Atypical Colony Morphology of Staphylococcus lugdunensis Isolated from a Wound Specimen Staphylococcus lugdunensis , Atipik Koloni Görünümü

The incidence of infections due to coagulase-negative staphylococci (CoNS) has been steadily increasing in recent years. In this report, we describe an isolate of the CoNS Staphylococcus lugdunensis from a wound specimen with a colony morphology distinct from that of a classical S. lugdunensis colony. Specifi cally, wrinkled, medium-sized, beta hemolytic, opaque, rough white colonies were detected on blood agar. Catalase-positive, coagulase-negative, gram-positive cocci-yielding such colonies should be suspected of being S. lugdunensis.


Introduction
Staphylococcal infections are usually caused by the organism Staphylococcus aureus.However, the incidence of infections due to coagulase-negative staphylococci (CoNS) has been steadily increasing in recent years.Infections with Staphylococcus epidermidis and (less commonly) Staphylococcus heamolyticus and Staphylococcus lugdunensis usually involve the implantation of medical devices.Other infections related to CoNS are wound infections, urinary infections, ophthalmic infections and septisemia.After 18-24 hours of incubation, staphylococci appear as opaque, smooth, circular colonies on the agar plate surface [1].In this report, an isolate of S. lugdunensis from a wound specimen with a different colony morphology from that of the classical CoNS colony is described.

Case Report
A swab sample taken from a burn wound lesion of a 22-year-old patient was cultured.For this purpose, the specimen was inoculated onto 5% blood agar and onto EMB agar medium.After a 24-hour incubation, the colonies on the plates were evaluated.In the evaluation, no colonies were seen on the EMB agar.At the blood agar surface, wrinkled, medium-sized, beta hemolytic, opaque, rough white colonies were detected.The colonies could not be easily removed from the surface of the agar by an inoculation loop, and they could be moved intact over the surface (Figure 1).Microscopic examination of the gram preparation made from the colony revealed Gram-positive cocci.Other test results of the bacteria were as fol-lows: catalase (+), oxidase (-), tube coagulase (-), slide coagulase (+).According to these test results, the bacterium was determined to be a species of the staphylococcus genus.
In additional tests to identify the bacterium at the species level, it was found to be PYR (+), susceptible to novobiocin and ornithine decarboxylase (+).Based on these results, the isolated bacterium appeared to be S. lugdunensis [2].This result was confirmed by API staph and automated Vitek2 system biochemical gram positive (GP) card (BioMerieux, France).
In addition, antibiotic susceptibility tests by the disc diffusion method revealed that the bacterium was susceptible to cefoxitin, penicillin, vancomycin, erithromycin, linezolid, clindamycin and tetracycline [3].

Discussion
As a group, the coagulase-negative staphylococci (CoNS) are among the most frequently isolated bacteria in clinical microbiology laboratories, and they are becoming increasingly important, especially as causes of hospital-acquired infections [4].
Coagulase-negative staphylococcal bacteremia is rarely life-threatening, especially if treated promptly and adequately.However, CoNS can cause fatal infections, especially in immunocompromised patients or if one of the more virulent species, such as S. lugdunensis, is involved [5].S. lugdunensis resembles S. aureus in that this species may express a clumping factor or produce a thermostable DNase [6].
Isolates such as S. lugdunensis and S. schliferi can also occasionally be mistaken for S. aureus because of the presence of a clumping factor.However, tube coagulase tests are negative for S. lugdunensis but positive for S. aureus.
The pathogenic mechanism by which S. lugdunensis causes infections remains unknown.About 25% of S. lugdunensis clinical isolates produce extracellular slime, which has a role in bacterial colonization and interferes with the phagocytosis-associated activities of neutrophils [7].In addition, enzymes that may act as invasion factors have been detected in S. lugdunensis strains, including esterase, fatty-acid modifying enzymes, proteases and lipases [6].The appearance and characteristics of S. lugdunensis colonies on blood agar have been described as medium to large size, smooth, glossy, smooth edges with slightly domed center, unpigmented or cream to orange pigment.The biochemical characteristics of S. lugdunensis are PYR-positive, ornithine decarboxylase-positive and susceptible to novobiocin.Although the bacterium in our study showed biochemical characteristics similar to those of S. lugdunensis, they yielded colonies with different characteristics.As described above, the colony morphology of our strain was wrinkled, medium size, non-pigmented, non-hemolytic, opaque and rough.
This report demonstrates that colonies of S. lugdunensis may be atypical in appearance.Therefore, catalase-positive, coagulase-negative, gram-positive, cocci-yielding, wrinkled, medium-sized, opaque, rough white colonies should be suspected of being S. lugdunensis.