First report of a catalase-negative methicillin-resistant Staphalococcus aureus

Rapid differentiation of Staphylococcus aureus subspecies based on MALDI-TOF MS profiles

Staphylococcus aureus encompasses 2 subspecies ( aureus and anaerobius) with significant differences in their epidemiology and pathogenicity. We evaluated the suitability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the rapid identification of both subspecies using a panel of 52 S. aureus isolates (30 subsp. anaerobius and 22 subsp. aureus) recovered from different origins, countries, and years. The on-board library identification system correctly identified 42 of 52 (81%) S. aureus isolates at the species level with score values >2.0. Limited performance was observed for differentiation of S. aureus subspecies (particularly subsp. anaerobius). Visual inspection of MALDI-TOF MS profiles identified 5 subspecies-specific mass peaks ( m/ z 3430 and 6861 in S. aureus subsp. anaerobius, and m/ z 4046, 6890, and 8093 in S. aureus subsp. aureus) with 100% sensitivity and specificity values, which is potentially useful for differentiating these subspecies. The suitability of 3 models, Genetic Analysis (GA), Quick Classifier (QC), and Supervised Neural Network, for automatic identification of both subspecies was evaluated using the Recognition Capability (RC) and Cross Validation (CV) values provided by the on-board ClinProTools software. The GA and QC models reached RC and CV values of 100%. Both models were externally validated using a panel of 26 S. aureus isolates of both subspecies, with both models correctly classifying all isolates of both subspecies. MALDI-TOF MS coupled with ClinProTools software represents a rapid and simple approach for S. aureus subspecies discrimination.

Novel nonsense mutation in the katA gene of a catalase-negative Staphylococcus aureus strain

We report the first description of a rare catalase-negative strain of Staphylococcus aureus in Chile. This new variant was isolated from blood and synovial tissue samples of a pediatric patient. Sequencing analysis revealed that this catalase-negative strain is related to ST10 strain, which has earlier been described in relation to S. aureus carriers. Interestingly, sequence analysis of the catalase gene katA revealed presence of a novel nonsense mutation that causes premature translational truncation of the C-terminus of the enzyme leading to a loss of 222 amino acids. Our study suggests that loss of catalase activity in this rare catalase-negative Chilean strain is due to this novel nonsense mutation in the katA gene, which truncates the enzyme to just 283 amino acids.

Mannitol-negative methicillin-resistant Staphylococcus aureus from nasal swab specimens in Brazil

The isolation of mannitol-negative methicillin-resistant Staphylococcus aureus from nasal swabs is reported. Among the 59 isolates, 9 (15%) isolates were mannitol-negative; all of these isolates were categorized as staphylococcal cassette chromosome mec (SCCmec) type IVa. This report emphasizes that mannitol fermentation on mannitol salt agar should not be used as the sole criterion when screening nasal swab specimens for S. aureus.

Characterization of a catalase-negative methicillin-resistant Staphylococcus aureus strain

We describe an unusual clinical strain of catalase-negative methicillin-resistant Staphylococcus aureus sensu stricto. Sequence analysis of its catalase gene showed 99.60% identities to the catalase genes of the reference strains. A 5-base deletion, however, led to a shift of the nucleotide reading frame and a loss of the enzymatic activity.

An outbreak of catalase-negative methicillin-resistant Staphylococcus aureus

The wide dissemination of a major epidemic methicillin-resistant Staphylococcus aureus (MRSA) clone in Brazilian hospitals (Brazilian clone) limits the value of molecular typing techniques such as pulsed-field gel electrophoresis (PFGE) for outbreak investigation. We report the first outbreak of a catalase-negative strain of MRSA, which was initially detected by the unusual result of this phenotypical test. The outbreak occurred in the Hospital Sanatorinhos de Carapicuíba, a 237-bed secondary hospital located in São Paulo, Brazil. From May to August 2002, a total of 11 MRSA isolates were recovered from four patients in the intensive care unit. All the isolates were catalase negative and susceptible only to vancomycin and linezolid. Three of the four patients eventually died. Molecular typing demonstrated an indistinguishable PFGE pattern among the 11 isolates, with similarities to the Brazilian clone and the hospital's usual MRSA strain. This report emphasizes the importance of an uncommon phenotypical result as a marker for initiating an outbreak investigation and should encourage clinical laboratories to recognize and report such isolates.

Molecular identification and characterization of mannitol-negative methicillin-resistant Staphylococcus aureus

We report on the isolation, molecular identification, and characterization of 5 mannitol-negative methicillin-resistant Staphylococcus aureus (MRSA) from clinical samples in KwaZulu-Natal (KZN) province, South Africa. Identification based on phenotypic testing and polymerase chain reaction detection of the S. aureus species-specific nuc gene and the coagulase gene indicated that the mannitol-negative isolates were S. aureus. Furthermore, they were mecA positive, and SCCmec typing demonstrated that all the isolates harbored type IV SCCmec. API STAPH (Biomerieux, Marcy-l'Etoile, France) misidentified 2 mannitol-negative MRSA that belonged to the major clone in KZN province, as Staphylococcus lugdunensis. Although the prevalence and mechanism of mannitol-negative MRSA is unknown, laboratories are encouraged to investigate S. aureus with atypical characteristics.