Salmonella lamphun: first isolation of a new Salmonella serovar in Thailand

Two isolates of a new Salmonella serovar, Salmonella Lamphun were discovered from animal feeds in Thailand, in 2003, which belongs to group C, with antigenic formula 6,8:y: 1,2. Both isolates were susceptible to all antimicrobials tested. The pulsed field gel electrophoresis pattern of both isolates comprises 11 DNA fractions sized 48, 65, 77, 105, 110, 170, 244, 330, 337,453 and 1,135 kbp. Up to April 2005, no human or animal infection by this new Salmonella serovar was reported.

Campylobacter concisus: an evaluation of certain phenotypic and genotypic characteristics

The clinical relevance of Campylobacter concisus in gastrointestinal disease has not been determined definitively. This study investigated the phenotypic and genotypic characteristics of 39 C. concisus isolates from Danish patients with diarrhoea, three isolates from healthy individuals and the type strain. A cytolethal distending toxin (CDT)-like effect on Vero cells was observed in 35 (90%) isolates from patients with diarrhoea, in all three isolates from healthy individuals and in the type strain. Analysis of SDS-PAGE protein profiles and PCR amplification of 23S rDNA assigned the isolates into two distinct, but discordant groups. Automated ribotyping (RiboPrinting) identified 34 distinct patterns among the 43 isolates, but cluster analysis did not separate isolates from patients with diarrhoea from isolates from healthy patients. Random amplified polymorphic DNA (RAPD) analysis with three primers identified 37 unique profiles, but requires further evaluation. The isolates obtained from healthy carriers were distinguished by cluster analysis from the isolates obtained from patients with diarrhoea. All the isolates were susceptible to 11 antimicrobial agents tested. Overall, there was considerable variability between the C. concisus isolates, but there were no clear phenotypic or genotypic differences between isolates from patients with diarrhoea and isolates from healthy carriers. Further evidence is needed to support the possible role of C. concisus as a human enteric pathogen.

beta-Lactamases among extended-spectrum beta-lactamase (ESBL)-resistant Salmonella from poultry, poultry products and human patients in The Netherlands

OBJECTIVES

The purpose of this work was to study the genetic determinants responsible for extended-spectrum beta-lactamase (ESBL) resistance of Salmonella isolated from Dutch poultry, poultry meat and hospitalized humans.

METHODS

Thirty-four ESBL-resistant Salmonella isolates from The Netherlands were tested towards 21 antimicrobial agents. PCR and sequencing were used to determine the underlying genetic determinants responsible for the ESBL phenotypes. The transferability of the ESBL phenotypes was tested by conjugation to a susceptible Salmonella enterica serovar Dublin and plasmid purification, restriction fragment length polymorphism (RFLP) and pulsed-field gel electrophoresis (PFGE) were employed to further characterize a subset of the isolates.

RESULTS

A great genetic diversity was seen among the isolates. The bla(TEM-52) gene was most predominant and was found among Salmonella enterica serovars Blockley, Thomson, London, Enteritidis phage type 14b, Paratyphi B, Virchow and Typhimurium phage types 11 and 507. We also found the bla(TEM-20) gene in S. Paratyphi B var. Java and the bla(TEM-63) gene in S. Isangi. Furthermore, we detected the bla(CTX-M-28) gene in S. Isangi and the bla(CTX-M-3) gene in S. Typhimurium phage type 507. The bla(CTX-M-2) gene was identified in S. Virchow, which also contained a copy of the bla(SHV-2) gene and a copy of the bla(TEM-1) gene. The bla(SHV-12) gene was found alone in S. Concord and together with the bla(TEM-52) gene in S. Typhimurium. Finally, the bla(ACC-1) gene was cloned from a S. Bareilly isolate and was found to be present on indistinguishable plasmids in all S. Bareilly isolates examined as well as in a S. Braenderup isolate and a S. Infantis isolate.

CONCLUSIONS

Our data underscore the diversity of ESBL genes in Salmonella enterica isolated from animals, food products and human patients.

Diversity and Stability of Plasmids from Glycopeptide-ResistantEnterococcus faecium(GRE) Isolated from Pigs in Denmark

In this paper, we examine the plasmid variation between a subset of unrelated GRE isolated from pigs in Denmark between 1995 and 2001 (five from each of the years). The isolates were tested with PFGE, plasmid RFLP, and subsequently Southern blotting with an IS1216V probe. Of the 35 isolates, 31 belonged to the same PFGE type (type I), and the last four belonged to a completely different PFGE type (type II). All 35 isolates contained the same type of large plasmid (approximate size of 150-200 kb), which could be divided into eight different variant types (V0 to V7). Most variance among the plasmid was seen at the end of the 7-year period, coinciding with the ban in 1998 of the macrolide tylosin as growth promoter for pig production. The stability of the plasmid in its original host was compared with stability of the same plasmid in BM4105RF, when both strains were maintained in liquid cultures without the presence of antibiotics for 1,100 generations. Here, the plasmid proved far more stable in its original host environment than in the new host.

Veterinary Drug Usage and Antimicrobial Resistance in Bacteria of Animal Origin

In the production of food animals, large amounts of antimicrobial agents are used for therapy and prophylaxis of bacterial infections and in feed to promote growth. There are large variations in the amounts of antimicrobial agents used to produce the same amount of meat among the different European countries, which leaves room for considerable reductions in some countries. The emergence of resistant bacteria and resistance genes due to the use of antimicrobial agents are well documented. In Denmark it has been possible to reduce the usage of antimicrobial agents for food animals significantly and in general decreases in resistance have followed. Guidelines for prudent use of antimicrobial agents may help to slow down the selection for resistance and should be based on knowledge regarding the normal susceptibility patterns of the causative agents and take into account the potential problems for human health. Current knowledge regarding the occurrence of antimicrobial resistance in food animals, the quantitative impact of the use of different antimicrobial agents on selection of resistance and the most appropriate treatment regimes to limit the development of resistance is incomplete. Programmes monitoring the occurrence and development of resistance and consumption of antimicrobial agents are strongly desirable, as is research into the most appropriate ways to use antimicrobial agents in veterinary medicine.

Relationship between copper, glycopeptide, and macrolide resistance among Enterococcus faecium strains isolated from pigs in Denmark between 1997 and 2003

A significant relationship between copper resistance (tcrB), glycopeptide resistance (Tn1546), and macrolide resistance [erm(B)] in Enterococcus faecium isolated from pigs was found. The tcrB gene was located closely upstream of the Tn1546 element. However, the continued use of copper sulfate has not been able to maintain high levels of macrolide and glycopeptide resistance.

Occurrence of integrons and resistance genes among sulphonamide-resistant Shigella spp. from Brazil

OBJECTIVES

To determine the occurrence of class 1 and 2 integrons and antimicrobial resistance genes among sulphonamide-resistant Shigella strains isolated in Brazil during 1999-2003.

METHODS

Sixty-two Shigella (Shigella flexneri, n = 47 and Shigella sonnei, n = 15) were tested against 21 antimicrobial agents. The presence of integrons classes 1 and 2 and antimicrobial resistance genes was investigated by PCR using specific primers.

RESULTS

A total of eight antimicrobial resistance profiles were identified, with the profile of resistance to sulfamethoxazole, trimethoprim, spectinomycin, streptomycin and tetracycline being the most common among S. sonnei, and additionally to ampicillin and chloramphenicol among S. flexneri. Class 1 integrons were found in only two strains, whereas class 2 integrons were found in 56 (90.3%) of the strains. All class 2-positive strains had a similar fragment of 2214 bp harbouring a gene cassette array conferring resistance to trimethoprim, streptothricin and spectinomycin/streptomycin. The genes coding for resistance to chloramphenicol (catA1), tetracycline [tet(A) and tet(B)] and ampicillin (bla(OXA) and bla(TEM)), were detected in resistant strains.

CONCLUSIONS

The detection of class 1 and 2 integrons and additional antimicrobial resistance genes allowed us to identify the most frequent antimicrobial resistance patterns of Shigella spp. isolated in Brazil.

Characterization of Streptococcus suis serotype 7 isolates from diseased pigs in Denmark

Isolates of Streptococcus suis serotype 7 from diseased pigs in Denmark were characterized by ribotyping, pulsed field gel electrophoresis (PFGE), MIC-determinations and detection of resistance genes. Forty-one different ribotype profiles were found among the 103 isolates and could be divided into two main clusters. No obvious relationship between ribotypes and the clinical origin of the isolates could be observed. Fifty-four isolates, including all 24 isolates belonging to the main ribotype profile were examined by PFGE and 50 different profiles were found. A high frequency of resistance to erythromycin (41%), tetracycline (24%) and streptomycin (28%) was observed. Furthermore, almost all isolates (101) were resistant to sulphamethoxazol. Most isolates were susceptible to ceftiofur, chloramphenicol, florfenicol, penicillin, ciprofloxacin, trimethoprim and trimethoprim + sulphonamides. The tet(M) gene was found among 11 (44%) and the tet(O) gene in six (24%) of 25 tetracycline resistant isolates. The tet(L) and tet(S) genes were not detected in any isolates. The erm(B) gene was detected in 39 (93%) of 42 erythromycin resistant isolates.

Monitoring of Antimicrobial Resistance Among Food Animals: Principles and Limitations

Large amounts of antimicrobial agents are in the production of food animals used for therapy and prophylactics of bacterial infections and in feed to promote growth. The use of antimicrobial agents causes problems in the therapy of infections through the selection for resistance among bacteria pathogenic for animals or humans. Current knowledge regarding the occurrence of antimicrobial resistance in food animals, the quantitative impact of the use of different antimicrobial agents on selection for resistance and the most appropriate treatment regimes to limit the development of resistance is incomplete. Programmes monitoring the occurrence and development of resistance are essential to determine the most important areas for intervention and to monitor the effects of interventions. When designing a monitoring programme it is important to decide on the purpose of the programme. Thus, there are major differences between programmes designed to detect changes in a national population, individual herds or groups of animals. In addition, programmes have to be designed differently according to whether the aim is to determine changes in resistance for all antimicrobial agents or only the antimicrobial agents considered most important in relation to treatment of humans. In 1995 a continuous surveillance for antimicrobial resistance among bacteria isolated from food animals was established in Denmark. Three categories of bacteria, indicator bacteria, zoonotic bacteria and animal pathogens are continuously isolated from broilers, cattle and pigs and tested for susceptibility to antimicrobial agents used for therapy and growth promotion by disc diffusion or minimal inhibitory concentration determinations. This programme will only detect changes on a national level. However, isolating the bacteria and testing for several antimicrobial agents will enable us to determine the effect of linkage of resistance. Since 1995 major differences in the consumption pattern of different antimicrobial agents have occurred in Denmark. The Danish monitoring programme has enabled us to determine the effect of these changes on the occurrence of resistance. The Danish monitoring is, however, not suited to determine changes on a herd level or to detect emergence of new types of resistance only occurring at a low level.

Antimicrobial susceptibility of Haemophilus parasuis and Histophilus somni from pigs and cattle in Denmark

A total of 52 Haemophilus parasuis and 80 Histophilus somni isolates were tested for antimicrobial susceptibility by MIC-determinations. None of the isolates were resistant to ampicillin, ceftiofur, ciprofloxacin, erythromycin, florphenicol, penicillin, spectinomycin, tetracycline, tiamulin, or tilmicosin. Two H. parasuis isolates were resistant to trimethoprim + sulfamethoxazole. Six H. parasuis isolates had reduced susceptibility (0.06-0.5 microg/ml) to ciprofloxacin and 10 reduced susceptibility to TMP + sulfamethoxazole (1-2 microg/ml). This study showed that Danish isolates of H. parasuis and H. somni in general are fully susceptible to antimicrobial agents currently used for treatment of infections with these pathogens.

Development of a Standardized Susceptibility Test forCampylobacterwith Quality-Control Ranges for Ciprofloxacin, Doxycycline, Erythromycin, Gentamicin, and Meropenem

A standardized agar dilution susceptibility testing method was developed for Campylobacter that consisted of testing on Mueller-Hinton medium supplemented with 5% defibrinated sheep blood in an atmosphere of 10% CO2, 5% O2, and 85% N2. Campylobacter jejuni ATCC 33560 was identified as a quality-control (QC) strain. Minimal inhibitory concentration (MIC) QC ranges were determined for two incubation time/temperature combinations: 36 degrees C for 48 hr and 42 degrees C for 24 hr. Quality-control ranges were determined for ciprofloxacin, doxycycline, erythromycin, gentamicin, and meropenem. For all antimicrobial agents tested at both temperatures, 95-100% of the QC MIC results fell within recommended QC ranges. Twenty-one Campylobacter clinical isolates, encompassing five species of Campylobacter (C. jejuni, C. coli, C. jejuni, subsp. doylei, C. fetus, and C. lari) were tested in conjunction with the C. jejuni QC strain. While C. jejuni and C. coli could be reliably tested under both test conditions, growth of C. jejuni subsp. doylei, C. fetus, and C. lari isolates was inconsistent when incubated at 42 degrees C. Therefore, it is recommended that these species only be tested at 36 degrees C.

Salmonella serovars from humans and other sources in Thailand, 1993-2002

We serotyped 44,087 Salmonella isolates from humans and 26,148 from other sources from 1993 through 2002. The most common serovar causing human salmonellosis in Thailand was Salmonella enterica Weltevreden. Serovars causing human infections in Thailand differ from those in other countries and seem to be related to Salmonella serovars in different food products and reservoirs.

Susceptibility of different bacterial species isolated from food animals to copper sulphate, zinc chloride and antimicrobial substances used for disinfection

A total of 569 different bacterial isolates (156 Salmonella, 202 E. coli, 43 S. aureus, 38 S. hyicus, 52 E. faecalis, 78 E. faecium) were tested for susceptibility to copper sulphate, benzalkonium chloride, hydrogen peroxide and chlorhexidine using MIC determinations. A total of 442 isolates were also tested for susceptibility to formaldehyde and 177 isolates for susceptibility to zinc chloride. Enterococcal isolates formed a bimodal distribution of MICs to copper sulphate, whereas the other bacterial species formed one large population. Otherwise the isolates formed one large population of susceptibilities to the different antimicrobial agents. Large variations were observed in the susceptibility of the different bacterial species to the different compounds. Staphylococci were in general very susceptible to all antimicrobial compounds tested. The Salmonella isolates were in general less susceptible to copper sulphate, benzalkonium chloride and chlorhexidine followed by E. coli and the Gram-positive species. The opposite was the case for zinc chloride. All isolates were very susceptible to H(2)O(2) with MICs ranging from 0.002 to 0.016%, and to formaldehyde with MICs at 0.003 and 0.006%. This study showed that Danish bacterial isolates from livestock so far have not or have only to a limited degree developed resistance to antimicrobial compounds commonly used for disinfection. Acquired copper resistance was only found in enterococci. There were large differences in the intrinsic susceptibility of the different bacterial species to these compounds, and Salmonella especially seems intrinsically less susceptible than the other bacterial species, which might have human health implications.

Harmonization of antimicrobial susceptibility testing among veterinary diagnostic laboratories in the five Nordic countries

A total of 100 bacterial strains (25 Escherichia coli, 25 Salmonella enterica, 25 Staphylococcus aureus, and 25 Enterococcus strains) and four reference strains were tested for susceptibility toward 8-12 antimicrobial agents in 12 veterinary diagnostic laboratories in the five Nordic countries using routine methodology. In addition, the 25 Enterococcus strains were identified to species level. A total of 22,598 (97.2%) out of 23,259 test results were in accordance when the data were categorized as susceptible or resistant. When the reported results were categorized according to the National Committee of Clinical Laboratory Standards breakpoints, the percentage of concordant results increased to 98.4% and the performance between laboratories varied between 94.2 and 99.4% concordant results. For E. coli, S. aureus, and Salmonella, all laboratories except one had more than 97% concordant results, whereas for Enterococcus spp., two laboratories had less than 90% concordant results. Susceptibility testing of Salmonella to fluoroquinolones gave rise to almost 0.5% nonconcordant results and susceptibility testing of S. aureus to vancomycin resulted in that 1.8% of the strains were incorrectly reported as vancomycin resistant. Ten laboratories identified the Enterococcus spp. to species level. All five Enterococcus faecium and 10 Enterococcus faecalis selected from the strain collection at the Danish Veterinary Institute were correctly identified by all laboratories, whereas some problems were observed identifying other enterococcal species. This study showed a good performance and agreement in antimicrobial susceptibility testing at the 12 participating laboratories and that surveillance data covering susceptibility test results of E. coli, S. aureus, and Salmonella from animals in the Nordic countries are comparable. But it also showed that some aspects can be improved. In addition, the study showed that the different laboratories are capable of identifying E. faecalis and E. faecium.

The effects of oral and intramuscular administration and dose escalation of enrofloxacin on the selection of quinolone resistance among Salmonella and coliforms in pigs

The effect of route of administration and dose of enrofloxacin (Baytril) on the development of fluoroquinolone resistance in Salmonella and Escherichia coli in the intestinal tract of pigs was investigated. Healthy pigs at the age of 8-10 weeks were infected with a mixture of susceptible wild-type (MICciprofloxacin = 0.03 microg/ml) and a mutant Salmonella typhimurium with reduced susceptibility to fluoroquinolones (MICciprofloxacin = 0.5 microg/ml) (in the ratio 99:1) and treated with 2.5 mg/kg bwt enrofloxacin by either intramuscular (i.m.) or oral (p.o.) administration at time points either 4 or 24 h after the infection. The treatment via the intramuscular route of administration (24 h after the infection) was carried out with elevated doses of 7.5 and 15 mg/kg bwt as well. Emergence of resistance during a 3-day treatment period and persistence up to 13 days after treatment, was monitored by counting the resistant and total number of coliforms and Salmonella in faeces of the pigs. High frequencies of fluoroquinolone resistance developed rapidly among the coliform flora independent of route of administration, dose or time of initiation of the treatment. Selection for resistance among the artificially introduced Salmonella was reduced by using the intramuscular route and by escalating the dose 3 or 6 times the recommended dose of 2.5 mg/kg bwt, which also resulted in shortening of the period, in which the pigs were shedding Salmonella. The resistance among the coliform flora persisted for at least 2 weeks. The Salmonella infection was cleared in all cases during the 2 weeks independent of frequency of resistance. The study showed that resistance is very easily selected by treatment with enrofloxacin at the recommended dose 2.5 mg/kg bwt, but also that the intensity of selection can be reduced by using intramuscular dosing (instead of oral dosing) and by escalating that i.m. dose. The results obtained with Salmonella also showed that even very small changes in the active drug concentrations might completely change the intensity of selection.

Antimicrobial susceptibility and occurrence of resistance genes among Salmonella enterica serovar Weltevreden from different countries

OBJECTIVES

This study was conducted to investigate the occurrence of antimicrobial resistance among Salmonella Weltevreden isolates from different sources in South-East Asia (Indonesia, Laos, Malaysia, Taiwan, Thailand, Vietnam), Australia, Denmark, New Zealand and the USA.

METHODS

A total of 503 isolates were examined for susceptibility to antimicrobial agents, and resistant isolates were examined for the presence of selected resistance genes by PCR.

RESULTS

Only 48 (9.5%) of the isolates were resistant to one or more of the antimicrobial agents tested. A low frequency of resistance was found towards ampicillin (1.8%), chloramphenicol (1.6%), florphenicol (0.4%), nalidixic acid (1.6%), neomycin (0.6%), streptomycin (4.4%), sulfamethoxazole (4.2%), tetracycline (4.0%) and trimethoprim (1.4%), whereas all isolates were susceptible to co-amoxiclav, ceftiofur, ciprofloxacin, colistin and gentamicin. All nine ampicillin-resistant isolates contained a sequence similar to the blaTEM-1b gene, one of the eight chloramphenicol-resistant isolates a sequence similar to the catA1 gene, all three neomycin-resistant isolates a sequence similar to the aphA-2 gene, 16 (73%) of the 22 streptomycin-resistant isolates a sequence similar to the aadA gene, the remaining six (27%) a sequence similar to the strA gene, and all 21 sulfamethoxazole-resistant isolates a sequence similar to the sul2 gene. Thirteen (65%) of the 20 tetracycline-resistant isolates contained the tet(A) gene, four (20%) the tet(B) gene, and one (5%) the tet(C) gene.

CONCLUSIONS

This study showed a low frequency of resistance among Salmonella Weltevreden isolated from humans and other reservoirs in South-East Asia and elsewhere. There was no major difference in the occurrence of resistance between source or geographical origin.

Susceptibility of Escherichia coli and Enterococcus faecium isolated from pigs and broiler chickens to tetracycline degradation products and distribution of tetracycline resistance determinants in E. coli from food animals

One hundred Escherichia coli isolates from diseased and healthy pigs, cattle and broiler chickens were screened for the presence of tetracycline resistance genes tet(A), (B), (C), (D) or (E). The tet(A) gene was the most abundant (71% of the 100 isolates) followed by tet(B) (25%). The predominance of tet(A) and tet(B) applied to all three animal species, and there was no difference between the distribution of tet(A) and tet(B) genes among non-pathogenic and pathogenic E. coli in any of the animal species. The susceptibility of 20 of these isolates together with 10 tetracycline sensitive E. coli and 18 tetracycline resistant and 10 sensitive Enterococcus faecium to tetracyclines and tetracycline degradation products was determined. The resistant isolates showed reduced resistance to anhydrotetracycline, 4-epi-anhydrotetracycline, anhydrochlortetracycline and 4-epi-anhydrochlortetracycline. In general both the tetracycline resistant and susceptible E. faecium were more susceptible to the compounds tested than E. coli.

Streptogramin resistance among Enterococcus faecium isolated from production animals in Denmark in 1997

The genetic background for streptogramin resistance was examined in Enterococcus faecium isolated from pigs (n = 55) and broilers (n = 207) in 1997 in Denmark. Fifty-one percent and 67%, respectively, of the isolates were resistant to streptogramins. Among streptogramin-resistant E. faecium (SREF), the genetic background for streptogramin A resistance could be determined in 96% of the isolates from broilers, compared with 14% among SREF from pigs. For broiler isolates 89% of SREF contained the vat(E) gene and 10% the vat(D) gene. Three of these isolates contained both resistance genes. Among SREF from pigs two isolates contained the vat(E) gene and two others the vat(D) gene. The genetic background for streptogramin B was most often identified as the erm(B) gene encoding macrolide, lincosamide, and streptogramin B (MLSB) resistance. Among SREF, 84% and 86% of isolates from broilers and pigs, respectively, contained the erm(B). In SREF from broilers, the erm(B) gene was physically linked to the vat(E) gene in 62% of the vat(E)-positive isolates and 79% of the isolates containing vat(D). erm(A) was detected in two SREF of broiler origin. Both isolates also contained the erm(B) gene. No SREF contained the vgb(A) gene encoding streptogramin B resistance. On the basis of genetic characterization, streptogramin-resistant isolates from broiler were divided into subgroups, according to the presence of the streptogramin A genes, to determine possible co-resistance to antimicrobials, especially glycopeptides. Twenty-five percent of the SREF from broilers were glycopeptide resistant (MIC > 16 microg/ml). None of the isolates containing the streptogramin A gene vat(D) was resistant to glycopeptide, whereas isolates containing the vat(E) gene had a lower prevalence to glycopeptide resistance than the streptogramin-sensitive isolates.

WHO global salm-surv external quality assurance system (EQAS): an important step toward improving the quality of Salmonella serotyping and antimicrobial susceptibility testing worldwide

Initiated in 2000, WHO Global Salm-Surv is a global network of epidemiologists and microbiologists involved in Salmonella surveillance. WHO Global Salm-Surv seeks to enhance the capacity of national and regional reference laboratories to conduct Salmonella serotyping and antimicrobial susceptibility testing through international training courses and an External Quality Assurance System (EQAS). In 2000, 44 WHO Global Salm-Surv member laboratories from 35 countries determined the serotype and antimicrobial susceptibility pattern for eight "blinded" Salmonella isolates. For serotyping, 73% of the results were correct. For susceptibility testing, 92% of the results were in agreement with the expected results. However, only 78% of the performed tests with the E. coli ATCC 25922 reference strain were within the quality control range specified by National Committee for Clinical Laboratory Standards (NCCLS) guidelines. These EQAS results demonstrate the need for further training to improve the performance of some of the laboratories. WHO Global Salm-Surv activities, including international training courses and EQAS, represent an important step toward improving the quality of Salmonella serotyping and antimicrobial susceptibility testing worldwide, and improving the current reliability and comparability of Salmonella surveillance data obtained from different countries,

Observing bacterial activity interferometrically

It is shown that bacterial activity, even of slowly growing species, can be detected by precise interferometric measurements of refractive index changes of the culture medium. The bacteria-containing sample is kept in an isothermal block together with a reference liquid without bacteria. The biological activity is obtained from the difference of the index changes of these samples. Experiments were performed with Bacilo Calmette-Guérin. The order of magnitude of the observed total refractive index change was compatible with theoretical estimates based on the amount of available oxygen. An unexpected positive index change during the lag phase was observed, which might permit fast diagnostics in medical applications. This technique may provide cheap and quick tests of bacterial susceptibility with respect to antibiotics.

Evaluation of the surveillance program of Streptococcus agalactiae in Danish dairy herds

The aim of this study was to evaluate the Danish surveillance program of Streptococcus agalactiae in dairy herds with respect to 1) fluctuation over time of the presence of S. agalactiae in bulk tank milk, 2) sensitivity and specificity of the bacteriological method used, and 3) contamination of bulk tank milk samples with milk from other herds. From June to September 1996, bulk tank milk was sampled from 100 Danish dairy herds seven times, with intervals of 2 wk. The samples were examined for the presence of S. agalactiae by four different methods: 1) by the method approved for the program, 2) after ultrasonic treatment of the milk before examination, 3) after freezing down the milk before examination, and 4) after selective preparation of the milk. Selected strains of S. agalactiae were examined by restriction fragment length polymorphism of the gene encoding rRNA to discriminate between the isolates. Streptococcus agalactiae was found in eight of 96 herds in which S. agalactiae had never previously been found during the surveillance program. Streptococcus agalactiae was not found in all seven sampling rounds in any of the eight herds. Comparing the approved method with supplemental findings by the other methods, the estimated sensitivity was (95% confidence limits): 0.786 (0.628; 0.892) and the estimated specificity (95% confidence limits): 0.995 (0.985; 0.999). Using all four methods on the same sample could increase the sensitivity, but by comparing the methods individually, there was no significant difference between any of them (P > 0.10). In milk samples from three herds, the ribotype of S. agalactiae was the same as in milk from herds sampled just before; therefore, it could not be ruled out that cross-contamination could occur. Taking into account that S. agalactiae in bulk tank milk reflects the presence of S. agalactiae in at least one udder quarter, this investigation gives further reason to assume that S. agalactiae can be seen sporadically in several herds. A surveillance program based on annual bulk tank milk sample examinations will only detect a limited number of S. agalactiae infected herds. If the overall aim is to identify herds where the infection is established, annual bulk tank milk sample examinations combined with the information of number of colonies of S. agalactiae in the sample will be sufficient.

Distribution of enrofloxacin in intestinal tissue and contents of healthy pigs after oral and intramuscular administrations

The concentration of enrofloxacin in plasma, intestinal tissue, lymph nodes and intestinal contents was investigated in healthy pigs after oral (p.o.) and intramuscular (i.m.) administration of a single dose of 2.5 mg/kg bw. Tissue and content samples were collected from jejunum, ileum, caecum and colon from pigs killed at 2, 3 and 6 h after dosing. Intramuscular administration resulted in significantly higher concentrations in plasma, intestinal tissue and lymph nodes at 2 h but not at 3 or 6 h compared with p.o. administration. The absorption and distribution phase was longer after oral administration, and maximum concentrations in tissue and plasma were determined later than after i.m. administration. No difference between route of administration was observed in the intestinal content. Enrofloxacin concentrations in faeces during a 5-day dosing regimen with i.m. and p.o. administration were determined by both HPLC and bio-assay. Higher concentrations were found after i.m. administration during the first day, but the difference was not significant after 2 days. The biologically active concentrations determined by bio-assay constituted 48-75% of the total concentrations determined by HPLC. On the basis of these results it was concluded that in order to ensure an immediate high concentration of enrofloxacin, and thereby avoid an initial selection for resistant mutants, the intramuscular route seems to be preferable to the oral route.