Reduction In Bacterial Numbers Research Articles

Inhibition of bacterial fish pathogens by Tetraselmis suecica

Abstract. Supernatants and extracts derived from a commercial heterotrophically grown spray‐dried preparation of Tetraselmis suecica were observed to inhibit Aeromonas hydrophila, A. salmonicida, Lactobacillus sp., Serratia liquefaciens, Staphylococcus epidermidis, Vibrio anguillariim, V. salmonicida and Yersinia ruckeri type I, but not Planococcus sp., Pseudomonas fluorescens, Streptococcus sp., V. ordalii or Y. ruckeri type II by in vitro methods. When used as a food supplement, the algal cells inhibited laboratory‐induced infections in Atlantic salmon. Moreover, there was a reduction in bacterial numbers in tank water. When used therapcutically, algal cells and their extracts reduced mortalities caused by A, salmonicida, Ser. liquefaciens, V. anguillariim, V. salmonicida and Y. ruckeri type I.

Factors affecting the susceptibility of meatborne pathogens and spoilage bacteria to organic acids

The bactericidal effects of lactic and acetic acids were assessed on artificially inoculated lean beef. The test bacteria included cold tolerant pathogens ( Listeria monocytogenes, Yersinia enterocolitica), mesophilic pathogens ( Salmonella typhimurium, Escherichia coli, Campylobacter jejuni and Staphylococcus aureus) and spoilage bacteria ( Pseudomonas fragi and Brochothrix thermosphacta). Acid temperature (20°C, 55°C), acid concentration (1%, 3%) and initial numbers of contaminating bacteria (log CFU/cm 2 of 3–6) were the variables studied. The bactericidal efficacy of organic acids was influenced by two- and three-way interactive effects that were often distinct for each organism. The magnitude of the reductions in bacterial numbers on acid-treated beef was similar with lactic and acetic acids. Bacterial numbers were maximally reduced with 3% acid at 55°C. The variations in the reductions in the numbers of bacteria on acid-treated beef were significantly affected by initial levels of bacterial contamination, but this effect followed no consistent pattern and varied with bacterial species. Of the pathogens tested, S. aureus was the most susceptible to acid (1·4 log cycle reduction) and S. typhimurium the least susceptible (0·4 log cycle reduction). The spoilage bacteria P. fragi (2·3 log cycle reduction) and B. thermosphacta (3·5 log cycle reduction) were more sensitive to the lethal effects of acid treatment than the pathogens.

Bactericidal effects of co-amoxiclav (amoxycillin clavulanic acid) against a Legionella pneumophila pneumonia in the immunocompromised weanling rat.

To evaluate the activity of co-amoxiclav (amoxycillin/clavulanic acid) against Legionella pneumophila in vivo, a model of L. pneumophila pneumonia was developed in weanling rats rendered leukopenic by pre-administration of cyclophosphamide. Assessment of therapy was by lung bacterial counts and histological examination. Amoxycillin was ineffective in reducing bacterial counts in the lungs of infected rats, whereas erythromycin, the standard agent, was significantly more effective (P < 0.01). Co-amoxiclav and erythromycin, administered parenterally, produced significant bactericidal effects (P < 0.01), reducing the counts of L. pneumophila strain 1624 at 96 h to 1.2 log10 cfu/lungs compared with counts of 6 log10 cfu/lungs in the untreated animals. Clavulanic acid was also highly effective in preventing development of the infection, and was as efficacious as co-amoxiclav. Because of the significant reduction in bacterial numbers, a marked reduction in inflammation and consolidation of lung tissue was seen in rats treated with erythromycin, clavulanic acid or co-amoxiclav. The activity of co-amoxiclav was no greater than clavulanic acid alone, and no synergy was noted between the two components. When therapy was delayed until 48 h after infection, co-amoxiclav was as effective as erythromycin, with both treatments reducing bacterial numbers to 3.3 and 3.6 log10 cfu/lungs by 96 h, after only two days of therapy, in comparison with non-treated rats (5.6 log10 cfu/lungs). In a prolonged infection, produced by extending the period of leucopenia, co-amoxiclav and erythromycin were equally effective in preventing growth of the organism, with 1.5 and 1.6 log10 cfu/lungs, respectively, present at 96 h, in contrast to the non-treated rats with 5.7 log10 cfu/lungs (P < 0.01). After cessation of therapy, regrowth of L. pneumophila occurred in the erythromycin-treated group to such a degree that by 168 h, lung viable counts from these rats were significantly higher (4.8 log10 cfu/lungs) than in co-amoxiclav-treated rats (2.1 log10 cfu/lungs) (P < 0.05). Oral therapy of this infection with erythromycin or clavulanic acid, either alone or in combination with amoxycillin, resulted in counts of 3.3, 3.6 and 3.5 log10 cfu/lungs at 96 h, respectively. Although oral therapy was significantly less effective than parenteral therapy (P < 0.05), the bacterial counts in the treated groups were significantly lower than in the non-treated animals. The data show that co-amoxiclav displayed bactericidal activity consistently against intracellular L. pneumophila in vivo.

Oligotrophic bacteria in ultra-pure water systems: Media selection and process component evaluations

Presently, tryptic soy agar (TSA) medium is used in the semiconductor industry to determine the concentration of viable oligotrophic bacteria in ultra-pure water systems. Deionized water from an ultra-pure water pilot plant was evaluated for bacterial growth at specific locations, using a non-selective medium (R2A) designed to detect injured heterotrophic as well as oligotrophic bacteria. Results were compared to those obtained using Tryptic Soy Agar. Statistically greater numbers of bacteria were observed when R2A was used as the growth medium. Total viable bacterial numbers were compared both before and after each treatment step of the recirculating loop to determine their effectiveness in removing bacteria. The reduction in bacterial numbers for the reverse osmosis unit, the ion exchange bed, and the ultraviolet sterilizer were 97.4%, 31.3%, and 72.8%, respectively, using TSA medium, and 98.4%, 78.4%, and 35.8% using R2A medium. The number of viable bacteria increased by 60.7% based on TSA medium and 15.7% based on R2A medium after passage of the water through an in-line 0.2-μm pore size nylon filter, probably because of the growth of bacteria on the filter. Our results suggest that R2A medium may give a better representation of the microbial water quality in ultra-pure water systems and therefore a better idea of the effectiveness of the various treatment processes in the control of bacteria.

Potential for the Low-Temperature Pasteurization of Dairy Fluids Using Membrane Processing

Raw milk, reconstituted skim milk, skim milk, sweet whey, and acid whey were membrane processed on different units from several manufacturers using various membranes with pore sizes ranging from nanofiltration through microfiltration. The bulk fluids were inoculated with either Staphylococcus aureus 196E, Salmonella typhimurium var. Hillfarm, and/or Pseudomonas fragi 4973. In addition, indigenous microorganisms were present. The permeate and retentate streams were monitored for bacterial numbers. Percent total solids of the permeate streams was determined. Temperatures and pressures were controlled. In no cases were the bacteria completely retained while concomitantly allowing permeated solids to equal the solids in the original bulk fluid. Findings indicated different membranes of same molecular weight cut-off exhibited dissimilar bacterial retention characteristics. Unit design/configuration appeared to play a role in retention of bacteria. Spiral wound microfiltration and ultrafiltration membranes reduced bacterial loads in the permeate by 98.9 to 99.99% while allowing 5 to 6% of the solids in the bulk fluid to pass through the membrane. The bulk fluid does not appear to affect the bacterial retention. The different wheys, milks, and reconstituted skim milk showed similar reductions in bacterial numbers when microfiltered or ultrafiltered through the same type of membrane. All three test microbes demonstrated similar declines during membrane processing. It appeared that bacterial morphology and size did not affect the bacterial retention characteristics. Results indicated that low-temperature membrane processing will not eliminate all microorganisms in the permeate nor did all milk components pass through the membrane into the permeate.

The activity in the chicken alimentary tract of bacteriophages lytic for Salmonella typhimurium

Bacteriophages lytic for Salmonella typhimurium were isolated in considerable numbers from thickens experimentally infected with S. typhimurium, and in much lower numbers from the chicken feed. Lytic phages were also regularly isolated from human sewerage systems. One of these was used to inoculate S. typhimurium — infected two day-old chickens orally and via the feed. The phage took longer to establish in the caeca than did the Salmonella and it disappeared when the caecal S. typhimurium counts fell to 10 6 CFU/ml. No neutralizing antibodies to the phage were detected in the serum of these chickens. In a second experiment, five of 30 chickens similarly infected with S. typhimurium were inoculated with the phage. Within 3 days, the phage was isolated from 72% of the “in-contact” birds. A second phage, isolated from sewage, when inoculated into newly-hatched chickens simultaneously with any of 3 strains of S. typhimurium, produced a considerable reduction in mortality in the birds. This effect was only produced by inoculation of high concentrations of phage (> 10 10 PFU/ml). The phage produced reductions in the viable numbers of S. typhimurium in the crop, small intestine and caeca for up to 12 h after inoculation, with smaller reductions in bacterial numbers in the liver at 24 and 48 h after infection.

Cytokine modulation of Mycobacterium lepraemurium infection in mice; Important involvement of tumor necrosis factor, interleukin-2 and dissociation from macrophage activation

Susceptible BALB/c and resistant A/J mice were infected by the intravenous route with 10 7 Mycobacterium lepraemurium (MLM), and mortality was followed in controls and in experimental animals infused i.p. with interleukin-2 (IL-2), tumour necrosis factor alpha (TNFα) and interferon-gamma (IFNγ). BALB/c mice injected with buffer and 10 7 M. lepraemurium i.v. died significantly earlier than A/J mice (111 days vs 158 days, respectively P<0.001), confirming earlier reports. Infusion of IFNγ (1 or 2 μg every day) led to no significant increase in survival of both strains of mice infected with M. lepraemurium. Injection of IL-2 (1 μg/day) led to a moderate increase in survival time in both strains of mice ( P<0.01) although not changing the differences between resistant and susceptible strains of mice. Injection of tumour necrosis factor (1 μg/day) significantly enhanced survival time in both strains ( P<0.001), although all infected mice eventually died. The beneficial effect of IL-2 and TNFα on progression of the disease was seen as a modest reduction in bacterial growth in the lymph nodes and livers of BALB/c mice injected subcutaneously (approximately a one-log reduction in bacterial numbers). There was no evidence that the beneficial effect seen in vivo in mice was related to superior macrophage activation, inasmuch as peritoneal macrophages from untreated infected mice released similar amounts of superoxide anion, upon PMA triggering, as macrophages from infected and cytokine-treated mice. Moreover, macrophages from infected mice responded better to IFNγ than cells from uninfected mice, in terms of developing tumour cytotoxicity in vitro. Indeed, macrophages from mice infected i.v. with MLM for more than 2 weeks developed high killing activity against P815 targets upon IFNγ pulsing, whereas macrophages from normal mice required IFNγ and small doses of LPS to develop similar killing activity. These findings suggest an important role for TNF in resistance to MLM, by an unclear mechanism.

Preservative effect of combinations of acetic acid with lactic or propionic acid on buffalo meat stored at refrigeration temperature

A silverside of buffalo was cut in 15 equal-sized steaks and divided into five groups, each group containing three steaks. The steaks from groups 1,2,3 and 4 were treated with 1, 2, 3 and 4% acetic:lactic acid combinations, respectively, and the fifth group was kept as a control. Similar treatments were also given with acetic: propionic acid mixtures. The microbial analysis and changes in colour and odour were noted at 0, 24, 72 and 168 h. The bacteriostatic and bacteriocidal action of the acid mixtures increased with increasing concentration but the effect was reduced as the time advanced. Both acid mixtures had pronounced antibacterial effect on gram negative organisms than gram positive ones. The 3% acetic: lactic acid combination showed reduction in bacterial numbers without affecting the colour and odour of buffalo meat and is recommended for decontamination and preservation of meat for up to seven days at refrigeration temperature (7 ± 1°C).

Storage Life of Chilled Scallops Treated with Low Dose Irradiation

The effect of low dose irradiation on the chilled storage life of saucer scallops (Amusium balloti) was investigated. Scallops were packed in polythene bags and treated with doses of 1, 0.5, 1.5, and 3 kGy, then stored at 0°C. Sensory assessment indicated that nonirradiated scallops had a storage life of 13 d and this was extended to 18, 23 and 42 d when scallops were treated with 0.5, 1.5, and 3 kGy, respectively. Irradiation resulted in a 2 to 4 log reduction in bacterial numbers from an initial total viable count of 2.5 × 107/g. No irradiation-induced off-odors or off-flavors were detected, but a naturally occurring garlic-like off-flavor was reduced in intensity by irradiation treatment.

Microbiological and Trihalomethane Responses to Booster Chlorination

ABSTRACTTwo zones of a water distribution supply area receiving treated surface water were used to study the effect of booster chlorination on bacterial regrowth. In the first year of the study general patterns of bacterial regrowth were observed, and in the second year one of the areas was booster chlorinated at the outlet from a surface reservoir. In both years of the study the heterotrophic plate counts showed a seasonal pattern. In the second year there was a large increase in plate counts from mid‐July to October in both of the study areas. During this period, booster chlorination was unable to prevent bacterial regrowth. The addition of chlorine to produce an initial free chlorine residual of 0.5 mg/1 resulted in a reduction in bacterial numbers, but with further retention in the distribution system bacterial regrowth occurred. There was little increase in the trihalomethane (THM) concentration following booster chlorination, but booster chlorination appeared to increase the assimilable organic carbon concentration.

Disinfection of bacteria in water systems by using electrolytically generated copper:silver and reduced levels of free chlorine

As an alternative disinfectant to chlorination, electrolytically generated copper:silver (400 and 40 micrograms/L copper and silver, respectively) with and without free chlorine (0.3 mg/L) was evaluated over a period of 4 weeks in indoor and outdoor water systems (100 L tap water with natural body flora and urine). Numbers of total coliform, pseudomonas, and staphylococci were all less than drinking water standards in systems treated with copper:silver and free chlorine and systems treated with free chlorine alone (1.0 mg/L). No significant differences (p less than or equal to 0.05) in bacterial numbers were observed between systems with copper:silver and free chlorine and those with free chlorine alone. Overall, free-chlorine treatments (0.3 or 1.0 mg/L) showed significantly lower heterotrophic plate numbers than those without free chlorine. When challenged with a natural Staphylococcus sp. isolate, water with copper:silver and free chlorine had a 2.4 log10 reduction in bacterial numbers within 2 min, while free chlorine alone or copper:silver alone showed 1.5 and 0.03 log10 reductions, respectively. Addition of copper:silver to water systems may allow the concentration of free chlorine to be reduced while still providing comparable sanitary quality of the water.

Efficacy of copper and silver ions and reduced levels of free chlorine in inactivation of Legionella pneumophila.

Water disinfection systems utilizing electrolytically generated copper and silver ions (200 and 20, 400 and 40, or 800 and 80 micrograms/liter) and low levels of free chlorine (0.1 to 0.4 mg/liter) were evaluated at room (21 to 23 degrees C) and elevated (39 to 40 degrees C) temperatures in filtered well water (pH 7.3) for their efficacy in inactivating Legionella pneumophila (ATCC 33155). At room temperature, a contact time of at least 24 h was necessary for copper and silver (400 and 40 micrograms/liter) to achieve a 3-log10 reduction in bacterial numbers. As the copper and silver concentration increased to 800 and 80 micrograms/liter, the inactivation rate significantly (P less than or equal to 0.05) increased from K = 2.87 x 10(-3) to K = 7.50 x 10(-3) (log10 reduction per minute). In water systems with and without copper and silver (400 and 40 micrograms/liter), the inactivation rates significantly increased as the free chlorine concentration increased from 0.1 mg/liter (K = 0.397 log10 reduction per min) to 0.4 mg/liter (K = 1.047 log10 reduction per min). Compared to room temperature, no significant differences were observed when 0.2 mg of free chlorine per liter with and without 400 and 40 micrograms of copper and silver per liter was tested at 39 to 40 degrees C. All disinfection systems, regardless of temperature or free chlorine concentration, showed increase inactivation rates when 400 and 40 micrograms of copper and silver per liter was added; however, this trend was significant only at 0.4 mg of free chlorine per liter.

Influence of etoposide and cyclophosphamide on the efficacy of cloxacillin and erythromycin in an experimental staphylococcal infection.

The effect of monocytopenia and granulocytopenia on the outgrowth of Staphylococcus aureus as well as on antibiotic efficacy was studied in an experimental thigh infection in mice. Pretreatment with etoposide reduced monocyte numbers in blood to 14% and those of granulocytes to 54% at the time of infection. Monocytopenia did not affect the proliferation of bacteria in the infected thigh or the reduction of bacterial numbers after treatment with cloxacillin or erythromycin. Pretreatment with cyclophosphamide reduced monocyte numbers to 15% and granulocyte numbers to 3%. This resulted in a marked increase in the number of bacteria at the site of infection and a decrease in the efficacy of antibiotic treatment.

Amdinocillin treatment of catheter-associated bacteriuria in rabbits.

The effect of the beta-lactam antibiotic, amdinocillin, on the bacterial biofilm adherent to the Foley catheter surface, the bacterial microcolonies attached to the urinary bladder mucosa, and on planktonic bacteria in the urine was studied in a rabbit model of the closed urinary catheter drainage system. Progressively increasing the dose of antibiotic in this experimental catheter-associated urinary tract infection model first eliminated the bacterial population adherent to the bladder mucosa and then the planktonic population in the urine. The bacterial biofilm on the Foley catheter could be eradicated only by the highest dose of antibiotic (400 mg/kg). Scanning electron microscopy showed a gradual deterioration of bacterial biofilm and reduction in bacterial numbers with increasing antibiotic dosages. These data suggest that antibiotics used in short-term catheterization may reduce the serious sequelae associated with catheter-related infections by clearing the potentially dangerous bladder mucosal bacterial populations and urine planktonic bacteria.

The effect of antimicrobial compounds on the gastrointestinal microflora of rainbow trout, Salmo gairdneri Richardson

Populations of aerobic and anaerobic heterotrophic bacteria occurring in the gastrointestinal tract of healthy rainbow trout were estimated using a dilution plate technique. Data revealed a progressive decline in numbers of aerobic bacteria along the digestive tract from oesophagus to lower intestine. However, the highest numbers were recovered from the intestinal contents and faeces. Anaerobes were generally restricted to the upper intestine and intestinal contents. The aerobic component of the bacterial microflora from the digestive tract was equated with Acinetobacter calcoaceticus, Aeromonas hydrophila, Bacillus circulans, Bac. megaterium, coryneforms, Grampositive irregularly shaped rods, Flavobacterium sp., Kurthia sp., Microhacterium sp., Providencia stuartii, Pseudomonas spp., Ps.fluorescens and Ps. pseudoalcaligenes. Evidence from scanning electron microscopy pointed to a general lack of colonization of the gut wall: instead, microorganisms were abundant in the intestinal contents. Antimicrobial compounds, i.e. oxolinic acid, oxytetracycline and sulphafurazole (which are commonly used to combat infections by Gramnegative bacterial fish pathogens), caused an increase in bacterial numbers throughout the digestive tract, with maximal numbers in the lower intestine. The bacteria, comprising an essentially different range of taxa, were generally resistant to the antibiotics in use. Conversely, erythromycin and penicillin G, which are used to treat some diseases caused by Gram‐positive bacteria, caused a rapid reduction in bacterial numbers within the gastrointestinal tract.

Ultrastructural observations of the process of Agrobacterium tumefaciens biovar 3 infection of grape cv. Chancellor

Ultrastructural observations of Agrobacterium tumefaciens during pathogenesis indicated that the bacteria became pleomorphic and formed inclusions that migrated to polar positions which at lysis were discharged with other cellular contents into the environment of the xylem vessel lumen. Pleomorphism and the development of the inclusions which precede lysis suggest that the lytic process provides a manner in which T-DNA may be released. Lysis also appears to be the cause of the observed large reduction in bacterial numbers detected in xylem vessels 48–60 h after inoculation. In contrast, A. tumefaciens cells in vitro do not lyse during a 60 h incubation period, nor do they form inclusions.

Production of colony-stimulating factors (CSFs) during infection: separate determinations of macrophage-, granulocyte-, granulocyte-macrophage-, and multi-CSFs

After infection of mice with Listeria monocytogenes, elevated levels of colony-stimulating factors (CSFs) in the serum were quantitated by six different assays: ability to stimulate colony formation, the proliferation of 2 suspension of bone marrow cells (both measuring total colony-stimulating activity), a radioimmunoassay for macrophage-CSF (CSF-1), the WEHI-3B differentiation assay for granulocyte-CSF, and proliferation of 32D-c1-3 and FDC-P1 cell lines (specific for multi-CSF and either multi- or granulocyte-macrophage-CSFs, respectively). The great bulk of serum colony-stimulating activity represented macrophage- and granulocyte-CSFs, with small but measurable amounts of granulocyte-macrophage-CSF. The degree of elevation of serum CSF depended on the infecting dose used and the numbers of bacteria growing in the spleens and livers of the two mouse strains compared, i.e., L. monocytogenes-resistant C57BL/10 and susceptible BALB/cJ. The increase in serum CSFs occurred before the peak in bone marrow granulocyte-macrophage progenitors and before the reduction in bacterial numbers which follows the onset of specific cell-mediated immunity.

Zooplankton feeding on size fractionated Microcystis colonies and Chlorella in a hypertrophic lake (Hartbeespoort Dam, South Africa): implications to resource utilization and zooplankton succession

Experiments measuring zooplankton filtration rates on radiolabelled Chlorella and on Microcystis colonies were carried out in situ during both the annual spring Daphnia phase and following the shift to the summer Ceriodaphnia phase in Hartbeespoort Dam. Cladoceran filtration rates on natural Microcystis of discrete colony size-classes (5–20, 20–40, 40–60 and 60–100 μm) were compared with rates measured on cultured Chlorella (∼ 8.5 μm cell diameter). The small bodied cladoceran species Ceriodaphnia reticulata, Moina micrura and Diaphanosoma exasum filtered Microcystis colonies at very low rates compared to Chlorella . Only the largest herbivore Daphnia pulex fed significantly on Microcystis colonies of up to 60–100 μm. Colonies of 100–150 μm were not ingested by any zooplankter tested. Both particle size limitation and low filtration rates on small Microcystis colonies and unicells led to low Daphnia filtration efficiencies and reduced grazing pressure on Microcystis . Suppression of Daphnia filtration rates in situ on Chlorella was evident during the mid-summer increase in Microcystis abundance. Daphnia filtration rates during this period when inedible phytoplankton were abundant were only 25–36% of the maximum filtration, rates measured during the spring clear water phase when the phytoplankton was largely composed of edible species. The aforementioned small cladoceran species exhibited high filtration rates on Chlorella when Microcystis was abundant, suggesting that filtration efficiency of the summer cladoceran community was not reduced by interference from Microcystis colonies. However, their low filtration rate on Microcystis suggests that this is not an important food resource. Concomitant reductions in bacterial numbers and edible phytoplankton food resources available in summer imply that the small body-sized cladoceran community rather relies on the smallest size fraction of the summer food resource.

Enoxacin in lower respiratory tract infections.

In this open, non-comparative study 45 lower respiratory tract infections were treated with the new 4-quinolone, enoxacin. Special attention was paid to infections caused by Pseudomonas aeruginosa. Pseudomonas infections were treated with 600 mg bd. whereas infections caused by other bacteria were treated with 400 mg enoxacin bd. In 43 cases efficacy could be assessed. In six out of 23 cases Pseudomonas spp. were eradicated from the sputum. In 12 of the remaining 17 cases a clear reduction in bacterial numbers and a decrease of sputum volume and purulence were obtained. Clinical improvement or cure was obtained in 20 out of the 23 cases. Most of the causative microorganisms in the other infections were eradicated. In two patients Staphylococcus aureus persisted. Overgrowth with streptococci occurred in three patients. Adverse reactions were frequent and occurred in 29 out of 45 treatment periods. They were mainly related to the gastrointestinal tract and the central nervous system. In 25 out of 30 patients on concomitant treatment with theophylline an elevation of plasma theophylline concentrations occurred. Twelve of these patients developed signs and symptoms possibly related to theophylline toxicity. After treatment with enoxacin the MICs of most persisting Pseudomonas strains were two to four times higher than pre-treatment values.

The virulence of strains of Corynebacterium bovis in the mammary gland of the mouse and the effect of corynebacterial mastitis on subsequent infection with Staphylococcus aureus.

Abstract Strains of Corynebacterium bovis which were isolated from clinically-infected and normal bovine udders showed a spectrum of virulence in the mammary gland of the mouse which was consistent with their origin. C. bovis strain P3 had a predilection for teat keratin and behaved as an environmental organism which casually invaded the mammary gland. A neutrophil infiltration in the mammary gland induced by endotoxin before challenge with strain P3 resulted in a reduction in bacterial numbers, but a neutrophil infiltration after corynebacterial challenge did not result in any reduction. Glands in which a neutrophil response was elicited by infection with a virulent or avirulent strain of C. bovis were subsequently challenged with an avirulent or virulent strain of Staph. aureus respectively. In neither case was the establishment of Staph. aureus prevented by the prior C. bovis infection; nor was there any significant influence on bacterial numbers. The results are discussed in relation to the role of C. bovis in udder infections of dairy cattle.