Cronobacter sakazakii is an emerging and opportunistic foodborne pathogen that causes severe infantile diseases, including meningitis, necrotizing enterocolitis, and septicemia. It has been reported in numerous countries around the world, including those in Africa. Although it has been isolated from food, environmental and clinical samples across Africa, the most implicated source of the C. sakazakii infection outbreaks across the globe has been the consumption of contaminated powdered infant formula (PIF).
PIF contamination can occur during the production stage for several reasons, such as poor Good Manufacturing Practices (GMP) and contaminated equipment. Owing to its high food safety risk and severity of C. sakazakii infections, especially for infants, the International Commission on Microbiological Specification for Foods in 2002 categorized Cronobacter spp. as “a serious hazard for restricted populations, life-threatening or with significant chronic sequelae over a long duration”. Neonatal infections associated with C. sakazakii have been reported to have a mortality rate as high as 80%, often leading to irreversible neurological disorders for survivors
Cronobacter has many unique characteristics that contribute to its survival in harsh environments and transmission along the food chain from production to consumption. These features include the formation of biofilm; the ability to withstand critical food control steps during food production such as osmotic stress, thermal treatment, pH, detergents, starvation, disinfectants, antibiotics, and sanitizers. In addition, the organism also possesses the ability to significantly resist high temperatures (the minimum, maximum, and optimum temperatures for growth are 6, 45, and 37–43°C) and desiccation that allows it to stay up to 2–5 years in an encapsulated form in dehydrated food products (with water activity range from 0.30 to 0.83).
Cronobacter impact goes unnoticed in Africa
Based on the current surveillance systems across the globe, available data shows that there is no active surveillance system for diseases caused by E. sakazakii (Cronobacter spp.), implying that most national foodborne disease surveillance centers of the world are yet to identify cases of C. sakazakii infection. Because C. sakazakii infection is rare, most sites where Cronobacter spp. disease has been reported have very low populations, and several years of monitoring/surveillance will be needed to develop a valid incidence estimate across affected populations
Generally, in less developed nations, including Africa, the impact of Cronobacter spp. often goes unnoticed. This is corroborated by findings from Ethiopia that the overall burden of Cronobacter is grossly underreported and, to some degree, considered non-reportable compared to the significant number of other foodborne pathogens reported. Furthermore, the available data on Cronobacter spp. prevalence in follow-up formula products for babies aged 6–11 months is very scarce. This scarcity is because only a few national regulatory bodies have been able to define the Microbiological Specifications for Cronobacter spp. in these items.
Despite the increase in the number of carefully documented cases of C. sakazakii (most infections in infants), this number is significantly low compared to many other infectious diseases. Currently, the actual burden of Cronobacter spp., in Africa or worldwide, cannot be determined as no effort has been made to estimate the factors that might be used to determine the overall burden. The capacity of environmental, clinical, and food laboratories to successfully identify C. sakazakii infections remains a major limitation in their diagnosis. Although significant advancement has been made with the identification methodology, there is still the need for increased awareness and capacity building, as with other emerging infections.
Prevalence and occurrence of Cronobacter sakazakii in African countries
Despite global research to determine C. sakazakii prevalence, its epidemiology remains incomplete and poorly understood. Given that C. sakazakii is ubiquitous in animate (man, animals) and inanimate (soil, water, plants) environments, it is not unusual that C. sakazakii has been isolated from a variety of foods as well as animal and vegetable sources of food products, though little is known about Cronobacter existence in their various environments. The most common food implicated in Cronobacter infection globally is PIF.
The prevalence of C. sakazakii in South Africa is similar to that observed globally. In 2008, 14% of the isolates obtained from South African newborn formula milk and the processing environment tested positive for C. sakazakii. This result corroborated a previous study that showed that 18% of South African infant formula milk and other baby food products were contaminated with C. sakazakii.
In North Africa, several studies on Cronobacter infection have been done. A 2013 study in Egypt revealed that C. sakazakii was present in the analyzed cheese, ice cream, and yoghurt samples. The isolation method employed chromogenic medium and traditional culture media. It was discovered that C. sakazakii was a significant cause of neonatal sepsis amongst preterm infants in North Africa. The identified means of bacterial infection were contaminated PIF, herbs, and water. In another research, 15% of the analyzed ground beef and beef burger samples sold in Egypt tested positive for C. sakazakii. Their results further established new epidemiological evidence that these pathogens are widespread in meat products sold in Egypt. However, this bacterium’s epidemiology remains incomplete and poorly described.
In West Africa, C. sakazakii was isolated from 13% of the 185 samples analyzed to determine the occurrence of Cronobacter spp. in PIFs sold in Abidjan, Ivory Coast. The study proved to be the first published work on the contamination of PIF with C. sakazakii from Abidjan. Also, the presence of C. sakazakii isolate from pharmaceutical industries wastewaters confirmed the prevalence of C. sakazakii in Nigeria’s ecosystem.
Conclusively, underreporting is attributable to the apparent absence of foodborne diseases caused by Cronobacter amongst malnourished children who are also vulnerable to severe infections in Africa. This is based on the argument that in the biggest and longest running holistic surveillance carried out for invasive bacterial infections in children and infants in sub-Saharan Africa, just a few instances of invasive Cronobacter infection were reported. Of the 65,426 samples collected between 1998 and 2013, 3953 were blood and cerebrospinal fluid cultures, of which only 60 tested positive and were identified as Cronobacter species.
Worthy of note is that 39 of those 60 cultures identified as Cronobacter species were samples obtained from newborns. However, employing an automated culture system to validate the isolated microorganisms further using a biochemical profile testing based on US Food & Drug Administration Bacteriological Analytical Manual, only two isolates, both from blood cultures, were confirmed to be consistent with Cronobacter. Their study took advantage of the continuous, systematic surveillance research carried out in Kenya by the Kenya Medical Research Institute and the Wellcome Trust Research Programme that lasted from 1998 to 2013.
Currently, the actual burden of Cronobacter in Africa or worldwide, cannot be determined as no effort has been made to estimate the factors that might be used to determine the overall burden.
Transmission routes of cronobacter sakazakii into the food chain and food safety concerns
Clinical presentations of foodborne diseases in newborns have been associated with pathogen-contaminated PIF, particularly C. sakazakii. Food contamination by C. sakazakii in PIF has been reported , and extrinsic contamination during PIF handling is thought to induce bacterial infection in infants; however, the transmission mechanism is not entirely known. Research has concentrated on food contamination by C. sakazakii during manufacture or from raw materials (i.e., intrinsic contamination).
Environmental health practices related to food preparation have been attributed to foodborne illnesses. Cronobacter infection has also been connected to unhygienic practices (extrinsic contamination source) by caregivers while preparing PIF.
Cross-contamination from the caregiver to spoon to PIF can be a direct pathway for the exposure to C. sakazakii from caregiver to infants; research is limited to observational and surveys studies that do not assess actual risk. Caregivers, and bacterial reservoirs, facilitate the transmission of the pathogen to foods through direct or indirect contact. Feeding utensils, including blenders, bottles, and spoons, have been connected to Cronobacter infection when contaminated utensils are used in mixing the formula. However, the simulation of PIF handling practices and cross-contamination of ground foods for the investigation of extrinsic contamination has not been reported.
Cronobacter is most commonly transmitted to babies through contaminated PIF from opened containers; it can also be transmitted to humans when manufacturers use contaminated raw materials during processing or when the formula powder comes in contact with a contaminated surface. The bacteria can live in water and on surfaces in the home, including a kitchen sink or counter. Therefore, the formula powder is likely to cross-contaminate at home after its container has been opened if not properly handled.
The pathogen has been reported in wheat and rice plants during the tillering, filling, and mature stages, in water from paddy fields, soil from rice, and soil from wheat flour milling plants. Subtyping using pulsed-field gel electrophoresis revealed that some strains shared a common profile, implying the widespread presence of Cronobacter in the environment, possible cross-contamination, and transmission routes in processing.
Cronobacter spp. has been isolated from dry milk powder, infant formulas, milk and milk-related beverages, candy and chocolate, and cereals. Additionally, research has been conducted to investigate the prevalence and distribution of C. sakazakii in a powdered milk manufacturing plant. In the spray-drying area, seven pulsed-field gel electrophoresis types were identified, which supposedly gained entrance into the plant via an improperly controlled roller shutter and a process air aperture. Also, both spray-drying towers’ textile filters for exhaust air were identified as the pathogen internal reservoirs. Infants have also become ill due to Cronobacter bacteria that grew on breastmilk pump parts that were not adequately cleaned.
The infection was found in families whose staple foods were made from Cronobacter-contaminated wheat flour. Cronobacter transmission from human to human is unknown, but there is a possibility because other types of bacteria can be transmitted from one person to another.
Molecular diagnosis of cronobacter sakazakii
Apart from the conventional screening and identifying C. sakazakii, new rapid molecular assay tools have been developed over the years. Some molecular diagnostic methods of detecting Cronobacter through specific targets and recognition of the pathogen nucleic acid include the polymerase chain reaction (PCR) method; real-time PCR; multiplex PCR; repetitive element sequence-based PCR; PCR-restriction fragment length polymorphism; pulsed-field gel electrophoresis; MLST; multilocus sequence analysis (MLSA); multiple-locus variable number tandem repeat analysis, duplex PCR in mix with slender electrophoresis–laser incited fluorescence locator; molecular O-antigen typing technique; fluorescence in situ hybridization technique; and so on.
These molecular methods can detect specific target genes of the pathogen, thus fast-tracking the identification of the pathogen and tracing the sources of infection. For example, the successful phylogenetic analysis of Cronobacter isolates obtained from various environmental and food sources in South Africa was achieved using MLSA of the pathogen’s strains based on two genes, 16S rRNA and rpoA. The 16S rRNA gene-based PCR identification system is a reliable tool for accurately identifying C. sakazakii isolates phylogenetically. Consequently, molecular tools can immensely aid epidemiological surveillance and investigation of Cronobacter infections and other foodborne diseases in Africa.
Ways to address transmission of cronobacter sakazakii along the food production chain
The occurrence of C. sakazakii in the food chain is a serious microbiological public health challenge. Food contamination by C. sakazakii may come from non-heated ingredients, contamination from the processing environment, or contamination post-thermal processing.
- sakazakii transmission can be prevented during food production; therefore, using appropriate microbiological procedures to avoid post-process contamination will have a positive impact. Standardized analytical procedures are required to ensure product safety. Hazard analysis and critical control point (HACCP), GMP guidelines, and efficient environmental monitoring systems should be developed to control the risk of Cronobacter contamination in the food production supply chain, starting from raw materials to finished products.
Manufacturers have acknowledged the importance of HACCP and good hygienic practice (GHP) in controlling microorganisms. Raw material quality, sifter screens, liquid and air filters, pasteurization, storage temperatures, and metal/magnets detectors are all critical control points (CCPs) that must be addressed. In addition, the heat treatments used in food manufacturing should be effective enough to inactivate C. sakazakii.
- Raw material selection
A variety of factors must be examined to guarantee that raw materials used in food production are microbiologically suitable: The possibility of occurrence of Cronobacter in ingredients—some are thought to be at high risk of harboring the microbe. In contrast, others are believed to be at low risk. Supplier selection is based on tight requirements (e.g., control measures that are appropriate, verification and release procedures in place, and GHPs). Testing of raw materials to ensure the efficiency of the steps is mentioned above. Because “raw” material testing alone cannot ensure adherence to the industry’s high-quality standards, manufacturers using these procedures must maintain strong ties with their suppliers of “raw” material and demand strict compliance with HACCP and GMPs.
- Heat treatment
Heat treatment may be a practical approach for removing C. sakazakii from abiotic and biotic surfaces. Elevated heat could be used to physically decontaminate important surfaces connected to the preparation and production of foods. It could be used as a processing aid to ensure product safety by using high-temperature short-time pasteurization. Temperatures of 70°C or higher were frequently required for C. sakazakii decontamination.
Other research, however, implies that the organism’s osmotolerance may be more relevant in this latter area. The osmotolerant ability of these microorganisms may enhance their chance of becoming much more dominant in the environment, raising the risk and chances of food contamination during post-processing. The use of typical pasteurization techniques has proven to inactivate C. sakazakii effectively.
- Post-processing and packaging
The higher heat resistance of vegetative cells in dry food products is a challenge that must be addressed by evaluating prospective treatments for inactivating microbial pathogens in food. Sterilizing finished products in their dry state in sachets or cans appears to be only conceivable via irradiation. However, because of the organoleptic deterioration of the product, the method does not appear viable with the doses needed to inactivate C. sakazakii in dry conditions. Other technologies like magnetic fields and ultrahigh pressure could be viable candidates.
- High-pressure processing
High-pressure processing (HPP) is a nonthermal method of inactivating germs by pressuring a packed food in a water-filled enclosed chamber for a brief period. The use of HPP has the advantage of preserving the freshness, flavor, color, and physical features of foods while causing minimum loss to nutritional values. HPP machines may operate at 100–1000 MPa pressure ranges. Pasteurization, previously known as a heat-based intervention, has been redefined, and HPP is now included in the definition of pasteurization as a nonthermal approach.
In an experiment to determine the sensitivity of C. sakazakii isolates to hydrostatic pressure, C. sakazakii strains were exposed to an increased hydrostatic pressure range between 200 and 600 MPa for 0 and 10 min in chicken soup, orange juice, rehydrated powdered milk, and vegetable soup. At 500 MPa, the most pressure-resistant strain of Cronobacter showed roughly three log decreases in all food. The findings demonstrated that applying increased hydrostatic pressure to biotic surfaces could help eradicate the pathogen.
The prevalence of C. sakazakii in food and environmental isolates, particularly infant foods, is a public health challenge in Africa. Still, there is evidently underreporting or underdiagnosis of this infection. The sporadic documentation of Cronobacter infection cases worldwide, particularly in Africa, means that Africa’s disease surveillance systems need to do more to detect Cronobacter spp. alongside other foods, environmental, and medical disease sources.
There is also a need to standardize control measures to prevent food contamination, introduce environmental monitoring systems, and strict adherence to thermal and nonthermal food processing and packaging controls.
Dr Helen Onyeaka is an industrial microbiologist with over 25 years of experience. She Associate Professor at the University of Birmingham where lectures and leads modules on various postgraduate and undergraduate courses in Food Microbiology, Food Safety and Chemical Engineering.
Ifeanyi Michael Mazi is a Microbiology graduate from the University of Benin and currently works with Promasidor as a Quality Assurance Officer
Nnabueze Darlington Nnaji is an Environmental Microbiologist, currently a PhD student at the Department of Microbiology, University of Nigeria. He engages his knowledge of Environmental Biology and Biotechnology in research on Bioremediation and the study of the Ecology and Biochemistry of many microbial processes.
This feature appeared in the March 2023 issue of Food Safety Africa. You can read the magazine HERE