A comparison of methods and the validity of deoxyribonuclease tests for the characterization of staphylococci isolated from animals

Bovine Staphylococcus aureus: diagnostic properties of specific media

As accurate discrimination between Staphylococcus (S.) aureus and NSA (non-S. aureus staphylococci) involved in bovine mastitis is essential in terms of clinical prognosis and outcome, the aim of this study was to reevaluate the classical bacteriological procedures to identify these agents. Various media and the coagulase tube test were investigated using 116 strains of S. aureus and 115 of NSA, all isolated from cows with spontaneous intramammary infections (IMI). Furthermore, 25 NSA reference strains were analyzed. The study demonstrated that a few media were appropriate for differentiating S. aureus from NSA, provided that the staphylococci were isolated from bovine IMI. Evaluation of hemolysis further revealed that double or incomplete hemolysis are specific for S. aureus and are, therefore, a decisive diagnostic criterion. For strains showing complete hemolysis, maximal discrimination between S. aureus and NSA was observed by subculturing them on CHROMagar Staph. aureus.

Staphylococcus agnetis sp. nov., a coagulase-variable species from bovine subclinical and mild clinical mastitis

Thirteen Gram-positive-staining coagulase-variable staphylococci were isolated from subclinical and mild clinical mastitic bovine milk (n = 12) and a teat apex (n = 1). The results of sequence analysis of the 16S rRNA gene and two housekeeping genes, rpoB and tuf, and DNA fingerprinting with amplified fragment length polymorphism (AFLP) analysis showed that the isolates formed a separate branch within the genus Staphylococcus. The phylogenetically most closely related species were Staphylococcus hyicus and Staphylococcus chromogenes. DNA–DNA hybridization with S. hyicus DSM 20459T and S. chromogenes DSM 20674T confirmed that the isolates belonged to a separate species. The predominant fatty acids were i-C15 : 0, ai-C15 : 0, i-C17 : 0 and C20 : 0 and the peptidoglycan type was A3α l-Lys–Gly5. Based on the results of genotypic and phenotypic analyses, it is proposed that the thirteen isolates represent a novel species, for which the name Staphylococcus agnetis sp. nov. is proposed. Strain 6-4T ( = DSM 23656T = CCUG 59809T) is the type strain.

Staphylococcus pseudintermedius sp. nov., a coagulase-positive species from animals

Four staphylococcal isolates from clinical and necropsy specimens from a cat, a dog, a horse and a parrot (Psittacus erithacus timneh) were found to constitute a distinct taxon. 16S rRNA gene sequence analysis revealed that its closest phylogenetic relatives are Staphylococcus intermedius and Staphylococcus delphini. Growth characteristics, biochemical features and DNA-DNA hybridizations demonstrated that the strains differ from these and other known species and that they represent a single, novel Staphylococcus species for which the name Staphylococcus pseudintermedius sp. nov. is proposed. The novel species is commonly confused with S. intermedius in routine diagnostic veterinary bacteriology. Although the strains described were isolated from lesions and show several characteristics typical of pathogenic staphylococci, such as coagulase, DNase and beta-haemolysin production, the pathogenic significance of the novel species remains unclear. The type strain, LMG 22219(T) (=ON 86(T)=CCUG 49543(T)), was isolated from lung tissue of a cat.

Identification and antimicrobial susceptibility of Staphylococcus chromogenes isolates from intramammary infections of dairy cows

Staphylococcus chromogenes is a highly prevalent species in subclinical mastitis with a well-established impact on somatic cell count. Few data are available on its antimicrobial susceptibility. The objective of this study was three-fold: (1) to evaluate simple identification tests by comparing them with a genomic method; (2) to determine minimal inhibitory concentrations (MICs) of different antibiotics; (3) to search for the presence of important resistance mechanisms and resistance-determining genes.Seventy-three staphylococcal strains, all collected on different dairy farms, were tentatively identified as S. chromogenes based on their lack of hemolysis and their characteristic intermediate DNase activity. The identification of 70 strains was confirmed as S. chromogenes by tRNA intergenic spacer PCR (tRNA PCR). Three strains were identified as S. sciuri, a species that is naturally cloxacillin- and lincomycin-resistant. All 70 S. chromogenes strains were found to be normally susceptible to neomycin, gentamicin, erythromycin, enrofloxacin, and to penicillinase-stable penicillins and cephalosporins, represented in this study by cloxacillin. The latter result was confirmed by the absence of the mecA gene in each of 13 strains in which this gene was searched for. Twenty-seven (38%) strains were penicillinase producers. Three lincomycin-resistant S. chromogenes strains were found to carry the linA gene. It was concluded that S. chromogenes can be identified reliably in routine mastitis bacteriology, and that the only resistance of importance is against penicillinase-susceptible penicillins.

An atypical Staphylococcus aureus intramammary infection in a dairy herd

An atypical Staphylococcus aureus (S. aureus) strain, isolated in a dairy herd over an 8 month period, was examined. The S. aureus strain was clumping factor negative, weakly heat-resistant deoxyribonuclease positive and produced narrow zones of double haemolysis. In total, 57 quarter infections were observed. Prevalence data per month, calculated as the percentage of quarters infected with this atypical S. aureus strain varied from 7.5% to 17.7% and the new infection rate varied from 0.14 to 0.55. In routine bacteriology, the large number of quarters infected with the atypical S. aureus could easily be misclassified as quarters infected with non-aureus staphylococci.

The differentiation of Staphylococcus aureus from other Micrococcaceae isolated from bovine mammary glands

Haemolysin production, the slide coagulase test and the tube coagulase test were assessed for their capability to differentiate Staphylococcus aureus among other Micrococcaceae in 199 isolates from udders of cows in herds with a low bulk milk somatic cell count. The API-Staph test was used as a reference. Haemolysin production was less effective in identifying Staph. aureus among Micrococcaceae than a combination of other tests. Differences were found in the predictive values of results from diagnostic protocols in which the slide coagulase test was performed on all Micrococcaceae, or on beta-haemolysin-negative Micrococcaceae only. Diagnostic protocols in which haemolysin production was combined with the results of the other tests resulted in excellent diagnostic performance and a reduction in diagnostic procedures. Recommendations for routine Staph. aureus identification in bovine mastitis bacteriology are given.

A simple identification scheme for coagulase negative staphylococci from bovine mastitis

Coagulase-negative staphylococci from cases of bovine mastitis were identified to species level by using an identification scheme based on a three-plate test system which tested for DNase on DNA agar, for protease on calcium caseinate agar, and for the organism's sensitivity to novobiocin, desferrioxaminine (deferoxamine) and fosfomycin by agar diffusion tests. Testing for the inhibition of Staphylococcus delta haemolysin (Skalka 1991) can replace the protease tests.

Binding of chicken, bovine, and rabbit immunoglobulins by avian, bovine, and human strains of Staphylococcus aureus

Sixty-six strains of Staphylococcus aureus of avian, bovine, and human origin were tested for their ability to bind chicken, bovine, and rabbit immunoglobulin G (IgG). A microtitration plate hemagglutination assay and a direct-tube enzyme immunoassay were used to determine qualitative differences. Twice as many chicken and bovine S. aureus isolates than human strains reacted positively to chicken IgG. Mean binding values of chicken IgG were also twice as high for chicken and bovine S. aureus isolates when compared with human-derived strains. Isolates of bovine and human origin displayed a high affinity for bovine IgG and rabbit IgG, whereas few isolates from chickens bound substantial quantities of the nonavian IgG species. These results demonstrate that preparations of staphylococcal protein A with affinities for immunoglobulins from poultry and other animals can be obtained by screening large numbers of isolates, especially those obtained from an animal species, such as chickens, that is the same as the source of the immunoglobulin one wishes to bind.

Identification of coagulase-negative staphylococci from farm animals

The species identify of 661 strains of coagulase-negative staphylococci isolated from the skin and nares of cattle, pigs, poultry, goats and sheep was determined. They belonged either to the novobiocin-sensitive species Staphylococcus hyicus, Staph. simulans, Staph. epidermidis, Staph. haemolyticus and Staph. warneri or to the novobiocin-resistant species Staph. sciuri, Staph. lentus, Staph. xylosus, Staph. cohnii, Staph. saprophyticus and Staph. gallinarum; twenty-one strains remained unidentified. The staphylococcal flora of the farm animals studied differed markedly from that associated with man; several species which do not occur in man were isolated and novobiocin-resistant strains, which occur infrequently in man, were present in large numbers in animals. Two simplified schemes for the identification of staphylococci from farm animals and man are presented.

Comparison of four methods for differentiation of Staphylococcus aureus from other Micrococcaceae in the routine laboratory

Four methods for the identification of Staphylococcus aureus (tube coagulase test, thermostable nuclease test, indirect agglutination of fibrinogen coated erythrocytes and a commercial latex kit: SeroSTAT Staphylococcus Test) have been compared. Clinical isolates (698) and 40 reference strains of Micrococcaceae were included in the study together with control organisms. The coagulase test gave no false positive results but 39/406 clinical isolates of S. aureus were negative at 2h and one half were only weakly positive. At 18 h, all but 2 of 406 isolates gave a positive reaction. The thermostable nuclease test was very specific; no clinical isolates of S. aureus gave negative results and no "coagulase-negative" clinical isolates gave a definite positive reaction. The indirect haemagglutination method was sometimes difficult to interpret and frequently gave negative or doubtful results for S. aureus. The SeroSTAT test was easy to use and interpret and was specific; the method is suitable for routine laboratory use, particularly when a rapid result is desirable.

Staphylococcus aureus in commercial laying flocks: incidence and characteristics of strains isolated from chicks, pullets and hens in an integrated commercial enterprise

1. Staphylococcus aureus was able to colonise the surface of chicks as young as 1 d old. 2. The organism was detected in a hatchery particularly in the debris from the hatchers and on the working surfaces at the sexing and vaccination areas. 3. The degree of surface colonisation of chicks and pullets was low during rearing but rose to a maximum at mid-lay (50 weeks) when the organism was readily detectable on almost all hens. 4. Strains of Staphylococcus aureus were characterised by phage-typing and cultural characteristics and found to belong predominantly to poultry phage group B2 of Gibbs et al. (1978a). 5. A detailed description of poultry phage group B2 strains is presented; strains of this type can be considered as a second "live-bird" ecovar when compared with Staph. aureus var. gallinae of Witte et al. (1977).