Evaluation of SARS-CoV-2 isolation in cell culture from nasal/nasopharyngeal swabs or saliva specimens of patients with COVID-19

Abstract

It has been revealed that SARS-CoV-2 can be efficiently isolated from clinical specimens such as nasal/nasopharyngeal swabs or saliva in cultured cells. In this study, we examined the efficiency of viral isolation including SARS-CoV-2 mutant strains between nasal/nasopharyngeal swab or saliva specimens. Furthermore, we also examined the comparison of viral isolation rates by sample species using simulated specimens for COVID-19. As a result, it was found that the isolation efficiency of SARS-CoV-2 in the saliva specimens was significantly lower than that in the nasal/nasopharyngeal swab specimens. In order to determine which component of saliva is responsible for the lower isolation rate of saliva specimens, we tested the abilities of lactoferrin, amylase, cathelicidin, and mucin, which are considered to be abundant in saliva, to inhibit the infection of SARS-CoV-2 pseudotyped viruses (SARS-CoV-2pv). Lactoferrin and amylase were found to inhibit SARS-CoV-2pv infection. In conclusion, even if the same number of viral genome copies was detected by the real-time RT-PCR test, infection of SARS-CoV-2 present in saliva is thought to be inhibited by inhibitory factors such as lactoferrin and amylase, compared to nasal/nasopharyngeal swab specimens.

Oral mouthwashes for asymptomatic to mildly symptomatic adults with COVID-19 and salivary viral load: a randomized, placebo-controlled, open-label clinical trial

“…In contrast, RT-PCR might produce false negatives in the diagnosis [ 55 ], and the detection of infectious virus in collected samples is an important step in preventing COVID-19 infection. A previous study reported that the isolation efficiency of SARS-CoV-2 was significantly lower in saliva specimens than in the nasal/nasopharyngeal swab specimens [ 56 ]. To address the limitation of RT-PCR and enhance the accuracy of detecting infectious virus in collected samples, future studies of the efficacy of CPC and on-demand aqueous chlorine dioxide mouthwash on the viral viability of SARS-CoV-2 should be conducted using different specimen types and in multiple populations and settings.…”

In Vitro Efficacy of Antivirals and Monoclonal Antibodies against SARS-CoV-2 Omicron Lineages XBB.1.9.1, XBB.1.9.3, XBB.1.5, XBB.1.16, XBB.2.4, BQ.1.1.45, CH.1.1, and CL.1

“…Vero E6 cell line (ATCC CRL-1586) was maintained in complete Dulbecco's modified Eagle's medium (DMEM), supplemented with 10% fetal bovine serum (FBS, Hy-Clone|Cytiva, Logan, UT, USA), 1× GlutaMAX and 1× Antibiotic-Antimycotic solution (all from Gibco, Grand Island, NY, USA). For the isolation of SARS-CoV-2, Vero E6 cells were inoculated with nasopharyngeal swabs, as described in an earlier [14]. When virusinduced cytopathic effects (CPE) were confirmed by visual observation under a microscope, the presence of SARS-CoV-2 was determined by qRT-PCR.…”