A three-year survey of raw cow’s milk from commercial dairy farms in western Turkey has uncovered widespread signs of microbial contamination, with most samples exceeding at least one hygiene-related threshold. The study, published in Environmental Monitoring and Assessment, analyzed 1,800 milk samples collected between 2023 and 2025 from mechanized farms in the İzmir region, one of Turkey’s major milk-producing areas. Researchers Gözde Türköz Bakırcı and Ulaş Baysan found that 64 percent of samples failed to meet the relevant limit for total colony count, while 22 percent exceeded the limit for somatic cell count. Coliform bacteria appeared in 69 percent of the samples, and Escherichia coli was detected in 52 percent. Staphylococcus aureus occurred in 15 percent, although Salmonella was not detected in any sample. The findings do not mean that every contaminated sample caused illness, but they reveal persistent weaknesses in farm-level hygiene and milk handling that could affect both food safety and dairy quality.
Raw milk is not sterile when it leaves the udder. It can acquire microorganisms from the animal, milking equipment, storage tanks, water, soil, manure, workers and the surrounding environment. Some microbes are harmless indicators of cleanliness, while others can cause disease or produce substances that damage milk quality. The study’s total colony count, or TCC, measures the number of viable aerobic microorganisms capable of growing under standardized laboratory conditions. It is a broad indicator rather than a direct inventory of all bacteria in the milk. A high TCC can signal inadequate cleaning, delayed cooling, contamination during milking or bacterial multiplication during storage. Because milk is rich in water, proteins, fats and sugars, it can support rapid microbial growth if its temperature is not controlled. Even when pathogens are absent, a large bacterial population can accelerate spoilage and interfere with processing into products such as cheese, yoghurt and butter.
The researchers also measured somatic cell count, or SCC, an important indicator of udder health. Somatic cells are primarily white blood cells, along with epithelial cells shed from mammary tissue. When a cow develops inflammation of the udder, particularly mastitis, immune cells move into the milk and the SCC rises. A high SCC can therefore point to subclinical infection that may not produce obvious swelling or changes in the animal. It can also alter the composition of milk by affecting proteins, enzymes, lactose and fat, reducing its technological performance and sometimes its yield. In the İzmir survey, 396 of the 1,800 samples, or 22 percent, were above the applicable SCC threshold. This measure differs from TCC: somatic cells are part of the cow’s biological response, whereas TCC estimates living microorganisms. Taken together, the two indicators can help distinguish problems originating inside the udder from broader contamination during production.
The most striking result was the frequency of coliforms, a group of bacteria commonly associated with soil, feces, water and contaminated surfaces. Their presence in 1,242 samples suggests that contamination was not confined to isolated incidents or a single farm. Coliforms are often used as hygiene indicators because they can enter milk when teats are not adequately cleaned, bedding is dirty, equipment is improperly sanitized or water supplies are contaminated. Their detection does not automatically prove that fecal pathogens are present, but it signals that routes exist by which more dangerous organisms could enter the food chain. The survey also found E. coli in 936 samples. Many strains of E. coli are ordinary inhabitants of the intestinal tract and are not dangerous, yet the species includes pathogenic variants capable of causing severe gastrointestinal disease. The methods used to enumerate E. coli followed the ISO 16649-2 standard, while coliform testing followed ISO 4832.
The researchers detected S. aureus in 15 percent of samples, adding a different dimension to the results. This bacterium is a major cause of bovine mastitis and can also contaminate milk through handlers, skin, equipment or the farm environment. Some strains produce heat-stable enterotoxins. Those toxins may remain active even after heating conditions that kill the bacteria themselves, making prevention and hygienic control essential. The study did not report whether the detected S. aureus isolates carried toxin genes, nor did it characterize their antibiotic-resistance profiles. Consequently, the result should be interpreted as evidence of bacterial presence rather than proof that toxin-producing strains entered the consumer supply. Earlier investigations in Turkey and elsewhere have reported S. aureus in animal-derived foods, underscoring why the organism is routinely monitored in dairy systems. In contrast, the complete absence of detected Salmonella in this survey is reassuring, while not demonstrating that the pathogen can never occur in the region.
Seasonal patterns added an environmental clue to the contamination story. SCC reached its highest levels in summer, when heat stress can weaken cattle’s resilience, alter behavior and increase susceptibility to udder inflammation. Hot conditions may also encourage bacterial growth in the environment and place additional demands on cooling and storage systems. Coliforms and E. coli peaked in spring, a pattern that could reflect changes in moisture, pasture conditions, mud, bedding or water contamination, although the study cannot establish a single cause. S. aureus was most prevalent in winter. That increase may be related to housing conditions, reduced ventilation, prolonged indoor contact among animals or changes in udder hygiene, but those mechanisms were not directly tested. TCC showed no statistically significant seasonal trend. The investigators assessed seasonal differences with the Kruskal–Wallis test, a nonparametric method suitable for comparing distributions among multiple groups when data may not follow a normal distribution. Parameters with a probability value below 0.05 were considered to show significant seasonal variation.
The three-year design gives the results greater weight than a one-time snapshot. Sampling across 2023, 2024 and 2025 allowed the researchers to observe recurring patterns rather than relying on conditions during a single outbreak, weather event or production cycle. The farms were mechanized commercial operations, meaning the findings are particularly relevant to structured dairy production rather than only to informal household systems. Yet the study also has boundaries. The available report does not provide a farm-by-farm breakdown, detailed sample volumes, exact regulatory thresholds for each test or molecular identification of bacterial strains. It also does not demonstrate whether contamination originated at the udder, during milking, in bulk tanks or during transport. The authors describe the work as environmental monitoring, and the indicators are most useful when integrated with information about cleaning schedules, equipment design, water quality, animal health, temperature records and worker practices.
For consumers, the distinction between raw milk and processed milk is crucial. Pasteurization is designed to reduce disease-causing microorganisms through controlled heat treatment, while refrigeration slows the growth of surviving organisms and limits multiplication before processing. Neither step should be treated as a substitute for clean production. Heavy microbial loads can degrade quality before pasteurization, and some bacterial toxins or enzymes may persist after cells are destroyed. Proper cold-chain management is therefore part of the safety system: milk should be cooled rapidly after milking, held at an appropriate temperature and protected from recontamination. The study itself did not test the effects of pasteurization or refrigeration on the sampled milk, and it did not assess illness among consumers. Its message is instead preventive. A clean raw material gives processors more control, reduces spoilage pressure and lowers the chance that pathogens will move through the dairy chain.
The authors argue that continuous monitoring could turn routine milk testing into an early-warning system for dairy farms. Tracking TCC, SCC, coliforms, E. coli and S. aureus over time can reveal whether an intervention is working and help managers identify which stage of production requires attention. A sudden rise in coliforms might prompt inspection of teat preparation, water sources or milking-machine sanitation. An increase in SCC could lead to veterinary evaluation for mastitis, improved milking order and closer attention to udder health. Seasonal surveillance could also allow farms to prepare for predictable risks, such as summer heat stress or winter housing. The study does not portray western Turkey’s milk supply as uniformly unsafe, and the absence of Salmonella in all 1,800 samples is an important counterpoint to the high indicator counts. Instead, it shows how apparently ordinary milk can contain measurable evidence of environmental and animal-health pressures—and why systematic microbiological surveillance, rapid cooling and rigorous hygiene remain the most effective defenses before milk reaches the processing plant or the public.
