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Fiona Stapleton, Man Choy, Hua Zhu; Susceptibility Of Ocular Isolates Of P.aeruginosa To Contact Lens Multipurpose Solutions. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6507.
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Persistent microbial contamination of contact lens (CL) storage cases may be a feature of biofilm growth conferring resistance of organisms to CL multipurpose solutions (MPS). This study investigated the susceptibility of keratitis isolates of P.aeruginosa to MPS.
47 isolates of P.aeruginosa recovered from corneal infections in Australia were grown overnight on Trypicase Soy (TS) agar and suspended to a concentration of 108 colony forming units (CFU)/mL . The susceptibility of planktonic organisms was assessed using serial dilutions of 2 MPS containing either polyhexamethyl biguanide (A) or polyquad (B) as their antimicrobial active and minimum inhibitory concentration (MIC) was estimated. 14 isolates capable of forming strong biofilms, were allowed to adhere for 24 hours in polypropylene CL storage cases. Washed biofilms were treated with 2.5mL of each of the MPS for the manufacturers recommended disinfection time. Two colorimetric assays; crystal violet for total biofilm and the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) for viable biofilm, were applied. Planktonic survivors, MICs, residual viable and total biofilm were enumerated and were compared between MPS.
All planktonic isolates were susceptible to 100% MPS, however, the MICs were higher for MPS A compared with MPS B (p<0.05). Susceptibility was not associated with phenotype. The mean percentage reduction in viable biofilm was 54±16% for MPS A and 70±20% for MPS B (p<0.005). The mean percentage reduction in total biofilm was 40±16% for MPS A and 54±12% for MPS B (p<0.05).
This study has confirmed the widespread susceptibility of planktonic keratitis isolates of P.aeruginosa to contemporary MPS and MIC was not associated with a cytotoxic phenotype. There were variable effects of different MPS on viable and total biofilm using a colorimetric assay, which may in part explain persistence of organisms within storage cases despite compliance with manufacturers’ guidelines
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