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J. Bacteriol. doi:10.1128/JB.00146-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Histidine auxotrophy in commensal and disease-causing non-typeable Haemophilus influenzae

Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, Michigan; Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, Michigan

^* To whom correspondence should be addressed. Email: gilsdorf{at}umich.edu.

	Abstract

Histidine biosynthesis is one of the best studied metabolic pathways in bacteria. Although this pathway is thought to be highly conserved within and between bacterial species, a previous study identified a genetic region within the histidine operon (his) of non-typeable strains of H. influenzae (NTHi) that was more prevalent among otitis media strains than among throat commensal NTHi. In the present study, we further characterized this region and showed that genes in the complete his operon (hisG, D, C, NB, H, A, F, and IE) are >99% conserved among four fully sequenced NTHi strains, are present in the same location in these four genomes, and are situated in the same gene order. Using PCR and dot blot hybridization, we determined that the his operon was significantly more prevalent in otitis media NTHi strains (106/121, 87.7%) than in throat strains (74/137, 54%), prevalence ratio = 1.62, p<.0001, suggesting a possible role in middle ear survival and/or acute otitis media. NTHi lacking the his operon showed attenuated growth in histidine restricted media, confirming them as his negative auxotrophs. Our results suggest that the ability to make histidine is an important factor in bacterial growth and survival in the middle ear where nutrients such as histidine may be found in limited amounts. Those isolates lacking the histidine pathway were still able to survive well in the throat, which suggests histidine is readily available in the throat environment.