title: Clinical characteristics and antimicrobial susceptibilities of anaerobic bacteremia in an acute care hospital.
abstract: This study investigated the clinical features of anaerobic bacteraemia in an acute-care hospital, and evaluated the antimicrobial susceptibility of these isolates to commonly available antibiotics. Microbiological and epidemiological data from 2009 to 2011were extracted from the laboratory information system and electronic medical records. One hundred and eleven unique patient episodes consisting of 116 anaerobic isolates were selected for clinical review and antibiotic susceptibility testing. Susceptibilities to amoxicillin-clavulanate, clindamycin, imipenem, metronidazole, moxifloxacin, penicillin and piperacillin-tazobactam were performed using Etest strips with categorical interpretations according to current CLSI breakpoints. Metronidazole-resistant and carbapenem-resistant anaerobic Gram-negative bacilli were screened for the nim and cfiA genes. Clinical data was obtained retrospectively from electronic medical records. During the 3 year period, Bacteroides fragilis group (41%), Clostridium species (14%), Propionibacterium species (9%) and Fusobacterium species (6%) were the most commonly isolated anaerobes. Patients with anaerobic bacteraemia that were included in the study were predominantly above 60 years of age, with community-acquired infections. The most commonly used empiric antibiotic therapies were beta-lactam/beta-lactamase inhibitor combinations (44%) and metronidazole (10%). The crude mortality was 25%, and appropriate initial antibiotic therapy was not significantly associated with improved survival. Intra-abdominal infections (39%) and soft-tissue infections (33%) accounted for nearly three-quarters of all bacteraemia. Antibiotics with the best anaerobic activity were imipenem, piperacillin-tazobactam, amoxicillin-clavulanate and metronidazole, with in-vitro susceptibility rates of 95%, 95%, 94% and 92% respectively. Susceptibilities to penicillin (31%), clindamycin (60%) and moxifloxacin (84%) were more variable. Two multidrug-resistant isolates of Bacteroides species were positive for nim and cfiA genes respectively, while another two imipenem-resistant Fusobacterium species were negative for cfiA genes. This study demonstrated that anaerobic bacteraemia in our patient population was predominantly associated with intra-abdominal and soft-tissue infections. Overall antibiotic resistance was high for penicillin and clindamycin, and the presence of emerging resistance to carbapenems and metronidazole warrants further monitoring.
authors.affiliation: Department of Laboratory Medicine, Changi General Hospital, 2 Simei Street 3, 529889, Singapore. Electronic address: thean_yen_tan@cgh.com.sg.
authors.forename: Thean Yen
authors.initials: TY
authors.lastname: Tan
authors.affiliation: Department of Laboratory Medicine, Changi General Hospital, 2 Simei Street 3, 529889, Singapore.
authors.forename: Lily Siew Yong
authors.initials: LS
authors.lastname: Ng
authors.affiliation: Department of Laboratory Medicine, Changi General Hospital, 2 Simei Street 3, 529889, Singapore.
authors.forename: Lee Ling
authors.initials: LL
authors.lastname: Kwang
authors.affiliation: Department of Medicine, Changi General Hospital, 2 Simei Street 3, 529889, Singapore.
authors.forename: Suma
authors.initials: S
authors.lastname: Rao
authors.affiliation: Department of Laboratory Medicine, Changi General Hospital, 2 Simei Street 3, 529889, Singapore.
authors.forename: Li Ching
authors.initials: LC
authors.lastname: Eng
mesh_terms: D000693:Anaerobiosis; D000890:Anti-Infective Agents / Q000494:pharmacology*; D016470:Bacteremia / Q000382:microbiology*; D001421:Bacteria, Anaerobic / Q000187:drug effects / Q000302:isolation & purification; D001439:Bacteroides / Q000187:drug effects* / Q000302:isolation & purification; D015780:Carbapenems / Q000494:pharmacology; D002981:Clindamycin / Q000494:pharmacology; D003013:Clostridium / Q000187:drug effects* / Q000302:isolation & purification; D004352:Drug Resistance, Microbial; D005673:Fusobacterium / Q000187:drug effects* / Q000302:isolation & purification; D006094:Gram-Positive Bacteria; D006801:Humans; D059413:Intraabdominal Infections / Q000382:microbiology*; D008795:Metronidazole / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D010397:Penicillanic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D010878:Piperacillin / Q000494:pharmacology; D000077725:Piperacillin, Tazobactam Drug Combination; D011424:Propionibacterium / Q000187:drug effects* / Q000302:isolation & purification; D012189:Retrospective Studies
chemical_list: D000890:Anti-Infective Agents; D015780:Carbapenems; D008795:Metronidazole; D000077725:Piperacillin, Tazobactam Drug Combination; D002981:Clindamycin; D010397:Penicillanic Acid; D010878:Piperacillin
keywords: Anaerobes; Antibiotic resistance; Bacteremia; Bacteroides