Molecular characterization of a catalase-negative Staphylococcus aureus subsp. aureus Strain collected from a patient with mitral valve endocarditis and pericarditis revealed a novel nonsense mutation in the katA gene

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.

First description of a catalase-negative Staphylococcus aureus from a healthy carrier, with a novel nonsense mutation in the katA gene

We have screened 2568 healthy individuals (mostly children) for Staphylococcus aureus and Streptococcus pneumoniae nasal carriage between 2010 and 2012. Out of the isolated 751 S. aureus strains, we found one methicillin-sensitive catalase-negative S. aureus (CNSA). Our CNSA isolate possessed a novel nonsense point mutation in the katA gene leading to early truncation of the protein product. The strain was resistant to penicillin and erythromycin, but sensitive to all other tested antibiotics and carried the enterotoxin A gene. It belonged to sequence type 5 (ST5), which is a successful, worldwide spread, usually MRSA clone. Catalase has been described as a virulence factor strictly required for nasal colonisation, and this is the first case contradicting this theory, as all previous CNSA isolates derived from infections. This is the first report of a CNSA from a symptomless carrier as well as the first occurrence in Hungary.

Draft Whole-Genome Sequence of a Catalase-Negative Staphylococcus aureus subsp. aureus (Sequence Type 25) Strain Isolated from a Patient with Endocarditis and Septic Arthritis

Staphylococcus aureus strains without catalase activity are rare, challenging to identify with conventional biochemical methods, and, despite a supposed decreased pathogenicity, can still cause disease. The first whole-genome sequence of a catalase-negative S. aureus isolate causing severe recurrent invasive infection with two novel missense mutations in the katA gene is reported here.

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.

Molecular Characterization of a Catalase-Negative Staphylococcus aureus Blood Culture Isolate

Here we report a catalase-negative methicillin-sensitive Staphylococcus aureus isolate collected from a blood culture. Sequencing through the gene encoding catalase, katA, demonstrated a 2-bp insertion. The resulting frameshift mutation generates a protein that has lost 26 amino acids (aa) at its C-terminal domain.

Prevalence, molecular characterization of Staphylococcus aureus isolated from cheese and in vitro antibacterial activity of silver nanoparticles against such strains

AIM

The aim was to investigate cheese samples for the prevalence of Staphylococcus aureus, evaluate multiplex polymerase chain reaction (PCR) methods for S. aureus identification, as well as to determine the antibacterial activity of silver nanoparticles against such strains.

MATERIALS AND METHODS

Total of 100 random locally manufactured cheese samples were collected from Qena dairy markets, Egypt, and examined conventionally for the prevalence of S. aureus then, confirmation of these isolates were done using multiplex PCR. The antibacterial activity of silver nanoparticles against such isolates was also checked.

RESULTS

Lower prevalence of S. aureus in Damietta cheese (54%) than in Kareish cheese (62%) was recorded. As well lower frequency distribution for both S. aureus (36%) and CNS (8%) was also reported for Damietta cheese. Using of multiplex PCR method for S. aureus identification have been confirmed all 58 S. aureus stains that were identified conventionally by detection of two PCR products on agarose gel: The 791 bp and the 638 bp. The correlation coefficient between conventional and multiplex PCR method was 0.91 and was significant at p≤0.001. Regarding antibacterial activity of silver nanoparticles using disk diffusion method on Baird Parker agar it was found that inhibition zone of silver nanoparticles against S. aureus, was 19.2±0.91 mm and it was higher than that produced by gentamicin (400 units/ml) 15.2±0.89 mm.

CONCLUSIONS

The present study illustrated the higher prevalence of S. aureus in cheese samples that may constitute a public health hazard to consumers. According to the results, it can be concluded that silver nanoparticles can be used as an effective antibacterial against S. aureus. Thereby, there is a need for an appropriate study for using silver nanoparticles in cleaning and disinfection of equipment and in food packaging.

First report of brain abscess caused by a satelliting phenotypic variant of Helcococcus kunzii

Helcococcus kunzii was isolated from a brain abscess in a diabetic patient with cholesteatoma and demonstrated satellitism around Staphylococcus aureus in culture. This is the first reported case of severe central nervous system infection due to H. kunzii and the first description of a satelliting phenotypic variant of this organism.

Molecular characterization of a catalase-negative methicillin-susceptible Staphylococcus aureus subsp. aureus strain collected from a patient with cutaneous abscess

We describe a cutaneous abscess caused by catalase-negative methicillin-susceptible Staphylococcus aureus subsp. aureus in a patient who was concomitantly colonized with virulent USA300 methicillin-resistant S. aureus (MRSA). Sequencing of the katA gene demonstrated a thymine insertion leading to a frameshift mutation and premature truncation of catalase to 21 amino acids.

Catalase-negative Staphylococcus lugdunensis strain with a novel point mutation in the catalase gene isolated from a patient with chronic suppurative otitis media

This report describes the results of the sequence analysis of a methicillin-susceptible strain of catalase-negative Staphylococcus lugdunensis. Molecular characterization of the deduced sequence revealed a novel point mutation in the catalase gene. To our knowledge, this is the first report of a catalase-negative S. lugdunensis strain, although catalase-negative isolates of Staphylococcus aureus and Staphylococcus epidermidis have been previously reported.

Production of 2-aminophenoxazin-3-one by Staphylococcus aureus causes false-positive results in β-galactosidase assays

Staphylococcus aureus can be distinguished from similar coagulase-positive staphylococci by its absence of β-galactosidase activity. This is commonly tested using o-nitrophenyl-β-D-galactopyranoside (ONPG) as the substrate. Unexpectedly, 111 and 58 of 123 isolates displayed apparent β-galactosidase activity in the ONPG assay and on the Vitek 2 system, respectively. Compositional analysis showed that the yellow coloration of the positive ONPG assay resulted from production of 2-aminophenoxazin-3-one. Alternative β-galactosidase substrates like X-Gal (5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside) should be used for testing staphylococci.

First report of spontaneous intrapartum Atopobium vaginae bacteremia

We report the first case of spontaneous intrapartum Atopobium vaginae bacteremia identified by 16S rRNA gene sequencing. The bacterium was misidentified by RapID ANA II, API Rapid ID 32A, and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The likely source of bacteremia was the female genital tract. In invasive infections caused by A. vaginae, β-lactams and clindamycin are the antibiotics of choice, as most strains are resistant to metronidazole.