The Penetration of Antibiotics into Aggregates of Mucoid and Non-mucoid Pseudomonas aeruginosa

Abstract

~~ ~ ~Cells of mucoid and non-mucoid Pseudomonas aeruginosa in colonies were at least onethousandfold less sensitive to the antibiotics tobramycin or cefsulodin than were cells of the same bacteria in dispersed suspension. We did not detect any difference between the mucoid form and the non-mucoid form in the antibiotic sensitivity of colonies, from which we infer that the exopolysaccharide of the mucoid form does not contribute to colony-resistance by forming a barrier to antibiotic diffusion. Mathematical models were constructed in order to estimate timecourses of penetration of tobramycin and cefsulodin into biofilms and microcolonies of mucoid and non-mucoid P. aeruginosa. For tobramycin penetration, adsorption of antibiotic to the exopolysaccharide of the glycocalyx and antibiotic uptake by cells were taken into account in the calculations. The longest time-period for the concentration of tobramycin at the base of a biofilm 100 prn deep to rise to 90% of the concentration outside the biofilm was predicted to be 2.4 h. For cefsulodin penetration, irreversible hydrolysis catalysed by p-lactamase was taken into account, using P-lactamase levels taken from the literature. The calculations predicted that the cefsulodin concentration at the base of a biofilm 100pm deep would rise to 90% of the external concentration in 29 s when the /I-lactamase was synthesized at the basal level. For a similar biofilm of bacteria synthesizing enhanced levels of fl-lactamase ('derepressed'), the concentration of cefsulodin at the base was calculated to rise to 41% of the external concentration in about 50s and then remain at that level. This was despite the fact that cefsulodin is a poor substrate for this P-lactamase.

Pseudomonas aeruginosa alginate is refractory to Th1 immune response and impedes host immune clearance in a mouse model of acute lung infection

“…Overproduction of alginate could be an important contributory factor for Alg þ PAOmucA22 persistence and virulence. This study supports previous inferences that alginate is a virulence factor that contributes to bacterial adherence and persistence (Marcus & Baker, 1985;Ramphal & Pier, 1985;Doig et al, 1987), formation of microcolony and biofilm growth (Høiby, 1975;Lam et al, 1980;, inhibition of PMN chemotaxis (Stiver et al, 1988;Pedersen et al, 1990), suppression of lymphocyte and PMN function (Pedersen et al, 1990;Mai et al, 1993), formation of a physical barrier to the immune system and antibiotics (Nichols et al, 1989;Evans et al, 1991;Hoyle & Costerton, 1991;Mathee et al, 1994) and resistance to opsonic killing by PMNs and macrophages (Meshulam et al, 1984;Cabral et al, 1987;Jensen et al, 1990;.…”

Electrical methods of controlling bacterial adhesion and biofilm on device surfaces

“…However, the concentration of antibiotics and biocides required to kill bacteria residing within the biofilm matrix can be 500 to 5,000 times those needed to kill planktonic cells of the same species [17,18,21,35,[71][72][73][74]. It is not known, however, whether the observed recalcitrance of bacteria in the biofilm mode of growth to antimicrobial challenge is also true for electrically induced toxicity and whether the biofilm provides a similar tolerance advantage to this approach.…”

Resistance mechanisms of bacteria to antimicrobial compounds

“…Hoyle and Costerton (1991) suggested that the barrier to drug penetration formed by the exopolysaccharide and the low growth rate of bacteria in biofilms were related to drug resistance. In contrast, Nichols et al (1989) reported that alginate, an exopolysaccharide of mucoid-type P. aeroginosa, had a very limited effect in reducing drug penetration. It therefore seems that the mechanism resulting drug resistance on biofilm-forming organisms remains unclear.…”

“…Cells of mucoid and non-mucoid Pseudomonas aeroginosa in colonies were at least one-thousandfold less sensitive to the antibiotics tobramycin or cefsulodin than were cells of the same bacteria in suspension. No difference was detected between the mucoid form and the non-mucoid form in the antibiotic sensitivity of colonies, from which it was concluded, that the exopolysaccharide of the mucoid form does not contribute to colony-resistance by forming a barrier to antibiotic diffusion (Nichols et al, 1989).…”