Pandemic printing: a novel 3D-printed swab for detecting SARS-CoV-2.

OBJECTIVES: To design and evaluate 3D-printed nasal swabs for collection of samples for SARS-CoV-2 testing. DESIGN: An iterative design process was employed. Laboratory evaluation included in vitro assessment of mock nasopharyngeal samples spiked with two different concentrations of gamma-irradiated SARS-CoV-2. A prospective clinical study compared SARS-CoV-2 and human cellular material recovery by 3D-printed swabs and standard nasopharyngeal swabs. SETTING, PARTICIPANTS: Royal Melbourne Hospital, May 2020. Participants in the clinical evaluation were 50 hospital staff members attending a COVID-19 screening clinic and two inpatients with laboratory-confirmed COVID-19. INTERVENTION: In the clinical evaluation, a flocked nasopharyngeal swab sample was collected with the Copan ESwab and a mid-nasal sample from the other nostril was collected with the 3D-printed swab. RESULTS: In the laboratory evaluation, qualitative agreement with regard to SARS-CoV-2 detection in mock samples collected with 3D-printed swabs and two standard swabs was complete. In the clinical evaluation, qualitative agreement with regard to RNase P detection (a surrogate measure of adequate collection of human cellular material) in samples collected from 50 hospital staff members with standard and 3D-printed swabs was complete. Qualitative agreement with regard to SARS-CoV-2 detection in three pairs of 3D-printed mid-nasal and standard swab samples from two inpatients with laboratory-confirmed SARS-CoV-2 was also complete. CONCLUSIONS: Using 3D-printed swabs to collect nasal samples for SARS-CoV-2 testing is feasible, acceptable to patients and health carers, and convenient.

A nanomechanical study of the effects of colistin on the Klebsiella pneumoniae AJ218 capsule.

Atomic force microscopy measurements of capsule thickness revealed that that the wild-type Klebsiella pneumoniae AJ218 capsular polysaccharides were rearranged by exposure to colistin. The increase in capsule thickness measured near minimum inhibitory/bactericidal concentration (MIC/MBC) is consistent with the idea that colistin displaces the divalent cations that cross-bridge adjacent lipopolysaccharide (LPS) molecules through the capsule network. Cryo-electron microscopy demonstrated that the measured capsule thickness at near MIC/MBC of 1.2 µM was inflated by the disrupted outer membrane, through which the capsule is excreted and LPS is bound. Since wild-type and capsule-deficient strains of K. pneumoniae AJ218 have equivalent MICs and MBCs, the presence of the capsule appeared to confer no protection against colistin in AJ218. A spontaneously arising colistin mutant showed a tenfold increase in resistance to colistin; genetic analysis identified a single amino acid substitution (Q95P) in the PmrB sensor kinase in this colistin-resistant K. pneumoniae AJ218. Modification of the lipid A component of the LPS could result in a reduction of the net-negative charge of the outer membrane, which could hinder binding of colistin to the outer membrane and displacement of the divalent cations that bridge adjacent LPS molecules throughout the capsular polysaccharide network. Retention of the cross-linking divalent cations may explain why measurements of capsule thickness did not change significantly in the colistin-resistant strain after colistin exposure. These results contrast with those for other K. pneumoniae strains that suggest that the capsule confers colistin resistance.