Haemophilus influenzae blood-stream infection and third-generation cephalosporin susceptibility testing: a comparative case study using EUCAST and CLSI guidelines.

Introduction: In this comparative case study, we discuss clinically relevant discrepancies of antimicrobial susceptibility testing (AST) interpretation for ceftriaxone against a non-typable, beta-lactamase negative, ampicillin-resistant (BLNAR) Haemophilus influenzae isolated from a blood culture. Case report: A 74-year-old man presented with a 3 day illness characterized by shortness of breath and dry cough, and was noted to be febrile and hypoxic on admission. A blood culture bottle flagged positive with Gram-negative coccobacilli, later identified as Haemophilus influenzae with the patient commenced on ceftriaxone. The isolate was beta-lactamase negative and antibiotic susceptibility testing (AST) using disc diffusion revealed the isolate resistant to ceftriaxone and ampicillin by EUCAST methodology, with the patient subsequently changed to amoxicillin/clavulanate. Further AST using the CLSI methodology in parallel demonstrated discrepant results between the two susceptibility methods. The patient recovered without complications. Conclusion: This discrepancy could lead to inconsistent reporting of susceptibilities between laboratories, and consequently antibiotic prescribing, especially for invasive isolates. As more laboratories adopt EUCAST methodologies for AST interpretation in Australia and globally, it is important for clinicians to consider the clinical implications of these methodological discrepancies.

Wound infection caused by Neisseria zoodegmatis, a zoonotic pathogen: a case report.

The isolation of Neisseria zoodegmatis from a 63-year-old female presenting to the emergency department following a cat bite injury to her right hand is described in this report. N. zoodegmatis , also known as Centers for Disease Control (CDC) group EF-4b, is considered to be a zoonotic pathogen, and is usually associated with dog or cat bites. Despite the potential of this organism to cause serious soft tissue infections, it can be overlooked in routine clinical laboratories due to its slow growth characteristics and when the history of animal bite is not provided to the laboratory. This case highlights the importance of appropriate clinical history provision to the microbiology laboratory to help provide important information about potential pathogens and allow microbiologists to optimize culture and identification methods. The introduction of tools such as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) into clinical laboratories allows identification and the interpretation of results to be performed within a few minutes of isolation on proper culture media, as opposed to traditional methods, whose slowness may be problematic, as shown in this case report.