COAGULASE-NEGATIVE MUTANTS OF STAPHYLOCOCCUS AUREUS: GENETIC STUDIES

Genetic relationship of Staphylococcus aureus isolated from humans, animals, environment, and Dangke products in dairy farms of South Sulawesi Province, Indonesia

Background and Aim:

Staphylococcus aureus is a bacterium that causes several infectious diseases, including mastitis, endocarditis, and osteomyelitis, and poses a threat to human and animal health. This study aims to phenotypically and genetically identify S. aureus from the isolates collected from humans, animals, environment, and Dangke products in the dairy farms of South Sulawesi Province, Indonesia, as well as to establish a genetic relationship among the isolated S. aureus strains.

Materials and Methods:

The total number of samples was 142, comprising 30 humans (skin swab), 58 animals (raw milk), 14 dairy products (Dangke), and 40 environmental samples (water). S. aureus was phenotypically identified using the culture method, followed by Gram staining, catalase test, and coagulase test. Simultaneously, genotypic identification of S. aureus was performed using the conventional polymerase chain reaction and sequencing methods. Sequencing data were analyzed using the MEGA X software by comparing BLAST National Center for Biotechnology Information databases.

Results:

The phenotypic methods revealed that 56/142 (39.4%) animal, human, and Dangke samples grew on culture, and 56/56 (100%) were Gram stain positive, 56/56 (100%) catalase-positive, and 23/56 (41.1%) coagulase positive. The genotypic method revealed that 32/56 (57.1%) samples amplified the nuc gene. The phylogenetic analysis of 12 isolates revealed that they are all closely related and do not belong to distinct clades.

Conclusion:

It indicates that S. aureus isolates from animals (S30) are probably the same strain as human isolates (H2, H3, H4, and H5). The findings of this study can be used as information regarding the importance of preventing and controlling diseases caused by S. aureus using a health approach involving the human, animal, and environmental sectors. This study was limited to the sequencing analysis of the nuc gene.

Biochemical and Molecular Analysis of Staphylococcus aureus Clinical Isolates from Hospitalized Patients

Staphylococcus aureus is opportunistic human as well as animal pathogen that causes a variety of diseases. A total of 100 Staphylococcus aureus isolates were obtained from clinical samples derived from hospitalized patients. The presumptive Staphylococcus aureus clinical isolates were identified phenotypically by different biochemical tests. Molecular identification was done by PCR using species specific 16S rRNA primer pairs and finally 100 isolates were found to be positive as Staphylococcus aureus. Screened isolates were further analyzed by several microbiological diagnostics tests including gelatin hydrolysis, protease, and lipase tests. It was found that 78%, 81%, and 51% isolates were positive for gelatin hydrolysis, protease, and lipase activities, respectively. Antibiogram analysis of isolated Staphylococcus aureus strains with respect to different antimicrobial agents revealed resistance pattern ranging from 57 to 96%. Our study also shows 70% strains to be MRSA, 54.3% as VRSA, and 54.3% as both MRSA and VRSA. All the identified isolates were subjected to detection of mecA, nuc, and hlb genes and 70%, 84%, and 40% were found to harbour mecA, nuc, and hlb genes, respectively. The current investigation is highly important and informative for the high level multidrug resistant Staphylococcus aureus infections inclusive also of methicillin and vancomycin.

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.

Recognition of coagulase-negative Staphylococcus aureus strains by primary polymyxin susceptibility testing

A prospective study evaluating the usefulness of polymyxin susceptibility testing in unveiling coagulase-negative S. aureus strains was undertaken. During a six months study period, 14 staphylococcal isolates from four patients were initially found to lack coagulase activity and to be polymyxin resistant; in comparison, approximately 1500 ordinary, coagulase-positive, polymyxin resistant S. aureus isolates were found during the same period. One isolate from each of the four patients together with a previously isolated coagulase-negative S. aureus strain from our own collection were further characterized. Two of the strains turned out to show delayed coagulase activity on retesting, while the other three strains failed to produce clotting in any coagulase assay. Judged by thermostable nuclease activity, phage typing and biochemical profiles these three coagulase-negative strains are bona fide S. aureus strains. The polymyxin test thus appears to be useful in disclosing S. aureus variants not identified as S. aureus by routinely performed coagulase assays.

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.

Lysogenic conversion for multiple characters in a strain of Staphylococcus aureus

Lysogenization of nonlysogenic strains of Staphylococcus aureus was performed with two different bacteriophages, LS1 and LS2, that were unable to plaque on any of the strains of S. aureus tested. Infection of recipient strains was achieved when protoplasts were inoculated with LS1 or LS2 or when bacterial cultures were simultaneously inoculated with a virulent phage together with LS1 or LS2. Lysogenization was demonstrated by changes in phenotypic characters of the host strain and by liberation of bacteriophages from the modified strains as shown by electron microscopic examination. The lysogenic strains differed from the host strains by the following characters: they were coagulase, deoxyribonuclease, and lipase negative; they were untypable by the basic set of phages; they did not ferment mannitol under anaerobic conditions; and they produced only l-(+)-lactic acid by glucose fermentation. Their cell walls contained less glycine and concomitantly more serine than those of the host strains. Furthermore, they were devoid of protein A. Conversely, some antigenic factors as well as the presence of ribitol in the cell wall teichoic acid, indicated a parental relationship between the host strains and the derived lysogenic ones. Phages LS1 and LS2 could be excluded from the lysogenic strains by invading phages, and the revertant nonlysogenic strains recovered all of the characteristics of the initial host strains. It was thus concluded that the phenomenon described was due to lysogenic conversion. The origin of phages LS1 and LS2 is discussed.

Morphological changes associated with novobiocin resistance in Bacillus licheniformis

Spontaneously occurring novobiocin-resistant (Nov) mutants of Bacillus licheniformis ATCC 9945, resistant to low levels of novobiocin (15 mug/ml), were isolated with a frequency of 3 in 106 organisms. Such isolates grew well, but nearly all exhibited consistent plleiotropic alterations in colonial and cell morphologies. One mutant, nov-12, grew as chains of unseparated but clearly distinct daughter cells in the absence of novobiocin in liquid culture. When novobiocin was present, nov-12 grew as very long "filaments" which were, however, septate. Septa formed in the presence of the antibiotic were normal, except that no annular clevage of the septal wall was observed. Septa were also irregularly positioned along the filament. These observations were compared with previous findings on the effects of novobiocin and novobiocin resistance described for other organisms. It was concluded that the primary action of novobiocin might differ in gram-positive and gram-negative organisms. However, when the low-level novobiocin sensitivity, normally associated with gram-positive organisms, was genetically abolished in Nov strains of B. licheniformis they became susceptible to an action of novobiocin more analogous to that found for gram-negative organisms. The morphological alterations associated with the Nov phenotype in this organism, together with observations in other organisms, indicate that novobiocin resistance might be generally useful in the search for mutants of gram-positive organisms with altered cell walls.

Some properties of coagulase-negative deoxyribonuclease-producing strains of staphylococci from human infections

Twenty-seven coagulase-negative and deoxyribonuclease-positive staphylococci were isolated from more than 3000 specimens from human infections. The strains were tested by conventional biochemical tests and by simple agar plate assays for production of different extracellular enzymes and toxins. Three strains were lysed by S. epidermidis phages and 7 strains by S. aureus phages. All strains produced thermolabile nuclease but only 21 strains produced thermostable nuclease. The investigated strains belonged to a heterogeneous intermediate group sharing characters of S. aureus and S. epidermidis. Tests for production of coagulase and thermostable nuclease should be used in the classification of these intermediate strains in diagnostic bacteriology.

Cell wall composition of novobiocin-resistant pleiotropic mutant staphylococci

Physically purified cell walls were prepared from selected pleiotropic novobiocin-resistant staphylococcal strains. The quantitative amino acid, amino sugar, and phosphorus contents of these walls are reported. This pleiotype was culturally diagnosed by its inability to support the growth of typing phages, inability to release latent bacteriophage, failure to elaborate coagulase, altered sugar catabolic pattern, and resistance to novobiocin. The strains were divided into two groups on the basis of wall composition. The walls of both groups of strains appeared to possess at least two phosphorus-containing polymers. On group of strains contained elevated levels of phosphorus in the cell walls. The second group contained the novel amino sugar galactosamine in the cell walls. This amino sugar is probably associated with one of the phosphorus-containing wall polymers of this group. On the basis of the data presented, it is suggested that the pleiotropy of these strains is the result of genetic change in the control of the biosynthesis of teichoic acids.

Bacteriophage-typable revertants from pleiotropic staphylococcal mutants

Cell walls were physically purified from bacteriophage-typable revertants that had been isolated from modified cell wall pleiotropic strains derived from Staphylococcus aureus NCTC 8511. The quantitative amino acid, amino sugar, and phosphorus contents of these cell walls are reported. Among the revertants were some whose walls possessed elevated serine and one strain whose walls contained the novel amino sugar galactosamine. The similarities in bacteriophage typing patterns between the revertants and the original parental strain lead to the conclusion that the previously described pleiotropic strains are mutants of NCTC 8511.

Deoxyribonucleic acid base composition and biochemical properties of certain coagulase-negative enterotoxigenic cocci

Eight coagulase-negative, enterotoxigenic strains of cocci and one weakly coagulase-positive strain isolated from a number of different sources, including cases of food poisoning incidents, were evaluated for their relationship to Staphylococcus aureus on the basis of deoxyribonucleic acid (DNA) buoyant density and physiological studies. One strain of cocci produced enterotoxins A and C, two strains produced types B and C, four strains produced only type C, and one strain only type D. The enterotoxin produced by one strain of cocci was serologically untypable. None of the test organisms produced detectable amounts of enterotoxin in broth cultures. The test strains of cocci exhibited the following profile: all produced catalase; all grew anaerobically and fermented glucse; five were sensitive to lysostaphin; the percentage of guanine plus cytosine content of their DNA varied from 32.7 to 37.6; five produced acid from mannitol both aerobically and anaerobically; two formed delta-hemolysin; five produced phosphatase and acetoin; and all produced heat-stable nuclease. None of the organisms exhibited typical characteristics of S. aureus, S. epidermidis, or S. saprophyticus. On the basis of the present data and data reported elsewhere, these organisms should be considered as variants or mutants of S. aureus.

In vitro incorporation of serine into the staphylococcal cell wall

A variant of Staphylococcus aureus 44A HJD was isolated by serial growth in Trypticase soy broth to which 2 M serine had been added (wt/vol). Amino acid analysis of hydrolysates of purified mucopeptides from the variant showed that they contained 1.266 serine and 2.156 glycine residues per glutamic acid residue, compared with 0.174 serine and 3.144 glycine residues per glutamic acid residue in the mucopeptide of the parent strain. In addition to this alteration in the chemical composition of the mucopeptide, the variant lost many of the biochemical and cultural characteristics of the parent organism. The variant was not sensitive to the lytic action of lysostaphin and was non-phage-typable. Moreover, in vitro tests indicated that the organism was coagulase negative, did not produce gelatinase or deoxyribonuclease, and did not hemolyze sheep erythrocytes. Apparently due to the change in the serine content in the cell wall of the parent S. aureus strain, the organism had become "epidermidis-like" in its properties.

Pleiotropic alteration of activities of several toxins and enzymes in mutants of Staphylococcus aureus

Pleiotropic alteration of several genetic characters including toxin production was quantitatively shown with a strain of Staphylococcus aureus of phage type 80, 81 which had been given a very specific genetic marker (temperature sensitivity of mannitol fermentation) to avoid confusion by contamination. Thus, alpha-hemolysin hyperproducers obtained by N-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutagenesis were very often hyperproducers of DNase, coagulase, and protease. Their colonies were less yellow than the parent. DNase hyperproducers obtained after NTG mutagenesis were also often hyperproducers of alpha-hemolysin, coagulase, and protease, with colonies less yellow than the parent. Almost all of the revertants obtained by mutagenesis with ethyl methane sulfonate with respect to alpha-hemolysin or DNase were shown to have simultaneously become hypoproducers of alpha-hemolysin, DNase, and protease. Since the pleiotropic alteration of multiple functions was thus quantitatively confirmed, the mechanism underlying this phenomenon should probably be related to a regulatory mechanism common to them.

Polyfunctional penicillinase plasmid in Staphylococcus epidermidis: bacteriophage restriction and modification mutants

Growth of multiply resistant Staphylococcus epidermidis BV strains at 45 C resulted in the independent elimination of tetracycline resistance, of kanamycin resistance coupled with oxacillin resistance, or of penicillinase activity. The pH optimum for the elimination of kanamycin and oxacillin resistance was 5.6, whereas that for elimination of penicillinase activity was 8.0. The genetic determinant for penicillinase activity was linked with the genetic determinants for the active uptake of mannitol and beta-glucosides, ribose fermentation, and phospho beta-glucosidase activity. The penicillinase linkage group also contained determinants for phage adsorption, restriction, and modification, and for growth factor requirements of still unknown nature. The same linkage group, which is apparently of extrachromosomal nature, was eliminated from several S. epidermidis BV strains. By selection for novobiocin resistance, deletion mutants affecting several loci of the penicillinase plasmid were isolated. The isolation of restriction-negative and modification-negative mutants which retained phage susceptibility allowed the investigation of restriction and modification phenomena. A preliminary deletion map of the polyfunctional penicillinase plasmid is proposed.

Use of bacteriophage-resistant mutants to study the nature of the bacteriophage receptor site of Staphylococcus aureus

Bacteriophage-resistant strains of Staphylococcus aureus H were isolated after mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. Cell walls isolated from about half of these resistant strains were incapable of inactivating phages and were shown to lack N-acetyl-d-glucosamine (GlcNAc) in their cell wall teichoic acid. Apart from the lack of GlcNAc, two of these mutant strains were deficient in cell wall phosphorus and ester-linked d-alanine. These two strains were also found to be resistant to both phage K and a host-range mutant isolated from the parent phage. These two phages could lyse the other phage-resistant mutants which lacked GlcNAc in their teichoic acid. Cell walls from the remaining phage-resistant mutant strains did inactivate phages and were found to have normal cell wall teichoic acid. Although GlcNAc in teichoic acid was required for phage inactivation, no difference in phage inactivation ability was detected with cell walls isolated from strains of S. aureus having exclusively alpha- or exclusively beta-linked GlcNAc in their cell wall teichoic acid.

Elevated cell wall serine in pleiotropic staphylococcal mutants

Korman, Ruth Z. (Cornell University, Ithaca, N.Y.). Elevated cell wall serine in pleiotropic staphylococcal mutants. J. Bacteriol. 92:762-768. 1966.-Physically purified cell walls were prepared from two staphylococcal strains and from pleiotropic variants derived from them. The quantitative amino acid and amino sugar content of these walls is reported. The pleiotypes, which are identified culturally by their failure to elaborate coagulase, their resistance to bacteriophage, and their sensitivity to mannitol, have altered molar ratios of amino acids and amino sugars in their cell walls. In comparison with lysine content, the serine content of the mutant wall is elevated and the glycine content is reduced. The glucosamine content is reduced also. It is postulated that the pleiotropic mutants possess an altered cell wall biosynthetic pathway.