In vitro antimicrobial activity of fluoroquinolones against clinical isolates obtained in 1989 and 1990

The in vitro activity of nine fluoroquinolones, enoxacin, norfloxacin, ofloxacin, ciprofloxacin, lomefloxacin, tosufloxacin, sparfloxacin, fleroxacin and levofloxacin, and two earlier quinolones, nalidixic acid and pipemidic acid, against 1,346 bacterial strains isolated clinically between 1989 and 1990, was evaluated by agar dilution method. The bacteria studied were Staphylococcus aureus (including methicillin-susceptible and -resistant strains), Staphylococcus epidermidis, Enterococcus species (including high-level gentamicin-resistant strains), Escherichia coli, Salmonella species, Proteus mirabilis, Proteus vulgaris, Morganella morganii, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Citrobacter spp., Pseudomonas aeruginosa, Pseudomonas cepacia, Acinetobacter baumannii, and Bacteroides fragilis. In contrast to the moderate to poor activity of two earlier quinolones, the fluoroquinolones acted well against most Enterobacteriaceae and A. baumannii. The minimum inhibitory concentrations for 90% of the drug strains (MIC90s) were < 1 microgram/mL against most tested species. Ciprofloxacin, tosufloxacin, sparfloxacin, and levofloxacin were more effective against multi-drug-resistant nosocomial pathogens. All fluoroquinolones assayed were very active against methicillin-susceptible S. aureus, with MIC90s < or = 1 microgram/mL. For methicillin-resistant strains, on the other hand, the MIC90s were > or = 4 micrograms/mL. There was no significant difference in fluoroquinolone susceptibility between methicillin-susceptible and -resistant S. epidermidis. Sparfloxacin, tosufloxacin, ciprofloxacin and levofloxacin were more active against enterococci. Most fluoroquinolones were relatively inactive against B. fragilis, with the exception of tosufloxacin, sparfloxacin and levofloxacin. The MIC90s of most quinolones assayed against K. pneumoniae, Citrobacter spp., E. cloacae, S. aureus and S. epidermidis were at least four-fold higher in our study. Therefore, it is important for physicians to use fluoroquinolones carefully so as to prevent or delay the emergence of resistant strains.     

Spontaneous intracranial hypotension: clinical and magnetic resonance imaging characteristics

OBJECTIVE: To evaluate the antimicrobial susceptibility pattern of oxacillin susceptible (OSSA) and resistant Staphylococcus aureus (ORSA) isolates to other antimicrobial agents that can be used for the treatment of staphylococcal infections. MATERIAL AND METHOD: We evaluated 117 clinical S. aureus isolates from several S?o Paulo hospitals. Clinical isolates from Campinas, SP and from Jo?o Pessoa, PB, were also included. The in vitro susceptibility testing was performed by broth microdilution as described by the National Committee for Clinical Laboratory Standards (NCCLS). The minimum inhibitory concentration (MIC) was evaluated for 24 antimicrobial agents, including beta-lactams, fluoroquinolones, aminoglycosides, glycopeptides, macrolides, lincosamides and streptogramins. Both commercially available and experimental drugs were included in the study. Cross-resistance among fluoroquinolones was evaluated by susceptibility testing 24 isolates to 10 fluoroquinolones. RESULTS: The antimicrobial agents that showed the highest in vitro activity were the glycopeptides, the streptogramin RP-59.500, and the mupirocin (100% susceptibility). Eighty-seven percent of the OSSA and only 38% of the ORSA isolates were susceptible to ciprofloxacin (MIC50 0.25 microgram/mL and > 4 micrograms/mL, respectively). Cross-resistance among fluoroquinolones were noted even for the experimental drugs. Two fluoroquinolones remained active against ciprofloxacin-resistant isolates, clinafloxacin and WIN-57.273. However, the ciprofloxacin-resistant isolates had MICs eight-to 64-fold higher than the ciprofloxacin-susceptible isolates, suggesting that the MICs may continue to increase when these fluoroquinolones become commercially available. CONCLUSION: Our results showed a high rate of antimicrobial resistance among S. aureus from the Brazilian hospitals. Very few drugs can still be used for the treatment of staphylococcal infections.     

Craniotomy procedures are associated with less analgesic requirements than other surgical procedures

NorA is a membrane-associated multidrug efflux protein that can decrease susceptibility to fluoroquinolones in Staphylococcus aureus. To determine the effect of NorA inhibition on the pharmacodynamics of fluoroquinolones, we evaluated the activities of levofloxacin, ciprofloxacin, and norfloxacin with and without various NorA inhibitors against three genetically related strains of S. aureus (SA 1199, the wild-type; SA 1199B, a NorA hyperproducer with a grlA mutation; and SA 1199-3, a strain that inducibly hyperproduces NorA) using susceptibility testing, time-kill curves, and postantibiotic effect (PAE) methods. Levofloxacin had the most potent activity against all three strains and was minimally affected by addition of NorA inhibitors. In contrast, reserpine, omeprazole, and lansoprazole produced 4-fold decreases in ciprofloxacin and norfloxacin MICs and MBCs for SA 1199 and 4- to 16-fold decreases for both SA 1199B and SA 1199-3. In time-kill experiments reserpine, omeprazole, or lansoprazole increased levofloxacin activity against SA 1199-3 alone by 2 log10 CFU/ml and increased norfloxacin and ciprofloxacin activities against all three strains by 0.5 to 4 log10 CFU/ml. Reserpine and omeprazole increased norfloxacin PAEs on SA 1199, SA 1199B, and SA 1199-3 from 0.9, 0.6, and 0.2 h to 2.5 to 4.5, 1.1 to 1.3, and 0.4 to 1.1 h, respectively; similar effects were observed with ciprofloxacin. Reserpine and omeprazole increased the levofloxacin PAE only on SA 1199B (from 1.6 to 5.0 and 3.1 h, respectively). In conclusion, the NorA inhibitors dramatically improved the activities of the more hydrophilic fluoroquinolones (norfloxacin and ciprofloxacin). These compounds may restore the activities of these fluoroquinolones against resistant strains of S. aureus or may potentially enhance their activities against sensitive strains.     

Comparative activities of clinafloxacin, grepafloxacin, levofloxacin, moxifloxacin, ofloxacin, sparfloxacin, and trovafloxacin and nonquinolones linozelid, quinupristin-dalfopristin, gentamicin, and vancomycin against clinical isolates of ciprofloxacin-resistant and -susceptible Staphylococcus aureus strains

The activities of eight fluoroquinolones and linezolid, quinupristin-dalfopristin (Synercid), gentamicin, and vancomycin were tested against 96 ciprofloxacin-susceptible and 205 ciprofloxacin-resistant Staphylococcus aureus strains. Overall, clinafloxacin, followed by moxifloxacin and trovafloxacin, was the most active quinolone tested. For all isolates, linezolid and quinupristin-dalfopristin showed activities that were at least comparable to vancomycin, with no cross-resistance to any other test compound.     

Ofloxacin. A reappraisal of its use in the management of genitourinary tract infections

Ofloxacin is an established fluoroquinolone agent which achieves good concentrations in genitourinary tract tissues and fluids. It has good in vitro activity against most Enterobacteriaceae, Staphylococcus saprophyticus, methicillin-susceptible S. aureus, Neisseria gonorrhoeae, Chlamydia trachomatis and Haemophilus ducreyi, intermediate activity against Ureaplasma urealyticum and most enterococci, but limited or no in vitro activity against enterococci, Serratia marcescens, Pseudomonas aeruginosa and many anaerobes. However, high concentrations achieved in the urine ensure its activity against most urinary tract pathogens. Ofloxacin demonstrates consistent efficacy in a broad range of urinary tract infections, achieving bacteriological response rates in excess of 80% in uncomplicated and 70% in complicated infections. The efficacy of ofloxacin was similar to that of all comparators tested including other fluoroquinolones, cephalosporins and cotrimoxazole (trimethoprim/sulfamethoxazole). Ofloxacin is also effective as a single-dose regimen in the treatment of uncomplicated gonorrhoea, as a 7-day regimen in uncomplicated C. trachomatis infections, and as monotherapy in uncomplicated pelvic inflammatory disease (PID). Again, ofloxacin demonstrated similar efficacy to alternative treatments in each type of infection. The availability of an intravenous formulation and near-complete oral bioavailability allow ofloxacin to be administered as a sequential regimen without loss of activity. The tolerability and drug interaction profile of ofloxacin is consistent with that of other fluoroquinolones. The most commonly reported adverse events with ofloxacin are gastrointestinal, neurological and dermatological. It was associated with a lower incidence of photosensitivity and tendinitis and higher incidence of some neurological events than some other fluoroquinolones. Ofloxacin seems to have a lower propensity to interact with xanthines than other fluoroquinolones. Conclusion: ofloxacin has established efficacy in the treatment of a wide variety of urinary tract infections, although, like other fluoroquinolones, it should be used rationally to preserve its activity. Currently, ofloxacin also holds an important place among fluoroquinolones in the treatment of C. trachomatis infections and uncomplicated PID, although its acceptance as monotherapy in PID is likely to depend on clarification of the causative role of anaerobic pathogens in this infection.     

Role of horn flies (Haematobia irritans) in Staphylococcus aureus-induced mastitis in dairy heifers

OBJECTIVE: To determine whether Staphylococcus aureus can colonize in horn flies and whether colonization is sufficiently persistent for transmission of the organism to cows by flies. ANIMALS: 2 Jersey heifers exposed to infected horn flies. PROCEDURE: Staphylococcus aureus was allowed to colonize in horn flies, and duration of colonization was determined. Flies with colonized S aureus were allowed to feed on teats of uninfected heifers to determine whether intramammary infection could be transmitted from fly to heifer. Scab material from naturally infected heifers was submitted for bacteriologic culture to determine whether S aureus was present and whether scabs could serve as a possible source of S aureus for flies. RESULTS: Staphylococcus aureus colonized in horn flies and remained for up to 96 hours after exposure. Exposure of teats of uninfected heifers to horn flies colonized with S aureus resulted in intramammary infection in 3 of 4 exposed teats. Culture of scab material from teats of naturally infected heifers revealed high concentration of S aureus (> 107 colony-forming units/mg), and flies without previously colonized S aureus were allowed to feed on scabs; S aureus colonized in them just as readily as it did in flies that had fed on experimentally infected blood. CONCLUSIONS: Horn flies are capable of transmitting S aureus-induced intramammary infection to heifers, and scabs on teats are a potential source of S aureus. Fly control on dairy cows in herds with known S aureus problems is recommended as a method to help prevent these infections.     

Efflux pump-mediated quinolone resistance in Staphylococcus aureus strains wild type for gyrA, gyrB, grlA, and norA

Fluoroquinolone efflux was studied in 47 Staphylococcus aureus clinical strains with MICs of ciprofloxacin (CFX) of < or = 2 micrograms/ml. Forty-three strains were wild type for gyrA, gyrB, and grlA quinolone resistance-determining regions and for norA and its promoter region. Forty of these strains (MICs of CFX, 0.1 to 0.2 microgram/ml) did not show efflux of fluoroquinolones. Three strains (MICs of CFX, 1 to 2 micrograms/ml) showed efflux. These results suggest that efflux can appear in S. aureus clinical strains in the absence of mutations in norA and its promoter.     

The postantibiotic effect of fusidic acid against gram-positive bacteria

The in-vitro postantibiotic effect (PAE) of fusidic acid was tested for six strains of Staphylococcus aureus and four strains of Streptococcus pyogenes. The maximum PAE that could be achieved was more than 3 h, but at concentrations of antibiotic attainable in humans, the PAE was less than 2 h. Additional experiments were performed in albumin, to examine the effect of the strong protein binding of fusidic acid on the MIC and PAE. MICs were increased, but at the same multiple of the MIC, PAEs were similar to those performed in Mueller-Hinton broth.     

The fluoroquinolones as treatment for infections caused by gram-positive bacteria

The fluoroquinolones have become attractive options as treatment for a broad range of infections caused by Gram-negative bacteria. However, the value of these antibiotics to patients with infections caused by Gram-positive pathogens remains controversial. Experience with quinolones as therapy for skin and skin structure infections, osteomyelitis and peritonitis in patients receiving continuous ambulatory peritoneal dialysis suggests that the concerns which have been expressed about the use of these agents against methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis and streptococci are justified; indeed, the frequent emergence of quinolone-resistant strains of MRSA and coagulase-negative staphylococci either during or following treatment is now well documented. The fluoroquinolones should be prescribed with caution to patients with community-acquired pneumonia or whenever severe infection of pneumococcal aetiology is proven or suspected. As prophylaxis for the granulocytopenic patient, quinolones such as norfloxacin and ciprofloxacin have been shown to be effective in reducing the incidence of morbidity attributable to Gram-negative bacteria, but they have not significantly affected the incidence of infection caused by Gram-positive bacteria. In the treatment of febrile episodes in the neutropenic patient, ciprofloxacin, the quinolone investigated most extensively in this clinical setting, produced high cure rates only when it was combined with an antibiotic which was predictably active against Gram-positive organisms. We review here the role of currently-available fluoroquinolones (norfloxacin, enoxacin, pefloxacin, ofloxacin and ciprofloxacin) as treatment for these and other infections.     

Antibacterial activity of gatifloxacin (AM-1155, CG5501, BMS-206584), a newly developed fluoroquinolone, against sequentially acquired quinolone-resistant mutants and the norA transformant of Staphylococcus aureus

Alternate mutations in the grlA and gyrA genes were observed through the first- to fourth-step mutants which were obtained from four Staphylococcus aureus strains by sequential selection with several fluoroquinolones. The increases in the MICs of gatifloxacin accompanying those mutational steps suggest that primary targets of gatifloxacin in the wild type and the first-, second-, and third-step mutants are wild-type topoisomerase IV (topo IV), wild-type DNA gyrase, singly mutated topo IV, and singly mutated DNA gyrase, respectively. Gatifloxacin had activity equal to that of tosufloxacin and activity more potent than those of norfloxacin, ofloxacin, ciprofloxacin, and sparfloxacin against the second-step mutants (grlA gyrA; gatifloxacin MIC range, 1.56 to 3.13 microg/ml) and had the most potent activity against the third-step mutants (grlA gyrA grlA; gatifloxacin MIC range, 1.56 to 6.25 microg/ml), suggesting that gatifloxacin possesses the most potent inhibitory activity against singly mutated topo IV and singly mutated DNA gyrase among the quinolones tested. Moreover, gatifloxacin selected resistant mutants from wild-type and the second-step mutants at a low frequency. Gatifloxacin possessed potent activity (MIC, 0.39 microg/ml) against the NorA-overproducing strain S. aureus NY12, the norA transformant, which was slightly lower than that against the parent strain SA113. The increases in the MICs of the quinolones tested against NY12 were negatively correlated with the hydrophobicity of the quinolones (correlation coefficient, -0.93; P < 0.01). Therefore, this slight decrease in the activity of gatifloxacin is attributable to its high hydrophobicity. Those properties of gatifloxacin likely explain its good activity against quinolone-resistant clinical isolates of S. aureus harboring the grlA, gyrA, and/or norA mutations.     

Clonal heterogeneity, distribution, and pathogenicity of methicillin-resistant Staphylococcus aureus

Four thousand eighty-eight Staphylococcus aureus isolates obtained from patients hospitalised in a university clinic and four community hospitals over a period of one year were screened for methicillin resistance. A resistance rate of 5% was detected among initial isolates. Distribution of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus showed an increased prevalence of MRSA in clinically significant specimens such as blood, central venous catheter tips, bronchial secretions, and wound secretions. Typing of 110 MRSA strains (initial isolates) by macrorestriction analysis of chromosomal DNA revealed 26 different genotypes that could be divided into five epidemic and 21 sporadic strains. More than 50% of all isolates belonged to one type that was confirmed to be closely related to the "southern-German" epidemic strain. Production of virulence factors such as enterotoxin A-D and toxic shock syndrome-toxin 1 among MRSA strains (initial isolates) occurred in ten of 26 different MRSA types. A strong correlation between genotype and toxin production was demonstrated.     

Synthesis and antimicrobial activity of new tetrahydro-2H-1,3,5-thiadiazine-2-thione derivatives

A series of 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazine-2-thiones was synthesized and evaluated for antibacterial and antifungal activity. All of the tested compounds were found active against Staphylococcus aureus and Staphylococcus epidermidis. The compounds were also active against yeast-like fungi and molds where the anticandidal activity of 3a against Candida albicans was superior to the standards miconazole and clotrimazole.     

Bactericidal activity of trovafloxacin (CP-99,219)

Trovafloxacin was found to be a typical quinolone producing a biphasic dose response against Escherichia coli, Staphylococcus aureus or Streptococcus pneumoniae. A reduced rate of kill was seen against Enterococcus faecalis, which is also typical of the quinolones. However, the bactericidal activity of trovafloxacin against S. aureus and S. pneumoniae was greater than most other quinolones previously tested. The enhanced bactericidal activity of trovafloxacin against S. aureus may be explained by the possession of a very strong bactericidal mechanism B. Trovafloxacin may prove to be a quinolone of choice against S. aureus infections.     

Facile total synthesis and antimicrobial activity of the marine fatty acids (Z)-2-methoxy-5-hexadecenoic acid and (Z)-2-methoxy-6-hexadecenoic acid

The total synthesis of the naturally occurring (Z)-2-methoxy-5-hexadecenoic acid and (Z)-2-methoxy-6-hexadecenoic acid was accomplished using as a key step Mukaiyama's trimethylsilyl cyanide addition to 4- and 5-pentadecenal, respectively. These syntheses further confirm the structures of the natural marine fatty acids and corroborate their cis double-bond stereochemistry. The title compounds were antimicrobial against the Gram-positive bacteria Staphylococcus aureus (MIC 0.35 micromol/mL) and Streptococcus faecalis (MIC 0.35 micromol/mL).     

The lipase from Staphylococcus aureus. Expression in Escherichia coli, large-scale purification and comparison of substrate specificity to Staphylococcus hyicus lipase

The genes coding for the mature part of the lipases from Staphylococcus aureus NCTC8530 and Staphylococcus hyicus have been cloned and overexpressed in Escherichia coli as fusion proteins with an N-terminal hexa-histidine tag. The enzymes accumulated in the cytoplasm and were purified using sequential precipitation with protamine sulphate and ammonium sulphate, followed by metal-affinity and hydroxyapatite chromatography. The yield of pure lipase was 4.5 mg/g wet cells for S. aureus lipase and 13 mg/g for S. hyicus lipase. The purified enzymes need calcium for activity, albeit with different affinities, and a low residual activity was found in the absence of calcium. In contrast to S. hyicus lipase, not only strontium but also barium can replace calcium with full retention of activity of S. aureus lipase. Whereas S. hyicus lipase is optimally active at pH 8.5, the optimum pH for enzymatic activity for S. aureus lipase was found to be pH 6.5. The S. aureus lipase has a narrow substrate specificity: short-chain triacylglycerols and acyl esters of both p-nitrophenol and umbelliferone are readily degraded, whereas medium- and long-chain lipids, as well as phospholipids, are poor substrates. In contrast, S. hyicus lipase prefers phospholipids as substrate and hydrolyses neutral lipids irrespective of their chain length. The results are discussed in view of the large sequence similarity between both lipases.     

Prevalence of Staphylococcus aureus among food handlers from a metropolitan university in Chile

BACKGROUND: An important agent of food intoxication is Staphylococcus aureus, that is able to produce enterotoxins. AIM: To detect Staphylococcus aureus contamination in cafeteria food handlers of a Chilean University. SUBJECTS AND METHODS: Nose, throat, hands and nail samples from 87 food handlers were obtained for microbiological examination. RESULTS: Fifty seven subjects (65.5%) were carriers of Staphylococcus aureus. Enterotoxigenic Staphylococcus aureus was found in 36 subjects (41%). The most frequently found enterotoxin was type B (18 samples) followed by type D (12 samples). Men bad a higher frequency of contamination than women (83 and 57% of positive samples respectively). CONCLUSIONS: The frequency of Staphylococcus aureus contamination among food handlers is high and should prompt personal and environmental hygienic measures.     

Antimicrobial activity of fluoroquinolones and other antibiotics on 1,116 clinical gram-positive and gram-negative isolates

A total of 1,116 clinically isolated strains belonging to Staphylococcus aureus (200), Staphylococcus epidermidis (200), Streptococcus pneumoniae (20), Escherchia coli (200), Klebsiella spp. (177), Serratia marcescens (22), Pseudomonas aeruginosa (224), Haemophilus influenzae (35) and Salmonella (38) from the Department of Infectious Diseases, La Sapienza University in Rome (Italy) were tested against three fluoroquinolones (ofloxacin, ciprofloxacin and levofloxacin) and 10 other antibiotics (augmentin, ampicillin, cefaclor, cefixime, cefotaxime, cotrimoxazole, gentamicin, minocycline, oxacillin and vancomycin). Fluoroquinolones inhibited essentially about 100% of H. influenzae, Salmonella and S. pneumoniae, more than 75% of Staphylococcus including methicillin-resistant strains, and about 90% of Enterobacteriaceae and 50% of P. aeruginosa. Minimal inhibitory concentration values ranged from < 0.015 to > 32 micrograms/ml for Klebsiella, S. aureus and epidermidis, E. coli and P. aeruginosa; from < 0.015 to 2 micrograms/ml for Salmonella; from 0.03 to 16 micrograms/ml for Serratia; from < 0.015 to 1 microgram/ml for Haemophilus; and from 0.5 to 2 micrograms/ml for S. pneumoniae. Levofloxacin and to a lesser extent ofloxacin and ciprofloxacin, generally exhibited a greater activity than the other agents against both Gram-positive and Gram-negative bacteria. Regarding the distribution of resistant strains in Italy, we found a peculiar pattern of resistance as far as E. coli and P. aeruginosa were concerned. Quality control parameters are also summarized. S. epidermidis resulted as a new emergent pathogen especially in immunocompromised patients and its level of sensitivity has been modified over the last few years. In fact, the percentage of resistant strains to antibiotics or the percentage of methicillin-resistant isolates (in our study 35%), has gradually increased. Levofloxacin and ofloxacin showed good activity against staphylococcal strains compared with the majority of other antibiotics. These results suggest that the newer quinolones are promising antimicrobial agents for various infections.     

Bacteria inhibit biosynthesis of bone matrix proteins in human osteoblasts

The effect of extracts from Staphylococcus aureus and Staphylococcus epidermidis on bone matrix production were assessed by analyzing the biosynthesis of osteocalcin and Type I collagen in a human osteoblastic osteosarcoma cell line (MG-63). In MG-63 cells, extracts from Staphylococcus aureus and Staphylococcus epidermidis decreased 1,25(OH)2-vitamin D3 stimulated osteocalcin biosynthesis, and insulin-like growth factor I induced production of Type I collagen in a concentration dependent manner. The basal rate of osteocalcin and Type I collagen formation was unaffected by the bacterial extracts. The inhibitory effect of the bacteria on osteocalcin biosynthesis was seen after 24 hours of treatment and was maintained for at least 96 hours. The extracts of Staphylococcus aureus and Staphylococcus epidermidis enhanced prostaglandin E2 formation in the MG-63 cells. Abolition of the prostaglandin E2 response by treatment with indomethacin and flurbiprofen did not affect bacteria induced inhibition of osteocalcin production. Stimulation of osteocalcin biosynthesis by 1,25(OH)2-vitamin D3 was associated with a decreased rate of cell proliferation. The inhibitory action of the bacterial extracts was not linked to any inhibition of [3H]-thymidine incorporation into deoxyribonucleic acid. These data show that extracts of Staphylococcus aureus and Staphylococcus epidermidis have the ability to inhibit the biosynthesis of bone matrix proteins by a nonprostaglandin and noncytotoxic dependent mechanism and suggest that bone loss in inflammatory processes containing Staphylococcus aureus or Staphylococcus epidermidis may not be caused only by enhanced bone resorption but also by decreased bone formation.     

Synthesis and antibacterial activity of novel 7-(3-substituted-3 or 4-trifluoromethyl-1-pyrrolidinyl)-8-methoxyfluoroquinolones

The titled compounds were synthesized and evaluated for in vitro antibacterial activity. The (3R, 4S)-3-aminomethyl-4-trifluoromethyl derivative (S-34109) was confirmed to be optimal because of its superior activity against quinolone and methicillin-resistant Staphylococcus aureus and low side effect potential.     

Use of liposome-immunopotentiated exopolysaccharide as a component of an ovine mastitis staphylococcal vaccine

Experiments on the development of a vaccine against staphylococcal mastitis were carried out in ewes. The vaccine (Spanish patent no. 9200223) has the following components: (i) inactivated (formalinized) bacteria (Staphylococcus aureus and a coagulase-negative staphylococcal species. Staphylococcus simulans) and S. aureus toxoid in presence of an adjuvant (dextran sulfate, Mw 500,000); and (ii) S. aureus exopolysaccharide included within liposomes. High serum antibody titres were obtained against whole cells from Staphylococcus aureus, Staphylococcus simulans, Staphylococcus hyicus and Staphylococcus epidermidis strains. However, there was no response to cells from Staphylococcus warneri and Staphylococcus chromogenes strains. An immune response (serum IgG) against the inoculated exopolysaccharide was obtained when > or = 20 micrograms of exopolysaccharide were included in liposomes and when > or = 20 mg of exopolysaccharide were adjuvanted with dextran sulfate instead of liposomes. For experimental infection assays, ewes were vaccinated during pregnancy and challenged either with a low virulence S. simulans strain or with a highly virulent S. aureus strain. In these assays, the incidence of S. simulans subclinical mastitis and of S. aureus acute mastitis was significantly lower in vaccinated animals than in unvaccinated controls. Specifically, on challenge with S. simulans, two out of 14 glands became infected among the vaccinated animals and nine out of ten glands in the unvaccinated group (p < 0.001). On challenge with S. aureus, no protection was detected when component (ii) was omitted from the vaccine; nine out of ten animals developed mastitis (two mild, two moderate and five severe).(ABSTRACT TRUNCATED AT 250 WORDS)