Rapid 4 to 6 hour detection of extended-spectrum beta-lactamases in a routine laboratory

A novel rapid bioluminescence-based antimicrobial susceptibility testing method based on adenosine triphosphate consumption

Introduction

Standard, phenotypic antimicrobial susceptibility testing (AST) methods require 16-20 h of incubation and are considered as the bottleneck in providing timely input for appropriate antimicrobial treatment. In this study, a novel adenosine triphosphate (ATP)-bioluminescence-based method which allows rapid AST within 3 h was described.

Methods

Standard AST was performed for 56 Enterobacterales isolates using EUCAST disk diffusion (DD) methodology. For the bioluminescence-based rapid AST, suspensions of bacteria were prepared using Mueller-Hinton broth to obtain a turbidity of 0.5 McFarland. The suspensions were distributed into 96-well microtiter plates. ATP (20 mM) and fixed concentrations of different antibiotics were added. Following incubation at 37°C for 1 h, a luminescent reaction mixture, including the substrate luciferin and luciferase enzyme solutions, was added. The chemiluminescence was monitored using an imaging system. Light production demonstrated the presence of ATP, indicating that the isolate was susceptible to the antibiotic in the well. Absence or decrease of light intensity, compared with the growth control well, indicated the use of ATP as an indirect measure of bacterial growth, and therefore resistance to the antibiotic in the well.

Results

The novel AST method was tested using a total of 348 test wells. Concordance was achieved for 290 (83.3%) of the tests, whereas 52 (14.9%) and 6 (1.7%) tests caused minor and major errors, respectively.

Discussion

In this study, a bioluminescence-based rapid AST was developed based on the consumption of ATP by bacteria. Our method's uniqueness relies on determining ATP consumption by microorganisms in the presence or absence of an antibiotic. The novel AST method described in this study lays the groundwork for obtaining rapid results, which should be considered as a proof of concept. With further optimization studies, this novel method can provide higher accuracy and be introduced into clinical practice as a routine AST method.

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Risk factors of organ failure in cholangitis with bacteriobilia

AIM: To identify the risk factors for organ failure (OF) in cholangitis with bacteriobilia.

METHODS: This study included 182 patients with acute cholangitis who underwent percutaneous transhepatic biliary drainage between January 2005 and April 2013. We conducted a retrospective analysis of comprehensive clinical and laboratory data.

RESULTS: There were 24 cases (13.2%) of OF and five deaths (2.7%). Bile culture was positive for microbial growth in 130 out of 138 (94.2%) patients. In multivariate analysis of 130 patients with positive bile cultures, significant predictive factors for OF were the presence of extended-spectrum beta-lactamase (ESBL) organisms in blood cultures, pre-existing renal dysfunction, and choledocholithiasis as an etiology, with odds ratios of 15.376, 6.319, and 3.573, respectively. We developed a scoring system with a regression coefficient of each significant variable. The OF score was calculated using the following equation: (2.7 × ESBL organisms in blood cultures) + (1.8 × pre-existing renal dysfunction) + (1.3 × choledocholithiasis). This scoring system for predicting OF was highly specific (99.1%) and had a positive predictive value of 86.2%.

CONCLUSION: ESBL organisms in blood cultures, pre-existing renal dysfunction, and choledocholithiasis are risk factors for OF in cholangitis with bacteriobilia. The OF scoring system may aid clinicians to identify a poor prognosis group.

Is rapid antibacterial susceptibility testing medium reliable for routine laboratory practices?

Objective:

Early detection of antibiotic susceptibility profile of the isolates has critical importance in terms of immediate beginning of the appropriate treatment and increasing of treatment success, such as meningitis, bacteriemia and sepsis. In the present study, it was aimed to compare the antibiotic susceptibility results of Quicolor (Salubris Inc., Massachusetts, USA) and standard disk diffusion method.

Methods:

One hundred twenty three isolates were included in this study (80 Enterobacteriaceae, 15 Staphylococci and 28 nonfermentative Gram-negative bacteria). Antibiotic susceptibility in clinical isolates was evaluated using Mueller-Hinton (MH) agar and Quicolor (ES and NF) agar plates.

Results:

For Enterobacteriaceae, frequency of total concordance, major error, and minor error between the tests were found as 96.8%, 0.8%, and 2.4%, respectively. For Staphylococci, frequency of total concordance, major error, and minor error among the tests were found as 95.7%, 3.5%, and 0.8%, respectively. For non fermentative bacteria, frequency of total concordance, major error, and minor error among the tests were found as 83.9%, 9.6%, and 6.4%, respectively.

Conclusions:

Quicolor media provided reliable susceptibility results in enteric bacteria and Staphylococci. However, further studies including higher number of nonfermentative bacteria are required to determine whether the chromogenic media are appropriate for this group of bacteria.

Risk factors of organ failure in patients with bacteremic cholangitis

BACKGROUND

Bacteremic cholangitis carries a high mortality rate of up to 10 % in relation to organ failure (OF), including septic shock.

AIM

The purpose of this study was to elucidate predictive factors for OF in bacteremic cholangitis.

METHODS

A retrospective review of all patients diagnosed with acute cholangitis and proven bacteremia from 2003 to 2011 was performed. Comprehensive clinical and laboratory data of 211 patients were analyzed.

RESULTS

There were 42 cases (19.9 %) of OF and 5 deaths (2.4 %). In the multivariate logistic regression analysis, significant predictive factors for OF were successful biliary decompression, presence of extended-spectrum beta-lactamase organism (ESBL), higher total bilirubin, and higher blood urea nitrogen (BUN) level at admission with odds ratios (ORs) of 0.129, 6.793, 1.148, and 1.089, respectively. Subgroup analysis of 165 patients who underwent biliary decompression before an event (with OF: 20, without OF: 145) was performed to elucidate the risk factors for organ failure even after successful biliary drainage. Variables significantly associated with OF included ESBL and BUN (OR = 4.123 and 1.177, respectively). We developed a scoring system with regression coefficient of each significant variable. The organ failure score was calculated using the following equation: (1.4 × ESBL) + (0.2 × BUN). This scoring system for predicting OF was highly sensitive (85.0 %) and specific (83.4 %).

CONCLUSIONS

Biliary decompression, ESBL, total bilirubin, and BUN are prognostic determinants in patients with bacteremic cholangitis. An organ failure scoring system may allow clinicians to identify groups with poor prognosis even after successful biliary decompression.

Colorimetric-plate method for rapid disk diffusion susceptibility testing of Escherichia coli

Here, we report a laboratory-developed colorimetric-plate method for rapid disk diffusion susceptibility testing of Escherichia coli. One hundred isolates were evaluated. Categorical agreement between the colorimetric plate and the standard disk diffusion method was 99%. Mean time to results was 7.07 h (95% confidence interval, 5.96 to 8.19).