Comparison of Moraxella catarrhalis isolates from children and adults for growth on modified New York City medium and potential virulence factors

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Abstract
Initial studies found that Moraxella catarrhalis isolates from adults that grew on modified New York City medium (MNYC+) that contained antibiotics selective for pathogenic neisseriae differed from strains that did not grow on this medium (MNYC−) in their potential virulence properties. It was predicted that higher usage of antibiotics to treat respiratory illness in children might result in higher proportions of MNYC+ isolates if antibiotics were an important selective pressure for this phenotype. Two of 100 adult isolates (2 %) were MNYC+, compared to 88 of 88 isolates (100 %) from children (P = 0.000). MNYC+ strains were serum-resistant and bound in higher numbers to HEp-2 cells that were infected with respiratory syncytial virus (RSV). Endotoxin from an MNYC+ isolate induced significantly higher pro-inflammatory response levels than endotoxin from an MNYC− strain. MNYC− adult isolates expressed haemagglutinins and bound in lower numbers to RSV-infected cells, but serum resistance was variable. All isolates from children were MNYC+, serum-resistant and bound in greater numbers to RSV-infected cells. These results indicate that both RSV infection and antibiotic usage select for the MNYC+ phenotype.