Production of latex agglutination reagents for pneumococcal serotyping

Here we describe a method for the production of latex agglutination reagents based on the passive adsorption of antibodies to latex particles. Sixty-five latex agglutination reagents were made using the PneuCarriage Project (PCP) method, of which 35 passed QC. The other 30 reagents failed QC due to auto-agglutination (n=2), no reactivity with target serotypes (n=8) or cross-reactivity with non-target serotypes (n=20). Dilution of antisera resulted in a further 27 reagents passing QC. The remaining three reagents passed QC when prepared without centrifugation and wash steps. Protein estimates indicated that latex reagents that failed QC when prepared using the PCP method passed when made with antiserum containing ≤ 500 μg/ml of protein. Sixty-one nasopharyngeal isolates were serotyped with our in-house latex agglutination reagents, with the results showing complete concordance with the Quellung reaction.The method described here to produce latex agglutination reagents allows simple and efficient serotyping of pneumococci and may be applicable to latex agglutination reagents for typing or identification of other microorganisms. We recommend diluting antisera or removing centrifugation and wash steps for any latex reagents that fail QC. Our latex reagents are cost-effective, technically undemanding to prepare and remain stable for long periods of time, making them ideal for use in low-income countries.To date, over 90 capsular serotypes of Streptococcus pneumoniae (the pneumococcus) have been described [1,2]. Current vaccines target pneumococcal capsular polysaccharide and protect against serotypes responsible for the majority of invasive disease [3,4]. However, widespread vaccination may lead to the replacement of vaccine serotypes by non-vaccine serotypes [5,6]. Serotyping is an important tool for evaluating the long-term effectiveness of pneumococcal vaccines and providing broader epidemiological information [7]. The ‘gold standard’ pneumococcal serotyping method is