Rapid methicillin resistance detection and subspecies discrimination in Staphylococcus hominis clinical isolates by MALDI-TOF MS

Highlights

• Staphylococcus hominis causes healthcare-associated bloodstream infections

• S. hominis produces biofilm and is multidrug-resistant

• MALDI-TOF MS marker peaks allow the discrimination of specific phenotypes

• Protein biomarkers allow the discrimination of methicillin resistance in S. hominis

• S. hominis subspecies can be discriminated by MALDI-TOF

Abstract

Purpose

Staphylococcus hominis is a coagulase-negative opportunistic pathogen responsible for implanted medical device infections. Rapid identification and virulence factors detection are crucial for appropriate antimicrobial therapy. We aimed to search protein biomarker peaks for rapid classification of antibiotic resistance and subspecies of S. hominis using MALDI-TOF MS.

Methods

S. hominis clinical isolates (n = 148) were screened for subspecies differentiation by novobiocin resistance. Biofilm composition and formation were determined by detachment assay and crystal violet staining, respectively. Antibiotic susceptibility was performed by the broth microdilution method. The search for potential biomarkers peaks was enabled by ClinProTools 3.0, flexAnalysis 3.4, and Biotools 3.2 for statistical analysis, peak visualization, and protein/peptide alignment, respectively.

Results

Of 148 isolates, 12.16% were classified as S. hominis subsp. novobiosepticus, 77.77% were biofilm producers, and ˃ 50% were multidrug-resistant. Two potential biomarker peaks, 8975 m/z and 9035 m/z were detected for the discrimination of methicillin resistance with a sensitivity of 96.72%. The following peaks were detected for subspecies differentiation: 2582 m/z, 2823 m/z, and 2619 m/z with 88.89–98.28% of sensitivity.

Conclusions

We found potential biomarker peaks to predict methicillin resistance and discriminate S. hominis subspecies during routine MALDI-TOF MS identification in a clinical setting to enable better antibiotic treatment.

Introduction

Between the coagulase-negative staphylococci (CoNS) group, Staphylococcus hominis is the third most frequent causal agent of bacteremia [1]. S. hominis subsp. novobiosepticus (SHN) is reported to be more virulent and resistant than S. hominis subsp. hominis (SHH) to last-resort antibiotics, such as linezolid [2,3]. Although S. hominis is an opportunistic pathogen, some strains cause severe infections that are difficult to treat due to multidrug resistance and other virulence characteristics such as biofilm formation. A biofilm protects the bacteria from the effect of antibiotics and the host's immune system, increasing their survival and prolonging the infection [4,5]. It was reported that up to 85% of clinical S. hominis strains can form a biofilm [6], of these, over 90% are strong biofilm producers (5).

Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) uses intact cells or cell extracts or rapid and early identification of diverse microorganisms by offering rapid, sensitive, and low-cost analysis in comparison with conventional phenotypic and molecular techniques [7]. Spectral patterns are obtained that provide a unique protein mass profile for each microorganism. These can be discriminated and identified using an established database. This approach has been used not only for microbial identification, but also for other purposes in clinical microbiology, including epidemiological studies, antibiotic resistance detection, and rapid discrimination of a specific phenotype or genotype [8].

This study aimed to search protein biomarker peaks based on MALDI-TOF MS profiles for rapid detection of antibiotic resistance and subspecies classification of S. hominis from clinical specimens.