High incidence of methicillin-resistant Staphylococcus aureus sepsis and death in patients with febrile neutropenia at Royal Darwin Hospital

Interleukin-33 facilitates neutrophil recruitment and bacterial clearance in S. aureus-caused peritonitis

Interleukin (IL)-33, a newly recognized member of IL-1 family of cytokines, plays an important role in polarizing Th2-associated immunity. Recently growing evidence indicates that IL-33 also represents a crucial mediator of antimicrobial infection. In this study, we investigated the effect of IL-33 on antibacterial response using an acute Staphylococcus aureus peritoneal infection model. Our results showed that IL-33 administration induced a rapid bacterial clearance and markedly reduced the S. aureus infection-related mortality. IL-33-treated mice displayed increased neutrophil influx into the focus of infection and higher concentrations of chemokine CXCL2 in the peritoneum than untreated mice. The beneficial effect of IL-33 priming was related to reversal of the S. aureus-induced reduction of CXCR2 expression on the surface of neutrophils. Furthermore, conditioning of neutrophils by IL-33 led to the enhancement of complement receptor 3 expression induced by S. aureus, which in turn facilitates the phagocytosis of opsonized S. aureus. Finally, neutrophils primed by IL-33 upregulated the production of reactive oxygen species and the subsequent killing activity for S. aureus. All together, these findings suggest that IL-33, through regulating multiple steps of neutrophil-mediated bactericidal function, provides a profound effect in host antimicrobial defense response.

The challenge of antibiotic resistance in haematology patients

Bacterial infections were once a major obstacle to the treatment of acute leukaemia. Improvement in management strategies, including the use of broad-spectrum antibacterial drugs targeting Gram-negative bacteria, has reduced the mortality in neutropenic patients developing blood stream infections and other severe infections. In many countries these achievements are threatened by development of multi-resistant bacteria, such as Klebsiella pneumoniae, Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus. This review addresses the epidemiology, clinical importance and possible management of these multi-resistant organisms.

Bacterial infections in hematopoietic stem cell transplantation recipients

PURPOSE OF REVIEW

Bacterial infections are among the most frequent complications of hematopoietic stem cell transplant (HSCT). This review describes current epidemiology and management of bacterial infections.

RECENT FINDINGS

Multidrug resistant (MDR) bacteria are increasingly frequent in HSCT recipients, but significant differences in etiology of bacterial infections and prevalence of resistant strains exist between different transplant centers. Methicillin-resistant coagulase-negative staphylococci, extended-spectrum beta-lactamase-producing Enterobacteriaceae, vancomycin-resistant enterococci and MDR Pseudomonas aeruginosa are the most relevant examples. Infection control measures are mandatory to limit the spread of resistant strains. Selective digestive decontamination is controversial and potentially associated with inducing resistance to antibiotics that might be the last treatment option, such as colistin or aminoglycosides. Empirical therapy should be individualized, and an escalation or de-escalation approach should be chosen depending on local epidemiology, colonization and clinical presentation. Antimicrobial stewardship, with the aim of improving management of bacterial infections, should be put in place in transplant units.

SUMMARY

Bacterial infections in the transplant population warrant currently particular attention to limit the negative impact of infections caused by resistant strains.

Bacterial Infections in Hematopoietic Stem Cell Transplant Recipients

Bacterial infections are major complications after Hematopoietic Stem Cell Transplant (HSCT). They consist mainly of bloodstream infections (BSI), followed by pneumonia and gastrointestinal infections, including typhlitis and Clostridium difficile infection. Microbiological data come mostly from BSI. Coagulase negative staphylococci and Enterobacteriaceae are the most frequent pathogens causing approximately 25% of BSI each, followed by enterococci, P. aeruginosa and viridans streptococci. Bacterial pneumonia is frequent after HSCT, and Gram-negatives are predominant. Clostridium difficile infection affects approximately 15% of HSCT recipients, being more frequent in case of allogeneic than autologous HSCT. The epidemiology and the prevalence of resistant strains vary significantly between transplant centres. In some regions, multi-drug resistant (MDR) Gram-negative rods are increasingly frequent. In others, vancomycin-resistant enterococci are predominant. In the era of increasing resistance to antibiotics, the efficacy of fluoroquinolone prophylaxis and standard treatment of febrile neutropenia have been questioned. Therefore, a thorough evaluation of local epidemiology is mandatory to decide the need for prophylaxis and the choice of the best regimen for empirical treatment of febrile neutropenia. For the latter, individualised approach has been proposed, consisting of either escalation or de-escalation strategy. De-escalation strategy is recommended since resistant bacteria should be covered upfront, mainly in patients with severe clinical presentation and previous infection or colonisation with a resistant pathogen. Non-pharmacological interventions, such as screening for resistant bacteria, applying isolation and contact precautions should be put in place to limit the spread of MDR bacteria. Antimicrobial stewardship program should be implemented in transplant centres.

Infection control issues in patients with haematological malignancies in the era of multidrug-resistant bacteria

Drug-resistant Gram-negative and Gram-positive bacteria are now increasingly identified as a cause of infections in immunocompromised hosts. Bacteria identified include the multidrug-resistant (MDR) and even pandrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa, as well as carbapenem-resistant Enterobacteriaceae spp. The threat from MDR pathogens has been well-documented in the past decade with warnings about the consequences of inappropriate use of antimicrobial drugs. Resistant bacteria can substantially complicate the treatment of infections in critically ill patients and can have a substantial effect on mortality. Inappropriate antimicrobial treatment can affect morbidity, mortality, and overall health-care costs. Evidence-based data for prevention and control of MDR pathogen infections in haematology are scarce. Although not yet established a bundle of infection control and prevention measures with an anti-infective stewardship programme is an important strategy in infection control, diagnosis, and antibiotic selection with optimum regimens to ensure a successful outcome for patients.

Applying Convergent Immunity to Innovative Vaccines Targeting Staphylococcus aureus

Recent perspectives forecast a new paradigm for future “third generation” vaccines based on commonalities found in diverse pathogens or convergent immune defenses to such pathogens. For Staphylococcus aureus, recurring infections and a limited success of vaccines containing S. aureus antigens imply that native antigens induce immune responses insufficient for optimal efficacy. These perspectives exemplify the need to apply novel vaccine strategies to high-priority pathogens. One such approach can be termed convergent immunity, where antigens from non-target organisms that contain epitope homologs found in the target organism are applied in vaccines. This approach aims to evoke atypical immune defenses via synergistic processes that (1) afford protective efficacy; (2) target an epitope from one organism that contributes to protective immunity against another; (3) cross-protect against multiple pathogens occupying a common anatomic or immunological niche; and/or (4) overcome immune subversion or avoidance strategies of target pathogens. Thus, convergent immunity has a potential to promote protective efficacy not usually elicited by native antigens from a target pathogen. Variations of this concept have been mainstays in the history of viral and bacterial vaccine development. A more far-reaching example is the pre-clinical evidence that specific fungal antigens can induce cross-kingdom protection against bacterial pathogens. This trans-kingdom protection has been demonstrated in pre-clinical studies of the recombinant Candida albicans agglutinin-like sequence 3 protein (rAls3) where it was shown that a vaccine containing rAls3 provides homologous protection against C. albicans, heterologous protection against several other Candida species, and convergent protection against several strains of S. aureus. Convergent immunity reflects an intriguing new approach to designing and developing vaccine antigens and is considered here in the context of vaccines to target S. aureus.

Where does a Staphylococcus aureus vaccine stand?

In this review, we examine the current status of Staphylococcus aureus vaccine development and the prospects for future vaccines. Examination of the clinical trials to date show that murine models have not predicted success in humans for active or passive immunization. A key factor in the failure to develop a vaccine to prevent S. aureus infections comes from our relatively limited knowledge of human protective immunity. More recent reports on the elements of the human immune response to staphylococci are analysed. In addition, there is some controversy concerning the role of antibodies for protecting humans, and these data are reviewed. From a review of the current state of understanding of staphylococcal immunity, a working model is proposed. Some new work has provided some initial candidate biomarker(s) to predict outcomes of invasive infections and to predict the efficacy of antibiotic therapy in humans. We conclude by looking to the future through the perspective of lessons gleaned from the clinical vaccine trials.

Multidrug-resistant bacteria: what is the threat?

Despite big advances in antimicrobial therapies and infection strategies, the emergence of antibiotic resistance represents an emergency situation, especially in immunocompromised hosts. Specifically, infections due to multidrug resistant, gram-negative pathogens are responsible for high mortality rates and may leave few effective antimicrobial options. Furthermore, although new compounds are available for severe methicillin-resistant staphylococcal infections, there is a paucity of novel classes of antimicrobials to target resistant gram-negatives. A careful assessment of the clinical conditions and underlying comorbidities, along with knowledge about the previous history of colonization or infections due to multidrug-resistant bacteria, represent key points in approaching the hematological patient with signs of infection. A de-escalation therapy with initial use of wide-spectrum antimicrobials followed by a reassessment after 72 hours of treatment may represent a good option in severe infections if a resistant pathogen is suspected. Prompt empiric or targeted therapy using combination regimens (ie, antipseudomonal beta-lactam plus an aminoglycoside or a quinolone) with the addition of colistin, along with increased dosage and therapeutic drug monitoring, represent options for these life-threatening infections. Continuous epidemiological surveillance of local bacteremias is necessary, along with stringent enforcement of antibiotic stewardship programs in cancer patients.

Recent changes in bacteremia in patients with cancer: a systematic review of epidemiology and antibiotic resistance

Bacteremia remains a major cause of life-threatening complication in patients with cancer. Significant changes in the spectrum of microorganisms isolated from blood culture have been reported in cancer patients over the past years. The aim of our systematic review was to inventory the recent trends in epidemiology and antibiotic resistance of microorganisms causing bacteremia in cancer patients. Data for this review was identified by searches of Medline, Scopus and Cochrane Library for indexed articles and abstracts published in English since 2008. The principal search terms were: "antimicrobial resistance", "bacteremia", "bacterial epidemiology", "bloodstream infection", "cancer patients", "carbapenem resistance", "Escherichia coli resistance", "extended-spectrum β-lactamase producing E. coli", "febrile neutropenia", "fluoroquinolone resistance", "neutropenic cancer patient", "vancomycin-resistant Enterococcus", and "multidrug resistance". Boolean operators (NOT, AND, OR) were also used in succession to narrow and widen the search. Altogether, 27 articles were selected to be analyzed in the review. We found that Gram-negative bacteria were the most frequent pathogen isolated, particularly in studies with minimal use of antibiotic prophylaxis. Another important trend is the extensive emergence of antimicrobial-resistant strains associated with increased risk of morbidity, mortality and cost. This increasing incidence of antibiotic resistance has been reported in Gram-negative bacteria as well as in Gram-positive bacteria. This exhaustive review, reporting the recent findings in epidemiology and antibiotic resistance of bacteremia in cancer patients, highlights the necessity of local continuous surveillance of bacteremia and stringent enforcement of antibiotic stewardship programs in cancer patients.

There should be no ESKAPE for febrile neutropenic cancer patients: the dearth of effective antibacterial drugs threatens anticancer efficacy

The success of modern anticancer treatment is a composite function of enhanced efficacy of surgical, radiation and systemic treatment strategies and of our collective clinical abilities in supporting patients through the perils of their cancer journeys. Despite the widespread availability of antibacterial therapies, the threat of community- or healthcare facility-acquired bacterial infection remains a constant risk to patients during this journey. The rising prevalence of colonization by multidrug-resistant (MDR) bacteria in the population, acquired through exposure from endemic environments, antimicrobial stewardship and infection prevention and control strategies notwithstanding, increases the likelihood that such organisms may be the cause of cancer treatment-related infection and the likelihood of antibacterial treatment failure. The high mortality associated with invasive MDR bacterial infection increases the likelihood that many patients may not survive long enough to reap the benefits of enhanced anticancer treatments, thus threatening the societal investment in the cancer journey. Since cancer care providers arguably no longer have, and are unlikely to have in the foreseeable future, the antibacterial tools to reliably rescue patients from harm's way, the difficult ethical debate over the risks and benefits of anticancer treatments must now be reopened.