In vitro antibacterial activity of rifampicin in combination with imipenem, meropenem and doripenem against multidrug-resistant clinical isolates of Pseudomonas aeruginosa

Outbreak of Pseudomonas aeruginosa High-Risk Clone ST309 Serotype O11 Featuring blaPER-1 and qnrVC6

Pseudomonas aeruginosa is a leading cause of hospital-acquired infections worldwide. Biofilm production, antibiotic resistance, and a wide range of virulence factors contribute to their persistence in nosocomial environments. We describe an outbreak caused by a multidrug-resistant P. aeruginosa strain in an ICU. Antibiotic susceptibility was determined and blaPER-1 and qnrVC were amplified via PCR. Clonality was determined using PFGE and biofilm formation was studied with a static model. A combination of antibiotics was assessed on both planktonic cells and biofilms. WGS was performed on five isolates. All isolates were clonally related, resistant to ceftazidime, cefepime, amikacin, and ceftolozane-tazobactam, and harbored blaPER-1; 11/19 possessed qnrVC. Meropenem and ciprofloxacin reduced the biofilm biomass; however, the response to antibiotic combinations with rifampicin was different between planktonic cells and biofilms. WGS revealed that the isolates belonged to ST309 and serotype O11. blaPER-1 and qnrVC6 were associated with a tandem of ISCR1 as part of a complex class one integron, with aac(6')-Il and ltrA as gene cassettes. The structure was associated upstream and downstream with Tn4662 and flanked by direct repeats, suggesting its horizontal mobilization capability as a composite transposon. ST309 is considered an emerging high-risk clone that should be monitored in the Americas.

Antibacterial and anti-biofilm activities of fosfomycin combined with rifampin against Carbapenem-resistant Pseudomonas aeruginosa

Increasing prevalence of carbapenem-resistant Pseudomonas aeruginosa(CRPA)strains in the hospital setting represents an emerging challenge to clinical treatment for Pseudomonas aeruginosa (PA) infections, as the range of therapeutic agents active against these pathogens becomes increasingly constrained. This study demonstrated for the first time that fosfomycin (FOS) combined with rifampin (RIF) showed strong synergistic effects against CRPA and carbapenem-susceptible PA, with 100% synergistic rates. Additionally, time-killing curve further proves dynamic antibacterial activity of FOS+RIF against CRPA. Further experiments determined that antibacterial mechanisms of FOS+RIF might be inhibition of biofilm formation and eradication of pre-formed biofilm. The results of inhibition biofilm formation assay demonstrated that RIF and FOS at 1/8MIC, 1/16MIC and 1/32MIC have better inhibitory effects on CRPA biofilm formation VS FOS alone (96%, 90% and 78% VS 29%, 24% and 22%) (p<0.0001) or RIF alone (96%, 90% and 78% VS 86%, 67% and 29%) (p<0.01). The rates of eradicating pre-formed biofilm with combination therapy at 1/2MIC, 1/4MIC and 1/8MIC of both antibiotics, increased 46%, 61% and 55% compared with FOS alone (p<0.001) and 37%, 33% and 46% compared with RIF alone (p<0.01). This finding will provide new insights for the treatment of bacterial infection caused by CRPA, which can be further explored in the clinical practice.

Risk Factors for Carbapenem-resistant Pseudomonas aeruginosa Infection in Children

BACKGROUND

Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is rapidly emerging as a life-threatening nosocomial infection. The study aimed to identify the risk factors for CRPA infection in children, especially antimicrobials use and invasive procedures.

METHODS

A retrospective study was conducted in the Children's Hospital of Chongqing Medical University, which involved a cohort of patients with PA infection from January 2016 to December 2020. Patients were assigned to a carbapenem-susceptible PA group or to a CRPA group and matched using propensity-score matching. Univariate analysis and multivariate analysis were performed to estimate the risk factors of CRPA.

RESULTS

One-thousand twenty-five patients were included in the study but 172 children were analyzed. Several factors were associated with CRPA infection according to univariate analysis ( P < 0.05), such as prior treatment with some antimicrobials and invasive procedures. However, only prior exposure to carbapenems (odds ratio [OR]: 0.102; confidence interval [CI]: 0.033-0.312; P < 0.001) and bronchoscopy (OR: 0.147; CI: 0.032-0.678; P = 0.014) during time at risk, previous invasive therapy in the last year (OR: 0.353; CI: 0.159-0.780; P = 0.013), and previous use of β-lactams/β-lactamase inhibitors within the last 90 days (OR: 0.327; CI: 0.121-0.884; P = 0.03) were considered independent risk factors by multivariate analysis.

CONCLUSIONS

Those who had prior exposure to carbapenems and bronchoscopy were high-risk population to develop CRPA infection. The spread of CRPA could be influenced by invasive therapy, and we need pay attention to it. Moreover, we should take restrictions in the clinical use of carbapenems into account.

Long-Term Dominance of Carbapenem-Non-Susceptible Pseudomonas aeruginosa ST111 in Hematologic Malignancy Patients and Hematopoietic Cell Transplant Recipients

An epidemiological study uncovered that fluoroquinolone (FQ) neutropenic prophylaxis in hematopoietic cell transplant and hematologic malignancy (HCT/HM) patients was associated with breakthrough Pseudomonas aeruginosa bloodstream infections (BSIs) with isolates non-susceptible to both FQs and meropenem. The molecular epidemiology of the FQ/meropenem-non-susceptible P. aeruginosa isolates causing FQ-breakthrough BSIs in the HCT/HM patients remains unclear. Through whole genome sequencing on 57 P. aeruginosa isolates from 54 patients diagnosed with HM or receiving an HCT, we found that ST111 strains predominated, accounting for 22 (38.6%) of the isolates. 17 of 33 (51.5%) FQ-breakthrough BSIs were caused by ST111 strains, of which 15 (88.2%) were meropenem non-susceptible. ST111 strains, but not other oprD-deficient, meropenem-non-susceptible clinical strains, were found to have a colonization advantage over P. aeruginosa strain PA14 in C. elegans and to outcompete PA14 in in vitro co-culture assays. Together, we found that breakthrough P. aeruginosa BSIs during FQ prophylaxis in HCT/HM patients are dominated by clonally-related FQ/meropenem non-susceptible strains, predominantly ST111 type, and that the dominance of ST111 strains may be explained by a relative fitness advantage over other clinical strains. Additional work is necessary to better understand the factors driving the dominance and persistence of these ST111 strains.

Effect of rifampicin combination-regimens against multi-drug resistant strains in North India

It is well-acknowledged that 'combination therapy' of antibiotics is indispensable for the treatment of patients suffering from serious bacterial infections. Therefore, it is of interest to collect data from the in vitro tests using 'rifampicin-cefotaxime' and 'rifampicin-tetracycline' combination regimens against multi drug resistant Escherichia coli and Klebsiella pneumoniae strains of nosocomial source in order to determine the effectiveness of the combination therapy. The minimum inhibitory concentration (MIC) values for cefotaxime, tetracycline and rifampicin antibiotics were found to be comparatively high for each of the antibiotics when given individually. However, carefully prepared combination-regimens exhibited significant inhibitory effect on the same bacterial isolates. DNA fragmentation study confirmed that 'rifampicin-cefotaxime' and 'rifampicin-tetracycline' combination-regimens could cause breakage of the bacterial DNA. Thus, we show that combination-regimens namely, 'rifampicin-cefotaxime' and 'rifampicin-tetracycline' were found to be capable of maintaining rifampicin susceptibility in the E. coli and K. pneumoniae strains. However, this susceptibility was not maintained by only rifampicin. More data using animal model experiments are needed for confirming and deriving translational benefits from these findings in future.

In Vitro Screening of a 1280 FDA-Approved Drugs Library against Multidrug-Resistant and Extensively Drug-Resistant Bacteria

Alternative strategies against multidrug-resistant (MDR) bacterial infections are suggested to clinicians, such as drug repurposing, which uses rapidly available and marketed drugs. We gathered a collection of MDR bacteria from our hospital and performed a phenotypic high-throughput screening with a 1280 FDA-approved drug library. We used two Gram positive (Enterococcus faecium P5014 and Staphylococcus aureus P1943) and six Gram negative (Acinetobacter baumannii P1887, Klebsiella pneumoniae P9495, Pseudomonas aeruginosa P6540, Burkholderia multivorans P6539, Pandoraea nosoerga P8103, and Escherichia coli DSM105182 as the reference and control strain). The selected MDR strain panel carried resistance genes or displayed phenotypic resistance to last-line therapies such as carbapenems, vancomycin, or colistin. A total of 107 compounds from nine therapeutic classes inhibited >90% of the growth of the selected Gram negative and Gram positive bacteria at a drug concentration set at 10 µmol/L, and 7.5% were anticancer drugs. The common hit was the antiseptic chlorhexidine. The activity of niclosamide, carmofur, and auranofin was found against the selected methicillin-resistant S. aureus. Zidovudine was effective against colistin-resistant E. coli and carbapenem-resistant K. pneumoniae. Trifluridine, an antiviral, was effective against E. faecium. Deferoxamine mesylate inhibited the growth of XDR P. nosoerga. Drug repurposing by an in vitro screening of a drug library is a promising approach to identify effective drugs for specific bacteria.

Control of extensively drug-resistant Pseudomonas aeruginosa co-harboring metallo-β-lactamase enzymes with oprD gene downregulation

PURPOSE

to study control and treatment of infection with extensive drug-resistant carbapenem-resistant Pseudomonas aeruginosa (XDR-CRPA).

METHODS

Eleven Pseudomonas aeruginosa (XDR-CRPA) strains used in this study were isolated from a clinical sample, identified, and antibiotics susceptibility recorded in a previous study. Real-time PCR (RT-PCR) was performed to determine the expression level of the OprD gene. Besides, a checkerboard technique was performed to assess the effect of polymyxin-B (POX), colistin (COL), rifampicin (RIF), imipenem (IPM), and meropenem (MEM) during 2 and 3- dimensional antibiotic combinations. Further, the time-kill study was determined for the most potent combination against four representative strains, log₁₀ changes of viable cell counts were expressed as their mean value (±SD) values.

RESULTS

Molecular analysis by Real-time PCR revealed that the diminished expression level of OprD mRNA was overwhelming to various degrees. The checkerboard method demonstrated that the relevant synergism was achieved in 90.9% of strains for both carbapenem antibiotics during the triple combinations. While an additive effect was noted for all the dual regimen assays. Regarding time-kill experiments, a remarkable bactericidal effect with [99.9% killing rate] was observed toward only one strain whilst a bacteriostatic attitude was proven with ≥95% bacterial eradication against the three remaining strains.

CONCLUSIONS

These findings underscore the promising implications of these combinations for treatment against XDR-Pseudomonas aeruginosa even they are resistant to carbapenems due to multiple mechanisms of action.

Comparison of Pharmaceutical Characteristics between Brand-Name Meropenem and Its Generics

This study aimed to provide comparative information of pharmaceutical properties, including particle morphology and distribution uniformity, solubility, presence of residual solvent and insoluble particles, and antimicrobial activities, between brand-name meropenem (Mepem^®, BNM) and its six generic products (GPs A-F) marketed in China. Particles of GP-A and -C in dry powder had similar diameters of BNM, while other GPs were larger. Only BNM and GP-A were completely dissolved within 100 s in the lab condition. No insoluble particles >25 μm in diameter were detected in BNM and GP-E. Regarding stability of GPs solutions evaluated by concentration of open-ring metabolites at 6 h and 8 h, BNM showed the lowest open-ringed metabolite concentrates. Residual solvent of acetone detected in one GP showed the maximum value, while ethanol and ethyl acetate were detected both in product E and product F. The concordance rates (%) of minimum inhibitory concentration (MIC) of each generic compared to BNM were 89.5, 85, 87.5, 88, 88.5, and 86.5, respectively, although no significant difference was reached in MIC. Pharmaceutical characteristic differences between the BNM and GPs identified in this study could provide insights into understanding the deviations in the drug manufacturing processes of generic drugs.

Synthesis, docking and antibacterial studies of more potent amine and hydrazone rifamycin congeners than rifampicin

New rifamycin congeners (1-33) with incorporated amine and hydrazone substituents leading to lipophilic and/or basic nature and altered rigidity of modified C(3) arm were synthesized and structurally characterized in detail. NMR spectroscopic studies at different temperatures indicate two types of structures of rifamycin congeners that are realized in solution: zwitterionic and non-ionic forms in dependence of the basicity of modified C(3) arm. The presence of rifamycin congeners in these two possible forms has a significant impact on the physico-chemical parameters such as lipophilicity (clogP) and water solubility and different binding mode of the C(3) arm of antibiotic at RNAP binding pocket (molecular target) leading to different antibacterial potency. The highest antibacterial potency against S. aureus (including MRSA and MLSB strains) and S. epidermidis strains, even higher than reference rifampicin (Rif) and rifaximin (Rifx) antibiotics, was found for rifamycin congeners bearing at the C(3) arm relatively rigid and basic substituents (bipiperidine and guanidine groups). These modifications provide favorable docking mode and excellent water solubility resulting in high potency (MICs 0.0078 μg/mL what gives ∼ 8.5 nM), irrespective whether rifamycin congener is a tertiary amine (15) or hydrazone (29). In turn, for a higher antibacterial potency of rifamycin congeners against E. faecalis strain (MICs 0.5 μg/mL that is 0.6 μM) as compared to Rif and Rifx, the most crucial factors are: bulkiness and the lipophilic character of the end of the C(3) rebuilt arm.

Distribution of species and antimicrobial resistance among enterococci isolated from the fecal microbiota of captive blue-fronted parrot (Amazona aestiva) in Rio de Janeiro, Brazil

Enterococcal strains recovered from fecal samples of captive blue-fronted parrots (Amazona aestiva) assisted at two wild animal screening centers in Rio de Janeiro, Brazil, were identified as Enterococcus hirae (the predominant species; 75.3%), followed by Enterococcus faecalis (17.3%), Enterococcus casseliflavus (4.8%), Enterococcus gallinarum (1.7%), and Enterococcus hermanniensis (0.9%). All strains were susceptible to linezolid and teicoplanin. Rates of nonsusceptibility (including resistant and intermediate categories) to other 16 antimicrobials tested varied from 69.3% to 0.4%, A considerable proportion (48.0%) of the strains was multidrug-resistant and diverse genetic determinants associated with antimicrobial resistance were identified. Tetracycline-resistant strains carried the tet(M) and/or tet(L) genes. Macrolides resistance was associated with the erm(B), erm(A) and mefA genes, while 43.2% of the isolates were negative for the investigated genes. High-level resistance to gentamicin associated with the aac(6')-le-aph(2″)-la gene was detected in one E. faecalis strain. The two strains presenting high-level resistance to streptomycin were negative for the ant(6')-Ia, ant(3')-Ia, ant(9')-Ia and ant(9')-Ib genes. The vat(D) gene was found in all the 47 quinupristin/dalfopristin resistant strains identified as non-E. faecalis. Analysis of PFGE profiles of E. hirae strains after restriction with SmaI demonstrated the occurrence of five clonal groups. The predominant E. hirae clone was distributed among birds in the two institutions, suggesting that this clone was well adapted to the host and environments investigated. The four clonal groups identified among E. faecalis were composed by small numbers of strains and, generally, restricted to birds in the same sector. The occurrence of enterococcal strains exhibiting antimicrobial resistance traits and carrying genetic determinants that represent potential threats to the health of both humans and animals, in the intestinal microbiota of A. aestiva, highlights the need for additional monitoring studies to elucidate the population structure and the dynamics of transmission of these microorganisms among animals, humans and the environment.

Multilocus sequence typing and variations in the oprD gene of Pseudomonas aeruginosa isolated from a hospital in China

Objectives

To provide information about the genetic relationships and mechanism underlying carbapenem resistance in Pseudomonas aeruginosa clinical isolates of a hospital in China.

Materials and methods

One hundred and sixty P. aeruginosa strains were isolated from a hospital in China. Susceptibility to 14 antimicrobial agents was determined by antimicrobial susceptibility testing. Multilocus sequence typing was used to characterize the genetic backgrounds of these clinical isolates. Forty-five strains were randomly selected for further evaluation of their carbapenem resistance mechanism. Their oprD gene was compared with the PAO1 sequence.

Results

Multilocus sequence typing analysis demonstrated that these isolates were highly diverse; 68 sequence types were identified, of which 28 were novel sequence types. Polygenic and eBURST analysis demonstrated genetically similar clones with dissimilar resistance profiles. Among the 45 randomly selected strains associated with carbapenem resistance, 2 were metallo β-lactamase producers; all the 45 strains were not AmpC overproducers. Sequence analysis revealed a high diversity in the oprD sequences among isolates. Strains susceptible to imipenem and meropenem with shortened L7 and L8 loops in oprD were the major strain types observed in this hospital.

Conclusion

This study indicated that oprD provided the main mechanism for carbapenem resistance. The shortened L7 and L8 loops are responsible for carbapenem susceptibility.

Assessment of Doripenem, Meropenem, and Imipenem against Respiratory Isolates of Pseudomonas aeroginosa in a Tertiary Care Hospital of North India

OBJECTIVE

Pseudomonas aeruginosa is one of the leading pathogen causing healthcare-associated infections, particularly in immunocompromised and critically ill patients. The development of carbapenem resistance in P. aeruginosa infections is worrisome. Data specifically comparing the susceptibility of the three available carbapenems are lacking in the Indian subcontinent.

MATERIALS AND METHODS

We evaluated the minimum inhibitory concentrations (MICs) of the three commonly used carbapenems- imipenem, meropenem, and doripenem against, 435 P. aeruginosa isolates obtained from respiratory samples and compared their susceptibility patterns to determine the best possible carbapenem among those available that may be used in combination regimes.

RESULTS

Overall, 222 (51.0%) of isolates were susceptible to doripenem followed by imipenem 206 (47.3%) and meropenem 195 (44.8%), respectively. Two hundred and sixty-two (60.23%) strains were intermediate or resistant to at least one carbapenem. The MIC90 of all three carbapenems was >32 μg/ml while the MIC50 of meropenem was 16 μg/ml which was higher than MIC50 of both imipenem (4 μg/ml) and doripenem (2 μg/ml).

CONCLUSION

Our study revealed that doripenem exerted better in vitro activity against the tested bacteria compared to imipenem and meropenem, but the difference was not statistically significant.