Study of vancomycin tolerance among clinical isolates of Streptococcus pneumoniae in Hong Kong

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Study of vancomycin tolerance among clinical isolates of Streptococcus pneumoniae in Hong Kong


Author: Tse, Shu-chiu Edmond
Title: Study of vancomycin tolerance among clinical isolates of Streptococcus pneumoniae in Hong Kong
Degree: M.Sc.
Year: 2007
Subject: Hong Kong Polytechnic University -- Dissertations.
Vancomycin resistance.
Streptococcus pneumoniae -- China -- Hong Kong.
Department: Dept. of Health Technology and Informatics
Pages: ix, 69 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record:
Abstract: The ability of Streptococcus pneumoniae to escape lysis and killing in the presence of antibiotic at or above a determined minimum inhibitory concentration (MIC) is termed as "tolerance". The emergence of vancomycin tolerance in S. pneumoniae has been reported sporadically and it represents a potential new health problem as vancomycin is used in the treatment of meningitis caused by penicillin resistant pneumococci. Levels of penicillin resistance in pneumococci are high in Hong Kong. The prevalence of vancomycin and penicillin tolerance among 200 clinical isolates of pneumococci was determined by monitoring lysis and viability after exposure to the respective antibiotic for 4 hours. Four percent of the isolates were tolerant to vancomycin and 6% were tolerant to penicillin. Of eight vancomycin-tolerant isolates, seven were also tolerant to penicillin. The prevalence of vancomycin tolerance was slightly higher than that in the previous pilot study (in which the prevalence was 2%) conducted in Hong Kong. The increased prevalence of vancomycin tolerance among clinical isolates of pneumococci will be a serious threat in Hong Kong, where there are significant rates of penicillin resistance in S. pneumoniae. Monitoring of the prevalence of vancomycin-tolerant S. pneumoniae and further investigation of the clinical relevance of vancomycin-tolerant S. pneumoniae are warranted, since tolerance may contribute to a precursor to resistance and it may lead to treatment failure (particularly in meningitis, in which bactericidal activity is critical for eradication). Specific primers were designed to amplify the sequence within the pep27 and vex2 of both the vancomycin-tolerant and vancomycin-nontolerant strains of pneumococci. Different results in polymerase chain reaction (PCR) between vancomycin-tolerant and vancomycin-nontolerant strains of pneumococci were obtained and compared. It was found that vancomycin-tolerant strains almost all lacked the pep27 sequence which was present in all vancomycin-nontolerant strains. Meanwhile, only two out of eight vancomycin-tolerant strains lacked the vex2 sequence. This suggests that the pep27 is a better molecular marker than vex2 for detection of vancomycin tolerance. Moreover, the absence of this sequence determined by molecular method can act as a rapid method to detect the presence of vancomycin tolerance trait in a clinical set up. This simple molecular method may be an important method to monitor the frequency of vancomycin tolerance in various clinical settings as an early alert indicator. It is possible that a simplified assay for the gene could be used routinely to determine the most appropriate therapy for patients with meningitis caused by penicillin-resistant pneumococci.

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