The Dual Nature of Streptococcus: Pathogens vs. Probiotics
The genus Streptococcus is a diverse group of bacteria, including species that are harmless and beneficial, as well as some that can cause illness. In the context of cheese, the key distinction is between food-grade, beneficial cultures and potential contaminants. The most important species in cheesemaking is Streptococcus thermophilus, a lactic acid bacterium that is deliberately added to milk to initiate the fermentation process. Its safety is well-established, and it has been granted “Generally Recognized as Safe” (GRAS) status in the United States and “Qualified Presumption of Safety” (QPS) in the European Union. Pathogenic streptococci, like those responsible for strep throat, are not found in properly manufactured cheese because they are destroyed by pasteurization and prevented from contaminating the product through strict hygiene protocols.
The Vital Role of Streptococcus thermophilus in Cheesemaking
Streptococcus thermophilus is a thermophilic bacterium, meaning it thrives at high temperatures, typically between 40–45°C. This makes it an ideal starter culture for cheeses that require heating during production, such as mozzarella and Swiss cheese. Its primary function is to rapidly ferment the lactose in milk, producing lactic acid. This process, known as acidification, is critical for several steps in cheesemaking:
- Curd Formation: The increase in acidity causes the milk protein (casein) to coagulate, forming the solid curds that will become cheese.
- Pathogen Control: The acidic environment created by the lactic acid helps to inhibit the growth of undesirable, harmful bacteria.
- Flavor and Texture: The metabolic activity of S. thermophilus contributes to the characteristic flavor and texture of the final cheese product.
S. thermophilus is often used in symbiotic relationships with other bacteria, such as Lactobacillus delbrueckii subsp. bulgaricus, to create specific flavor profiles and textures, most notably in yogurt and Italian cheeses.
How Food Safety Controls Address Harmful Bacteria
For most commercially produced cheese, food safety is ensured through a combination of milk treatment and rigorous hygiene. Pasteurization is the most important step, where milk is heated to a high temperature for a short time to kill disease-causing microorganisms like Listeria, Salmonella, and E. coli. This process effectively eliminates any potential pathogenic streptococci that could be present in raw milk. The two most common pasteurization methods are:
- High-Temperature Short-Time (HTST): Heats milk to 72°C (161°F) for 15 seconds. This is a common method for large-scale production.
- Low-Temperature Long-Time (LTLT): Heats milk to 63°C (145°F) for 30 minutes. This gentler method is preferred for certain cheese types.
While pasteurization is highly effective, contamination can still occur after the heat treatment. This is why dairy plants implement strict sanitation practices, regular testing, and Hazard Analysis and Critical Control Points (HACCP) systems to prevent post-pasteurization contamination.
In contrast, some artisanal cheeses are made from unpasteurized or “raw” milk. In many countries, strict regulations apply to raw milk cheeses, such as the 60-day aging rule in the U.S., which requires these cheeses to be held at or above 1.7°C (35°F) to allow the natural acidity and salt content to kill most pathogens. However, these cheeses carry a higher food safety risk, especially for vulnerable populations like pregnant women and the immunocompromised, who are often advised to avoid them entirely.
Probiotics, Fermentation, and Your Gut Health
Fermented foods, including certain cheeses, can be a source of beneficial, living microorganisms known as probiotics. When consumed in adequate amounts, these bacteria can provide health benefits, such as improving gut health by balancing the microbiome.
Some probiotic strains of Lactobacillus and Bifidobacterium are often added to cheeses, which serve as an excellent delivery system. The fat and high calcium content of the cheese matrix provide a protective buffer, helping the bacteria survive the acidic conditions of the stomach and reach the intestines alive. Aged cheeses, such as cheddar, Swiss, and Gouda, are more likely to contain significant amounts of live cultures than fresh cheeses, though this can vary greatly depending on the specific manufacturing process.
Nutritional Comparison of Cheeses
While cheese offers a variety of nutrients, its composition can differ significantly depending on the type and how it's made. The table below compares the nutritional aspects of several popular cheeses, highlighting key differences in their fat, protein, and probiotic content.
| Cheese Type | Fat Content (per oz) | Protein (per oz) | Sodium (per oz) | Probiotic Potential |
|---|---|---|---|---|
| Cheddar (Aged) | High (~9.4g) | Moderate (~6.4g) | High | High (Aged) |
| Mozzarella | Moderate (~6.3g) | Moderate (~6.3g) | Moderate | Variable |
| Swiss (Aged) | High (~8.8g) | High (~7.7g) | Low | High (Aged) |
| Cottage (4% Fat) | Low (~3g per 1/2 cup) | High (~14g per 1/2 cup) | High | High (some types) |
| Feta | High (~7.9g) | High (~7.2g) | Very High | Variable |
Selecting Cheese for Your Diet
When choosing cheese, consider how it fits into your overall nutritional goals. While it provides protein and calcium, many types are also high in saturated fat and sodium. For most people, consuming cheese in moderation as part of a balanced diet is perfectly healthy. However, individuals with high blood pressure or those on a low-fat diet may need to be more selective, opting for lower-sodium or lower-fat options like Swiss or part-skim mozzarella. The way cheese is consumed also matters; pairing it with whole-grain crackers and fruits is more beneficial than adding it to processed, high-glycemic foods.
Conclusion
While the name Streptococcus might cause concern due to its association with illness, it is important to remember that the genus is diverse. The presence of Streptococcus thermophilus in many cheeses is not a food safety risk but rather a hallmark of proper fermentation. The extensive safety protocols in commercial cheesemaking, including pasteurization and strict hygiene, effectively prevent the growth of harmful bacteria. For consumers, this means they can confidently enjoy their favorite cheeses, taking comfort in the knowledge that cheesemaking relies on beneficial, safe bacterial cultures. Enjoyed in moderation, and chosen mindfully, cheese can be a nutritious part of a healthy diet, potentially offering probiotic benefits along with its rich flavor and texture. For more information, the Harvard School of Public Health's Nutrition Source provides an excellent overview of cheese within a healthy diet.
