Encapsulation of coagulase-negative staphylococci of bovine origin

Capsule expression was assessed in six coagulase-negative staphylococcal strains in serum-soft agar and by india ink and electron microscopy. Classification of strains as encapsulated by serum-soft agar and india ink methods differed. Staphylococcus chromogenes, Staph. hyicus, and Staph. simulans grew as diffuse colonies in serum-soft agar and unstained halos were detected in india ink preparations. Staphylococcus hominis and Staph. simulans grew as diffuse colonies in serum-soft agar but no unstained halo was seen in india ink preparations. Staphylococcus hyicus was the only strain that gave negative results with serum-soft agar and india ink assays. Conventional electron microscopy revealed the presence of capsular polysaccharides on the cell surface of Staph. chromogenes, Staph. hominis and Staph. hyicus. Conventional electron microscopic technique used to examine the surface of cells was detrimental to capsule structure. During dehydration the capsule collapsed and appeared as electron dense aggregates at the surface of cells. To confirm results of conventional electron microscopy and to visualize clearly the cell surface, encapsulated Staph. hyicus and unencapsulated Staph. simulans were observed after freeze-fracture and etching by scanning electron microscopy. The fibrous nature of capsular polysaccharides surrounding cells of Staph. hyicus were distinct and confirmed observation by conventional electron microscopy. A rapid transmission electron microscopic technique is described also for observation of capsule. Results of the rapid TEM method agreed with conventional TEM and SEM. The finding that coagulase-negative staphylococci isolated from bovine milk are capable of capsule production may be important when investigating pathogenicity of these micro-organisms.

Effect of naturally occurring coagulase-negative staphylococci infections on new infections by mastitis pathogens in the bovine

Microbiological data from 1123 uninfected quarters and 216 quarters with preexisting coagulase-negative staphylococci infections were analyzed to determine the influence of infection status on subsequent new infection rate. Overall, prevalence of new infections in uninfected quarters was approximately two times that in quarters already harboring a coagulase-negative Staphylococcus infection. New infections by coagulase-negative staphylococci were greater in uninfected quarters than in quarters with preexisting coagulase-negative staphylococci infections. However, no differences were observed between uninfected and infected quarters in number of new infections by major pathogens (Staphylococcus aureus, streptococci, and coliforms). No differences were observed in uninfected or coagulase-negative Staphylococcus-infected quarters in infections with minor pathogens compared with major pathogens. The influence of individual coagulase-negative Staphylococcus species on new infections was also analyzed. However, numbers of existing infections by Staphylococcus species other than Staphylococcus chromogenes were limited. Therefore, the protective capacity of each coagulase-negative Staphylococcus species was difficult to assess. Overall, a significant restriction of bacterial invasion was observed in quarters with a preexisting infection. These results suggest that quarters harboring a coagulase-negative Staphylococcus infection suppress colonization of the mammary gland by mastitis-causing pathogens.

Expression of glycocalyx by coagulase-negative Staphylococcus species isolated from bovine milk

Two hundred and six strains of coagulase-negative Staphylococcus species were assessed for expression of glycocalyx on serum soft agar, india ink and adherence techniques. The organisms were maintained on trypticase soy agar plates at 4 degrees C for 30 d (120 strains) or stored at -80 degrees C in skim milk for 90 d (60 strains). Additionally, 26 milk samples from cows known to have excreted coagulase-negative staphylococci were used to inoculate serum soft agar directly. Nine of 26 direct culture samples and 43 of 180 strains maintained for an extended period had diffuse-type growth on serum soft agar. The proportion that exhibited an unstained halo by india ink was similar regardless of storage time. Slime production determined by in vitro adherence revealed a higher proportion of positive strains than had been predicted by serum soft agar or india ink techniques. More strains of Staphylococcus chromogenes, Staph. epidermidis, Staph. hominis, Staph. simulans and Staph. warneri expressed glycocalyx than other coagulase-negative Staphylococcus species. These results suggest that most coagulase-negative staphylococci produce slime rather than a capsule. However, evidence for classical encapsulation was demonstrated in several strains by india ink. The finding that Staphylococcus species other than Staph. aureus isolated from bovine milk are capable of glycocalyx production may be of importance in investigations on the relationship between staphylococci and host defence mechanisms.

Evaluation of two fluorogenic assays for identification of Streptococcus species isolated from bovine mammary glands

Liquid and agar assays that utilized 4-methylumbelliferyl-conjugated beta-D-glucuronide, beta-D-galactoside, or N-acetyl-beta-D-glucosaminide, and agglutination by Dolichos biflorus lectin were evaluated for identification of Streptococcus species isolated from bovine mammary glands. A greater number of Streptococcus uberis isolates were negative for N-acetyl-beta-D-glucosaminidase by the liquid assay compared with the agar assay. Enzyme profiles for Streptococcus dysgalactiae were similar by both assays. Streptococcus dysgalactiae was the only species that agglutinated when mixed with lectin from D. biflorus. Most Streptococcus agalactiae isolates were positive for beta-D-glucuronidase and beta-D-galactosidase by both assays. Two Streptococcus equinus strains had negative enzyme profiles by the liquid assay; however, both strains had enzyme profiles consistent for S. equinus by the agar method. Incorporation of 4-methylumbelliferyl-conjugated substrates into trypticase soy agar did not appear to alter agar characteristics and eliminated aliquoting substrates and inoculating tubes. More than one enzyme profile was produced per Streptococcus species or serogroup by both methods. However, some profiles were similar between species, which hindered accurate identification of Streptococcus species.

Comparative evaluation of Vitek gram-positive identification system and API Rapid Strep system for identification of Streptococcus species of bovine origin

The Vitek Gram-positive identification system (GPI, Vitek Systems, Inc., Hazelwood, MO) and the API Rapid Strep system (Analytab Products, Plainview, NY) were evaluated for species identification of streptococci isolated from bovine mammary glands and compared to conventional biochemical methods. A total of 144 strains including Streptococcus uberis (60), S. dysgalactiae (32), S. agalactiae (15), S. bovis (15), Enterococcus faecium (10) and Ent. faecalis (12) were evaluated. All reference strains were identified correctly by both systems. Vitek GPI card system identified 94.4% of strains, including 95% of S. uberis, 93.8% of S. dygalactiae, 93.3% of S. agalactiae and S. bovis II, 90% of Ent. faecium and 100% of Ent. faecalis. Majority of strains were identified with a 90-99% level of confidence, with an average of 8 h needed for identification. The API Rapid Strep system identified 96.5% of strains correctly, including 95% of S. 96.9% of S. dysgalactiae, 93.3% of S. agalactiae, and 100% of S. bovis II, Ent. faecium, and Ent. faecalis. Majority of strains were identified with excellent level of identification. With the exception of S. uberis, most strains were identified at 4 h of incubation.

Duplicative activation mechanisms of two trypanosome telomeric VSG genes with structurally simple 5' flanks

In the mammalian bloodstream, African trypanosomes express variant surface glycoprotein (VSG) genes from a family of long and complex telomeric expression sites. VSG switching generally occurs by the duplication of different VSG genes into these sites by gene conversion involving a series of 70 base pair (70bp) repeats in the 5' flank. In contrast, when VSG is first synthesised by trypanosomes in the tsetse fly at the metacyclic stage, a separate set of telomeric expression sites is activated. These latter telomeres appear not to act as recipients in gene conversion. We have found that the structure of two such expression sites is simple, with very short 70bp repeat regions and very little other sequence in common with bloodstream expression sites. However, the two telomeres readily act as donors in VSG gene conversion in the bloodstream and we show for one a consistent association of the conversion 5' end point with the short 70bp repeat region. These findings help explain why a very predictable set of VSGs is expressed in the tsetse fly and have implications for VSG gene conversion mechanisms.

Protective effect of Staphylococcus chromogenes infection against Staphylococcus aureus infection in the lactating bovine mammary gland

The susceptibility of uninfected or Staphylococcus chromogenes-infected quarters to challenge with Staphylococcus aureus was measured. Seventeen S. chromogenes-infected quarters were challenged by infusion of S. aureus into the teat sinus; 47% (8 of 17) became infected and all 18 uninfected quarters challenged similarly with S. aureus became infected. No differences in daily milk yield were seen between uninfected quarters and S. chromogenes-infected quarters prior to S. aureus infusion. Postinfusion, milk yield for S. aureus-infected, S. chromogenes-infected, and S. chromogenes- and S. aureus-infected quarters differed. Somatic cell counts were elevated in S. chromogenes-infected quarters compared with uninfected quarters prior to S. aureus infusion. Somatic cell counts were not different between S. aureus- and S. chromogenes- and S. aureus-infected quarters postinfusion, but were different for S. chromogenes-infected quarters. Chloride concentrations in S. chromogenes- and S. aureus-infected quarters were different from either S. aureus-infected or S. chromogenes-infected quarters. Staphylococcus aureus colony forming units in quarters with preexisting S. chromogenes infections were lower than S. aureus colony-forming units in previously uninfected quarters. Possible protective mechanisms induced by S. chromogenes against superinfection by S. aureus are discussed.

Distinct, developmental stage-specific activation mechanisms of trypanosome VSG genes

The metacyclic form of African trypanosomes is the first to express genes for the Variant Surface Glycoprotein (VSG) and it uses an unusually predictable subset of the VSG gene repertoire. We have developed a model system for the analysis of metacyclic VSG (M-VSG) gene expression and have used this to demonstrate that, for two M-VSG genes, different modes of expression operate in the insect and mammalian phases of the life-cycle. In metacyclic-derived clones, these genes are expressed in situ, whereas they are routinely activated by duplication in bloodstream trypanosomes. The expression loci for both M-VSG genes studied are structurally simple and we present a model, based on this, for the maintenance of a separate M-VSG repertoire and expression system.

Efficacy of chlorhexidine as a postmilking teat disinfectant for the prevention of bovine mastitis during lactation

A natural exposure trial was conducted for 12 mo in a herd of 150 lactating Jersey cows to determine efficacy of a .35% chlorhexidine teat dip containing a glycerine emollient for the prevention of bovine intramammary infections. Right teats of cows were dipped in the experimental teat dip after milking machine removal and left teats were not dipped. The herd was free of Streptococcus agalactiae and had a low prevalence of Staphylococcus aureus. Most new major pathogen intramammary infections resulted from Streptococcus species, primarily Streptococcus uberis and Streptococcus dysgalactiae. New infections by Streptococcus species were significantly lower in teats dipped in chlorhexidine than in undipped teats. Overall efficacy of the chlorhexidine teat dip against major mastitis pathogens was 50%. The experimental teat dip also reduced coagulase-negative Staphylococcus species infections 49.0% and Corynebacterium bovis infections 65.2%. Overall efficacy against minor mastitis pathogens was 54.0%. No irritation or chapping of teats dipped in the experimental teat dip was observed.

Comparison of Vitek Gram-Positive Identification system with API Staph-Trac system for species identification of staphylococci of bovine origin

Staphylococci (n = 130) of bovine origin representing 14 species were evaluated. Agreements of Vitek and API systems with conventional methods were 44.6 and 80.8%, respectively. The poor performance of the Vitek system was attributed primarily to inability to identify S. chromogenes. Incorporation of additional veterinary strains into the Vitek data base is needed to increase accuracy.

Use of latex teat dip with germicide during the prepartum period

The efficacy of an acrylic latex barrier teat dip with germicide on new infections at parturition was tested on 113 cows and heifers during the prepartum period. A split udder design was used in which right quarters were undipped controls and left quarters were dipped with latex dip once daily for approximately 14 d prior to parturition. Distal streak canal swabs were taken from all quarters prior to the beginning of dipping, and all cows were quarter sampled in duplicate at drying off, parturition, and the first 5 consecutive wk of lactation. All quarters received antibiotic therapy at drying off. Excluding infections detected by distal streak canal swabs, the number of new infections at parturition in control and dipped quarters was 32 and 36. New infections at parturition in control and dipped quarters were Staphylococcus aureus, 2 and 2; coagulase-negative staphylococci, 8 and 9; stretptococci, 10 and 12; coliforms, 8 and 8; and others, 4 and 5. Differences were not significant. These results suggest no benefit to use of prepartum latex teat dip with germicide on new infections at parturition.