Atomic force microscopy and scanning electron microscopy as alternative methods of early identification of pathogens causing catheter-related bloodstream infections of patients in ICU
Authors: Kluzik Anna , Tomczak Hanna , Nowicki Marek , Koszel Tomasz , Bartkowska-Śniatkowska Alicja , Kusza Krzysztof , Grześkowiak Małgorzata 
Published: May 2022

Abstract

Introduction
Vascular catheters are an indispensable element of the therapy of patients in intensive care. Their use is associated with the possibility of complications, including infectious. According to various sources, the incidence of catheter-related bloodstream infections (CRBSIs) ranges from 0.1 to 22.7 per 1,000 catheter days.

Materials and Methods
The central venous catheter tip culture samples were collected from 24 patients with suspected catheter-related bloodstream infection, from three intensive care units (ICUs). The results of microscopic examinations: atomic force microscope (AFM) and scanning electron microscope (SEM) were compared with the results of microbiological analysis of the central venous catheter tip and blood collected from the catheter.

Results
The microscopic examination and microbiological analysis of both the blood and central venous catheter samples confirmed the presence of microorganisms in 16 cases (double positive result). Our study was conducted in a short period of time (up to 6 hours) and it gave an initial answer to the question about the type of microorganisms colonising the central venous catheter. In one patient the infection was not caused by removal of the central venous catheter. However, not all results were fully consistent within the two diagnostic methods. The colonisation of the central venous catheter with Pseudomonas aeruginosa and Staphylococcus epidermidis was microbiologically confirmed, but it was not confirmed by the microscopic examination of the sample collected from patient No. 20. However, the examination enabled preliminary assessment of the microorganism colonising the catheter, which may have caused the blood infection. It cannot be ruled out that Pseudomonas aeruginosa bacilli were grown on the catheter that came into contact with blood from another source of infection, e.g. the respiratory, nervous or urinary systems. Information on the presence of cocci-shaped bacteria forming characteristic clusters or rods may enable initial diagnosis of catheter-related bloodstream infection if it is accompanied by typical clinical symptoms. Alternative diagnostics also provides valuable information on the presence of biofilm, which is a factor hindering the body’s response to infection and penetration of antibiotics.

Conclusions
Our pilot study presents new diagnostic possibilities of microscopic imaging with the atomic force microscope (AFM) and scanning electron microscope (SEM) to identify pathogens on routinely used disposable medical devices, such as the central venous catheter. On the other hand, this range of diagnostics reveals the potential to constantly improve medical materials which come into direct contact with patients’ tissues. It is important to create a database of microscopic images, which would be a repeatable diagnostic pattern and fully correlated with the results of microbiological analysis, because it would facilitate initial quick diagnosis of a potential CRBSI.