[Septic arthritis byAggregatibacteraphrophilus: Case report] / Artritis séptica por Aggregatibacter aphrophilus.

Introduction: Septic arthritis by Aggregatibacter aphrophilus is an uncommon entity, so it's important to diagnose it early, to avoid serious consequences. In adults, the knee is the most affected site. Methods: We present a case of a 17-year-old boy, with pain in the left knee since one month ago. It shows an increase in local temperature, erythema and movement inability. A nuclear magnetic resonance (NMR) was performed and empirical treatment was given with cephalothin and clindamycin. A knee arthrotomy was realized, and intramedullary secretion and bone tissue was sent to study. Results: the NMR images were suggestive of an infectious process. In the culture gram-negative coccobacilli were isolated, later identified like as Aggregatibacter aphrophilus. According to this diagnostic, the treatment was changed to ceftriaxone The main conclusions: the rapidity and certainty in the choice of antimicrobial therapy is the most important step for a well evolution of this infection, therefore is very important to emphasize the importance of a correct identification of these rare microorganisms

Introducción: Aunque la artritis séptica es una entidad poco común, es importante debido a las graves consecuencias de un diagnóstico tardío o un incorrecto tratamiento. En adultos, la rodilla es el sitio más afectado. El objetivo de este trabajo es presentar un caso clínico de artritis séptica por Aggregatibacter aphrophilus en rodilla en un paciente joven, inmunocompetente, sin antecedentes patológicos. Materiales y métodos: Se estudia el caso de un joven de 17 años, tabaquista, con un cuadro de 1 mes de evolución caracterizado por gonalgia izquierda, aumento de la temperatura local, eritema e impotencia funcional. Se realizan análisis de sangre, una ecografía,y resonancia magnética (RMN).Se solicitan hemocultivos y cultivos de líquido intrarticular de rodilla. En la RMN se observa una lesión expansiva en la región femoral, sugestiva de un proceso infeccioso. Se comienza tratamiento empírico con cefalotina y clindamicina. Se realiza una artrotomia de rodilla enviándose para su estudio secreción endomedular, tejido óseo y endomedular. Resultados: Los hemocultivos y el cultivo del líquido intraarticular fueron negativos, pero los materiales obtenidos por técnica quirúrgica fueron positivos para el cultivo, aislándose cocobacilos gram negativos, posteriormente identificados como Aggregatibacter aphrophilus Se realizó el diagnóstico de artritis séptica por Aggregatibacter aphrophilus y se roto el tratamiento antimicrobiano a ceftriaxona. Conclusión: La rapidez y la certeza en la elección de la terapia antimicrobiana son un paso decisivo para la evolución de la enfermedad, por lo tanto se remarca la importancia de una correcta identificación de estos microorganismos poco frecuentes.

Estimating the likelihood of success with the initial empiric antimicrobial therapy in patients with nosocomial infections.

In order to estimate the likelihood of success (SL) with the initial empiric antimicrobial therapy, the following formula was constructed with data subjected to prior clinical validation in real time: SL (%) = (Nº isolates susceptible to IEAT/Nº patients with MDI) × 100. Where the numerator of the formula represents the total number of isolates recovered from the assessed type of infection, that was susceptible to any component of empiric antimicrobial therapy (IEAT) used, and the denominator represents the total number of patients with the same assessed, but microbiologically documented infection (MDI). For male hospital-acquired urinary tract infection, only imipenem reached a suitable SL value (i.e. ≥80%). In patients with hospital-acquired peritonitis, imipenem and tigecycline-ceftazidime showed the highest coverage rates. For ventilator-associated pneumonia only imipenem yielded acceptable coverage as a single drug. Implementing the present formula instead of the regular global antibiograms used to guide the selection of the initial treatment may benefit the patient outcome and improve antimicrobial usage.

Comparative time-kill study of doxycycline, tigecycline, cefazolin and vancomycin against several clones of Staphylococcus aureus.

BACKGROUND: We present herein, a comparative study assessing the bactericidal kinetics of tigecycline, doxycycline, cefazolin and vancomycin against several methicllin-susceptible (MSSA) and -resistant (MRSA) Staphylococcus aureus isolates recovered from patients of 24 different cities in Argentina. METHODS: After genotypic characterization, 20 strains (10 MRSA and 10 MSSA) were selected for time-kill studies. RESULTS: Vancomycin showed bactericidal effect (i.e. ≥3-log(10) CFU/mL decrease) against 50% and 10% of the MRSA strains at 4 x Minimal Inhibitory Concentration (MIC) and 2xMIC, respectively, after 24 h of incubation and displayed bactericidal activity against all MSSA isolates at 4xMIC. Cefazolin was bactericidal against 30% of MSSA strains at the higher concentration (4xMIC) and against 10% at 2 x MIC and MIC dose concentrations. The bactericidal magnitude of cefazolin observed after 24 h of incubation was lower than the vancomycin one. Albeit bacteriostactic, tigecycline at 2xMIC exerted a -1 to2-log decrease in the viable cell counts after 24-h incubation against 19 of the 20 S. aureus strains. Doxycycline was the least inhibitory of the antibiotics tested against both MRSA and MSSA, displaying no bactericidal activity in any of the cases and showing regrowth after 24 h of incubation at MIC level. CONCLUSION: Vancomycin at high concentrations showed the best activity. Cefazolin did not show the activity expected for a beta-lactam antibiotic against MSSA. Tigecycline may be a useful option in infections caused by MRSA, where bactericidal activity is not an exclusive requirement and doxycycline does not seem an attractive alternative in serious infections.

[Comparative evaluation of the sensitivity of Acinetobacter to colistin, using the prediffusion and minimum inhibitory concentration methods: detection of heteroresistant isolates]. / Sensibilidad de Acinetobacter a la colistina evaluada mediante los métodos de predifusión y de concentración inhibitoria mínima: Detección de aislamientos heterorresistentes.

The objective of this study is to perform a comparative evaluation of the prediffusion and minimum inhibitory concentration (MIC) methods for the detection of sensitivity to colistin, and to detect Acinetobacter baumanii-calcoaceticus complex (ABC) heteroresistant isolates to colistin. We studied 75 isolates of ABC recovered from clinically significant samples obtained from various centers. Sensitivity to colistin was determined by prediffusion as well as by MIC. All the isolates were sensitive to colistin, with MIC = 2µg/ml. The results were analyzed by dispersion graph and linear regression analysis, revealing that the prediffusion method did not correlate with the MIC values for isolates sensitive to colistin (r² = 0.2017). Detection of heteroresistance to colistin was determined by plaque efficiency of all the isolates with the same initial MICs of 2, 1, and 0.5 µg/ml, which resulted in 14 of them with a greater than 8-fold increase in the MIC in some cases. When the sensitivity of these resistant colonies was determined by prediffusion, the resulting dispersion graph and linear regression analysis yielded an r² = 0.604, which revealed a correlation between the methodologies used.

Sensibilidad de Acinetobacter a la colistina evaluada mediante los métodos de predifusión y de concentración inhibitoria mínima: Detección de aislamientos heterorresistentes / Comparative evaluation of the sensitivity of Acinetobacter to colistin, using the prediffusion and minimum inhibitory concentration methods: Detection of heteroresistant isolates

El objetivo de este estudio fue evaluar comparativamente los métodos de predifusión y de concentración inhibitoria mínima para establecer la sensibilidad de aislamientos del complejo Acinetobacter calcoaceticus-baumannii (ABC) a la colistina y detectar a aquellos que presenten heterorresistencia a dicho antibiótico. Se estudiaron 75 aislamientos de ABC recuperados de materiales clínicamente significativos. Se determinó su sensibilidad a la colistina por el método de predifusión y de concentración inhibitoria mínima. Todos los aislamientos resultaron sensibles, con CIM = 2 µg/ml y halos de inhibición en el ensayo de la predifusión = 20 mm. Mediante el método de eficiencia de plaqueo se evaluó la presencia de heterorresistencia a la colistina. Se encontraron 14 aislamientos que originaron colonias heterorresistentes; sus CIM aumentaron en algunos casos en más de 8 veces. Con estas colonias seleccionadas se repitió el ensayo de predifusión. Finalmente se confeccionaron los gráficos de dispersión y se realizaron los análisis de regresión lineal, tanto para el conjunto inicial de todos los aislamientos clínicos como para el subgrupo de los aislamientos resistentes generados durante la evaluación de la heterorresistencia. Se obtuvieron coeficientes de determinación (r²) de 0,2017 y 0,604, respectivamente, lo que indica correlación entre los métodos sólo al evaluar aislamientos preseleccionados por su resistencia a este agente.

The objective of this study is to perform a comparative evaluation of the prediffusion and minimum inhibitory concentration (MIC) methods for the detection of sensitivity to colistin, and to detect Acinetobacter baumanii-calcoaceticus complex (ABC) heteroresistant isolates to colistin. We studied 75 isolates of ABC recovered from clinically significant samples obtained from various centers. Sensitivity to colistin was determined by prediffusion as well as by MIC. All the isolates were sensitive to colistin, with MIC = 2µg/ml. The results were analyzed by dispersion graph and linear regression analysis, revealing that the prediffusion method did not correlate with the MIC values for isolates sensitive to colistin (r² = 0.2017). Detection of heteroresistance to colistin was determined by plaque efficiency of all the isolates with the same initial MICs of 2, 1, and 0.5 µg/ml, which resulted in 14 of them with a greater than 8-fold increase in the MIC in some cases. When the sensitivity of these resistant colonies was determined by prediffusion, the resulting dispersion graph and linear regression analysis yielded an r² = 0.604, which revealed a correlation between the methodologies used.

Comparative time-kill study of doxycycline, tigecycline, sulbactam, and imipenem against several clones of Acinetobacter baumannii.

To assess potential alternative options for the treatment of infections caused by Acinetobacter baumannii, we performed time-kill studies of doxycycline and tigecycline using several isolates recovered from patients residing in 10 different cities in Argentina. Imipenem and sulbactam were also included for comparison purposes. Eleven isolates representing 5 distinctive clones, or isolates with different susceptibility patterns within the same clone, were selected. Tubes containing cation-supplemented Mueller-Hinton broth with and without antibiotics were seeded with a log-phase inoculum of roughly 5 x 10(5) CFU/mL. By using the viable counts determined at 2-, 4-, 6-, 8-, and 24-h intervals after inoculation, a 24-h time-kill curve was constructed for each isolate. No bactericidal activity (defined as a >or=3-log(10) CFU/mL decrease in the viable cell counts with respect to the original inoculum) was observed at any time with sulbactam (4 microg/mL) or tigecycline (1 microg/mL), whereas low bactericidal rate (18% of the isolates) was shown for doxycycline (1 microg/mL) and sulbactam (16 microg/mL) after 24 h of incubation. Doxycycline (4 microg/mL) and tigecycline (8 microg/mL) displayed bactericidal activity at 24 h of incubation against 36% and 54% of the isolates, respectively, including the carbapenem-resistant isolate. Corresponding values for imipenem (1 and 4 microg/mL) against the 10 carbapenem-susceptible isolates were 60% and 90%, respectively. The present study confirms the in vitro efficacy of imipenem against A. baumannii, suggests that doxycycline could be a suitable, cost-effective, alternative option in some instances, and sheds light on the potential role of tigecycline in the treatment of infections with this organism.