Original Research ArticleRapid methicillin resistance detection and subspecies discrimination in Staphylococcus hominis clinical isolates by MALDI-TOF MS
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.
Section snippets
Clinical isolates and identification
We included 148 S. hominis clinical isolates from blood (n = 145, 97.9%) and cerebrospinal fluid (n = 3, 2.0%) collected from January 2006 to December 2016 at the Hospital Civil de Guadalajara “Fray Antonio Alcalde” and Hospital Universitario “Dr José Eleuterio González”, third-level hospitals in Jalisco and Nuevo Leon, Mexico, respectively.
Isolates were identified using direct colony method by MALDI TOF MS (Microflex LT system, Bruker Daltonics, Bremen, Germany), flowing the manufacturer's
Subspecies classification, biofilm formation and composition
Novobiocin resistance was detected in 18 (12.2%) isolates, which were classified as SHN; the remaining 130 (87.3%) isolates were novobiocin susceptible and classified as SHH.
A total of 115 (77.7%) were biofilm producers, of which 96 (83.5%) were strong producers, whereas 19 (16.5%) were weak producers.
Proteins were the primary biofilm component with 91.2% mean detachment and a mean OD595 of 0.262 ± 0.1. The detachment values for carbohydrates varied from 5% to 80%, with a mean OD595 of
Discussion
Rapid identification and antibiotic resistance detection of etiological agents are crucial for accurate antimicrobial treatment and reduced patient mortality rate [15]. In the present study, we found two potential biomarker peaks (8975 and 9035 m/z), which allowed the discrimination of methicillin-resistant S. hominis isolates. The presence of the 8975 m/z peak and the absence of the 9035 m/z peak in non-susceptible isolates were associated with a methicillin resistance phenotypic profile
Conclusion
We found two potential biomarker peaks to predict methicillin resistance and three potential marker peaks to identify S. hominis subsp. novobiosepticus using the conventional identification procedure in MALDI-TOF MS. This method allows shortening time between bacterial identification, testing, and reporting antimicrobial resistance with no additional methods to conventional MALDI-TOF MS methodology identification, which is critical for an early and specific selection of drug treatment.
Funding information
This work was supported by the Fondo Sectorial de Investigación para la Educación of the Consejo Nacional de Ciencia y Tecnología (CONACyT) under Grant [number A1-S-16392].
CRediT author statement
Verónica Villarreal-Salazar: Investigation, Methodology, Validation, Formal analysis, Writing - Original Draft. Soraya Mendoza-Olazarán: Conceptualization, Visualization, Supervision, Writing - Original Draft. Samantha Flores-Treviño: Conceptualization, Visualization, Supervision, Writing - Original Draft. Paola Bocanegra-Ibarias: Resources, Writing - Review & Editing. Elvira Garza-González: Resources, Writing - Review & Editing. Rayo Morfín-Otero: Resources, Writing - Review & Editing. Eduardo
Declaration of competing interest
No conflict of interest declared.
Acknowledgements
We wish to thank to the Consejo Nacional de Ciencia y Tecnología (CONACyT) for the founding.
References (30)
Matrix-assisted laser desorption ionization time-of-flight mass spectrometry: usefulness for taxonomy and epidemiology
Clin Microbiol Infect
(2010)- et al.
The presence of a single MALDI-TOF mass spectral peak predicts methicillin resistance in staphylococci
Diagn Microbiol Infect Dis
(2016) - et al.
Nosocomial spread of a Staphylococcus hominis subsp. novobiosepticus strain causing sepsis in a neonatal intensive care unit
J Clin Microbiol
(2005) - et al.
Linezolid resistance in Brazilian Staphylococcus hominis strains is associated with L3 and 23S rRNA ribosomal mutations
Antimicrob Agents Chemother
(2013) - et al.
Detection of new mutations conferring resistance to linezolid in glycopeptide-intermediate susceptibility Staphylococcus hominis subspecies hominis circulating in an intensive care unit
Eur J Clin Microbiol Infect Dis
(2010) - et al.
Molecular basis of resistance to macrolides, lincosamides and streptogramins in Staphylococcus hominis strains isolated from clinical specimens
Folia Microbiol
(2016) - et al.
Antibiotic susceptibility of biofilm cells and molecular characterisation of Staphylococcus hominis isolates from blood
PLoS One
(2015) - et al.
Biofilm formation by Staphylococcus hominis strains isolated from human clinical specimens
Folia Microbiol (Praha)
(2015) - et al.
MALDI-TOF mass spectrometry: an emerging technology for microbial identification and diagnosis
Front Microbiol
(2015) - et al.
Staphylococcus horninis subsp. novobiosepticus subsp. nov., a novel trehalose- and N-acetyl-D-gIucosamine-negative, novobiocin- and multiple-antibiotic-resistant subspecies isolated from human blood cultures
Int J Syst Bacteriol
(1998)