The Study On The Susceptibility Of Biocides And The Arginine Metabolic Mobile Element In Multidrug-resistant Bacteria

Objective1. To investigate the susceptibility of clinical Acinetobacter baumannii isolates to commonly used biocides, especially that of imipenem-resistant A. baumannii.2. To explore the relevant mechanisms giving rise to the reduced susceptibility of A. baumannii to biocides.Materials and methodsChapter 1: A total of 700 A. baumannii isolates were obtained from 25 hospitals in 16 cities in China through December 2004 to December 2005. MICs of benzalkonium chloride, chlorhexidine digluconate and triclosan against A. baumannii were determined by agar dilution methods. MICs of three biocides were compared between imipenem-resistant A. baumannii (IRAB) and imipenem-sensitive A. baumannii (ISAB).Chapter 2: Twenty-one IRAB isolates representative of different clones were selected according to stratified random sampling, against which the in-vitro activity of benzalkonium chloride, chlorhexidine digluconate and triclosan were determined by quantitative suspension test. The susceptibility to three biocides was compared among IRAB isolates of different clones, on the basis of MICs and quantitative suspension test.Chapter 3: Twenty isolates with reduced susceptibility (MICs > MIC₉₀) to triclosan were selected. Susceptibilities to 4 antimicrobial agents were compared between triclosan-sensitive and -insensitive isolates. PFGE was used to investigate the clonal relatedness of triclosan-insensitive isolates. The fabI mutation was determined by PCR and sequencing. The expression of fabI and three efflux pumps were determined using real-time RT-PCR.ResultsSection 1: (1) MICs of benzalkonium chloride, chlorhexidine digluconate and triclosan against 700 clinical A. baumannii isolates were extremely lower than the actual in-use concentration. (2) The mean MIC values of chlorhexidine digluconate and triclosan against IRAB were higher than those against ISAB. No significant difference of the mean MIC value of benzalkonium chloride was found between IRAB and ISAB.Section 2: (1) Benzalkonium chloride, chlorhexidine digluconate and triclosan showed good activity against IRAB of different clones using quantitative suspension test. Concentration is a major factor affecting three biocides' activity. (2) MICs showed that the susceptibility of F clones isolates to benzalkonium chloride and chlorhexidine digluconate decreased, and the susceptibility of C clones isolates to triclosan decreased. However, no difference in biocides activity against IRAB was observed among different clones and sporadic isolates using quantitative suspension test.Section 3: High-level triclosan tolerance to A. baumannii was accounted for by Gly95Ser mutation of fabI. Overexpression of wild-type fabI was responsible for low-level tolerance. The relationship of active efflux to triclosan tolerance needed to be investigated further.Conclusion1. The investigated biocides have good activity against clinical A. baumannii in China, if used at concentrations recommended by the manufacturer. Strict adherence to the infection control measures is prerequisite to prevent the dissemination of multidrug-resistant A. baumannii.2. Given the potential of IRAB to develop increased tolerance to biocides, it is necessary to monitor the susceptibility of A. baumannii to biocides.3. As clinical isolates could acquire resistance to triclosan by fabI mutation and fabI overexpression, it is necessary to rationalize triclosan usage and monitor triclosan susceptibility. ObjectivesTo investigate the prevalence and characteristic of ACME-arcA -positive isolates among meticillin-resistant Staphylococcus haemolyticus (MRSH).MethodsEighty-eight MRSH isolates were collected from the inpatients in our hospital, from April 2002 to April 2003. The ACME-arcA, native arcA and SCCmec elements were detected by PCR. Susceptibilities to 10 antimicrobial agents were compared between ACME-arcA -positive and -negative isolates by chi-square test. PFGE was used to investigate the clonal relatedness of ACME-arcA-positive isolates. The phylogenetic relationships of ACME-arcA and native arcA were analyzed by using neighbor joining methods in MEGA software.ResultsForty-two (47.7%) of 88 isolates distributing in 13 PFGE types were positive for the ACME-arcA gene. There were no significant differences in antimicrobial susceptibility between ACME-arcA-positive and -negative isolates. Phylogenetic analysis of arcA showed that native arcA in S. haemolyticus had a closer relationship with ACME-arcA rather than with native arcA in Staphylococcus aureus and Staphylococcus epidermidis. A novel ccr allotype (ccrAB_SHP) was identified in ACME-arcA-positive isolates. In 42 ACME-arcA-positive isolates, 8 isolates harbored SCCmec V, 8 isolates harbored class C1 mec complex and ccrAB_SHP, 22 isolates harboring class C1 mec complex and 4 isolates harboring class C2 mec complex were negative for all known ccr allotypes.ConclusionsThe ACME-arcA-positive isolates were first found in MRSH with high prevalence and clonal diversity, which suggests the mobility of ACME within MRSH. Result from this study revealed that MRSH is likely to be one of the potential reservoirs of ACME for S. aureus.