Identification of non-Listeria spp. bacterial isolates yielding a β-d-glucosidase-positive phenotype on Agar Listeria according to Ottaviani and Agosti (ALOA)

• Published in: International journal of food microbiology Vol. 193; pp. 114 - 129
• Main Authors: Angelidis, Apostolos S., Kalamaki, Mary S., Georgiadou, Sofia S.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 16.01.2015
• Subjects: Agar - metabolism; ALOA; Bacillus; Bacteria - enzymology; Bacteria - growth & development; Bacteria - isolation & purification; Bacterial Typing Techniques - standards; Cellulosimicrobium; Cheese - microbiology; Chromogenic Compounds - metabolism; Colony Count, Microbial; Enterococcus; Food Microbiology; Glucosidases - metabolism; Kocuria; Listeria monocytogenes; Marinilactibacillus; Phenotype; RNA, Ribosomal, 16S - genetics; Rothia; Staphylococcus; Listeria monocytogenes; Marinilactibacillus; Cellulosimicrobium; Kocuria; ALOA; Rothia
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2014.10.022

Agar Listeria according to Ottaviani and Agosti (ALOA) is the mandatory medium used for the detection and enumeration of Listeria monocytogenes in foods according to the official International Organization for Standardization (ISO) methods. On ALOA, Listeria spp. appear as bluish-green colonies due to the production of β-d-glucosidase, an enzyme that cleaves 5-bromo-4-chloro-3-indolyl-β-d-glucopyranoside, a chromogenic substrate included in the formulation of the medium. The present work reports on bacterial isolates (n=64) from ready-to-eat soft cheeses, which are able to grow on ALOA, forming bluish-green colonies and therefore phenotypically resemble Listeria spp. All isolates were also capable of growing on the selective media PALCAM and RAPID L'mono™. The isolates were characterised with biochemical tests including those specified in the ISO standards for the confirmation of Listeria spp. and identified via partial sequencing of their 16S rRNA gene. According to sequencing results the isolates represented 12 different bacterial species or species-groups belonging to seven different genera: Bacillus spp. (B. circulans, B. clausii, B. licheniformis and B. oleronius), Cellulosimicrobium spp. (C. funkei), Enterococcus spp. (E. faecalis, E. faecium/durans), Kocuria spp. (K. kristinae), Marinilactibacillus spp. (M. psychrotolerans), Rothia spp. (R. terrae) and Staphylococcus spp. (S. sciuri and S. saprophyticus subsp. saprophyticus/xylosus). Cellulosimicrobium spp. have never been previously isolated from foods. These results significantly extend the list of bacteria previously known as capable of growing on ALOA as bluish-green colonies and suggest that there may be room for further improvement in the medium's inhibitory properties towards non-Listeria spp., Gram-positive bacteria present in foods. •Seven bacterial genera other than Listeria grow on ALOA as bluish-green colonies.•Cellulosimicrobium, Kocuria, Marinilactibacillus, Rothia were among the β-d-glucosidase-positive isolates.•Cellulosimicrobium spp. have never been previously isolated from foods.•The specificity of ALOA for Listeria spp. may need to be improved.