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PubMed1992

Expression and regulation of the antimonite, arsenite, and arsenate resistance operon of Staphylococcus xylosus plasmid pSX267.

The arsenate, arsenite, and antimonite resistance region of the Staphylococcus xylosus plasmid pSX267 was subcloned in Staphylococcus carnosus. The sequenced DNA region revealed three consecutive open reading frames, named arsR, arsB, and arsC. Expression studies in Escherichia coli with the bacteriophage T7 RNA polymerase-promoter system yielded three polypeptides with apparent molecular weights of 8,000, 35,000, and 15,000, which very likely correspond to ArsR, ArsB, and ArsC, respectively. ArsB was distinguished by its overall hydrophobic character, suggesting a membrane association. The arsenate, arsenite, and antimonite resistance was shown to be inducible by all three heavy metal ions. Inactivation of the first gene, arsR, resulted in constitutive expression of resistance. Similar results were obtained with transcriptional fusions of various portions of the ars genes with a lipase reporter gene, indicating a function of ArsR as a negative regulator of a putative promoter in front of arsR. The inactivation of arsR also resulted in reduction of resistance to arsenite and antimonite, while arsenate resistance was unaffected. The three ars genes conferred arsenite resistance in E. coli and arsenite as well as arsenate resistance in Bacillus subtilis.

Adenosine Triphosphatases↗

PubMed1992

Regulation and expression of the arsenic resistance operon from Staphylococcus aureus plasmid pI258.

The arsenic resistance operon from Staphylococcus aureus plasmid pI258 was cloned and sequenced. The DNA sequence contains three genes in the order arsR, arsB, and arsC. The predicted amino acid sequences of the gene products are homologous with those of the products of the ars operons of plasmids pSX267 from Staphylococcus xylosus and R773 from Escherichia coli. The cloned staphylococcal ars operon confers resistances to arsenate, arsenite, and antimonite in S. aureus and Bacillus subtilis. The same operon was also expressed in E. coli and conferred resistance to arsenite but less resistance to arsenate and antimonite. Regulation of the pI258 ars operon was studied by using a translational arsB-blaZ fusion in S. aureus and a transcriptional arsB-luxAB fusion in E. coli. The ars operon was induced by arsenate [As(V)], arsenite [As(III)], and antimonite [Sb(III)], to which the strains were resistant, plus Bi(III) in S. aureus. Only arsenate and arsenite induced the operon in E. coli. Northern (RNA) blot DNA-RNA hybridization analysis showed inducible synthesis of a full-length ars mRNA, about 2.1 kb in size, both in S. aureus and in E. coli. S. aureus ars proteins were expressed in E. coli from the T7 phage promoter under the control of the T7 RNA polymerase. Primer extension (reverse transcriptase) analysis showed that the ars mRNA started at the same position (nucleotides 17 and 18 upstream from the arsR ATG) both in S. aureus and in E. coli. An internal deletion mutation in arsB resulted in decreased resistance to arsenate and total loss of arsenite and antimonite resistances. Partial deletion of 56 bp from the 3' end of the arsC gene resulted in loss of resistance to arsenate; the determinant retained arsenite and antimonite resistances.

Adenosine Triphosphatases↗

PubMed1994

Biochemical properties of a novel metalloprotease from Staphylococcus hyicus subsp. hyicus involved in extracellular lipase processing.

Two extracellular proteases from Staphylococcus hyicus subsp. hyicus, ShpI and ShpII, have been characterized. ShpI is a neutral metalloprotease with broad substrate specificity; the gene has been cloned and sequenced. ShpII, characterized here, is mainly produced in the late logarithmic growth phase in contrast to ShpI, which is mainly produced in the late stationary growth phase. ShpII was purified from culture medium of S. hyicus by ammonium sulfate precipitation and DEAE-Sepharose chromatography. The molecular mass, estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was 34 kDa. The temperature optimum of ShpII was 55 degrees C, and the pH optimum was 7.4. ShpII, a neutral metalloprotease, was strongly inhibited by zinc and calcium chelators. The amino-terminal sequence of the active enzyme was similar to the corresponding region of a Staphylococcus epidermidis metalloprotease. The substrate specificity of ShpII was similar to that of thermolysin-like proteases, with the exception that ShpII also recognized aromatic amino acids. We demonstrated in vitro that ShpII, but not ShpI, cleaved the 86-kDa S. hyicus subsp. hyicus prolipase between Thr-245 and Val-246 to generate the mature 46-kDa lipase. Results of additional in vivo experiments supported the model that ShpII is necessary for the extracellular processing and maturation of S. hyicus subsp. hyicus lipase.

Amino Acid Sequence↗

PubMed1995

Staphylococcus haemolyticus contains two D-glutamic acid biosynthetic activities, a glutamate racemase and a D-amino acid transaminase.

Two D-glutamic acid biosynthetic activities, glutamate racemase and D-amino acid transaminase, have been described previously for bacteria. To date, no bacterial species has been reported to possess both activities. Genetic complementation studies using Escherichia coli WM335, a D-glutamic acid auxotroph, and cloned chromosomal DNA fragments from Staphylococcus haemolyticus revealed two distinct DNA fragments containing open reading frames which, when present, allowed growth on medium without exogenous D-glutamic acid. Amino acid sequences of the two open reading frames derived from the DNA nucleotide sequences indicated extensive identity with the amino acid sequence of Pediococcus pentosaceous glutamate racemase in one case and with that of the D-amino acid transaminase of Bacillus spp. in the second case. Enzymatic assays of lysates of E. coli WM335 strains containing either the cloned staphylococcal racemase or transminase verified the identities of these activities. Subsequent DNA hybridization experiments indicated that Staphylococcus aureus, in addition to S. haemolyticus, contained homologous chromosomal DNA for each of these genes. These data suggest that S. haemolyticus, and probably S. aureus, contains genes for two D-glutamic acid biosynthetic activities, a glutamate racemase (dga gene) and a D-amino acid transaminase (dat gene).

Amino Acid Isomerases↗

PubMed1997

Purification and molecular characterization of glycylglycine endopeptidase produced by Staphylococcus capitis EPK1.

A novel staphylolytic enzyme, ALE-1, acting on Staphylococcus aureus, was purified from a Staphylococcus capitis EPK1 culture supernatant. The optimal pH range for staphylolytic activity was 7 to 9. ALE-1 contains one Zn2+ atom per molecule. Analysis of peptidoglycan fragments released by ALE-1 indicated that the enzyme is a glycylglycine endopeptidase. The effects of various modulators were determined, and we found that o-phenanthroline, iodoacetic acid, diethylpyrocarbonate, and Cu2+ reduced the staphylolytic activity of ALE-1. beta-Casein, elastin, and pentaglycine were poor substrates for ALE-1. Molecular cloning data revealed that ALE-1 is composed of 362 amino acid residues and is synthesized as a precursor protein which is cleaved after Ala at position 35, thus producing a mature ALE-1 of 35.6 kDa. The primary structure of mature ALE-1 is very similar to the proenzyme form of lysostaphin. It has the modular design of an N-terminal domain of tandem repeats of a 13-amino-acid sequence fused to the active site containing C-terminal domain. Unlike lysostaphin, ALE-1 does not undergo processing of the N-terminal repeat domain in broth culture. ale-1 is encoded on the plasmid. Protein homology search suggested that ALE-1 and lysostaphin are members of the novel Zn2+ protease family with a homologous 38-amino-acid-long motif, Tyr-X-His-X(11)-Val-X(12/20)-Gly-X(5-6)-His.

Amino Acid Sequence↗

PubMed1998

Influence of Lif, the lysostaphin immunity factor, on acceptors of surface proteins and cell wall sorting efficiency in Staphylococcus carnosus.

Proteins harboring a C-terminal cell wall sorting signal are covalently linked to pentaglycine acceptors within the staphylococcal peptidoglycan. This pentaglycine was modified when the lysostaphin immunity factor (Lif) of Staphylococcus simulans was expressed in Staphylococcus carnosus, likely by the exchange of two glycine residues for serine residues. A reporter protein was efficiently linked to the modified acceptor, indicating that the sorting reaction is not strictly dependent on the wild-type structures of the acceptors.

Anti-Bacterial Agents↗

PubMed1998

Genetic organization of the mecA region in methicillin-susceptible and methicillin-resistant strains of Staphylococcus sciuri.

A homolog of the Staphylococcus aureus methicillin resistance gene mecA was recently shown to be ubiquitous in independent isolates of the animal species Staphylococcus sciuri. The mecA gene homolog and regions flanking it were cloned and sequenced from four strains of S. sciuri: strain K1 (ATCC 29062), a representative of S. sciuri subsp. sciuri; two strains (K3 and K8) representing S. sciuri subsp. rodentius; and strain K11, a representative of S. sciuri subsp. carnaticum. Strains K1 and K11 were susceptible to methicillin, while strains K3 and K8 showed heterogeneous resistance. The mecA genes of strains K1 and K11 and one of the two copies of mecA (mecA1) present in strain K3 had virtually identical DNA sequences in the mecA gene and were similar in genetic organization in the flanking regions. In contrast, the single copy of mecA in strain K8 and the second copy of mecA (mecA2) in strain K3 had mecA DNA sequences identical to that of S. aureus mecA, and the mecA region in these two strains was also similar to that of the same region in the S. aureus strain used for comparison. Interestingly, an open reading frame defining an N-terminal truncated polypeptide, NTORF101, with a high degree of homology to a DNA segment in the hypervariable region of methicillin-resistant S. aureus (and also similar to the Escherichia coli gene ugpQ) was also identified downstream of the mecA homolog of strain K11, representing S. sciuri subsp. carnaticum. The ugpQ-like gene is not present in methicillin-susceptible strains of S. aureus. The presence of such a ugpQ-like gene together with the homolog of mecA in strain K11 supports the speculation that these genetic elements may be evolutionary relatives and/or precursors of the genetic determinant of methicillin resistance in S. aureus.

Amino Acid Sequence↗

PubMed1999

Adherence of Staphylococcus aureus is enhanced by an endogenous secreted protein with broad binding activity.

A novel mechanism for enhancement of adherence of Staphylococcus aureus to host components is described. A secreted protein, Eap (extracellular adherence protein), was purified from the supernatant of S. aureus Newman and found to be able to bind to at least seven plasma proteins, e.g., fibronectin, the alpha-chain of fibrinogen, and prothrombin, and to the surface of S. aureus. Eap bound much less to cells of Staphylococcus epidermidis, Streptococcus mutans, or Escherichia coli. The protein can form oligomeric forms and is able to cause agglutination of S. aureus. Binding of S. aureus to fibroblasts and epithelial cells was significantly enhanced by addition of Eap, presumably due to its affinity both for plasma proteins on the cells and for the bacteria.

Bacterial Adhesion↗

PubMed2001

Biofilm formation by Staphylococcus epidermidis depends on functional RsbU, an activator of the sigB operon: differential activation mechanisms due to ethanol and salt stress.

Staphylococcus epidermidis is a common pathogen in medical device-associated infections. Its major pathogenetic factor is the ability to form adherent biofilms. The polysaccharide intercellular adhesin (PIA), which is synthesized by the products of the icaADBC gene cluster, is essential for biofilm accumulation. In the present study, we characterized the gene locus inactivated by Tn917 insertions of two isogenic, icaADBC-independent, biofilm-negative mutants, M15 and M19, of the biofilm-producing bacterium S. epidermidis 1457. The insertion site was the same in both of the mutants and was located in the first gene, rsbU, of an operon highly homologous to the sigB operons of Staphylococcus aureus and Bacillus subtilis. Supplementation of Trypticase soy broth with NaCl (TSB(NaCl)) or ethanol (TSB(EtOH)), both of which are known activators of sigB, led to increased biofilm formation and PIA synthesis by S. epidermidis 1457. Insertion of Tn917 into rsbU, a positive regulator of alternative sigma factor sigma(B), led to a biofilm-negative phenotype and almost undetectable PIA production. Interestingly, in TSB(EtOH), the mutants were enabled to form a biofilm again with phenotypes similar to those of the wild type. In TSB(NaCl), the mutants still displayed a biofilm-negative phenotype. No difference in primary attachment between the mutants and the wild type was observed. Similar phenotypic changes were observed after transfer of the Tn917 insertion of mutant M15 to the independent and biofilm-producing strain S. epidermidis 8400. In 11 clinical S. epidermidis strains, a restriction fragment length polymorphism of the sigB operon was detected which was independent of the presence of the icaADBC locus and a biofilm-positive phenotype. Obviously, different mechanisms are operative in the regulation of PIA expression in stationary phase and under stress induced by salt or ethanol.

Bacterial Proteins↗

PubMed2002

The superoxide dismutase gene sodM is unique to Staphylococcus aureus: absence of sodM in coagulase-negative staphylococci.

Superoxide dismutase (SOD) profiles of clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci (CoNS) were determined by using whole-cell lysates and activity gels. All S. aureus clinical isolates exhibited three closely migrating bands of activity as previously determined for laboratory strains of S. aureus: SodM, SodA, and a hybrid composed of SodM and SodA (M. W. Valderas and M. E. Hart, J. Bacteriol. 183:3399-3407, 2001). In contrast, the CoNS produced only one SOD activity, which migrated similarly to SodA of S. aureus. Southern analysis of eight CoNS species identified only a single sod gene in each case. A full-length sod gene was cloned from Staphylococcus epidermidis and determined to be more similar to sodA than to sodM of S. aureus. Therefore, this gene was designated sodA. The deduced amino acid sequence of the S. epidermidis sodA was 92 and 76% identical to that of the SodA and SodM proteins of S. aureus, respectively. The S. epidermidis sodA gene expressed from a plasmid complemented a sodA mutation in S. aureus, and the protein formed a hybrid with SodM of S. aureus. Both hybrid SOD forms as well as the SodM and SodA proteins of S. aureus and the S. epidermidis SodA protein exist as dimers. These data indicate that sodM is found only in S. aureus and not in the CoNS, suggesting an important divergence in the evolution of this genus and a unique role for SodM in S. aureus.

Amino Acid Sequence↗

PubMed2003

Development of methicillin resistance in clinical isolates of Staphylococcus sciuri by transcriptional activation of the mecA homologue native to s.

The beta-lactam resistance gene mecA was acquired by Staphylococcus aureus from an extraspecies source. The search for the possible origin of this gene has led to the identification of a close structural homologue of mecA as a native gene in the animal species Staphylococcus sciuri. Surprisingly, the overwhelming majority of S. sciuri isolates were fully susceptible to beta-lactam antibiotics in spite of the ubiquitous presence of the mecA homologue in the bacteria. We now describe two unusual S. sciuri strains isolated from humans-SS-37 and SS-41-that showed resistance to methicillin associated with high rates of transcription of the mecA homologue and production of a protein resembling penicillin binding protein 2a, the gene product of S. aureus mecA. In strain SS-37 increased transcription of the mecA homologue was related to insertion of an IS256 element upstream of the structural gene, and strain SS-41 had single nucleotide alterations in the promoter region of the mecA homologue which appear to be related to up-regulation of the rate of transcription. A third methicillin-resistant human isolate of S. sciuri that carries both the native mecA homologue and a methicillin-resistant S. aureus (MRSA) type mecA, strain K3, was now shown to be unstable in the absence of drug selection, causing the segregation of antibiotic-susceptible cells accompanied by the loss of the MRSA type mecA. These observations illustrate the remarkable variety of strategies available to bacteria for acquiring mechanisms of drug resistance in the in vivo environment.

Bacterial Proteins↗

PubMed2004

High-resolution structure of the histidine-containing phosphocarrier protein (HPr) from Staphylococcus aureus and characterization of its interaction with the bifunctional HPr kinase/phosphorylase.

A high-resolution structure of the histidine-containing phosphocarrier protein (HPr) from Staphylococcus aureus was obtained by heteronuclear multidimensional nuclear magnetic resonance (NMR) spectroscopy on the basis of 1,766 structural restraints. Twenty-three hydrogen bonds in HPr could be directly detected by polarization transfer from the amide nitrogen to the carbonyl carbon involved in the hydrogen bond. Differential line broadening was used to characterize the interaction of HPr with the HPr kinase/phosphorylase (HPrK/P) of Staphylococcus xylosus, which is responsible for phosphorylation-dephosphorylation of the hydroxyl group of the regulatory serine residue at position 46. The dissociation constant Kd was determined to be 0.10 +/- 0.02 mM at 303 K from the NMR data, assuming independent binding. The data are consistent with a stoichiometry of 1 HPr molecule per HPrK/P monomer in solution. Using transversal relaxation optimized spectroscopy-heteronuclear single quantum correlation, we mapped the interaction site of the two proteins in the 330-kDa complex. As expected, it covers the region around Ser46 and the small helix b following this residue. In addition, HPrK/P also binds to the second phosphorylation site of HPr at position 15. This interaction may be essential for the recognition of the phosphorylation state of His15 and the phosphorylation-dependent regulation of the kinase/phosphorylase activity. In accordance with this observation, the recently published X-ray structure of the HPr/HPrK core protein complex from Lactobacillus casei shows interactions with the two phosphorylation sites. However, the NMR data also suggest differences for the full-length protein from S. xylosus: there are no indications for an interaction with the residues preceding the regulatory Ser46 residue (Thr41 to Lys45) in the protein of S. xylosus. In contrast, it seems to interact with the C-terminal helix of HPr in solution, an interaction which is not observed for the complex of HPr with the core of HPrK/P of L. casei in crystals.

Amino Acids↗

PubMed2004

The teicoplanin-associated locus regulator (TcaR) and the intercellular adhesin locus regulator (IcaR) are transcriptional inhibitors of the ica locus in Staphylococcus aureus.

Infections involving Staphylococcus aureus are often more severe and difficult to treat when the organism assumes a biofilm mode of growth. The polysaccharide poly-N-acetylglucosamine (PNAG), also known as polysaccharide intercellular adhesin, is synthesized by the products of the intercellular adhesin (ica) locus and plays a key role in biofilm formation. Numerous conditions and exogenous factors influence ica transcription and PNAG synthesis, but the regulatory factors and pathways through which these environmental stimuli act have been only partially characterized. We developed a DNA affinity chromatography system to purify potential regulatory proteins that bind to the ica promoter region. Using this technique, we isolated four proteins, including the staphylococcal gene regulator SarA, a MarR family transcriptional regulator of the teicoplanin-associated locus TcaR, DNA-binding protein II, and topoisomerase IV, that bound to the ica promoter. Site-directed deletion mutagenesis of tcaR indicated that TcaR was a negative regulator of ica transcription, but deletion of tcaR alone did not induce any changes in PNAG production or in adherence to polystyrene. We also investigated the role of IcaR, encoded within the ica locus but divergently transcribed from the biosynthetic genes. As has been shown previously in Staphylococcus epidermidis, we found that IcaR was also a negative regulator of ica transcription in S. aureus. We also demonstrate that mutation of icaR augmented PNAG production and adherence to polystyrene. Transcription of the ica locus, PNAG production, and adherence to polystyrene were further increased in a tcaR icaR double mutant. In summary, TcaR appeared to be a weak negative regulator of transcription of the ica locus, whereas IcaR was a strong negative regulator, and in their absence PNAG production and biofilm formation were enhanced.

Acetylglucosamine↗

PubMed2005

SarA is an essential positive regulator of Staphylococcus epidermidis biofilm development.

Staphylococcus epidermidis biofilm formation is associated with the production of the polysaccharide intercellular adhesin (PIA)--poly-N-acetylglucosamine polysaccharide (PNAG) by the products of the icaADBC operon. Recent evidence indicates that SarA, a central regulatory element that controls the production of Staphylococcus aureus virulence factors, is essential for the synthesis of PIA/PNAG and the ensuing biofilm development in this species. Based on the presence of a sarA homolog, we hypothesized that SarA could also be involved in the regulation of the biofilm formation process in S. epidermidis. To investigate this, we constructed nonpolar sarA deletions in two genetically unrelated S. epidermidis clinical strains, O-47 and CH845. The SarA mutants were completely defective in biofilm formation, both in the steady-state conditions of a microtiter dish assay and in the flow conditions of microfermentors. Reverse transcription-PCR experiments showed that the mutation in the sarA gene resulted in downregulation of the icaADBC operon transcription in an IcaR-independent manner. Purified SarA protein showed high-affinity binding to the icaA promoter region by electrophoretic mobility shift assays. Consequently, mutation in sarA provoked a significant decrease in the amount of PIA/PNAG on the cell surface. Furthermore, heterologous complementation of S. aureus sarA mutants with the sarA gene of S. epidermidis completely restored biofilm formation. In summary, SarA appeared to be a positive regulator of transcription of the ica locus, and in its absence, PIA/PNAG production and biofilm formation were diminished. Additionally, we present experimental evidence showing that SarA may be an important regulatory element that controls S. epidermidis virulence factors other than biofilm formation.

Acetylglucosamine↗

PubMed2006

Cross-linked peptidoglycan mediates lysostaphin binding to the cell wall envelope of Staphylococcus aureus.

Staphylococcus simulans bv. staphylolyticus secretes lysostaphin, a bacteriocin that cleaves pentaglycine cross bridges in the cell wall of Staphylococcus aureus. The C-terminal cell wall-targeting domain (CWT) of lysostaphin is required for selective binding of this bacteriocin to S. aureus cells; however, the molecular target for this was unknown. We used purified green fluorescent protein fused to CWT (GFP-CWT) to reveal species-specific association of the reporter with staphylococci. GFP-CWT bound S. aureus cells as well as purified peptidoglycan sacculi. The addition of cross-linked murein, disaccharides linked to interconnected wall peptides, blocked GFP-CWT binding to staphylococci, whereas murein monomers or lysostaphin-solubilized cell wall fragments did not. S. aureus strain Newman variants lacking the capacity for synthesizing polysaccharide capsule (capFO), poly-N-acetylglucosamine (icaAC), lipoprotein (lgt), cell wall-anchored proteins (srtA), or the glycolipid anchor of lipoteichoic acid (ypfP) bound GFP-CWT similar to wild-type staphylococci. A tagO mutant strain, defective in the synthesis of polyribitol wall teichoic acid attached to the cell wall envelope, displayed increased GFP-CWT binding. In contrast, a femAB mutation, reducing both the amount and the length of peptidoglycan cross-linking (monoglycine cross bridges), showed a dramatic reduction in GFP-CWT binding. Thus, the CWT domain of lysostaphin directs the bacteriocin to cross-linked peptidoglycan, which also serves as the substrate for its glycyl-glycine endopeptidase domain.

Cell Wall↗

PubMed1963

ROLE OF ALPHA-TOXIN IN LESION FORMATION BY STAPHYLOCOCCUS AUREUS ON SUTURES SUBCUTANEOUSLY IMPLANTED IN MICE.

Taubler, James H. (University of Pennsylvania, Philadelphia), Frank A. Kapral, and Stuart Mudd. Role of alpha-toxin in lesion formation by Staphylococcus aureus on sutures subcutaneously implanted in mice. J. Bacteriol. 86:51-57. 1963.-Evidence was obtained that alpha-hemolysin is essential for the development of purulent lesions by several strains of Staphylococcus aureus adsorbed onto sutures subcutaneously implanted in mice. This evidence consisted of findings that active immunization with staphylococcal toxoid afforded significant protection to subcutaneous challenge with this organism and that alpha-hemolysin-negative mutants, derived from strains 18Z and P78, were almost devoid of the ability to produce lesions by this route of infection. However, other unknown factors also appear to be essential for lesion formation since passive immunization of mice with antialpha-toxin, obtained from rabbits immunized with purified toxin, failed to afford protection. A dose-response curve for this type of infection is also presented.

Animals↗

PubMed1964

Factors affecting growth of Staphylococcus aureus L forms on semidefined medium.

Banville, Robert R. (The Catholic University of America, Washington, D.C.). Factors affecting growth of Staphylococcus aureus L forms on semidefined medium. J. Bacteriol. 87:1192-1197. 1964.-A semidefined agar medium was found suitable for production and cultivation of the L form of Staphylococcus aureus. In semidefined liquid medium, growth of the L form took place in the form of a sediment containing large masses of cells, but heavy and diffuse growth occurred in the same medium with 0.05% agar. The optimal pH for L-colony formation on solid medium was 6.5. More L colonies developed on 0.75% agar than at higher agar concentrations. L colonies developed in greater numbers on pour plates than on streak plates, and in some cases more L colonies appeared under anaerobic incubation. L-colony formation appeared to be inhibited by sodium citrate. The vitamin requirements of the L forms studied were similar to those of the classical form.

Agar↗

PubMed1965

Inactivation of cephalothin and cephaloridine by Staphylococcus aureus.

Benner, Ernest J. (University of Washington School of Medicine, Seattle), John V. Bennett, Jean L. Brodie, and William M. M. Kirby. Inactivation of cephalothin and cephaloridine by Staphylococcus aureus. J. Bacteriol. 90:1599-1604. 1965.-Marked differences were observed in the susceptibility of penicillinase-producing staphylococci to cephalothin and cephaloridine. All of 100 strains of penicillin G-resistant Staphylococcus aureus, with the use of a large inoculum, were found to be susceptible to 2 mug/ml of cephalothin, whereas only 50% were susceptible to this concentration of cephaloridine, and 15% required 15 mug/ml or more for inhibition. In contrast, penicillin G-sensitive strains were more susceptible to cephaloridine and did not show the marked inoculum effect observed with the cephaloridine-resistant strains. These differences were due to a much greater destruction of cephaloridine than of cephalothin by staphylococcal penicillinase. Cephaloridine-resistant staphyloccoci were stronger penicillinase producers than were susceptible strains, and the resistant strains were found to inactivate cephaloridine by hydrolysis of the beta-lactam ring. In population studies, cephaloridine-resistant cells differed from methicillin-resistant cells in that they decreased in numbers as the drug concentration was increased, and the survivors in higher drug concentrations were no more resistant than was the parent strain. Treatment with acriflavine eliminated resistance of the cells to both penicillin G and cephaloridine. It was concluded that cephaloridine resistance was due to hydrolysis by penicillinase, and that this was related to the pyridine ring substitution in the cephalosporanic acid nucleus.

Anti-Bacterial Agents↗