Mortality and clinical cure rates for pneumonia: A systematic review, meta-analysis, and trial sequential analysis of randomized control trials comparing bactericidal and bacteriostatic antibiotic treatments

How to approach a patient hospitalized for pneumonia who is not responding to treatment?

Pneumonia is a frequent cause of intensive care unit (ICU) admission and is the most common infection in ICU patients across all geographic regions. It takes 48-72h for most patients to respond to appropriate antibiotic therapy. Non-response is typically defined as the persistence/worsening of clinical signs-such as fever, respiratory distress, impaired oxygenation and/or radiographic abnormalities-with rates ranging 20-30%. Several factors can contribute to non-response. Host factors, including immunosuppression, chronic lung disease, or ongoing aspiration, may impair resolution. Additionally, incorrect antibiotic dosing, atypical or resistant pathogens (such as multidrug-resistant bacteria, Mycobacterium tuberculosis, or fungal infections) may be responsible, requiring alternative antimicrobial strategies. A septic complication related to pneumonia (e.g., empyema) or not (e.g., acalculous cholecystitis) may need to be excluded. Finally, non-infectious conditions (e.g., pulmonary embolism, malignancy, secondary ARDS or vasculitis) that can mimic or potentiate pneumonia must be considered. Although non-responding pneumonia is frequent, its management lacks strong evidence, and its approach is based mostly on the art of medicine and clinical judgement. Clinicians should continuously reassess the medical history and physical exam, review microbiological data, and consider imaging such as chest CT. Bronchoscopy or repeat sputum sampling may aid in identifying alternative pathogens or non-infectious causes. The management of a non-responding pneumonia depends on the findings of a structured reassessment. Herein, we provide guidance on how to identify and manage non-responding pneumonia. Ultimately, addressing pneumonia that does not respond to antibiotics is crucial for preventing complications, optimizing antimicrobial stewardship, and improving patient outcomes.

Bactericidal versus bacteriostatic antibacterials: clinical significance, differences and synergistic potential in clinical practice

Antibacterial activity can be classified as either bactericidal or bacteriostatic, using methods such as the MBC/MIC ratio and time-kill curves. However, such categorization has proven challenging in clinical practice, as these definitions only apply under specific laboratory conditions, which may differ from clinical settings. Several factors, such as the specific bacteria or infectious medium, can affect the action of antibiotics, with many antibacterials exerting both activities. These definitions have also led to the belief that bactericidal antibacterials are superior to bacteriostatic, especially in more severe cases, such as endocarditis, neutropenia and bacteraemia. Additionally, current dogma dictates against the combination of bactericidal and bacteriostatic antibacterials in clinical practice, due to potential antagonism. This review aimed to assess the differences in antibacterial activity of bactericidal and bacteriostatic antibacterials based on in vitro and in vivo studies and examine their antagonistic or synergistic effects. Our findings show that specific bacteriostatic agents, such as linezolid and tigecycline, are clinically non-inferior to bactericidals in multiple infections, including pneumonia, intra-abdominal infections, and skin and soft tissue infections. Studies also support using several bacteriostatic agents as salvage therapies in severe infections, such as neutropenic fever and endocarditis. Additionally, not all combinations of bacteriostatic and bactericidal agents appear to be antagonistic, with many combinations, such as linezolid and rifampicin, already being used. The findings should be interpreted with caution, as most evidence is from observational studies and there is a need for randomized controlled trials to assess their effectiveness and combinations, especially within the context of rising antimicrobial resistance.

Antioxidant and Pro-Oxidant Properties of Selected Clinically Applied Antibiotics: Therapeutic Insights

BACKGROUND

The balance between antioxidants and pro-oxidants plays a significant role in the context of oxidative stress, influenced by both physiological and non-physiological factors.

OBJECTIVES

In this study, 18 prescribed antibiotics (including doxycycline hydrochloride, tigecycline, rifampicin, tebipenem, cefuroxime, cefixime, potassium clavulanate, colistin, ampicillin, amoxicillin, amikacin, nalidixic acid, azithromycin, pipemidic acid trihydrate, pivmecillinam, aztreonam, fosfomycin sodium, and ciprofloxacin) were subjected to simultaneous determination of antioxidant and pro-oxidant potential to assess if pro-oxidant activity is a dominant co-mechanism of antibacterial activity or if any antibiotic exhibits a balanced effect.

METHODS

This study presents a recently developed approach for the simultaneous assessment of antioxidant and pro-oxidant potential on a single microplate in situ, applied to prescribed antibiotics.

RESULTS

Ten antibiotics from eighteen showed lower antioxidant or pro-oxidant potential, while five exhibited only mild potential with DPPH50 values over 0.5 mM. The pro-oxidant antioxidant balance index (PABI) was also calculated to determine whether antioxidant or pro-oxidant activity was dominant for each antibiotic. Surprisingly, three antibiotics-doxycycline hydrochloride, tigecycline, and rifampicin-showed significant measures of both antioxidant and pro-oxidant activities. Especially notable was tebipenem, a broad-spectrum, orally administered carbapenem, showed a positive PABI index ratio, indicating a dominant antioxidant over pro-oxidant effect.

CONCLUSIONS

These findings could be significant for both therapy, where the antibacterial effect is enhanced by radical scavenging activity, and biotechnology, where substantial pro-oxidant activity might limit microbial viability in cultures and consequently affect yield.

Identifying the Best Initial Oral Antibiotics for Adults with Community-Acquired Pneumonia: A Network Meta-Analysis

BACKGROUND

The objective of this network meta-analysis was to compare rates of clinical response and mortality for empiric oral antibiotic regimens in adults with mild-moderate community-acquired pneumonia (CAP).

METHODS

We searched PubMed, Cochrane, and the reference lists of systematic reviews and clinical guidelines. We included randomized trials of adults with radiologically confirmed mild to moderate CAP initially treated orally and reporting clinical cure or mortality. Abstracts and studies were reviewed in parallel for inclusion in the analysis and for data abstraction. We performed separate analyses by antibiotic medications and antibiotic classes and present the results through network diagrams and forest plots sorted by p-scores. We assessed the quality of each study using the Cochrane Risk of Bias framework, as well as global and local inconsistency.

RESULTS

We identified 24 studies with 9361 patients: six at low risk of bias, six at unclear risk, and 12 at high risk. Nemonoxacin, levofloxacin, and telithromycin were most likely to achieve clinical response (p-score 0.79, 0.71, and 0.69 respectively), while penicillin and amoxicillin were least likely to achieve clinical response. Levofloxacin, nemonoxacin, azithromycin, and amoxicillin-clavulanate were most likely to be associated with lower mortality (p-score 0.85, 0.75, 0.74, and 0.68 respectively). By antibiotic class, quinolones and macrolides were most effective for clinical response (0.71 and 0.70 respectively), with amoxicillin-clavulanate plus macrolides and beta-lactams being less effective (p-score 0.11 and 0.22). Quinolones were most likely to be associated with lower mortality (0.63). All confidence intervals were broad and partially overlapping.

CONCLUSION

We observed trends toward a better clinical response and lower mortality for quinolones as empiric antibiotics for CAP, but found no conclusive evidence of any antibiotic being clearly more effective than another. More trials are needed to inform guideline recommendations on the most effective antibiotic regimens for outpatients with mild to moderate CAP.

Specific Antimicrobial Activities Revealed by Comparative Evaluation of Selected Gemmotherapy Extracts

Nowadays, unprecedented health challenges are urging novel solutions to address antimicrobial resistance as multidrug-resistant strains of bacteria, yeasts and moulds are emerging. Such microorganisms can cause food and feed spoilage, food poisoning and even more severe diseases, resulting in human death. In order to overcome this phenomenon, it is essential to identify novel antimicrobials that are naturally occurring, biologically effective and increasingly safe for human use. The development of gemmotherapy extracts (GTEs) using plant parts such as buds and young shoots has emerged as a novel approach to treat/prevent human conditions due to their associated antidiabetic, anti-inflammatory and/or antimicrobial properties that all require careful evaluations. Seven GTEs obtained from plant species like the olive (Olea europaea L.), almond (Prunus amygdalus L.), black mulberry (Morus nigra L.), walnut (Juglans regia L.), blackberry (Rubus fruticosus L.), blackcurrant (Ribes nigrum L.) and bilberry (Vaccinium myrtillus L.) were tested for their antimicrobial efficiency via agar diffusion and microbroth dilution methods. The antimicrobial activity was assessed for eight bacterial (Bacillus cereus, Staphylococcus aureus, Salmonella enterica subsp. enterica, Proteus vulgaris, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Listeria monocytogenes), five moulds (Aspergillus flavus, Aspergillus niger, Aspergillus ochraceus, Penicillium citrinum, Penicillium expansum) and one yeast strain (Saccharomyces cerevisiae). The agar diffusion method revealed the blackberry GTE as the most effective since it inhibited the growth of three bacterial, four moulds and one yeast species, having considered the total number of affected microorganism species. Next to the blackberry, the olive GTE appeared to be the second most efficient, suppressing five bacterial strains but no moulds or yeasts. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were then determined for each GTE and the microorganisms tested. Noticeably, the olive GTE appeared to feature the strongest bacteriostatic and bactericidal outcome, displaying specificity for S. aureus, E. faecalis and L. monocytogenes. The other GTEs, such as blueberry, walnut, black mulberry and almond (the list indicates relative strength), were more effective at suppressing microbial growth than inducing microbial death. However, some species specificities were also evident, while the blackcurrant GTE had no significant antimicrobial activity. Having seen the antimicrobial properties of the analysed GTEs, especially the olive and black mulberry GTEs, these could be envisioned as potential antimicrobials that might enhance antibiotic therapies efficiency, while the blackberry GTE would act as an antifungal agent. Some of the GTE mixtures analysed have shown interesting antimicrobial synergies, and all the antimicrobial effects observed argue for extending these studies to include pathological microorganisms.

A stochastic analysis of the interplay between antibiotic dose, mode of action, and bacterial competition in the evolution of antibiotic resistance

The use of an antibiotic may lead to the emergence and spread of bacterial strains resistant to this antibiotic. Experimental and theoretical studies have investigated the drug dose that minimizes the risk of resistance evolution over the course of treatment of an individual, showing that the optimal dose will either be the highest or the lowest drug concentration possible to administer; however, no analytical results exist that help decide between these two extremes. To address this gap, we develop a stochastic mathematical model of bacterial dynamics under antibiotic treatment. We explore various scenarios of density regulation (bacterial density affects cell birth or death rates), and antibiotic modes of action (biostatic or biocidal). We derive analytical results for the survival probability of the resistant subpopulation until the end of treatment, the size of the resistant subpopulation at the end of treatment, the carriage time of the resistant subpopulation until it is replaced by a sensitive one after treatment, and we verify these results with stochastic simulations. We find that the scenario of density regulation and the drug mode of action are important determinants of the survival of a resistant subpopulation. Resistant cells survive best when bacterial competition reduces cell birth and under biocidal antibiotics. Compared to an analogous deterministic model, the population size reached by the resistant type is larger and carriage time is slightly reduced by stochastic loss of resistant cells. Moreover, we obtain an analytical prediction of the antibiotic concentration that maximizes the survival of resistant cells, which may help to decide which drug dosage (not) to administer. Our results are amenable to experimental tests and help link the within and between host scales in epidemiological models.

Growth Arrest of Staphylococcus aureus Induces Daptomycin Tolerance via Cell Wall Remodelling

Almost all bactericidal drugs require bacterial replication and/or metabolic activity for their killing activity. When these processes are inhibited by bacteriostatic antibiotics, bacterial killing is significantly reduced. One notable exception is the lipopeptide antibiotic daptomycin, which has been reported to efficiently kill growth-arrested bacteria. However, these studies employed only short periods of growth arrest (<1 h), which may not fully represent the duration of growth arrest that can occur in vivo. We found that a growth inhibitory concentration of the protein synthesis inhibitor tetracycline led to a time-dependent induction of daptomycin tolerance in S. aureus, with an approximately 100,000-fold increase in survival after 16 h of growth arrest, relative to exponential-phase bacteria. Daptomycin tolerance required glucose and was associated with increased production of the cell wall polymers peptidoglycan and wall-teichoic acids. However, while the accumulation of peptidoglycan was required for daptomycin tolerance, only a low abundance of wall teichoic acid was necessary. Therefore, whereas tolerance to most antibiotics occurs passively due to a lack of metabolic activity and/or replication, daptomycin tolerance arises via active cell wall remodelling. IMPORTANCE Understanding why antibiotics sometimes fail to cure infections is fundamental to improving treatment outcomes. This is a major challenge when it comes to Staphylococcus aureus because this pathogen causes several different chronic or recurrent infections. Previous work has shown that a lack of replication, as often occurs during infection, makes bacteria tolerant of most bactericidal antibiotics. However, one antibiotic that has been reported to kill nonreplicating bacteria is daptomycin. In this work, we show that the growth arrest of S. aureus does in fact lead to daptomycin tolerance, but it requires time, nutrients, and biosynthetic pathways, making it distinct from other types of antibiotic tolerance that occur in nonreplicating bacteria.