The occurrence of Listeria monocytogenes is associated with built environment microbiota in three tree fruit processing facilities

Table 1 MPN-based quantification of L. monocytogenes in samples collected from three tree fruit packing facilities at two time points in March 2018

Log MPN/sponge sample	Facility F1^c			Facility F2			Facility F3^c
Log MPN/sponge sample	Wash	Dry	Wax	Wash	Dry	Wax	Wash	Dry	Wax
Trial 1^a	< LD	< LD	< LD	3.87	5.02	4.38	LD < 1.55^d	< LD	LD < 1.55^d
Trial 2^b	< LD	< LD	< LD	3.15	3.32	5.35	1.55	1.55	2.63
Average	< LD	< LD	< LD	3.51	4.17	4.87	< 1.55	0.82	< 2.63

^aFour dilutions (10⁻², 10⁻³, 10⁻⁴, 10⁻⁵) were used in the MPN calculation. Each dilution was tested in triplicates. Sample homogenate (a sponge in 90 ml of BLEB) was also enriched
^bFive dilutions (10⁻², 10⁻³, 10⁻⁴, 10⁻⁵, 10⁻⁶) were used in MPN calculation. Each dilution was tested in triplicates. Sample homogenate (a sponge in 90 ml of BLEB) was also enriched
^c< LD indicates that L. monocytogenes was below the limit of detection, which was at least one viable cell per sample, grown to at least 10⁵ cells/ml by the time the enrichment was completed
^dThe level of L. monocytogenes was between the limit of detection and 1.55 log₁₀ MPN/sponge sample. L. monocytogenes was detected in enriched sponge homogenate; however, none of the MPN dilution tubes were positive

ISSN: 2049-2618