Group B Hemolytic Streptococcus (Non-D Group)

Streptococcal infections are zoonotic diseases caused by pathogenic bacteria belonging to the genus Streptococcus, capable of triggering infections in the skin, respiratory tract, soft tissues, as well as serious conditions such as pneumonia, erysipelas, puerperal fever, scarlet fever, bacteremia, endocarditis, and meningitis—severely threatening both human and animal health. These infections rank among the most significant bacterial infectious diseases. According to the 2nd edition (2004) of the "Berger's Manual of Systematic Bacteriology," Streptococcus is currently classified into 71 species and subspecies, with Group A beta-hemolytic streptococci being the most virulent among them, frequently responsible for a wide array of illnesses in humans and animals. Moreover, the newly implemented national standard GB19422-2022, effective July 2023, continues to list Group A beta-hemolytic streptococci as a mandatory testing item for rats, mice, guinea pigs, gerbils, and rabbits when necessary.

Beta-hemolytic streptococci are Gram-positive cocci that typically arrange in chains. They produce beta-hemolysin on culture media, which induces complete hemolysis, leading to the lysis of red blood cells and posing a serious threat to both human and animal health.

Group A beta-hemolytic streptococcus is widely distributed in nature and serves as a commensal bacterium in both humans and animals, commonly found on human skin, in the oral cavity, nasal passages, intestines, and genital tract. Based on differences in group-specific antigens, β-hemolytic streptococci can be classified into 20 serogroups, including A, B, C, D, F, G, H, and others, with groups A, B, C, and G being the most prevalent.

Group A Streptococcus (GAS): This is the most common group of beta-hemolytic streptococci. GAS can cause a wide range of diseases, from superficial skin infections, pharyngitis, and scarlet fever, to severe invasive illnesses such as puerperal sepsis, pneumonia, necrotizing soft tissue infections (NSTI)—also known as necrotizing fasciitis/myositis—meningitis, and streptococcal toxic shock syndrome (STSS), among others.

Group B Streptococcus (GBS): GBS is widely present in healthy individuals, colonizing areas such as the intestines, vagina, and urinary tract. In newborns and people with compromised immune systems, GBS infection can lead to serious illnesses, including neonatal sepsis, meningitis, and pneumonia.

Group C beta-hemolytic streptococcus (GCS): Compared to Groups A and G, Group C beta-hemolytic streptococcal infections are relatively more common. They can lead to conditions such as pharyngitis, skin infections, and otitis media. Additionally, Group C beta-hemolytic streptococcus has also been linked to more severe infections, including sepsis and soft-tissue infections.

Group G Streptococcus (GGS): Group G Streptococcus is a group of bacteria as significant as Groups A and B. It can cause a variety of infections, including pharyngitis, skin infections, otitis media, and urinary tract infections. Moreover, Group G Streptococcus has also been linked to more severe conditions, such as soft tissue infections, foodborne illnesses, and sepsis.

Group B hemolytic streptococcus has broad transmission routes, spreading horizontally through the respiratory tract, digestive tract, bloodstream, and more, as well as via vertical transmission. Different species of streptococcus infect varying hosts and are widely found in both humans and animals—both inside and on their surfaces—often acting as opportunistic pathogens. Some laboratory animals (such as mice, rats, hamsters, guinea pigs, rabbits, dogs, pigs, and primates) are also highly susceptible to infection, primarily due to environmental contamination in experimental settings (including contaminated animal feed, bedding, water, and inadequate cleaning and disinfection practices), direct human-to-animal transmission, or cross-infection (infected animals within the lab can spread the bacteria to others via airborne droplets, direct contact, or shared environments). Infections typically occur in the respiratory tract, digestive system, and at sites of injury.

For experimentally raised animals, outbreaks of streptococcal infections do not exhibit a clear seasonality; instead, these outbreaks are closely linked to changes in the animal housing environment and management practices, as well as the overall level of husbandry. When husbandry management and hygiene conditions are poor, animals become particularly susceptible to illness.

Beta-hemolytic Streptococcus associated with laboratory animals:

Different animals infected with Group B hemolytic streptococcus exhibit varying clinical symptoms. For instance, rats infected with Streptococcus pyogenes typically show signs of depression, lethargy, rough and disheveled fur, increased nasal discharge—including bloody secretions—and enlarged mammary glands; some even develop diarrhea. In lactating rats, the primary manifestation is extensive inflammatory exudates and infiltration of immune cells within the alveoli, ducts, and interstitial tissues of the mammary glands, often accompanied by abscess formation at sites where inflammatory cells cluster. Meanwhile, in nursing pups, inflammatory lesions of varying degrees can be observed in key organs such as the liver, spleen, kidneys, and lungs. Histological sections of the small intestine reveal hemorrhage, hemolysis, as well as degeneration, shedding, and necrosis of intestinal epithelial cells. In guinea pigs, however, the main symptoms include otitis media, pneumonia, and urolithiasis. Post-mortem examinations reveal that pneumonia is frequently accompanied by consolidation of one or both lung lobes, along with hemothorax and pericardial hematoma.

For example, when guinea pigs are infected with Streptococcus equi subsp. zooepidemicus, they typically develop cervical lymphadenitis, with pus formation at the inflamed sites. In some cases, the infection can even progress to conditions like torticollis, pneumonia, or septicemia. Meanwhile, dogs mainly exhibit acute hemorrhagic necrotizing pneumonia, septicemia, and canine respiratory disease; in severe cases, they may even experience nasal bleeding and vomiting blood.

It can cause diseases such as canine polyarthritis, otitis externa, endocarditis, fibrinous pericarditis, abortion, sepsis in newborn puppies, and necrotizing myositis. Additionally, there have been reports from primate centers in Germany of animals exhibiting severe purulent conjunctivitis, rhinitis, pharyngitis, respiratory distress, and lethargy. Infections with Group A Streptococcus not only lead to bacteremia and toxic shock syndrome but also mimic human rheumatic heart disease in their clinical manifestations.

Some streptococcal infections may lead to autoimmune diseases, and Streptococcus pyogenes can cause rheumatic fever. Infection with Streptococcus pyogenes and Streptococcus equi subsp. zooepidemicus may also result in glomerulonephritis.

Currently, the most commonly used detection method is the bacterial blood agar plate isolation and culture technique mandated by national standards. To address this, our company has introduced the Vitek2 fully automated biochemical identification system, which enables rapid and precise identification. For any questionable results, we can further verify them using PCR or sequencing methods, ensuring absolute accuracy. Additionally, MALDI-TOF MS mass spectrometry directly analyzes microbial protein mixtures, allowing for swift species identification—with results available in as little as one minute. The introduction and implementation of these advanced detection methods have significantly enhanced both efficiency and accuracy, while also delivering more reliable testing outcomes to our customers.

For prevention and control measures against Group B Streptococcus, prevention should always take precedence over treatment. Regularly improve animal husbandry management practices, maintain appropriate stocking densities, and ensure thorough group hygiene. At the same time, remain vigilant for any signs of illness in animals, promptly isolating or removing affected individuals. When handling animals on a daily basis, staff should take proper protective measures—wearing masks and work attire—to prevent transmitting pathogens to either animals or humans. If contact with sick animals is unavoidable, take precautions against bites and avoid direct contact with animal excretions and secretions; instead, clean and disinfect hands and equipment immediately afterward.

References

[1]. Tian Kegong, He Zhengming, Liu Qun, et al. Experimental Animal Epidemiology [M]. China Agricultural Press, 2015: 689-695. [2]. Davis KL, Gonzalez O, Kumar S, et al. Pathology Associated with Streptococcus spp. Infection in Baboons (Papio spp.). Vet Pathol. 2020 Sep;57(5):714-722. doi: 10.1177/0300985820941496. Epub 2020 Aug 3. PMID: 32744146; PMCID: PMC7528403.

[3]. Lu Chengping, Huang Qingyun, et al. Veterinary Microbiology [M]. China Agricultural Press, 2005: 205-210.

[4]. GB14922-2022. Laboratory Animals: Microbiological and Parasitological Classification and Monitoring.

[5]. Eibl C, Baumgartner M, Urbantke V, et al. An Outbreak of Subclinical Mastitis in a Dairy Herd Caused by a Novel Streptococcus canis Sequence Type (ST55). Animals (Basel). 2021 Feb 20;11(2):550. doi: 10.3390/ani11020550. PMID: 33672442; PMCID: PMC7923261.