William J. Meaney

Potential of the Polyvalent Anti-Staphylococcus Bacteriophage K for Control of Antibiotic-Resistant Staphylococci from Hospitals

ABSTRACT The increasing prevalence of antibiotic-resistant staphylococci has prompted the need for antibacterial controls other than antibiotics. In this study, a lytic bacteriophage (phage K) was assessed in vitro for its ability to inhibit emerging drug-resistant Staphylococcus aureus strains from hospitals and other species of Staphylococcus isolated from bovine infections. In in vitro inhibitory assays, phage K lysed a range of clinically isolated methicillin-resistant S. aureus (MRSA) strains, S. aureus with heterogeneous vancomycin resistance and vancomycin resistance, and teicoplanin-resistant strains. In these assays, 14 of the MRSA strains were initially only weakly sensitive to this phage. However, propagation of phage K on these less-sensitive strains resulted in all 14 being sensitive to the modified phages. The results enforce the principle that, while certain target bacteria may be relatively insensitive to lytic phage, this can be overcome by obtaining modified phage variants from passage of the phage through the insensitive strains. Model in situ hand wash studies using a phage-enriched wash solution resulted in a 100-fold reduction in staphylococcal numbers on human skin by comparison with numbers remaining after washing in phage-free solution. Infusion of the phage into a nonimmunogenic bismuth-based cream resulted in strong anti-Staphylococcus activity from the cream on plates and in broth.

Genome of Staphylococcal Phage K: a New Lineage of Myoviridae Infecting Gram-Positive Bacteria with a Low G+C Content

Phage K is a polyvalent phage of the Myoviridae family which is active against a wide range of staphylococci. Phage genome sequencing revealed a linear DNA genome of 127,395 bp, which carries 118 putative open reading frames. The genome is organized in a modular form, encoding modules for lysis, structural proteins, DNA replication, and transcription. Interestingly, the structural module shows high homology to the structural module from Listeria phage A511, suggesting intergenus horizontal transfer. In addition, phage K exhibits the potential to encode proteins necessary for its own replisome, including DNA ligase, primase, helicase, polymerase, RNase H, and DNA binding proteins. Phage K has a complete absence of GATC sites, making it insensitive to restriction enzymes which cleave this sequence. Three introns (lys-I1, pol-I2, and pol-I3) encoding putative endonucleases were located in the genome. Two of these (pol-I2 and pol-I3) were found to interrupt the DNA polymerase gene, while the other (lys-I1) interrupts the lysin gene. Two of the introns encode putative proteins with homology to HNH endonucleases, whereas the other encodes a 270-amino-acid protein which contains two zinc fingers (CX(2)CX(22)CX(2)C and CX(2)CX(23)CX(2)C). The availability of the genome of this highly virulent phage, which is active against infective staphylococci, should provide new insights into the biology and evolution of large broad-spectrum polyvalent phages.

The Recombinant Phage Lysin LysK Has a Broad Spectrum of Lytic Activity against Clinically Relevant Staphylococci, Including Methicillin-Resistant Staphylococcus aureus

This study concerns the cloning, characterization, and expression of the lysin (LysK) from staphylococcal phage K in Lactococcus lactis. Lactococcal lysates containing recombinant LysK were found to inhibit a range of different species of staphylococci isolated from bovine and human infection sources, including methicillin-resistant Staphylococcus aureus. LysK thus has potential as an antimicrobial for applications in the prevention and/or treatment of infections caused by staphylococci.

Fine-structure molecular epidemiological analysis of Staphylococcus aureus recovered from cows.

Sixty-three Staphylococcus aureus isolates recovered from bovine sources in the USA and the Republic of Ireland were characterized by multilocus enzyme electrophoresis (MLEE), ribotyping, and random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) typing at two separate laboratories. The S. aureus isolates were assigned by MLEE to 10 electrophoretic types (ETs) (Index of Discrimination, D = 0.779). In contrast, the same isolates were assigned to 13 ribotypes (D = 0.888), and to 12 RAPD types (D = 0.898). A common clone, ET3, of worldwide distribution, was represented by six distinct combinations of ribotypes and RAPD types. S. aureus clones recovered from cows in Ireland were also associated with mastitis in dairy cows in the USA. These findings are consistent with the hypothesis that only a few specialized clones of S. aureus are responsible for the majority of cases of bovine mastitis, and that these clones have a broad geographic distribution.

Developing applications for lactococcal bacteriocins

While much of the applied research carried out to date with bacteriocins has concerned nisin, lactococci produce other bacteriocins with economic potential. An example is the two component bacteriocin lacticin 3147, which is active over a wide pH range and has a broad spectrum of activity against Gram-positive bacteria. Since the genetic determinants for lacticin 3147 are encoded on a large self-transmissible plasmid, the bacteriocin genes may be conveniently transferred to different lactococcal starters. The resulting food-grade strains can then be used to make a significant impact on the safety and quality of a variety of fermented foods, through the inhibition of undesirable microflora. The bacteriocin is heat stable so it can also be used as an ingredient in a powdered form such as a spray-dried fermentate. Given the observation that lacticin 3147 is effective at physiological pH, there is also considerable potential for biomedical applications. Field trials have demonstrat ed its efficacy in the prevention of mastitis infections in dairy cows. In contrast to lacticin 3147, the lactococcin bacteriocins A, B and M have a narrow spectrum of activity limited to lactococci. Strains which produce these inhibitors can be exploited in the acceleration of cheese ripening by assisting the premature lysis of starter cultures.

Molecular genetic typing reveals further insights into the diversity of animal-associated Staphylococcus aureus.

Staphylococcus aureus is an important pathogen of man, but is also able to colonize and cause disease in a wide variety of mammals and birds. An extended multilocus sequencing approach, involving multilocus sequence typing (MLST), sas typing, spa typing and agr typing, was used to examine the molecular diversity of 118 S. aureus isolates recovered from a range of host species and to compare these data with the known diversity of human-derived isolates. MLST revealed that the commonest animal-associated MLST types were ST133, ST5, ST71, ST97, ST126 and ST151. ST133 appears to be an ungulate-animal-specific genotype, as no evidence of ST133 associating with humans has yet been found in the literature. Novel and unique sas alleles were identified in the animal-associated strains that may represent animal-associated sas alleles. However, sas typing exhibited a lower typeability than MLST for the animal strains (91.3 %). Phylogenetic analyses using neighbour-joining and maximum-parsimony trees localized ruminant-associated MLST lineages to both previously identified S. aureus subspecies aureus subgroups, thus explaining the finding of all four agr types within the ruminant-associated strains. S. aureus isolates recovered from chickens and rabbits were genotypically more similar to known human genotypes than the ruminant-associated lineages.

Molecular population and virulence factor analysis of Staphylococcus aureus from bovine intramammary infection

Staphylococcus aureus isolates from cows in Ireland (n = 102) and the USA (n = 42) were characterized by RAPD‐PCR and analysed for the production of a number of putative virulence factors. Of these strains 63 representative isolates were screened for the corresponding virulence factor genes by PCR or Southern hybridization or both. The isolates were divided into 12 distinct clonal types on the basis of their RAPD fingerprint profiles. Of the isolates, 107 (74·3%) tested positive for clumping factor in a slide agglutination test, all 24 RAPD type 7 isolates being negative for clumping factor. PCR analysis of region R, a repeat region of the clfA gene, revealed eight region‐R sizes. There was a strong association between RAPD type and the clfA region‐R genotype among Irish isolates. Of the RAPD type 7 isolates, 21 (87·5%) coproduced toxic shock syndrome toxin‐1 (TSST‐1) and staphylococcal enterotoxin C (SEC). Over 90% of isolates demonstrated haemolytic activity on sheep or rabbit red blood cells and all isolates harboured the gamma‐haemolysin (hlg) locus. Of the Irish isolates, all those of RAPD type 7 were sensitive to penicillin G, whereas 86% of RAPD types 4 and 5 strains were resistant. Furthermore, RAPD types 5 and 7 were more likely to be associated with clinical mastitis whereas RAPD type 4 isolates were more often associated with a latent infection. The current study identifies some of the putative virulence factors produced by the predominant clonal types of bovine Staph. aureus that may be considered as components of a vaccine.

Inhibition of bacteriophage K proliferation on Staphylococcus aureus in raw bovine milk

Aims:  To assess the ability of staphylococcal bacteriophage K to inhibit Staphylococcus aureus in raw milk.

Intramammary infusion of a live culture of Lactococcus lactis for treatment of bovine mastitis: comparison with antibiotic treatment in field trials

A treatment containing a live food-grade organism, Lactococcus lactis DPC3147, was compared with conventional antibiotic therapy for its potential to treat bovine chronic subclinical or clinical mastitis in two separate field trials. Effects on disease symptoms and bacteriology were monitored in response to infusion with the culture in each trial. In the first trial, the live culture treatment was compared with an intramammary antibiotic (n=11 quarters for each treatment). Results from this small trial demonstrated that the live culture had potential to be as effective at eliminating chronic subclinical infections as an antibiotic treatment. By day 12, 7 of the 11 quarters treated with the live culture were pathogen-free compared with 5 of the 11 antibiotic-treated infected quarters. Somatic cell counts (SCC) remained relatively unchanged regardless of treatment: average log SCC pre- and post-treatment in the lactococci-treated group were 6.33+/-0.41 (day 0) and 6.27+/-0.43 cells/ml (day 12) and average log SCC pre- and post-treatment in the antibiotic-treated group were 6.34+/-0.37 and 6.22+/-0.46 cells/ml on day 0 and on day 12, respectively. In the second trial, the live culture was compared with an intramammary antibiotic for the treatment of naturally occurring clinical mastitis cases (n=25 quarters for each treatment). Following a 14-d experimental period, similar bacteriological responses were observed in 7 out of 25 live culture treated quarters and 9 out of 25 antibiotic-treated quarters. Additionally, 15 of 25 cases treated with the culture and 18 of 25 cases treated with the antibiotic did not exhibit clinical signs of the disease following treatment. The results of these trials suggest that live culture treatment with Lc. lactis DPC3147 may be as efficacious as common antibiotic treatments in some instances.

Heterogeneity of proteolytic enzyme activities in milk samples of different somatic cell count.

Milk contains the alkaline proteinase plasmin and lysosomal proteinases; the significance of the latter is ill-defined. The objective of this study was to investigate composition and activities of several different proteolytic enzymes in milk samples of varying somatic cell count (SCC). Increasing milk SCC was correlated with increased plasmin, cathepsin D and cysteine protease activities, with concomitant increases in proteolysis in milk. Addition of plasmin inhibitors confirmed the heterogeneity of proteinase activities in milk, as urea-PAGE analysis of milk samples showed casein hydrolysis in milk after 7 d storage even in samples with inhibitors added; extent and heterogeneity of proteolysis was correlated with milk SCC. Rennet coagulation properties were not significantly correlated with SCC, or activities of measured enzymes. Milk of increasing SCC also exhibited decreased physical stability during incubation of milk at 37 degrees C. Pasteurized milk was more stable than raw milk, suggesting that the enzyme(s) or mechanisms leading to such instability are impaired by pasteurization. Overall, milk has a very heterogeneous proteolytic enzyme population, with a higher significance of non-plasmin enzymes, such as cathepsin D and cysteine proteinases, than perhaps previously recognised.