Publication: Marmara Üniversitesi hastanesi’nde izole edilen ilk Metronidazole dirençli Bacteroides kökeni: Bacteroides thetaiotaomicron
Abstract
İnsan bağırsak mikrobiyotasının önemli bir kısmını oluşturan Bacteroides türleri, ağır batın içi enfeksiyonları, cerrahi yara enfeksiyonları ve bakteriyemiye neden olabilirler. Ayrıca bu bakteriler, diğer anaerop bakterilere göre antibiyotiklere daha fazla dirençlidirler. Karbapenemler, beta-laktam/beta-laktamaz inhibitörleri ve nitroimidazol gibi sınırlı sayıda antibiyotikler Bacteroides türlerinin eliminasyonunda etkilidirler. Ancak son zamanlarda bazı ülkelerde nadiren de olsa nitroimidazollere dirençli Bacteroides kökenleri bildirilmiştir. Metronidazole direnç mekanizmasının çoğunda nim genleri (nim A-G) suçlanmaktadır. Bu raporda, kan kültüründen izole edilen metronidazole dirençli bir Bacteroides thetaiotaomicron kökeni bildirilmektedir. Pankreas başı adenokarsinomu tanısı alan 62 yaşındaki erkek hastanın cerrahi girişim sonrası 5. günde, kan kültüründen gram-negatif zorunlu anaerop bir çomak izole edilmiştir. Geleneksel testler ve ticari biyokimyasal kitler kullanılarak köken, B.thetaiotaomicron olarak tanımlanmıştır. İzolatın antimikrobiyal duyarlılık paterni agar dilüsyon yöntemiyle belirlenmiştir. Direnç genleri, nim genine özgül primer çiftleri kullanılarak polimeraz zincir reaksiyonu (PCR) ile araştırılmıştır. Saflaştırılan PCR ürünü dizilenmiş ve GenBank’da bulunan dizilerle karşılaştırılarak analizi yapılmıştır. Metronidazolün MİK değeri 16 mg/L olarak tespit edilmiştir. Köken CLSI kriterlerine göre ara değerde (intermediate) olmakla beraber, EUCAST kriterlerine göre dirençli (> 4 mg/L) bulunmuştur. Bakteride nim geni saptanmış; yapılan dizi analizinde, PCR ürününün nimE geni (emb|AM042593.1|) ile %100 benzer olduğu görülmüştür. Diğer yandan izolat, karbapenemlere ve sulbaktam-ampisiline duyarlı bulunmuştur. Sulbaktam-ampisilin ile tedavi edilen hastanın ateşi 24 saat sonra düşmüştür. Klinik durumunda kayda değer bir düzelme olan hasta 8. günde taburcu edilmiştir. Operasyon sonrası altı ay süreyle onkoloji polikliniğinde takip edilen hasta, hastalığın progresi nedeniyle kaybedilmiştir. Anaerop bakterilere bağlı bakteriyemilerde mortalite oranının yüksek olması nedeniyle, tanının hızlı yapılması ve uygun tedavinin verilmesi hayati önem taşır. Çalışmalar, Bacteroides türlerine bağlı bakteriyemilerde, hastaya, bakterinin duyarlı olmadığı antibiyotiklerin verilmesi halinde olumsuz sonuçların alınacağını göstermiştir. Bu olguda, metronidazole dirençli mikroorganizma, CLSI breakpoint değerlerine göre duyarlı bildirilebilir, buna bağlı olarak da klinik yanıtsızlık görülebilirdi. Dolayısıyla Bacteroides türleri için antibiyotik duyarlılık sonuçlarının, EUCAST MİK değerleriyle yorumlanması daha akılcı gözükmektedir.
Bacteroides species, the predominant constituents of the human intestinal microbiota can cause serious intraabdominal and postoperative wound infections and bacteremia. Moreover, these bacteria are more resistant to antimicrobial agents than the other anaerobes. The limited number of the antimicrobials, such as carbapenems, beta-lactam/beta-lactamase inhibitors and nitroimidazoles are highly effective in eliminating Bacteroides. However, a few metronidazole-resistant isolates have been reported from several countries recently. The nim genes (nim A-G) are suggested to be responsible for the majority of the metronidazole resistance. Here, we describe a metronidazole-resistant Bacteroides thetaiotaomicron isolated from a blood culture. A gram-negative obligate anaerobic rod was isolated from the postoperative 5th day blood culture of a 62-year-old male patient with adenocarcinoma of the pancreas head. The strain was identified as B.thetaiotaomicron by using a combination of conventional tests and commercially available biochemical kits. Antimicrobial susceptibility testing was performed by agar dilution method. The resistance genes were investigated by means of PCR using specific primer pairs for nim gene. The purified PCR product was sequenced and analyzed by comparison of the consensus sequences with GenBank sequences. The MIC for metronidazole was 16 mg/L. Although the strain was intermediate according the CLSI criteria, it was resistant (> 4 mg/L) according to EUCAST criteria. The isolate was nim gene positive, and nucleotide sequencing of the PCR product shared 100% similarity with nimE gene (emb|AM042593.1|). On the other hand the isolate was susceptible to carbapenems and sulbactam-ampicillin. Following administration of ampicillin-sulbactam, the patient’s fever disappeared after 24 hours. The clinical condition improved considerably and he was discharged at day 8. The patient was followed up at the medical oncology clinic; however he died due to disease progression six months after surgery. Since anaerobic bacteremia is associated with high mortality rate, prompt diagnosis and proper management are critical. The studies on Bacteroides bacteremia have revealed adverse outcomes in patients receiving antibiotics to which the bacterium was resistant. In the present case, the metronidazole-resistant organism would be reported as susceptible according to CLSI breakpoint value and on account of this result the treatment might lead to clinical failure. Therefore EUCAST MIC values seem to be more rational in case of Bacteroides antibiotic susceptibility testing.
Bacteroides species, the predominant constituents of the human intestinal microbiota can cause serious intraabdominal and postoperative wound infections and bacteremia. Moreover, these bacteria are more resistant to antimicrobial agents than the other anaerobes. The limited number of the antimicrobials, such as carbapenems, beta-lactam/beta-lactamase inhibitors and nitroimidazoles are highly effective in eliminating Bacteroides. However, a few metronidazole-resistant isolates have been reported from several countries recently. The nim genes (nim A-G) are suggested to be responsible for the majority of the metronidazole resistance. Here, we describe a metronidazole-resistant Bacteroides thetaiotaomicron isolated from a blood culture. A gram-negative obligate anaerobic rod was isolated from the postoperative 5th day blood culture of a 62-year-old male patient with adenocarcinoma of the pancreas head. The strain was identified as B.thetaiotaomicron by using a combination of conventional tests and commercially available biochemical kits. Antimicrobial susceptibility testing was performed by agar dilution method. The resistance genes were investigated by means of PCR using specific primer pairs for nim gene. The purified PCR product was sequenced and analyzed by comparison of the consensus sequences with GenBank sequences. The MIC for metronidazole was 16 mg/L. Although the strain was intermediate according the CLSI criteria, it was resistant (> 4 mg/L) according to EUCAST criteria. The isolate was nim gene positive, and nucleotide sequencing of the PCR product shared 100% similarity with nimE gene (emb|AM042593.1|). On the other hand the isolate was susceptible to carbapenems and sulbactam-ampicillin. Following administration of ampicillin-sulbactam, the patient’s fever disappeared after 24 hours. The clinical condition improved considerably and he was discharged at day 8. The patient was followed up at the medical oncology clinic; however he died due to disease progression six months after surgery. Since anaerobic bacteremia is associated with high mortality rate, prompt diagnosis and proper management are critical. The studies on Bacteroides bacteremia have revealed adverse outcomes in patients receiving antibiotics to which the bacterium was resistant. In the present case, the metronidazole-resistant organism would be reported as susceptible according to CLSI breakpoint value and on account of this result the treatment might lead to clinical failure. Therefore EUCAST MIC values seem to be more rational in case of Bacteroides antibiotic susceptibility testing.