Antimicrobial susceptibility of Brazilian Clostridium difficile strains determined by agar dilution and disk diffusion

Abstract Clostridium difficile is a leading cause of diarrhea in hospitalized patients worldwide. While metronidazole and vancomycin are the most prescribed antibiotics for the treatment of this infection, teicoplanin, tigecycline and nitazoxanide are alternatives drugs. Knowledge on the antibiotic susceptibility profiles is a basic step to differentiate recurrence from treatment failure due to antimicrobial resistance. Because C. difficile antimicrobial susceptibility is largely unknown in Brazil, we aimed to determine the profile of C. difficile strains cultivated from stool samples of inpatients with diarrhea and a positive toxin A/B test using both agar dilution and disk diffusion methods. All 50 strains tested were sensitive to metronidazole according to CLSI and EUCAST breakpoints with an MIC90 value of 2 μg/mL. Nitazoxanide and tigecycline were highly active in vitro against these strains with an MIC90 value of 0.125 μg/mL for both antimicrobials. The MIC90 were 4 μg/mL and 2 μg/mL for vancomycin and teicoplanin, respectively. A resistance rate of 8% was observed for moxifloxacin. Disk diffusion can be used as an alternative to screen for moxifloxacin resistance, nitazoxanide, tigecycline and metronidazole susceptibility, but it cannot be used for testing glycopeptides. Our results suggest that C. difficile strains from São Paulo city, Brazil, are susceptible to metronidazole and have low MIC90 values for most of the current therapeutic options available in Brazil.

Outpatient parenteral antimicrobial therapy for orthopedic infections – a successful public healthcare experience in Brazil

Abstract Treatment of orthopedic infections usually requires prolonged antimicrobial therapy, ranging from 14 days up to 6 months. Nowadays, rising levels of antimicrobial resistance demands parenteral therapy for many patients. Outpatient parenteral antimicrobial therapy (OPAT) is a modality that allows treatment out of hospital in these situations. In Brazil, where a public universal healthcare system allows full coverage for all citizens, implantation and dissemination of OPAT programs would be beneficial for patients and for the system, because it would allow a better allocation of health resources. The Instituto de Ortopedia e Traumatologia do Hospital das Clínicas da Faculdade de Medicina da USP (IOT) started, in July 2013, a partnership with municipal health authorities in Sao Paulo, Brazil, in order to initiate an OPAT program in which patients discharged from that hospital would be able to continue antimicrobial therapy at primary care facilities. When necessary, patients could also receive their therapy at the day-hospital located at IOT. Primary care nursing and physician staff were trained about antimicrobial infusion and peripherally inserted central catheter manipulation. An OPAT specific antimicrobial protocol was designed and a special reference and counter-reference organized. As a result, 450 primary healthcare professionals were trained. In the first year of this program, 116 patients were discharged for OPAT. Chronic and acute osteomyelitis were most frequent diagnosis. Teicoplanin, ertapenem and tigecycline were the most used drugs. Duration of treatment varied from 10 to 180 days (average 101, median 42). Total sum of days in OPAT regimen was 11,698. Only 3 patients presented adverse effects. Partnership between services of different levels of complexity allowed implantation of a safe and effective public healthcare OPAT program for treatment of orthopedic infections. This program can serve as a model for developing similar strategies in other regions of Brazil and Latin America.

Over expression of AdeABC and AcrAB-TolC efflux systems confers tigecycline resistance in clinical isolates of Acinetobacter baumannii and Klebsiella pneumoniae

Abstract: INTRODUCTION: Due to the wide use of tigecycline in the treatment of severe infections caused by multidrug-resistant (MDR) bacteria, clinical resistance to tigecycline has increased in recent years. Here, we investigated the relationship between tigecycline resistance and the expression of efflux pumps. METHODS: Clinical isolates of Acinetobacter baumannii and Klebsiella pneumoniae were consecutively collected from hospitalized patients in three hospitals. The minimum inhibitory concentration (MIC) of tigecycline was determined using the broth microdilution method. Expression levels of efflux pump genes and regulators were examined by quantitative real-time reverse transcription polymerase chain reaction. The correlations between tigecycline MICs and gene expression levels were analyzed. RESULTS: Overall, 1,026 A. baumannii and 725 K. pneumoniae strains were collected. Most strains were isolated from sputum. The tigecycline resistance rate was 13.4% in A. baumannii isolates and 6.5% in K. pneumoniae isolates. Overexpression of AdeABC and AcrAB-TolC efflux systems was observed found in clinical tigecycline-resistant isolates. The tigecycline MIC had a linear relationship with the adeB expression level in A. baumannii isolates, but not with the acrB expression level in K. pneumoniae isolates. There were significant linear trends in the overexpression of ramA as the tigecycline MIC increased in K. pneumoniae isolates. CONCLUSIONS: Tigecycline resistance in A. baumannii and K. pneumoniae was strongly associated with the overexpression of efflux systems. More studies are needed to elucidate whether there are other regulators that affect the expression of adeB in A. baumannii and how ramA affects the expression of acrB in K. pneumoniae.

In Vitro Interactions of Antibiotic Combinations of Colistin, Tigecycline, and Doripenem Against Extensively Drug-Resistant and Multidrug-Resistant Acinetobacter baumannii

BACKGROUND: Acinetobacter baumannii infections are difficult to treat owing to the emergence of various antibiotic resistant isolates. Because treatment options are limited for multidrug-resistant (MDR) A. baumannii infection, the discovery of new therapies, including combination therapy, is required. We evaluated the synergistic activity of colistin, doripenem, and tigecycline combinations against extensively drug-resistant (XDR) A. baumannii and MDR A. baumannii. METHODS: Time-kill assays were performed for 41 XDR and 28 MDR clinical isolates of A. baumannii by using colistin, doripenem, and tigecycline combinations. Concentrations representative of clinically achievable levels (colistin 2 microg/mL, doripenem 8 microg/mL) and achievable tissue levels (tigecycline 2 microg/mL) for each antibiotic were used in this study. RESULTS: The colistin-doripenem combination displayed the highest rate of synergy (53.6%) and bactericidal activity (75.4%) in 69 clinical isolates of A. baumannii. Among them, thedoripenem-tigecycline combination showed the lowest rate of synergy (14.5%) and bacteri-cidal activity (24.6%). The doripenem-tigecycline combination showed a higher antagonistic interaction (5.8%) compared with the colistin-tigecycline (1.4%) combination. No antagonism was observed for the colistin-doripenem combination. CONCLUSIONS: The colistin-doripenem combination is supported in vitro by the high rate of synergy and bactericidal activity and lack of antagonistic reaction in XDR and MDR A. baumannii. It seems to be necessary to perform synergy tests to determine the appropri-ate combination therapy considering the antagonistic reaction found in several isolates against the doripenem-tigecycline and colistin-tigecycline combinations. These findings should be further examined in clinical studies.

The Resistance Mechanism and Clonal Distribution of Tigecycline-Nonsusceptible Klebsiella pneumoniae Isolates in Korea

PURPOSE: Tigecycline is one of the drugs used to treat multi-drug resistant Klebsiella pneumoniae (K. pneumoniae) infections, including complicated skin and soft tissue infections, complicated intra-abdominal infection, and community-acquired pneumonia in the Republic of Korea. However, since its commercial release, K. pneumoniae resistance against tigecycline has been reported, and there is a serious concern about the spread of tigecycline resistant bacteria. MATERIALS AND METHODS: In this study, we collected and analyzed 342 isolates from 23 hospitals in the Republic of Korea to determine the mechanisms of tigecycline susceptibility and their clonal types. The hospitals include several from each province in the Republic of Korea, except Jeju, an island province, and nonsusceptibility among the isolates was tested by the disk diffusion method. In our lab, susceptibility was checked again using the broth dilution method, and clonal types were determined using the multilocus sequence typing protocol. Real-time PCR was performed to measure the ramR mutation in the isolates nonsusceptible to tigecycline, which would suggest an increased expression of the AcrAB multidrug pump. RESULTS: Fifty-six K. pneumoniae isolates were found to be nonsusceptible, 16% of the 342 collected. Twenty-seven and nine isolates of the tigecycline nonsusceptible isolates had mutations in the ramR and rpsJ genes, respectively; while 18 nonsusceptible isolates harbored the tetA gene. Comparison of isolates with and without ramR mutation showed a significant statistical difference (p<0.05) for expression of AcrAB. Moreover, the most common clonal types, as observed in our study, appear to be ST11 and ST789. CONCLUSION: Several dominate clonal types infer tigecycline resistance to K. pneumoniae, including ST11, ST768, ST15, ST23, ST48, and ST307. There does not seem to be a transferrable medium, such as plasmid, for the resistance yet, although mutation of the ramR gene may be a common event, accounting for 48% of the nonsusceptibility in this study.

In Vitro Activity of Tigecycline Against Orientia tsutsugamushi

Scrub typhus is a zoonosis caused by Orientia tsutsugamushi (O. tsutsugamushi) occurring mainly in autumn in Korea. The need of new antibiotics has arisen with a report on strains resistant to antibiotics and chronic infection. This study aims to identify susceptibility of tigecycline in-vitro as a new therapeutic option for O. tsutsugamushi. Antibacterial activity of tigecycline against the O. tsutsugamushi was compared with doxycycline using flow cytometry assay. The inhibitory concentration 50 (IC50) was 3.59×10(-3) µg/mL in doxycycline-treated group. Whereas in 0.71×10(-3) µg/mL tigecycline-treated group. These findings indicate that tigecycline may be a therapeutic option for the treatment of scrub typhus.

Worrisome trends in rising minimum inhibitory concentration values of antibiotics against methicillin resistant Staphylococcus aureus - Insights from a tertiary care center, South India

ABSTRACT INTRODUCTION: Appearance of isolated reports of resistance to anti-methicillin-resistantStaphylococcus aureus (MRSA) drugs is worrisome underscoring the need to continuously monitor the susceptibility of clinical MRSA isolates to these drugs. Hence, the present study is conducted to determine the susceptibility of MRSA isolates to various classes of anti-MRSA drugs such as vancomycin (glycopeptide), daptomycin (lipopeptide), tigecycline (glycylcycline), and linezolid (oxazolidinone) to determine the MIC50 and MIC90 values, and to observe MIC creep over a three year period, if any, with respect to these drugs. METHODS: A total of 200 isolates of MRSA obtained from clinical specimens were included. MIC was determined by E-test for anti-MRSA antibiotics vancomycin, linezolid, daptomycin, and tigecycline. Non-parametric methods (Kruskal-Wallis and Chi-square test) were used to assess MIC trends over time. In addition, MIC50 and MIC90 values were also calculated. RESULTS: No isolate was found resistant to vancomycin, daptomycin, or linezolid; five isolates were resistant to tigecycline. Seven VISA isolates were encountered with the MIC value for vancomycin of 4 µg/mL. MIC values for vancomycin, tigecycline, linezolid showed a definite increase over a 3-year period which was statistically significant with p-values <0.0001, 0.0032, 0.0242, respectively. When the percentage of isolates with a median MIC value less than or equal to that of the index year was calculated, the change was most striking with vancomycin. The proportion of isolates with higher MIC values was greater in 2014 than 2012 and 2013. CONCLUSION: MIC creep was notably observed with vancomycin, and to some extent with tigecycline and linezolid. Selection pressure may result in creeping MICs, which may herald the emergence of resistant organisms.

Resistencia a antibióticos de última línea en cocos Gram positivos: la era posterior a la vancomicina / Resistance to "last resort" antibiotics in Gram-positive cocci: The post-vancomycin era

En los últimos años se han desarrollado nuevas alternativas para el tratamiento de infecciones por patógenos Gram positivos multirresistentes, entre los cuales Staphylococcus aureus resistente a la meticilina (SARM) y los enterococos resistentes a la vancomicina (ERV) se consideran un verdadero reto terapéutico, y aunque el uso de la vancomicina en infecciones graves causadas por SARM ha generado serias dudas en los últimos años, continúa siendo escasa la información clínica de respaldo al uso de agentes terapéuticos que la superen en eficacia. El linezolid, la daptomicina y la tigeciclina son agentes que tienen actividad contra los cocos Gram positivos y que fueron aprobados e introducidos en la terapia clínica en la década pasada. Además, se han probado o están en las fases finales de desarrollo otros agentes como las cefalosporinas de última generación (ceftarolina y ceftobiprol). El propósito de esta revisión fue describir las nuevas alternativas terapéuticas, particularmente en la era posterior a la vancomicina, y repasar las características químicas más relevantes de los compuestos y su espectro de actividad, haciendo énfasis en sus mecanismos de acción y resistencia.

New therapeutic alternatives have been developed in the last years for the treatment of multidrug-resistant Gram-positive infections. Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are considered a therapeutic challenge due to failures and lack of reliable antimicrobial options. Despite concerns related to the use of vancomycin in the treatment of severe MRSA infections in specific clinical scenarios, there is a paucity of solid clinical evidence that support the use of alternative agents (when compared to vancomycin). Linezolid, daptomycin and tigecycline are antibiotics approved in the last decade and newer cephalosporins (such as ceftaroline and ceftobiprole) and novel glycopeptides (dalvavancin, telavancin and oritavancin) have reached clinical approval or are in the late stages of clinical development. This review focuses on discussing these newer antibiotics used in the "post-vancomycin" era with emphasis on relevant chemical characteristics, spectrum of antimicrobial activity, mechanisms of action and resistance, as well as their clinical utility.

In vitro antimalarial activity of tigecycline against Plasmodium falciparum culture-adapted reference strains and clinical isolates from the Brazilian Amazon

Introduction: We evaluated the in vitro antimalarial activity of tigecycline as an alternative drug for the treatment of severe malaria. Methods: A chloroquine-sensitive Plasmodium falciparum reference strain, a chloroquine-resistant reference strain, and three clinical isolates were tested for in vitro susceptibility to tigecycline. A histidine-rich protein in vitro assay was used to evaluate antimalarial activity. Results: The geometric-mean 50% effective concentration (EC50%) of tigecycline was 535.5 nM (confidence interval (CI): 344.3-726.8). No significant correlation was found between the EC50% of tigecycline and that of any other tested antimalarial drug. Conclusions: Tigecycline may represent an alternative drug for the treatment of patients with severe malaria. .

In vitro antibacterial activity of tigecycIine against clinical isolates of linezolid-Intermediate and linezolid-resistant enterococci by time-kill assay

Introduction: Enterococci have become the third leading cause of nosocomial bacteraemia, an infection which is significantly associated with the risk of developing infective endocarditis. Linezolid provides high rates of clinical cure and microbiologic success in complicated infections due to Enterococcus spp. However, several instances of emergence of resistance during linezolid treatment have been reported. The aim of this study was evaluate the activity of tigecycline against linezolidintermediate (LIE) and linezolid-resistant enterococcus faecalis(LRE) by the timekill assay. Methods: Five isolates of LRE and two isolates of LIE were used in this study. Minimum inhibitory concentration (MIC) was determined by broth dilution following the guidelines from the Clinical and Laboratory Standards Institute (CLSI). Time-kill assay was employed to access the in vitro response profile of tigecycline. Results: All seven isolates presented MIC of 0.125 ìg/mL. Tigecycline activity was individually evaluated according to CLSI criteria. This antibiotic showed bactericidal activity against three of the five isolates of LRE and bacteriostatic activity against the other isolates. Conclusions: Tigecycline presented both bacteriostatic and bactericidal activity against tested isolates, which is an important data that must be considered for new studies.

Evaluación de la eficacia y seguridad de tigeciclina en el tratamiento de infecciones del tracto respiratorio: Revisión sistemática de la literatura científica / Evaluation of the efficacy and safety of tigecycline for treatment of respiratory tract infections: Systematic review of literature

Background: Tigecycline is indicated for the treatment of complicated skin infections, soft tissue and intraabdominal infections. Its use could be extended to community-acquired pneumonia (CAP) and hospital pneumonia (HN). The objective was to evaluate the efficacy and safety of tigecycline in the treatment of respiratory infections. Methods: systematic review (2012). Databases used were MEDLINE, EMBASE, Cochrane Library, CRD and WOK. We identified clinical trials of adults with respiratory infection, treated with tigecycline. The quality of the studies was assessed using CASPe checklist. Results: We selected four clinical trials of high-moderate quality. Three studies with patients with CAP and a trial with HN patients. In patients with CAP, efficacy of tigecycline (88.6 to 90.6%) was higher than levofloxacin (85.3 to 87.2%). The non inferiority testing was statistically significant (p < 0.001). In the study of patients with HN tigecycline showed an efficiency of 67.9% versus 78.2% for imipenem/cilastatin. Main adverse effects were gastrointestinal. Conclusions: The efficacy of tigecycline is non inferior than levofloxacin in patients with CAP, but less than imipenem in patients with HN. Tigecycline demonstrates noninferiority versus others tested antibiotics, and it shows a good safety profile.

Introducción: Tigeciclina está indicada en el tratamiento de infecciones complicadas de piel, tejidos blandos e intra-abdominales. Su utilización podría extenderse para neumonías adquiridas en la comunidad (NAC) y neumonías hospitalarias (NH). El objetivo ha sido evaluar la eficacia y seguridad de tigeciclina en el tratamiento de infecciones respiratorias. Material y Métodos: Revisión sistemática (2012). Se realizaron búsquedas en MedLine, Embase, Cochrane Library, CRD y WOK. Se localizaron ensayos clínicos de adultos con infección respiratoria, tratados mediante tigeciclina. La calidad de los estudios se valoró mediante los criterios CASPe. Resultados: Se seleccionaron cuatro ensayos clínicos de calidad alta-moderada. Tres estudios incluyeron pacientes con NAC y un estudio a pacientes con NH. En pacientes con NAC la eficacia de tigeciclina (88,6-90,6%) fue no inferior a la de levofloxacina (85,3-87,2%). El "test de no inferioridad" fue estadísticamente significativo (p < 0,001). En el estudio de pacientes con NH, tigeciclina presentó una eficacia de 67,9% frente a 78,2% de imipenem/cilastatina. Los principales efectos adversos fueron gastrointestinales. Conclusiones: la eficacia de tigeciclina es no inferior a la de levofloxacina en pacientes con NAC, pero inferior a imipenem en pacientes con NH. Tigeciclina ha demostrado no inferioridad frente a los otros antimicrobianos testados. Tigeciclina demuestra tener un buen perfil de seguridad.

Prevalence of colistin and tigecycline resistance in Acinetobacter baumannii clinical isolates from 2 hospitals in Riyadh Region over a 2-year period

To describe the rates and patterns of colistin and tigecycline resistance among Acinetobacter baumannii [A. baumannii] isolates from clinical specimens from 2 major hospitals in Riyadh Region over a 2-year period. This is a retrospective review of records of all clinical isolates of A. baumannii from the departments of microbiology at King Faisal Specialist Hospital and Research Center [KFSHRC] and Prince Sultan Military Medical City [PSMMC], Riyadh, Kingdom of Saudi Arabia for the period from January 2010 to December 2011. Records for 1307 Acinetobacter species isolates were identified. The overall tigecycline resistance rates were 9.7% and colistin 1.8%. Among Acinetobacter isolates from KFSHRC, tigecycline resistance rate increased from 10.4% in 2010 to 20.5% in 2011. Colistin resistance increased over the same period from 2.6% to 4.7%. No Acinetobacter isolates from PSMMC were reported to be colistin resistant, while tigecycline resistance rates increased from 1.3% in 2010 to 6.6% in 2011. In KFSHRC, resistance to tigecycline was reported significantly more in isolates from samples that originated in the intensive care units, whereas in PSMMC tigecycline resistance was reported exclusively from clinical areas other than intensive care. No temporal clustering of Acinetobacter isolates was apparent in either hospital over the study period. Tigecycline and colistin resistance were reported from a considerable proportion of Acinetobacter clinical isolates from the study hospitals over a 2-year period

Experiencia con el uso compasivo de tigeciclina en pacientes pediátricos infectados por Klebsiella pneumoniae productora de carbapenemasas / Experience with tigecycline compassionate use in pediatric patients infected with carbapenem resistant Klebsiella pneumoniae

Introduction: Infections produced by multidrug-resistant pathogens represent a therapeutic challenge because of the few therapeutic options available. Tigecycline is a relatively new antibiotic, with a wide spectrum of activity including some of these resistant bacteria. In adults is prescribed for the treatment of some infections caused by carbapenem resistant K. pneumoniae, however it has not been approved in children because of potential adverse effects in the dental enamel. Materials and Methods: Case series study. Medical records were reviewed in all children from 0 to 14 years of age that received tigecycline between January of 2008 and March of 2010. Results: 9 patients received Tigecycline mainly for treatment of peritonitis, bacteremia, pneumonia and sepsis caused by carbapenem resistant K. pneumoniae. A dose of 1 mg/kg q 12 hours was administered to all patients. No adverse events were reported and a total of 6 patients had complete resolution of the infection. Conclusions: Tigecycline could be considered a therapeutic option for treating infections produced by multidrug-resistant pathogens in children. The use in children is still compassionate and in this serie of cases Tigecycline was well tolerated and safe.

Introducción: Las infecciones causadas por bacterias multi-resistentes son difíciles de tratar debido a las pocas opciones terapéuticas disponibles. Tigeciclina es un antimicrobiano relativamente nuevo que tiene un amplio espectro de acción, incluyendo algunas de estas bacterias. En adultos se utiliza para el tratamiento de algunas infecciones producidas por Klebsiella pneumoniae productora de carbapenemasas (Kpn KPC). Sin embargo, por pertenecer al grupo de las tetraciclinas, su uso no ha sido aprobado en niños temiendo los posibles efectos adversos sobre el esmalte dental. Material y Métodos: Estudio de serie de casos. Se realizó una revisión de las historias clínicas de todos los niños de 0 a 14 años que recibieron tigeciclina en forma compasiva entre enero de 2008 y marzo de 2010. Resultados: 9 pacientes recibieron tigeciclina para tratamiento de peritonitis, bacteriemia, neumonía y sepsis por Kpn KPC. La dosis utilizada fue de 1 mg/kg/dosis cada 12 horas. No se encontraron efectos adversos importantes. La infección se consideró curada en 6 pacientes. Conclusiones: Tigeciclina puede ser considerada como una alternativa en el tratamiento de infecciones por bacterias multi-resistentes en niños. Su uso en la edad pediátrica sigue siendo compasivo y en esta serie de casos fue seguro.

Leuconostoc garlicum: An unusual pathogen in the era of vancomycin therapy.

Leuconostoc garlicum, belonging to the family of Leuconostocaceae, is a catalase-negative, Gram-positive ovoid cocci, intrinsically resistant to vancomycin. Clinical infection by Leuconostoc garlicum is rare. We report a case of respiratory tract infection subsequent to vancomycin therapy.

Antimicrobial susceptibility patterns of multidrugresistant Pseudomonas aeruginosa and Acinetobacter baumannii against carbapenems, colistin, and tigecycline

To examine susceptibility of Pseudomonas aeruginosa [P. aeruginosa] and Acinetobacter baumannii [A. baumannii] against carbapenems along with colistin and tigecycline as alternative therapeutic options. A total of 117 strains of multidrug-resistant [MDR] non-fermenting Gram negative bacteria isolated from non-duplicate samples were collected consecutively. We included one sample from each patient [84 isolates of A. baumannii and 33 isolates of P. aeruginosa isolated from patients seen at King Khalid University Hospital, Riyadh, Saudi Arabia, from June to December 2010]. Isolates were identified by the MicroScan WalkAway 96 Plus system. The minimum inhibitory concentrations [MICs] were determined by E-test following the Clinical and Laboratory Standards Institute breakpoint recommendations. Most A. baumannii strains were resistant to imipenem [90.5%], meropenem [90.5%], and doripenem [77.4%]. Whereas, a higher percentage of P. aeruginosa was resistant to imipenem [90.9%], and meropenem [81.8%], only 39.4% were resistant to doripenem. Colistin had excellent activity against both A. baumannii [100%] and P. aeruginosa [93.9%], while 89.3% of A. baumannii strains were susceptible to tigecycline. Among the carbapenems, doripenem was found to be the most potent antimicrobial agent against P. aeruginosa, whereas colistin proved to be an effective alternative antimicrobial agent for treatment of A. baumannii or P. aeruginosa. Tigecycline remains the best therapeutic option for MDR A. baumannii