Resumen de Antimicrobial Resistance and Prevalence of Resistance Genes of Obligate Anaerobes Isolated From Periodontal Abscesses
Background: This study attempts to determine the antimicrobial resistance profiles of obligate anaerobic bacteria that were isolated from a periodontal abscess and to evaluate the prevalence of resistance genes in these bacteria.
Methods: Forty-one periodontal abscess samples were cultivated on selective and non-selective culture media to isolate the oral anaerobes. Their antibiotic susceptibilities to clindamycin, doxycycline, amoxicillin, imipenem, cefradine, cefixime, roxithromycin, and metronidazole were determined using the agar dilution method, and polymerase chain reaction assays were performed to detect the presence of the ermF, tetQ, nim, and cfxA drug resistance genes.
Results: A total of 60 different bacterial colonies was isolated and identified. All of the isolates were sensitive to imipenem. Of the strains, 6.7%, 13.3%, 16.7%, and 25% were resistant to doxycycline, metronidazole, cefixime, and amoxicillin, respectively. The resistance rate for both clindamycin and roxithromycin was 31.7%. Approximately 60.7% of the strains had the ermF gene, and 53.3% of the amoxicillin-resistant strains were found to have the cfxA gene. Two nim genes that were found in eight metronidazole-resistant strains were identified as nimB.
Conclusions: In the present study, the Prevotella species are the most frequently isolated obligate anaerobes from periodontal abscesses. The current results show their alarmingly high resistance rate against clindamycin and roxithromycin; thus, the use of these antibiotics is unacceptable for the empirical therapy of periodontal abscesses. A brief prevalence of four resistance genes in the anaerobic bacteria that were isolated was also demonstrated.
Periodontal abscess has been defined as a suppurative lesion that is associated with periodontal breakdown and localized pus in the gingival wall of the periodontal pocket.1 The vast majority of dental abscesses with endodontic or periodontal pocket origins are polymicrobial anaerobic infections.2 These infections are predominantly attributable to strict anaerobes, such as Gram-negative anaerobic bacteria, and partially facultative anaerobes, such as the Streptococcus milleri group.3 However, in dental abscess, anaerobes outnumber aerobic and facultative bacteria in ratios ranging from 10:1 to 10,000:1, with anaerobic Gram-negative bacilli predominating.3 In periodontal abscesses, Bacteroides forsythus, Fusobacterium spp., Prevotella intermedia, Prevotella nigrescens, and Porphyromonas gingivalis are the most prevalent species,4,5 and these bacteria are more commonly isolated from periodontal abscesses than endodontic abscesses. However, previous studies using swabs of purulent material have demonstrated poor recovery of strict anaerobes, which implicated streptococci or staphylococci as the causative microorganisms of suppurative dental infection. This difference in recovery was attributable to poor sampling techniques and inadequate culture methods in these investigations.6,7 Antibiotics are often prescribed to limit the spread of the infection after the surgical drainage of pus from periodontal abscesses. However, reports have indicated that abscess formation may be attributable to the overgrowth of resistant pathogens.8 Therefore, it is critical to know the susceptibility profiles of clinically relevant oral pathogens (which may vary considerably between patients in different countries) for effective antibiotic treatment.
Amoxicillin, metronidazole, roxithromycin, and clindamycin are commonly used to treat oral infections. Resistance against metronidazole was long considered to be rare in anaerobes. However, recent studies have shown that this resistance is no longer uncommon.9 Metronidazole resistance in Bacteroides spp. appears to be encoded by the nimA through nimG genes.9-11 The use of tetracycline has decreased because of the high resistance rates observed in various microorganisms. The resistance in Gram-negative anaerobic bacteria, especially in the genus Prevotella, was primarily attributable to the presence of the tetQ gene,12,13 which encodes the ribosomal protection protein.14 In oral anaerobes, resistance to clindamycin�erythromycin has significantly increased during the past 20 years15 and is usually encoded by the ermF gene (which has the widest host range and was found in 10 of the examined anaerobic genera).16 Amoxicillin continues to exhibit a high level of activity against the majority of oral anaerobes.17 However, cfxA (class A/group 2e) has been characterized recently in and cloned from oral amoxicillin-resistant Prevotella species.18 In this study the aim is to investigate the antimicrobial resistance profiles of clinically cultured anaerobes from periodontal abscesses and their resistance to clindamycin, doxycycline, amoxicillin, imipenem, cefradine, roxithromycin, cefixime, and metronidazole, which are commonly used in the treatment of periodontitis. The prevalence of four relevant resistance genes is also studied.
