sou · GLB3132d3 · 1998-01-01 00:00:00 — -ILLER # 2 0HILIP * 2 &REE 3 - *R AND ,, - , 1972. Virginiamycin for prevention of swine dysentery. 6ETERINARY -EDICINE AND 3MALL !NIMAL #LINICIAN -OLNAR , , 1996. Sensitivity of strains of 3ERPULINA HYODYSENTERIAE isolated in to chemotheraputic drugs. 6ETERINARY 2ECORD 158-160. -OORE ' - AND :IMMERMAN ! ' Efficacy of tylosin phosphate administered in feed for the prevention and control of porcine proliferative enteropathies in commercial swine herds. )N PROCEEDINGS OF TH )063 CONGRESS 7-10, . -OORE * % -ADDEN 2 ( +ERR * 2 7ILSON 4 3 AND -URPHY 0 ' , 1996. Erythromycin-resistant thermophilic Campylobacter species isolated from pigs. 4HE 6ETERINARY 2ECORD 306-307. -ULLANY 0 7ILKS - AND 4ABAQCHALI 3 , 1995. Transfer of macrolide-lincosamide- streptogramin B (MLS) resistance in #LOSTRIDIUM DIFFICILE is linked to a gene homologous with toxin A and is mediated by a conjugative transposon, Tn5398. *OURNAL OF !NTIMICROBIAL #HEMOTHERAPY 305-315. .ATURV¥RDSVERKET, 1996. Läkemedel och miljön. Rapport nr 4660. .ICAS 4 ) :- , AND "$ + , 1997. Beyond vancomycin: new therapies to meet the challenge of glycopeptide resistance. 4RENDS IN -ICROBIOLOGY 240-249. .OBLE 7 # 6IRANI : AND #REE 2 ' , 1992. Co-transfer of vancomycin and other resistance genes from %NTEROCOCCUS FAECALIS NCTC 12201 to 3TAPHYLOCOCCUS AUREUS. &%-3 -ICROBIOLY ,ETTERS 195-198. 0ECH¨RE * # , 1996. Streptogramins, a unique class of antibiotics. 0ECHERE * # , 1992. In-vitro activity of RP 59500, a semisynthetic streptogramin, against staphylococci and streptococci. *OURNAL OF !NTIMICROBIAL #HEMOTHERAPY 15-8. 0ERITI 0 -AZZEI 4 -% AND .OVELLI ! Adverse effects of macrolide antibacterials. $RUG 3AFETY 346-364 . 0OYART 3ALMERON # #ARLIER # 4RIEU #UOT 0 #OURTIEU ! , AND #OURVALIN 0 , Transferable plasmid-mediated antibiotic resistance in ,ISTERIA MONOCYTOGENES. ,ANCET 1422-1426. 0RESCOTT * & AND "AGGOT * $ EDS , 1993. !NTIMICROBIAL THERAPY IN VETERINARY MEDICINE 2nd ed. 1UEDNAU - !HRNE 3 AND ' , 1996. Antibiotic resistant enterococci in Swedish and Danish pork and poultry. )N PROCEEDINGS OF &OOD ASSOCIATED PATHOGENS . SLU repro, , . 2EINA * "ORRELL . Emergence of resistance to erythromycin and fluoroquinolones in thermotolerant Campylobacter strains isolated from faeces 1987-1991. %UROPEAN *OURNAL OF #LINICAL -ICROBIOLOGY AND )NFECTIOUS $ISEASES 2ENDE &OURNIER 2 ,ECLERCQ 2 'ALIMAND - $UVAL * AND #OURVALIN 0 , 1993. Identification of the satA gene encoding a streptogramin A acetyltransferase in Enterococcus faecium BM4145. !NTIMICROBIAL !GENTS AND #HEMOTHERAPY 2119- 2OBERTS - # AND "ROWN - " , 1994. Macrolide-lincosamide resistance determinants in streptococcal species isolated from the bovine mammary gland. 6ETERINARY -ICROBIOLOGY 253-261. 2OLLINS , $ ,EE , . AND ,E"LANC $ * , 1985. Evidence for a disseminated erythromycin resistance determinant mediated by Tn -like sequences among group D streptococci isolated from pigs, chickens and humans. !NTIMICROBIAL !GENTS AND #HEMOTHERAPY 439-444. 2ONNE ( AND *ENSEN * # % , 1992. Virginiamycin susceptibility of 3ERPULINA HYODYSENTERIAE, IN . 6ETERINARY 2ECORD 239-240. 2ONNE ( AND 3ZANCER * , 1990. In vitro susceptibility of Danish field isolates of 4REPONEMA HYODYSENTERIAE to chemotherapeutics in swine dysentery (SD) therapy. Interpretation of results based on the pharmacokinetic properties of the antibacterial agents. )N PROCEEDINGS OF TH )063 #ONGRESS 1 5, . 3CHALEN # 'EBRESELASSIE $ AND 3TAHL 3 , 1995. Characterization of an erythromycin resistance (erm) plasmid in Streptococcus pyogenes. !CTA 0ATHOLOGICA -ICROBIOLOGICA ET )MMUNOLOGICA 3CANDINAVICA 59-68. 3HAH 0 - 3CHAFER 6 AND +NOTHE ( , 1993. and veterinary use of antimocrobial agents: implications for public health. A clinicians view on antimicrobial resistance. 6ETERINARY -ICROBIOLOGY 269-274. 3MITH ( AND 'REEN 3 ) , 1980. Effect of feed additives on the incidence of naturally acquired salmonella in . 6ETERINARY 2ECORD 289. 3MITH ( 7 AND 4UCKER * & , 1975a. The effect of antibiotic therapy on the faecal excretion of 3ALMONELLA TYPHIMURIUM by experimentally infected chickens. *OURNAL OF (YGIENE 275-292. 3MITH ( 7 AND 4UCKER * & , 1978. The effect of antimicrobial feed additives on the colonization of the alimentary tract of chickens by 3ALMONELLA TYPHIMURIUM. *OURNAL OF (YGIENE 217-231. 3MITH 3 # -UIR 4 (OLMES - AND #OLOE 0 * , 1991. )N antimicrobial susceptibility of Australian isolates of 4REPONEMA HYODYSENTERIAE. !USTRALIAN 6ETERINARY *OURNAL 408-409. 3MITH 7 ( AND 4UCKER * & , 1975b. The effect of feeding diets containing permitted antibiotics on the faecal excretion of 3ALMONELLA TYPHIMURIUM by experimentally infected chickens. *OURNAL OF (YGIENE 293-301. 3MITH 7 ( AND 4UCKER * & , 1980. Further observations on the effect of feeding diets containing avoparcin, bacitracin and sodium arsenilate on the colonization of the alimentary tract of poultry by salmonella organisms. *OURNAL OF (YGIENE 137- 3T 'EORGIEV 6 , 1994. Management of toxoplasmosis. 3TUART * ' :IMMERER % * AND -ADDUX 2 , , 1992. Conjugation of antibiotic resistance in 3TREPTOCOCCUS SUIS. 6ETERINARY -ICROBIOLOGY 213-222. 3TUTZ - 7 *OHNSON 3 , AND *UDITH & 2 , 1983. Effects of diet and bacitracin on growth, feed efficiency, and populations of #LOSTRIDIUM PERFRINGENS in the intestine of broiler chicks. 0OULTRY 3CIENCE 1619-1625. 3UTTER ( - %NGELI * -0 3CHNEIDER " 2IOND * , AND 7ARNER - , 1992. Pharmacokinetics and bioavailability of spiramycin in pigs. +ASSING & +ALINOWSKI * AND 0UHLER ! The #ORYNEBACTERIUM XEROSIS composite transposon Tn consists of two identical insertion sequences, designated IS1249, flanking the erythromycin resistance gene ERMCX. 0ERRI - " $ONABEDIAN 3 -C-AHON * #HOW * 7 AND :ERVOS - * , 1996. Antimicrobial resistance in enterococci isolated from fed virginiamycin. )N PROCEEDINGS OF TH )#! 2AVIZZOLA ' 0ERONI , #ERUTI 4 'RECO , - 0ITZUS % 3ANTINI ' #RESTI 3 AND 3ATTA ' , 1994. A multicentre study: Staphylococcus and Enterococcus susceptibility to antibiotics. %UROPEAN *OURNAL OF %PIDEMIOLOGY 567-72 issn: 0392-2990. Vitamin A, iron and virginiamycin in broiler diets. Effects on performance and immune responsiveness. (Thesis). * 0 - ,ONDON . ( AND 3TOBBERING % % , 1997. High prevalence of colonisation with vancomycin- and pristinamycin -resistant enterococci in humans and pigs in The : is the addition of antibiotics to animal feeds to blame? *OURNAL OF !NTIMICROBIAL #HEMOTHERAPY 454-456. 7ANG 7 , 2ELLER , " AND "- * , 1984. Comparison of antimicrobial susceptibility patterns of #AMPYLOBACTER JEJUNI and #AMPYLOBACTER COLI. !NTIMICROBIAL !GENTS AND #HEMOTHERAPY 351-353. 7ASTESON 9 (OIE 3 AND 2OBERTS - # , 1994. Characterization of antibiotic resistance in 3TREPTOCOCCUS SUIS. 6ETERINARY -ICROBIOLOGY 41-49. 7EISBLUM " , 1985. Inducible resistance to macrolides, lincosamides and streptogramin type B antibiotics: the resistance phenotype, its biological diversity, and structural elements that regulate the expression - a review. *OURNAL OF !NTIMICROBIAL CHEMOTHERAPY 63-90. 7EISBLUM " , 1995a. Erythromycin resistance by ribosome modification. !NTIMICROBIAL !GENTS AND #HEMOTHERAPY 577-585. 7EISBLUM " , 1995b. Insights into erythromycin action from studies of its activity as inducer of resistance. !NTIMICROBIAL !GENTS AND #HEMOTHERAPY 797-805. 7ESTH ( , 1996. Ertythromycin resistant 3TAPHYLOCOCCUS AUREUS in . !CTA 0ATHOLOGICA -ICROBIOLOGICAET )MMUNOLOGICA 3CANDINAVICA. 7ILLIAMS " * AND 3HIVELY * % , 1978. )N 6ITRO antitreponemal activities of carbadox, virginiamycin, olaquindox, and tylosin as of their effectiveness for preventing swine dysentery. 6ETERINARY -EDICINE AND 3MALL !NIMAL #LINICIAN 0ALEPOU - & *OHNSON ! 0 #HADWICK 0 2 AND "ATES * , 1997. 4HE ,ANCET 738. : Carbadox and olaquindox Carbadox and olaquindox belong to the group of quinoxaline-di-N-dioxide derivatives, or quinoxalines. This group consists of synthetically produced substances with activity against anaerobic bacteria but also against certain gram-negative facultative anaerobes such as salmonellae (Prescott and Baggot, 1993). Carbadox is also against gram-positive bacteria such as staphylococci (Devriese, 1980). The antibacterial activity of the quinoxalines is markedly improved under anaerobic conditions (Prescott and Baggot, 1993). Quinoxalines that are presently approved as antibacterial feed additives () in Union are carbadox and olaquindox. Other substances of this class are quindoxin and cyadox. After oral administration, olaquindox and carbadox are rapidly absorbed and are extensively metabolised (FAO/WHO, 1991; FAO/WHO, 1994). The concentration profiles of the substances in the gut show a gradual decline from the stomach to the colon where the concentrations are below detectable levels (Baars ET AL , 1988; de Graaf ET AL , 1988; Spierenburg ET AL , 1988c). The quinoxalines are not used for in human medicine. Carbadox and olaquindox are approved as feed additives for swine for growth promoting purposes at dosages ranging from 20 to 50 ppm and 50 to 100 ppm respectively. Quinoxalines are also used at similar or higher dosages for prevention of intestinal infections (see F.7). The use of quinoxalines has been questioned for toxicological reasons, mainly due to their genotoxic and/or carcinogenic potential (Anonymous, 1995), they are also known to have toxic effects on the target species (Prescott and Baggot, 1993). F.2 Mode of action and resistance mechanisms As mentioned above, the activity of the quinoxalines is markedly improved under anaerobic conditions. The mode of action of the quinoxalines on bacteria was investigated by Suter and co-workers (1978). The authors showed that the antibacterial effect of quindoxin was always accompanied by a reduction of the drug. Such a reduction only occurred under anaerobic conditions, and generated free radicals. Based on a series of experiments, the authors suggested that radicals produced during the intracellular reduction of The figures in this report is only available in the printed version Tentative sketch of carbadox, olaquindox, nalidixic acid and enrofloxacin the parent substance or some decomposition products thereof damage DNA without being bound to this target. As a consequence, DNA synthesis ceases, breakdown of chromosome ensues and the bacterial cell dies. The quinoxalines are somewhat structurally related to the quinolones (see figure F.1) which also exert their antibacterial activity by interfering with the bacterial DNA synthesis. The quinolones inhibit the activity of bacterial topoisomerases, i.e. enzymes controlling the supercoiling of DNA, converting relaxed covalently closed circular DNA to a superhelical form by an energy dependent strand breakage and resealing process (, 1997). Although there are still unclarities as to the precise bactericidal mechanism of the quinolones, it is thought that when the gyrase is inhibited, resealing following breakage is prevented and DNA is exposed to and degraded by exonucleases. Resistance to quinolones develop through alterations of the target of the drug and to some extent through altered permeability or increased efflux. As the information on mechanisms of action of the quinoxalines predates the discovery of bacterial gyrases, possible similarities with the precise mechanism of action of the quinolones cannot be determined. No information on the molecular background of observed quinoxaline resistance, nor on cross-resistance between quinoxalines and other drugs such as quinolones has been found. It is likely, however, that were resistance due to altered permeability or efflux to occur, this would confer cross- resistance to at least the other quinoxalines. F.3 Development of resistance An experimental study on germ-free mice fed carbadox, olaquindox, flavomycin and chlortetracycline was reported by Corpet (1984). The mice were inoculated with intestinal microflora from 4 piglets, and the drugs were given at dosages corresponding to those used for growth promotion in livestock. effect on coliform resistance against olaquindox and carbadox was observed, nor was there any effect of the quinoxalines on tetracycline resistance. A prospective study to monitor the development of olaquindox resistance in coliforms following the introduction of olaquindox as a feed additive was conducted in commercial farms in by and co-workers (1988). Olaquindox resistance in coliforms from farms with and without use of the antibacterial are shown in table F.I. As is often the case in field studies, there were problems with sampling variability and difficulties to control the management on the farms. In spite of this, the overall results were consistent and showed an increasing level of resistance to olaquindox in coliforms from farms using olaquindox. Incidence and level of resistance increased on neighbouring farms not using olaquindox as well, but to a lesser extent. The latter finding is not surprising as the herds were not isolated from the environment. The average percentage of coliforms resistant to /ml olaquindox in each year of the survey (from , 1988) 1 Sampled before olaquindox was used in the UK The ecological aspects of olaquindox resistance were investigated by and (1988). In a prospective study, chosen pens in four pig farms, two of which used olaquindox were sampled weekly. Coliform bacteria were isolated from the samples and biovariant along with sensitivity to olaquindox and other antibacterials was determined. The overall proportions of coliforms resistant to olaquindox (counts on selective medium divided by counts on non-selective medium) were 0 and , respectively, for control farms and and for the farms using olaquindox. A transient appearance of olaquindox-resistant strains in one of the control farms coincided with a changeover in the occupancy of the pen. The weekly fluctuations in proportion of resistant strains were very marked. An increase in carbadox resistance in salmonellae over time was noted in a study from by Mills and (1986). The study included clinical isolates from necropsied swine in during 1980-1983. A steady increase in carbadox resistance, from 1980 to 1983 was noticed. The authors note that in-feed carbadox in is labelled for prevention of swine dysentery and for treatment of salmonella infections. Ohmae and co-workers (1983) reported the incidence of carbadox resistance in %SCHERICHA COLI from cattle, pigs and chickens, collected during Carbadox resistance was only found in isolates from pigs. All isolates with a minimum inhibitory concentration () of carbadox under anaerobic conditions of >25µg/ml originated from 1 farm, where carbadox was used for prevention of swine dysentery. Baumgartner and co-workers (1985), investigating samples from the same animal species in , found olaquindox-resistant coliforms in samples from pigs () and calves () but none in samples from chickens. (1987) reported a 5 times higher prevalence of carbadox-resistance in coliforms from pigs receiving carbadox, as compared to pigs not fed antibacterials, in a material collected in various European countries. Several investigations report on a uniform sensitivity of 3ERPULINA spp to carbadox (Molnar and Magyar, 1987; and Kinyon, 1990; Molnar, 1996) with reported MICs generally considerably below 0.4µg/ml. to this, in a study from , a MIC90 (minimal inhibitory concentration for of the isolates) of carbadox for 3ERPULINA HYODYSENTERIAE of >6µg/ml was reported (Messier ET AL , 1990). This figure is considerably higher than those reported by other authors, indicating an emerging resistance. In an investigation from , carbadox had a of >0.1µg/ml for 3 out of 67 () of the Serpulina isolates investigated. Although MICs in this range might not cause the isolates to be classified as resistant, their sensitivity seems reduced as the modal in this study was 0.012µg/ml. This might indicate a gradual increase in MICs, a phenomenon which is seen when stepwise mutations are needed for full resistance. Interestingly, carbadox was not used in at the time when the isolates were collected. Two reports show the MICs of olaquindox and carbadox for individual strains of 3ERPULINA spp (and Shively, 1978; Fellström ET AL , 1996). No clear relation between MICs of carbadox and olaquindox can be noted in the data presented. In the study by (1978), a good correlation between MICs obtained IN and therapeutic efficacy of respective drug in experimental infections was noted. Infection with the three strains with MICs for olaquindox of 2.5µg/ml or more resulted in considerable morbidity in spite of olaquindox treatment, while the treated pigs infected with a strain with a of olaquindox of 0.3µg/ml remained healthy. The same 4 strains were uniformely sensitive to carbadox both IN VIVO Taken together, these studies indicate that strains resistant to olaquindox are not cross-resistant to carbadox. The mechanisms for the observed resistance were not investigated. Concerning the activity of carbadox against gram-positive bacteria, few publications are available. Devriese (1980) reported on the carbadox- sensitivity of 950 isolates of 3TAPHYLOCOCCUS AUREUS from cattle, poultry and All the isolates had values <1.6µg/ml and no indications of acquired resistance were found. Similarly, in an investigation of of carbadox for clostridia from the same animal species, all 68 isolates had values below 0.25µg/ml (Dutta ET AL , 1983). Indications of a simultaneous increase in minimum inhibitory concentrations for olaquindox and the quinolone enrofloxacin was recently detected in a Swedish survey (Greko, 1997). The investigated strains originated from three different cathergories of piglet producing herds; 10 herds were using olaquindox as medicated feed (160 ppm), 10 herds were using zinc oxide (2500 ppm) and 10 herds used no medication. phenotypes with respect to olaquindox and enrofloxacin sensitivity are shown in table F.II. 16 out of 61 isolates with resistance to olaquindox according to the break-points assigned had values of 0.25 for enrofloxacin. This intermediary value of enrofloxacin was not found in isolates sensitive to carbadox. Only two isolates had higher values (/ml). Phenotypes with respect to olaquindox and enrofloxacin sensitivity in % COLI isolated from piglets in herds using different regimes (Greko, 1997) 0ROPORTION OF ISOLATES WITH PHENOTYPE 1Determined according to MICs (µg/ml); Olaquindox R >32, OlaquindoxS<64, EnrofloxacinR >0.25, EnrofloxacinI=0.25, EnrofloxacinS<0.25 2n= number of isolates F.4 Acquisition of resistance Omahae and co-workers (1983) investigated the transferability of carbadox resistance from resistant % COLI originating from one farm. The carbadox- resistance was transferable by conjugation to other strains of % COLI Transfer was invariably linked to transfer of resistance to spectinomycin, streptomycin The resistance determinants were shown to reside on a conjugative plasmid. No transfer to 3ERPULINA spp was observed. and (1987) tested COLI strains with anaerobic values for carbadox of >8µg/ml for their ability to transfer resistance (including carbadox). The experiments were successful in 55 and of the attempts when two % COLI strains were used as recipients. Transfer of carbadox resistance to salmonellae was achieved only in of the experiments. Transfer of carbadox resistance was constantly associated with co-transfer of resistance to at least one other antibacterial. The most frequently linked transfer was carbadox-streptomycin-tetracycline resistance. In contrast, in similar experiments reported by Baumgartner and co-workers (1985), transfer was successful from only 3 out of 64 strains tested and no co-transfer was observed. and co-workers (1988) demonstrated transfer of olaquindox- resistance from 6 out of COLI strains to a laboratory strain of % COLI. Transfer of resistance did not correlate to the appearence of a plasmid nor was it linked to transfer or other resistance traits. The evidence therefore suggests that the gene(s) conferring olaquindox resistance were located on the chromosome. An apparent suppression of coliforms carrying R-plasmids has been reported for carbadox and olaquindox (Gedek, 1979) but no mechanism explaining this was provided. Quinolones and novobiocin, inhibitors of DNA gyrase, have been shown to eliminate plasmids IN both by inhibiting their replication (Uhlin and , 1985) and their transfer (Weisser and Wiedemann, 1987). No information on the precise genetic nature of either carbadox or olaquindox resistance has been found. Plasmid mediated resistance to nalidixic acid, a quinolone, was reported from in 1987 (Munshi ET AL , 1987). This was later found to be due to a mutation of the recipient strain. Possibly, the transferred plasmid induced mutations leading to nalidixic acid resistance (, cit. by Courvalin, 1990). Although speculative, a similar phenomenon could explain why the transconjugant strains in the experiments cited above had markedly lower MICs than those of the donor strains (Ohmae ET AL , 1983; Baumgartner ET AL , 1985). If stepwise mutations are necessary to reach higher MICs, single or two-step mutations induced by a transfered gene element might result in the comparatively lower MICs observed in the recipients. F.5 Effects on specific animal diseases The preventive effect of the quinoxalines, especially carbadox, against certain intestinal diseases in animals, especially swine dysentery, is well documented. Studies on the pharmacokinetics of the quinoxalines have shown that the intestinal concentrations gradually decline from the stomach to the colon (Baars ET AL , 1988; de Graaf ET AL , 1988; Spierenburg ET AL , 1988c). As swine dysentery is primarily a disease of the lower intestine, a preventive rather than a therapeutic effect is to be expected. and (1978) investigated presence and development of carbadox-resistance IN in 3 HYODYSENTERIAE and prevention of experimentally induced infection by carbadox. were found and carbadox at 5 ppm above maximum growth promoting level was found to be effective in preventing swine dysentery. obtained by and Shively (1978), who found no carbadox-resistance in isolates of 3 HYODYSENTERIAE and managed to prevent swine dysentery by carbadox at, or slightly above, growth promoting levels. and Froe (1985) prevented experimentally induced swine dysentery by feeding carbadox at growth promoting levels to pigs. In a study by Jacks and co- workers (1986), carbadox was fed at 5 ppm above growth promoting level and was found to successfully prevent swine dysentery. Raynaud and co-workers (1980a; 1980b) developed a swine dysentery model for evaluation of drug prophylaxis. Using this model carbadox was found to effectively prevent the outbreak of swine dysentery. Olaquindox only prevented the disease during the medication period, but not post- medication. It is not clear what dosages were used in this experiment. and (1980) found that carbadox at maximum growth promoting levels prevented the onset of swine dysentery and eliminated 3 HYODYSENTERIAE infection in experimentally infected pigs. workers (1980b) investigated therapeutic effects and prevention of the state in pigs experimentally infected with 3 HYODYSENTERIAE. ppm above permitted growth promoting levels effectively eliminated the infectious agent from the host, thereby curing the disease without leaving any asymptomatic . Similar results were shown in a similar study by the same authors (, 1980a). Biehl and co-workers (1984) used the same dosage of carbadox and were able to successfully treat pigs experimentally infected with 3 HYODYSENTERIAE. In a large scale trial in commercial pig herds in (Raynaud and Bretheau, 1973), 50 ppm carbadox was found to be sufficient for both prophylaxis and treatment of swine dysentery. As mentioned under F.3, olaquindox at growth promoting levels completely prevented swine dysentery induced by an olaquindox-susceptible strain (and Shively, 1978).