Thermonuclease test accuracy is preserved in methicillin-resistant Staphylococcus aureus isolates.

Introduction. The nuc gene encodes a thermonuclease which is present in Staphylococcus aureus but not in coagulase-negative staphylococci (CoNS) and is the target of the rapid phenotypic thermonuclease test. The effect of nuc gene variation in methicillin-resistant S. aureus (MRSA) on the performance of PCR testing has been noted, although there are no reports about the effect of MRSA on the activity of the thermonuclease enzyme.Aim. Our goals were to examine the sensitivity and specificity of the thermonuclease test used to distinguish S. aureus from CoNS cultured from blood. In addition, we aimed to assess differences in the sensitivity, specificity and accuracy of the thermonuclease test between methicillin-sensitive S. aureus (MSSA) and MRSA isolates.Methodology. We performed a retrospective analysis of 1404 isolates. Each isolate from a positive blood culture was identified as a Gram-positive coccus by microscopy then analysed with the thermonuclease test (Southern Group Laboratory) prior to confirmatory identification using VITEK microbial identification platforms (bioMérieux) and cefoxitin disc diffusion testing.Results. Of 1331 samples included in the final analysis, 189 were thermonuclease-positive, of which 176 were identified as S. aureus. Of the 1142 thermonuclease-negative samples, 13 were finally identified as S. aureus, giving a sensitivity of 93.1 % (95 % confidence interval [CI] 88.5-96.3) and specificity of 98.9 % (95 % CI 98.1-99.4). Of the nine proven MRSA samples, eight were thermonuclease-positive, giving a sensitivity of 88.9 % (95 % CI 51.8-99.7). Thermonuclease test accuracy for MSSA and MRSA isolates was 98.1 % (95 % CI 97.2-98.8) versus 98.8 % (95 % CI 98.0-99.3), respectively.Conclusions. In the era of increasing use of molecular-based microbiology assays, the thermonuclease test remains a simple, inexpensive and robust test for the presumptive identification of S. aureus cultured from blood, irrespective of methicillin sensitivity.

High community faecal carriage rates of CTX-M ESBL-producing Escherichia coli in a specific population group in Birmingham, UK.

OBJECTIVES: To determine the proportion of E. coli carrying specific CTX-M extended-spectrum ß-lactamase (ESBL) genotypes in a community population of East and North Birmingham. METHODS: General practice and outpatient stool samples from 732 individuals submitted for examination for faecal pathogens in 2010 were screened for ESBL-producing E. coli using chromogenic agar. Multiplex PCR, denaturing HPLC, DNA sequencing and PFGE were used to determine the CTX-M genotype and clonal subtype. Isolates from people were assigned to 'Europe', 'Middle East/South Asia' (MESA) or 'uncategorized' groups using software to determine probable global origin based on the subject's full name. RESULTS: Prevalence of CTX-M carriage in the sample population was 11.3%. There was a statistically significant difference (P < 0.001) between carriage in the Europe group (8.1%) and the MESA group (22.8%). There was also a higher rate of carriage of CTX-M-15-producing E. coli (P < 0.001) in MESA subjects. CONCLUSIONS: The high community carriage rate and the significant difference in carriage between the Europe and MESA subjects may have important consequences for therapy. If the rising trend in carriage of bacteria producing ESBLs continues, guidelines for empirical therapy for patients presenting from the community may need to be modified. The findings also raise the concern that the pattern and routes of spread of CTX-M-15 may be replicated in the future by broader-spectrum ß-lactamases, such as New Delhi metallo-ß-lactamase ('NDM-1').

Bilateral endophthalmitis as a primary manifestation of Streptococcus dysgalactiae endocarditis and the role of 16S rDNA polymerase chain reaction in identification.

Bilateral endogenous endophthalmitis is a rare complication of endocarditis. We present the case of a 72-year-old female who presented with heart failure and bilateral endogenous endophthalmitis. Endocarditis was confirmed on transesophageal echocardiography. All cultures were negative, but 16S rDNA sequencing on vitreal aspirates identified Streptococcus dysgalactiae as the likely pathogen.