Persistence of multidrug-resistant Staphylococcus haemolyticus in an animal veterinary teaching hospital clinic.

In the recent decades, coagulase-negative staphylococci (CNS) have emerged as important nosocomial pathogens with the ability to develop resistance to antibiotics and disinfectants. Multidrug-resistant CNS are currently a common finding in hospital settings and hospitalized patients. Little is known about the occurrence and persistence of multidrug-resistant CNS in animal clinics. A survey of the environmental bacterial flora in a small animal clinic showed a predominance of bacterial species commonly isolated from skin and feces of warm-blooded animals and the environment. At samplings separated by 3 years, multidrug-resistant Staphylococcus haemolyticus was isolated from the floor of four separate animal cages and from a cat's postoperative wound infection. Pulsed-field electrophoresis, multilocus enzyme typing, susceptibility testing, and genotypic characterization suggested that the multidrug-resistant S. haemolyticus isolates belonged to an epidemiological clone. All isolates harbored a chromosomal copy of the mecA gene, a 45-kb plasmid harboring the blaZ and qacA/B determinants, and all except one isolate carried multiple plasmids in the size range 1-22 kb, of which those <5 kb encoded resistance to tetracycline (tetK), macrolides (ermB), and chloramphenicol (cat). One isolate carried a chromosomal copy of the bifunctional gene aacA-aphD conferring resistance to gentamicin. The isolate that was deficient of small plasmids had reverted to a macrolide and chloramphenicol-susceptible phenotype, but had retained its tetracycline resistance due to IS257-mediated integration of the tetK plasmid into the mec region of the chromosome. This finding illustrates bacterial intracellular mobility of resistance genes in natural environments, and highlights the role of insertion sequences in the evolution of multidrug resistance islands on the bacterial chromosome.

Genetic linkage between erm(B) and vanA in Enterococcus hirae of poultry origin.

Vancomycin-resistant enterococci (VRE) have frequently been isolated from Norwegian poultry production following the prohibition of the glycopeptide growth promoter avoparcin since 1995. In the present study, a close genetic linkage between the vanA and erm(B) determinants in an Enterococcus hirae isolate of poultry origin is demonstrated, a result that indicates a mechanism for co-selection and maintenance of vancomycin resistance in absence of selective pressure from avoparcin. A total of 36 vanA-positive enterococci of poultry origin, also phenotypically resistant to erythromycin and/or tetracycline, were analyzed by PCR for identification of erm and tet resistance determinants. An E. hirae isolate harbored erm(B) and tet(K), and in this isolate vanA and erm(B) were located on a BamHI fragment of an approximately 50-kb plasmid. Approximately 3 kb of this fragment was amplified by PCR with vanA and erm(B) primers. Sequence analysis of the region between erm(B) and vanZ of Tn1546 showed a truncated IS1216V inserted downstream of the erm(B) stop codon, aligned with a conserved copy of the 3'-inverted terminal repeat of Tn1546. Mating experiments with the E. hirae isolate as donor and E. faecalis JH2-2 as recipient did not result in any transconjugants, indicating that the vanA/erm(B)-carrying plasmid was nonconjugative under the given experimental conditions.

Review of Shiga-toxin-producing Escherichia coli (STEC) and their significance in dairy production.

The involvement of the pathogenic Shiga-toxin-producing Escherichia coli (STEC; also called verocytotoxic-producing E. coli or VTEC) in sporadic cases and disease outbreaks is presently increasing. Infrequent cases are due to ingestion of milk and dairy products. As ruminants are healthy carriers of STEC and most dairy products may provide these bacteria with favourable conditions for their growth, milk and dairy products are a potential source of STEC. But not all STEC serotypes are pathogens; only relatively small numbers in the entire family of STEC are pathogenic. This review focuses on the recent advances in understanding of STEC and their significance in milk and dairy products. It is intended to gather the information that is needed to understand how these bacteria are described, detected and characterised, how they contaminate milk and grow in dairy products, and how the dairy industry can prevent them from affecting the consumer.

Fusidic acid resistance, mediated by fusB, in bovine coagulase-negative staphylococci.

OBJECTIVES: The aim of this study was to determine the occurrence of fusidic acid resistance, mediated by the fusB gene, among coagulase-negative staphylococci (CoNS) isolated from bovine mastitis. METHODS: A total of 113 CoNS isolates were screened for susceptibility to fusidic acid by using a disc diffusion method. The fusB gene was detected by using PCR and subsequent DNA sequencing. The localization of fusB was determined by hybridization. RESULTS: The fusB gene was detected in 3 of 11 fusidic acid-resistant bovine CoNS isolates. The organization of the fusB downstream region on a 40 kb plasmid in a Staphylococcus haemolyticus isolate (288/96) was highly similar to the previously reported organization of fusB on plasmid pUB101 from a Staphylococcus aureus isolate of human origin. The fusB gene was chromosomally located in the remaining two isolates. CONCLUSIONS: Fusidic acid resistance mediated by fusB is not the dominant resistance mechanism in fusidic acid-resistant CoNS studied in this work. The similarity between the organization of the fusB downstream region in S. haemolyticus (isolate 288/96) and on plasmid pUB101 from an S. aureus isolate of human origin indicates a common ancestral origin of these genes.

Deletion of pT181-like sequence in an smr-encoding mosaic plasmid harboured by a persistent bovine Staphylococcus warneri strain.

OBJECTIVES: The aim was to study the persistence and characteristics of Staphylococcus warneri strains resistant to quaternary ammonium compounds (QACs), including sequencing and analysis of two plasmids proved to carry the smr gene. METHODS: During a 3.5 year period quarter milk samples were collected on three occasions from all lactating cows in a dairy herd. The samples were screened with regard to QAC-resistant bacteria using a selective medium. Thirty randomly selected QAC-resistant S. warneri were typed by PFGE and subjected to plasmid isolation and analysis followed by gene detection using PCR. Two smr-containing plasmids in S. warneri isolates were sequenced. RESULTS: All isolates from the initial collection of quarter milk contained smr residing on a 5.8 kb plasmid (pSW174), which contained regions with high similarities to various plasmids, including pT181, pSK108 and pPI-2. The pT181-like sequence was flanked by 148 bp direct repeats, denoted ISLE49, with high similarity to previously reported sequences of approximately 148 bp, including ISLE39 flanking the insertion sequence IS257 in methicillin-resistant Staphylococcus aureus. All isolates from subsequent collections of quarter milk harboured a smaller smr-containing plasmid (pSW49). Sequence analyses revealed pSW49 (3552 bp) to be an in-part deleted version of pSW174 (5767 bp). CONCLUSIONS: The IS-associated elements found in this study may have a wider role in the integration and excision of DNA sequences in staphylococci than previously reported. The mosaic plasmid structure based on genetic elements of various origins contributes to further knowledge on the flexibility of smr-encoding plasmids.

Acidified litter benefits the intestinal flora balance of broiler chickens.

The alterations in the balance of the normal intestinal bacterial flora of chickens exposed to acidified wood-derived litter were analyzed and compared to those of a control group exposed to nonacidified litter. A total of 1,728 broilers were divided into two groups, with six replicates in each. One group was exposed to dry wood-derived litter, and the other was exposed to dry wood-derived litter sprayed with a mixture of sodium lignosulfonate, formic acid, and propionic acid. At five different times, five chickens from each pen were killed and the intestinal contents from ileum and caeca were collected. The samples were diluted and plated onto selective media to identify coliforms, Lactobacillus spp., Clostridium perfringens, and Enterococcus spp. Covariance analysis of bacterial counts showed significantly lower counts for C. perfringens in the caeca and the ileum and for Enterococcus spp. and Lactobacillus spp. in the ileum in chickens exposed to the acidified litter. Lactobacillus spp. showed significantly higher counts in the caeca in chickens exposed to acidified litter. There was no difference between the two litters with regard to coliforms in the ileum and the caeca or to Enterococcus spp. in the caeca. The study shows that exposing the chickens to acidified litter lowers the intestinal bacterial number, especially in the ileum, without negative consequences for the chicken's health or performance. Of special interest are the lower counts of C. perfringens and Enterococcus spp. that might reduce the risk of developing clinical or subclinical necrotic enteritis and growth depression.