Equipment contact surfaces as sources of Staphylococcus carrying enterotoxin-encoding genes in goat milk dairy plants

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Abstract

Potential contamination sources and the enterotoxigenic profiling of Staphylococcus isolates were investigated in four goat dairy plants. Samples (n = 160) were collected from different processing points in five samplings. Staphylococcus spp. isolates were confirmed by polymerase chain reaction and genotyped using repetitive extragenic palindromic PCR (Rep-PCR). Classical (sea, seb, sec, sed) and novel (seg, seh, sei) staphylococcal enterotoxin-encoding genes were detected by PCR. seb, sec, see and sei were identified in isolates originated from raw and pasteurised milk, pre- and post-pasteurisation tanks and wall surfaces. SE-harbouring isolates were mostly identified as non-aureus staphylococci. Genotypic profiles and contamination levels indicate that the packaging machine is a critical point for staphylococcal contamination. Equipment surfaces are important contamination sources to pasteurised milk considering the indistinguishable genotypic patterns of isolates from pre- and post-pasteurisation points. Cleaning and disinfection of milk contact surfaces should be revisited to warrant quality and safety of goat milk.

Introduction

Staphylococci are commonly isolated from food and environmental sources. Some strains can produce staphylococcal enterotoxins (SEs) that have been associated with staphylococcal food poisoning outbreaks in humans worldwide. SEs are resistant to heat, freezing and drying conditions (Kadariya, Smith, & Thapaliya, 2014). Moreover, they are fully functional in the gastrointestinal tract after ingestion because they can resist low pH and proteolytic enzymes such as pepsin or trypsin (Argudín, Mendoza, & Rodicio, 2010). Significant social and economic impacts have been attributed to staphylococcal foodborne poisoning (Jamali, Paydar, Radmehr, Ismail, & Dadrasnia, 2015).

At food processing plants, food contact surfaces remain as potential sources of contamination by pathogenic and spoilage organisms (Sheraba, Yassin, & Amin, 2010) and must be carefully cleaned and disinfected to reduce the risks of microbial contamination of the final product. Dairy processing plant surfaces are particularly susceptible to contamination by Staphylococcus spp., as these organisms are commonly found in milk and on the body surfaces of farmers and employees in the industry, who are considered asymptomatic carriers.

Although Staphylococcus is recognised as a leading cause of foodborne poisoning in humans and highly abundant in the dairy sector, there is a lack of information on the staphylococcal contamination in the goat dairy industry. Staphylococcus spp. are the main cause of subclinical intramammary infections in dairy goats (Acosta, Silva, Medeiros, Pinheiro, & Mota, 2016) and have been commonly cultured from raw goat milk (Lyra et al., 2013). The biofilm-producing ability of some Staphylococcus strains contributes to their survival in clean equipment surfaces in the food industry, and facilitates cross-contamination. The development and implementation of preventive measures, such as Hazard Analysis and Critical Control Point (HACCP), to control the potential risks associated with staphylococcal contamination, require accurate data on the Staphylococcus occurrence in different processing points.

The sources of contamination and enterotoxigenic potential of Staphylococcus aureus and species other than S. aureus in goat dairy plants was investigated with genotypic relatedness analysis of Staphylococcus spp. cultured from different processing points.

Section snippets

Samplings and Staphylococcus isolation

Four goat milk dairy plants (A, B, C and D) located in Paraiba State, Northeastern Brazil, were investigated. Each of these goat milk processing plants process around 400 L of milk daily and belong to associations of smallholder producers in the different regions of the State. Pasteurised milk and cheese are regularly produced by these plants. The majority of pasteurised milk is purchased by the federal government and distributed to public schools and day-care centres as part of public social

Isolation and identification of staphylococci

Out of the 160 samples from the different points in the four dairy plants, 66 samples (41.2%) were positive for Staphylococcus spp. The frequencies of Staphylococcus spp. positive samples were 40% (16/40), 35% (14/40), 50% (20/40) and 40% (16/40) in the goat dairy plants A, B, C and D, respectively.

Fifty percent of the isolates (33/66) originated from milk samples (27.2% and 22.7% from raw and pasteurised milk, respectively). The remaining isolates originated from the packaging machine (27.2%;

Discussion

The high level of staphylococcal contamination in raw and pasteurised goat milk samples, as well as the frequent occurrence of these microorganisms on the equipment surfaces and the environment of dairy plants, might be associated with the fact that goat milk is a major source of Staphylococcus. In Brazil, similarly to other countries, subclinical infectious mastitis in small ruminants is usually caused by Staphylococcus spp. (Acosta et al., 2016; Machado, 2018). Therefore, one can expect that

Conclusion

Contact surface residual contamination by Staphylococcus spp. can occur frequently in goat dairy plants and play a major role in cross-contamination, affecting pasteurised milk. Viable Staphylococcus organisms in pasteurised goat milk can harbour enterotoxin-encoding genes, posing a threat to public health. Improved hygiene procedures seem to be critical for the mitigation of staphylococcal contamination of pasteurised goat milk, especially those addressing the cleaning and disinfection of

Credit author statement

Candice M. C. G. De Leon (Investigation, methodology, validation, writing-original draft; review and editing), Francisca G. C. Sousa (Investigation, methodology, validation), Mauro M. S. Saraiva (Investigation, formal analysis, methodology, validation, writing – original draft), Patricia E. N. Givisiez (conceptualization, supervision, resources, writing – original draft; review and editing), Núbia M. V. Silva (methodology, data curation, visualization, writing-original draft), Rafael F. C.

Acknowledgements

This study was supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Finance code 001), Financiadora de Estudos e Projetos (FINEP) and Conselho Nacional de Pesquisa e Desenvolvimento (CNPq, proc. 311793/2016-9).

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