Pragmatic Value of Identifying Coagulase-negative Staphylococci up to Species Level
Year: 2025
Type: article
Abstract: Coagulase-negative staphylococci (CoNS) are Gram-positive, aerobic organisms often isolated from clinical samples in microbiology laboratories. These include Staphylococcus species such as Staphylococcus epidermidis, Staphylococcus saprophyticus, Staphylococcus haemolyticus, Staphylococcus lugdunensis, Staphylococcus schleiferi, and others. Traditionally regarded as less virulent than Staphylococcus aureus, these bacteria are a broad variety of organisms often isolated from clinical specimens.[1] Staphylococcal bacteria, on the other hand, are opportunistic pathogens that live in the skin and mucous membranes of healthy people but only become true pathogens in predisposed patients, such as immunocompromised individuals, along with the catheter and/or implants introduce in the body, regular dialysis dependency or malignancy, and neonates. CoNS infections are increasing due to the increased usage of catheters and other synthetic devices that are introduced into the skin. CoNS form biofilms on both nonliving and living surfaces which allows them to easily spread from the skin to sterile areas, especially in vulnerable patients.[2] Extended hospital stays and progress in invasive procedures have made it easier for CoNS to become opportunistic pathogens. Hence, to identify CoNS up to the species level sometimes becomes crucial due to their different pathogenic potential and resistance profiles, which can guide to select from only susceptible drugs.[3] Furthermore, there has been a proportional rise in CoNS-related bloodstream infections in recent times. As per the study conducted by Yusuf et al., they found positive blood culture due to CoNS in 11.6% out of 16.1% positive blood cultures in the non-COVID-19 period while 27.2% out of 30.1% positive blood culture during COVID-19 period.[4] These numbers show the importance of CoNS in bloodstream infections specifically in arterial catheter-inserted intensive care unit patients. The clinical criteria for determining whether isolated CoNS from blood cultures indicate bloodstream infections are not highly sensitive or specific. To have clinical significance, recurring CoNS infection must be of the same strain and validated using genotyping procedures that are not readily accessible.[1] The uncertainties surrounding the importance of CoNS found in blood cultures can lead to delay in diagnosis and unnecessary use of anti-staphylococcal drugs, particularly vancomycin. This can contribute to the development of multidrug resistance, higher frequency of serious infection, and increased hospital costs. CoNS in a microbiological sample could indicate contamination due to inadequate sampling and testing methods, natural colonization of the skin and mucous membranes, or an active infection. This poses a diagnostic challenge in accurately distinguishing cases where CoNS are the actual cause rather than mere contaminants. Distinguishing pathogen from a commensal on the basis of clinical presentation of the patient, history, and ruling out other commonly associated infectious pathogens can help for the establishing CoNS as a pathogen.[5] Recently, S. lugdunensis and S. haemolyticus have been widely acknowledged as human pathogens, especially among those with implanted medical equipment such as catheters and prosthetic joints.[6]S. saprophyticus is a well-established uropathogen in sexually active young females.[7] In addition, S. lugdunensis is recognized for its capacity to induce serious illnesses that closely mirror those produced by S. aureus, such as skin and soft-tissue infections, endocarditis, and osteomyelitis.[6] When cultured, the majority of CoNS species exhibit colonies that are nonpigmented, smooth, whole, shiny, and opaque. Slime producers with high strength may exhibit a colony which looks slimy and mucoid. Following a period of incubation lasting 2–3 days, the diameter of the colony expands to a range of 3–6 mm.[1,8] Some Staphylococcus species such as Staphylococcus devriesei, Staphylococcus lugdunensis, Staphylococcus sciuri, Staphylococcus chromogenes, Staphylococcus vitulinus, Staphylococcus warneri, and Staphylococcus xylosus produce more or less yellow, yellow gray, or yellow orange-colored colonies. Other CoNS species may show a kind of yellowish pigmentation. S. haemolyticus displays a hazy or distinct zone of beta-hemolysis around the colonies.[8] The antibiotic susceptibility of CoNS may show a similar resistance pattern as that of methicillin-resistant S. aureus (MRSA). Staphylococci acquire methicillin resistance via staphylococcal chromosomal cassette mec, the mobile genetic element carrying mecA, which encodes an altered penicillin-binding protein (PBP2a) that mediates resistance to nearly all beta-lactam drugs.[9] Similarly, CoNS that are methicillin resistant are known as methicillin-resistant CoNS (MR-CoNS) and are resistant to penicillin, cefoxitin, and other commonly used lower-level antibiotic drugs.[10] MR-CoNS detection can be done in the same way as MRSA detection methods using cefoxitin antibiotic disc. Commonly used method includes Kirby-Bauer disc diffusion in which lawn/carpet culture of the organism strain is performed on the cation-adjusted Mueller Hinton agar and the cefoxitin (30 μg) disc is placed in the center. After incubation at 37°C for 18–24 h, the zone of inhibition is measured as per antibiotic susceptibility testing breakpoint guidelines.[11] Other methods such as broth dilution, automated instrument (VITEK 2C and others), and molecular methods can be used to phenotypic and/or genotypic methods of MR-CoNS detection. Fortunately, most CoNS are susceptible to vancomycin and teicoplanin, providing clinicians with a favorable therapeutic alternative. Several studies have noted resistance not only to vancomycin but also to rifampicin, daptomycin, and fosfomycin.[12] For such resistant strains, linezolid, a synthetic drug of the oxazolidinone class of antibiotics, is the better and more successful alternative which works against the resistant CoNS strains. CoNS species produce various virulence factors in the host body either in live conditions or after lysis. The majority of the CoNS doing colonization at the host surface produce biofilm as an important virulence factor. In addition, they produce bacteriocins and enterotoxins within the host organism, leading to the onset of the disease.[12] The development of antibiotic resistance in CoNS is due to virulence factors specifically due to biofilm production. Co-infection of the CoNS along the S. aureus can be more difficult to treat as there is a chance of horizontal gene transfer of several genes and other factors between causative organisms which may increase the antibiotic resistance. Due to horizontal gene transfer, they develop a tolerance against the antibiotics which makes their treatment difficult. Detection of CoNS to species level along with antibiotic susceptibility testing helps to prepare an effective treatment strategy against the CoNS species infections.[12] Many studies have concluded that commensal CoNS are more susceptible to common antibiotics such as penicillin, cefazolin, and methicillin. Nevertheless, pathogenic CoNS species exhibit greater resistance to commonly used antibiotics, as well as more potent drugs such as vancomycin and rifampicin.[13] Patterns of CoNS isolated from sterile body locations and the knowledge about cultural characteristics can help to identify clinical aspects of various species. Therefore, treatment, infection control, and understanding of the pathogenic mechanisms depend on subspecies identification of CoNS. The wide range of pathogenic potential in this group is best shown by S. haemolyticus and S. lugdunensis, which emphasizes the need for accurate microbiological diagnoses in microbiology laboratories.[14] The upsurge of various species from CoNS in the last few years has gotten attention to identifying them at the species level for prompt treatment and prevention. In a nutshell, increasing trends of CoNS isolation as pathogens in various clinical specimens need to be identified and treated on time to prevent severe conditions. Presently, contemporary medical treatments depend on medical devices for many serious diseases and have more chance of contamination with CoNS species which colonize and form biofilm on the device surface. Due to this, the infection rate of CoNS species is increasing. As a clinical microbiologist, we should not neglect them as negligence of drug-resistant CoNS as a commensal can be fatal for the patients. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Language: English
Subfield: Clinical Biochemistry
Domain: Life Sciences
Open Access status: diamond
OpenAlex ID: W4408868682