Antibiotic resistance in Campylobacter spp. isolated from human faeces (1980-2000) and foods (1997-2000) in Northern Ireland: an update.

Sir, Thermophilic Campylobacter spp. , particularly Campylobacter jejuni and Campylobacter coli, continue to be the faecal pathogens most frequently isolated in Northern Ireland, with approximately 1000 laboratory reports per year. Although oral antibiotics are not normally prescribed in the majority of cases, antimicrobial therapeutic intervention may be required owing to the immunocompromised state of the patient or any other predisposing complication. Presently, there are very limited data in the literature on fluoroquinolone resistance in food and human faecal sources from Northern Ireland. Furthermore, as there is growing concern regarding rates of fluoroquinolone resistance in human isolates and the associated employment of similar agents within animal production, a study was initiated to examine the trends and rates of antibiotic resistance within human isolates submitted to the Northern Ireland Public Health Laboratory (NIPHL) over the last 20 years, 1980–2000, as well as to examine trends in resistance rates in campylobacters isolated from food sources in Northern Ireland over a more recent time period (1997–2000). Human isolates were obtained from faecal specimens submitted to NIPHL for routine analysis from general practitioners, as well as from hospital wards, over the period 1980–2000 (n 2066). Isolates were obtained by direct selective plating onto Preston’s selective agar and incubated at 42°C for 48 h. Food samples were collected from retail premises by Environmental Health Officers from the 26 local council authorities within Northern Ireland and campylobacters (n 729) were isolated in accordance with a method previously described by the Public Health Laboratory Service, modified to include 25 g chicken neck skin. Antibiotic susceptibility studies were performed at 37°C for both food and human isolates by a disc diffusion method employing the following antibiotic agents at the given disc concentrations: penicillin (2 g), cefalexin (30 g), erythromycin (5 g), chloramphenicol (10 g), gentamicin (10 g), tetracycline (10 g) and ciprofloxacin (1 g). In addition, all human isolates for the period 1980–1995 were also tested against novobiocin (5 g), kanamycin (30 g) and neomycin (30 g). Food isolates were also examined for trimethoprim susceptibility employing a 5 g disc concentration. Antibiotic resistance trends for erythromycin, ciprofloxacin, and tetracycline for foods (1997–2000) and human isolates (1996–2000) are shown in the Table. All food and human isolates examined were resistant to penicillin and cefalexin and susceptible to chloramphenicol and gentamicin. In addition, all food isolates were resistant to trimethoprim. For faecal isolates prior to 1996, chloramphenicol resistance was first noted in 1993 (1.4%) and also 1995 (0.8%); macrolide resistance in faecal isolates remained low with 2.0% and 2.6% of clinical isolates being resistant to erythromycin in 1987 and 1994, respectively; fluoroquinolone resistance in human isolates was 3.8% in 1992, increasing to 10% in 1993. Prior to 1992, over the 11 year period 1980–1991, no resistance to nalidixic acid was detected. The NIPHL has historically received between onequarter and one-third of all Northern Ireland Campylobacter faecal isolates and the majority of all isolates received generally originate from a mainly urban population. Like most other UK clinical diagnostic laboratories, confirmed human campylobacters are not characterized to the species level, as a generic identification accompanied by an antibiogram of suitable antimicrobial agents relating to the isolate is sufficient and cost-effective for the clinical management of most infected individuals. For the period 1989–1990 only 17% of human campylobacters reported to the CDSC were characterized to the species level, and hence it should be noted that failure to speciate these organism may mask shifts in rates of infection between the species. In 2000, a slight rise to 4.2% in the frequency of erythromycin resistance was noted in the human population and concurrent to this, an approximately four-fold rise in macrolide resistance was noted in retail raw chicken. In comparison to overall UK resistance rates for erythromycin of 1.8%, Northern Ireland rates are slightly higher