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Cases in clinical microbiology.

The case description on this page and its follow-up discussion presented elsewhere in this issue is the 27th in a series of articles presenting clinical microbiology cases that will appear in this journal. Readers should study the case description below and formulate their own answers to the questions posed. After coming up with a solution to the problem, turn to page 8 in this issue and read the Case Follow-up and Discussion. This is followed by Questions for STEP Participants on page 14.

Case Description: A healthy 16 year-old male was involved in an all-terrain vehicle (ATV) rollover accident. He was transported to a local hospital with an open fracture of the left distal humerus and an injury of the left brachial artery and upper arm median nerve. An open reduction internal fixation of the humerus was performed with irrigation and debridement, followed by a thrombectomy of the left brachial artery.

Three months later the patient was referred to Cincinnati Children's Hospital Medical Center with suspected brachial plexus palsy on the left side. There was limited improvement of his left upper extremity peripheral nerve injuries sustained in the accident, as well as a recent history of infections of the wound sites. An additional left humerus open reduction internal fixation and a right iliac crest bone graft were performed. Bone pieces and anaerobic and aerobic swab specimens were obtained from the surgical site and submitted to the microbiology laboratory for cultures.

Laboratory Specimen Processing and Analysis

In the laboratory, the bone fragments were placed in approximately 2 mL of sterile saline and were ground using a Precision[TM] tissue grinder. The ground bone and aerobic swab specimens were each inoculated onto trypticase soy agar with 5% sheep blood, chocolate, and MacConkey agars and enriched thioglycollate medium with vitamin K and hemin. Aerobic solid media was incubated in a 5% C[O.sub.2] atmosphere at 35[degrees]C, and the thioglycollate medium was incubated at 35[degrees]C in ambient air. Bone tissue and anaerobic swabs were also inoculated onto a Brucella Blood Agar, Brucella Laked Blood Agar with Kanamycin and Vancomycin (LKV), and Brucella Blood Agar with Phenylethyl Alcohol (PEA). Anaerobic media was incubated in Whitley A35 Anaerobic Workstation by Don Whitley Scientific Limited. The atmosphere inside the chamber was kept at 5% hydrogen, 5% carbon dioxide, and 90% nitrogen. Gram-stained smears from both specimens showed no organisms and small quantities of white blood cells.



No anaerobic bacteria were isolated. Growth of a single colony morphology was noted on the aerobic media after 24 hours of incubation. Medium sized, smooth, and circular colonies with entire borders were observed. Lactose fermenting, Gram-negative bacilli were observed on the MacConkey agar (Figure 1a). Gram-stained smears from the growth on the blood agar plate showed small to medium length Gram-negative bacilli.

Given the clinical situation and the laboratory findings, what are the three organisms on your list of "most likely" causes?

Joel E. Mortensen, PhD, MLT(AMT), Series Editor

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Article Details
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Title Annotation:brachial plexus palsy
Author:Mortensen, Joel E.
Publication:Journal of Continuing Education Topics & Issues
Article Type:Clinical report
Date:Jan 1, 2014
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