Clinical characteristics and antimicrobial susceptibilities of anaerobic bacteremia in an acute care hospital.

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.

Five clinical cases of Necropsobacter rosorum bacteremia.

Five cases of bacteremia with Necropsobacter rosorum are described, originating from intra-abdominal infections or localized soft tissue infections in the pelvic region. N. rosorum is consistently misidentified by commercial identification systems, which may delay recognition of this organism as a human pathogen.

Characterisation of significant Gram positive bacilli from soft tissue infections.

INTRODUCTION: Gram positive bacilli (GPB) isolated from soft tissue infections are often neglected or ignored due to their fastidious nature and the lack of reliable phenotypic identification methods. This study was done to characterise clinically significant aero-tolerant GPB isolated from surgically obtained samples in patients with soft tissue infections. METHODS: Forty-six GPB isolates collected during a 2 year study period were identified using partial 16s rRNA sequencing and API Coryne. Antibiotic susceptibility testing to penicillin, amoxycillin/clavulanate, moxifloxacin and erythromycin was performed on these isolates using Etest. Clinical data were gathered from patients' medical records. RESULTS: The most common isolates identified by 16s rRNA sequencing were Actinomyces species (n = 30, 65%) and Corynebacterium species (n = 9, 20%). The majority of the Actinomyces species infections were located below the waist, in particular the perianal region. There was poor agreement between API Coryne and genotypic identification, with only one-third of the isolates being correctly identified to species level. Actinomyces species were uniformly susceptible to penicillin and amoxicillin/clavulanate. Antibiotic susceptibilities were more varied for the other genera isolated. CONCLUSION: Actinomyces species comprised two-thirds of aerobically growing GPB isolates and may represent an under-reported cause of bacterial soft tissue infections. Penicillin and amoxycillin/clavulanate may be the empiric antibiotics of choice for Actinomyces species as all isolates were susceptible.