Methods: Sterile swab samples were obtained from plastic NCHs used for one year (n=50; polycarbonate, 7x9cm) and from new NCHs (n=3). Bacterial contaminations on NCHs were analyzed by molecular biological techniques. Bacterial 16S rDNAs isolated from NCHs were amplified by PCR and cloned into Escherichia coli and after each 16S rDNA was sequenced. Selected antibiotic-resistant genes, mecA, blaIMP,blaVIM, vanA and vanB in nosocomial pathogens were identified by PCR. The nucA specific for Staphylococcus aureus was also determined by PCR.
Results: Bacterial contamination and accumulation of potentially pathogenic microorganisms on NCHs were approximately 10-fold greater than those on new NCHs based on the patterns of PCR-amplified bands. However, blaIMP, blaVIM, vanA and vanB were not detected on any NCH tested. There were 3 nucA-positive and 4 mecA-positive findings on different NCHs. These resistant forms suggested the presence of S. aureus and methicillin-resistant coagulase-negative Staphylococci causing nosocomial infections. On 16S rDNA sequence analysis, oral Streptococci, Prevotella, Atopobium and Veillonella species of apparently human origin were identified as the most dominant bacteria contaminating NCHs. Soil and environmental bacteria, Geobacillus, Delftia, Agrobacterium, Xanthobacter, Mesorhizobium species were identified as contaminants of new NHCs.
Conclusions: NCHs of dentists may also serve as reservoirs for the transmission of microorganisms, similar to doctor's neckties and pens. Conventional PCR for the specific bacterial gene and antibiotic-resistant genes on NCHs may be available for rapid monitoring of nosocomial infection in dental clinics.