Understanding the mechanisms of augmented bacterial pathogenicity in post-viral infections is the first step in the development of an effective therapy. This study assessed the effect of human coronavirus NL63 (HCoV-NL63) on the adherence of bacterial pathogens associated with respiratory tract illnesses. It was shown that HCoV-NL63 infection resulted in an increased adherence of Streptococcus pneumoniae to virus-infected cell lines and fully differentiated primary human airway epithelium cultures. The enhanced binding of bacteria correlated with an increased expression level of the platelet-activating factor receptor (PAF-R), but detailed evaluation of the bacterium-PAF-R interaction revealed a limited relevance of this process. INTRODUCTIONThe concept of excessive morbidity and mortality of bacterial infection occurring during or shortly after viral infection was first formulated for influenza virus in the early 19th century. Analysis of influenza pandemics showed that the incidence of bacterial pneumonia was increased and contributed substantially to mortality rates (Abrahams et al., 1919;Muir & Wilson, 1919;Stone & Swift, 1919;Wilson & Steer, 1919). Comparison of bacteriological and virological data from children hospitalized for respiratory disease shows a high degree of occurrence of viral and bacterial infections positively correlating with the severity of illness (Duttweiler et al., 2004;Kneyber et al., 2005;Randolph et al., 2004;Thorburn et al., 2006). Although the role of a preceding viral infection in development and severity of bacterial respiratory diseases is a clinically welldocumented phenomenon, the exact mechanism has not been elucidated fully.Initially, it was proposed that respiratory viruses facilitate bacterial colonization through physical damage of the respiratory tract epithelium, with exposed basement membrane components being responsible for increased bacterial adherence (Louria et al., 1959;Muir & Wilson, 1919;Wilson & Steer, 1919;Wolbach, 1919). Such a mechanism undoubtedly occurs for highly pathogenic viral species, but it does not explain the occurrence of increased severity of bacterial infection during and shortly after relatively mild viral infections. Analysis of published data suggests that interplay between viruses and bacteria is a complex process, where the final outcome depends heavily on multiple factors, including modulation of innate immune responses resulting in delayed clearance of bacteria, hypersensitization of infected cells leading to enhanced immune-mediated lung damage and modulation of bacterial adherence (Okamoto et al., 2004). The increase in bacterial adherence occurs due to exposure of novel binding sites for bacteria on the epithelial surface, either by expression of highly glycosylated viral proteins (McCullers & Bartmess, 2003;Peltola & McCullers, 2004) or by the alteration of a bacterial receptor expression pattern (McCullers & Rehg, 2002;Patel et al., 1995;Terajima et al., 1997).Bacterial pathogens predominantly involved in secondary infection of the r...

The CRISPR-Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated genes) system provides prokaryotic cells with an adaptive and heritable immune response to foreign genetic elements, such as viruses, plasmids, and transposons. It is present in the majority of Archaea and almost half of species of Bacteria. Porphyromonas gingivalis is an important human pathogen that has been proven to be an etiological agent of periodontitis and has been linked to systemic conditions, such as rheumatoid arthritis and cardiovascular disease. At least 95% of clinical strains of P. gingivalis carry CRISPR arrays, suggesting that these arrays play an important function in vivo. Here we show that all four CRISPR arrays present in the P. gingivalis W83 genome are transcribed. For one of the arrays, we demonstrate in vivo activity against double-stranded DNA constructs containing protospacer sequences accompanied at the 3= end by an NGG protospacer-adjacent motif (PAM). Most of the 44 spacers present in the genome of P. gingivalis W83 share no significant similarity with any known sequences, although 4 spacers are similar to sequences from bacteria found in the oral cavity and the gastrointestinal tract. Four spacers match genomic sequences of the host; however, none of these is flanked at its 3= terminus by the appropriate PAM element. IMPORTANCEThe CRISPR-Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated genes) system is a unique system that provides prokaryotic cells with an adaptive and heritable immunity. In this report, we show that the CRISPR-Cas system of P. gingivalis, an important human pathogen associated with periodontitis and possibly also other conditions, such as rheumatoid arthritis and cardiovascular disease, is active and provides protection from foreign genetic elements. Importantly, the data presented here may be useful for better understanding the communication between cells in larger bacterial communities and, consequently, the process of disease development and progression.

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