Principles of Antibiotic Penetration into Abscess Fluid

Heterogeneous host-pathogen encounters: act locally, think globally

Recent studies are revealing astonishing heterogeneity in host-pathogen interactions occurring simultaneously within the same host tissue. As highlighted in this review, growing knowledge of the in vivo complexity is altering our understanding of infection biology. In particular, pathogen subsets reside in diverse tissue microenvironments and detect and respond to local conditions. The individual pathogen-host encounters have disparate outcomes, depending on differential molecular interactions. As a result, disease progression can result from failure to control individual infection foci, despite successful eradication of others, and antibiotic therapy can be delayed by distinct pre-existing pathogen subsets. Together, these data are unraveling rich biology with implications for infectious disease progression and control.

The association between sterilizing activity and drug distribution into tuberculosis lesions

Finding new treatment-shortening antibiotics to improve cure rates and curb the alarming emergence of drug resistance is the major objective of tuberculosis (TB) drug development. Using a MALDI mass spectrometry imaging suite in a biosafety containment facility, we show that the key sterilizing drugs rifampicin and pyrazinamide efficiently penetrate the sites of TB infection in lung lesions. Rifampicin even accumulates in necrotic caseum, a critical lesion site where persisting tubercle bacilli reside¹. In contrast, moxifloxacin which is active in vitro against persisters, a sub-population of Mycobacterium tuberculosis that persists in specific niches under drug pressure, and achieved treatment shortening in mice², does not diffuse well in caseum, concordant with its failure to shorten therapy in recent clinical trials. We also suggest that such differential spatial distribution and kinetics of accumulation in lesions may create temporal and spatial windows of monotherapy in specific niches, allowing the gradual development of multidrug resistant TB. We propose an alternative working model to prioritize new antibiotic regimens based on quantitative and spatial distribution of TB drugs in the major lesion types found in human lungs. The finding that lesion penetration contributes to treatment outcome has wide implications for TB.

Antimicrobial use in critically ill horses

OBJECTIVE

To discuss controversies surrounding antimicrobial use in critically ill horses.

DATA SOURCES

PubMed searches from 1970-present for terms including, but not limited to: "horse," "foal," "antimicrobial," "prophylaxis," "infection," "surgery," "sepsis," and "antimicrobial resistance."

HUMAN DATA SYNTHESIS

Increasing bacterial antimicrobial resistance has changed first-line antimicrobial choices and prompted shortening of the duration of prophylactic and therapeutic treatment. The need to decrease bacterial resistance development to critically important antimicrobials has been highlighted.

VETERINARY DATA SYNTHESIS

Veterinary medicine has followed a similar trend but often without a high-level evidence. Common dilemmas include diseases in which the theoretically most effective drug is a reserved antimicrobial, the inability to differentiate infectious from noninfectious disease, the duration and necessity of prophylactic antimicrobials and use of antimicrobials in primary gastrointestinal disease. These problems are illustrated using examples of purulent infections, neonatal sepsis, colic surgery, and treatment of colitis. Although enrofloxacin, cephalosporins, and doxycycline, in contrast to gentamicin, reach therapeutic concentrations within the lungs of healthy horses, the first two should not be used as first line treatment due to their reserved status. Due to the high risk of bacterial sepsis, antimicrobial treatment remains indispensable in compromised neonatal foals but shortening the length of antimicrobial treatment might be prudent. One prospective randomized study demonstrated no difference between 3 and 5 days of perioperative antimicrobial treatment in colic surgery but shorter durations were not evaluated. High-level evidence to recommend antimicrobial treatment of adult horses with undifferentiated diarrhea does not exist.

CONCLUSIONS

Few evidence-based recommendations can be made. Commonly used antimicrobial combinations remain the mainstay for treating purulent infections. Antimicrobial treatment for compromised foals should not extend beyond recovery. Continuation of prophylactic antimicrobials >3 days is likely unnecessary after colic surgery; shorter durations might be equally effective. Antimicrobial prophylaxis in adult horses with diarrhea is unlikely to be beneficial.

Intra-abscess administration of antibiotics through ultrasound-guided percutaneous catheter for the treatment of pyogenic liver abscess

Pyogenic liver abscess is a potentially life-threatening disease. The treatment of a pyogenic liver abscess usually involves ultrasound guided percutaneous drainage because of the poor penetration of the systemic administration of antibiotics inside the abscess. However, a sizable proportion of patients will necessitate surgical interventions, which involves high peri- and post-operative risks. Theoretically, the local instillation of antibiotics inside the pyogenic liver abscess fluid could achieve a high concentration of the antibiotic for a long period of time. This could be especially beneficial for time-dependent bactericidal antibiotics such as beta-lactams, because their bactericidal effectiveness depends on the amount of time that bacteria are exposed to the antibiotic. We are reporting two patients with complicated pyogenic liver abscesses, who were successfully treated with systemic antibiotics and local instillation of meropenem inside the cavities of the abscesses. These cases suggest that the local instillation of the beta-lactam antibiotics could be an effective and a safe strategy for the treatment of pyogenic liver abscesses that cannot be completely drained through an ultrasound guided percutaneous catheter.

A medicinal chemists' guide to the unique difficulties of lead optimization for tuberculosis

Tuberculosis is a bacterial disease that predominantly affects the lungs and results in extensive tissue pathology. This pathology contributes to the complexity of drug development as it presents discrete microenvironments within which the bacterium resides, often under conditions where replication is limited and intrinsic drug susceptibility is low. This consolidated pathology also results in impaired vascularization that limits access of potential lead molecules to the site of infection. Translating these considerations into a target-product profile to guide lead optimization programs involves implementing unique in vitro and in vivo assays to maximize the likelihood of developing clinically meaningful candidates.

The pharmaco -, population and evolutionary dynamics of multi-drug therapy: experiments with S. aureus and E. coli and computer simulations

There are both pharmacodynamic and evolutionary reasons to use multiple rather than single antibiotics to treat bacterial infections; in combination antibiotics can be more effective in killing target bacteria as well as in preventing the emergence of resistance. Nevertheless, with few exceptions like tuberculosis, combination therapy is rarely used for bacterial infections. One reason for this is a relative dearth of the pharmaco-, population- and evolutionary dynamic information needed for the rational design of multi-drug treatment protocols. Here, we use in vitro pharmacodynamic experiments, mathematical models and computer simulations to explore the relative efficacies of different two-drug regimens in clearing bacterial infections and the conditions under which multi-drug therapy will prevent the ascent of resistance. We estimate the parameters and explore the fit of Hill functions to compare the pharmacodynamics of antibiotics of four different classes individually and in pairs during cidal experiments with pathogenic strains of Staphylococcus aureus and Escherichia coli. We also consider the relative efficacy of these antibiotics and antibiotic pairs in reducing the level of phenotypically resistant but genetically susceptible, persister, subpopulations. Our results provide compelling support for the proposition that the nature and form of the interactions between drugs of different classes, synergy, antagonism, suppression and additivity, has to be determined empirically and cannot be inferred from what is known about the pharmacodynamics or mode of action of these drugs individually. Monte Carlo simulations of within-host treatment incorporating these pharmacodynamic results and clinically relevant refuge subpopulations of bacteria indicate that: (i) the form of drug-drug interactions can profoundly affect the rate at which infections are cleared, (ii) two-drug therapy can prevent treatment failure even when bacteria resistant to single drugs are present at the onset of therapy, and (iii) this evolutionary virtue of two-drug therapy is manifest even when the antibiotics suppress each other's activity.

In this study, we combine pharmacodynamic experiments using pathogenic strains of E. coli and S. aureus with mathematical and computer simulation models to explore the relative efficacies of two-drug antibiotic combinations in clearing infections and preventing the emergence of resistance. We develop a pharmacodynamic method that provides a convenient way to determine whether drug combinations will interact synergistically, antagonistically, additively or suppressively. We find that it is not possible to predict the nature and form of drug interactions based on what is known about the mode of action of individual drugs, thus illustrating the necessity of assessing the efficacy of drug combinations empirically. Our simulations of the within-host population and evolutionary dynamics of bacteria undergoing multi-drug treatment indicate that the form of the interaction between drugs observed experimentally can substantially affect the rate of clearance of the infection. On the other hand, the form of these interactions plays a minimal role in the emergence of resistance. Even when antibiotics are suppressive, two-drug therapy can prevent the ascent of bacteria resistant to single drugs that are present at the start of therapy and/or generated during the course of the infection.

2013 WSES guidelines for management of intra-abdominal infections

Despite advances in diagnosis, surgery, and antimicrobial therapy, mortality rates associated with complicated intra-abdominal infections remain exceedingly high.The 2013 update of the World Society of Emergency Surgery (WSES) guidelines for the management of intra-abdominal infections contains evidence-based recommendations for management of patients with intra-abdominal infections.

Abscess penetration of cefpirome: concentrations and simulated pharmacokinetic profiles in pus

PURPOSE

Abscess patients frequently receive antibiotic therapy when incision cannot be performed or in addition to incision. However, antibiotic concentrations in human abscesses are widely unknown.

METHODS

Pharmacokinetics of cefpirome in 12 human abscesses located in different body regions was studied. Cefpirome (2 g) was administered as an intravenous short infusion, and concentrations were measured in plasma over an 8-h period and in abscesses at incision. A pharmacokinetic two-stage model was applied.

RESULTS

At abscess incision performed 158 ± 112 min after the start of the infusion, the cefpirome concentrations in the abscess fluid varied markedly, ranging from ≤0.1 (limit of quantification) to 47 (mean 8.4 ± 14.1 ) mg/L. Cefpirome was detectable in nine of 12 abscesses. Maximum concentrations were calculated to be 183 ± 106 mg/L in plasma and 12 ± 16 mg/L in the abscess. A cefpirome concentration of 2 mg/L, which is the minimum concentration inhibiting growth of 90% of the most relevant bacterial pathogens, was exceeded spontaneously in six of 12 abscesses after a single dose. Cefpirome concentrations in the abscess did not correlate with either the pH or the ratio of surface area to volume of the abscesses, nor with plasma pharmacokinetics.

CONCLUSIONS

Cefpirome may be useful to treat abscess patients because it was detectable in most abscesses after a single dose. However, the penetration of cefpirome into abscesses is extremely variable and cannot be predicted by measuring other available covariates.

Particle-size dependent effects in the Balb/c murine model of inhalational melioidosis

Deposition of Burkholderia pseudomallei within either the lungs or nasal passages of the Balb/c murine model resulted in different infection kinetics. The infection resulting from the inhalation of B. pseudomallei within a 12 μm particle aerosol was prolonged compared to a 1 μm particle aerosol with a mean time-to-death (MTD) of 174.7 ± 14.9 h and 73.8 ± 11.3 h, respectively. Inhalation of B. pseudomallei within 1 μm or 12 μm particle aerosols resulted in a median lethal dose (MLD) of 4 and 12 cfu, respectively. The 12 μm particle inhalational infection was characterized by a marked involvement of the nasal mucosa and extension of bacterial colonization and inflammatory lesions from the olfactory epithelium through the olfactory nerves (or tracts) to the olfactory bulb (100%), culminating in abscessation of the brain (33%). Initial involvement of the upper respiratory tract lymphoid tissues (nasal-associated lymphoid tissue (NALT) and cervical lymph nodes) was observed in both the 1 and 12 μm particle inhalational infections (80-85%). Necrotising alveolitis and bronchiolitis were evident in both inhalational infections, however, lung pathology was greater after inhalation of the 1 μm particle aerosol with pronounced involvement of the mediastinal lymph node (50%). Terminal disease was characterized by bacteraemia in both inhalational infections with dissemination to the spleen, liver, kidneys, and thymus. Treatment with co-trimoxazole was more effective than treatment with doxycycline irrespective of the size of the particles inhaled. Doxycycline was more effective against the 12 μm particle inhalational infection as evidenced by increased time to death. However, both treatment regimes exhibited significant relapse when therapy was discontinued with massive enlargement and abscessation of the lungs, spleen, and cervical lymph nodes observed.

Pharmacokinetic evaluation of the penetration of antituberculosis agents in rabbit pulmonary lesions

Standard antituberculosis (anti-TB) therapy requires the use of multiple drugs for a minimum of 6 months, with variable outcomes that are influenced by a number of microbiological, pathological, and clinical factors. This is despite the availability of antibiotics that have good activity against Mycobacterium tuberculosis in vitro and favorable pharmacokinetic profiles in plasma. However, little is known about the distribution of widely used antituberculous agents in the pulmonary lesions where the pathogen resides. The rabbit model of TB infection was used to explore the hypothesis that standard drugs have various abilities to penetrate lung tissue and lesions and that adequate drug levels are not consistently reached at the site of infection. Using noncompartmental and population pharmacokinetic approaches, we modeled the rate and extent of distribution of isoniazid, rifampin, pyrazinamide, and moxifloxacin in rabbit lung and lesions. Moxifloxacin reproducibly showed favorable partitioning into lung and granulomas, while the exposure of isoniazid, rifampin, and pyrazinamide in lesions was markedly lower than in plasma. The extent of penetration in lung and lesions followed different trends for each drug. All four agents distributed rapidly from plasma to tissue with equilibration half-lives of less than 1 min to an hour. The models adequately described the plasma concentrations and reasonably captured actual lesion concentrations. Though further refinement is needed to accurately predict the behavior of these drugs in human subjects, our results enable the integration of lesion-specific pharmacokinetic-pharmacodynamic (PK-PD) indices in clinical trial simulations and in in vitro PK-PD studies with M. tuberculosis.

Two cases of monomicrobial intraabdominal abscesses due to KPC--3 Klebsiella pneumoniae ST258 clone

BACKGROUND

Knowledge of the etiology of pyogenic liver and pancreatic abscesses is an important factor in determining the success of combined surgical and antibiotic treatment. Literature shows geographical variations in the prevalence and distribution of causative organisms, and the spread of Klebsiella pneumoniae carbapenemase-producing bacteria is an emerging cause of abdominal infections.

CASE PRESENTATION

We herein describe two cases of intra-abdominal abscesses due to monomicrobial infection by Klebsiella pneumoniae Sequence Type 258 producing K. pneumoniae carbapenemase 3 (KPC-Kp). In case 1, a 50-year-old HIV-negative Italian woman with chronic pancreatitis showed infection of a pancreatic pseudocystic lesion caused by KPC-Kp. In case 2, a 64-year-old HIV-negative Italian woman with pancreatic neoplasm and liver metastases developed a liver abscess due to KPC after surgery. Both women were admitted to our hospital but to different surgical units. The clonal relationship between the two isolates was investigated by pulsed-field gel electrophoresis (PFGE). In case 2, the patient was already colonized at admission and inter-hospital transmission of the pathogen was presumed. A long-term combination regimen of colistin with tigecycline and percutaneous drainage resulted in full recovery and clearance of the multidrug-resistant (MDR) pathogen.

CONCLUSIONS

Timely microbiological diagnosis, the combined use of new and old antibiotics and radiological intervention appeared to be valuable in managing these serious conditions. The emergence and dissemination of MDR organisms is posing an increasing challenge for physicians to develop new therapeutic strategies and control and prevention frameworks.

Adaptation and antibiotic tolerance of anaerobic Burkholderia pseudomallei

The Gram-negative bacterium Burkholderia pseudomallei is the etiological agent of melioidosis and is remarkably resistant to most classes of antibacterials. Even after months of treatment with antibacterials that are relatively effective in vitro, there is a high rate of treatment failure, indicating that this pathogen alters its patterns of antibacterial susceptibility in response to cues encountered in the host. The pathology of melioidosis indicates that B. pseudomallei encounters host microenvironments that limit aerobic respiration, including the lack of oxygen found in abscesses and in the presence of nitric oxide produced by macrophages. We investigated whether B. pseudomallei could survive in a nonreplicating, oxygen-deprived state and determined if this physiological state was tolerant of conventional antibacterials. B. pseudomallei survived initial anaerobiosis, especially under moderately acidic conditions similar to those found in abscesses. Microarray expression profiling indicated a major shift in the physiological state of hypoxic B. pseudomallei, including induction of a variety of typical anaerobic-environment-responsive genes and genes that appear specific to anaerobic B. pseudomallei. Interestingly, anaerobic B. pseudomallei was unaffected by antibacterials typically used in therapy. However, it was exquisitely sensitive to drugs used against anaerobic pathogens. After several weeks of anaerobic culture, a significant loss of viability was observed. However, a stable subpopulation that maintained complete viability for at least 1 year was established. Thus, during the course of human infection, if a minor subpopulation of bacteria inhabited an oxygen-restricted environment, it might be indifferent to traditional therapy but susceptible to antibiotics frequently used to treat anaerobic infections.

High-sensitivity MALDI-MRM-MS imaging of moxifloxacin distribution in tuberculosis-infected rabbit lungs and granulomatous lesions

MALDI-MSI is a powerful technology for localizing drug and metabolite distributions in biological tissues. To enhance our understanding of tuberculosis (TB) drug efficacy and how efficiently certain drugs reach their site of action, MALDI-MSI was applied to image the distribution of the second-line TB drug moxifloxacin at a range of time points after dosing. The ability to perform multiple monitoring of selected ion transitions in the same experiment enabled extremely sensitive imaging of moxifloxacin within tuberculosis-infected rabbit lung biopsies in less than 15 min per tissue section. Homogeneous application of a reference standard during the matrix spraying process enabled the ion-suppressing effects of the inhomogeneous lung tissue to be normalized. The drug was observed to accumulate in granulomatous lesions at levels higher than that in the surrounding lung tissue from 1.5 h postdose until the final time point. MALDI-MSI moxifloxacin distribution data were validated by quantitative LC/MS/MS analysis of lung and granuloma extracts from adjacent biopsies taken from the same animals. Drug distribution within the granulomas was observed to be inhomogeneous, and very low levels were observed in the caseum in comparison to the cellular granuloma regions. In this experiment the MALDI-MRM-MSI method was shown to be a rapid and sensitive method for analyzing the distribution of anti-TB compounds and will be applied to distribution studies of additional drugs in the future.

WSES consensus conference: Guidelines for first-line management of intra-abdominal infections

Intra-abdominal infections are still associated with high rate of morbidity and mortality.A multidisciplinary approach to the management of patients with intra-abdominal infections may be an important factor in the quality of care. The presence of a team of health professionals from various disciplines, working in concert, may improve efficiency, outcome, and the cost of care.A World Society of Emergency Surgery (WSES) Consensus Conference was held in Bologna on July 2010, during the 1st congress of the WSES, involving surgeons, infectious disease specialists, pharmacologists, radiologists and intensivists with the goal of defining recommendations for the early management of intra-abdominal infections.This document represents the executive summary of the final guidelines approved by the consensus conference.

Clinical pharmacology and lesion penetrating properties of second- and third-line antituberculous agents used in the management of multidrug-resistant (MDR) and extensively-drug resistant (XDR) tuberculosis

Failure of first-line chemotherapy to cure tuberculosis (TB) patients occurs, in part, because of the development of resistance to isoniazid (INH) and rifampicin (RIF) the two most sterilizing agents in the four-drug regimen used to treat primary infections. Strains resistant to both INH and RIF are termed multidrug-resistant (MDR). Treatment options for MDR patients involve a complex array of twenty different drugs only two classes of which are considered to be highly effective (fluoroquinolones and aminoglycosides). Resistance to these two classes results in strains known as extensively drug-resistant (XDR) and these types of infections are becoming increasingly common. Many of the remaining agents have poorly defined pharmacology but nonetheless are widely used in the treatment of this disease. Several of these agents are known to have highly variable exposures in healthy volunteers and little is known in the patients in which they must be used. Therapeutic drug monitoring (TDM) is infrequently used in the management of MDR or XDR disease yet the clinical pharmacokinetic studies that have been done suggest this might have a large impact on disease outcome. We review what is known about the pharmacologic properties of each of the major classes of second- and third-line antituberculosis agents and suggest where judicious use of TDM would have the maximum possible impact. We summarize the state of knowledge of drug-drug interactions (DDI) in these classes of agents and those that are currently in clinical trials. Finally we consider what little is known about the ability of TB drugs to reach their ultimate site of action--the interior of a granuloma by penetrating the diseased lung area. Careful consideration of the pharmacology of these agents is essential if we are to avoid further fueling the growing epidemic of highly drug-resistant TB and critical in the development of new antituberculosis drugs.

Detection and treatment options for Klebsiella pneumoniae carbapenemases (KPCs): an emerging cause of multidrug-resistant infection

Bacteria producing Klebsiella pneumoniae carbapenemases (KPCs) are rapidly emerging as a cause of multidrug-resistant infections worldwide. Bacterial isolates harbouring these enzymes are capable of hydrolysing a broad spectrum of beta-lactams including the penicillins, cephalosporins, carbapenems and monobactam. Detection of isolates harbouring carbapenemases can be inconsistent using automated systems, often requiring subsequent confirmatory tests. Phenotypic methods utilizing boronic acid disc tests have demonstrated promising results and appear practical for use in clinical microbiology laboratories. Treatment of infection caused by KPC bacteria is particularly worrisome as the carbapenems are often agents of the last resort for resistant Gram-negative infections. The optimal treatment of infections caused by KPC bacteria is not well established and clinical outcome data remain sparse. We reviewed the current literature regarding clinical outcomes following KPC infections, with a specific effort to summarize the clinical data available for specific antimicrobial agents. A total of 15 papers involving 55 unique patient cases were reviewed. While the total number of patients is relatively small, some useful insights could still be gathered to guide clinicians in the management of KPC infections. Tigecycline and the aminoglycosides were associated with positive outcomes in the majority of cases. Clinical success rates were low when the polymyxins were used as monotherapy, but were much higher when they were used in combination. Studies examining combination therapy and well-controlled clinical trials are needed to ascertain the optimal treatment of infections caused by KPC bacteria.

The spectrum of latent tuberculosis: rethinking the biology and intervention strategies

Immunological tests provide evidence of latent tuberculosis in one third of the global population, which corresponds to more than two billion individuals. Latent tuberculosis is defined by the absence of clinical symptoms but carries a risk of subsequent progression to clinical disease, particularly in the context of co-infection with HIV. In this Review we discuss the biology of latent tuberculosis as part of a broad range of responses that occur following infection with Mycobacterium tuberculosis, which result in the formation of physiologically distinct granulomatous lesions that provide microenvironments with differential ability to support or suppress the persistence of viable bacteria. We then show how this model can be used to develop a rational programme to discover effective drugs for the eradication of M. tuberculosis infection.

Capnocytophaga cynodegmi in a rottweiler dog with severe bronchitis and foreign-body pneumonia

Capnocytophaga cynodegmi is a zoonotic, gram-negative, capnophilic bacterium that is usually seen in people with infections associated with dog or cat bites. The first reported case of C. cynodegmi infection in a dog is described here.

Plasminogen activator, but not systemic antibiotic therapy, prevents abscess formation in an experimental model of secondary peritonitis

Background

Intra-abdominal abscesses are sources of recurrent or ongoing abdominal sepsis. They are an important target for prevention and treatment during or after surgical treatment of peritonitis. Experimental data suggest that fibrinolytic therapy may be effective when antibiotics are not.

Methods

Peritonitis was induced via intra-abdominal injection of a faeces and bacteria mixture in male Wistar rats. Surgical debridement was performed after 1 h. Next to untreated controls, animals were treated with antibiotics (ceftriaxone plus metronidazole), recombinant tissue plasminogen activator (rtPA) or both. Abdominal fluid samples were taken at 24, 72 and 120 h for interleukin 6, interleukin 10 and tumour necrosis factor α measurements and cell counts. After 5 days the abdomen was inspected for the presence of abscesses.

Results

Antibiotics did not significantly affect abscess formation. However, giving rtPA significantly reduced the number of rats with abscesses and the abscess load per rat, both in the absence and presence of concomitant antibiotic therapy. No adverse side-effects were observed and no meaningful differences in the local inflammatory response were found.

Conclusion

In this rat model, rtPA consistently reduced abscess formation after surgical treatment of secondary peritonitis. It therefore represents a promising adjuvant to conventional therapy.