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

Introduction

In the last few years, numerous studies indicate that several food-borne diseases are related to domestic infection sources (EFSA, 2015). Improper food handling and un-hygienic practices are considered the major factors in foodborne illness episodes. Cross-contamination in household kitchens represent another important domestic source of infection (Azevedo et al., 2014). However, consumers risk perception of food borne illness in home environment is reported as very low (European Commission, 2016). Kitchens are included among the most contaminated domestic environments, even more of some bath’s areas (toilette seat, door knob, light switch, toilet handle) or commonly used objects such as pen, keys, cellular phone, keyboards, etc. (Donofrio et al., 2012). Furthermore, 37.3% of food borne outbreaks in EU in 2014, founded their infection sources in home environments (EFSA, 2015). This evidence is confirmed by the frequent isolation of food-borne pathogens in tools, cloths, towels, sponges and kitchen surfaces (Mattick et al., 2003). Among these, dish sponges were the most contaminated item in the household, and deserve great attention, for their potential role as vehicle for foodborne pathogens (Donofrio et al., 2012). Their role as microbiological hot spots in domestic settings was recently well established (Cardinale et al., 2017). They are, indeed, frequently used not only to clean dishes and cookware, but also, different surfaces or even refrigerators shelves, increasing the risk of cross-contamination (Catellani et al., 2014). Thanks to their large surface/volume ratio, their constant humidity and the nutrients for bacterial growth contained, sponges are, indeed, an ideal habitat for microorganisms (Cardinale et al., 2017). Several authors have investigated the microbiological quality of sponges used in domestic kitchens, reporting a highlevel contamination and the frequent isolation of pathogens, such as Salmonella spp., Staphylococcus aureus, Campylobacter spp. and Listeria monocytogenes (Hilton and Austin, 2000).

These findings induce much more concern, considering that common dishwashing soaps or chemical compounds do not reduce significantly microbial load in kitchen sponges (Sharma et al., 2009). Moreover, multi-drug resistance bacteria were common in household’s environment, and no significant differences were noted between biocide users and non-users; as well as the frequency of pathogen recovery (Marshall et al., 2012). Among this, ESBLs (Extended Spectrum Beta Lactamase) are a group of evolving enzymes that are able to hydrolyze extended spectrum cephalosporin. ESBL producing enterobacteria are a wide range of resistant strains that have gained much more importance in public health in the recent years. Infections due to ESBL producers range from uncomplicated urinary tract infections to life-threatening sepsis representing a serious challenge for clinical treatments. It is well established the role of animals and derived products as a source of diffusion of resistant strains (Beninati et al., 2015; EFSA, 2011) For all these reasons, the aim of the present study was to improve the knowledge on the microorganisms frequently involved “in-use” kitchen sponges’ colonization, and their role in maintaining and diffuse ESBL-producing organisms in domestic environment.

Materials and Methods

Results

Discussion

The macroscopic results reported in our sponges confirm the low consumers risk perception of food borne illness related to cross-contamination in home environment (European Commission, 2006). The presence of foreign particles such as human or pets’ hairs, in fact, underlines the promiscuous use of sponges in real-life domestic conditions, like the cleaning of pet’s bowls or other tools and surfaces non-related to kitchen environment. The microbiological data of this study confirms a great level of sponge contamination and poor hygienic conditions, as observed by other authors (Azevedo et al., 2014; Mattick et al., 2003; Cardinale et al., 2017). The role of kitchen cleaning tools in bacterial transfer to surfaces was, already, confirmed by Hilton and Austin (2000) on cloths contamination. In that study, no significant differences between the microbial load of wet cloths, dry cloths, those used for short and prolonged periods and cloths used for different activities were observed. Our results confirm, as just previously reported, that in kitchen sponges’ bacterial colonization and subsequent replication occur rapidly and high loads were maintained all over their period of use (Cardinale et al., 2017).

The detection of Listeria monocytogenes, also if only in one sample, confirms the potential role of kitchen sponges as food-borne pathogen vehicle, considering its ability in adhesion and surviving on different surfaces (Kilonzo-Nthenge et al., 2012; Mattick et al., 2003). Among foodborne pathogen bacteria deserve particular attention the presence in 16 sponges (16%) of Cronobacter sakazakii (previously Enterobacter sakazakii). This occurrence confirms, as reported by Kilonzo-Nthenge et al. (2012), that it can colonize several kitchen districts. To date and based on the recently paper of Cardinale et al. (2017) on the microbiome analysis on used kitchen sponges this is the first evidence of Cronobacter sakazakii presences among the bacteria involved in kitchen sponges’ colonization. These bacteria, frequently isolated from environment and humans and animals’ intestinal tract, can cause necrotizing enterocolitis, bacteremia, and meningitis in children and infants, with a 40-80% mortality rate. It can also cause diarrhea and urinary tract infections in people of all ages, especially in YOPI subjects (young, old, pregnant, immunosuppressed) (Healy et al., 2010). C. sakazakii has been found in several foods, but mostly powdered infant formula has been linked to disease outbreaks (Adekunte et al., 2010). Its presence in this food is related to contamination in raw ingredients, during the manufacturing process or during the preparation/reconstitution process. Contamination also may occur through blenders, feeding bottles and utensils used to cleanse feeding bottles (Adekunte et al., 2010). This occurrence deserves particular attention considering that kitchen sponges are commonly used for baby tools cleaning (baby bottles, children’s cutlery, bowls ecc.). This study confirms the high stress, environmental resistance of C. sakazakii and also reports the diffusion of ESBL+ strains in household settings (Abdel-Galil et al., 2015). In regards of other Enterobacteriaceae identified in our kitchen sponges, the higher prevalence reported for Enterobacter cloacae, is probably related to its high diffusion and resistance. Moreover, these bacteria, with Citrobacter freundii, Klebsiella oxytoca and Klebsiella pneumoniae have been reported as important opportunistic and multiresistant bacterial pathogens for humans during the last three decades in hospital wards (Mezzatesta et al., 2012; Munoz-Price et al., 2013; Whalen et al., 2007). L. adecarboxylata, often found in water environments, is reported as occasionally pathogenic agent, even in healthy subjects (Keren et al., 2014). The pathogenic potential of Providencia rettgeri is well known, as well as the diffusion of extended spectrum beta lactamase (ESBL) and metallo-beta lactamase (NDM-1) strains (Tada et al., 2014). Finally, S. liquefaciens is widely isolated in nature, including river water, mineral water, domestic sewage, fish, minced meat and pasteurized milk or cream (Muscolino et al., 2014; Ziino et al., 2010). In humans, it has been, rarely, reported as a cause of nosocomial infections, including urinary tract infection, pneumonia, neonatal meningitis, endocarditis and septicemia (Mossad, 2000). As reported, in our study the highest prevalence of ESBLs was assigned to P. rettgeri and L. adenocarboxilata whose beta-lactamase resistance was already reported for nosocomial infections (Sheng et al., 2013). Resistance patterns for Klebsiella genus, are well-known and several strains represent the most prevalent clinical isolates in complicated infections (Barrios et al., 2017). The situation becomes even more worrying, considering that Klebsiella is one of the most widespread opportunistic pathogens in nosocomial infections with fatal prognosis (Tuon et al., 2011). Klebsiella ESBL-producing strains, often, carry resistance determinants against fluoroquinolones, cotrimoxazole and aminoglycosides. These microorganisms are rapidly evolving in response to the selective pressure created by antibiotics abuse, resulting in a serious clinical and epidemiological problem (Tuon et al., 2011). E. cloacae and C. freundii ESBL strains are more and more frequently implied in multiple resistance patterns against insidious infections (Lagha et al., 2016).

The results of this study (Figures 1 and 2) obtained with traditional microbiology methodology on a relevant number of samples (n. 100) reveled difference on Enterobacteriaceae abundance respect to the those of Cardinale et al. (2017) on the total of 223,741 raw sequences obtained by 454-pyrosequencing of 16S rRNA gene amplicon libraries from 28 sponge samples. In our samples Enterobacteriaceae have a considerable influence (45%) on the AMB, while for Cardinale et al. (2017) have a cumulative relative abundance of 1.18% only after Bacteroidaceae, Bdellovibrionaceae, Brevibacteriaceae, Caulobaceriaceae, and Comamobacteriaceae family. Except for Escherichia, were in accordance the reported genera Enterobacter, Citrobacter and Leclercia with our results among those reported in the Enterobacteriaceae family (Cardinale et al., 2017).

Conclusions

In conclusion, the high contamination level observed in our samples must be assumed as unacceptable for a kitchen tool, considering the potential role of sponges in cross contamination events. Sponges create a setting for colonization and subsequent microbial replication thanks to favorable factors such as high-level humidity, presence of organic residuals and promiscuous use. Moreover, the presence of ESBL-producing strains in kitchen sponges confirms how the domestic settings are potential transmission pathways, explaining the spread of ESBL Enterobacteriaceae from the food chain to humans (Tschudin-Sutter et al., 2014).

Microorganisms, in fact, in kitchen cloths and sponges are protected by soil aggregates, surviving thermal or chemical stress of washing (Park et al., 2006). For all these reasons in order to reduce microbial loads, it would be necessary change, frequently, kitchen sponges and make, periodically, efficient sanification treatments. Microwave and dishwasher, reaching high temperatures, represent the most effective treatments to reduce, significantly, microbial loads (Park et al., 2006; Sharma et al., 2009). High temperature in combination with washing is more effective in reducing bacteria in kitchen sponges than using heat alone (Tate, 2006). As reported by Erdoğrul and Erbilir (2005), the regular dish washing liquid was not effective in reduction of bacteria in the house hold in use sponges, as the presence of food residues strongly reduces the product’s efficacy, while in the laboratory tests, the regular dish washing liquid was demonstrated to be effective in reduction of bacteria. The necessity of efficient sanification treatments is supported by the detection of pathogenic and ESBL producing strains, confirming kitchen sponges as vehicle of their transmission and permanence in domestic settings.

Funding Statement

Funding: none