National Center for Biotechnology Information NCBI NLM MEDLINE humans pubmed abstract nih national institutes of health national library of medicine adult female male adolescent aged middle aged 80 and over Bacterial phenotype drug resistance respiratory tract infections / complications streptococcal infections / microbiology* streptococcus / isolation & purification* streptococcal infections / complications sputum / microbiology* respiratory tract infections / microbiology* streptococcus / drug effects david r murdoch pmid:16517877 pmc1393130 doi:10.1128/jcm.44.3.923-927.2006 elaine r keith roslyn g podmore pulmonary disease chronic obstructive / complications streptococcus / classification streptococcus / pathogenicity