacterial infections, 22 (81%) occurred in the first 2 months after transplantation. Of the 40 bacterial isolates in the 27 bacterial infections, gram-positive aerobic bacteria were isolated in 26 (65%), anaerobic bacteria in 8 (20%), and aerobic gram-negative bacteria in 6 (15%). Only 1 of 16 bacteremic episodes was due to a gram-negative aerobic bacterium. Cytomegalovirus (CMV) infection occurred in 30 of the 53 patients (57%) and was symptomatic and invasive in 18. CMV infection was diagnosed a mean of 26 days after transplantation. Infections due to Pneumocystis carinii occurred later (2 to 3 months after transplantation). Death from infection occurred in 4 of the 53 patients (8%). In the group of 16 patients with two or more liver transplantations, fungal infection occurred in 2 and CMV infection in 13. In all 16 patients who underwent more than one liver transplantation, a major infection developed. The observations made in the main study group were consistent with findings in 13 patients with one liver transplantation but less than 6 months of follow-up. Infection is a major complication after liver transplantation, generally occurring in the first 2 months. Our observations suggest that the use of selective bowel decontamination may be associated with a relatively lower incidence of gram-negative aerobic bacterial infections.

Comparative activity of newer antibiotics against gram-negative bacilli

The in vitro activities of cefoperazone, cefotaxime, ceftriaxone, ceftazidime, azlocillin, mezlocillin, piperacillin, ticarcillin/clavulanate, aztreonam, imipenem, and ciprofloxacin were concurrently determined against over 1,000 isolates of gram-negative bacilli from clinical specimens of patients at the Cleveland Clinic. Cephalosporins, penicillins, and aztreonam were active against species of Enterobacteriaceae other than Citrobacter freundii, Enterobacter aerogenes, and Enterobacter cloacae. Ceftazidime was the most active cephalosporin against Pseudomonas aeruginosa. Against the Enterobacteriaceae, the rank order of activity of penicillins was ticarcillin/clavulanate greater than piperacillin greater than mezlocillin greater than azlocillin. Against P. aeruginosa, the rank order of activity of penicillins was piperacillin greater than ticarcillin/clavulanate greater than azlocillin greater than mezlocillin. Aztreonam was less active v P. aeruginosa than ceftazidime, cefoperazone, or piperacillin. The most active antimicrobials against all isolates tested were imipenem and ciprofloxacin.

Role of beta-lactamase and different testing conditions in oxacillin-borderline-susceptible staphylococci

A group of staphylococcal isolates for which oxacillin MICs were intermediate (1 to 4 micrograms/ml) were studied to establish the role of beta-lactamase in this phenomenon. MICs and MBCs of oxacillin and penicillin with and without clavulanic acid or sulbactam (4 or 16 micrograms/ml, respectively) were determined for 11 Staphylococcus aureus and 2 coagulase-negative Staphylococcus isolates for which oxacillin MICs were 1 to 4 micrograms/ml. The susceptibility studies were done with incubation at 35 and 30 degrees C, and the MICs were read at 24 and 48 h. Of the 13 isolates, 4 became resistant when longer incubation or 30 degrees C incubation was used, and the MICs for 9 remained in the intermediate range. Only three of these strains were susceptible to penicillin, and beta-lactamase was not detected. For 6 of 10 beta-lactamase-positive strains, there was a greater-than-twofold-dilution reduction in oxacillin MICs with the addition of clavulanic acid or sulbactam. Of the four strains that became resistant with incubation at the lower temperature, a clavulanic acid effect was observed in three but only at 35 degrees C. The oxacillin MIC for one of the beta-lactamase-negative strains was also reduced with clavulanic acid; however, this strain was inhibited by 1 microgram of clavulanic acid per ml alone. Bactericidal activity was observed with two or four times the oxacillin MIC in eight strains tested at both temperatures, and the combination with clavulanic acid was bactericidal at higher than four times the MIC in five of the strains at 30 degrees C. Our results suggest that oxacillin intermediate MICs for staphylococcal isolates are due not only to beta-lactamase hyperproduction but also some other unidentified factor. The reduction in oxacillin MIC observed when clavulanic acid was added to one strain was probably due to the intrinsic inhibitory activity of clavulanic acid.

Antibacterial activities of cefpodoxime, cefixime, and ceftriaxone

Cefpodoxime, cefixime, and ceftriaxone inhibited Branhamella catarrhalis at less than or equal to 1 microgram/ml, beta-hemolytic streptococci at less than or equal to 0.25 microgram/ml, Neisseria meningitidis at less than or equal to 0.06 microgram/ml, and Haemophilus influenzae (other than beta-lactamase-negative, ampicillin-resistant isolates) at less than or equal to 0.12 microgram/ml. The MICs for 50% of isolates of the family Enterobacteriaceae other than Citrobacter freundii, Enterobacter aerogenes, and Enterobacter cloacae were less than or equal to 1 microgram/ml for all three cephalosporins. The MICs of each cephalosporin for 90% of staphylococci, enterococci, and Pseudomonas aeruginosa isolates were greater than 16 micrograms/ml. Inoculum effects were noted with cefpodoxime and cefixime with beta-lactamase-positive H. influenzae.

Detection of bacteria in the presence of antibiotics by using specific monoclonal antibodies to neutralize the antibiotics

Inactivation of penicillin and gentamicin in cultures was achieved by using monoclonal antibodies against these antibiotics. A viridans group streptococcus (penicillin MIC, less than or equal to 0.06 micrograms/ml) and Escherichia coli ATCC 35218 (gentamicin MIC, less than or equal to 1 microgram/ml) were able to grow in broth containing 0.25 micrograms of penicillin per ml and 4 micrograms of gentamicin per ml, respectively, when the specific antibodies were added. This procedure may be useful to increase the yield of bacteria from body fluid specimens that contain antibiotics.

Cilofungin (LY121019), an antifungal agent with specific activity against Candida albicans and Candida tropicalis

Cilofungin (LY121019) is an antifungal agent that interferes with beta-glucan synthesis in the cells walls of fungi. The activity of this agent against 256 clinical isolates of yeasts was determined. It was found to be very active in vitro against Candida albicans (MIC for 90% of isolates [MIC90], less than or equal to 0.31 microgram/ml; minimal fungicidal concentration for 90% of isolates [MFC90], less than or equal to 0.31 micrograms/ml) and C. tropicalis (MIC90, less than or equal to 0.31 microgram/ml; MFC90, less than or equal to 0.31 microgram/ml) and moderately active against Torulopsis glabrata (MIC90 and MFC90, less than or equal to 20 micrograms/ml). All C. parapsilosis, Cryptococcus, and Saccharomyces cerevisiae strains were resistant. The activity of cilofungin was affected by medium and inoculum size. Antibiotic medium no. 3 was used as the standard medium. Isolates of C. albicans and C. tropicalis demonstrated a paradoxical effect in Sabouraud dextrose broth and yeast nitrogen base broth in that growth was partially inhibited at MICs equivalent to those in antibiotic medium no. 3, but growth continued, in many instances, throughout all concentrations tested. There was decreased activity of cilofungin with inocula greater than 10(5) CFU/ml. The temperature and duration of incubation did not affect its activity.

Multicenter in vitro evaluation of lomefloxacin (NY-198, SC-47111), including tests against nearly 7,000 bacterial isolates and preliminary recommendations for susceptibility testing

Lomefloxacin (NY-198 or SC-47111) is a difluoro-quinolone derivative having a C-methyl at the 3-position of the piperazine ring, thus minimizing its metabolic alteration in vivo. In our research, its antimicrobial activity was most similar to that of difloxacin, enoxacin, fleroxacin, and norfloxacin but usually less than that of ciprofloxacin and ofloxacin against most species. Lomefloxacin shared cross-resistance with other 4-quinolones but remained very active against ceftazidime-resistant organisms, including stably derepressed beta-lactamase producing Gram-negative bacilli. Lower pH increased the lomefloxacin MICs. MBCs were usually identical to the measured MIC, and the lomefloxacin MICs were not significantly increased by high inoculum concentrations. The Enterobacteriaceae were found to have a very low rate of spontaneous mutation to lomefloxacin resistance (10(-8)-10(-9). In vitro tests by 5-micrograms and 10-micrograms lomefloxacin disks and dilution methods were correlated, and the 10-micrograms disk was recommended for clinical trials using a less than or equal to 4 micrograms/ml susceptible breakpoint. The quality assurance guidelines for dilution tests were determined by a multilaboratory study.

A new bowel preparation for elective colon and rectal surgery. A prospective, randomized clinical trial

A two-day cathartic/enema preparation with oral administration of erythromycin and neomycin was compared with an orthograde lavage preparation with oral administration of metronidazole and neomycin in a prospective randomized trial in 300 and 293 eligible patients, respectively, who were undergoing elective colon and rectal surgery. Patients were assessed for infections at six weeks after discharge from the hospital. The major infection rate was less than 1% and the minor infection rate was less than 4%. The overall infection rate was 4.2%. The type of bowel preparation used, the type of operation, and the addition of systemic antibiotic therapy did not affect infection rates significantly. We conclude that this one-day lavage technique, as described, is a safe, effective, economical, and preferred method of colonic preparation for elective colon and rectal surgery.

Effective use of the clinical microbiology laboratory

The clinician's expectations of the clinical microbiology laboratory, while valid, have not always been fulfilled. Major limitations in the accurate identification of an aetiological agent are imposed by cost considerations and poor communication between clinician and laboratory personnel. Other difficulties arise in the entire process of making use of a clinical microbiology laboratory, ranging from specimen collection to interpretation of results. These problems can be partially overcome by the use of guidelines for specimen collection which are designed to provide a sufficient amount of material and number of specimens for complete examination. Additional assistance to the clinician may be rendered by the current trends in clinical microbiology practice to limit the processing of inappropriate specimens and to develop rapid, economical procedures for the detection of pathogenic microorganisms. The clinician should not routinely request antibiotic susceptibility testing but rather base the decision to test on specimen source, type of organism isolated, whether the organisms was isolated in pure or mixed culture, and how predictable the susceptibility of the organism is to the drug of choice.

Accuracy of microdilution and the AutoMicrobic System in detection of beta-lactam resistance in gram-negative bacterial mutants with derepressed beta-lactamase

Microdilution and the AutoMicrobic System (AMS) were compared with macrodilution for accuracy in detecting beta-lactam resistance in 16 isogenic pairs of gram-negative wild-type bacterial strains and mutant strains with derepressed class I beta-lactamase; an additional 12 gram-negative derepressed mutants were also tested. Of a total of 352 organism-beta-lactam combinations resulting in 840 determinations of minimum inhibitory concentration, the overall rates of very major discrepancy were 3% between macrodilution and microdilution and 2% between macrodilution and AMS. The corresponding rates of very major discrepancies with the derepressed mutants were both 2.7%. All but three of the wild-type strains were susceptible to all beta-lactam drugs tested but cefoxitin, while nearly 90% of derepressed mutants were resistant to these antibiotics. When careful attention was given to inoculum size and incubation time, microdilution and the AMS yielded results comparable to those obtained by macrodilution.

Selective bowel decontamination to decrease gram-negative aerobic bacterial and Candida colonization and prevent infection after orthotopic liver transplantation

Gram-negative bacterial and fungal infections are a major cause of morbidity and mortality following liver transplantation. We therefore used selective bowel decontamination (SBD) to eliminate the endogenous source of gram-negative aerobic bacteria and Candida pathogens in an attempt to reduce the high incidence of infection related to these organisms. Thirty consecutive patients undergoing liver transplantation were treated with SBD starting 3 days prior to donor search and continuing for 21 days postliver transplantation. Selective bowel decontamination consisted of administering nonabsorbable antibiotics (Polymixin E, gentamicin, Nystatin) and a low bacterial diet. Surveillance cultures of the throat and rectum were obtained to monitor efficacy of selective bowel decontamination. In addition, in the posttransplant period, tracheal, wound, blood, and bile cultures were obtained to screen for gram-negative bacterial and Candida colonization and infection. Our baseline surveillance culture revealed that 29/30 (97%) of recipients were colonized with gram-negative aerobic bacteria and 16/30 (53%) with Candida. Three days after selective bowel decontamination was started, 26/30 (87%) were free of gram-negative bacteria, and 100% were free of Candida colonization of the gastrointestinal tract. There was a similar reduction in the oropharyngeal gram-negative aerobic bacteria and Candida colonization. In the first 30 days following liver transplantation, gram-negative infections were not diagnosed in any of our patients. Following discontinuation of SBD, recolonization of the gastrointestinal tract with gram-negative aerobic bacteria and Candida occurred within 5 days in 26/28 (90%) and 11/28 (35%), respectively. Our study suggests that prophylactive administration of nonabsorbable antibiotics will markedly reduce gram-negative aerobic bacterial and Candida colonization and appears to reduce the high incidence of infection related to these organisms in the early posttransplant period.

Characterization of resistance phenotype and cephalosporin activity in oxacillin-resistant Staphylococcus aureus

Forty isolates of methicillin-resistant Staphylococcus aureus were tested versus oxacillin at 30 and 35 degrees C with and without 2% NaCl supplementation of Mueller-Hinton broth and classified as having resistance that was low (MIC, less than or equal to 16 micrograms/ml) or high (MIC, greater than or equal to 32 micrograms/ml) and temperature or NaCl dependent. Only three isolates had low-grade resistance at both 30 and 35 degrees C; for two isolates the MICs at 35 degrees C were greater than or equal to 4 X the MICs at 30 degrees C. NaCl usually increased the MICs two- to fourfold. Efficiency of plating studies were performed on strains selected for their level of oxacillin resistance and according to temperature-related difference in MICs. Most strains appeared to represent the heterogeneous resistance phenotype. Cefamandole MICs were little affected by temperature but increased with NaCl. With three exceptions, cefamandole MCBs were less than or equal to 4 X MICs. For only six isolates were cefuroxime MICs less than or equal to 16 micrograms/ml. Four strains that were susceptible to both cefuroxime and cefamandole were selected for time-killing curve studies at inocula of 10(7) CFU/ml. At 8 X MIC, cefuroxime failed to reduce the concentration of any strain by greater than or equal to 3 X log10 CFU/ml. Killing of greater than or equal to 3 X log10 CFU/ml was achieved by cefamandole at 4X and 8 X MIC in one strain, at 8 X MIC only in two strains, and by neither 4 X nor 8 X MIC in one strain. Within therapeutically attainable blood levels, cefuroxime is essentially inactive and cefamandole is variably bactericidal against oxacillin-resistant s. aureus.

In vitro activities of LY163892, cefaclor, and cefuroxime

The in vitro activity of LY163892, a synthetic oral cephalosporin, was compared with those of cefaclor and cefuroxime against 1,193 clinical isolates. MIC ranges and MICs for 50 and 90% of isolates of the three cephalosporins were comparable. The activities of LY163892 and cefaclor were, however, highly inoculum dependent against beta-lactamase-positive Haemophilus influenzae and Staphylococcus aureus; that of cefuroxime was not. LY163892 and cefuroxime appeared stable in microdilution trays stored at 5 and -20 degrees C for 5 weeks, in contrast to cefaclor which remained stable for more than a week only at -5 degrees C.

Comparison of conventional and revised isolator blood culture tubes

A paired clinical study compared bacterial and fungal recovery from 4,553 blood cultures processed by the conventional Isolator (Du Pont Co.) and a revised Isolator consisting of a single-stoppered, round-bottom tube containing the same ingredients as the conventional tube except for an inert fluorochemical. Excluding contaminants, there were 425 positive blood cultures with 450 isolates representing 208 patients. There were no statistically significant differences between systems in the number of positive cultures or patients with positive cultures for each organism group studied, nor were there any statistically significant differences between systems in the time required for detection of positive cultures.

The microbiological diagnosis of infective endocarditis

Variables affecting the isolation of microorganisms causing endocarditis include the volume of blood cultured, the number of blood cultures obtained, prior antimicrobial therapy, the type of microorganism involved, and blood culture technique. Culture-negative infective endocarditis is most frequently associated with prior antimicrobial therapy and nonbacterial agents, such as fungi, chlamydiae, and rickettsiae. For the diagnosis of bacterial endocarditis, culture of two to three separately collected blood samples of at least 10 ml, and preferably 20 ml, each generally suffices; however, in cases who have recently received antibiotics it may be necessary to culture an additional two to three blood samples or to consider use of beta-lactamase, antimicrobial adsorbent resins, or lysis-concentration, the last of which is also the most effective method for recovering mycobacteria and fungi from blood.

Relationship between cefamandole and cefuroxime activity against oxacillin-resistant Staphylococcus epidermidis and oxacillin resistance phenotype

The activity of cefamandole and cefuroxime against oxacillin-resistant staphylococcus epidermidis was studied in vitro to determine whether there was any relationship between oxacillin resistance phenotypes and cephalosporin activity. Oxacillin resistance phenotypes were determined by efficiency-of-plating studies on Mueller-Hinton agar containing oxacillin, with and without NaCl, and incubated at 30 and 35 degrees C. On the basis of MIC and MBC determinations, cefamandole was more active than cefuroxime against oxacillin-resistant S. epidermidis. Although temperature had minimal effect on the activity of either cefamandole or cefuroxime, NaCl significantly decreased the activity of cefuroxime but not of cefamandole. Neither cephalosporin consistently produced greater than or equal to 99.9% bactericidal activity within 24 h in timed killing-curve studies. No consistent relationship was observed between cefamandole or cefuroxime activity and oxacillin resistance phenotype.

Comparison of methods for processing dialysate in suspected continuous ambulatory peritoneal dialysis-associated peritonitis

Three methods of processing dialysate from patients on continuous ambulatory peritoneal dialysis and with suspected peritonitis were compared: (a) direct inoculation of 10 ml of dialysate into an Isolator tube, (b) direct inoculation of 5 ml of dialysate into each of two Bactec blood culture bottles (NR 6A and 7A), and (c) centrifugation of 50 ml upon receipt in the laboratory and culture of the sediment. A diagnosis of peritonitis was made in 33 of 52 suspected episodes. Pathogens were recovered by Isolator in 26 of the 33 specimens, by Bactec in 21, by centrifugation in 25, and by any method in 27. Time to detection of positivity was the same for Isolator and Bactec in 20 of 21 cases and for Isolator and centrifugation in 21 of 24 cases. Identification was available 24-48 hr earlier with Isolator than with centrifugation in three of 24 cases and 24 hr earlier with Isolator than Bactec in 20 of 21 cases.