In vitro activity of two old antibiotics against clinical isolates of methicillin-resistant Staphylococcus aureus

Antibiotics with antibiofilm activity - rifampicin and beyond

The management of prosthetic joint infections is a complex and multilayered process that is additionally complicated by the formation of bacterial biofilm. Foreign material provides the ideal grounds for the development of an intricate matrix that hinders treatment and creates a difficult environment for antibiotics to act. Surgical intervention is often warranted but requires appropriate adjunctive therapy. Despite available guidelines, several aspects of antibiotic therapy with antibiofilm activity lack clear definition. Given the escalating challenges posed by antimicrobial resistance, extended treatment durations, and tolerance issues, it is essential to ensure that antimicrobials with antibiofilm activity are both potent and diverse. Evidence of biofilm-active drugs is highlighted, and alternatives to classical regimens are further discussed.

hptA Mutation May Mediate Fosfomycin Resistance in Methicillin-Resistant Staphylococcus aureus Clinical Isolates

Fosfomycin can be used alone or in combination to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. However, fosfomycin resistance has been observed in MRSA. In S. aureus, fosfomycin resistance is mediated by the fosfomycin-modifying enzyme FosB, or mutations in the target enzyme MurA. Mutations in the chromosomal glpT and uhpT genes, which encode fosfomycin transporters, also result in fosfomycin resistance. The three-component regulatory system HptRSA mediates the expression of uhpT and glpT in S. aureus. This study aimed to investigate the role of hptRSA mutation in fosfomycin resistance in MRSA clinical isolates. We found that hptRSA mutations were common in MRSA strains isolated from our hospital. Most mutations were amino acid substitutions and widely distributed in fosfomycin-sensitive and fosfomycin-resistant strains. However, HptA-truncated mutations were only found in fosB-negative fosfomycin-resistant strains with wild-type uhpT and glpT genes. Quantitative real-time PCR results showed that the transcription level of uhpT decreased by 13.7-25.6-fold in the HptA-truncated strains. Concordantly, the fosfomycin minimum inhibitory concentration (MIC) of HptA-truncated strains was 64-128 μg/mL, while SA240 was 2 μg/mL. The low transcription level of uhpT and high increase in MIC suggest that hptA mutation may lead to fosfomycin resistance in MRSA. We complemented hptA in one of the HptA-truncated clinical strains (SA179), showing reversal of fosfomycin resistance (from 128 to 32 μg/mL). Then we knocked out hptA in S. aureus Newman; fosfomycin MIC increased from 4 to 64 μg/mL, suggesting that HptA mutation may play an important role in fosfomycin resistance.

The dose regimen formulation of doxycycline hydrochloride and florfenicol injection based on ex vivo pharmacokinetic-pharmacodynamic modeling against the Actinobacillus pleuropneumoniae in pigs

Doxycycline hydrochloride and florfenicol combination (DoxHcl&FF) is an effective treatment for respiratory diseases. In the study, our objective was to evaluate the activity of DoxHcl&FF against Actinobacillus pleuropneumoniae (APP) in porcine pulmonary epithelial lining fluid (PELF) and the optimal dosage scheme to avoid the development of resistance. The DoxHcl&FF was administered intramuscularly (IM) at 20 mg/kg, and the PELF was collected at different time points. The minimum inhibitory concentration (MIC) and time-mortality curves were also included in the study. Based on the sigmoid Emax equation and dose equations, the study integrated the in vivo pharmacokinetic data of infected pigs and ex vivo pharmacodynamic data to obtain the area under concentration time curve (AUC0-24h)/MIC values in PELF and achieve bacteriostatic activity, bactericidal activity and the virtual eradication of bacteria. The study showed that the combination of DoxHcl and FF caused no significant changes in PK parameters. The peak concentration (Cmax) of FF in healthy and diseased pigs was 8.87 ± 0.08 μg/mL and 8.67 ± 0.07 μg/mL, the AUC0-24h were 172.75 ± 2.52 h·μg/mL and 180.22 ± 3.13 h·μg/mL, the Cmax of DoxHcl was 7.91 ± 0.09 μg/mL and 7.99 ± 0.05 μg/mL, and the AUC0-24h was 129.96 ± 3.70 h·μg/mL and 169.82 ± 4.38 h·μg/mL. DoxHcl&FF showed strong concentration-dependent tendencies. The bacteriostatic, bactericidal, and elimination activity were calculated as 5.61, 18.83 and 32.68 h, and the doses were 1.37 (bacteriostatic), 4.59 (bactericidal) and 7.99 (elimination) mg/kg. These findings indicated that the calculated recommended dose could assist in achieving more precise administration, increasing the effectiveness of DoxHcl&FF treatment for APP infections.

Fosfomycin as Partner Drug for Systemic Infection Management. A Systematic Review of Its Synergistic Properties from In Vitro and In Vivo Studies

Fosfomycin is being increasingly prescribed for multidrug-resistant bacterial infections. In patients with systemic involvement, intravenous fosfomycin is usually administered as a partner drug, as part of an antibiotic regimen. Hence, the knowledge of fosfomycin pharmacodynamic interactions (synergistic, additive, indifferent and antagonistic effect) is fundamental for a proper clinical management of severe bacterial infections. We performed a systematic review to point out fosfomycin’s synergistic properties, when administered with other antibiotics, in order to help clinicians to maximize drug efficacy optimizing its use in clinical practice. Interactions were more frequently additive or indifferent (65.4%). Synergism accounted for 33.7% of total interactions, while antagonism occurred sporadically (0.9%). Clinically significant synergistic interactions were mostly distributed in combination with penicillins (51%), carbapenems (43%), chloramphenicol (39%) and cephalosporins (33%) in Enterobactaerales; with linezolid (74%), tetracyclines (72%) and daptomycin (56%) in Staphylococcus aureus; with chloramphenicol (53%), aminoglycosides (43%) and cephalosporins (36%) against Pseudomonas aeruginosa; with daptomycin (97%) in Enterococcus spp. and with sulbactam (75%) and penicillins (60%) and in Acinetobacter spp. fosfomycin-based antibiotic associations benefit from increase in the bactericidal effect and prevention of antimicrobial resistances. Taken together, the presence of synergistic interactions and the nearly total absence of antagonisms, make fosfomycin a good partner drug in clinical practice.

The Potential Role of Fosfomycin in Neonatal Sepsis Caused by Multidrug-Resistant Bacteria

The broad-spectrum activity of fosfomycin, including against multidrug-resistant (MDR) strains, has led to renewed interest in its use in recent years. Neonatal sepsis remains a substantial cause of morbidity and mortality at a global level, with evidence that MDR bacteria play an increasing role. The evidence for use of fosfomycin in neonatal subjects is limited. We summarise current knowledge of the pharmacokinetics and clinical outcomes for the use of fosfomycin in neonatal sepsis and issues specific to neonatal physiology. While fosfomycin has a broad range of coverage, we evaluate the extent to which it may be effective against MDR bacteria in a neonatal setting, in light of recent evidence suggesting it to be most effective when administered in combination with other antibiotics. Given the urgency of clinical demand for treatment of MDR bacterial sepsis, we outline directions for further work, including the need for future clinical trials in this at-risk population.

Mutations of the Transporter Proteins GlpT and UhpT Confer Fosfomycin Resistance in Staphylococcus aureus

With the increasing spread of methicillin-resistant Staphylococcus aureus worldwide, fosfomycin has begun to be used more often, either alone or in combination with other antibiotics, for treating methicillin-resistant S. aureus infections, resulting in the emergence of fosfomycin-resistant strains. Fosfomycin resistance is reported to be mediated by fosfomycin-modifying enzymes (FosA, FosB, FosC, and FosX) and mutations of the target enzyme MurA or the membrane transporter proteins UhpT and GlpT. Our previous studies indicated that the fos genes might not the major fosfomycin resistance mechanism in S. aureus, whereas mutations of glpT and uhpT seemed to be more related to fosfomycin resistance. However, the precise role of these two genes in S. aureus fosfomycin resistance remains unclear. The aim of the present study was to investigate the role of glpT and uhpT in S. aureus fosfomycin resistance. Homologous recombination was used to knockout the uhpT and glpT genes in S. aureus Newman. Gene complementation was generated by the plasmid pRB473 carrying these two genes. The fosfomycin minimal inhibitory concentration (MIC) of the strains was measured by the E-test to observe the influence of gene deletion on antibiotic susceptibility. In addition, growth curves were constructed to determine whether the mutations have a significant influence on bacterial growth. Deletion of uhpT, glpT, and both of them led to increased fosfomycin MIC 0.5 μg/ml to 32 μg/ml, 4 μg/ml, and >1024 μg/ml, respectively. By complementing uhpT and glpT into the deletion mutants, the fosfomycin MIC decreased from 32 to 0.5 μg/ml and from 4 to 0.25 μg/ml, respectively. Moreover, the transporter gene-deleted strains showed no obvious difference in growth curves compared to the parental strain. In summary, our study strongly suggests that mutations of uhpT and glpT lead to fosfomycin resistance in S. aureus, and that uhpT mutation may play a more important role. The high resistance and low biological fitness cost resulting from uhpT and glpT deletion suggest that these strains might have an evolutionary advantage in a fosfomycin-rich clinical situation, which should be closely monitored.

Fosfomycin

The treatment of bacterial infections suffers from two major problems: spread of multidrug-resistant (MDR) or extensively drug-resistant (XDR) pathogens and lack of development of new antibiotics active against such MDR and XDR bacteria. As a result, physicians have turned to older antibiotics, such as polymyxins, tetracyclines, and aminoglycosides. Lately, due to development of resistance to these agents, fosfomycin has gained attention, as it has remained active against both Gram-positive and Gram-negative MDR and XDR bacteria. New data of higher quality have become available, and several issues were clarified further. In this review, we summarize the available fosfomycin data regarding pharmacokinetic and pharmacodynamic properties, the in vitro activity against susceptible and antibiotic-resistant bacteria, mechanisms of resistance and development of resistance during treatment, synergy and antagonism with other antibiotics, clinical effectiveness, and adverse events. Issues that need to be studied further are also discussed.

In Vitro activities of combinations of rifampin with other antimicrobials against multidrug-resistant Acinetobacter baumannii

The antimicrobial treatment of multidrug-resistant (MDR) Acinetobacter baumannii infections has become a great challenge for medical staff all over the world. Increasing numbers of MDR A. baumannii infections have been identified and reported, but effective clinical treatments for them are decreasing. The objective of this study was to investigate the in vitro activities of combinations of rifampin (an established antimicrobial) and other antimicrobials, including biapenem, colistin, and tigecycline, against 73 clinical isolates of MDR A. baumannii. In total, 73 clinical isolates of MDR A. baumannii were collected from two A-level general hospitals in Beijing, and the MICs of rifampin, biapenem, colistin, and tigecycline were determined. The checkerboard method was used to determine the fractional inhibitory concentration indices (FICIs), that is, whether the combinations acted synergistically against these isolates. The MIC50, MIC90, and MICrange of rifampin combined with biapenem, colistin, and tigecycline against the isolates were clearly lower than those for four antimicrobials (rifampin, biapenem, colistin, and tigecycline) that were used alone. Combinations of rifampin with biapenem, colistin, and tigecycline individually demonstrated the following interactions: synergistic interactions (FICI ≤ 0.5) for 31.51%, 34.25%, and 31.51% of the isolates, partially synergistic interactions (0.5 < FICI < 1) for 49.31%, 43.83%, and 47.94% of the isolates, and additive interactions (FICI = 1) for 19.18%, 21.92%, and 20.55% of the isolates, respectively. There were no indifferent (1 < FICI < 4) or antagonistic (FICI ≥ 4) interactions. Therefore, combinations of rifampin with biapenem, colistin, or tigecycline may be future therapeutic alternatives for the treatment of MDR A. baumannii infections.

The revival of fosfomycin

Fosfomycin, originally named phosphonomycin, was discovered in Spain in 1969. There are three forms of fosfomycin: fosfomycin tromethamine (a soluble salt) and fosfomycin calcium for oral use, and fosfomycin disodium for intravenous use. Fosfomycin is a bactericidal antibiotic that interferes with cell wall synthesis in both Gram-positive and Gram-negative bacteria by inhibiting the initial step involving phosphoenolpyruvate synthetase. It has a broad spectrum of activity against a wide range of Gram-positive and Gram-negative bacteria. It is highly active against Gram-positive pathogens such as Staphylococcus aureus and Enterococcus, and against Gram-negative bacteria such as Pseudomonas aeruginosa and Klebsiella pneumoniae. Its unique mechanism of action may provide a synergistic effect to other classes of antibiotics including beta-lactams, aminoglycosides, and fluoroquinolones. Oral fosfomycin is mainly used in the treatment of urinary tract infections, particularly those caused by Escherichia coli and Enterococcus faecalis. Intravenous fosfomycin has been administered in combination with other antibiotics for the treatment of nosocomial infections due to multidrug-resistant (MDR) Gram-positive and Gram-negative bacteria. Fosfomycin has good distribution into tissues, achieving clinically relevant concentrations in serum, kidneys, bladder wall, prostate, lungs, inflamed tissues, bone, cerebrospinal fluid, abscess fluid, and heart valves. Fosfomycin is well tolerated, with a low incidence of adverse events. Further randomized controlled trials are needed in order to evaluate the efficacy of intravenous fosfomycin for the management of nosocomial infections due to MDR pathogens.