Antimicrobial susceptibilities of Campylobacter isolated from food-producing animals on farms (1999–2001): results from the Japanese Veterinary Antimicrobial Resistance Monitoring Program

Campylobacter Express Resistance Array for detecting the presence of fluoroquinolone- and macrolide-resistant Campylobacter jejuni and Campylobacter coli in broiler farms

AIMS

The aim of the study was to develop a microarray-based method for the detection of antibiotic-resistant Campylobacter in broiler farms to decrease the risk of contamination of chicken meat.

METHODS AND RESULTS

A combination of DNA microarray and primer extension for rapid and simultaneous detection of fluoroquinolone- and macrolide-resistant Campylobacter jejuni/Campylobacter coli, termed Campylobacter Express Resistance Array (CAMERA), was used to analyse chicken caecal droppings. CAMERA assays could detect at least 10⁵ colony forming units of C. jejuni/C. coli g^-1 of chicken caecal contents spiked with C. jejuni/C. coli. To compare the CAMERA method and direct culturing method for screening antibiotic-resistant C. jejuni/C. coli in poultry farms, chicken caecal droppings obtained from 42 poultry houses were analysed using both methods. In total, 95.2% of the results (40/42 poultry houses) obtained using the CAMERA and culturing method were identical. In the remaining two poultry houses, the CAMERA could detect the prevalent strain of C. jejuni/C. coli based on results of the culturing method.

CONCLUSIONS

The culturing method required >3 days to isolate and identify antibiotic-resistant C. jejuni/C. coli. In contrast, the CAMERA required only 6 h.

SIGNIFICANCE AND IMPACT OF THE STUDY

This method can facilitate quick screening and control of fluoroquinolone- and macrolide-resistant C. jejuni/C. coli in broiler farms.

Genomic Analysis Reveals the Genetic Determinants Associated With Antibiotic Resistance in the Zoonotic Pathogen Campylobacter spp. Distributed Globally

The genus Campylobacter groups 32 Gram-negative bacteria species, several being zoonotic pathogens and a major cause of human gastroenteritis worldwide. Antibiotic resistant Campylobacter is considered by the World Health Organization as a high priority pathogen for research and development of new antibiotics. Genetic elements related to antibiotic resistance in the classical C. coli and C. jejuni species, which infect humans and livestock, have been analyzed in numerous studies, mainly focused on local geographical areas. However, the presence of these resistance determinants in other Campylobacter species, as well as in C. jejuni and C. coli strains distributed globally, remains poorly studied. In this work, we analyzed the occurrence and distribution of antibiotic resistance factors in 237 Campylobacter closed genomes available in NCBI, obtained from isolates collected worldwide, in different dates, from distinct hosts and comprising 22 Campylobacter species. Our data revealed 18 distinct genetic determinants, genes or point mutations in housekeeping genes, associated with resistance to antibiotics from aminoglycosides, β-lactams, fluoroquinolones, lincosamides, macrolides, phenicols or tetracyclines classes, which are differentially distributed among the Campylobacter species tested, on chromosomes or plasmids. Three resistance determinants, the bla_OXA–493 and bla_OXA–576 genes, putatively related to β-lactams resistance, as well as the lnu(AN2) gene, putatively related to lincosamides resistance, had not been reported in Campylobacter; thus, they represent novel determinants for antibiotic resistance in Campylobacter spp., which expands the insight on the Campylobacter resistome. Interestingly, we found that some of the genetic determinants associated with antibiotic resistance are Campylobacter species-specific; e.g., the bla_OXA–493 gene and the T86V mutation in gyrA were found only in the C. lari group, whereas genes associated with aminoglycosides resistance were found only in C. jejuni and C. coli. Additional analyses revealed how are distributed the resistance and multidrug resistance Campylobacter genotypes assessed, with respect to hosts, geographical locations, and collection dates. Thus, our findings further expand the knowledge on the factors that can determine or favor the antibiotic resistance in Campylobacter species distributed globally, which can be useful to choose a suitable antibiotic treatment to control the zoonotic infections by these bacteria.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): bovine genital campylobacteriosis

Bovine genital campylobacteriosis has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of bovine genital campylobacteriosis to be listed, Article 9 for the categorisation of bovine genital campylobacteriosis according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to bovine genital campylobacteriosis. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, bovine genital campylobacteriosis can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in sections 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (d) and (e) of Article 9(1). The assessment here performed on compliance with the criteria as in section 3 of Annex IV referred to in point (c) of Article 9(1) is inconclusive. The animal species to be listed for bovine genital campylobacteriosis according to Article 8(3) criteria is mainly cattle as susceptible and reservoir.

[Antimicrobial Susceptibility and Resistance Mutations in Campylobacter jejuni and C. coli Isolates from Human and Meat Sources]

Recently, there has been a marked increase in the number of reports of fluoroquinolone-resistant Campylobacter jejuni and Campylobacter coli. The aim of this study was to evaluate the prevalence of antimicrobial resistance and its genetic determinants in Campylobacter species isolated from meat and human subjects in Fukuoka Prefecture, Japan. Between 2011 and 2013, 55 and 64 isolates were collected from meat (chicken meat and beef liver) and humans, respectively, in this prefecture. Antimicrobial susceptibility tests were conducted using the agar dilution method in accordance with the Clinical and Laboratory Standards Institute guidelines, using the following 11 antimicrobial agents : cephalexin, cefoxitin, nalidixic acid, ciprofloxacin, levofloxacin, tetracycline, minocycline, ampicillin, streptomycin, kanamycin and erythromycin. The susceptibility rates of the isolates to three quinolones (nalidixic acid, ciprofloxacin, levofloxacin) were 43.7%, 41.2%, 40.3%, respectively. All the isolates were multidrug resistant. Whereas 46.9%-51.6% of the human isolates were resistant to one or more of the quinolones, only 32.7%-34.5% of the meat isolates were resistant to one or more of the drugs. DNA sequencing showed that of the 50 quinolone resistant isolates 44 had position 86 isoleucine (Ile) substituted for threonine (Thr) in the GyrA protein (Thr86Ile). This amino acid substitution resulted from ACA to ATA and ACT to ATT mutations of codon 86 in C. jejuni and C. coli, respectively. Furthermore, two of the four C. jejuni isolates lacking the Thr86Ile mutation had combined Ser22Gly-Asn203Ser substitutions, while the remaining two isolates had combined Ser22Gly-Asn203Ser-Ala 206Val substitutions. These four isolates also had cmeABC sequences that differed from the quinolone sensitive C. jejuni ATCC33560(T) strain. In conclusion, C. jejuni and C. coli have relatively high quinolone resistance, and are resistant to other antibiotics. The new combination of amino acid substitutions in the GyrA protein could pose a potential threat to public health in Japan.

Prevalence and Antimicrobial Susceptibility of Campylobacter spp. in Oklahoma Conventional and Organic Retail Poultry

Campylobacter is one of the most important foodborne pathogens that cause bacterial gastroenteritis.This study was conducted to investigate the prevalence and antimicrobial resistance of Campylobacter in conventional and organic retail poultry samples purchased from grocery stores in Tulsa, Oklahoma.One hundred and fifty six chilled retail chicken samples (85 conventional and 71 organic) and 65 chilled retail conventional turkey samples were collected in this study. The prevalence of Campylobacter in the conventional chicken samples 32/85 (38%) was higher than in the organic ones 21/71 (30%). The prevalence of Campylobacter in the conventional turkey samples was 11/65 (17%). Of the 53 positive chicken samples, 42 were C. jejuni, 8 were C. coli and three isolates were contaminated with both species. Of the 11 positive turkey samples, 8 contained C. jejuni and 3 harbored C. coli isolates. The antimicrobial susceptibility of one hundred and forty nine recovered Campylobacter isolates (130 chickens and 19 turkeys) towards sixteen antimicrobials was determined. The majority of the recovered turkey isolates (13/19) showed resistance to more than 7 antimicrobials while most of the recovered chicken ones (82/130) were resistant to 5 to 7 antimicrobials. Multidrug resistance was not limited to isolates from conventional sources but was also available in isolates of an organic background and was generally lower in C. jejuni isolates when compared to the C. coli ones.

Serotypes, Antimicrobial Susceptibility, andgyr AGene Mutation ofCampylobacter jejuniIsolates from Humans and Chickens in Thailand

In Thailand, 51% (36/70) Campylobacter jejuni isolates from humans and 68% (47/69) isolates from poultry were classified into 10 Penner serotypes (serotype B, C, R, E, G, A, K, D, I, and L) and 9 serotypes (serotype A, C, I, K, B, E, S, D, and L), respectively. The rate of antimicrobial drug resistance to nalidixic acid, ciprofloxacin, ampicillin, tetracycline, and erythromycin shown by human isolates were 96%, 96%, 29%, 57%, and 14%, while that shown by poultry isolates were 77%, 77%, 22%, 26%, and 17%, respectively. All quinolone-resistant strains contained a mutation in the gyrA gene (T(86)-->I(86)), suggesting that the strains were already widespread in Thailand.

Prevalence of Campylobacter spp., Salmonella spp., Listeria monocytogenes, and hepatitis E virus in swine livers collected at an abattoir

We investigated the prevalence of Campylobacter spp., Salmonella spp., Listeria monocytogenes, and hepatitis E virus (HEV) in swine liver. We collected swine livers from 110 pigs at an abattoir from September 2011 to March 2012 [corrected] . Pathogens were detected in the liver samples of 19 (17.3%) pigs. Campylobacter spp. were isolated from the liver samples of 14 (12.7%) pigs. In 10 of the 14 Campylobacter-positive pigs, bacteria were present in the internal regions of the liver. Salmonella spp. and L. monocytogenes were detected in the liver samples of 5 (4.5%) pigs and 1 (1%) pig, respectively. No HEV was detected in the swine liver samples tested. Regarding antimicrobial resistance in Campylobacter and Salmonella isolates, all isolates, except 1 Campylobacter jejuni isolate, were resistant to 1 or more antimicrobial agent. Campylobacter spp. resistant to erythromycin and/or enrofloxacin were isolated from the liver samples of 9 (8%) pigs. These results suggest that the consuming swine liver without proper heat treatment may increase the risk of foodborne illnesses.

Prevalence and characterization of foodborne pathogens in dairy cattle in the eastern part of Japan

To investigate the prevalence and characterization of foodborne pathogens [Campylobacter spp., Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes and Salmonella spp.] in dairy cows, rectal content grab samples were collected from 250 dairy cows reared on 25 dairy farms in eastern Japan from December 2010 through February 2011. Campylobacter jejuni was isolated from 106 (42%) cows on 23 (92%) farms, STEC O157 from three cows on one farm, L. monocytogenes from three cows on another three farms and Salmonella enterica subsp. enterica serovar Typhimurium from eight cows on another farm. STEC O26 was not isolated from any of the dairy farms investigated. The results suggest that C. jejuni is widespread in dairy farms in eastern Japan.

Epidemiology of bovine venereal campylobacteriosis: geographic distribution and recent advances in molecular diagnostic techniques

Bovine venereal campylobacteriosis (BVC) is a major cause of economic loss to the cattle industries in different parts of the world. Camplylobacter fetus subsp. venerealis (Cfv), the main causative agent of BVC, is highly adapted to the genital tract of cattle and is transmitted by carrier bulls. However, infertility and abortions can also be caused by the intestinal pathogens C. fetus subsp. fetus (Cff), and C. jenuni, which are not venereally transmitted. Bovine venereal campylobacteriosis, caused by Cfv associated with lowered fertility, embryo mortality and abortion, repeated returns to service, reduced pregnancy rates and extended calving intervals, has the highest prevalence in developing countries where natural breeding in cattle is widely practised. The epidemiology, pathogenesis and diagnosis of the disease have been the subject of previous reviews. The main focus of this review is to highlight the epidemiology of this disease with particular reference to geographical distribution and recent advances in molecular diagnostic techniques. It is hoped that further research interest of scientists will be stimulated with a view to finding lasting solutions to the reproductive problems associated with the disease for better livestock productivity, particularly in developing endemic countries.

Characterization of erythromycin-resistant porcine isolates of Campylobacter coli

Erythromycin-resistant Campylobacter organisms were isolated from swine, and their resistance to the antibiotic was characterized. One hundred fourteen Campylobacter organisms were isolated from 572 swine intestinal samples. All isolates were identified as Campylobacter coli by sequence analysis of 16S rRNA gene and polymerase chain reactions with primers specific to hippuricase gene in Campylobacter jejuni and aspartokinase gene in C. coli. Minimal inhibitory concentrations (MICs) of erythromycin were determined by using the agar dilution method, and 80 isolates were found to be resistant to erythromycin (MIC ≥ 4 μg/ml). Of these, 31 isolates had low-level resistance (MIC =4-16 μg/ml), and 49 isolates had high-level resistance (HLR, MIC ≥ 32 μg/ml). The HLR isolates carried a point mutation at position A2075 → G in domain V of the 23S rRNA gene, whereas the low-level resistance isolates carried no mutation. These 49 HLR isolates were characterized by pulsed-field gel electrophoresis and multilocus sequence typing to study their genetic diversity. Pulsed-field gel electrophoresis identified 16 distinct types with 50% genetic similarity as the cutoff. On the other hand, 28 different sequence types (STs), including 10 new STs, were identified with multilocus sequence typing. Forty-six of 49 erythromycin HLR isolates showed crossresistance to 6 macrolide derivatives. The correlation between the inhibitory activity of carbonyl cyanide m-chlorophenylhydrazone and the existence of cmeB, which is responsible for efflux in HLR isolates, was found to be low. Erythromycin resistance was transferred from 38 of the 43 HLR isolates to susceptible C. coli by natural transformation, with a frequency of 1.217 x 10(-8)-4.618 x 10(-5) per recipient cell. All transformants were erythromycin resistant and had A2075 → G mutation in at least one of three copies of the 23S rRNA gene. Results indicate that variable genotypes of HLR C. coli coexist in swine and high-level erythromycin resistance can be transferred to other strains.

National surveillance of Salmonella enterica in food-producing animals in Japan

A total of 518 fecal samples collected from 183 apparently healthy cattle, 180 pigs and 155 broilers throughout Japan in 1999 were examined to determine the prevalence and antimicrobial susceptibility of Salmonella. The isolation rates were 36.1% in broilers, 2.8% in pigs and 0.5% in cattle. S. enterica Infantis was the most frequent isolate, found in 22.6% of broiler fecal samples. Higher resistance rates were observed against oxytetracycline (82.0%), dihydrostreptomycin (77.9%), kanamycin (41.0%) and trimethoprim (35.2%). Resistance rates to ampicillin, ceftiofur, bicozamycin, chloramphenicol and nalidixic acid were <10%. CTX-M-2 β-lactamase producing S. enterica Senftenberg was found in the isolates obtained from one broiler fecal sample. This is the first report of cephalosporin-resistant Salmonella directly isolated from food animal in Japan.

Prevalence of antimicrobial resistance among serotypes of Campylobacter jejuni isolates from cattle and poultry in Japan

Penner serotypes of C. jejuni in a total of 601 isolates from apparently healthy cattle, layer and broiler chickens in Japan were examined between 2001 and 2006. Predominant serotypes were B (O: 2, 19.1%), D (O: 4, 13.5%), Y (O: 37, 7.3%) and G (O: 8, 5.8%), whereas the remaining serotypes made up less than 5% of the total isolates. The frequency of ampicillin resistance in serotype G (65.6%) was significantly higher than in serotypes D (12.5%), B (11.2%), and Y (0%). Our results suggest that serotype is one factor contributing to the prevalence of ampicillin resistance in C. jejuni isolates.

Antimicrobial susceptibility patterns of thermotolerant Campylobacter strains isolated from food animals in Ethiopia

Thermotolerant Campylobacter spp. are frequent causes of diarrhoea in humans worldwide mostly originating from poultry. It has been suggested that extensive veterinary use of antibiotics is largely responsible for resistance in human isolates. During a 4-month period from January to April 2004, 192 Campylobacter spp. were isolated from fecal samples of 485 healthy food animals. The in vitro susceptibility to 12 antibiotics was determined by the agar disk diffusion method. Among the 192 Campylobacter spp. isolated, 135 (70.3%) were identified to be C. jejuni, 51 (26.6%) were C. coli and 6 (3.1%) were C. lari. C. jejuni was the most prevalent species in chickens (80.8%) versus 16.2% C. coli and 3.0% C. lari. All isolates found in pigs were C. coli. All strains were sensitive to chloramphenicol and ciprofloxacin and all were resistant to cephalothin. More than 90% of the strains were sensitive to clindamycin, erythromycin, gentamicin, nalidixic acid, norfloxacin, streptomycin and tetracycline. Resistance was found against ampicillin in 20% and trimethoprim-sulphamethoxazole in 37.5%. Resistance was not statistically different among C. jejuni, C. coli and C. lari (p>0.05). Multidrug resistance to two or more drugs was detected in 14.5% of strains. In conclusion, the study showed that antimicrobial resistance is found only at relatively low frequencies for most antimicrobial agents tested except for ampicillin and trimethoprim-sulphamethoxazole. The low percentages of resistance to most antimicrobial agents tested in this study may be the result of low/no usage of these agents as a growth promoters or treatment in the Ethiopian animal farm setting. The detection of multidrug resistant isolates may pose a threat to humans and further limits therapeutic options.

The epidemiology of antibiotic resistance in Campylobacter

Antibiotic resistance, particularly with the fluoroquinolones and macrolide antibiotics, has now emerged globally with thermophilic campylobacters, including Campylobacter jejuni and C. coli, giving rise to concerns about how these organisms have acquired such resistance characteristics, as well as consequences for human and animal treatment. This review examines (i) the clinical epidemiology of antibiotic resistance in human and animal thermophilic campylobacters, (ii) an update on resistance rates globally, (iii) surveillance of antimicrobial resistance in campylobacters originating from animals, particularly poultry, (iv) the role of the environment in the acquisition and transmission of antibiotic-resistant campylobacters, as well as (v) issues of biocide resistance in campylobacters.

Characterization of Macrolide-Resistant Campylobacter coli Isolates from Food-Producing Animals on Farms Across Japan during 2004

We investigated the susceptibilities against 7 antimicrobial agents in Campylobacter jejuni and C. coli isolates from food-producing animals in 2004. In comparison with the results of past surveillance, no significant difference was observed in resistance rates against all of the antimicrobials tested in Campylobacter isolates. However, slight increase of erythromycin (EM) resistance was found in C. coli isolates from pigs. We examined the mutation of the 23S rRNA gene and their susceptibilities against azithromycin, tylosin, and lincomycin in 44 EM-resistant isolates and 28 susceptible isolates of porcine origin. All the EM-resistant isolates contained A2075G in the 23S rRNA gene and showed cross-resistance to azithromycin, tylosin, and lyncomycin.

Comparison of Campylobacter isolated from humans and food-producing animals in Japan

AIMS

To compare the antimicrobial resistance, serotypes and flagellin gene types of Campylobacter isolated from humans and food-producing animals and thereby facilitate elucidation of the origin of Campylobacter causing human infection in Japan.

METHODS AND RESULTS

The MIC values of ampicillin, dihydrostreptomycin, gentamicin, erythromycin, oxytetracycline, nalidixic acid and enrofloxacin for Campylobacter isolated from humans (134 isolates), cattle (38 isolates), pigs (69 isolates), layers (84 isolates) and broilers (51 isolates) were compared. The MIC(90) values of ampicillin for Campylobacter jejuni isolates from poultry were higher than those from humans and cattle. Campylobacter coli that was resistant to dihydrostreptomycin and erythromycin was observed at a higher frequency in humans and pigs than in poultry. The restriction fragment profiles of flaA of human, bovine and broiler isolates were analysed by clustering, and the isolates were classified into five clusters. Cluster I contained only human and bovine isolates. Clusters III, IV and V contained human, bovine and broiler isolates.

CONCLUSIONS

Campylobacter isolates from humans included isolates that exhibited characteristics identical to those of the bovine, porcine and poultry isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

In addition to poultry, cattle and pigs are believed to be sources of campylobacteriosis in Japan.

The Dynamics of Antimicrobial-Resistant Campylobacter jejuni on Japanese Broiler Farms

We investigated for dynamics of Campylobacter clones on 2 different managerial broiler farms. Campylobacter isolates were differentiated by resistance typing and molecular typing methods. On farm I, the same C. jejuni clones resistant to fluoroquinolone and oxytetracycline were isolated after one and half years again and another susceptible clone was invaded. The susceptible clone was isolated again after half year. Broiler flocks on the farm may be repeatedly infected with a few C. jejuni clones. On farm II, new clones including antimicrobial resistant one, were often invaded. The change of predominant C. jejuni clone in each flock on both the farms was observed, in the absence of antimicrobial selective pressure.

An investigation of the molecular mechanisms contributing to high-level erythromycin resistance in Campylobacter

The molecular mechanisms contributing to high-level erythromycin resistance in Campylobacter jejuni and Campylobacter coli isolates were investigated. The A2075G mutation in the 23S rRNA target genes was identified in all high-level erythromycin-resistant isolates. A number of amino acid substitutions together with insertions and deletions were identified in the corresponding genes encoding L4 and L22 ribosomal proteins both of resistant and susceptible isolates. Amino acid substitutions identified in the resistant strains were located outside regions known to be altered in these proteins. The efflux pump inhibitor L-phenylalanine-L-arginine-beta-naphthylamide (PAbetaN) increased the susceptibility to erythromycin in one of four isolates displaying high-level erythromycin resistance, and reduced the minimal inhibitory concentration displayed by an erythromycin-susceptible C. coli isolate. The A2075G mutation in the 23S rRNA appeared to be the main contributor to high-level erythromycin resistance in Campylobacter. Other mutations/amino acid substitutions found in the 50S ribosomal subunit encoding proteins L4 and L22 do not appear to be linked to the high-level erythromycin-resistant phenotype. Active efflux contributes to the intrinsic resistance to erythromycin in Campylobacter and may contribute to high-level resistance in some isolates.

Emergence of Fluoroquinolone Resistance in Campylobacter jejuni in Chickens Exposed to Enrofloxacin Treatment at the Inherent Dosage Licensed in Japan

The objective of the present study was to determine whether selection of fluoroquinolone resistance could be easily induced in Campylobacter jejuni-colonized chickens by treatment with enrofloxacin of representative fluoroquinolones at the inherent dosage licensed in Japan (50 ppm in drinking water for 3 days). In the case of isolates from chickens of study 1, an increase in the population of susceptible isolates appeared after the cessation of treatment and maintained throughout the experiments. On the contrary, our results of study 2 demonstrated that administration of enrofloxacin generated a rapid increase of fluoroquinolone resistance in C. jejuni showing the mutation of Asp-90-Asn in the gyrA gene. Present results indicate that the enrofloxacin treatment for broilers at the inherent dosage is able to select fluoroquinolone resistance in C. jejuni. We conclude that whatever enrofloxacin dosage is used, an emergence of fluoroquinolone resistant of C. jejuni occurs.

Macrolide resistance in Campylobacter jejuni and Campylobacter coli: molecular mechanism and stability of the resistance phenotype

A collection of 23 macrolide-resistant Campylobacter isolates from different geographic areas was investigated to determine the mechanism and stability of macrolide resistance. The isolates were identified as Campylobacter jejuni or Campylobacter coli based on the results of the hippurate biochemical test in addition to five PCR-based genotypic methods. Three point mutations at two positions within the peptidyl transferase region in domain V of the 23S rRNA gene were identified. About 78% of the resistant isolates exhibited an A-->G transition at Escherichia coli equivalent base 2059 of the 23S rRNA gene. The isolates possessing this mutation showed a wide range of erythromycin and clarithromycin MICs. Thus, this mutation may incur a greater probability of treatment failure in populations infected by resistant Campylobacter isolates. Another macrolide-associated mutation (A-->C transversion), at E. coli equivalent base 2058, was detected in about 13% of the isolates. An A-->G transition at a position cognate with E. coli 23S rRNA base 2058, which is homologous to the A2142G mutation commonly described in Helicobacter pylori, was also identified in one of the C. jejuni isolates examined. In the majority of C. jejuni isolates, the mutations in the 23S rRNA gene were homozygous except in two cases where the mutation was found in two of the three copies of the target gene. Natural transformation demonstrated the transfer of the macrolide resistance phenotype from a resistant Campylobacter isolate to a susceptible Campylobacter isolate. Growth rates of the resulting transformants containing A-2058-->C or A-2059-->G mutations were similar to that of the parental isolate. The erythromycin resistance of six of seven representative isolates was found to be stable after successive subculturing in the absence of erythromycin selection pressure regardless of the resistance level, the position of the mutation, or the number of the mutated copies of the target gene. One C. jejuni isolate showing an A-2058-->G mutation, however, reverted to erythromycin and clarithromycin susceptibility after 55 subcultures on erythromycin-free medium. Investigation of ribosomal proteins L4 and L22 by sequence analysis in five representative isolates of C. jejuni and C. coli demonstrated no significant macrolide resistance-associated alterations in either the L4 or the L22 protein that might explain either macrolide resistance or enhancement of the resistance level.

In vitro activity of 24 antimicrobial agents against Staphylococcus and Streptococcus isolated from diseased animals in Japan

A total of 88 Staphylococcus and 61 Streptococcus isolates from diseased animals throughout Japan were examined in 2000 for the minimum inhibitory concentrations of 24 different antimicrobials by the agar dilution method standardized by the Japanese Society of Chemotherapy. The resistance rates to aminobenzylpenicillin (36.4%) and benzylpenicillin (35.2%) were high in Staphylococcus isolates, and those to oxytetracycline (45.9%) and kanamycin (21.3%) were high in Streptococcus isolates. Two isolates resistant to oxacillin harbored the mecA gene. One was Staphylococcus epidermidis derived from a pig with arthritis, and the other Staphylococcus cohnii from a head of cattle with mastitis.