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Title: Effects of long term use of contact lens disinfecting solutions on the presence of bacteria-harbouring antiseptic-resistance genes in the conjunctival sac, eyelid and on the lens and lens accessories of orthokeratology lens wearers
Authors: Shi, Guang Sen
Degree: Ph.D.
Issue Date: 2016
Abstract: Microbial keratitis (MK) is a rare, but sight-threatening complication associated with contact lens wear. Various factors have been reported as being responsible for contact lens-related MK. Microbial contamination of the contact lens and lens accessories is frequently detected in contact lens wearers and is a known risk factor for MK. Staphylococcus species, which are not only commonly isolated from the periorbital region (including conjuctival sac, eye lids, and eyelashes), but also from the contact lenses and lens accessories, are the most common pathogens associated with MK. In published reports, the contamination rates of contact lenses, lens cases, and lens care solutions are high. Contact lenses are considered as vectors capable of transporting potential pathogens contaminating both the lens and lens accessories into the eyes. To reduce the incidence of ocular infections associated with contact lens wear, the use of contact lens disinfecting and cleaning systems are required. Multipurpose disinfecting solutions (MPS) are essential to inactivate microorganisms on the lenses and lens accessories. Some of the active ingredients of MPS, such as chlorhexidine gluconate (CHX) and benzalkonium chloride (BAK), which have been widely used in hospital and other clinical settings, can cause selective pressure on bacteria which is one of the main reasons for the development of resistance to disinfectants. There is an increased concern about the emergence of disinfectant-resistant microorganisms, notably in Staphylococcus. Antiseptic resistance in staphylococci is attributable to several genes that are mainly plasmid-borne and confer reduced susceptibility to cationic antiseptic agents including dyes, Quaternary ammonium compounds (QACs), and biguanides by coding for efflux pumps, which reduce disinfectant concentration in the cell. The distribution of QAC genes in staphylococci has been investigated not only in clinical isolates, but also in isolates from the general population. In addition, there is evidence that presence of QAC genes may contribute to the emergence of cross-resistance and co-resistance between widely used biocides and antibiotics. Currently, over 125 million people use contact lenses and lens accessories. More than 90% contact lens wearers are using MPS to clean and disinfect their contact lens and lens accessories. In actual use, especially if not handled properly, MPS are inevitably diluted by water, saline, or other solutions, which will serve to decrease the effects of MPS. Some microorganisms may survive and be exposed to the selective pressure for a prolonged period. However, it is unknown whether long-term use of MPS can select for ocular pathogens harbouring QAC genes, having increased resistance to several antiseptics, antibiotics, and MPS. The purpose of this research was to provide significant and original contributions to the knowledge base of distribution of QAC genes in S. aureus and coagulase-negative staphylococci (CNS) in selected orthokeratology (ortho-k) lens and spectacle wearers in Hong Kong and observe the trend of resistant organism acquisition over 6 months. It aimed to determine the antimicrobial susceptibility of S. aureus and CNS harbouring QAC genes and their association with the presence of QAC genes. It also aimed to investigate the effectiveness of four MPSs for RGP lenses against S. aureus and CNS harbouring QAC genes isolated in this research.
This is the first study of the prevalence of QAC gene in staphylococci isolated from ortho-k lens wearers. Samples were collected from several sites in the periorbital region of all subjects, as well as from the lenses and lens accessories of ortho-k lens wearers and from the spectacle frames of controls. Following isolation and identification of bacterial species, all staphylococci were investigated for the presence of QAC genes by polymerase chain reaction. The higher prevalence of QAC genes in staphylococci isolated from ortho-k lens wearers and the gradually increasing prevalence of QAC genes in staphylococci isolated from ortho-k wearers over a 6-month period supported the hypothesis that use of MPS may cause selective pressure to staphylococci to acquire QAC genes. For all staphylococcal isolates harbouring QAC genes, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) to two disinfectants, CHX and BAK, and susceptibility to several antibiotics were determined by broth microdilution method and disc diffusion test, respectively. The results demonstrated that the presence of QAC genes in staphylococci commonly contributed to higher MIC and MBC to disinfectants and higher resistance rates to antibiotics. Four commonly used MPS for RGP lens were challenged with staphylococci harbouring QAC genes by the standalone test and MIC and MBC to each MPS were determined by broth microdilution method. The results demonstrated that the presence of QAC genes in staphylococci significantly decreased their susceptibility to MPS for rigid lenses and viability of some staphylococcal isolates, especially strains harbouring QAC genes, could not be reduced by the required 3-logs after exposure to MPS. In conclusion, this study has demonstrated that staphylococci harbouring QAC genes are widely distributed in both ortho-k lens and spectacle wearers in Hong Kong, and use of contact lenses increases the likelihood of colonization and contamination with such strains. Use of MPS may contribute to higher carriage rate of gene-positive staphylococci as a result of increased tolerance to disinfectants (including MPS) and antibiotics. Further investigation may be required to investigate the risk of reduced antiseptic and antibiotic susceptibility to MK and its association in the control of MK.
Subjects: Contact lenses.
Contact lenses -- Care and hygiene.
Staphylococcus aureus.
Hong Kong Polytechnic University -- Dissertations
Pages: xxviii, 293 pages : color illustrations
Appears in Collections:Thesis

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