Rate of isolation of Staphylococcus aureus strains possessing coagulase or clumping factor

Cytidine deamination assay to differentiate Staphylococcus aureus from other staphylococci

AIMS

Adoption of the property of cytidine (cytosine-beta-d-riboside) deamination in staphylococci to distinguish Staphylococcus aureus from other staphylococci.

METHODS AND RESULTS

A total of 560 staphylococcal strains were examined. The test demonstrated a sensitivity of 97.1% and a specificity of 98.8%. Of the 249 S. aureus strains (115 oxacillin-resistant) 58 strains were coagulase-negative S. aureus and another 16 strains were clumping factor-negative S. aureus. The 74 deficient S. aureus strains were identified by 16S rRNA gene sequencing and further investigated by spa typing and 13 spa types were found.

CONCLUSIONS

The cytidine deaminase test (CDT) is useful especially for distinguishing coagulase- and clumping factor-negative S. aureus from other staphylococci and the results correlated well with 16S rRNA sequencing and the polymerase chain reaction (PCR) amplification of the nuc gene.

SIGNIFICANCE AND IMPACT OF THE STUDY

Cytidine deamination assay differentiates S. aureus from other staphylococci. This method is fast (6 h) and reliable in distinguishing between non-S. aureus and the defective (coagulase-negative, clumping factor-negative) S. aureus isolates which could have major consequences for therapy.

Characteristics of bovine Staphylococcus aureus with special regard to clumping factor activity

The occurrence of the following groups of bovine Staphylococcus aureus with characteristic patterns of biochemical reactions and sensitivities to phages was confirmed by the present investigation of 662 isolates from the udders of cows in 53 dairy herds: (1) host-specific variety (v) bovis, (2) not alloted strains with the basic marker, crystal violet type A (group na CV A), (3) group na CV C. The latter was split into three subgroups clearly differing in phage susceptibility patterns: I/119, I without 119 and III, respectively. Lack of clumping factor activity occurred in 323 out of 346 (93%) phage pattern I/119 strains examined while most or all isolates of the other groups of bovine strains proved to be clumping-positive.

Comparative evaluation of a latex test for the identification of Staphylococcus aureus

A rapid latex agglutination test, Staphaurex, was tested for its ability to identify Staphylococcus aureus using 72 reference strains and 785 clinical isolates of the family Micrococcaceae. All reference strains of Staphylococcus aureus were Staphaurex-positive. Non-Staphylococcus aureus reference strains were negative. Using clinical strains, the results of the Staphaurex test were compared with the results of other tests commonly used to identify Staphylococcus aureus. A total of 393 clinical isolates were classified as Staphylococcus aureus. The Staphaurex, slide coagulase, tube coagulase/human plasma and tube coagulase/rabbit plasma tests correctly identified 98%, 93.6%, 93.6% and 97.5% of the Staphylococcus aureus strains, respectively. The performance of the Staphaurex test, in terms of sensitivity and specificity, was significantly better than the slide coagulase test. It was as sensitive and almost as specific as the tube coagulase rabbit test and more sensitive than the tube coagulase human test.

Comparison of a yellow latex reagent with other agglutination methods for the identification of Staphylococcus aureus

A new commercial yellow latex agglutination reagent (Bacto-Staph) was compared with the slide and tube coagulase tests and three other commercial reagents for the identification of 283 Staphylococcus aureus and 54 non-S. aureus staphylococcal strains. Test sensitivities for the identification of S. aureus were as follows: tube coagulase, 99.6%; slide coagulase, 98.6%; Bacto-Staph, 99.6%; Staphylatex, 98.6%; Sero STAT Staph, 98.2%; and Staphyloslide, 97.5%. No false-positive reactions were observed with any of the commercial reagents.