Sarcina bacteria are a unique genus of microorganisms known for their distinct cellular arrangement. These Gram-positive cocci retain a purple stain in a Gram test and have a spherical shape. While generally uncommon as human pathogens, reports of Sarcina infections, particularly Sarcina ventriculi, have been increasing due to their association with specific health conditions.
Unique Characteristics
A defining feature of Sarcina bacteria is their cuboidal packet arrangement, often appearing as groups of four, eight, or more cells. This unique morphology results from cell division occurring in multiple perpendicular planes, with cells remaining attached after division, forming structures that resemble bales or bundles. Individual Sarcina cells measure between 1.8 and 3 micrometers in diameter. Their cell walls are notably thick and refractile under a light microscope.
Sarcina species are obligate anaerobes, meaning they cannot grow in oxygen. They are chemoorganotrophic, relying on fermentative metabolism for energy. This process allows them to break down carbohydrates, producing substances like ethanol, acetaldehyde, carbon dioxide, and hydrogen. Sarcina ventriculi is notable for thriving in extremely acidic environments, with some strains growing at a pH as low as 2 and surviving at pH 1. This tolerance is attributed to their expression of pyruvate decarboxylase, which directs pyruvate into ethanol fermentation, helping them manage acidic conditions.
Where Sarcina Resides
Sarcina bacteria are broadly distributed in natural environments, commonly found in soil, water, and even in the air as spores. The primary route of human and animal exposure is through the ingestion of food or water contaminated with soil particles containing the bacteria.
In mammals, Sarcina species, especially Sarcina ventriculi, are frequently found in the gastrointestinal tract. The stomach is the most common site, though they have also been detected in the esophagus, duodenum, and feces of healthy individuals. The stomach’s highly acidic environment, typically inhospitable to many bacteria, surprisingly favors Sarcina ventriculi growth. Conditions leading to delayed gastric emptying, such as gastric stasis or obstruction, create an environment where Sarcina can proliferate.
Health Implications
Sarcina ventriculi is increasingly recognized for its role in gastric conditions, particularly those involving delayed gastric emptying. This provides an opportunity for Sarcina to proliferate, leading to bacterial overgrowth. This can cause various gastrointestinal symptoms, including nausea, vomiting, abdominal pain, and dyspepsia. A characteristic “sarcinous vomit,” described as intractable, frothy vomit, may occur in patients with chronic stomach issues.
The bacterium’s fermentative metabolism, which produces carbon dioxide and hydrogen gas, can contribute to significant gas accumulation within the stomach. This gas production is a factor in the development of emphysematous gastritis, a serious condition characterized by gas within the stomach wall. Patients may experience symptoms like acute abdominal pain, nausea, vomiting, and sometimes fever and chills. Emphysematous gastritis can progress to gastric perforation, a life-threatening complication that can lead to peritonitis and multi-organ failure. While Sarcina can be an incidental finding in asymptomatic individuals, its presence in patients with pre-existing gastric mucosal defects or conditions like gastroparesis can heighten the risk of severe outcomes.
Identifying and Managing Sarcina
Diagnosing Sarcina infections primarily relies on identifying its distinctive morphology. Microscopic examination of gastric contents or biopsies, typically stained with hematoxylin-eosin or Gram stain, reveals the characteristic cuboidal packets of bacteria. The individual bacterial cells are basophilic and refractile, making them identifiable even on routine stains. While culture can be challenging due to the bacterium’s strict anaerobic requirements, molecular methods such as polymerase chain reaction (PCR) and 16S ribosomal RNA gene sequencing can confirm its presence.
Managing Sarcina-related conditions involves a multi-faceted approach. Antibiotics are a primary treatment, with metronidazole often used alone or in combination with other antimicrobial agents like ciprofloxacin or amoxicillin-clavulanic acid. Proton pump inhibitors (PPIs) are also frequently administered to reduce stomach acid. Addressing underlying issues that contribute to delayed gastric emptying is important.
Dietary modifications, such as consuming small, frequent meals and limiting high-fat and high-fiber foods, can help improve gastric motility and reduce symptoms. In some cases, nutritional support, including total parenteral nutrition, may be necessary. Surgical intervention might be considered for severe complications like gastric perforation or necrosis.