Clinical outcome from hematopoietic cell transplant patients with bloodstream infection caused by carbapenem-resistant P. aeruginosa and the impact of antimicrobial combination in vitro

Bloodstream infection (BSI) caused by carbapenem-resistant P. aeruginosa (CRPA) has high mortality in hematopoietic stem cell transplant (HSCT) recipients. We performed MIC, checkerboard, time-kill assay, PFGE, PCR, and whole genome sequence and described the clinical outcome through Epi Info comparing the antimicrobial combination in vitro. Mortality was higher in BSI caused by CRPA carrying the lasB virulence gene. The isolates were 97% resistant to meropenem displaying synergistic effect to 57% in combination with colistin. Seventy-three percent of the isolates harbored bla_SPM-1 and Tn4371 and belonged to ST277. The synergistic effect in vitro with meropenem with colistin appeared to be a better therapeutic option.

In vitro synergy of β-lactam combinations against KPC-producing Klebsiella pneumoniae strains

BACKGROUND

Double carbapenem therapy has been promoted as an alternative treatment for infections due to carbapenemase-producing Enterobacteriaceae where carbapenemase inhibitors are unavailable or when other agents have demonstrated toxicity with equally limited evidence. The capacity of other β-lactams and β-lactamase inhibitors to provide synergistic activity with carbapenems is unclear.

OBJECTIVES

This study sought to investigate the in vitro synergistic potential of other β-lactam/β-lactamase combinations with meropenem against KPC producers.

METHODS

Time-kill assays were performed on 24 unique strains of KPC-producing Klebsiella pneumoniae. Combinations evaluated included meropenem or imipenem with one of the following: ertapenem, piperacillin/tazobactam or ceftolozane/tazobactam. Concentrations used for each drug were those considered physiologically attainable in patients with a time above the concentration exceeding 40%-50% of the dose interval. Combinations were considered to be synergistic when they reduced bacterial cfu/mL by ≥2 log10 at 24 h as compared with the single most active agent.

RESULTS

The combination of piperacillin/tazobactam with meropenem was found to be synergistic against 70.8% of the isolates, followed by ertapenem with meropenem (58.3%) and ceftolozane/tazobactam with meropenem (41.7%). The piperacillin/tazobactam combination was found to be more bactericidal than the other combinations, with 58.3% of isolates demonstrating a ≥4 log10 cfu/mL reduction at 24 h, as compared with 37.5% for ertapenem and 20.8% for ceftolozane/tazobactam combinations.

CONCLUSIONS

The combination of piperacillin/tazobactam with meropenem may be a potential therapy against KPC-producing K. pneumoniae when other therapies are unavailable or prohibitively toxic.

Stability of Biological Activity of Frozen β-lactams over Time as Assessed by Time-Lapsed Broth Microdilutions

To evaluate the antimicrobial agent's stability stored at -80 °C, six β-lactams (meropenem, ertapenem, imipenem, ceftriaxone, ceftazidime, and piperacillin-tazobactam) were studied using the broth microdilution (BMD). The minimum inhibitory concentration (MIC) remained accurate with the same amount of frozen drug for at least six months. Thereafter, there was a diminishing drug concentration due to instability. At this temperature, most β-lactams can be frozen as a stock concentration for up to six months without a significant loss in antibiotic activity.

Carbapenem-resistant Pseudomonas aeruginosa carrying blaVIM-36 assigned to ST308: Indicated non-virulence in a Galleria mellonella model

OBJECTIVES

Based on pulsed-field gel electrophoresis (PFGE) profile, whole-genome sequencing (WGS) of eight carbapenem-resistant Pseudomonas aeruginosa isolates from a bone marrow transplant unit in São Paulo, Brazil, was performed to investigate the presence of resistance and virulence genes as well as to determine the sequence type (ST) by multilocus sequence typing (MLST).

METHODS

The initial phenotypic susceptibility pattern of the isolates was determined by VITEK^®2. Minimum inhibitory concentrations (MICs) were determined by the broth microdilution method for amikacin, meropenem and colistin. WGS was performed using an Illumina MiSeq system. A Galleria mellonella infection model was used to evaluate the virulence of the strains.

RESULTS

WGS demonstrated that mutations in genes encoding outer membrane proteins and efflux pumps in an isolate harbouring bla_VIM-36 (ST308) differed from those in isolates harbouring bla_SPM (ST277). The mexT gene harboured a mutation resulting in a frameshift in all isolates; in addition, the oprD gene of the bla_VIM-36-carrying isolate had an insertion leading to a frameshift. Virulence genes did not differ between ST277 and ST308 strains. Moreover, only two isolates harbouring bla_SPM showed virulence in the G. mellonella model, killing 100% of larvae after 18-24h.

CONCLUSIONS

P. aeruginosa carrying bla_VIM-36 belonging to ST308 was identified for the first time in our hospital. Although the virulence gene profiles were similar in isolates carrying bla_SPM and the isolate carrying bla_VIM-36, only two isolates harbouring bla_SPM showed virulence in the G. mellonella model.

Characterization of carbapenem-resistant Pseudomonas aeruginosa clinical isolates, carrying multiple genes coding for this antibiotic resistance

Background

Carbapenemase genes are one of the most frequent mechanisms reported in carbapenem-resistant P. aeruginosa; however, description of P. aeruginosa co-harbouring two or more carbapenemases is unusual.

Methods

In this study we evaluated the presence of carbapenemase genes and the clonality of P. aeruginosa isolates obtained from a hospital over a 12-year period. A total of 127 isolates of carbapenem-resistant P. aeruginosa recovered from 109 patients feces (four samples), rectal swab (three samples), nasal swab (one sample) and anal abscess (one sample), were evaluated. Minimum inhibitory concentrations of the following antibiotics imipenem, meropenem and polymyxin E were determined by broth microdilution. The molecular profile of isolates was evaluated by pulsed field gel electrophoresis (PFGE). PCR for the following carbapenemase genes bla_IMP;bla_SPM;bla_VIM;bla_SIM;bla_NDM;bla_KPC;bla_GES and nucleotide sequencing to confirm the enzyme gene types were performed and compared with the database available on the Internet (BLAST-http://www.ncbi.nlm.nhi.gov/blast/).

Results

All isolates were carbapenem-resistant, their MIC₅₀ and MIC₉₀ were respectively 64 μg/mL and 256 μg/mL to imipenem and 32 μg/mL and 256 μg/mL to meropenem, all isolates except one (MIC = 8 mg/L) were susceptible to polymyxin E. The most frequent carbapenemase genes identified were bla_SPM identified in 41 isolates (32%), followed by 10 with bla_kpc and 5 with bla_VIM (3.9%). All belonged to the class SPM-1 and VIM-2. In 2011, one isolate harbouring three carbapenemase genes (SPM-1, VIM-2 and KPC-2) that belonged to a new clone was identified in a hematopoietic stem cell transplanted patient. Then, 19 carbapenem-resistant P. aeruginosa were identified in an outbreak that occurred in the bone marrow transplant unit, all positive for SPM-1 gene, and 9 (47.3%) harbored both SPM-1 and KPC.

Conclusion

Our findings showed that PCR for KPC gene should be performed to evaluate carbapenem resistance in P. aeruginosa and that this agent can harbor more than one carbapenemase gene. Attention should be focused on the possible rapid spread of KPC in P. aeruginosa isolates and for the fact that P. aeruginosa may become a reservoir of this transmissible resistance mechanism.

Plasma hydroxy-metronidazole/metronidazole ratio in patients with liver disease and in healthy volunteers

Metronidazole pharmacokinetics were studied in patients with different degrees of liver cirrhosis, classified according to the Child-Pugh algorithm (A, B or C, as liver disease severity increases) and in schistosomic patients. Metronidazole (500 mg) was administered i.v. as a slow infusion over 20 min, and blood samples were collected at set intervals after the end of the infusion. The plasma concentrations of metronidazole and its main metabolite hydroxy-metronidazole were quantified by reversed-phase h.p.l.c. with u.v. detection. The metronidazole and hydroxy-metronidazole areas under the curve from 0 to 24 h (AUC0,24h), the metronidazole terminal elimination half-life (t1/2), the total clearance (CL), the metronidazole volume of distribution (V) values and the hydroxy-metronidazole/metronidazole concentration ratios as a function of time were calculated for each group. Comparison of the metronidazole AUC0,24h, t1/2 and CL values revealed that metronidazole metabolism is progressively impaired as the severity of liver disease increases. There were no variations in these parameters between the schistosomic and Child-Pugh A groups. In addition, there were no differences in the V and hydroxy-metronidazole AUC0,24h among the various groups studied. However, metronidazole metabolism was delayed in patients with hepatic disease, as illustrated by the hydroxy-metronidazole/metronidazole ratio 10 min after the end of metronidazole infusion. These results indicate that the clinical assessment of liver disease is paralleled by an impairment of metronidazole metabolism. Of the studied variables, we propose the hydroxy-metronidazole/metronidazole ratio 10 min after metronidazole infusion as a suitable and practical index for liver function evaluation.

Inquérito sôbre a Doença de Chagas em candidatos a doadores de sangue

Em 576 indivíduos que se apresentaram ao Banco de Sangue do Hospital do Pronto Socorro de Belo Horizonte, para a prova de seleção de doadores de sangue, foi feita a reação de fixação do complemento (antígeno de cultura do S. cruzi) para o diagnóstico da doença de CHAGAS. Em 14 casos a reação foi positiva. Sete candidatos a doador, com reação positiva, foram estudados clìnicamente, e nêles foi praticado xenodiagnóstico, eletrocardiograma e tele-radiografia do coração e vasos da base. Em todos os 7 casos estudados apurou-se que já haviam habitado casas infestadas por triatomíneos em zonas endêmicas e 3 deles apresentaram sinais de comprometimento miocárdico, revelando o eletrocardiograma, em dois, bloqueio do ramo direito, e, em um, bloqueio A-V total. Em 3 candidatos conseguiu-se a comprovação parasitológica da infecção chagásica pela positividade do xenodiagnóstico. Foram feitas considerações sobre o problema da transmissibilidade da doença de CHAGAS pela transfusão de sangue e da necessidade de se tornar obrigatória a inclusão da reação de fixação do complemento para esquizotripanose entre as provas de rotina exigidas na seleção de doadores de sangue.