Occurrence and Antibiotic Sensitivity of Listeria monocytogenes Strains Isolated from Oysters, Fish, and Estuarine Water

Abstract

We analyzed the presence of Listeria spp. in oyster, fish, and seawater samples and tested isolates for antibiotic sensitivity. Listeria monocytogenes was found in 4.5% of fish samples and 8.3% of seawater samples and was not recovered from oysters. Multiresistant environmental strains were found, representing a potential threat to human health.Human listeriosis is a public health problem of low incidence but high mortality, requiring prompt diagnosis and adequate antibiotic therapy (1). Over the last 2 decades a high number of food-borne listeriosis outbreaks have occurred, some with high mortality rates (2,13,19). Antibiotic resistance and inefficient empirical treatment of Listeria infections could be responsible for this increased mortality (4). Since the first multiresistant Listeria monocytogenes strain was observed in France (14), different antibiotic resistance patterns in environmental, food, and clinical sources have been reported (7,12,20). Information on the presence of Listeria monocytogenes in Mexico is scarce, and the frequency of listeriosis is unknown. The purpose of this study was to determine the presence of Listeria spp. in fish, oysters, and saline waters in an area where fish are caught for local and regional consumption and to determine the sensitivities of the L. monocytogenes isolates to different antimicrobial agents.A total of 66 oyster, 66 fish, and 144 estuarine water samples were collected over a 12-month period (June 2001 to May 2002) from 12 sites of the Pueblo Viejo lagoon, Veracruz, Mexico (Fig. 1). Fish and oyster samples were transported on dry ice in separate thermal containers, and estuarine water samples were collected in sterile plastic bottles (Nalgene) and transported to the laboratory on ice. Oyster and fish samples were processed as previously described (9). Seawater samples were filtered through a 14-cm-diameter and 0.45-m-pore membrane (Millipore). Twenty-five milliliters of seawater or 25 g oyster or fish samples was added to 225 ml enrichment broth (EB; Merck) and incubated at 30°C for 24 to 48 h. The filter used for the water samples was washed with 100 ml peptone solution (0.1%), added to 225 ml EB, and incubated at 4°C for 7 days. Afterwards, a 0.1-ml sample was streaked in Oxford agar (Oxoid) and incubated at 30°C for 24 to 48 h. L. monocytogenes isolates were identified and serotyped as previously described (8). Antibiotic sensitivity was assessed using the Kirby-Bauer disk diffusion assay. The test and control strains were seeded in Mueller-Hinton agar supplemented with 0.5% defibrinated sheep blood and 0.1% esculin (17). Commercially available disks (Bio-Rad) with the following antibiotics were used: ampicillin, cephalothin, cefotaxime, ceftazidime, cefuroxime, dicloxacillin, erythromycin, gentamicin, pefloxacin, penicillin, tetracycline, and trimethoprim-sulfamethoxazole. MICs at which 50% of the isolates were inhibited (MIC 50 s) and MIC 90 s were calculated by following the CLSI (formerly NCCLS) guidelines (11). L. monocytogenes ATCC 19114, Escherichia co...

Outdoor environment as a source of Listeria monocytogenes in food chain

“…The environmental isolates were also susceptible to other antimicrobials tested. Although l. monocytogenes is commonly susceptible to a wide range of antimicrobials, some authors have reported tetracycline resistance in environmental strains of l. monocytogenes (MacGowan et al 1994) or multidrug resistance to ampicillin, erythromycin, tetracycline, dicloxacillin, and co-trimoxazole (Rodas-Suárez et al 2006). The monitoring of l. monocytogenes resistance to antimicrobials is currently needed as well as the development of international criteria for the evaluation of resistant strains.…”

Scientific Opinion on the minimum hygiene criteria to be applied to clean seawater and on the public health risks and hygiene criteria for bottled seawater intended for domestic use

“…monocytogenes is widespread in the environment and commonly occurs in surface waters (Colburn et al, 1990;Wilkes et al, 2011) which will consequently contaminate estuarine and coastal waters (Beleneva, 2011;Bou-m'handi et al, 2007;Colburn et al, 1990;El-Shenawy and El-Shenawy, 2006;El Marrakchi et al, 2005;Hansen et al, 2006;Rodas-Suarez et al, 2006;Rorvik et al, 1995). Consumption of contaminated processed fish and shellfish has been associated with transmission of infection (Brett et al, 1998;Ericsson et al, 1997;Facinelli et al, 1989;Farber et al, 2000;Lyytikainen et al, 2006;Misrachi, 1991;Mitchell, 1991;Riedo et al, 1994;Tham et al, 2000).…”

Listeria monocytogenes in mussels (Mytilus galloprovincialis) harvested from North Aegean coastal area

“…Although most isolates of L. monocytogenes and other Listeria spp. are susceptible to antibiotics active against gram-positive bacteria, there are several reports on the occurrence of antibiotic resistance in L. monocytogenes isolated from a variety of food items such as dairy, meat, and seafood products (5,(15)(16)(17). Since the food origin of human listeriosis is now recognized, the presence of antimicrobial-resistant L. monocytogenes strains in foods may be of public health concern.…”

“…The bacterium has been isolated from molluscan shellfish and especially mussels, which are filter feeders and notoriously liable to become contaminated with pathogenic bacteria such as Listeria derived from polluted aquatic environments (4,5). Compared with other food products, very few studies have been carried out on the prevalence of L. monocytogenes in mussels (6,7).…”

“…3a, 3b, 3c, 4a, 4c, 4e, 4d, and 7) are very infrequent in food and rarely responsible for human L. monocytogenes infections (10,11). Listeriosis is a rare human disease, but it may have lifethreatening clinical manifestations, requiring antibiotic therapy for the resolution of infections (5,12). The annual incidence in the Europe Union for 2010 was 0.35 cases per 100,000 inhabitants (13).…”