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Rapid method for detection, identification, and susceptibility testing of enteric pathogens
Abstract:
Three hundred and seven colonies believed to be enteric pathogens were selected from primary plates of MacConkey, xylose desoxycholate, or salmonella-shigella agar for inoculation to lactose-sucrose broth, urea-41 motility medium, modified Andrade glucose broth with inverted Durham tube, pregrowth broth, triple sugar iron agar, lysine iron agar (LIA), and Christensen urea agar. The rapid screen consisted of interpreting the lactose-sucrose, urea-41 motility, and modified Andrade glucose broth gas reactions after 4 to 6 h at 35 degrees C. These rapid screening biochemicals plus LIA were incubated for 24 h if further interpretation was required. Reference biochemicals (triple sugar iron, LIA, and Christensen urea agars) were interpreted at 24 h. Of 307 isolates, 49 (16%) were reported as negative for enteric pathogens after 4 to 6 h because their biochemical profiles were not compatible with those for enteric pathogens. A total of 87 (28.3%) isolates produced biochemical profiles at 4 to 6 h that were presumptive for enteric pathogens. The 87 presumptive pathogens were inoculated into the AutoMicrobic system Gram-Negative General Susceptibility Card and the AutoMicrobic system Enterobacteriaceae-Plus Biochemical Card (AMS-EBC+) after 4 to 6 h of growth in pregrowth broth. Of these isolates, 63 were confirmed to be enteric pathogens, of which 61 (96.8%) were correctly identified by the AMS-EBC+. One isolate was identified as Shigella dysenteriae by AMS-EBC+ but confirmed as Shigella flexneri biotype 6 by a reference laboratory. The other isolate was identified as Arizona hinshawii by AMS-EBC+ but was confirmed as Salmonella enteritidis. Of the 307 isolates, 166 (54.1%) required further interpretation of the rapid screening biochemicals plus LIA at 24 h; 5 of these were detected as enteric pathogens. The same 68 enteric pathogens were detected by both the rapid method and the reference method. The results from the general susceptibility card agreed with agar diffusion results at 99.2%. One Salmonella enteritidis and four Shigella spp. showed minor discrepancies with tetracycline. No very major or major discrepancies were observed.
Insights
A rapid biochemical screening method accurately identified enteric pathogens in 4-6 hours, with the AutoMicrobic system Enterobacteriaceae-Plus Biochemical Card (AMS-EBC+) achieving 96.8% accuracy for presumptive pathogens.
Area of Science:
- Clinical Microbiology
- Diagnostic Bacteriology
- Infectious Diseases
Background:
- Accurate and rapid identification of enteric pathogens is crucial for timely clinical intervention and infection control.
- Traditional biochemical methods for enteric pathogen identification can be time-consuming, delaying diagnosis and treatment.
Purpose of the Study:
- To evaluate a rapid biochemical screening method for the identification of enteric pathogens.
- To assess the performance of the AutoMicrobic system Enterobacteriaceae-Plus Biochemical Card (AMS-EBC+) in identifying presumptive enteric pathogens.
Main Methods:
- A panel of 307 suspected enteric pathogen isolates was subjected to rapid biochemical screening (4-6 hours) and traditional 24-hour reference methods.
- Presumptive pathogens identified by rapid screening were further analyzed using the AutoMicrobic system Enterobacteriaceae-Plus Biochemical Card (AMS-EBC+).
- Antimicrobial susceptibility testing was performed using agar diffusion and compared with AutoMicrobic system general susceptibility card results.
Main Results:
- The rapid screening method identified 87 (28.3%) isolates as presumptive enteric pathogens within 4-6 hours.
- The AMS-EBC+ correctly identified 61 out of 63 confirmed enteric pathogens (96.8%) from the presumptive group.
- Minor discrepancies in antimicrobial susceptibility testing were observed for some Salmonella and Shigella isolates with tetracycline, but no major or very major discrepancies were noted.
Conclusions:
- The rapid biochemical screening method, coupled with the AMS-EBC+, offers a highly accurate and efficient approach for the presumptive identification of enteric pathogens.
- This rapid method can significantly reduce the time to identification compared to traditional 24-hour biochemical assays.
- The study validates the utility of the AMS-EBC+ for routine clinical microbiology laboratories handling enteric pathogen detection.