Study on microbial communities in domestic kitchen sponges: Evidence of Cronobacter sakazakii and Extended Spectrum Beta Lactamase (ESBL) producing bacteria

Domestic environment, in particular, kitchen setting is a well established source of microbial contamination. Kitchen sponges represent an important vehicle of microbial transmission and maintenance of spoilage bacteria and pathogenic strains responsible for food borne diseases.
The aims of this study was to evaluate the microbial communities of 100 ‘in-use’ kitchen sponges, improving the knowledge on their role in cross-contamination in domestic environment and transmission of ESBL-producing strains. Sponges were processed for: aerobic mesophilic bacteria (AMB), Enterobacteriaceae (EB), yeasts and moulds (YM), coagulase-positive staphylococci (CPS), micrococci (MCC), anaerobic sulfite reducing bacteria (ASR), and for the detection of Listeria monocytogenes, Salmonella spp. and Yersinia enterocolitica. A total of 309 enterobacteria strains were identified and then processed for ESBL (Extended Spectrum Beta Lactamase) phenotypical expression. A high contamination level of kitchen sponges was observed (mean value AMB 8.25±1.1; EB 5.89±1.2; YM 5.57±1.1; MCC 4.82±0.1 log CFU/g). Identified enterobacteria strains revealed several opportunistic and pathogenic agents such as Enterobacter cloacae (28%), Citrobacter freundii (23.3%), Cronobacter sakazakii (14.6%) and other strains in lower percentage. Listeria monocytogenes was found in only one sponge (1%). A total of 69 (22.3%) enterobacteria resulted ESBL+, with the following prevalence: P. rettgeri (50%), L. adenocarboxilata (30%), K. pneumoniae (25%), K. oxytoca (25%), C. sakazakii (20%), E. cloacae (20.7%), C. freundii (20.1%). Results confirm the potential role of kitchen sponges as vehicle for food-borne pathogens such as, C. sakazakii for the first time, infectious agents and spoilage microorganisms. The observed high contamination level and the presence of several ESBLs opportunistic pathogens, stresses the necessity to improve a proper education of the consumers on the effective treatment to reduce their microbial loads.