Lysogenic conversion for multiple characters in a strain of Staphylococcus aureus

Dissemination Of t437-SCCmecIV And Coagulase-Negative t037-SCCmecIII Types Among Borderline Oxacillin-Resistant Staphylococcus aureus Isolated From Skin Infections And Diabetic Foot Ulcers

Background

In a recent decade, the occurrence of S. aureus isolates with low-level oxacillin resistance, have been reported increasingly. The aim of this study was to estimate the prevalence of S. aureus with low-level of oxacillin resistance and to determine their molecular characteristics, including spa types, SCCmec types and presence of toxin genes.

Methods

A total of 249 S. aureus strains were analyzed. Antimicrobial susceptibility was preliminarily tested by the disk diffusion method, and further was verified with the E-test and agar dilution methods. All borderline oxacillin-resistant strains (BORSA) were screened for the mecA gene and virulence factors, including Panton-Valentine leukocidin (PVL). Staphylococcal cassette chromosome mec (SCCmec) typing and spa typing were also carried out.

Results

Twelve (4.8%) borderline oxacillin-resistant strains with MIC ≤4 µg/mL were identified. Almost all strains (11/12) were oxacillin-susceptible methicillin resistant S. aureus carrying mecA gene (OS-MRSA). Among the 12 bordeline strains, five spa types (t437, t037, t015, t216, t267) and two SCCmec types (III, IV) were identified, with the most prevalent being t437-SCCmecIV pvl-positive. The second most frequent spa type, t037-SCCmecIII, was sea-positive and did not produce coagulase. The majority of borderline strains originated from skin infections and diabetic foot ulcers and were multidrug-resistant (macrolides, lincosamides and chloramphenicol).

Conclusion

This study demonstrated that S. aureus with borderline resistance to oxacillin represented primarily SCCmecIV spa type t437 and coagulase-negative SCCmecIII spa type t037 and were isolated from skin infections and diabetic foot ulcers.

Effect of bacteriophage lysin on lysogens

OBJECTIVE

To study the effect of phage lysin on the growth of lysogens.

METHODS

Sputum specimens processed by modified Petroff's method were respectively treated with phagebiotics in combination with lysin and lysin alone. The specimens were incubated at 37 °C for 4 days. At the end of day 1, 2, 3 and day 4, the specimens were streaked on blood agar plates and incubated at 37 °C for 18-24 hours. The growth of normal flora observed after day 1 was considered as lysogens.

RESULTS

Sputum specimens treated with phagebiotics-lysin showed the growth of lysogens. When specimens treated with lysin alone, lysogen formation was avoided and normal flora was controlled.

CONCLUSIONS

Lysin may have no effect on the growth of lysogens.

Characteristics of Staphylococcus aureus strains isolated in Poland in 1996 to 2004 that were deficient in species-specific proteins

One hundred seventy Staphylococcus aureus isolates, collected in 1996 to 2004, were reidentified by phenotypic and genotypic methods. One hundred ten of these (65%) were confirmed, as previously denoted, to be clumping factor (CF)- or free coagulase-deficient S. aureus, based on their phenotype. Based on the CF or coagulase production, three groups of phenotypically deficient S. aureus isolates were distinguished. Group 1 encompassed CF-positive and coagulase-deficient isolates, group 2 consisted of CF-deficient and coagulase-positive isolates, and group 3 included isolates that were CF positive, had delayed coagulase activity, and were deficient in other species-specific features. All investigated strains harbored the clfA, clfB, coa, spa, and nuc genes, but the presence of their products was not detected by the phenotypic methods. Glycopeptide susceptibility testing showed that 26 isolates (23.6%) were hetero-glycopeptide-intermediate S. aureus(hGISA) or hetero-teicoplanin-intermediate S. aureus (hTISA), based on the population analysis profile. The relatedness of the isolates was evaluated by multiple-locus variable number of tandem repeats analysis, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing. The phenotypically deficient S. aureus isolates were classified into PFGE types B (ST239-III) and D (ST246-IA) and were related to the common clones, Hungarian and Iberian, respectively, which have been widely disseminated in Poland and globally. The simultaneous occurrence of hGISA/hTISA and the CF-deficient phenotypes was found for 62.1% of isolates belonging to group 2. The majority of these isolates were assigned to the Iberian clone (PFGE type D; ST247-IA). An association between the defect in coagulase and that in thermonuclease production was observed, which concerned 59.2% of isolates of group 1. The majority of these isolates belonged to the Hungarian clone (PFGE type B; ST239-III).

Genomic relatedness ofStaphylococcus aureusphages of the International Typing Set and detection of serogroup A, B, and F prophages in lysogenic strains

On the basis of HindIII-restriction digest analysis of genomic DNAs, the S. aureus bacteriophages of the International Typing Set were divided into five clusters designated as A, F, Ba, Bb, and Bc. The clusters A and F include all the phages of serogroups A and F and correspond to species 3A and 77 proposed by Ackermann and DuBow (1987). On the other hand, the phages of serogroup B were divided into three clusters designated as Ba, Bb, and Bc that differ significantly each from the other in their restriction patterns. The clusters Ba and Bb may represent two separate species, while the cluster Bc may include more than one phage species. For each of the phage serogroups A, B, and F, common HindIII-restriction fragments of phage 3A (1700 bp), of 53 (4060 bp), and of 77 (8300 bp) were used for the preparation of probes specific to the phages of serogroups A, B, and F. These probes were very effective, making it possible to detect up to three different prophages in a given lysogenic strain at the same time. Restriction enzyme maps of phages 3A, 53, and 77, each representing a different serogroup, were constructed. The restriction maps of phage 3A and that of phage 77 are linear, whereas that of phage 53 is circular and exhibits a circular permutation. DNAs of the phages of serogroups A and F have cohesive ends. On each restriction map, the sites corresponding to specific probes are indicated. The size of intact genomic DNA of all phages estimated by PFGE varies within the range of 41.5-46.2 kb.Key words: Staphylococcus aureus, bacteriophages, prophage specific probes, restriction endonuclease maps.

Coagulase-negative variants of methicillin-resistant Staphylococcus aureus subsp. aureus strains isolated from hospital specimens

At the Department of Clinical Bacteriology of Medical University of Warsaw, S. aureus strains displaying negative reactions in the coagulase tube-test were isolated with a relatively high frequency from clinical specimens. As many as seventeen of such strains all from different patients were isolated during 1994 among MRSA strains. Despite coagulase negativity all strains were positive in tests for clumping factor (CF), protein A and thermonuclease. Biochemical characteristics, phage patterns and antibiotic resistance characteristics of these strains were tested. Most of the coagulase-negative strains possessed a heterogenous type of methicillin resistance. Apart from methicillin most of them were resistant to many other antimicrobials. All were resistant to gentamicin, tetracyclines and macrolide-lincosamide-streptogramine B. An occurrence of coagulase-negative S. aureus strains may lead to problems in their identification and the necessity of an application of other methods like CF, protein A or biochemical reactions.

Localization of prophages of serological group B and F on restriction fragments defined in the restriction map of Staphylococcus aureus NCTC 8325

Several Staphylococcus aureus strains were lysogenized by the phages of serological group B (phages phi 53, phi 85) as well as by some of serological group F (phages phi 77, phi 84) and macrorestriction fragment patterns of genomic DNA were estimated in the lysogenized, non-lysogenic and delysogenized (cured of prophages) strains. It was shown that the integration of phage DNA into chromosome of S. aureus leads to specific changes in restriction fragment pattern in all the lysogenized strains. These changes correlate well with the SmaI restriction map of S. aureus NCTC 8325 since they concern the restriction fragments defined in this map. Phages phi 53 and phi 85 integrate into SmaI fragment B. On the other hand, phages phi 77 and phi 84 integrate into SmaI fragment E of the S. aureus restriction map. The prophages of strain NCTC 8511 have their integration sites, as follows: the phage designated by us phi M integrates in fragment A, whereas the integration site for phage phi J lies in fragment E. Phage phi M was estimated to be genetically related to phages of serological group A and phage phi J to those of serological group F. Evidence was given that lysogenization of S. aureus strains by at least four prophages does not cast any doubt upon the estimation of their genetic relatedness based on their similarity in restriction pattern.

Pathogenicity in mice of Staphylococcus aureus mutants deficient in exoprotein synthesis

Twelve mutants were isolated from a Staphylococcus aureus strain derived from bovine mastitis after mutagenesis by ultraviolet light. These mutants were found to be deficient for several characteristics such as production of most exoproteins and had altered phage type and/or colonial morphology in serum-soft agar medium. They also differed in virulence when assayed in mice by intraperitoneal administration; the ratio of the LD50 of the mutants vs. that of the parental strain ranged from 1 to 123. The different virulence of the mutants could not be associated with lack of production of exoproteins or altered colonial morphology. On the other hand, a clear correlation was evidenced between lowered virulence and slower growth rate at 37 degrees C. Three mutants were assayed in the mouse mastitis model. One of them, which was about 40 times less virulent when assayed by intraperitoneal administration, induced a histopathological lesion similar to that produced by the parent strain; the other two mutants, which were about 70 to 120 times less virulent by intraperitoneal administration, induced only a very slight lesion. Mice were vaccinated by the intraperitoneal route with two of the less virulent mutants; the LD50 in the vaccinated mice that were challenged with the parental strain increased 11 to 14 times compared with that for the unvaccinated mice.

Mechanism of bacteriophage conversion of lipase activity in Staphylococcus aureus

Staphylococcus aureus PS54 harbors two temperate bacteriophages and manifests no lipase activity on egg yolk agar. Curing of one of the resident prophages (L54a) restores lipase activity. To study the mechanism of bacteriophage conversion, the prophage was cured, and the gene encoding lipase activity was cloned into pBR322 in Escherichia coli on a 2.9-kilobase DNA fragment of the chromosome. The fragment was subcloned into a shuttle vector and subsequently transformed into S. aureus and Bacillus subtilis. Lipase activity was expressed in all three genetic backgrounds. Transformation and transductional data indicated that conversion is due to insertional inactivation of the lipase gene. Hybridization analysis with probes made from converting-phage DNA and from the cloned fragment confirmed that the phage insertion site resides within the terminal 0.8 kilobase of the insert.

Molecular relationships among serogroup B bacteriophages of Staphylococcus aureus

The typing bacteriophages 55, 80, 83A, and 85 of Staphylococcus aureus, representative of the three major lytic groups of serological group B aureophages, have been examined for relatedness of their genomes and virion proteins. Phages 11 and 80 alpha were also examined to determine the relationship of phage 80 alpha to phages 11 and 80. Total genome hybridization measurements divided the phages into two groups. Phages 55 and 80, in the first group, had DNA homology of 50%. Phages 11, 80 alpha, 83A, and 85 formed a second group with 27 to 65% homology. Homology between the two groups was in the range of 14 to 22%. Phage 80 alpha is more closely related to phage 11 than to phage 80, though it is probably not a simple recombinant of phages 11 and 80. Restriction enzyme digestion and phage [32P]DNA hybridization analysis of the endonuclease-generated fragments from each phage DNA confirmed the findings of the DNA homology measurements. The endonuclease fragment patterns generated by EcoRI and HindIII were distinctive for each phage, confirming that none of the phages are closely related. Common sequences were present in most fragments from the phage DNAs when the labeled probe DNA was from a different phage in the same group. Cross-group probing of endonuclease fragments revealed both a diminished level of homology when similar sequences were present and the probable absence of some sequences. Virion proteins, examined by polyacrylamide gel electrophoresis, were similar in number and molecular weight for phages 11, 80 alpha, 83A, and 85, reflecting the DNA homology analyses. The virion proteins from phages 55 and 80, however, were more distinctive, and both differed from the phages in the other group.

The nature of the competitive ability of spontaneous staphylocoagulase-negative mutants of Staphylococcus aureus with respect to growth of the parent strains in continuous culture

During prolonged cultivation of S. aureus strains 104 and NCTC 8178 in continuous culture, staphylocoagulase-negative mutants arose and accumulated progressively in increasing proportions. The resulting loss of production of staphylocoagulase was accompanied by a simultaneous loss of production of alpha-haemolysin and PV-leucocidin. Characterization of the strains revealed no further difference in biotype, exoenzymes phage pattern and plasmid content. Cultivation in batch cultures showed that the maximal specific growth rates and specific oxygen-consumption rates of the mutant strains were slightly higher than those of the parent strains, whereas the production of total extracellular protein of the mutant strains had decreased significantly. From competition experiments between parent and mutant strains in chemostat cultures at different dilution rates and cultivation temperatures, it was concluded that the underlying mechanism of accumulation of staphylocoagulase-negative mutants in the chemostat is based on differences in affinity for the limiting substrate(s) rather than on differences in the production rates of total extracellular proteins. The complete repression of three exoenzymes, an partial repression of the total extracellular protein production, and an increased affinity for the limiting substrate(s) suggested that a mutation in a regulatory gene is involved. The possible role of a transposon in this mutation is discussed.

Modulation of protein A formation in Staphylococcus aureus by genetic determinants for methicillin resistance

Many methicillin-resistant (Mec(r)) strains of Staphylococcus aureus either produce no protein A or secrete it extracellularly (S. Winblad and C. Ericson, Acta Pathol. Microbiol. Scand. Sect. B 81:150-156, 1973). We found that methicillin resistance and protein A production were apparently lost coordinately from the natively Mec(r) strain A676. Restoration of the genetic determinant for methicillin resistance (mec) by transduction or transformation restored protein A production. In two other Mec(r) strains, loss of mec was accompanied by marked reduction in protein A formation. Genetic transfer of mec to derivatives of S. aureus 8325 affected protein A formation differently with different mec determinants. Those derived from strain A676 and two other Mec(r) strains reduced the scanty amount of protein A produced by strain 8325 to even lower or undetectable levels, whereas mec from two more Mec(r) strains increased its protein A content. This "mec-effect," i.e., stimulation or inhibition of protein A formation dependent on the combination of host strain and mec determinant, was reduced in methicillin-susceptible (Mec(s)) mutants produced by ethyl methane sulfonate treatment of Mec(r) strains. The mec-effect reappeared in spontaneous revertants to methicillin resistance. Phenotypic reduction of methicillin resistance in Mec(r) strains grown at 44 degrees C was accompanied by reduction of the mec-effect on protein A, but it had no effect on protein A formation in Mec(s) strains. Two independent mutants of strain 8325 produced large amounts of protein A at rates that were unaffected by growth at 44 degrees C or by the introduction of mec determinants.