Updating antimicrobial susceptibility testing: challenging cases.

1. Cynthia B. Schofield, MPH, MT (CAMT)[⇑][1] 1. VA San Diego Healthcare System (retired), San Diego, CA 1. Address for Correspondence: Cynthia B. Schofield, MPH, MT (CAMT), VA San Diego Healthcare System (retired), 7050 Weller St., San Diego, CA, (858) 450-9651, cschofield{at}san.rr.com 1. Consider the effect of Acinetobacter baumannii on the underlying comorbidities of the 2 patients. 2. Define and discuss necrotizing fasciitis and its treatment. 3. Summarize the events leading to the transmission of Escherichia coli ST131. 4. Discuss the effect of treatment with a fluoroquinolone and the patient outcome. A series of cases is presented to demonstrate the tenacity of organisms known for acquired resistance through mechanisms of mutation or selection as a result of antibiotic exposure. The cases describe the devastating effects and frightening speed with which multi-drug resistant (MDR) organisms may overwhelm a patient by increasing morbidity and mortality. Also apparent is the frustration and powerlessness felt by physicians who expeditiously attempt to diagnose and treat patients at risk for hospital-associated infection (HAI) and community-associated infection (CAI). Acinetobacter baumannii , 2 cases of necrotizing fasciitis In 2007 and 2008, two unusual cases of necrotizing fasciitis were seen at a regional medical center. These cases were notable for necrosis of leg muscle and intercostal tissue caused by A. baumannii . Etiologic agents commonly associated with this type of infection are streptococci mixed with anaerobic organisms.1 The first patient was a 21 year old male with medical problems including end-stage renal disease, systemic lupus erythematosus, thrombotic thrombocytopenic purpura and mesenteric vasculitis. Treatment with corticosteroids, intermittent rituximab, plasmapheresis, blood transfusions and hemodialysis preceded his admission to the hospital for pulmonary edema and rectal passage of bright red blood. His blood cultures grew vancomycin-resistant Enterococcus faecium (VRE) and Candida albicans , which were treated with daptomycin and fluconazole. Although subsequent blood cultures were negative, his stool tested positive for Clostridium difficile -associated colitis requiring the addition of metronidazole to his regimen. Gastrointestinal bleeding continued 3 weeks after his admission, prompting performance of an exploratory laparotomy. The surgical findings mandated an ileocecal resection and ileostomy. Although… ABBREVIATIONS: MDR-multi-drug resistant; HAI-hospital-associated infection; CAI-community-associated infection; WBC-white blood cell; VRE-vancomycin-resistant Enterococcus species; MRSA-methicillin-resistant Staphylococcus aureus ; PCR-polymerase chain reaction; UTI-urinary tract infection; GNB-gram-negative bacilli; MIC-minimal inhibitory concentration; ICU-intensive care unit; ESBL-extended-spectrum beta-lactamase enzyme; MLST-multi-locus sequence typing; PFGE-pulse-field gel electrophoresis 1. Consider the effect of Acinetobacter baumannii on the underlying comorbidities of the 2 patients. 2. Define and discuss necrotizing fasciitis and its treatment. 3. Summarize the events leading to the transmission of Escherichia coli ST131. 4. Discuss the effect of treatment with a fluoroquinolone and the patient outcome. [1]: #corresp-1