Synergy between amoxicillin and gentamicin in combination against a highly penicillin-resistant and -tolerant strain of Streptococcus pneumoniae in a mouse pneumonia model

Critical role of growth medium for detecting drug interactions in Gram-negative bacteria that model in vivo responses

The rise in infections caused by multidrug-resistant (MDR) bacteria has necessitated a variety of clinical approaches, including the use of antibiotic combinations. Here, we tested the hypothesis that drug-drug interactions vary in different media, and determined which in vitro models best predict drug interactions in the lungs. We systematically studied pair-wise antibiotic interactions in three different media, CAMHB, (a rich lab medium standard for antibiotic susceptibility testing), a urine mimetic medium (UMM), and a minimal medium of M9 salts supplemented with glucose and iron (M9Glu) with three Gram-negative ESKAPE pathogens, Acinetobacter baumannii (Ab), Klebsiella pneumoniae (Kp), and Pseudomonas aeruginosa (Pa). There were pronounced differences in responses to antibiotic combinations between the three bacterial species grown in the same medium. However, within species, PaO1 responded to drug combinations similarly when grown in all three different media, whereas Ab17978 and other Ab clinical isolates responded similarly when grown in CAMHB and M9Glu medium. By contrast, drug interactions in Kp43816, and other Kp clinical isolates poorly correlated across different media. To assess whether any of these media were predictive of antibiotic interactions against Kp in the lungs of mice, we tested three antibiotic combination pairs. In vitro measurements in M9Glu, but not rich medium or UMM, predicted in vivo outcomes. This work demonstrates that antibiotic interactions are highly variable across three Gram-negative pathogens and highlights the importance of growth medium by showing a superior correlation between in vitro interactions in a minimal growth medium and in vivo outcomes.

IMPORTANCE

Drug-resistant bacterial infections are a growing concern and have only continued to increase during the SARS-CoV-2 pandemic. Though not routinely used for Gram-negative bacteria, drug combinations are sometimes used for serious infections and may become more widely used as the prevalence of extremely drug-resistant organisms increases. To date, reliable methods are not available for identifying beneficial drug combinations for a particular infection. Our study shows variability across strains in how drug interactions are impacted by growth conditions. It also demonstrates that testing drug combinations in tissue-relevant growth conditions for some strains better models what happens during infection and may better inform combination therapy selection.

Pharmacokinetics and relative bioavailability of an oral amoxicillin-apramycin combination in pigs

A new compound granular premix of amoxicillin (20% w/w dry mass)/apramycin (5% w/w dry mass) was developed, and its pharmacokinetics and relative bioavailability were determined in pigs following oral administration following a cross-over study design. The pharmacokinetic parameters of amoxicillin (t1/2λ = 6.43 ± 4.85h, Cmax = 3.2 ± 1.35 μg·mL-1, Tmax = 1.92 ± 0.58, AUCINF = 8.98 ± 2.11 h·μg·mL-1) and apramycin (t1/2λ = 8.67±4.4h, Cmax = 0.23 ± 0.12 μg·mL-1, Tmax = 2.25 ± 0.82 h, AUCINF = 12.37 ± 8.64h·μg·mL-1) when administered as the amoxicillin-apramycin granular premix did not significantly differ from those for the single-ingredient powder form of each component. The relative bioavailability of amoxicillin following oral administration of the amoxicillin-apramycin granular premix was 22.62% when compared to the intramuscular administration of commercial amoxicillin sodium-powder. This is the first report of a new amoxicillin-apramycin combination which has a potential veterinary application the for prevention and treatment digestive tract infections in pigs.

Clinical findings and management of patients with meningitis with an emphasis on Haemophilus influenzae meningitis in rural Tanzania

INTRODUCTION

The spectrum of meningitis pathogens differs depending on the age of patients and the geographic region, amongst other. Although meningitis vaccination programs have led to the reduction of incidence rates, an imbalance between low- and high-income countries still exists.

METHODS

In a hospital-based study in rural northern Tanzania, we consecutively recruited patients with confirmed meningitis and described their clinical and laboratory characteristics.

RESULTS

A total of 136 patients with meningitis were included. Fever (85%), meningism (63%) and impairment of consciousness (33%) were the most frequent clinical symptoms/signs. Nearly 10% of all patients tested were positive for malaria. The majority of the patients with bacterial meningitis (39%), especially those under 5years of age, were confirmed to be infected with Haemophilus influenzae (26%), Streptococcus pneumoniae (19%) and Neisseria meningitidis (15%). Haemophilus influenzae represented the dominant causative organism in children under 2years of age.

CONCLUSION

Our study emphasizes the importance of recognizing warning symptoms like fever, meningism and impairment of consciousness, implementing laboratory tests to determine responsible pathogens and evaluating differential diagnoses in patients with meningitis in sub-Saharan Africa. It also shows that Haemophilus influenza meningitis is still an important cause for meningitis in the young, most probabaly due to lack of appropriate vaccination coverage.

Medical treatment of prosthetic vascular graft infections: Review of the literature and proposals of a Working Group

More than 400000 vascular grafts are inserted annually in the USA. Graft insertion is complicated by infection in 0.5-4% of cases. Vascular graft infections (VGIs) are becoming one of the most frequent prosthesis-related infections and are associated with considerable mortality, ranging from 10 to 25% within 30 days following the diagnosis. Treatment of VGI is based on urgent surgical removal of the infected graft followed by prolonged antibiotherapy. Data regarding the best antibiotherapy to use are lacking since no well designed trial to study antimicrobial treatment of VGI exists. Moreover, since VGIs demonstrate very specific pathophysiology, guidelines on other material-related infections or infective endocarditis treatment cannot be entirely applied to VGI. A French multidisciplinary group gathering infectious diseases specialists, anaesthesiologists, intensivists, microbiologists, radiologists and vascular surgeons was created to review the literature dealing with VGI and to make some proposals regarding empirical and documented antibiotic therapy for these infections. This article reveals these proposals.

Antimicrobial treatment of febrile neutropenia: pharmacokinetic-pharmacodynamic considerations

Patients with cancer or hematologic diseases are particularly at risk of infection leading to high morbidity, mortality and costs. Extensive data show that optimization of the administration of antimicrobials according to their pharmacokinetic and pharmacodynamic parameters improves clinical outcome. Evidence is growing that when pharmacokinetic and pharmacodynamic parameters are used to target not only clinical cure but also eradication, the selection resistance is also contained. This is of particular importance in patients with neutropenia in whom increasing rates of drug-resistant Gram-negative bacteria have been reported, particularly Pseudomonas aeruginosa. Based on experimental and clinical studies, pharmacokinetic and pharmacodynamic parameters are discussed in this review for each antibiotic used in febrile neutropenia in order to help physicians improve dosing and optimization of antimicrobial agents.

An alternate pathophysiologic paradigm of sepsis and septic shock: implications for optimizing antimicrobial therapy

The advent of modern antimicrobial therapy following the discovery of penicillin during the 1940s yielded remarkable improvements in case fatality rate of serious infections including septic shock. Since then, pathogens have continuously evolved under selective antimicrobial pressure resulting in a lack of significant improvement in clinical effectiveness in the antimicrobial therapy of septic shock despite ever more broad-spectrum and potent drugs. In addition, although substantial effort and money has been expended on the development novel non-antimicrobial therapies of sepsis in the past 30 years, clinical progress in this regard has been limited. This review explores the possibility that the current pathophysiologic paradigm of septic shock fails to appropriately consider the primacy of the microbial burden of infection as the primary driver of septic organ dysfunction. An alternate paradigm is offered that suggests that has substantial implications for optimizing antimicrobial therapy in septic shock. This model of disease progression suggests the key to significant improvement in the outcome of septic shock may lie, in great part, with improvements in delivery of existing antimicrobials and other anti-infectious strategies. Recognition of the role of delays in administration of antimicrobial therapy in the poor outcomes of septic shock is central to this effort. However, therapeutic strategies that improve the degree of antimicrobial cidality likely also have a crucial role.

Combination therapy for treatment of infections with gram-negative bacteria

Combination antibiotic therapy for invasive infections with Gram-negative bacteria is employed in many health care facilities, especially for certain subgroups of patients, including those with neutropenia, those with infections caused by Pseudomonas aeruginosa, those with ventilator-associated pneumonia, and the severely ill. An argument can be made for empiric combination therapy, as we are witnessing a rise in infections caused by multidrug-resistant Gram-negative organisms. The wisdom of continued combination therapy after an organism is isolated and antimicrobial susceptibility data are known, however, is more controversial. The available evidence suggests that the greatest benefit of combination antibiotic therapy stems from the increased likelihood of choosing an effective agent during empiric therapy, rather than exploitation of in vitro synergy or the prevention of resistance during definitive treatment. In this review, we summarize the available data comparing monotherapy versus combination antimicrobial therapy for the treatment of infections with Gram-negative bacteria.

The human milk protein-lipid complex HAMLET sensitizes bacterial pathogens to traditional antimicrobial agents

The fight against antibiotic resistance is one of the most significant challenges to public health of our time. The inevitable development of resistance following the introduction of novel antibiotics has led to an urgent need for the development of new antibacterial drugs with new mechanisms of action that are not susceptible to existing resistance mechanisms. One such compound is HAMLET, a natural complex from human milk that kills Streptococcus pneumoniae (the pneumococcus) using a mechanism different from common antibiotics and is immune to resistance-development. In this study we show that sublethal concentrations of HAMLET potentiate the effect of common antibiotics (penicillins, macrolides, and aminoglycosides) against pneumococci. Using MIC assays and short-time killing assays we dramatically reduced the concentrations of antibiotics needed to kill pneumococci, especially for antibiotic-resistant strains that in the presence of HAMLET fell into the clinically sensitive range. Using a biofilm model in vitro and nasopharyngeal colonization in vivo, a combination of HAMLET and antibiotics completely eradicated both biofilms and colonization in mice of both antibiotic-sensitive and resistant strains, something each agent alone was unable to do. HAMLET-potentiation of antibiotics was partially due to increased accessibility of antibiotics to the bacteria, but relied more on calcium import and kinase activation, the same activation pathway HAMLET uses when killing pneumococci by itself. Finally, the sensitizing effect was not confined to species sensitive to HAMLET. The HAMLET-resistant respiratory species Acinetobacter baumanii and Moraxella catarrhalis were all sensitized to various classes of antibiotics in the presence of HAMLET, activating the same mechanism as in pneumococci. Combined these results suggest the presence of a conserved HAMLET-activated pathway that circumvents antibiotic resistance in bacteria. The ability to activate this pathway may extend the lifetime of the current treatment arsenal.

Antimicrobial therapy of sepsis and septic shock--when are two drugs better than one?

In clinical practice, physicians frequently use combination therapy despite the conflicting evidence for its effectiveness. The results of recent studies have contributed to our understanding of this important issue. In this article, we examine the evidence for, or against, the use of combination drug therapy compared with monotherapy in the management of serious infections, sepsis, and septic shock.

Early combination antibiotic therapy yields improved survival compared with monotherapy in septic shock: a propensity-matched analysis

BACKGROUND

Septic shock represents the major cause of infection-associated mortality in the intensive care unit. The possibility that combination antibiotic therapy of bacterial septic shock improves outcome is controversial. Current guidelines do not recommend combination therapy except for the express purpose of broadening coverage when resistant pathogens are a concern.

OBJECTIVE

To evaluate the therapeutic benefit of early combination therapy comprising at least two antibiotics of different mechanisms with in vitro activity for the isolated pathogen in patients with bacterial septic shock.

DESIGN

Retrospective, propensity matched, multicenter, cohort study.

SETTING

Intensive care units of 28 academic and community hospitals in three countries between 1996 and 2007.

SUBJECTS

A total of 4662 eligible cases of culture-positive, bacterial septic shock treated with combination or monotherapy from which 1223 propensity-matched pairs were generated.

MEASUREMENTS AND MAIN RESULTS

The primary outcome of study was 28-day mortality. Using a Cox proportional hazards model, combination therapy was associated with decreased 28-day mortality (444 of 1223 [36.3%] vs. 355 of 1223 [29.0%]; hazard ratio, 0.77; 95% confidence interval, 0.67-0.88; p = .0002). The beneficial impact of combination therapy applied to both Gram-positive and Gram-negative infections but was restricted to patients treated with beta-lactams in combination with aminoglycosides, fluoroquinolones, or macrolides/clindamycin. Combination therapy was also associated with significant reductions in intensive care unit (437 of 1223 [35.7%] vs. 352 of 1223 [28.8%]; odds ratio, 0.75; 95% confidence interval, 0.63-0.92; p = .0006) and hospital mortality (584 of 1223 [47.8%] vs. 457 of 1223 [37.4%]; odds ratio, 0.69; 95% confidence interval, 0.59-0.81; p < .0001). The use of combination therapy was associated with increased ventilator (median and [interquartile range], 10 [0-25] vs. 17 [0-26]; p = .008) and pressor/inotrope-free days (median and [interquartile range], 23 [0-28] vs. 25 [0-28]; p = .007) up to 30 days.

CONCLUSION

Early combination antibiotic therapy is associated with decreased mortality in septic shock. Prospective randomized trials are needed.

A survival benefit of combination antibiotic therapy for serious infections associated with sepsis and septic shock is contingent only on the risk of death: a meta-analytic/meta-regression study

OBJECTIVE

To assess whether a potential benefit with combination antibiotic therapy is restricted to the most critically ill subset of patients, particularly those with septic shock.

DATA SOURCES

OVID MEDLINE (1950-October 2009), EMBASE (1980-October 2009), the Cochrane Central Register of Controlled Trials (to third quarter 2009), the ClinicalTrial.gov database, and the SCOPUS database.

STUDY SELECTION

Randomized or observational studies of antimicrobial therapy of serious bacterial infections potentially associated with sepsis or septic shock. Fifty studies met entry criteria.

DATA EXTRACTION

Study design, mortality/clinical response, and other variables were extracted independently by two reviewers. When possible, study datasets were split into mutually exclusive groups with and without shock or critical illness.

DATA SYNTHESIS

Although a pooled odds ratio indicated no overall mortality/clinical response benefit with combination therapy (odds ratio, 0.856; 95% confidence interval, 0.71-1.03; p = .0943; I = 45.1%), stratification of datasets by monotherapy mortality risk demonstrated substantial benefit in the most severely ill subset (monotherapy risk of death >25%; odds ratio of death, 0.51; 95% confidence interval, 0.41-0.64; I = 8.6%). Of those datasets that could be stratified by the presence of shock/critical illness, the more severely ill group consistently demonstrated increased efficacy of a combination therapy strategy (odds ratio, 0.49; 95% confidence interval, 0.35-0.70; p < .0001; I = 0%). An increased risk of death was found in low-risk patients (risk of death <or=15% in the monotherapy arm) exposed to combination therapy (odds ratio, 1.53; 95% confidence interval, 1.16-2.03; p = .003; I = 8.2%). Meta-regression indicated that efficacy of combination therapy was dependent only on the risk of death in the monotherapy group.

CONCLUSION

Combination antibiotic therapy improves survival and clinical response of high-risk, life-threatening infections, particularly those associated with septic shock but may be detrimental to low-risk patients.

Amoxicillin is effective against penicillin-resistant Streptococcus pneumoniae strains in a mouse pneumonia model simulating human pharmacokinetics

High-dose oral amoxicillin (3 g/day) is the recommended empirical outpatient treatment of community-acquired pneumonia (CAP) in many European guidelines. To investigate the clinical efficacy of this treatment in CAP caused by Streptococcus pneumoniae strains with MICs of amoxicillin > or =2 microg/ml, we used a lethal bacteremic pneumonia model in leukopenic female Swiss mice with induced renal failure to replicate amoxicillin kinetics in humans given 1 g/8 h orally. Amoxicillin (15 mg/kg of body weight/8 h subcutaneously) was given for 3 days. We used four S. pneumoniae strains with differing amoxicillin susceptibility and tolerance profiles. Rapid bacterial killing occurred with an amoxicillin-susceptible nontolerant strain: after 4 h, blood cultures were negative and lung homogenate counts under the 2 log(10) CFU/ml detection threshold (6.5 log(10) CFU/ml in controls, P < 0.01). With an amoxicillin-intermediate nontolerant strain, significant pulmonary bacterial clearance was observed after 24 h (4.3 versus 7.9 log(10) CFU/ml, P < 0.01), and counts were undetectable 12 h after treatment completion. With an amoxicillin-intermediate tolerant strain, 24-h bacterial clearance was similar (5.4 versus 8.3 log(10) CFU/ml, P < 0.05), but 12 h after treatment completion, lung homogenates contained 3.3 log(10) CFU/ml. Similar results were obtained with an amoxicillin-resistant and -tolerant strain. Day 10 survival rates were usually similar across strains. Amoxicillin with pharmacokinetics simulating 1 g/8 h orally in humans is bactericidal in mice with pneumonia due to S. pneumoniae for which MICs were 2 to 4 microg/ml. The killing rate depends not only on resistance but also on tolerance of the S. pneumoniae strains.

Antibiothérapie des pneumonies aiguës communautaires à Streptococcus pneumoniae : impact clinique de la résistance bactérienne

The emergence of Streptococcus pneumoniae strains with reduced susceptibility to beta-lactams and with multiple drug resistance has not led to major changes in recommendations for antibiotic therapy in patients with acute community-acquired pneumococcal pneumonia. Numerous factors explain the limited clinical impact of this major microbiological change. The frequency of intermediate strains is high but the frequency of resistant strains to beta-lactams is very low. There is a complex relation between the acquisition of resistance to beta-lactams and the decreased virulence of S. pneumoniae strains. The only finding in studies of humanized experimental animal models of lethal bacteremic pneumonia caused by resistance and tolerant strains was a slowing in the kinetics of beta-lactams bactericidal activity, especially for amoxicillin. Taken together, this preclinical data shows that microbiological resistance of pneumococci to beta-lactams has very little influence on a possible failure of recommanded treatment regimens for pneumococcal pneumonia. The high rate of multiple drug resistance, particularly among beta-lactam resistant strains, rules out the probabilistic use of macrolides. Conversely, fluoroquinolone (FQ) resistance remains low, inferior to 3%, and the same is true for ketolides (<1%). Only a global strategy of patient management in the use of these new drugs could ensure their long-term activity. The high mortality rate of hospitalized S. pneumoniae pneumonia will only be improved with a better understanding of the complex host-bacteria interactions.

Pulmonary damage and bacterial load in assessment of the efficacy of simulated human treatment-like amoxicillin (2,000 milligrams) therapy of experimental pneumococcal pneumonia caused by strains for which amoxicillin MICs differ

An experimental rat pneumonia model using two amoxicillin-susceptible (MICs, < or =0.015 and 2 microg/ml) and two non-amoxicillin-susceptible (MIC, 4 microg/ml) Streptococcus pneumoniae strains was developed for testing the efficacy of amoxicillin administered to simulate human serum kinetics after treatment with amoxicillin-clavulanate (2,000 and 125 mg, respectively, twice a day, for 2.5 days). The end points for efficacy were reductions in bacterial loads in the lungs and reductions in levels of pulmonary damage. For the amoxicillin-susceptible strains (serotypes 23F and 14), a decrease greater than 4.5 log(10) CFU/pair of lungs was obtained, and the time for which the serum antibiotic concentration (SAC) was higher than the MIC (T(S)(A)(C)(>)(MIC)) was greater than 60% of the dosing interval. For non-amoxicillin-susceptible strains, the decrease in bacterial load was 1.34 to 1.75 log(10) CFU/pair of lungs, with a T(S)(A)(C)(>)(MIC) of 46.7% of the dosing interval. An in vitro study showed that serotype 9V non-amoxicillin-susceptible strains behaved as tolerant-like to concentrations similar to those in the in vivo model. The high and maintained SACs (T(S)(A)(C)(>)(MIC), >46% for all strains) significantly diminished lung injury (affected area of the lung and lung weight), compared to that in controls, by all strains, regardless of the MIC, bactericidal behavior in in vitro killing curves, or the serotype of the infecting strain. These results show the importance of host therapeutic end points in the evaluation of antibiotic efficacy. The antibiotic was more efficacious, for one nonsusceptible strain tested, when the treatment was started early (1 h postinoculation [p.i.]) than when treatment was delayed (24 h p.i.).

Re-evaluation of the therapy of severe pneumonia caused by Streptococcus pneumoniae

Pneumonia caused by Streptococcus pneumoniae is the most deadly form of community-acquired pneumonia. The death rate of bacteremic pneumococcal pneumonia has remained constant over the past 50 years. Several retrospective reviews of bacteremic pneumococcal pneumonia suggest that dual therapy with a beta-lactam and a macrolide antimicrobial agent is associated with a lower case fatality rate than therapy with a beta-lactam alone. These studies are reviewed, potential mechanisms are suggested, and future studies are discussed.

Treatment of drug-resistant pneumococcal pneumonia

The increasing prevalence of resistance to penicillin and other drugs among pneumococci has considerably complicated the empirical treatment of community-acquired pneumonia. Penicillin resistance has become widespread and is a worldwide occurrence. Resistance to other classes of antibiotics traditionally used as alternatives in the treatment of pneumococcal infections has also increased markedly during recent years. In some areas of the USA, Europe, and east Asia a prevalence of macrolide resistance as high as 35% or more has been reported recently. From the clinical standpoint, a growing number of failures following the use of these agents has been described. Resistance to fluoroquinolones remains low but several failures have been reported in different parts of the world. Pharmacokinetic/pharmacodynamic parameters have become essential at the time of making a rational choice and calculation of dosage. Penicillin G remains the mainstay of therapy for the treatment of penicillin-susceptible pneumococcal pneumonia. Penicillin-resistant pneumococcal pneumonia (minimum inhibitory concentration <4 microg/mL) can be safely treated with adequate betalactams at the right dosage. The new fluoroquinolones are very active and effective in pneumococcal pneumonia. Caution should be exercised in the widespread prescription of these drugs if we are to limit the rate of resistance to these agents.

Comparative in-vitro activity of penicillin alone and combined with gentamicin against clinical isolates of Streptococcus pneumoniae with decreased susceptibility to penicillin

The worldwide emergence of Streptococcus pneumoniae with decreased susceptibility to penicillin has led to the suggestion that drug combinations might be used. The aim of this study was to determine possible synergy using a combination of penicillin with sub-inhibitory doses of gentamicin against 26 clinical isolates of S. pneumoniae with decreased susceptibility to penicillin, using half-chequerboards and killing curves. Synergy was demonstrated for ten of the 26 isolates with the combination of penicillin with gentamicin at 1 mg/l and for 22 isolates with penicillin and gentamicin at 2 mg/l. Killing curves on three isolates showed synergy and confirmed the chequerboard results. Further synergy studies using penicillin or cefotaxime/ceftriaxone, plus low dose gentamicin against penicillin-resistant pneumococci are indicated.

Gentamicin increases the efficacy of vancomycin against penicillin-resistant pneumococci in the rabbit meningitis model

In experimental meningitis a single dose of gentamicin (10 mg/kg of body weight) led to gentamicin levels in around cerebrospinal fluid (CSF) of 4 mg/liter for 4 h, decreasing slowly to 2 mg/liter 4 h later. The CSF penetration of gentamicin ranged around 27%, calculated by comparison of areas under the curve (AUC in serum/AUC in CSF). Gentamicin monotherapy (-1.24 log(10) CFU/ml) was inferior to vancomycin monotherapy (-2.54 log(10) CFU/ml) over 8 h against penicillin-resistant pneumococci. However, the combination of vancomycin with gentamicin was significantly superior (-4.48 log(10) CFU/ml) compared to either monotherapy alone. The synergistic activity of vancomycin combined with gentamicin was also demonstrated in vitro in time-kill assays.

Streptococcus pneumoniae in community-acquired pneumonia. How important is drug resistance?

Patients hospitalized with community-acquired pneumonia caused by S. pneumoniae strains with intermediate susceptibility to penicillin according to the conventional definition respond well to treatment with adequate doses of beta-lactam antibiotics. All studies currently available comparing mortality between patients with pneumonia caused by nonsusceptible and susceptible pneumococci agree that resistance of MIC 2 mg/L is not associated independently with an increased mortality. Most but not all studies could not prove an effect of microbial resistance on morbidity. There are data suggesting, however, that pneumococcal pneumonia caused by highly resistant strains (MIC > or = 4 mg/L) does affect the outcome. Pneumococcal resistance remains a matter of concern. Most reports show an increase not only of resistance rates, but also of the proportion of highly resistant strains. The selection of initial empirical antimicrobial treatment of patients with community-acquired pneumonia should be performed judiciously. Because the serum and pulmonary levels achieved with penicillin or related drugs are several times higher than the MICs of most strains, pneumonias caused by S. pneumoniae currently defined as not susceptible to penicillin should respond well to treatment with a beta-lactam antibiotic, used in optimal doses. Consequently, there is no reason fundamentally to change the current approach to initial empiric antimicrobial treatment of patients with community-acquired pneumonia. Nevertheless, increases in resistance to macrolides may prompt a limited use of these drugs in the outpatient setting. In any case, treatment failures may occur at higher levels of resistance, and a change in the definition of susceptibility categories toward higher cutoffs for S. pneumoniae seems to be reasonable.

Limiting the spread of resistant pneumococci: biological and epidemiologic evidence for the effectiveness of alternative interventions

Streptococcus pneumoniae infections are a leading cause of respiratory illness in young children, the elderly, and persons with chronic medical conditions. The emergence of multidrug-resistant pneumococci has compromised the effectiveness of antibiotic therapy for pneumococcal infections. As antibiotic-resistant strains increase in prevalence, there is a need for interventions that minimize the spread of resistant pneumococci. In this review we provide a framework for understanding the spread of pneumococcal resistance and evaluate proposed interventions to reduce this spread. Pneumococci differ from many drug-resistant pathogens because asymptomatic carriers play a key role in transmission of resistant strains and the genes encoding resistance are spread primarily by transformation and conjugative transposons. Evidence suggests that modifications of treatment regimens that have proved effective at limiting resistance in other pathogens may not prevent the spread of pneumococcal resistance. In contrast, programs encouraging more judicious antibiotic use have been shown to be effective. Additionally, a newly developed conjugate pneumococcal vaccine holds great potential as an "antiresistance vaccine" that simultaneously reduces the burden of invasive disease and the prevalence of resistant strains. Several areas of future epidemiologic and laboratory research hold promise to contribute to the reduced spread of pneumococcal resistance.

Limiting the spread of resistant pneumococci: biological and epidemiologic evidence for the effectiveness of alternative interventions

Streptococcus pneumoniae infections are a leading cause of respiratory illness in young children, the elderly, and persons with chronic medical conditions. The emergence of multidrug-resistant pneumococci has compromised the effectiveness of antibiotic therapy for pneumococcal infections. As antibiotic-resistant strains increase in prevalence, there is a need for interventions that minimize the spread of resistant pneumococci. In this review we provide a framework for understanding the spread of pneumococcal resistance and evaluate proposed interventions to reduce this spread. Pneumococci differ from many drug-resistant pathogens because asymptomatic carriers play a key role in transmission of resistant strains and the genes encoding resistance are spread primarily by transformation and conjugative transposons. Evidence suggests that modifications of treatment regimens that have proved effective at limiting resistance in other pathogens may not prevent the spread of pneumococcal resistance. In contrast, programs encouraging more judicious antibiotic use have been shown to be effective. Additionally, a newly developed conjugate pneumococcal vaccine holds great potential as an "antiresistance vaccine" that simultaneously reduces the burden of invasive disease and the prevalence of resistant strains. Several areas of future epidemiologic and laboratory research hold promise to contribute to the reduced spread of pneumococcal resistance.

Development of a new experimental model of penicillin-resistant Streptococcus pneumoniae pneumonia and amoxicillin treatment by reproducing human pharmacokinetics

The increase of penicillin-resistant Streptococcus pneumoniae (PRSP) pneumonia results in a greater risk of antibiotic treatment failure. In vitro data are not sufficient predictors of clinical efficacy, and animal models may be insufficiently contributive, since they often use immunocompromised animals and do not always respect the human pharmacokinetics of antibiotics. We developed an experimental PRSP pneumonia model in immunocompetent rabbits, by using intrabronchial instillation of PRSP (MIC = 4 mg/liter), without any adjuvant. This reproducible model was used to assess amoxicillin efficacy by reproducing human serum pharmacokinetics following 1-g oral or intravenous administrations of amoxicillin every 8 h. Evaluation was performed by using clinical, CT scan, macroscopic, histopathologic, and microbiological criteria. Experimental pneumonia in untreated rabbits was similar to untreated severe human bacteremic untreated pneumonia; in both rabbits and humans, (i) cumulative survival was close to 50%, (ii) red or gray lung congestion and pleuritis were observed, and (iii) lung and spleen concentrations reached 5 and 4 log(10) CFU/g. A 48-h treatment resulted in a significant bacterial clearance in the lungs (1.53 versus 5.07 log(10) CFU/ml, P < 0.001) and spleen (1.00 versus 4.40 log(10) CFU/ml, P < 10(-6)) and a significant decrease in mortality (0% versus 50%, P = 0.02) in treated versus untreated rabbits. No difference was observed on macroscopic and histopathologic lesions between treated and untreated rabbits (P = 0.36 and 0.78, respectively). Similar results were obtained by using a fully penicillin-susceptible S. pneumoniae strain (MIC = 0.01 mg/liter). Our findings suggest that (i) this new model can be contributive in the evaluation of antibacterial agents and (ii) 1 g of amoxicillin three times a day may be sufficient to treat PRSP pneumonia in immunocompetent humans.

The antibacterial efficacy of trovafloxacin against an experimental infection with Listeria monocytogenes in hydrocortisone-treated mice

The efficacy of trovafloxacin in treating Listeria monocytogenes infections in glucocorticosteroid-treated mice was compared with the efficacy of amoxycillin. Swiss mice were treated with daily injections of 2.5 mg hydrocortisone s.c. and then infected i.v. with 1 x 10(7) cfu of L. monocytogenes. Untreated, this level of infection resulted in 100% mortality between day 3 and day 5 after infection. Both s.c. trovafloxacin and amoxycillin were effective in reducing the number of viable L. monocytogenes in the liver and spleen. Although the MIC of amoxycillin for this isolate of L. monocytogenes was lower than that of trovafloxacin (0.063 mg/L versus 0.5 mg/L, respectively), trovafloxacin was more efficacious in vivo after a single dose in the dose range between 12.5 and 100 mg/kg than was amoxycillin. After treatment with trovafloxacin at 100 mg/kg bodyweight od for 3 days, a mean log10 cfu of 1.58 and 2.52 L. monocytogenes could be recovered from the spleens and livers, respectively, whereas after treatment with amoxycillin at 100 mg/kg bodyweight every 8 h for 3 days, the mean 1og10 cfu values were 2.36 and 2.02, respectively. These differences were statistically not significant. Results of the present study show that the antibacterial efficacy of trovafloxacin against L. monocytogenes in our animal model is equivalent to that of amoxycillin.