Evaluation of phenotypic methods for detection of polymyxin B-resistant bacteria.

Determination of sensitivity to polymyxins has always been a challenge, especially in clinical laboratory routines. This study evaluated two rapid, simple, and inexpensive phenotypic methods to test polymyxin B (PMB) susceptibility in Enterobacterales and non-fermenting Gram-negative bacilli. One hundred isolates were used in the tests. The isolates were collected in three hospitals in southern and southeastern Brazil from 1995 to 2019. We compared broth microdilution (reference method) with the broth disk elution test and modified drop test, using polymyxin B -disk or PMB -powder in 2 concentrations (12 and 16 µg/ml). For the broth disk elution and modified drop test with the concentration of 12 µg/ml, categorical agreement values exceeded 90%. The modified drop test with a concentration of 12 µg/ml and broth disk elution may be excellent for initial screening of polymyxin-resistance in laboratory routines. Moreover, these methods are simple and use inexpensive supplies, and may optimize therapeutic decisions.

Consecutive outbreaks of Burkholderia cepacia complex caused by intrinsically contaminated chlorhexidine mouthwashes.

BACKGROUND: We report 2 consecutive outbreaks of the Burkholderia cepacia complex (Bcc) in an intensive care unit (ICU) and describe its characteristics and consequences. METHODS: Over a 72-day period, a multidisciplinary ICU team detected 2 distinct periods of high and unusual incidence of Bcc isolates that were recovered from cultures of endotracheal aspirate. Cultures of tap water, ultrasound gel and mouthwash (opened and unopened bottles) were performed. Bcc was identified with the BD-Phoenix and MALDI-TOF MS systems, with molecular typing using the enterobacterial repetitive intergenic consensus-polymerase chain reaction technique. RESULTS: In both outbreak 1 (6 patients) and outbreak 2 (5 patients), the point sources of Bcc were chlorhexidine mouthwashes of 2 different brands, both of them intrinsically contaminated. All patients had a clinical diagnosis of ventilator-associated pneumonia (VAP), and 6 died. MALDI-TOF MS identified 2 species of Bcc (B. cenocepacia and B. cepacia). Enterobacterial repetitive intergenic consensus-polymerase chain reaction typing confirmed 100% genetic similarity between patient and mouthwash isolates from each period. The first outbreak was controlled in 20 days and the second in 6 days. CONCLUSIONS: The surveillance program for multidrug-resistant organisms, especially in high-risk patients, with the active participation of a multidisciplinary team, was crucial for success in controlling these outbreaks.

Epidemiologic surveillance of multidrug-resistant bacteria in a teaching hospital: A 3-year experience.

BACKGROUND: The objective of this prospective study was to verify the effectiveness of a multidisciplinary surveillance program that was implemented in a teaching hospital in southern Brazil, to prevent and control the spread of multidrug-resistant organisms. METHODS: The program implemented involved establishment of prevention guidelines, hand-hygiene promotion, isolation of patients colonized or infected by such organisms, enforced contact precautions, and terminal cleaning and disinfection of isolation rooms. A microbiology service, previously provided by an external laboratory, was established in the hospital. Detection of bacteria-resistant genes and molecular typing were performed also. RESULTS: Statistically significant differences were observed between the pre- and post-intervention periods (P = .00198). Control measures were effective in blocking the dissemination of a previously endemic clone of Acinetobacter baumannii. Changes were observed in the dissemination pattern, from a monoclonal to a polyclonal mode. The incidence of vancomycin-resistant Enterococcus during the surveillance period was low. Only 2 isolates of BLAKPC-positive Klebsiella pneumoniae (distinct profiles), and 5 isolates of BLASPM-positive Pseudomonas aeruginosa (a single cluster), were detected. CONCLUSIONS: These results indicate that the surveillance program implemented was effective in preventing the spread of multidrug-resistant organisms in the hospital.

In vitro activity of polymyxins in combination with ß-lactams against clinical strains of Pseudomonas aeruginosa.

The emergence of multidrug-resistant (MDR) strains has made it difficult to treat infections caused by Pseudomonas aeruginosa. In order to develop new alternative therapies for the treatment of MDR P. aeruginosa infections, the antimicrobial activities of different antibiotic combinations have been studied in vitro and in vivo. In this study, the in vitro antimicrobial activities of six different combinations of polymyxins and ß-lactams against 34 clinical isolates of P. aeruginosa were evaluated. For the combinations tested by the checkerboard method, an indifferent effect was observed for all strains. However, 27 strains (19 MDR) showed reductions in their minimal inhibitory concentration (MIC) for at least one of the antibiotics in the combinations evaluated. Combination with polymyxins resulted in reductions of the ß-lactam MICs, with a change in the resistance category to susceptible in eight MDR strains. These results from the in vitro evaluation suggest that combinations of polymyxins and ß-lactams may significantly reduce the MICs of the antibiotics tested. These combinations require further evaluation for use in medical practice.

Efeito antimicrobiano in vitro da associação de polimixina B e ceftazidima em amostras clínicas de pseudomonas aeruginosa / The in vitro antimicrobial effect of polymyxin b associated with ceftazidime in pseudomonas aeruginosa clinical isolates

A associação de antibióticos é uma alternativa para tratar doenças infecciosas de etiologia polimicrobiana ou causadas por bactérias multirresistentes, como por exemplo, Pseudomonas aeruginosa. No presente estudo, investigamos a atividade antimicrobiana “in vitro” da combinação de polimixina B e ceftazidima, em 20 amostras clínicas de P. aeruginosa. Inicialmente, a concentração inibitória mínima (CIM) dos agentes foi determinada pela técnica de microdiluição em caldo para cada uma das amostras selecionadas. Posteriormente, com base nos valores das CIMs, o efeito antimicrobiano da combinação da polimixina B e ceftazidima foi avaliado por meio do método de “checkerboard”. Os resultados demonstraram que todas as amostras de P. aeruginosa estudadas foram sensíveis à polimixina B, com CIMs variando entre 1 e 2 μg/ml. Em relação à ceftazidima, as CIMsvariaram de 2 a 8 μg/ml, em nove amostras sensíveis, e de 16 a 1.024 μg/ml, em 11 amostras, resistentes a esse antibiótico. Para todas amostras testadas, o efeito antimicrobiano da combinação de polimixina B eceftazidima foi indiferente, sugerindo que esta associação, quando utilizada na forma de terapia combinada invivo, pode não apresentar atividade superior àquela obtida pela monoterapia.

The antibiotics association is an alternative to treat infectious diseases, either caused by polymicrobial etiologyor those caused by multidrug-resistant bacteria, such as Pseudomonas aeruginosa. In this study, the in vitroantimicrobial activity of the polymyxin B and ceftazidime combination was investigated in 20 clinical isolates of P.aeruginosa. Initially, the minimum inhibitory concentration (MIC) of those agents was determined by using thebroth microdilution technique for each of the selected strains. Afterwards, based on MIC values, the antimicrobialeffect of the polymyxin B and ceftazidime combination was evaluated by making use of "checkerboard" method. The results demonstrated that all P. aeruginosa strains studied were sensitive to polymyxin B, with MICs varying from 1 to 2 μg/ml. In relation to ceftazidime, MICs varied from 2 to 8 μg/ml in nine sensitive strains, and from 16 to 1.024 μg/ml in 11 strains resistant to that antibiotic. For all strains tested, the antimicrobial effect of thepolymyxin B and ceftazidime combination was indifferent, thus suggesting that such an association, when used as a combined in vivo therapy, sometimes does not present any activity superior to the one obtained with monotherapy.

La asociación de antibióticos es una alternativa para tratar enfermedades infecciosas de etiología polimicrobianao causadas por bacterias multiresistentes, como por ejemplo Pseudomonas aeruginosa. En el presente estudio, investigamos la actividad antimicrobiana in vitro de la combinación de polimixina B y ceftazidima en 20 muestras clínicas de P. aeruginosa. Inicialmente, la concentración inhibitoria mínima (CIM) de los agentes fue determinada por la técnica de microdiluición en caldo para cada una de las muestras seleccionadas. Posteriormente, con base en los valores de las CIMs, el efecto antimicrobiano de la combinación de la polimixinaB y ceftazidima fue evaluado a través del método de “checkerboard”. Los resultados demostraron que todas lasmuestras de P. aeruginosa estudiadas fueron sensibles a la polimixina B, con CIMs variando entre 1 y 2 μg/ml.En relación con la ceftazidima, las CIMs variaron de 2 a 8 μg/ml en nueve muestras sensibles, y de 16 a 1.024μg/ml en 11 muestras resistentes a ese antibiótico. Para todas las muestras testadas, el efecto antimicrobianode la combinación de polimixina B y ceftazidima fue indiferente, sugiriendo que esta asociación, cuando utilizadaen la forma de terapia combinada in vivo, puede no presentar actividad superior a aquella obtenida por lamonoterapia.