Cefepime, piperacillin-tazobactam, and the inoculum effect in tests with extended-spectrum beta-lactamase-producing Enterobacteriaceae

There is little information about the clinical effectiveness of cefepime and piperacillin-tazobactam in the treatment of infections caused by extended-spectrum beta-lactamase (ESBL)-producing pathogens. Some inferences have been drawn from laboratory studies, which have usually involved only one or a few strains of ESBL-producing Klebsiella pneumoniae or Escherichia coli that produced only a limited range of ESBLs. Such studies are indirect, sometimes conflicting, indicators of efficacy. To extend previous laboratory findings, a study was designed to investigate organism-drug interactions by determining the in vitro activities of eight parenteral beta-lactam agents against 82 clinical and laboratory strains of Klebsiella, Escherichia, Enterobacter, Citrobacter, Serratia, Morganella, and Proteus species that produced 22 different ESBLs, alone or in combination with other beta-lactamases. Activities were determined in broth microdilution MIC tests using standard and 100-fold-higher inocula. An inoculum effect, defined as an eightfold or greater MIC increase on testing with the higher inoculum, was most consistently detected with cefepime, cefotaxime, and ceftriaxone and least frequently detected with meropenem and cefoteten. Piperacillin-tazobactam was intermediate between these two groups of agents. Although the inoculum effect is an in vitro laboratory phenomenon, if it has any predictive value in identifying increased risk of therapeutic failure in serious infections, these results support suggestions that cefepime may be a less-than-reliable agent for therapy of infections caused by ESBL-producing strains.

Inactivation of FtsI inhibits constriction of the FtsZ cytokinetic ring and delays the assembly of FtsZ rings at potential division sites

A universally conserved event in cell division is the formation of a cytokinetic ring at the future site of division. In the bacterium Escherichia coli, this ring is formed by the essential cell division protein FtsZ. We have used immunofluorescence microscopy to show that FtsZ assembles early in the division cycle, suggesting that constriction of the FtsZ ring is regulated and supporting the view that FtsZ serves as a bacterial cytoskeleton. Assembly of FtsZ rings was heterogeneously affected in an ftsI temperature-sensitive mutant grown at the nonpermissive temperature, some filaments displaying a striking defect in FtsZ assembly and others displaying little or no defect. By using low concentrations of the beta-lactams cephalexin and piperacillin to specifically inhibit FtsI (PBP3), an enzyme that synthesizes peptidoglycan at the division septum, we show that FtsZ ring constriction requires the transpeptidase activity of FtsI. Unconstricted FtsZ rings are stably trapped at the midpoint of the cell for several generations after inactivation of FtsI, whereas partially constricted FtsZ rings are less effectively trapped. In addition, FtsZ rings are able to assemble in newborn cells in the presence of cephalexin, suggesting that newborn cells contain a site at which FtsZ can assemble (the nascent division site) and that the transpeptidase activity of FtsI is not required for assembly of FtsZ at these sites. However, aside from this first round of FtsZ ring assembly, very few additional FtsZ rings assemble in the presence of cephalexin, even after several generations of growth. One interpretation of these results is that the transpeptidase activity of FtsI is required, directly or indirectly, for the assembly of nascent division sites and thereby for future assembly of FtsZ rings.

A two-component signal-transducing system is involved in competence and penicillin susceptibility in laboratory mutants of Streptococcus pneumoniae

Penicillin resistance in Streptococcus pneumoniae has been attributed so far to the production of penicillin-binding protein (PBP) variants with decreased affinities for beta-lactam antibiotics. Cefotaxime-resistant laboratory mutants, selected after several steps on increasing concentrations of this beta-lactam, become deficient in transformation as well. A DNA fragment conferring both cefotaxime resistance and transformation deficiency was isolated and cloned from the mutant C306. The cefotaxime resistance associated with this resistance determinant was not accompanied with apparent changes in PBP properties, and it mapped on the chromosome distinct from the known resistance determinants, genes encoding PBP2x, PBP1a or PBP2b. Determination of a 2265 bp DNA sequence of the resistance determinant revealed two open reading frames, ciaR and ciaH, whose deduced amino acid sequence identified the corresponding proteins as the response regulator and histidine kinase receptor, respectively (members of the two families of bacterial signal-transducing proteins). Two hydrophobic peptide regions divided the histidine kinase CiaH into two putative domains: an N-terminal extracellular sensor part, and an intracellular C-terminal domain with the conserved His-226 residue, the presumed phosphorylation site. The single point mutations responsible for cefotaxime-resistance and transformation deficiency of C306 and of another two independently isolated cefotaxime-resistant mutants were each located in the C-terminal half of CiaH. A small extracellular protein, the competence factor, is required for induction of competence. Neither C306 nor the transformants obtained with the mutated ciaH gene produced competence factor, and exogenous competence factor could not complement the transformation deficiency, indicating that the signal-transducing system cia is involved in early steps of competence regulation.

Reappraisal of the antimicrobial susceptibilities of Chryseobacterium and Flavobacterium species and methods for reliable susceptibility testing

Several Flavobacterium species, comprising a heterogeneous group of gram-negative bacilli that are capable of causing opportunistic infections in humans, have recently been reclassified as Chryseobacterium or Myroides species. Intrinsically resistant to a number of antibiotics, these organisms have been reported to be susceptible to vancomycin and certain other drugs that are normally active against gram-positive bacteria. By using the National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution procedure, 58 clinical isolates of former flavobacteria (36 Chryseobacterium meningosepticum isolates, 11 C. indologenes isolates, 3 C. gleum isolates, 4 unspeciated former members of Flavobacterium group IIb, and 4 Myroides odoratum isolates) were tested with 23 antibiotics, including conventional and investigational agents. In addition, the broth microdilution results were compared to those generated by agar dilution, E-test, and disk diffusion for vancomycin and piperacillin-tazobactam. Compared to the NCCLS microdilution results, there were 7.1 and 17.9% very major errors with piperacillin-tazobactam by agar dilution and E-test, respectively. In addition, there were from 12.1 to 48.3% minor errors with both procedures with vancomycin and piperacillin-tazobactam. The very major and minor error rates were unacceptably high with disk testing of piperacillin-tazobactam; the use of enterococcal vancomycin disk breakpoints (zone diameter of > or =17 mm = susceptible) resulted in >20% minor errors but only one very major error. All of the isolates were susceptible to minocycline; over 90% were susceptible to sparfloxacin, levofloxacin, and clinafloxacin; and 88% were susceptible to rifampin. None was susceptible to vancomycin. When Chryseobacterium or Myroides species are isolated from serious infections, susceptibility testing by broth microdilution should be performed and therapy should be guided by those results.

Antimicrobial resistance in gram-positive bacteria

Gram-positive bacteria are common causes of bloodstream and other infections in hospitalized patients in the United States, and the percentage of nosocomial bloodstream infections caused by antibiotic-resistant gram-positive bacteria is increasing. Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are of particular concern. In the United States, approximately 60% of staphylococcal infections in the intensive care unit are now caused by MRSA, and percentages continue to rise. Outbreaks of hospital-acquired MRSA (HA-MRSA) are typically the result of clonal spread by MRSA being transferred from patient to patient, frequently using healthcare personnel as intermediaries. HA-MRSA strains are generally multidrug resistant. Vancomycin is the standard treatment for serious MRSA infections, but a few cases of vancomycin-resistant S aureus (VRSA) have recently emerged in the United States. Community-acquired MRSA (CA-MRSA) is also increasing. Soft tissue infections are the most frequent presentations of CA-MRSA, but life-threatening invasive infections occur as well, including necrotizing pneumonia. The mechanisms of methicillin resistance are the same for CA-MRSA and HA-MRSA, but susceptibilities to non-beta-lactam antibiotics often differ. CA-MRSA exhibits broader antibiotic susceptibility than does HA-MRSA. The proportion of enterococci resistant to vancomycin continues to rise in the hospital setting, with the overwhelming majority of infections due to Enterococcus faecium. Clonal spread of VRE has been documented, but polyclonal outbreaks associated with antimicrobial use are also common. The relations between antibiotic use and VRE colonization are complex and related to the antienterococcal activity, biliary excretion, and antianaerobic activity of the antibiotic. Recent results show a decline in invasive pneumococcal disease (IPD) since the introduction of 7-valent pneumococcal conjugate vaccine, and suggest that, where available, vaccines may be useful in the battle to slow the spread of resistant gram-positive cocci.

Antibiotic resistance and production of extended-spectrum beta-lactamases amongst Klebsiella spp. from intensive care units in Europe

Consecutive klebsiellae were collected from ICU patients at 35 centres in Western and Southern Europe. Of 966 isolates obtained, 716 were Klebsiella pneumoniae, 248 were Klebsiella oxytoca and two were Klebsiella ozaenae. Most were from Belgium, France, Germany, Holland, Italy, Portugal, Spain, Turkey and a few from Greece and the UK. Production of extended-spectrum beta-lactamases (ESBLs) was inferred in 220 isolates on the basis of synergy between ceftazidime and clavulanate. Putative ESBL producers were received from 23 centres, including 20 of the 27 that contributed more than 10 klebsiellae. Over 88% of putative ESBL producers were resistant to ceftazidime 2 mg/L, ceftriaxone 1 mg/L and aztreonam 1 mg/L, whereas, amongst ESBL-negative isolates, more than 98% of K. pneumoniae and 87% of K. oxytoca were susceptible to these concentrations. Putative ESBL producers wre also more resistant to cefuroxime and cefoxitin than non-producers, but not to biapenem. MIC distributions of ciprofloxacin, piperacillin/tazobactam and aminoglycosides were bimodal for ESBL producers, with some isolates highly sensitive and others very resistant. For example, 70% of putative ESBL producers were susceptible to piperacillin/tazobactam 16 + 4 mg/L, but 30% were resistant, some highly so. Resistance to this combination, and to ciprofloxacin, was clustered in certain centres. Two other groups of cephalosporin-resistant isolates were identified besides ESBL producers, viz. (i) nine isolates, from three centres, with AmpC beta-lactamases and (ii) 20 K. oxytoca, from 15 centres, that hyperproduced K1 enzyme. Examination of the hospitals' own susceptibility data indicated that up to 33% of putative ESBL producers had been reported susceptible to third-generation cephalosporins or monobactams. This is disturbing, since ESBLs have been associated with clinical failure even when only low-level resistance was apparent in vitro.

In vitro activity of AVE1330A, an innovative broad-spectrum non-beta-lactam beta-lactamase inhibitor

OBJECTIVES

Production of beta-lactamases is the main mechanism of beta-lactam resistance in Gram-negative bacteria. Despite the current use of clavulanic acid, sulbactam and tazobactam, the prevalence of class A and class C enzymes is increasing worldwide, demanding new beta-lactamase inhibitors. Here we report the antimicrobial properties of AVE1330A, a representative of a novel class of bridged bicyclico[3.2.1]diazabicyclo-octanones in combination with ceftazidime.

MATERIALS AND METHODS

IC(50) and kinetic parameters of the hydrolysis reaction were used to characterize beta-lactamase inhibition by AVE1330A. MICs for >600 strains were determined with the combination ceftazidime/AVE1330A at a fixed ratio of 4:1.

RESULTS

IC(50)s of AVE1330A for TEM-1 and P99 enzymes were 0.0023 mg/L (8 nM) and 0.023 mg/L (80 nM), compared with 0.027 mg/L (130 nM) and 205.1 mg/L (1 x 10(6) nM) of clavulanic acid and 0.013 mg/L (40 nM) and 1.6 mg/L (5000 nM) of tazobactam. A highly stable covalent complex led to a low turnover of AVE1330A. MICs of ceftazidime/AVE1330A for Enterobacteriaceae were at least eight-fold lower than those of ceftazidime alone. All of the Escherichia coli, Klebsiella pneumoniae, Citrobacter and Proteus mirabilis strains, including ceftazidime-resistant isolates, were inhibited at 4-8 mg/L. Only 2 mg/L were required to inhibit other Proteeae, Enterobacter, Salmonella and Serratia.

CONCLUSION

The combination of ceftazidime with AVE1330A exhibited broad-spectrum activity against Ambler class A- and class C-producing Enterobacteriaceae.

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.

Synergistic, collaterally sensitive β-lactam combinations suppress resistance in MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent multidrug-resistant pathogens worldwide, exhibiting increasing resistance to the latest antibiotic therapies. Here we show that the triple β-lactam combination meropenem-piperacillin-tazobactam (ME/PI/TZ) acts synergistically and is bactericidal against MRSA subspecies N315 and 72 other clinical MRSA isolates in vitro and clears MRSA N315 infection in a mouse model. ME/PI/TZ suppresses evolution of resistance in MRSA via reciprocal collateral sensitivity of its constituents. We demonstrate that these activities also extend to other carbapenem-penicillin-β-lactamase inhibitor combinations. ME/PI/TZ circumvents the tight regulation of the mec and bla operons in MRSA, the basis for inducible resistance to β-lactam antibiotics. Furthermore, ME/PI/TZ subverts the function of penicillin-binding protein-2a (PBP2a) via allostery, which we propose as the mechanism for both synergy and collateral sensitivity. Showing in vivo activity similar to that of linezolid, ME/PI/TZ demonstrates that combinations of older β-lactam antibiotics could be effective against MRSA infections in humans.

Pseudomonas aeruginosa ventilator-associated pneumonia: comparison of episodes due to piperacillin-resistant versus piperacillin-susceptible organisms

We sought to determine the epidemiological characteristics of patients in an intensive care unit (ICU) who developed ventilator-associated pneumonia (VAP) caused by piperacillin-resistant Pseudomonas aeruginosa (PRPA; n=34) or piperacillin-susceptible P. aeruginosa (PSPA; n=101). According to univariate analysis, the factors associated with the development of PRPA VAP were presence of an underlying fatal medical condition, immunocompromised status, longer previous hospital stay, less-severe illness at the time of ICU admission, duration of mechanical ventilation before onset of VAP, number of classes of antibiotic received, and previous exposure to imipenem or fluoroquinolone. Multivariate logistic regression analysis identified the following significant independent factors: presence of an underlying fatal medical condition (odds ratio [OR], 5.6), previous fluoroquinolone use (OR, 4.6), and initial disease severity (OR, 0.8). We concluded that the clinical characteristics of patients who develop PRPA VAP differ from those of patients who develop PSPA VAP. Restricted fluoroquinolone use is the sole independent risk factor for PRPA VAP that is open to medical intervention.

The control of hyperendemic glycopeptide-resistant Enterococcus spp. on a haematology unit by changing antibiotic usage

The rectal carriage of glycopeptide-resistant Enterococcus spp. (GRE) had been established at approximately 50% in a series of prevalence studies on a busy haematological malignancy unit. The aim of this study was to reduce the chance of patients acquiring GRE. A prospective three-phase sequential study was performed. In Phase 1, the acquisition rate of GRE detectable by rectal swab was measured without any intervention for a period of 4 months. For the following 8 months (Phase 2), the first-line treatment for febrile neutropenic episodes was changed from monotherapy with ceftazidime to piperacillin/tazobactam. In addition, an intense education programme was introduced to improve hygiene to reduce the risk of case-to-case spread. In the final 4 months (Phase 3), ceftazidime was again used as the first-line antimicrobial, while continuing the same level of training in relation to hygiene. The carriage of GRE was measured from rectal swabs done weekly. During the initial 4 months, at any time, 40-50% of patients in the unit were colonized with GRE, and 43 of 75 (57%) new patients initially negative for GRE acquired it within 6 weeks of their admission. In Phase 2, 25 patients out of 129 (19%) acquired GRE, with the acquisition rate falling progressively so that in the last 3 months, only one new patient acquired GRE (logrank comparison of probabilities for cohort 1 vs cohort 2b: P < 0.0001). A return to ceftazidime in Phase 3 was associated with a return of the risk of acquiring detectable GRE colonization, despite continued hygiene teaching and surveillance, with 21 out of 58 patients (36%) acquiring GRE (cohort 1 vs cohort 3: P = 0.08). Glycopeptide usage was not reduced during the period of the study. Clinical cases were seen only in Phases 1 and 3. Although the reduction in the risk of acquiring GRE may have been due in part to hygiene practices as well as to the change in antimicrobial usage, or may have occurred spontaneously for other reasons, the return of the problem with the reintroduction of ceftazidime strongly suggests that this antibiotic was responsible for encouraging the acquisition of detectable GRE.

Piperacillin, a new penicillin active against many bacteria resistant to other penicillins

The in vitro activity of piperacillin, a new semisynthetic piperazine penicillin derivative, was evaluated against 626 clinical isolates and compared with the activity of other beta-lactam antibiotics. At a concentration of 0.1 microgram/ml, piperacillin inhibited all streptococci except enterococci. Non-beta-lactamase-producing staphylococci were inhibited by 1.6 microgram or less per ml. Both beta-lactamase- and non-beta-lactamase-producing Haemophilus were inhibited by 0.1 microgram/ml. Piperacillin inhibited non-beta-lactamase-producing Escherichia coli, Salmonella, and Shigella at a concentration of 6.3 micrograms/ml, but 20% of strains of these species containing type III beta-lactamase were not inhibited by 100 micrograms/ml. Piperacillin at 25 micrograms/ml, inhibited 83% of Citrobacter, 58% of Klebsiella, 88% of Enterobacter, and 50% of indole-positive Proteus, Acinetobacter, and Providencia. At 25 micrograms/ml, piperacillin inhibited 95% of Pseudomonas aeruginosa and 78% of Bacteroides fragilis. The minimal inhibitory concentration of piperacillin against Pseudomonas was affected by increasing the inoculum size and by pH. Minimum bactericidal concentrations against Pseudomonas and Serratia often were eightfold greater than the minimum inhibitory concentrations. Piperacillin was equal in activity to ampicillin against enterococci. It was more active than carbenicillin against E. coli, Klebsiella, Enterobacter, and Bacteroides. It was the most active penicillin against Pseudomonas and inhibited many strains of Pseudomonas for which the MICs of carbenicillin were above 200 micrograms/ml. Piperacillin was hydrolyzed by many different beta-lactamases. Synergistic activity of piperacillin was demonstrated when it was combined with amikacin, gentamicin, and cefazolin against P. aeruginosa and members of the Enterobacteriaceae. No antagonism was observed when piperacillin was combined with aminoglycosides; however, antagonism was observed rarely against E. coli when piperacillin was combined with cefazolin.

The synthesis and SAR of rhodanines as novel class C beta-lactamase inhibitors

Beta-lactam antibiotics such as the cephalosporins and penicillins have diminished clinical effectiveness due to the hydrolytic activity of diverse beta-lactamases, especially those in molecular classes A and C. A structure activity relationship (SAR) study of a high-throughput screening lead resulted in the discovery of a potent and selective non-beta-lactam inhibitor of class C beta-lactamases.

Systematic comparison of the population pharmacokinetics and pharmacodynamics of piperacillin in cystic fibrosis patients and healthy volunteers

Respiratory tract infections cause 90% of premature mortality in patients with cystic fibrosis (CF). Treatment of Pseudomonas aeruginosa infection is often very problematic. Piperacillin-tazobactam has good activity against P. aeruginosa, but its pharmacokinetics (PK) in CF patients has not been compared to the PK in healthy volunteers in a controlled clinical study. Therefore, we compared the population PK and pharmacodynamics (PD) of piperacillin between CF patients and healthy volunteers. We studied 8 adult (median age, 20 years) CF patients (average total body weight [WT], 43.1 +/- 7.8 kg) and 26 healthy volunteers (WT, 71.1 +/- 11.8 kg) who each received 4 g piperacillin as a 5-min intravenous infusion. We determined piperacillin levels by high-performance liquid chromatography, and we used NONMEM for population PK and Monte Carlo simulation. We used a target time of nonprotein-bound concentration above the MIC of 50%, which represents near-maximal bacterial killing. Unscaled total clearance was 25% lower, and the volume of distribution was 31% lower in CF patients. Allometric scaling by lean body mass reduced the unexplained (random) between-subject variability in clearance by 26% compared to the variability of linear scaling by WT. A standard dosage regimen of 3 g/70 kg body WT every 4 h as a 30-min infusion (daily dose, 18 g) achieved a robust (> or =90%) probability-of-target attainment (PTA) for MICs of < or =12 mg/liter in CF patients and < or =16 mg/liter in healthy volunteers. Alternative modes of administration allowed a marked dose reduction to 9 g daily. Prolonged (4-h) infusions of 3 g/70 kg WT every 8 h and continuous infusion (daily dose, 9 g), achieved a robust PTA for MICs of < or =16 mg/liter in both groups. Piperacillin achieved PTA expectation values of 64% and 89% against P. aeruginosa infection in CF patients, based on susceptibility data from two German CF clinics.

Evaluation of antibiotic synergy against Acinetobacter baumannii: a comparison with Etest, time-kill, and checkerboard methods

Acinetobacter baumannii is becoming increasingly resistant to antibiotics, often requiring combination therapy. Numerous methods exist to detect the presence of in vitro synergy with the time-kill and checkerboard tests being widely used. The Epsilometer test (E test) is a new method that is less labor intensive, but has not been evaluated using a wide range of antimicrobials and organisms. We assessed synergy using the time-kill and checkerboard tests and compared the results to the E test method using 10 clinical isolates of A. baumannii. Antimicrobial combinations evaluated consisted of trovafloxacin or tobramycin in combination with cefepime or piperacillin. Synergy was detected with all combinations by either the checkerboard or time-kill method. Synergy was not detected by the Etest method. The agreement between the time-kill test and Etest method was 72% (range 42-97%); for the time-kill and checkerboard tests, agreement was 51% (range 30-67%). The Etest method appears promising although further testing should be performed with additional antimicrobial agents and organisms.

Enhanced activity of combination of tobramycin and piperacillin for eradication of sessile biofilm cells of Pseudomonas aeruginosa

An in vitro chemostat system in which Pseudomonas aeruginosa can be cultivated at a slow growth rate and under iron limitation conditions was used to study the susceptibilities of sessile bacteria of mucoid and nonmucoid P. aeruginosa strains to tobramycin and piperacillin. Planktonic cells of both mucoid and nonmucoid P. aeruginosa strains were susceptible to tobramycin and piperacillin. None of the cells was found to be viable after 2 h of exposure to 200 micrograms of piperacillin plus 10 micrograms of tobramycin per ml. Young sessile bacteria were slightly more resistant to piperacillin or tobramycin than the planktonic cells were. However, eradication of young sessile bacteria could be achieved with a combination of piperacillin and tobramycin. None of these young biofilm bacteria were found to be viable after a 2-h exposure to 200 micrograms of piperacillin plus 10 micrograms of tobramycin per ml. Old sessile bacteria were very resistant to these antibiotics. Eradication of old sessile bacteria could not be achieved with either tobramycin (200 micrograms/ml) or piperacillin (200 micrograms/ml) alone. Combination of higher concentrations of tobramycin with piperacillin resulted in an enhancement of killing of the old sessile bacteria. Exposure of old sessile bacteria to 200 micrograms of piperacillin plus 100 micrograms of tobramycin per ml resulted in the reduction of the viable count to approximately 0.02%. The data suggest that the eradication of biofilm-associated infections is best carried out as early as possible. Enhanced activities against the sessile bacteria were achieved when higher concentrations of aminoglycosides were combined with beta-lactam antibiotics.

High-level expression of chromosomally encoded SHV-1 beta-lactamase and an outer membrane protein change confer resistance to ceftazidime and piperacillin-tazobactam in a clinical isolate of Klebsiella pneumoniae

We describe Klebsiella pneumoniae 15571, a clinical isolate resistant to ceftazidime MIC = 32 microg/ml) and piperacillin-tazobactam (MICs = 1,024 and 128 microg/ml). K. pneumoniae 15571 expresses a single beta-lactamase with a pI of 7.6. However, when cloned in a high-copy-number vector in Escherichia coli, this bla(SHV-1) gene did not confer resistance to ceftazidime, a spectrum consistent with the nucleotide sequence, which was nearly identical to those of previously described bla(SHV-1) genes. Outer membrane protein (OMP) analysis of K. pneumoniae 15571 revealed a decrease in the quantity of a minor 45-kDa OMP in comparison to that in K. pneumoniae 44NR, a low-level ampicillin-resistant strain that also expresses a chromosomally determined bla(SHV-1). Crude beta-lactamase enzyme extracts from K. pneumoniae 15571 produced roughly 200-fold more beta-lactamase activity than K. pneumoniae 44NR. Northern hybridization analysis revealed that this difference was explainable by quantifiable differences in transcription of the bla(SHV-1) gene in the two strains. Primer extension analysis of bla(SHV-1) mRNA from K. pneumoniae 15571 and 44NR indicated that the transcriptional start sites were identical in the two strains. DNA sequencing of the promoter regions upstream of the of bla(SHV-1) open reading frames in the two K. pneumoniae strains revealed an A-->C change in the second position of the -10 region in K. pneumoniae 44NR compared to that in 15571. Site-directed mutagenesis of the cloned K. pneumoniae 15571 bla(SHV-1), in which the A in the second position of the 15571 -10 region was changed to a C, resulted in a substantial lowering of the MIC of ampicillin. When the levels of beta-lactamase enzyme expression in E. coli were compared, the bla(SHV-1) downstream of the altered -10 region produced 17-fold less beta-lactamase enzyme. These results indicate that elevated levels of ceftazidime resistance can result from a combination of increased enzyme production and minor OMP changes and that levels of chromosomally encoded SHV-1 beta-lactamase production can vary substantially with a single-base-pair change in promoter sequence.

Induction of beta-lactamase production in Pseudomonas aeruginosa biofilm

Imipenem induced high levels of beta-lactamase production in Pseudomonas aeruginosa biofilms. Piperacillin also induced beta-lactamase production in these biofilms but to a lesser degree. The combination of beta-lactamase production with other protective properties of the biofilm mode of growth could be a major reason for the persistence of this sessile bacterium in chronic infections.

Piperacillin-tazobactam: a beta-lactam/beta-lactamase inhibitor combination

Piperacillin-tazobactam is a beta-lactam/beta-lactamase inhibitor combination with a broad spectrum of antibacterial activity that includes Gram-positive and -negative aerobic and anaerobic bacteria. Piperacillin-tazobactam retains its in vitro activity against broad-spectrum beta-lactamase-producing and some extended-spectrum beta-lactamase-producing Enterobacteriaceae, but not against isolates of Gram-negative bacilli harboring AmpC beta-lactamases. Piperacillin-tazobactam has recently been reformulated to include ethylenediaminetetraacetic acid and sodium citrate; this new formulation has been shown to be compatible in vitro with the two aminoglycosides, gentamicin and amikacin, allowing for simultaneous Y-site infusion, but not with tobramycin. Multicenter, randomized, double-blinded clinical trials have demonstrated piperacillin-tazobactam to be as clinically effective as relevant comparator antibiotics. Clinical trials have demonstrated piperacillin-tazobactam to be effective for the treatment of patients with intra-abdominal infections, skin and soft tissue infections, lower respiratory tract infections, complicated urinary tract infections, gynecological infections and more recently, febrile neutropenia. Piperacillin-tazobactam has an excellent safety and tolerability profile and continues to be a reliable option for the empiric treatment of moderate-to-severe infections in hospitalized patients.

Mass spectrometric characterization of circulating and functional antigens derived from piperacillin in patients with cystic fibrosis

A mechanistic understanding of the relationship between the chemistry of drug Ag formation and immune function is lacking. Thus, mass spectrometric methods were employed to detect and fully characterize circulating Ags derived from piperacillin in patients undergoing therapy and the nature of the drug-derived epitopes on protein that can function as an Ag to stimulate T cells. Albumin modification with piperacillin in vitro resulted in the formation of two distinct haptens, one formed directly from piperacillin and a second in which the dioxopiperazine ring had undergone hydrolysis. Modification was time and concentration dependent, with selective modification of Lys(541) observed at low concentrations, whereas at higher concentrations, up to 13 out of 59 lysine residues were modified, four of which (Lys(190), Lys(195), Lys(432), and Lys(541)) were detected in patients' plasma. Piperacillin-specific T lymphocyte responses (proliferation, cytokines, and granzyme B release) were detected ex vivo with cells from hypersensitive patients, and analysis of incubation medium showed that modification of the same lysine residues in albumin occurred in situ. The antigenicity of piperacillin-modified albumin was confirmed by stimulation of T cells with characterized synthetic conjugates. Analysis of minimally modified T cell-stimulatory albumin conjugates revealed peptide sequences incorporating Lys(190), Lys(432), and Lys(541) as principal functional epitopes for T cells. This study has characterized the multiple haptenic structures on albumin in patients and showed that they constitute functional antigenic determinants for T cells.

Clinical cure of ventilator-associated pneumonia treated with piperacillin/tazobactam administered by continuous or intermittent infusion

The standard mode of administration of piperacillin treatment is by intermittent infusion. However, continuous infusion may be advantageous as beta-lactam antibiotics exhibit time-dependent antibacterial activity. In previous studies, we found a higher rate of clinical cure of ventilator-associated pneumonia (VAP) by continuous infusion rather than intermittent infusion of meropenem and ceftazidime. Therefore, the objective of this historical cohort study was to establish the clinical efficacy of piperacillin/tazobactam (PIP/TAZ) administered by continuous and intermittent infusion in the treatment of VAP in patients without renal failure. Logistic regression analysis showed a higher probability of clinical cure of VAP by continuous compared with intermittent infusion when the microorganism responsible for VAP had a minimum inhibitory concentration (MIC) of 8 microg/mL [8/9 (88.9%) vs. 6/15 (40.0%); odds ratio (OR)=10.79, 95% confidence interval (CI) 1.01-588.24; P=0.049] or 16 microg/mL [7/8 (87.5%) vs. 1/6 (16.7%); OR=22.89, 95% CI 1.19-1880.78; P=0.03]. Thus, administration of PIP/TAZ by continuous infusion may be considered more effective than intermittent infusion for the treatment of VAP caused by Gram-negative bacteria when the MIC of the microorganism responsible for VAP is 8-16 microg/mL in patients without renal failure.

Long-term surveillance of cefotaxime and piperacillin-tazobactam prescribing and incidence of Clostridium difficile diarrhoea

OBJECTIVES

We followed the effects of changes to a new antibiotic policy favouring a ureidopenicillin as opposed to a third-generation cephalosporin on the long-term incidence of Clostridium difficile diarrhoea (CDD) and antibiotic utilization in a large Elderly Medicine Unit.

PATIENTS AND METHODS

In 1999, piperacillin-tazobactam was added to the formulary in Elderly Medicine and its use promoted in preference to cefotaxime. Following review and feedback to clinicians of surveillance data, cefotaxime prescribing was actively restricted during 2000-2001. An audit of prescriber adherence to antibiotic policy was carried out by reviewing the records of 159 patients during February-April 2001. In December 2001, due to manufacturer production problems, supply of piperacillin-tazobactam was stopped. We performed standardized period prevalence surveillance (February-April) allowing comparisons of antibiotic utilization and CDD incidence during the 5 year study period (1998-2002).

RESULTS

CDD incidence did not change significantly (P>0.1) during 1998-1999 despite a marked increase in piperacillin-tazobactam prescribing. However, when cefotaxime prescribing was curtailed in 2001, CDD rates decreased (in four of five wards) and overall by 52% (P=0.008). When piperacillin-tazobactam became unavailable in 2002, despite advice to the contrary cefotaxime prescribing rose five-fold, and CDD rates increased in four of five wards and by 232% (P<0.01) overall. Adherence to antibiotic policy introduced in 2000 was good (81% accordance); 94%, 88% and 73% of patients with cellulitis, urinary tract and respiratory tract infection, respectively, received appropriate antibiotics.

CONCLUSIONS

Long-term prescribing of piperacillin-tazobactam in Elderly Medicine in preference to cefotaxime is associated with reduced rates of CDD. However, unless cephalosporin prescribing is curtailed, the beneficial effects on CDD rates may be missed. This is one of few studies to document adverse effects due to loss of antibiotic supply.

Dynamic interactions of biofilms of mucoid Pseudomonas aeruginosa with tobramycin and piperacillin

The dynamic interaction of planktonic and biofilm cells of mucoid Pseudomonas aeruginosa with tobramycin and piperacillin was investigated in a chemostat system. The results indicated that planktonic and young biofilm cells of the 2-day-old chemostat culture of P. aeruginosa were susceptible to killing by chemostat-controlled doses of either 250 micrograms of piperacillin per ml plus 5 micrograms of tobramycin per ml or 500 micrograms of piperacillin per ml plus 5 micrograms of tobramycin per ml. Complete eradication of the planktonic and young biofilm cells was observed after exposure of the cells to six chemostat-controlled doses of these antibiotic at 8-h intervals for 7 days. Regrowth of the organism was not observed after the termination of antibiotic therapy on day 7. A different picture was observed when antibiotic treatment was initiated on day 10 after inoculation. Viable old biofilm cells were reduced to approximately 20% after exposure to the chemostat-controlled doses of 500 micrograms of piperacillin per ml plus 5 micrograms of tobramycin per ml. Complete eradication of old biofilm cells could not be achieved, and regrowth of the organism occurred after the termination of antibiotic therapy. These data suggest that young biofilm cells of mucoid P. aeruginosa can be effectively eradicated with the combination of piperacillin and tobramycin, while old biofilm cells are very resistant to these antibiotics and eradication of old biofilm cells is not achievable with the chemostat-controlled doses of piperacillin and tobramycin used in this study.

Population pharmacokinetics and pharmacodynamics of piperacillin/tazobactam in patients with complicated intra-abdominal infection

OBJECTIVES

We investigated the population pharmacokinetics and pharmacodynamics of piperacillin and tazobactam in hospitalized patients.

PATIENTS AND METHODS

A multicentre, randomized clinical trial was conducted in hospitalized patients with complicated intra-abdominal infection. Patients received piperacillin/tazobactam administered by either continuous infusion (13.5 g over 24 h, n = 130) or intermittent infusion (3.375 g every 6 h, n = 132). NONMEM was used to perform population pharmacokinetic analysis in a subset of patients (n = 56) who had serum samples obtained at steady-state for drug concentration analyses. Classification and regression tree analysis was used to identify the breakpoints of piperacillin PK-PD indexes in 94 patients with causative pathogen's MIC.

RESULTS

A one-compartment model was applied to fit the data. Creatinine clearance and body weight were the most significant variables to explain patient variability in piperacillin and tazobactam clearance and volume of distribution. The infusion method had no influence on PK parameters. For patients (n = 30) receiving intermittent infusion in the pharmacokinetic study, mean Cmax and half-life were 122.22 mg/L and 1.17 h for piperacillin, and 15.74 mg/L and 1.81 h for tazobactam. For patients (n = 26) receiving continuous infusion in the pharmacokinetic study, mean steady-state concentration was 35.31 +/- 12.15 mg/L for piperacillin and 7.29 +/- 3.28 mg/L for tazobactam. As a result of a low rate of failures (<11%) observed in the trial and the low MICs for infecting pathogens, no association could be established between clinical/microbiological outcome and drug exposure.

CONCLUSIONS

Intermittent infusion and continuous infusion of piperacillin and tazobactam provided sufficient drug exposure to treat those pathogens commonly implicated in intra-abdominal infections.

Unstable Escherichia coli L forms revisited: growth requires peptidoglycan synthesis

Growing bacterial L forms are reputed to lack peptidoglycan, although cell division is normally inseparable from septal peptidoglycan synthesis. To explore which cell division functions L forms use, we established a protocol for quantitatively converting a culture of a wild-type Escherichia coli K-12 strain overnight to a growing L-form-like state by use of the beta-lactam cefsulodin, a specific inhibitor of penicillin-binding proteins (PBPs) 1A and 1B. In rich hypertonic medium containing cefsulodin, all cells are spherical and osmosensitive, like classical L forms. Surprisingly, however, mutant studies showed that colony formation requires d-glutamate, diaminopimelate, and MurA activity, all of which are specific to peptidoglycan synthesis. High-performance liquid chromatography analysis confirmed that these L-form-like cells contain peptidoglycan, with 7% of the normal amount. Moreover, the beta-lactam piperacillin, a specific inhibitor of the cell division protein PBP 3, rapidly blocks the cell division of these L-form-like cells. Similarly, penicillin-induced L-form-like cells, which grow only within the agar layers of rich hypertonic plates, also require d-glutamate, diaminopimelate, and MurA activity. These results strongly suggest that cefsulodin- and penicillin-induced L-form-like cells of E. coli-and possibly all L forms-have residual peptidoglycan synthesis which is essential for their growth, probably being required for cell division.