Letter to the Editor: Regarding Staphylococcus haemolyticus : An Emerging and Difficult to Treat Pathogen in Orthopedic-Related Infections: Response to Gabardo S et al.,Staphylococcus lugdunensis,A Not So Infrequent Pathogen in Orthopedic Surgery (doi: 10.1089/sur.2023.035)

To the Editor:

We read with interest the article by Gabardo et al. ¹ on the increasing prevalence of Stapylococcus lugdenensis, a coagulase-negative staphylococcus (CoNS) in musculoskeletal infections (MSI), and want to share our views on the same. This study has brought to light the importance of this hitherto under reported pathogen. As rightly pointed out by the authors, recognition of the pathogenic potential of this CoNS species can be attributed to the availability of automated diagnostic systems. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) is one such automated identification system that has made it easier to identify this pathogen, thereby increasing its incidence in recent years. Moreover, better understanding of the pathogenic potential of CoNS further underlines the ebullient identification of CoNS isolates until the species level.

The authors at their center observed a statistically significant increase in MSIs caused by Stapylococcus lugdenensis between 2012 and 2020. However, we wish to add that other CoNS species particularly Stapylococcus haemolyticus is also being recognized as a cause of orthopedic surgery-related infections. Unlike Stapylococcus lugdenensis, Stapylococcus haemolyticus is known to exhibit high level of drug resistance, cause a variety of infections including MSIs, and hence cannot be ignored. Methicillin-resistant, vancomycin-resistant, and linezolid-resistant Stapylococcus haemolyticus (LR-SH) isolates are also being frequently reported.^2–4 Clonal spread of such multi- drug–resistant (MDR) strains are a potential threat in any hospital setting and can undermine even the best infection control measures.

At our center, a tertiary care hospital of India, we have been closely monitoring the incidence and susceptibility profile of CoNS isolates for past two decades.^2–9 Stapylococcus haemolyticus has been the predominant CoNS species at our center. Over the years, the gradual increase in the MDR-CoNS isolates have been noted with emergence of LR-SH in 2016. ⁷ Infections due to these LR-SH isolates has become a therapeutic challenge at our center. Similar observations are being reported worldwide. ¹⁰

In 2019 we reported 13 LR-SH isolates from our center, nine from patients with chronic osteomyelitis and four from patients with pemphigus vulgaris. ⁴ All the 13 isolates demonstrated a dual mechanism of resistance with a mutation at domain V of 23S rRNA gene and presence of cfr (chloramphenicol-florfenicol resistance) gene thus limiting the treatment options. In another study from our center, CoNS comprised 12% of the total bacterial isolates from patients with prosthetic joint infections. Stapylococcus haemolyticus comprised 36.4% of these CoNS isolates, which were uniformly resistant to methicillin and exhibited MDR attribute. ⁹

In view of the range of infections caused by CoNS, varying degree of susceptibility patterns exhibited by them, emergence of MDR strains, and the diverse epidemiology of CoNS species from one geographical locale to another, it seems more imperative to speciate all the CoNS isolates for therapeutic as well as epidemiologic purposes. Periodic surviellance studies in this regard with continous monitoring of MDR isolates, will help in tailoring the existing antibiotic policies and implementation of effective and efficient infection control measures, thereby preventing the dissemination of resistant clones in a health care setting.

To conclude, although Stapylococcus lugdenensis is an important CoNS species, other CoNS species, particularly Stapylococcus haemolyticus, is also gaining importance in a plethora of infections including MSIs and orthopedic surgery-related infections.