Automated image analysis for quantification of filamentous bacteria.

Marlene Fredborg,Flemming S Rosenvinge,Erik Spillum,Stine Kroghsbo,Teis E Sondergaard,Mikala Wang

doi:10.1186/s12866-015-0583-5

Abstract

BackgroundAntibiotics of the β-lactam group are able to alter the shape of the bacterial cell wall, e.g. filamentation or a spheroplast formation. Early determination of antimicrobial susceptibility may be complicated by filamentation of bacteria as this can be falsely interpreted as growth in systems relying on colorimetry or turbidometry (such as Vitek-2, Phoenix, MicroScan WalkAway). The objective was to examine an automated image analysis algorithm for quantification of filamentous bacteria using the 3D digital microscopy imaging system, oCelloScope.ResultsThree E. coli strains displaying different resistant profiles and differences in filamentation kinetics were used to study a novel image analysis algorithm to quantify length of bacteria and bacterial filamentation. A total of 12 β-lactam antibiotics or β-lactam–β-lactamase inhibitor combinations were analyzed for their ability to induce filamentation. Filamentation peaked at approximately 120 min with an average cell length of 30 μm.ConclusionThe automated image analysis algorithm showed a clear ability to rapidly detect and quantify β-lactam-induced filamentation in E. coli. This rapid determination of β-lactam-mediated morphological alterations may facilitate future development of fast and accurate AST systems, which in turn will enable early targeted antimicrobial therapy. Therefore, rapid detection of β-lactam-mediated morphological changes may have important clinical implications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0583-5) contains supplementary material, which is available to authorized users.

Highlights

Antibiotics of the β-lactam group are able to alter the shape of the bacterial cell wall, e.g. filamentation or a spheroplast formation
When focusing on early detection of antimicrobial susceptibility within the first 60–120 min, antibioticinduced bacterial filamentation may lead to deceptive interpretation of results
To be able to distinguish between these two growth patterns is important when focusing on early determination of antimicrobial susceptibility, since this is complicated by filamentous bacteria as their elongated cell length may falsely be interpreted as normal growth

Summary

Introduction

Antibiotics of the β-lactam group are able to alter the shape of the bacterial cell wall, e.g. filamentation or a spheroplast formation. Determination of antimicrobial susceptibility may be complicated by filamentation of bacteria as this can be falsely interpreted as growth in systems relying on colorimetry or turbidometry (such as Vitek-2, Phoenix, MicroScan WalkAway). Antibiotics of the β-lactam group are able to alter the shape of the bacterial cell wall, e.g. inducing filamentation or a spherical shape of rod-shaped bacteria (Fig. 1) [1,2,3]. Filamentous morphology provides survival advantages: inhibits phagocytic uptake by immune cells [5], promote survival within host tissue [6, 7], and decrease susceptibility to certain antimicrobial agents [4].

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Results

Conclusion