Cold Shock Response of the UspA1 Outer Membrane Adhesin of Moraxella catarrhalis

Abstract

ABSTRACT Colonization of the human nasopharynx exposes Moraxella catarrhalis , a common cause of otitis media in children and exacerbations of chronic obstructive pulmonary disease in adults, to sudden downshifts in temperature, occurring when the host breathes cold air. We investigated whether in vitro cold shock influences the expressions of the outer membrane adhesins UspA1 and hemagglutinin, which are considered virulence factors, and of an M. catarrhalis homolog of recA , a housekeeping gene, which in Escherichia coli is induced by cold shock. Quantitative real-time reverse transcriptase PCR was used for measuring mRNA copy number. A screening experiment revealed that a cold shock at 26°C maximally induced the copy number of uspA1 . In comparison with 37°C conditions, a 1-hour cold shock at 26°C increased copy numbers of uspA1 and recA by 2.5-fold (11.2 ± 1.8 versus 4.5 ± 0.8 copies/CFU) and 2.7-fold (0.30 ± 0.10 versus 0.11 ± 0.06), respectively, but did not induce transcription of hag . Exposure to 26°C increased surface expression of UspA1, as assessed by fluorescence-activated cell sorter analysis, and resulted in a significant increase in adherence of strain O35E to Chang human conjunctival cells (97.1% ± 2.0% versus 48.3% ± 9.2% at 37°C; P = 0.01). Cold shock induction of uspA1 and recA was detected in strains belonging to either phylogenetic subpopulation of M. catarrhalis (16S rRNA types 1 and 2/3) and was most pronounced in type 2/3 strains (4- to 25-fold for uspA1 ), which do not express detectable amounts of UspA1 protein at 37°C. These data indicate that cold shock at a physiologically relevant temperature of 26°C induces the expression of at least one virulence factor (UspA1). To our knowledge, no similar data are available for other nasopharyngeal pathogens.