Staphylococcus Saprophyticus: Classification, Clinical Manifestations, Identification and Resistance

◉ Classification and Nomenclature

The name Staphylococcus saprophyticus was first proposed by Shaw et al. in 1951, based on the isolation of this bacterium from human urine samples.

The classification of different species within the genus Staphylococci is based on a variety of factors, including morphology, chemical properties, amino acid sequences, biochemical characteristics, and nucleotide sequences.

◉ Clinical Manifestations

Staphylococcus saprophyticus is one of the main causes of uncomplicated urinary infections in sexually active young women and more rarely in young men or the elderly.

S. saprophyticus has been associated with cases of peritonitis during peritoneal dialysis, endocarditis on native valves, and nosocomial pneumonia.

◉ Identification and Bacteriological Characters

Some of the methods used for identification include:

◉ 1- Direct examination

Staphylococcus saprophyticus is a Gram-positive cocci, non-motile, non-sporulating, usually non-capsulated with an average diameter of 0.8 to 1.2 µm. It can appear as small, round, and isolated cells or in diplococci, or in irregular clusters.

◉ 2- Culture

Like all Staphylococci, the culture of Staphylococcus saprophyticus generally poses no problem, as it has no specific nutritional requirements. It can be cultivated in a facultative aerobic-anaerobic atmosphere, on simple, enriched, chromogenic media, or on selective agar for staphylococci.

The appearance of colonies can vary from one culture media to another; typically, colonies appear round, convex, opaque, white, and somewhat creamy after 18 hours at 37°C, with a diameter of 2 to 3 mm.

◉ 3- Identification of the genus Staphylococcus

The genus Staphylococcus comprises Gram-positive cocci bacteria that are catalase-positive and oxidase-negative, and non-demanding. These characteristics allow differentiation from bacteria of the genera Streptococcus, Enterococcus, and Micrococcus.

◉ 4- Identification of the staphylococcus saprophyticus species and biochemical characterization

Identifying the species Staphylococcus saprophyticus and differentiating it from other species is essential, especially in cases of urinary tract infections.

Staphylococcus saprophyticus belongs to the group of coagulase-negative Staphylococcus. That's why the initial test to perform is aimed at eliminating Staphylococcus aureus, such as the coagulase test, DNase test, or agglutination test.

For more complete biochemical identification, biochemical galleries such as Api 20 staph or bacteriological identification automates (MicroScan WalkAway plus System, ALFRED 60/AST.. ) can be used.

◉ 5- Antibiotic resistance profile

S. saprophyticus has intrinsic resistance to novobiocin and fosfomycin, which can help detect it from other species.

◉ 6- Molecular diagnosis

PCR (Polymerase Chain Reaction)

PCR can be used to identify S. saprophyticus by targeting its 16S rRNA gene. This gene has a unique sequence that can be distinguished from other staphylococci through the use of specific primers.

RFLP (Restriction Fragment Length Polymorphism)

RFLP can be employed to identify S. saprophyticus by utilizing a restriction enzyme that cuts the S. saprophyticus DNA into a distinctive pattern of fragments. These fragments can be separated through gel electrophoresis and compared to those of other staphylococci.

◉ Resistance

Staphylococcus saprophyticus is naturally resistant to nalidixic acid, fosfomycin, novobiocin due to a mutation in the GyrB subunit of DNA gyrase, and to fusidic acid due to the presence of the chromosomal gene fusD, encoding a protein that protects the elongation factor G.

◉ Conclusion

In conclusion, Staphylococcus saprophyticus poses a significant health concern, especially for young women with urinary tract infections. By enhancing our understanding of this bacterium and implementing preventive measures, we can strive to reduce the burden of Staphylococcus saprophyticus infections and improve patient outcomes.