Improving Gram stain proficiency in hospital and satellite laboratories that do not have microbiology

Fc-MBL-modified Fe3O4 magnetic bead enrichment and fixation in Gram stain for rapid detection of low-concentration bacteria

Functional bacterial enrichment magnetic beads (Fe₃O₄@SiO₂@Fc-MBL) and Gram staining were combined for the fast diagnosis of infecting bacteria in meningitis. Fe₃O₄@SiO₂@Fc-MBL has excellent microbial binding ability and can be used for bacterial enrichment from cerebrospinal fluid (CSF). The enriched bacteria are recognized by Gram stain at very low concentrations (10 CFU·mL^-1). The feasibility of this method was verified by five common bacteria in meningitis infection (Gram-positive: Staphylococcus epidermidis, Staphylococcus haemolyticus, and Staphylococcus capitis; Gram-negative: Klebsiella pneumoniae and Escherichia coli). The extraction efficiency of Fc-MBL-modified Fe₃O₄ magnetic beads was approximately 90% in artificial CSF for the selected bacteria, with the exception of E. coli (~ 60%). The bacteria were successfully recognized by Gram staining and microscopic observation. Fe₃O₄@SiO₂@Fc-MBL acts by capturing and fixing the bacteria in a magnetic field throughout the experiment. Compared with traditional CSF Gram staining, this new method avoids interference by inflammatory cells and red blood cells during microscopic examination. Furthermore, the sensitivity of this method is much better than the centrifugation smear method. The whole process can be accomplished within 30 min. This novel method may have potential as a clinical tool for analysis of bacteria in the CSF.

Development of a standardized Gram stain procedure for bacteria and inflammatory cells using an automated staining instrument

Gram stain is a subjective and poorly controlled test, and the resultant errors often perplex laboratory scientists. To reduce errors and make Gram stain a precisely controllable and meritorious test, a standardized Gram stain procedure for bacteria and inflammatory cells was developed using an automated staining instrument in this study. Freshly expectorated sputum specimens, used as the optimized targets, were smeared on slides by laboratory technicians, defining each slide loaded with uniform matrix and monolayer cell. And then, the staining and decolorizing time, as well as the stain and decolorant volume, were optimized as 15, 105, 1, and 25 s and 1.1, 1.4, 0.3, and 0.7 ml, respectively. Culture‐positive blood specimens and original purulent fluids were used for confirming the developed standardized Gram stain procedure. Distinct tinctures of bacteria and inflammatory cells adhered to slide uniformly in a monolayer were observed, and the obtained staining results of these samples were highly consistent with their cultured results. Furthermore, according to the staining results under different staining conditions, an updated molecular mechanism of Gram stain for bacteria and the probable staining mechanism for inflammatory cells were also proposed in this study.