Over 350 bacterial species are known to form communities on tooth surfaces in the oral cavity, and opportunistic pathogens are frequently isolated from samples taken from the oral cavities of immunocompromised hosts, as well as elderly people with poor oral hygiene. To confirm the correlation between the prevalence of opportunistic pathogens in the oral cavity and oral hygiene, dental plaque and saliva samples from 15 dental hygienists and 15 healthcare workers were investigated. No opportunistic pathogens were found in the samples from dental hygienists, however, they were isolated from 10 of the 15 healthcare workers (66.7%). The total amounts of Streptococcus sp. and Lactobacillus sp. were also significantly higher in the healthcare workers. The amount of Streptococcus mutans was also higher, although the difference was not significant. From our results, we concluded that the prevalence of opportunistic pathogens and cariogenic bacteria in the oral cavity may be reduced by proper oral hygiene measures.