Deoxyribonuclease-positive Staphylococcus epidermidis strains

Oxidative stress is intrinsic to staphylococcal adaptation to fatty acid synthesis antibiotics

Antibiotics inhibiting the fatty acid synthesis pathway (FASII) of the major pathogen Staphylococcus aureus reach their enzyme targets, but bacteria continue growth by using environmental fatty acids (eFAs) to produce phospholipids. We assessed the consequences and effectors of FASII-antibiotic (anti-FASII) adaptation. Anti-FASII induced lasting expression changes without genomic rearrangements. Several identified regulators affected the timing of adaptation outgrowth. Adaptation resulted in decreased expression of major virulence factors. Conversely, stress responses were globally increased and adapted bacteria were more resistant to peroxide killing. Importantly, pre-exposure to peroxide led to faster anti-FASII-adaptation by stimulating eFA incorporation. This adaptation differs from reports of peroxide-stimulated antibiotic efflux, which leads to tolerance. In vivo, anti-FASII-adapted S. aureus killed the insect host more slowly but continued multiplying. We conclude that staphylococcal adaptation to FASII antibiotics involves reprogramming, which decreases virulence and increases stress resistance. Peroxide, produced by the host to combat infection, favors anti-FASII adaptation.

Species identification, antibiotic sensitivity and slime production of coagulase-negative staphylococci isolated from clinical specimens

Two hundred and seventy-five consecutive clinical isolates of coagulase-negative staphylococci, including strains associated with disease, contaminants and skin colonizers, were speciated, tested for slime production and for their sensitivity to a range of antibiotics. Staphylococcus epidermidis was the most commonly identified species, comprising 63% of all isolates. Slime production was detected in half the strains of Staph. epidermidis, Staph. haemolyticus and Staph. saprophyticus but was rare in other species. Most Staph. haemolyticus strains and approximately half of the Staph. epidermidis strains were resistant to five or more antibiotics. A significant association was found between slime production and multiple antibiotic resistance. For catheter-associated strains, clinical relevance was predictable by species i.e. Staph. epidermidis. Multi-resistant slime-positive Staph. haemolyticus strains, although infrequently associated with disease, were common skin colonizers, presumably acquired from the hospital environment. We describe a practical and inexpensive scheme for the speciation of human coagulase-negative staphylococcal isolates.

Comparison of coagulase, deoxyribonuclease (DNase), and heat-stable nuclease tests for identification of Staphylococcus aureus

One thousand and thirty-five clinical isolates of the genus staphylococcus were used to compare the coagulase test with the deoxyribonuclease (DNase) and heat-stable nuclease tests as methods for identifying Staphylococcus aureus. Conflicting results were obtained with 65 isolates when the coagulase test was compared with the DNase test but with only one isolate when the coagulase test was compared with the heat-stable nuclease test. The heat-stable nuclease test produced reliable results after four hours' incubation and was considered a satisfactory substitute for the coagulase test in the clinical laboratory.

Coagulase and deoxyribonuclease activities of staphylococci isolated from clinical sources

A total of 504 clinical isolates of the family Micrococcaceae were tested for coagulase, deoxyribonuclease, clumping factor, and phosphatase to determine whether there is a correlation between the results of these tests and the pathogenicity of staphylococci. In the tests for coagulase production, it was found that either human or rabbit plasma could be used with broth cultures, whereas rabbit but not human plasma was satisfactory when microorganisms removed from solid culture medium were used. Deoxyribonuclease production correlated better than the fermentation of mannitol with coagulase production. The use of methyl green, Toluidine Blue O, or acridine orange offered no advantage over the use of HCl for detecting the production of deoxyribonuclease. Neither the presence of clumping factor nor the production of phosphatase correlated well with coagulase production. Strains of staphylococci that did not produce coagulase and deoxyribonuclease were isolated as frequently as, and from a greater variety of clinical sources than, strains which produced these substances. It is concluded that the production of coagulase and deoxyribonuclease are properties of staphylococci which are not necessarily indicative of potential pathogenicity of the organisms for man.

Nuclease production and lysostaphin susceptibility of Staphylococcus aureus and other catalase-positive cocci

Some strains of Staphylococcus epidermidis and Micrococcus sp. produce nucleases. However, thermal stability was shown to be unique to the nucleases of S. aureus. In addition, two micromethods for susceptibility testing to lysostaphin were more precise and convenient than anaerobic glucose fermentation in distinguishing between the genera Staphylococcus and Micrococcus.