Hemant Sabharwal

A folding variant of alpha-lactalbumin with bactericidal activity against Streptococcus pneumoniae

This study describes an α‐lactalbumin folding variant from human milk with bactericidal activity against antibiotic‐resistant and ‐susceptible strains of Streptococcus pneumoniae. The active complex precipitated with the casein fraction at pH 4.6 and was purified from casein by a combination of anion exchange and gel chromatography. Unlike other casein components, the active complex was retained on the ion‐exchange matrix and eluted only with high salt. The eluted fraction showed N‐terminal and mass spectrometric identity with human milk α‐lactalbumin, but native α‐lactalbumin had no bactericidal effect. Spectroscopic analysis demonstrated that the active form of the molecule was in a different folding state, with secondary structure identical to α‐lactalbumin from human milk whey, but fluctuating tertiary structure. Native α‐lactalbumin could be converted to the active bactericidal form by ion‐exchange chromatography in the presence of a cofactor from human milk casein, characterized as a C18:1 fatty acid. Analysis of the antibacterial spectrum showed selectivity for streptococci; Gram‐negative and other Gram‐positive bacteria were resistant. The folding variant of α‐lactalbumin is a new example of naturally occurring molecules with antimicrobial activity.

Nasopharyngeal colonization in Costa Rican children during the first year of life

BACKGROUND The establishment of the nasopharyngeal flora was followed in Costa Rican children from birth to 1 year of age. METHODS Nasopharyngeal cultures were obtained at 1 (n = 413), 3 (n = 393), 6 (n = 376) and 12 months (n = 356) of age from children representative of the population in the Puriscal district. Weekly cultures were obtained from a subcohort of these children (n = 101). Mother-infant diads (n = 95) and preschool children (n = 208) attending day-care centers were also studied. RESULTS The estimated proportion of colonized children in the population differed markedly depending on the frequency of culture. Quarterly cultures showed a slow increase in carrier rates from 3.9% for Haemophilus influenzae, 3.1% for Streptococcus pneumoniae and 6.5% for Moraxella catarrhalis at 1 month of age to 10.1% carrying H. influenzae and 19.4% carrying S. pneumoniae by the end of the first year. By quarterly culture the proportion of children colonized at least once was 36% for S. pneumoniae, 26% for H. influenzae and 28% for M. catarrhalis. In contrast weekly sampling showed that 95 to 100% of the children were colonized at least once during the first year of life with H. influenzae, S. pneumoniae or M. catarrhalis. Nasopharyngeal carriage of H. influenzae, S. pneumoniae and M. catarrhalis was low in the mothers, and very few mother-infant pairs carried identical bacteria at the same time. In contrast carrier rates were high in the siblings attending day care (H. influenzae 27.9%, S. pneumoniae 39.4%, both organisms 26.6%). Infants with siblings had significantly higher bacterial carriage at all ages than infants without siblings. CONCLUSIONS Quarterly nasopharyngeal cultures showed that Costa Rican infants acquire their nasopharyngeal flora at a rate comparable with that for infants in developed countries and that siblings are an important source of the bacteria. Weekly samplings showed that virtually all children were colonized at least once during the first year of life.

Antibodies to pneumococcal polysaccharides in human milk: lack of relationship to colonization and acute otitis media

BACKGROUND This study analyzed antibodies to pneumococcal polysaccharides in human milk and their effect on nasopharyngeal colonization and acute otitis media in breast-fed infants. METHODS A total of 503 milk samples were collected from 310 mothers. Nasopharyngeal cultures were obtained from their children at 2, 6 and 10 months postpartum, and the capsular groups/types of the Streptococcus pneumoniae isolates were determined. RESULTS Types 6A, 6B, 19A, 19F and 23F accounted for 54% of the pneumococcal isolates, but type 3 isolates were uncommon. Milk samples were analyzed for antibody activity to the common capsular polysaccharide types 6A, 19F and 23F; to the type 3 polysaccharide; to C-polysaccharide; and to phosphorylcholine (PC), a major component of the pneumococcal cell wall polysaccharide (CWPS). Anti-capsular antibody activity was low or absent in > 90% of the milk samples. In contrast anti-PC antibody activity was detected in 88% and anti-CWPS in 84% of the samples. The frequency of acute otitis media did not vary with the milk anti-capsular, anti-PC or anti-CWPS antibody activity. CONCLUSIONS There was no reduction in nasopharyngeal carriage of S. pneumoniae among children fed milk with anti-capsular or anti-PC antibody activity, but carriage was increased in those children who received milk with anti-CWPS antibody activity. A protective role of antipolysaccharide or anti-CWPS antibodies in milk was not detected under the study conditions.

Erratum: A folding variant of α-lactalbumin with bactericidal activity against Streptococcus pneumoniae (Molecular Microbiology, 35, 3 (589-600))

As the result of a typesetting error, Fig.2 in the article by Håkansson et al. on pages 589–600 of Molecular Microbiology, Volume 35, Issue 3, was unfortunately reproduced as a low‐resolution image. The correct version is reproduced here.