Serratia, or serratia as they are also called, belong to the family of intestinal bacteria (enterobacteria). The majority of pathogens are harmless to people with intact immune systems. However, they pose a great risk in hospitals and infant wards.
What are serratia?
Serratia is the name of a rod-shaped bacterium discovered in 1819 by Italian pharmacist and physicist Bartolomeo Bizio. He found it on spoiled polenta and named it after Serafino Serrati, an 18th century physicist he revered. The genus Serratia includes 15 species. Serratia marcescens is the most common species of the bacterium. It received the names miracle bacillus and host fungus because it forms reddish pigments on hosts that resemble drops of blood. The discolorations were considered a divine miracle at the time.
Occurrence, distribution and properties
Serratia, in addition to being found in human and animal intestinal flora, are also found in soil, water, and even plants. Individual Serratia species differ in terms of the habitats they choose. Colored Serratia strains prefer freshwater habitats such as spring water and wells, while non-pigmented ones tend to prefer river water. Pathogens living on plants and vegetables have the task of breaking down organic material. In addition, Serratia strains can be detected in foods such as eggs, poultry meat, and dairy products. Since the rod-shaped bacterium is found worldwide in all types of media, it is almost impossible not to come into contact with it. Another route of transmission is from person to person. To become infected via droplets containing Serratia, it is sufficient to cough and sneeze briefly. Serratia can live aerobically but also anaerobically and is gram-negative. The pathogen moves with the help of tiny flagella. It does not form spores. Most Serratia cultures grown on solid culture media have a reddish or pink coloration. Some Serratia species are non-pigmented. The discoloration is due to the prodigiosin produced by the serratia in question. The bacteria feed on carbohydrates such as glucose, fructose, galactose, maltose, and some sugar alcohols. Acids and gases are produced as by-products. Some representatives of the enterobacteria, such as Serratia odorifera, emit an intense potato-like odor. Serratia are capable of producing beta-lactamases. These enzymes render the use of beta-lactam antibiotics ineffective by decomposing their beta-lactam ring. Serratia bacteria grow optimally at temperatures between 20 and 37°C and pH up to 9. They produce the virulence factors gelatinase, DNAse, lipase, endotoxin, and bacteriocin. Serratia marcescens can cause the deadly White Pox disease in Acrospora corals, which now threatens large portions of coral reefs worldwide. Coral mortality is caused by Serratia pathogens that originate from sewage that is discharged untreated into seawater.
Diseases and ailments
Serratia is completely harmless to most people. However, in people with weakened immune systems and in newborns, the enterobacteria can cause serious infections. This usually happens during hospital stays. Those affected come into contact with the bacterium in the intensive care unit. The insertion of endoprostheses also carries a high risk of becoming infected with serratia. The enterobacteria enter the human body via contaminated infusion solutions and catheters. In the worst case, blood poisoning (sepsis) is the result. Serratia marcescens and Serratia liquefaciens are the most dangerous for the human body. Sick people who are treated as inpatients are at greater risk of contracting the pathogen than those who are treated as outpatients. The infection rate is about two percent for urinary tract infection and one percent for sepsis and pneumonia (based on outpatients). In addition, infections with the bacterium sometimes occur in infant wards (premature babies) and nursing homes. The causes are poor hygiene and inadequate disinfection of the implants and cannulas used. Newborn children, especially premature infants, are at high risk because their immune systems are not yet fully developed. They also have thinner skin, so serratia can penetrate their bodies more easily.People who consume drugs intravenously also have an increased risk of contracting an infection from the bacterium. Serratia can cause various diseases. These include sepsis (blood poisoning), respiratory infections up to and including pneumonia, urinary tract infections, meningitis (inflammation of the brain), wound infections, endocarditis (inflammation of the inner lining of the heart), and osteomyelitis (inflammation of the bone marrow). Only a few species of Serratia are well controlled with antibiotics. The pathogens are resistant to cephalosporins. To find the appropriate drug, an antibiogram is made (resistance test). Proven agents are acylaminopenicillins, aminoglycosides such as amikacin and ciprofloxacin. In addition, carbapenems (meropenem, imipenem) are helpful in treating disease caused by serratia.
