Detection of colonisation by extended-spectrum beta-lactamase or carbapenemase producing Enterobacterales from frozen st
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RESEARCH NOTE
Detection of colonisation by extended‑spectrum beta‑lactamase or carbapenemase producing Enterobacterales from frozen stool specimens Pisey Tan1, Shweta R. Singh2, Bunsoth Mao3, Konstantin Evdokimov2, Vonthanak Saphonn3, Li Yang Hsu2 and Paul Turner1,4*
Abstract Objective: To determine the impact of pre-culture ultra-low temperature (ULT, − 80 °C) storage of human stool specimens on recovery of Extended-Spectrum Beta-Lactamase (ESBL) or Carbapenemase (CPM) producing Enterobacterales. Results: Twenty stool specimens from a community-based household colonisation study in Cambodia were cultured fresh and after 4–5 days and ~ 6 months of ULT storage (as a slurry in tryptone soya broth–10% glycerol). Presumptive ESBL- and CPM-Escherichia coli isolates were detected in 19/20 (95%) and 1/20 (5%) freshly cultured specimens, respectively. The specimens yielded identical results when re-cultured after ULT storage at both time points. Detection of presumptive ESBL- and CPM-Klebsiella / Enterobacter / Citrobacter group was less frequent and slightly less stable over time. Comparison of antimicrobial susceptibility test profiles between pairs of E. coli and K. pneumoniae isolates from the two frozen culture time points revealed concordance in only 13/28 (46%) pairs, indicating likely colonisation by multiple strains. In conclusion, ULT storage of human stool specimens prior to culture appears to be an acceptable method for managing laboratory workflow in culture-based ESBL / CPM Enterobacterales colonisation studies in high prevalence settings. Keywords: Frozen, Storage, Detection, Faeces, Antimicrobial resistance, Escherichia coli, Klebsiella pneumoniae Introduction The gastro-intestinal tract is a major reservoir for antimicrobial resistant bacteria in humans. High rates of gastro-intestinal tract colonisation by extended-spectrum beta-lactamase (ESBL) and carbapenemase (CPM) producing Enterobacterales have been reported in many studies [1].
*Correspondence: [email protected] 1 Cambodia Oxford Medical Research Unit, Angkor Hospital for Children, Siem Reap, Cambodia Full list of author information is available at the end of the article
Practical coordination of laboratory work for large colonisation studies can be a challenge, especially with community-based sampling where multiple specimens may be received by the laboratory at the end of the working day. Delays to processing specimens may result in sub-optimal results. However, storage at ultra-low temperatures (ULT) with delayed processing has been well validated for certain specimen types. For example, culture of fresh or − 80 °C stored nasopharyngeal swabs collected into skim milk–tryptone soya broth–glucose– glycerol (STGG) medium results in similar detection rates of Streptococcus pneumoniae [2]. Thus, pre-culture ULT storage of swabs in STGG has become an approved
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