Antibiotic resistance among indicator bacteria isolated from healthy pigs in New Zealand.

AIM: To determine the resistance to antibiotics among the indictor bacteria, Escherichia coli and Enterococcus spp, isolated from the faeces of healthy pigs on three conventional pig farms and one organic farm in the North Island of New Zealand. METHODS: Faecal samples, collected at intervals between March and October 2001, were plated onto MacConkey agar and Slanetz-Bartley agar and examined after 1-3 days incubation for colonies resembling E. coli and Enterococcus spp, respectively. Typical colonies were subcultured for further identification and storage. The isolates were tested for antibiotic resistance, using disc diffusion, to ampicillin, gentamicin, streptomycin, and tetracycline. Escherichia coli isolates were also tested for resistance to ciprofloxacin, cotrimoxazole and neomycin. Enterococcus spp isolates were also tested for resistance to vancomycin, erythromycin and virginiamycin. RESULTS: A total of 296 E. coli and 273 Enterococcus spp isolates were obtained from the three conventional farms, and 79 E. coli and 80 Enterococcus spp isolates were obtained from the organic farm. All the E. coli isolates from both the conventional and organic pig farms were susceptible to ciprofloxacin, and all the Enterococcus spp isolates were susceptible to ampicillin, gentamicin and vancomycin. Isolates of E. coli from conventional pig farms were resistant to gentamicin (0.7%), neomycin (0.7%), ampicillin (2.7%), cotrimoxazole (11%), streptomycin (25%) and tetracycline (60%). Enterococcus spp isolates from the same farms were resistant to erythromycin (68%), tetracycline (66%), streptomycin (54%) and virginiamycin (49%). By contrast, for the organic pig farm

Humoral immunity in cats infected with feline immunodeficiency virus or leukaemia virus.

The humoral antibody responses of 82 domestic cats to the common commensal bacteria Pasteurella multocida and Staphylococcus aureus were measured by an indirect immunofluorescence assay to give a subjective quantification of specific IgG in serum. There was no significant difference in specific serum IgG levels between sick cats which tested antibody-positive to feline immunodeficiency virus or antigen-positive to feline leukaemia virus and sick, virus-negative cats. This finding suggested that there was no change in immune status, as measured by this method, in both feline leukemia and feline immunodeficiency virus infections, although, based on clinical signs shown by the virus-positive cats, overall immunosuppression was indicated. Feline immunodeficiency virus and feline leukemia virus infection may have an effect on cellular immunity, as is the case with human immunodeficiency virus.

A second community outbreak of waterborne giardiasis in Canada and serological investigation of patients.

A waterborne outbreak of giardiasis which occurred 5 years after another in the same town in Canada was investigated. Sera from residents defined as cases or non-cases were tested by enzyme-linked immunosorbent assay (ELISA) and compared with sera from symptomatic and asymptomatic control groups. The outbreak-associated Giardia isolate was retrieved from contaminated drinking water and antigen from this strain was used in the serological investigation. Up to 84% of cases were identified by ELISA. More cases were identified by elevated immunoglobulin (Ig) G than by either elevated anti-Giardia IgA or IgM levels. Residents of the community infected during the first outbreak were significantly less likely to have been reinfected during the second outbreak. This is the first report of a second waterborne outbreak occurring in a community and results of the investigations are consistent with an acquired, protective immunity lasting at least 5 years.

Pathogenesis of intraabdominal abscess formation: abscess-potentiating agents and inhibition of complement-dependent opsonization of abscess-inducing bacteria.

Bacteroides fragilis and Escherichia coli are synergistic in the production of intraabdominal abscesses. However, these bacteria initiate abscess formation only when inoculated with an agent such as autoclaved colonic contents (ACC) or bran (a fiber analogue). The mechanism of action of the abscess-potentiating agent was studied. Opsonins in normal mouse serum were determined for phagocytic killing by murine neutrophils of B. fragilis and E. coli. Opsonization required fixation of complement by the alternative pathway. ACC (0.2 mg/ml) and bran (1.0 mg/ml) inhibited phagocytic killing of Proteus mirabilis in the presence of normal but not immune serum. Assay of the alternative pathway of complement activation indicated that both bacterial components and abscess-potentiating agents in an abscess-inducing mixture activated complement. These findings suggest that abscess-potentiating agents inhibit opsonization and therefore the subsequent phagocytic killing of bacteria in the nonimmune host.

Bacterial killing in vitro by abscess-derived neutrophils.

In the absence of antimicrobial therapy, bacteria such as Bacteriodes fragilis, Escherichia coli and Proteus mirabilis may persist within an intra-abdominal abscess in the presence of large numbers of neutrophils which, under optimal conditions in vitro, can readily phagocytose and kill the same bacterial strains. Neutrophils taken from abscesses induced by gram-negative bacteria such as those above contain viable organisms. On incubation in vitro in the presence of serum, these neutrophils kill the bacteria phagocytosed in the abscess poorly, if at all, yet can readily kill organisms added in vitro. To determine possible mechanisms that might explain this, we examined the bactericidal activity in vitro of neutrophils from a range of abscesses induced by one or two species of bacteria plus an abscess-potentiating agent, bran. The organisms studied were B. fragilis, E. coli, P. mirabilis and Staphylococcus aureus. The killing in vitro of E. coli and P. mirabilis, engulfed within an abscess, was significantly less than that of the same organisms when they were added to the in-vitro assay. In contrast, the killing of S. aureus was similar, whether engulfed in vivo or in vitro. However, S. aureus was less susceptible to phagocytosis and killing in vitro than P. mirabilis or E. coli, and the killing of S. aureus during in-vitro incubation of neutrophils that had engulfed the organism with in the abscess was similar to that of the gram-negative bacteria engulfed within the abscess.(ABSTRACT TRUNCATED AT 250 WORDS)

T-lymphocyte involvement in abscess formation in nonimmune mice.

Athymic mice formed significantly smaller abscesses than euthymic mice in response to the intraperitoneal inoculation of an abscess-inducing mixture of Escherichia coli, Bacteroides fragilis, and autoclaved colonic contents, an abscess-potentiating agent. Adoptive transfer of nonimmune, Thy-1-positive spleen cells to athymic mice restored their ability to make abscesses of sizes similar to those in controls, indicating that T lymphocytes contribute to abscess formation in normal mice.

Neutrophil activity in abscess-bearing mice: comparative studies with neutrophils isolated from peripheral blood, elicited peritoneal exudates, and abscesses.

Intraabdominal abscesses were induced in mice by intraperitoneal inoculation of Bacteroides fragilis and Escherichia coli plus bran as the abscess-potentiating agent. Six- or seven-day-old abscesses were mechanically disaggregated in buffer, and the cells obtained were fractionated on discontinuous Percoll density gradients. Neutrophil populations of different density, each approximately 90% pure, were isolated. When the abscess-derived neutrophils were subsequently incubated with normal serum in vitro under aerobic conditions, the viability of the gram-negative bacteria that had been phagocytosed within the abscess did not change significantly. This anergy to intracellular bacteria (on subsequent incubation in vitro under optimal conditions for phagocytic killing) was also found for neutrophils that had been obtained from abscesses induced by a mixture that included Proteus mirabilis plus B. fragilis and from those induced by E. coli plus P. mirabilis. While unable to significantly kill intracellular organisms that had been phagocytosed in vivo, the abscess-derived neutrophils could engulf and kill organisms to which they were exposed in vitro. Neutrophils from abscesses induced by P. mirabilis only plus bran killed that organism introduced in vitro significantly more effectively than the organisms that had been engulfed in vivo. In contrast, neutrophils from abscesses induced by the gram-positive organism Staphylococcus aureus plus bran were able to kill their intracellular organisms on subsequent incubation in vitro as effectively as they could kill added S. aureus. Neutrophils isolated from the peripheral blood and from induced peritoneal exudates of abscess-bearing mice were able to phagocytose and kill organisms in vitro with greater efficiency than abscess-derived neutrophils. The mechanism whereby neutrophils from abscesses induced by the gram-positive organism S. aureus can kill the organisms phagocytosed in vivo on subsequent in vitro incubation, in contrast to the relative anergy to their intracellular organisms displayed by neutrophils derived from abscesses induced by combinations of gram-negative bacteria, is not known.

Opsonins in normal mouse serum for the phagocytic killing of Proteus mirabilis by murine neutrophils.

An assay of phagocytic killing by murine neutrophils in homologous serum was used to determine the nature of the opsonins in normal mouse serum for phagocytic killing of Proteus mirabilis. Leucocytes from the peritoneal cavities of mice given an intraperitoneal inoculation of brain-heart infusion broth 3 h previously, phagocytosed and killed P. mirabilis in a 2-h assay in the presence of 10% serum from normal mice. The serum factors supporting phagocytic killing were heat-labile (50 degrees C or 56 degrees C for 30 min) and could be absorbed at 37 degrees C but not 4 degrees C by three different species of Gram-negative bacteria. The tested species of Gram-positive bacterium did not absorb the activity. At the end of the assays, greater than 90% of leucocyte-associated bacteria were associated with neutrophils. Leucocytes from unstimulated peritoneal cavities (less than I% neutrophils) did not kill bacteria in this assay, in contrast to leucocyte suspensions containing up to 98% neutrophils. These findings indicated that the phagocytic killing of P. mirabilis in this assay was mediated by neutrophils, and that complement fixation by the alternative pathway provided necessary opsonins in normal mouse serum.

Intra-abdominal abscess formation in mice: quantitative studies on bacteria and abscess-potentiating agents.

A model of intra-abdominal (IA) abscess formation has been developed in mice. Intraperitoneal (i.p.) injection of a mixture of a potentiating agent (autoclaved colonic and caecal contents (ACC), 0.2 mg dry wt/mouse or sterile bran, 1 mg dry wt/mouse), Escherichia coli (1 X 10(6) colony forming units (cfu)/mouse) and Bacteroides fragilis (5 X 10(8) cfu/mouse) induced abscesses in 98% of mice inoculated. The abscesses persisted for at least 4 weeks in 60% of inoculated animals, and for 10 weeks in 36%. From 1 to 5 abscesses per mouse were found. Abscess formation was quantified by weighing the dissected abscesses and by culturing bacteria from them. Histologically, the abscesses were characterized by a central region of polymorphonuclear leucocytes, often with a thin mononuclear phagocyte infiltrate surrounding it, and an outer wall of vascularized connective tissue. Fluorescent antibody studies demonstrated that antigens from both bacterial species were distributed throughout the abscess. At the concentrations used, neither ACC nor sterile bran induced formation in the absence of viable bacteria.