Evaluation of filter paper as a means to transport inactivated bacteria for identification using the MALDI-TOF MS system

Detection of KPC enzyme by MALDI-TOF MS from bacteria impregnated in filter paper

The main mechanism that causes resistance to carbapenem, one of the most potent antibiotic available, in Enterobacterales bacterial isolates, is due to Klebsiella pneumoniae carbapenemase (KPC) production by the bacterium. KPC is spread worldwide, requiring laboratories to be capable of identifying this enzyme, however some methods can be expensive for small laboratories, especially in developing countries. Therefore, the development of methods with low cost of reagents for the detection of KPC enzyme is necessary. The objective of this study was to evaluate the detection of KPC enzyme by MALDI-TOF MS from inactivated bacteria impregnated in filter paper. A total of 129 Enterobacterales isolates were impregnated in filter paper, and after 7 days at room temperature, they were subjected to a protein extraction protocol and spectra acquisition, in triplicates, by MALDI-TOF MS. The spectra were evaluated and KPC was identified according to the presence of a peak of 28,712.62 ± 27.80 m/z. Considering the presence of the KPC peak in at least one spectrum of the triplicates, this method presented 60.8% sensitivity and 96.4% specificity. However, considering the presence of KPC peak in at least two spectra of the triplicate, a specificity of 100% was achieved. The detection of KPC enzyme from inactivated bacteria impregnated in filter paper can be used as a method to confirm the presence of KPC, which could be very significant for small laboratories with limited resources.

Evaluation of filter paper to transport oro/nasopharyngeal samples to detect SARS-CoV-2 by RT-qPCR

Purpose

To evaluate filter paper as a means to transport oro/nasopharyngeal samples from laboratories with few resources for SARS-CoV-2 detection by RT-qPCR in a central laboratory that usually performs this technique as routine.

Methods

A total of 40 specimens were evaluated in parallel by RT-qPCR carried out after RNA extraction using two different protocols: direct RNA extraction (Protocol A - reference method) and RNA extraction after impregnation in filter paper (Protocol B).

Results

The RT-qPCR for SARS-CoV-2 using Protocol B presented 97.22% (35/36) of agreement for SARS-CoV-2-positive samples when compared to the reference method (Protocol A), even for specimens with low viral load (increased Ct values). Noteworthy, three clinical specimens which were categorized as inconclusive by Protocol A presented amplification of both N1 and N2 targets using Protocol B, presenting positive results for SARS-CoV-2.

Conclusion

The use of filter paper to transport oro/nasopharyngeal clinical samples presented very satisfactory results to detect SARS-CoV-2 by RT-qPCR. In addition, it proved to be a feasible and sensitive approach, being able to generate the detection of SARS-CoV-2 even at low concentrations, without presenting false-negative results.

Evaluation of filter paper to transport inactivated bacteria to detect carbapenem resistance genes by multiplex real-time PCR using high-resolution melting

Infections caused by resistant microorganisms are a complex global public health challenge, and the way to combat the increase of resistance is the development of more modern and faster techniques for resistance detection. This study aimed to evaluate the transport of inactivated bacteria impregnated in a filter paper disk to detect carbapenem resistance genes by multiplex real-time PCR (qPCR) using high-resolution melting (HRM). A total of 88 isolates of 10 different species of Enterobacterales harboring well-characterized carbapenem resistance genes were evaluated. A full 10-µL loop of fresh growth of bacteria were impregnated in a filter paper disk, which was left at room temperature for 2 days in order to simulate the time spent in transportation. Bacterial inactivation was performed with 70% ethanol at 15 min. Afterwards, the DNA was extracted from the paper disks for further analysis by qPCR HRM. The time of 15 min in 70% ethanol was enough to inactivate all the isolates tested. It was possible to correctly identify the presence of the carbapenem resistance gene by HRM qPCR in 87 isolates (98.87%) that were transported in the filter paper disks. Our results indicated that it is possible to use filter paper to transport inactivated bacteria and to identify carbapenem resistance genes by qPCR HRM. This alternative tends to facilitate the access to this technology by many laboratories which do not have the qPCR equipment.

Ethanol treatment does not inactivate spore-forming bacteria - A cautionary note about the safe transport of bacteria prior to identification by MALDI-TOF MS

Treatment with 70% ethanol has been proposed as a safe and effective way to inactive bacteria for transport between laboratories prior to identification by MALDI-TOF MS. Ethanol alone does not inactivate spore-forming bacteria and additional chemical or physical treatment is necessary to guarantee inactivation of bacterial spores.