In vitro activity of minocycline combined with aminoglycosides against Klebsiella pneumoniae carbapenemase-producing K. pneumoniae

Comparison of Mutant Prevention Concentrations of Fluoroquinolones Against ESBL-Positive and ESBL-Negative Klebsiella pneumoniae Isolates from Orthopedic Patients

The majority of Klebsiella pneumonia isolates possess the extended-spectrum beta-lactamase (ESBL) enzymes. Therefore, K. pneumoniae can easily develop drug resistance. How to effectively overcome the problem of drug resistance in K. pneumoniae is still a research hotspot. This study aimed to compare the mutant prevention concentration (MPC) of ESBL-positive and ESBL-negative K. pneumoniae isolated from orthopedic patients, which may provide a basis for the effective use of drugs to control the enrichment of resistance mutants of K. pneumoniae. The MPC90 values of 55 isolates of ESBL-positive K. pneumoniae against 4 fluoroquinolones were 32 µg/mL for levofloxacin and gatifloxacin, 16 µg/mL for ciprofloxacin, and 4 µg/mL for gemifloxacin. The selection index value was 8 for levofloxacin and ciprofloxacin and 2 for gemifloxacin and gatifloxacin, respectively. For ESBL-negative K. pneumoniae isolates, the MPC90 values were 16 µg/mL for levofloxacin and ciprofloxacin, 4 µg/mL for gemifloxacin, and 32 µg/mL for gatifloxacin. The selection index value was 8 for levofloxacin and ciprofloxacin, 2 for gemifloxacin, and 4 for gatifloxacin. For the ESBL-positive K. pneumoniae, the %T>MIC90 order was gemifloxacin > levofloxacin > ciprofloxacin > gatifloxacin. For the ESBL-negative K. pneumoniae, the %T>MIC90 order was levofloxacin > gemifloxacin > ciprofloxacin > gatifloxacin. The mutant-preventing ability of gatifloxacin and gemifloxacin was the strongest among the 4 fluoroquinolones. So gemifloxacin may be the first choice of drug to treat K. pneumoniae infection.

Joint effects about antibiotics combined using with antibiotics or phytochemicals on Aeromonas hydrophila

Aeromonas hydrophila is highly prevalent in aquaculture animals and aquaculture environment. Due to the abuse of antibiotics, A. hydrophila can change the antibiotic resistance spectrum directly and affect human health indirectly. The use of combined drugs replacement therapy and the long-term coexistence with drug-resistant bacteria are the reality that human beings have to face in dealing with the problem of antibiotic resistance in the future. This study showed the characteristics and trends through abundant results of combined effects related with the combinations of antibiotic and the combinations of antibiotic and phytochemical on A. hydrophila, and revealed the antagonism probability of combinations of antibiotic and phytochemical is significantly higher than that of the combinations of antibiotic. Meanwhile, the combinations of antibiotic and phytochemical could protect the host cells which also achieved the same effectiveness as combination of antibiotics, and the enrichment pathway was proved to be relatively discrete. In addition, the possible mechanism about the reverse "U" shape of the combined effect curve on wild/antibiotic-resistant bacteria was clarified, and it was confirmed that the antagonism for the combinations of antibiotic and phytochemical might has the significance in inhibiting the evolution of bacterial resistance mutations. This study was aims to provide theoretical basis and some clues for the antibiotic resistance control associated with A. hydrophila.

Ceftazidime/Avibactam, Polymyxin or Tigecycline as a Rescue Strategy for the Treatment of Carbapenem-Resistant Klebsiella pneumoniae in Bloodstream Infection: A Retrospective Cohort Study

Objective

To analyze the clinical characteristics, outcomes, and risk factors of patients treated with ceftazidime/avibactam, polymyxin, or tigecycline (CPT) compared with those receiving a conventional therapy (CT) (ie, imipenem, levofloxacin, or gentamicin).

Methods

A single-center retrospective cohort study included patients with carbapenem-resistant Klebsiella pneumoniae bloodstream infection (CRKP-BSI) treated at one Chinese tertiary hospital between March 2012 and November 2022 was performed. Clinical characteristics, outcomes, and risk factors of patients treated with CPT or CT were compared. Predictors of 30-day mortality of patients with CRKP-BSI were also analysed in our study.

Results

Among 184 recruited patients with CRKP-BSI, 39.7% (73/184) were treated with CPT, while 60.3% (111/184) were treated with CT. Compared to patients treated with CT, patients treated with CPT had worse conditions, as evidenced by a higher rate of underlying diseases and invasive procedures; however, they also had a better prognosis and lower rates of 14-day treatment failure (p = 0.024). In addition, univariate analysis and multivariate analysis showed that SOFA score [odds ratio (OR) = 1.310, 95% confidence interval (CI) 1.157-1.483; p < 0.001] and cold weather (OR = 3.658, 95% CI 1.474-9.081; p = 0.005) were independent risk factors for 30-day mortality.

Conclusion

Compared to CRKP-BSI patients treated with CT, patients treated with CPT had worse conditions but better prognoses. CRKP-BSI occurred more frequently in hot weather; however, higher 30-day mortality was associated with cold weather. A randomized trial is needed to confirm these observational results.

Assessing Clinical Potential of Old Antibiotics against Severe Infections by Multi-Drug-Resistant Gram-Negative Bacteria Using In Silico Modelling

In the light of increasing antimicrobial resistance among gram-negative bacteria and the lack of new more potent antimicrobial agents, new strategies have been explored. Old antibiotics, such as colistin, temocillin, fosfomycin, mecillinam, nitrofurantoin, minocycline, and chloramphenicol, have attracted the attention since they often exhibit in vitro activity against multi-drug-resistant (MDR) gram-negative bacteria, such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. The current review provides a summary of the in vitro activity, pharmacokinetics and PK/PD characteristics of old antibiotics. In silico modelling was then performed using Monte Carlo simulation in order to combine all preclinical data with human pharmacokinetics and determine the probability of target (1-log kill in thigh/lung infection animal models) attainment (PTA) of different dosing regimens. The potential of clinical efficacy of a drug against severe infections by MDR gram-negative bacteria was considered when PTA was >95% at the epidemiological cutoff values of corresponding species. In vitro potent activity against MDR gram-negative pathogens has been shown for colistin, polymyxin B, temocillin (against E. coli and K. pneumoniae), fosfomycin (against E. coli), mecillinam (against E. coli), minocycline (against E. coli, K. pneumoniae, A. baumannii), and chloramphenicol (against E. coli) with ECOFF or MIC90 ≤ 16 mg/L. When preclinical PK/PD targets were combined with human pharmacokinetics, Monte Carlo analysis showed that among the old antibiotics analyzed, there is clinical potential for polymyxin B against E. coli, K. pneumoniae, and A. baumannii; for temocillin against K. pneumoniae and E. coli; for fosfomycin against E. coli and K. pneumoniae; and for mecillinam against E. coli. Clinical studies are needed to verify the potential of those antibiotics to effectively treat infections by multi-drug resistant gram-negative bacteria.

Drug Combinations to Prevent Antimicrobial Resistance: Various Correlations and Laws, and Their Verifications, Thus Proposing Some Principles and a Preliminary Scheme

Antimicrobial resistance (AMR) has been a serious threat to human health, and combination therapy is proved to be an economic and effective strategy for fighting the resistance. However, the abuse of drug combinations conversely accelerates the spread of AMR. In our previous work, we concluded that the mutant selection indexes (SIs) of one agent against a specific bacterial strain are closely related to the proportions of two agents in a drug combination. To discover probable correlations, predictors and laws for further proposing feasible principles and schemes guiding the AMR-preventing practice, here, three aspects were further explored. First, the power function (y = axb, a > 0) correlation between the SI (y) of one agent and the ratio (x) of two agents in a drug combination was further established based on the mathematical and statistical analyses for those experimental data, and two rules a1 × MIC1 = a2 × MIC2 and b1 + b2 = −1 were discovered from both equations of y = a1xb1 and y = a2xb2 respectively for two agents in drug combinations. Simultaneously, it was found that one agent with larger MPC alone for drug combinations showed greater potency for narrowing itself MSW and preventing the resistance. Second, a new concept, mutation-preventing selection index (MPSI) was proposed and used for evaluating the mutation-preventing potency difference of two agents in drug combination; a positive correlation between the MPSI and the mutant prevention concentration (MPC) or minimal inhibitory concentration (MIC) was subsequently established. Inspired by this, the significantly positive correlation, contrary to previous reports, between the MIC and the corresponding MPC of antimicrobial agents against pathogenic bacteria was established using 181 data pairs reported. These results together for the above three aspects indicate that the MPCs in alone and combination are very important indexes for drug combinations to predict the mutation-preventing effects and the trajectories of collateral sensitivity, and while the MPC of an agent can be roughly calculated from its corresponding MIC. Subsequently, the former conclusion was further verified and improved via antibiotic exposure to 43 groups designed as different drug concentrations and various proportions. The results further proposed that the C/MPC for the agent with larger proportion in drug combinations can be considered as a predictor and is the key to judge whether the resistance and the collateral sensitivity occur to two agents. Based on these above correlations, laws, and their verification experiments, some principles were proposed, and a diagram of the mutation-preventing effects and the resistant trajectories for drug combinations with different concentrations and ratios of two agents was presented. Simultaneously, the reciprocal of MPC alone (1/MPC), proposed as the stress factors of two agents in drug combinations, together with their SI in combination, is the key to predict the mutation-preventing potency and control the trajectories of collateral sensitivity. Finally, a preliminary scheme for antimicrobial combinations preventing AMR was further proposed for subsequent improvement research and clinic popularization, based on the above analyses and discussion. Moreover, some similar conclusions were speculated for triple or multiple drug combinations.

Evaluation of ceftazidime/avibactam alone and in combination with amikacin, colistin and tigecycline against Klebsiella pneumoniae carbapenemase-producing K. pneumoniae by in vitro time-kill experiment

Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp) poses a major threat to human health worldwide. Combination therapies of antibiotics with different mechanisms have been recommended in literatures. This study assessed in vitro antibacterial activities and synergistic activities of ceftazidime/avibactam alone and in combinations against KPC-Kp. In total, 70 isolates from 2 hospitals in Beijing were examined in our study. By using the agar dilution method and broth dilution method, we determined the minimum inhibitory concentration (MIC) of candidate antibiotics. Ceftazidime/avibactam demonstrated promising susceptibility against KPC-Kp (97.14%). Synergistic activities testing was achieved by checkerboard method and found ceftazidime/avibactam-amikacin displayed synergism in 90% isolates. Ceftazidime/avibactam-colistin displayed partial synergistic in 43% isolates, and ceftazidime/avibactam-tigecycline displayed indifference in 67% isolates. In time-kill assays, antibiotics at 1-fold MIC were mixed with bacteria at 1 × 105 CFU/ml and Mueller-Hinton broth (MHB). Combinations of ceftazidime/avibactam with amikacin and tigecycline displayed better antibacterial effects than single drug. Ceftazidime/avibactam-colistin combination did not exhibit better effect than single drug. In KPC-Kp infections, susceptibility testing suggested that ceftazidime/avibactam may be considered as first-line choice. However, monotherapy is often inadequate in infection management. Thus, our study revealed that combination therapy including ceftazidime/avibactam colistin and ceftazidime/avibactam tigecycline may benefit than monotherapy in KPC-Kp treatment. Further pharmacokinetic/pharmacodynamic and mutant prevention concentration studies should be performed to optimize multidrug-regimens.

In vitro and in vivo synergistic effects of tigecycline combined with aminoglycosides on carbapenem-resistant Klebsiella pneumoniae

OBJECTIVES

Carbapenem-resistant Klebsiella pneumoniae (CR-KP) infections represent severe threats to public health worldwide. The aim of this study was to assess potential synergistic interaction between tigecycline and aminoglycosides via in vitro and in vivo studies.

METHODS

Antibiotic resistance profiles and molecular characteristics of 168 CR-KP clinical isolates were investigated by susceptibility testing, PCR and MLST. Chequerboard tests and time-kill assays were performed for 20 CR-KP isolates to evaluate in vitro synergistic effects of tigecycline combined with aminoglycosides. A tissue-cage infection model of rats was established to evaluate in vivo synergistic effects. Different doses of tigecycline and aminoglycosides alone or in combination were administered for 7 days via tail vein injection. Antibiotic efficacy was evaluated in tissue-cage fluid and emergence of resistance was screened.

RESULTS

The chequerboard tests showed that this combination displayed synergistic or partial synergistic activity against CR-KP. The time-kill assays further demonstrated that strong synergistic effects of such a combination existed against isolates that were susceptible to both drugs but for resistant isolates no synergy was observed if clinical pharmacokinetics were taken into consideration. The in vivo study showed that the therapeutic effectiveness of combination therapies was better than that of monotherapy for susceptible isolates, suggesting in vivo synergistic effects. Furthermore, combinations of tigecycline with an aminoglycoside showed significant activity in reducing the occurrence of tigecycline-resistant mutants.

CONCLUSIONS

Compared with single drugs, tigecycline combined with aminoglycosides could exert synergistic effects and reduce the emergence of tigecycline resistance. Such a combination might be an effective alternative when treating CR-KP infections in clinical practice.

Synergistic Combination of Linezolid and Fosfomycin Closing Each Other's Mutant Selection Window to Prevent Enterococcal Resistance

Enterococci, the main pathogens associated with nosocomial infections, are resistant to many common antibacterial drugs including β-lactams, aminoglycosides, etc. Combination therapy is considered an effective way to prevent bacterial resistance. Preliminary studies in our group have shown that linezolid combined with fosfomycin has synergistic or additive antibacterial activity against enterococci, while the ability of the combination to prevent resistance remains unknown. In this study, we determined mutant prevention concentration (MPC) and mutant selection window (MSW) of linezolid, fosfomycin alone and in combination including different proportions for five clinical isolates of Enterococcus and characterized the resistance mechanism for resistant mutants. The results indicated that different proportions of linezolid combined with fosfomycin had presented different MPCs and MSWs. Compared with linezolid or fosfomycin alone, the combination can restrict the enrichment of resistant mutants at a lower concentration. A rough positive correlation between the selection index (SI) of the two agents in combination and the fractional inhibitory concentration index (FICI) of the combination displayed that the smaller FICI of linezolid and fosfomycin, the more probable their MSWs were to close each other. Mutations in ribosomal proteins (L3 and L4) were the mechanisms for linezolid resistant mutants. Among the fosfomycin-resistant mutants, only two strains have detected the MurA gene mutation related to fosfomycin resistance. In conclusion, the synergistic combination of linezolid and fosfomycin closing each other’s MSW could effectively suppress the selection of enterococcus resistant mutants, suggesting that the combination may be an alternative for preventing enterococcal resistance. In this study, the resistance mechanism of fosfomycin remains to be further studied.

Antimicrobial and antibiofilm activities of ursolic acid against carbapenem-resistant Klebsiella pneumoniae

Previous studies demonstrated that ursolic acid (UA) present in apple pomace displays antimicrobial activity against some microorganisms, but the underlying mechanisms associated with this activity remain unexplored. Furthermore, there are no reports on the effect of UA on carbapenem-resistant Klebsiella pneumoniae (CRKP). This study examined the antimicrobial activity and mode of action of UA against CRKP was examined. Minimum inhibitory concentration (MIC) of UA against CRKP was determined by the agar dilution method. Variations in the intracellular pH (pHin), ATP concentration, and cell membrane potential were measured to assess the influence of UA on the cell membrane. Our results show that UA was effective against CRKP at an MIC of 0.8 mg ml-1. UA disrupted the cell membrane integrity of CRKP, exhibited strong inhibitory effects against biofilm formation and biofilm-related gene expression, and inactivated CRKP cells encased in biofilms. Thus, UA shows promise for use in combination with other antibiotics to treat multidrug resistant K. pneumoniae infections.

Minocycline, focus on mechanisms of resistance, antibacterial activity, and clinical effectiveness: Back to the future

OBJECTIVES

The increasing crisis regarding multidrug-resistant (MDR) and extensively drug-resistant microorganisms leads to appealing therapeutic options.

METHODS

During the last 30 years, minocycline, a wide-spectrum antimicrobial agent, has been effective against MDR Gram-positive and Gram-negative bacterial infections. As with other tetracyclines, the mechanism of action of minocycline involves attaching to the bacterial 30S ribosomal subunit and preventing protein synthesis.

RESULTS

This antimicrobial agent has been approved for the treatment of acne vulgaris, some sexually transmitted diseases and rheumatoid arthritis. Although many reports have been published, there remains limited information regarding the prevalence, mechanism of resistance and clinical effectiveness of minocycline.

CONCLUSION

Thus, we summarize here the currently available data concerning pharmacokinetics and pharmacodynamics, mechanism of action and resistance, antibacterial activity and clinical effectiveness of minocycline.