National survey of the in vitro spectrum of piperacillin-tazobactam tested against more than 40,000 aerobic clinical isolates from 236 medical centers

Study of the comparative activity of piperacillin/tazobactam with currently available antibiotics against 8206 aerobic isolates

OBJECTIVES

To compare the activity of piperacillin-tazobactam with piperacillin and other parenterally administered antibiotics against aerobic Gram-negative bacilli and Gram-positive cocci isolated from across Canada, and to determine the prevalence of resistance mediated by extended-spectrum cephalosporinases.

METHODS

Sixty-one laboratories participated. Disk diffusion testing was performed in accordance with methods outlined by the National Committee for Clinical Laboratory Standards. Susceptibilities were performed on 8206 strains. Escherichia coli and Klebsiella pneumoniae with reduced susceptibilities to third-generation cephalosporins were screened for extended-spectrum beta-lactamases (ESBLs).

RESULTS

Piperacillin-tazobactam was active against 92% of the strains, piperacillin against 81% and ticarcillin-clavulanic acid against 88%. Few differences were observed in the relative susceptibility of strains from teaching or community hospitals, from different anatomic sites or from different regions of the country. Aerobic Gram-negative bacilli tested tended to be more susceptible to all the agents than was recently reported in a similar American study. Only 43% of Enterococcus faecium were susceptible to ampicillin and 42% to piperacillin piperacillin with and without tazobactam. Only two enterococcal strains were resistant to vancomycin, and 19 had intermediate zone sizes. Of the 10 strains of E coli and eight strains of K pneumoniae with reduced susceptibility to extended spectrum cephalosporins, only one demonstrated typical ESBL activity.

CONCLUSIONS

Canadian aerobic Gram-positive cocci and Gram-negative bacilli remain highly susceptible to many currently available antibiotics. The findings confirm a broad spectrum of activity of piperacillin-tazobactam and indicate that the pattern of susceptibility is quite uniform from different body sites, in both teaching and community hospitals, and across the country.

Citrobacter infections in a tertiary care hospital in Northern India

OBJECTIVES

This prospective study was carried out to look for the frequency of isolation of Citrobacter species from clinical specimens and study their antimicrobial susceptibility pattern.

METHODS

Patients from whom Citrobacter species were isolated during routine diagnostic testing from January to December 2004 were included in the study. Isolates were identified by standard biochemical tests. Antimicrobial susceptibility testing was performed by disk diffusion method as per National Committee of Clinical Laboratory Standards (NCCLS) guidelines.

RESULTS

Citrobacter species were isolated from a total of 205 patients. Infection was nosocomially acquired in 94.6% patients. One hundred eighty one (88.3%) patients had significant underlying illnesses. Culture yielded Citrobacter koseri in 185 (90.2%) and Citrobacter freundii in 20 (9.8%) patients. The distribution of isolates was as follows: urine (46.2%), respiratory tract (16.3%), blood (15.8%), pus (12.1%) and sterile body fluids (9.3%). Drug resistance was observed to be more in C. koseri as compared to C. freundii.

CONCLUSIONS

Citrobacter infections are often nosocomially acquired, seen in patients with significant underlying diseases and isolates are commonly drug-resistant. Adoption of hospital infection control practices and a good antibiotic policy may prevent their spread.

Serum bactericidal activity of piperacillin/tazobactam against Staphylococcus aureus, piperacillin-susceptible and piperacillin-resistant Escherichia coli and Pseudomonas aeruginosa

BACKGROUND

The serum bactericidal test measures the highest level of an antibiotic-containing serum dilution at which 99.9% of bacteria are killed. In this study the serum bactericidal activity of piperacillin/tazobactam was determined for bacteria often involved in severe infections. In earlier studies titres >/=1:8 in the serum bactericidal tests correlated well with clinical success in the treatment of endocarditis and osteomyelitis as well as bacterial eradication.

METHODS

Blood samples of 6 healthy volunteers were taken before and 1 and 4 h after piperacillin/tazobactam (4.5 g) administration. Serum concentrations and serum bactericidal activity were determined for 10 strains each of Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli, both piperacillin-resistant and piperacillin-susceptible according to NCCLS guidelines.

RESULTS

100% of S. aureus and piperacillin-susceptible E. coli, 90% of piperacillin-resistant E. coli and 80% of P. aeruginosa were killed 1 h after drug administration. 4 h after drug administration serum bactericidal activity decreased to 60% for S. aureus, 90% for piperacillin-susceptible E. coli, 80% for piperacillin-resistant E. coli and 30% for P. aeruginosa.

CONCLUSIONS

Excellent serum bactericidal activity of piperacillin/tazobactam was recorded 1 h after drug administration for S. aureus, E. coli and P. aeruginosa. After 4 h limited killing rates for P. aeruginosa could be detected, which supports the idea of a combination therapy.

Comparison of four antimicrobial susceptibility testing methods to determine the in vitro activities of piperacillin and piperacillin-tazobactam against clinical isolates of Enterobacteriaceae and Pseudomonas aeruginosa

Susceptibility to piperacillin was similar to that to piperacillin-tazobactam (<1% difference) for 6,938 isolates of Enterobacter aerogenes and 13,954 isolates of Enterobacter cloacae tested using a Vitek system; for the same species, in contrast, susceptibility rates to piperacillin-tazobactam were 5.9 to 13.9% higher than to piperacillin using disk diffusion, MicroScan, and Vitek 2 testing. Unprecedented phenotypes (piperacillin susceptible and piperacillin-tazobactam intermediate; piperacillin intermediate and piperacillin-tazobactam resistant; piperacillin susceptible and piperacillin-tazobactam resistant) accounted for 6.1% of the results for E. aerogenes isolates and 6.0% of the results for E. cloacae isolates tested with the Vitek system.

Decreased antimicrobial resistance following changes in antibiotic use

The widespread use of perioperative antibiotic prophylaxis makes surgical procedures an important component of overall antibiotic use. Attempts to reduce costs and limit the emergence of resistance among pathogenic bacteria by altering antibiotic use must therefore encompass surgical prophylaxis. Several recent reports have linked the use of third-generation cephalosporins with beta-lactam resistance in gram-negative bacteria and with vancomycin resistance in Enterococcus. Fortunately, susceptibility can often be restored by replacing third-generation cephalosporins with drugs that are less likely to foster resistance; a penicillin/beta-lactamase inhibitor combination is often a suitable substitute. An antibiotic resistance management program can effect the type of changes in antimicrobial use necessary to forestall or reverse an outbreak of resistant pathogens. Such a plan was implemented at Methodist Hospital, Indianapolis, Indiana, in 1995. Piperacillin/tazobactam (in combination with an aminoglycoside) was added to the formulary, primarily as empiric therapy, replacing the use of third-generation cephalosporins such as ceftazidime. Following this change, the prevalences of vancomycin-resistant Enterococcus, methicillin-resistant Staphylococcus aureus, and other resistant gram-negative bacilli were all reduced. As this effective formulary change shows, appropriate changes in antibiotic drug, dosage, and administration route can limit the emergence of resistance and ultimately lower costs.

Low-virulence Citrobacter species encode resistance to multiple antimicrobials

Citrobacter spp. are gram-negative commensal bacteria that infrequently cause serious nosocomial infections in compromised hosts. They are often resistant to cephalosporins due to overexpression of their chromosomal beta-lactamase. During a recent study of multidrug-resistant Enterobacteriaceae (MDRE) in solid-organ transplant patients, we found that almost half of patients colonized with MDRE carried one or more cefpodoxime-resistant Citrobacter freundii, Citrobacter braakii, or Citrobacter amalonaticus strains. Pulsed-field gel electrophoresis showed that 36 unique strains of Citrobacter were present among 32 patients. Genetic and phenotypic analysis of the resistance mechanisms of these bacteria showed that the extended-spectrum beta-lactamase (ESBL) SHV-5 or SHV-12 was encoded by 8 strains (26%) and expressed by 7 strains (19%). A number of strains were resistant to other drug classes, including aminoglycosides (28%), trimethoprim-sulfamethoxazole (31%), and fluoroquinolones (8%). PCR and DNA analysis of these multiresistant strains revealed the presence of class I integrons, including the first integrons reported for C. braakii and C. amalonaticus. The integrons encoded aminoglycoside resistance, trimethoprim resistance, or both. Despite the prevalence of MDR Citrobacter spp. in our solid-organ transplant patients, only a single infection with a colonizing strain was recorded over 18 months. Low-virulence Citrobacter spp., which can persist in the host for long periods, could influence pathogen evolution by accumulation of genes encoding resistance to multiple antimicrobial classes.

Potency and antimicrobial spectrum update for piperacillin/tazobactam (2000): emphasis on its activity against resistant organism populations and generally untested species causing community-acquired respiratory tract infections

The in vitro activity of piperacillin/tazobactam and several comparison broad-spectrum compounds was assessed against recent clinical isolates of Gram-positive and -negative bacteria from geographically diverse medical centers in Europe, North and Latin America participating in various surveillance programs in 2000. Several organisms were characterized for phenotypic expression of various resistant determinants such as extended-spectrum beta-lactamase (ESBL) or amp C cephalosporinase hyperproduction, and vancomycin resistance in enterococci (VRE). Piperacillin/tazobactam retained activity (MIC50) against oxacillin-susceptible Staphylococcus spp. (0.12-0.5 microg/ml), Bacillus spp. (0.5 microg/ml), vancomycin-susceptible enterococci (>4 microg/ml), and Corynebacterium spp. (2 microg/ml; not including C. jeikeium) with susceptibility rates of 100.0, 91.7, 85.7 and 81.8%, respectively. Piperacillin/tazobactam inhibited all Streptococcus spp. strains at < or = 16 microg/ml, including penicillin-resistant strains many of which were co-resistant to erythromycin (90%) and other beta-lactams. A specific breakpoint for these streptococci when testing piperacillin/tazobactam appears needed to prevent false-resistant reports using penicillin as a class representative. The carbapenems among beta-lactams were the most active agents against the ESBL-producing species of Escherichia coli and Klebsiella pneumoniae and those strains which hyper-express amp C enzymes including Citrobacter spp. and Enterobacter spp. Piperacillin/tazobactam only exhibited modest activity against the "amp C resistance group" strains (68.8% susceptible or intermediate, MIC < or = 64 microg/ml). Piperacillin/tazobactam (MIC50, 8 microg/ml; 79.5% susceptible) was the most active agent tested against multi-drug resistant isolates of Pseudomonas aeruginosa. Against sampled Haemophilus influenzae (39.2% ampicillin-resistant), piperacillin/tazobactam (MIC(90,) < or = 0.06 microg/ml), ceftriaxone and ceftazidime inhibited 100.0% of the isolates at < or = 0.25 microg/ml. These in vitro surveillance results from the year 2000 on three continents, demonstrated a sustained potent activity of piperacillin/tazobactam against selected problematic nosocomial and community-acquired pathogens. The potential importance of these findings is that this beta-lactamase inhibitor combination can be used an empiric treatment of serious infections in hospital environments where resistance has emerged, as well as covering nearly all isolates of fastidious respiratory tract pathogens acquired in the community setting.

Use of ampicillin/sulbactam and sultamicillin in pediatric infections: a re-evaluation

Ampicillin/sulbactam is an effective solution to the emergence of beta-lactamase-mediated resistance among common pediatric pathogens, and is a widely recognized treatment option for a variety of pediatric infections. Recent antimicrobial surveillance data confirm the continued susceptibility of many Gram-positive and Gram-negative aerobes and anaerobes to ampicillin/sulbactam. Pharmacokinetic studies have demonstrated high drug concentrations at a variety of infection sites, including cerebrospinal fluid and bone. Furthermore, clinical studies have shown that ampicillin/sulbactam, administered intravenously, intramuscularly or orally (as the mutual prodrug sultamicillin), is clinically and bacteriologically effective against upper and lower respiratory tract infections, urinary tract infections, skin, bone and soft-tissue infections, and meningitis, and provides effective surgical prophylaxis. Sultamicillin has an excellent tolerability profile, which is associated with a low rate of treatment discontinuation. Accordingly, ampicillin/sulbactam and sultamicillin should be considered first-choice options for the management of a variety of pediatric infections.

Properties of multidrug-resistant, ESBL-producing Proteus mirabilis isolates and possible role of beta-lactam/beta-lactamase inhibitor combinations

At our institution, isolation rates of clinical strains of ESBL-producing Proteus mirabilis increased to 8.8% of all P. mirabilis isolates during the period 1997-1999. To evaluate the susceptibility of ESBL-producing P. mirabilis strains against commonly used drugs, we studied 50 non-duplicated isolates selected on the basis of synergy between clavulanate and beta-lactams (ceftazidime, aztreonam, cefotaxime, and ceftriaxone). The presence of ESBL-coding genes was confirmed by colony hybridization with bla(TEM-1) and bla(SHV-1) probes. Minimum inhibitory concentrations of several antimicrobial agents for each isolate were obtained using the Etest method. All strains were encoding for TEM-derived enzymes. Gene sequencing showed that at least three different genes (TEM-15, TEM-20, and TEM-52) were present. These enzymes have not been previously reported in P. mirabilis. Isolates were characterized by: (a) reduced susceptibility or resistance to third- and fourth-generation cephalosporins (MIC > or = 2 mg/l), (b) resistance to piperacillin that was abolished by tazobactam (MIC > or = 256 vs. < or = 2 mg/l, respectively), (c) multiple antibiotic resistance that included gentamicin, fluoroquinolones and co-trimoxazole. Therapeutic failure and lack of eradication of ESBL-positive P. mirabilis by third-generation cephalosporins has been repeatedly observed both at our Institution and elsewhere. Piperacillin-tazobactam, as well as amikacin and meropenem appear to be important therapeutic options for infections due to multidrug-resistant, ESBL-producing P. mirabilis isolates.

Increasing antimicrobial resistance in gram-negative bacilli isolated from patients in intensive care units

BACKGROUND

We investigated gram-negative bacilli from patients in intensive care units to determine whether antimicrobial resistance was increasing.

METHODS

Minimal inhibitory concentrations were determined by broth microdilution on 334 gram-negative bacilli collected in 1990, 1995, and 1998.

RESULTS

During the 3 study years, the types of gram-negative bacilli encountered in our intensive care units changed with proportional increases of Pseudomonas sp and decreases of inducible enterics. Dramatic increases in resistance for ceftazidime, cefotaxime, and piperacillin were paralleled between respiratory-tract isolates and inducible enterics. By 1998, ticarcillin was more active than piperacillin against most isolates except Escherichia coli and Klebsiella sp, and most isolates became more resistant to gentamicin and tobramycin.

CONCLUSIONS

Continuous changes in the types of gram-negative bacilli and antimicrobial resistance complicate empirical selection of antimicrobials in the intensive care units. These complications will place more emphasis on communication and strategy formations among health care workers (nurses, physicians, laboratorians, and pharmacists) in an effort to treat infections in a timely and effective manner.

Pharmacokinetics of Intraperitoneal Piperacillin/Tazobactam in Patients on Peritoneal Dialysis with and without Pseudomonas Peritonitis

Objective

The objective of this study was to assess the pharmacokinetics of intraperitoneal (IP) administration of the antibiotic combination piperacillin/tazobactam (PIP/TAZ) to patients on chronic ambulatory peritoneal dialysis (CAPD) with and without pseudomonas peritonitis.

Design

Open-labeled study.

Setting

The study was carried out in the CAPD unit of Assaf Harofeh Medical Center, Zerifin, Israel.

Patients and Methods

Six patients participated in the study, 4 had pseudomonas peritonitis, all were given an IP loading dose of 4 g/0.5 g PIP/TAZ. Twenty-four hours after the initial dose, a maintenance dose of 0.5 g/0.0625 g PIP/TAZ was administered with each dialysate exchange for a period of 1 week. The patients without peritonitis received only the loading dose. High performance liquid chromatography was used to determine the concentrations of PIP/TAZ in plasma obtained at 0, 30, 60, 90, 120, 360, 480, 600, 720, and 1440 minutes after administration. Samples of the dialysate fluid for determination of PIP/TAZ concentration were collected at 6, 10, 14, 24, and 72, 120, and 168 hours.

Results

After the loading dose, the highest plasma PIP concentration (Cmax) was 51.6 ± 21.25 μg/mL and appeared at 1.5 ± 0.45 hours (tmax). During the maintenance period plasma PIP concentration was 5.2 ± 4.75 μg/mL. Tazobactam was detected in the plasma of 1 patient only. The concentration of TAZ in the dialysate fluid during the maintenance period was 2.3 ± 0.5 μg/mL.

Conclusions

Piperacillin administered IP at 4 g reached plasma concentrations comparable to intravenous administration and considered therapeutic (above the MIC90for Pseudomonas aeruginosa) in CAPD patients with or without peritonitis. The maintenance dose, however, should be augmented. Tazobactam could not be detected in the plasma of most patients and the therapeutic implications of IP administration of TAZ cannot be directly correlated to intravenous administration.

In vitro efficacy of beta-lactam/beta-lactamase inhibitor combinations against bacteria involved in mixed infections

Mixed infections are usually caused by a relatively limited range of bacteria, with the anaerobes and opportunistic pathogens contributing to their severity. In order to make the best therapeutic choice for a patient with a life-threatening infection, which is probably of mixed etiology, clinicians must be aware of the organisms that are likely to be involved, and the fact that most of them will produce beta-lactamase. Of the options available for empiric therapy, the beta-lactam/beta-lactamase inhibitor combinations represent a good choice. Their antibacterial spectra include both aerobic and anaerobic pathogens. Five combinations are available in clinical practice: ampicillin-sulbactam, piperacillin-tazobactam, ticarcillin-clavulanic acid, amoxicillin-clavulanic acid, and cefoperazone-sulbactam. More strains of clinically important anaerobic bacteria are susceptible to ampicillin-sulbactam than to either piperacillin-tazobactam or ticarcillin-clavulanic acid, which are also available widely and suitable for more life-threatening infections. In addition, sulbactam itself has the highest intrinsic activity of the beta-lactamase inhibitors against the opportunistic pathogen, Acinetobacter baumannii. Thus, ampicillin-sulbactam could be considered a drug of choice for the empirical treatment of mixed infections where there is a reasonable possibility of the presence of A. baumannii.

Piperacillin/tazobactam: an updated review of its use in the treatment of bacterial infections

Piperacillin/tazobactam is a beta-lactam/beta-lactamase inhibitor combination with a broad spectrum of antibacterial activity encompassing most Gram-positive and Gram-negative aerobic bacteria and anaerobic bacteria, including many pathogens producing beta-lactamases. Evidence from clinical trials in adults has shown that piperacillin/tazobactam, administered in an 8:1 ratio, is an effective treatment for patients with lower respiratory tract, intra-abdominal, urinary tract, gynaecological and skin/soft tissue infections, and for fever in patients with neutropenia. Combination regimens of piperacillin/tazobactam plus an aminoglycoside are used to treat patients with severe nosocomial (hospital-acquired) infections. In clinical trials, piperacillin/tazobactam was significantly more effective than ticarcillin/clavulanic acid in terms of clinical and microbiological outcome in patients with community-acquired pneumonia. In patients with intra-abdominal infections, clinical and bacteriological response rates were significantly higher with piperacillin/tazobactam than with imipenem/cilastatin (administered at a dosage lower than is recommended in countries outside Scandinavia). Piperacillin/tazobactam in combination with amikacin was at least as effective as ceftazidime plus amikacin in the treatment of ventilator-associated pneumonia and was significantly more effective than ceftazidime plus amikacin in the empirical treatment of febrile episodes in patients with neutropenia or granulocytopenia. In other trials, the efficacy of piperacillin/tazobactam was similar to that of standard aminoglycoside-containing and other treatment regimens in patients with intra-abdominal, skin/soft tissue or gynaecological infections. Piperacillin/tazobactam is generally well tolerated. The most frequent adverse events are gastrointestinal symptoms (most commonly diarrhoea) and skin reactions. The incidence of adverse events with piperacillin/tazobactam is higher when the combination is given in combination with an aminoglycoside than when given as monotherapy.

CONCLUSION

Because of the broad spectrum of antibacterial activity provided by piperacillin/tazobactam, it is useful for the treatment of patients with polymicrobial infections caused by aerobic or anaerobic beta-lactamase-producing bacteria. Piperacillin/tazobactam appears to have a particularly useful role in the treatment of patients with intra-abdominal infections and, in combination with amikacin, in the treatment of patients with febrile neutropenia, especially given the current prevalence of Gram-positive infections in this group.

In-vitro activity of piperacillin/tazobactam relative to other antibiotics against blood culture isolates

Resistance of bacteria to antibiotics is an increasing problem in many countries. Accurate locally relevant information is essential for detection and control of emerging resistance and to facilitate choice of empirical antibiotic therapy in the immediate management of seriously ill patients. We have determined the minimum inhibitory concentration of piperacillin/tazobactam for 97 strains of bacteria (55 Enterobacteriaceae, 13 non-fermentative Gram-negative bacilli, 22 Staphylococcus aureus, 6 Enterococcus faecalis and 1 Bacillus cereus) isolated from blood cultures and compared its activity to that of amoxycillin, co-amoxiclav, cephalothin, cefotaxime, ceftazidime, ciprofloxacin, gentamicin, piperacillin, cefotaxime. The strains were consecutive non-fastidious isolates with the following qualifications: coagulase negative staphylococci and diphtheroids were excluded and the number of Staphylococcus aureus isolates was limited to 12 methicillin-resistant and 10 methicillin-sensitive strains. Multiple isolates of the same species from individual patients were not included. The minimum inhibition concentrations of methicillin, penicillin, teichoplanin and vancomycin were also determined for specific groups of organisms. MICs were determined by the Etest method (AB Biodisk, Solna, Sweden) on Mueller Hinton agar. The MICs of appropriate American Type Culture Collection control strains were determined. Based on the interpretative criteria of the National Committee for Clinical Laboratory Standards (USA), 87 per cent of Gram-negative bacilli were susceptible to piperacillin/tazobactam compared with amoxycillin 26 per cent, cephalothin 35 per cent, co-amoxiclav 54 per cent, piperacillin 56 per cent, cefotaxime 69 per cent, ceftazidime 84 per cent, gentamicin 85 per cent and ciprofloxacin 91 per cent. Of all isolates 75 per cent were sensitive to piperacillin/tazobactam, compared with amoxycillin 22 per cent, cephalothin 35 per cent, piperacillin 41 per cent, co-amoxiclav 52 per cent, cefotaxime 59 per cent, ceftazidime 60 per cent, gentamicin 74 per cent and ciprofloxacin 77 per cent. Two isolates (1 E. coli and 1 Klebsiella pneumoniae) with antibiograms consistent with the relatively new resistance phenomenon of extended spectrum beta-lactamase production were identified. The spectrum of activity of piperacillin-tazobactam for empirical antibiotic therapy is significantly greater than that of piperacillin alone and is similar to that of ciprofloxacin and gentamicin.

In vitro evaluation of sparfloxacin activity and spectrum against 24,940 pathogens isolated in the United States and Canada, the final analysis

Sparfloxacin, a recently marketed oral fluoroquinolone, was tested against 24,940 recent clinical strains isolated from blood stream and respiratory tract cultures at 187 hospitals in the USA and Canada. Sparfloxacin activity was compared with 5 to 13 antimicrobial agents using either Etest (AB BIODISK, Solna, Sweden) and a reference broth microdilution or a standardized disk diffusion method. When applying recommended MIC breakpoint criteria of sparfloxacin susceptibility (< or = 0.5 microgram/mL) for Streptococcus pneumoniae (4,410 strains) and other Streptococcus spp. (554 isolates), 93% and 88% were inhibited, respectively. Furthermore, at < or = 1 microgram/mL sparfloxacin susceptibility rates for streptococci increased to 98% overall and 99.3% for S. pneumoniae. In contrast, only 46% and 68% of pneumococci were susceptible to ciprofloxacin (MIC90, 3 micrograms/mL; susceptible at < or = 1 microgram/mL) and penicillin (MIC90, 1.5 microgram/mL; susceptible at < or = 0.06 microgram/mL), respectively. Differences between regions in the USA for rates of penicillin-resistant pneumococcal strains were observed (greatest resistances in southeast and midwest), but results indicate that the sparfloxacin potency was not adversely influenced (MIC90, 0.5 microgram/mL). Also pneumococcal isolates from the lower respiratory tract were more resistant to penicillin and other beta-lactams. Nearly all Haemophilus species and Moraxella catarrhalis strains, including those harboring beta-lactamases, were susceptible to tested fluoroquinolones (sparfloxacin, ciprofloxacin), amoxicillin/clavulanic acid, and newer oral cephalosporins. Sparfloxacin was very active against oxacillin-susceptible Staphylococcus aureus (MIC90, 0.12 microgram/mL; 96-97% susceptible), Klebsiella spp. (MIC90 0.12 microgram/mL), and other tested enteric bacilli (92-95% susceptible). Comparisons between the broth microdilution MIC and disk diffusion interpretive results demonstrated excellent intermethod susceptibility category agreement (> 95%) using current sparfloxacin breakpoints, but some compounds (cefpodoxime disk diffusion tests for S. aureus) may require modifications. These results demonstrate that new Gram-positive focused fluoroquinolones (sparfloxacin) possess an excellent in vitro activity and spectrum against pathogens that cause respiratory tract infections. This spectrum of activity includes strains resistant to other antimicrobial classes, including the oral cephalosporins, macrolides, amoxicillin/clavulanic acid, and earlier fluoroquinolones (ciprofloxacin, ofloxacin). Overall, sparfloxacin inhibited 89% to nearly 100% of the isolates (species variable) tested against those species against which it has Food and Drug Administration indications for clinical use.

Activities and time-kill studies of selected penicillins, beta-lactamase inhibitor combinations, and glycopeptides against Enterococcus faecalis

The activities of piperacillin, piperacillin-tazobactam, ticarcillin, ticarcillin-clavulanate, ampicillin, ampicillin-sulbactam, vancomycin, and teicoplanin were tested against 212 Enterococcus faecalis strains (9 beta-lactamase producers) by standard agar dilution MIC testing (10[4] CFU/spot). The MICs at which 50 and 90% of the isolates were inhibited (MIC50s and MIC90s, respectively) were as follows (microg/ml): piperacillin, 4 and 8; piperacillin-tazobactam, 4 and 8; ticarcillin, 64 and 128; ticarcillin-clavulanate, 64 and 128; ampicillin, 2 and 2; ampicillin-sulbactam, 1 and 2; vancomycin, 1 and 4; and teicoplanin, 0.5 and 1. Agar dilution MIC testing of the nine beta-lactamase-positive strains with an inoculum of 10(6) CFU/spot revealed higher beta-lactam MICs (piperacillin, 64 to >256 microg/ml; ticarcillin, 128 to >256 microg/ml; and ampicillin, 16 to 128 microg/ml); however, MICs with the addition of inhibitors were similar to those obtained with the lower inoculum. Time-kill studies of 15 strains showed that piperacillin-tazobactam was bactericidal (99.9% killing) for 14 strains after 24 h at four times the MIC, with 90% killing of all 15 strains at two times the MIC. After 12 and 6 h, 90% killing of 14 and 13 strains, respectively, was found at two times the MIC. Ampicillin gave 99.9% killing of 14 beta-lactamase-negative strains after 24 h at eight times the MIC, with 90% killing of all 15 strains at two times the MIC. After 12 and 6 h, 90% killing of 14 and 13 strains, respectively, was found at two times the MIC. Killing by ticarcillin-clavulanate was slower than that observed for piperacillin-tazobactam, relative to the MIC. For the one beta-lactamase-producing strain tested by time-kill analysis with a higher inoculum, addition of the three inhibitors (including sulbactam) to each of the beta-lactams resulted in bactericidal activity at 24 h at two times the MIC. For an enzyme-negative strain, addition of inhibitors did not influence kinetics. Kinetics of vancomycin and teicoplanin were significantly slower than those of the beta-lactams, with bactericidal activity against 6 strains after 24 h at eight times the MIC, with 90% killing of 12 and 14 strains, respectively, at four times the MIC. Slower-kill kinetics by both glycopeptides were observed at earlier periods.

Comparative in vitro evaluation of piperacillin/tazobactam in a tertiary care hospital

Bacterial resistance is usually a serious problem in tertiary care hospitals. The aim of this in vitro study was to evaluate the beta-lactamase inhibitor combination piperacillin/tazobactam in a hospital environment with high bacterial resistance rates and compare it with other beta-lactam agents. Three hundred and sixty-two isolates from various clinical materials were studied during the period March-August 1996. Material for culture was collected from patients of all the wards of our hospital, with the majority being from the Intensive Care Unit (45%). Pathogenic Gram-positive and Gram-negative bacteria with high resistance rates and beta-lactamase production were studied (staphylococci, enterococci, Enterobacteriaceae, Pseudomonas). Significant bacterial resistance rates were identified for ceftazidime (50% for Klebsiellae, 60% for Enterobacter spp, 60% for Proteus spp, 33% for Pseudomonas spp, 75% for Acinetobacter spp) and ciprofloxacin (33% for both Klebsiellae and Enterobacter spp, 67% for Pseudomonas spp, 50% Acinetobacter spp). Fifty percent of Enterococcus isolates were resistance to ciprofloxacin but all of them were susceptible to piperacillin/tazobactam, amoxicillin/clavulanate and imipenem. The antibacterial activity of piperacillin/tazobactam (susceptibility rates 83 to 100% for Enterobacteriaceae, 83% for Pseudomonas spp and 75% for Acinetobacter spp) was higher than that of ceftazidime, piperacillin and ciprofloxacin. Imipenem, being mostly a reserve product, showed higher activity against Acinetobacter, Klebsiella and Enterobacter species.

Microbiologic and pharmacodynamic principals applied to the antimicrobial susceptibility testing of ampicillin/sulbactam: analysis of the correlations between in vitro test results and clinical response

The correlation between various ampicillin/sulbactam in vitro antimicrobial susceptibility test results and the clinical outcome of patients treated with this agent have been examined. A survey of over 29,000 clinical isolates of the family Enterobacteriaceae found that the proportion of susceptible pathogens as assessed by current susceptibility testing interpretive guidelines (NCCLS) for disk diffusion and dilution (MIC) assays was significantly less than the proportion of patients cured or clinically improved in ampicillin/sulbactam clinical trials. Also, the results of two NCCLS methods differ greatly in the perceived percentages of susceptible strains (63.9% versus 72.2%; unacceptable variation). Furthermore, the current interpretive criteria resulted in high false-susceptible (4.2%) and total (19.7%) error rates. When proposed interpretive guidelines were applied, approximately 73 to 87% of the Enterobacteriaceae strains were observed to be susceptible, the variation between methods was minimized, and the error rates were reduced. A retrospective analysis of data from clinical trials with ampicillin/sulbactam indicated that the proportion of patients who were cured or clinically improved and bacterially eradicated was not appreciably different in patients having baseline Enterobacteriaceae pathogens with MICs of 16 or 32 micrograms/ml (ampicillin MIC component) as compared to those with pathogens having MICs of < or = 8 micrograms/ml. Studies in animals, in vitro models, and pharmacokinetic considerations indicate that a change in the MIC breakpoint for ampicillin/sulbactam should be considered. The proposed interpretive guideline revisions for ampicillin/sulbactam susceptibility testing of the Enterobacteriaceae were 1) use current diagnostic reagents with criteria of < or = 16/8 micrograms/ml (> or = 14 mm) as susceptible and > or = 64/32 micrograms/ml (< or = 10 mm) as resistant; e.g., 75.9 to 76.0% spectrum and 1.3% false-susceptible error; 2) use alternative diagnostic reagents (1:1 ratio MIC; 20/20 micrograms disks) with criteria of < or = 8/8 micrograms/ml (> or = 18 mm) as susceptible and > or = 32/32 micrograms/ml (< or = 14 mm) as resistant; e.g., 73.3 to 76.9% spectrum and 1.8% false-susceptible error; or 3) use alternative diagnostic reagents with criteria of < or = 16/16 micrograms/ml (> or = 14 mm) as susceptible and > or = 64/64 micrograms/ml (< or = 10 mm) as resistant; e.g., 84.7 to 86.9% spectrum and 1.3% false-susceptible error. Data from a comprehensive in vitro survey of clinical isolates, retrospective analyses of clinical trials, and studies of animal models support the modification of contemporary interpretive guidelines for ampicillin/sulbactam antimicrobial susceptibility tests. The best short-term criteria would apply current in vitro diagnostic reagents and a modified susceptible breakpoint (< or = 16/8 micrograms/ml as susceptible; option 1 above) until new diagnostic reagents can be qualified by means of studies needed for quality assurance of standardized methods (NCCLS M23-A and FDA procedures). These changes would provide a better in vitro prediction of ampicillin/sulbactam efficacy in clinical practice.

The emergent needs for basic research, education, and surveillance of antimicrobial resistance. Problems facing the report from the American Society for Microbiology Task Force on Antibiotic Resistance

The American Society for Microbiology (ASM) convened a task force to study the current prevelance of antibiotic resistance and the problems associated with it. The task force produced a series of recommendations centered around three key elements: (a) education of the physician and the public; (b) encouragement of more basic research directed to the development of new antimicrobials and vaccines; and (c) the setting-up of a national surveillance system to both confirm and monitor the extent of the problem. Since the publication of this report in 1995, progress has been slow. No "consortium-style" funding has been set aside and any initiatives, such as the first steps in an education program by the ASM, are still in their planning phases. The spirit of cooperation and trust needed to deal with this problem appears to be lacking.

Imipenem/cilastatin: an update of its antibacterial activity, pharmacokinetics and therapeutic efficacy in the treatment of serious infections

The prototype carbapenem antibacterial agent imipenem has a very broad spectrum of antibacterial activity, encompassing most Gram-negative and Gram-positive aerobes and anaerobes, including most beta-lactamase-producing species. It is coadministered with a renal dehydropeptidase inhibitor, cilastatin, in order to prevent its renal metabolism in clinical use. Extensive clinical experience gained with imipenem/cilastatin has shown it to provide effective monotherapy for septicaemia, neutropenic fever, and intra-abdominal, lower respiratory tract, genitourinary, gynaecological, skin and soft tissues, and bone and joint infections. In these indications, imipenem/cilastatin generally exhibits similar efficacy to broad-spectrum cephalosporins and other carbapenems and is at least equivalent to standard aminoglycoside-based and other combination regimens. Imipenem/cilastatin is generally well tolerated by adults and children, with local injection site events, gastrointestinal disturbances and dermatological reactions being the most common adverse events. Seizures have also been reported, occurring mostly in patients with impaired renal function or CNS pathology, or with excessive dosage. Although it is no longer a unique compound, as newer carbapenems such as meropenem are becoming available, imipenem/cilastatin nevertheless remains an important agent with established efficacy as monotherapy for moderate to severe bacterial infections. Its particular niche is in treating infections known or suspected to be caused by multiresistant pathogens.

Cefotaxime in the treatment of staphylococcal infections. Comparison of in vitro and in vivo studies

Staphylococcus aureus strains are well-established pathogens that may cause mild to serious life-threatening disease. Coagulase-negative staphylococci, particularly Staphylococcus epidermidis, also have a pathogenic role in humans and cause infections primarily associated with prosthetic devices and indwelling catheters, whereas Staphylococcus saprophyticus usually causes urinary tract infections. Cefotaxime is a "third-generation" cephalosporin that is stable to the staphylococcal beta-lactamases. In vitro studies over the last 15 years have shown that this parenteral cephalosporin has remained highly active (MIC90 ranges of < or = 2-8 micrograms/ml) against oxacillin-susceptible staphylococci. Cefotaxime therapy of staphylococcal infections has resulted in clinical cure/improvement rates ranging from 78%-100% and bacteriologic eradication rates ranging from 85%-100% in a wide variety of infections. Contrary to contemporary dogma, this "third-generation" cephalosporin appears to be efficacious against staphylococcal infections from a review of 15 years of clinical experience.

Comparative antimicrobial activity of piperacillin-tazobactam tested against more than 5000 recent clinical isolates from five medical centers. A reevaluation after five years

Piperacillin combined with tazobactam at a fixed concentration (4 micrograms/ml) and a ratio (8:1) was tested against 5,029 aerobic isolates and 447 fastidious organisms, including anaerobes. Among the Enterobacteriaceae, > 95% inhibition was shared only by imipenem (99.1% at < or = 4 micrograms/ml), and some newer cephalosporins (95.1% - 99.8% at < or = 8 micrograms/ml), and piperacillin-tazobactam (95.8% at < or = 16/4 micrograms/ml). Piperacillin-tazobactam was the most active agent tested against nonenteric Gram-negative bacilli (93.5% at < or = 8 micrograms/ml). Ampicillin-sulbactam was the most active agent against staphylococci (95.0% at < or = 8 micrograms/ml), followed by imipenem (91.8%), piperacillin-tazobactam (89.3% at < or = 8/4 micrograms/ml), and cefepime (86.2% at < or = 8 micrograms/ml). Against the enterococci, only ampicillin (93.0% at < or = 8 micrograms/ml) with or without sulbactam, piperacillin (91.0% at < or = 16 micrograms/ml) with or without tazobactam, and imipenem (91.0%) had acceptable activity. Piperacillin-tazobactam and imipenem were the most active drugs tested against all aerobic isolates, inhibiting 93.5% of isolates each. Piperacillin-tazobactam inhibited all fastidious isolates tested, including Haemophilus influenzae (MIC90, 0.094/4 micrograms/ml), Moraxella catarrhalis (MIC90, 0.064/4 micrograms/ml), Neisseira gonorrhoeae (MIC90, < or = 0.016/4 micrograms/ml), and Streptococcus pneumoniae (all MICs, < or = 4/4 micrograms/ml). Against the anaerobic isolates, the most broad-spectrum antimicrobial agents tested were imipenem (100.0%), piperacillin-tazobactam (99.5% at < or = 32/4 micrograms/ml), metronidazole (98.4% at < or = 8 micrograms/ml), and ticarcillin-clavulanic acid (95.1% at < or = 32/2 micrograms/ml). These results are nearly identical to a previous study involving the same five medical centers in 1989. Piperacillin-tazobactam appears to remain a highly effective beta-lactamase inhibitor combination with a wide empiric spectrum and potency in teaching hospitals.