Uncovering Differences in Virulence Markers Associated with Achromobacter Species of CF and Non-CF Origin

Achromobacter spp. are recognized as emerging pathogens in hospitalized as well as in cystic fibrosis (CF) patients. From 2012 to 2015, we collected 69 clinical isolates (41 patient) of Achromobacter spp. from 13 patients with CF (CF isolates, n = 32) and 28 patients receiving care for other health conditions (non-CF isolates, n = 37). Molecular epidemiology and virulence potential of isolates were examined. Antimicrobial susceptibility, motility, ability to form biofilms and binding affinity to mucin, collagen, and fibronectin were tested to assess their virulence traits. The nrdA gene sequencing showed that A. xylosoxidans was the most prevalent species in both CF and non-CF patients. CF patients were also colonized with A. dolens/A. ruhlandii, A. insuavis, and A. spiritinus strains while non-CF group was somewhat less heterogenous, although A. insuavis, A. insolitus, and A. piechaudii strains were detected beside A. xylosoxidans. Three strains displayed clonal distribution, one among patients from the CF group and two among non-CF patients. No significant differences in susceptibility to antimicrobials were observed between CF and non-CF patients. About one third of the isolates were classified as strong biofilm producers, and the proportion of CF and non-CF isolates with the ability to form biofilm was almost identical. CF isolates were less motile compared to the non-CF group and no correlation was found between swimming phenotype and biofilm formation. On the other hand, CF isolates exhibited higher affinity to bind mucin, collagen, and fibronectin. In generall, CF isolates from our study exhibited in vitro properties that could be of importance for the colonization of CF patients.

Mucin biopolymers prevent bacterial aggregation by retaining cells in the free-swimming state

Many species of bacteria form surface-attached communities known as biofilms. Surrounded in secreted polymers, these aggregates are difficult both to prevent and eradicate, posing problems for medicine and industry. Humans play host to hundreds of trillions of microbes that live adjacent to our epithelia, and we are typically able to prevent harmful colonization. Mucus, the hydrogel overlying all wet epithelia in the body, can prevent bacterial contact with the underlying tissue. The digestive tract, for example, is lined by a firmly adherent mucus layer that is typically devoid of bacteria, followed by a second, loosely adherent layer that contains numerous bacteria. Here, we investigate the role of mucus as a principle arena for host-microbe interactions. Using defined in vitro assays, we found that mucin biopolymers, the main functional constituents of mucus, promote the motility of planktonic bacteria and prevent their adhesion to underlying surfaces. The deletion of motility genes, however, allows Pseudomonas aeruginosa to overcome the dispersive effects of mucus and form suspended antibiotic-resistant flocs, which mirror the clustered morphology of immotile natural isolates found in the cystic fibrosis lung mucus. Mucus may offer new strategies to target bacterial virulence, such as the design of antibiofilm coatings for implants.

Different roles for lactococcal aggregation factor and mucin binding protein in adhesion to gastrointestinal mucosa

Adhesion of bacteria to mucosal surfaces and epithelial cells is one of the key features for the selection of probiotics. In this study, we assessed the adhesion property of Lactococcus lactis subsp. lactis BGKP1 based on its strong autoaggregation phenotype and the presence of the mucin binding protein (MbpL). Genes involved in aggregation (aggL) and possible interaction with mucin (mbpL), present on the same plasmid pKP1, were previously separately cloned in the plasmid pAZIL. In vivo and in vitro experiments revealed potentially different physiological roles of these two proteins in the process of adherence to the intestine during the passage of the strain through the gastrointestinal tract. We correlated the in vitro and in vivo aggregation of the BGKP1-20 carrying plasmid with aggL to binding to the colonic mucus through nonspecific hydrophobic interactions. The expression of AggL on the bacterial cell surface significantly increased the hydrophobicity of the strain. On the other hand, the presence of AggL in the strain reduced its ability to adhere to the ileum. Moreover, MbpL protein showed an affinity to bind gastric type mucin proteins such as MUC5AC. This protein did not contribute to the binding of the strain to the ileal or colonic part of the intestine. Different potential functions of lactococcal AggL and MbpL proteins in the process of adhesion to the gastrointestinal tract are proposed.