Phenotypic characterization of the biological properties of coagulase-negative staphylococci isolated in a cardiac surgery department

Rationale: A  significant proportion of post-operative infectious complications in cardiovascular surgery is caused by Staphylococcus spp, with an increasing role of Staphylococcus epidermidis. Aim: To identify biological characteristics of coagulase-negative staphylococci isolated from various biotopes in a cardiac surgery department, in order to assess their pathogenic potential. Materials and methods: The study was performed with Staphylococcus isolates (n = 73) obtained in a cardiac surgery department in 2015–2016. Biochemical identification of the cultures was done with the use of Vitek 2  compact microbiological analyzer (BioMerieux, France) and test systems Staphytest (ERBA Lachema, Czech Republic). The biological properties of staphylococci were assessed by classical microbiological techniques. Statistical analysis was done with the Microbe-2  software package. Results: S. aureus and 6 strains of coagulase-negative staphylococci with predominance of S.  epidermidis were isolated in the department of cardiac surgery. In most cases S.  epidermidis was isolated from post-operative wounds (n = 16, 30.8 ± 6.4%) and environmental swabs (n = 11, 21.1 ± 5.7%). All S.  epidermidis studied (n = 52) hydrolyzed maltose with formation of the acid without gas, could ferment glucose and tregalose, and were lacking β-galactosidase (except the cultures isolated from post-operative wounds). They also could not degrade mannitol in aerobic environment (excluding staphylococci isolated from the environmental objects and from the medical staff). S.  epidermidis displayed variable biochemical activity towards lactose and saccharose. Hemolytic activity (more often of the β-type) was characteristic for 69.2 ± 6.4%  of S.  epidermidis cultures. The majority of cultures (92.4 ± 3.6%) displayed proteolytic activity irrespective of the type of staphylococci and the source of isolation. Lipolytic activity was more frequent in staphylococci isolated from clinical materials (airway secretions of the medical personnel [9/10  cultures], patients [9/10  cultures] and post-operative wounds [16/20 cultures]), than in those isolated from the environmental objects. There was a direct significant correlation between the lipase activity and the presence of β-galactosidase (φ=0.40), lipase and proteolytic activities (φ=0.33), β-galactosidase and gelatin liquation (φ=0,65), hemolytic and proteolytic activities (φ=0.37). Conclusion: S. epidermidis was the most prevalent pathogen in all ecotopes of the department of cardiac surgery. Biochemical properties of coagulase-negative staphylococci and their fermentative activity related to factors of pathogenicity were different depending on the site of isolation. This illustrates their contribution in the development of inflammation in a given biotope.