Doi:10.1016/j.fm.2004.03.007

MICROBIOLOGY
Prevalence and antibiotic resistance of Listeria species in meat Department of Biology, Faculty of Science and Art, Gazi University, 06500 Teknikokullar, Ankara, Turkey Received 2 July 2003; accepted 24 March 2004 In this study, a total of 146 raw (minced, chicken, beef) and cooked (red meat, chicken) meat samples were analysed for the presence of Listeria spp. The isolates were characterized by morphological, cultural, biochemical tests according to Bergey’s manualand confirmed by API-Listeria kit. Out of a total of 146 meat samples, 79 (54.10%) were found to be contaminated with Listeriaspp., with the highest incidence (86.4%) occurring in raw minced meat. Listeria monocytogenes was isolated from 9 (6.16%) of the 79samples examined. Other species isolated included L. innocua 68 (46.57%), L. welshimeri one (0.68%) and L. murrayi one (0.68%).
Of the Listeria species, L. innocua (46.57%) was the most predominantly isolated species in a variety of meat samples. Overall, theListeria strains isolated from meat and meat products were mostly resistant to cephalothin and nalidixic acid but exhibited a highdegree of susceptibility to kanamycin, chloramphenicol and tetracycline. The importance of finding antibiotic resistant Listeria spp.
in food is discussed.
r 2004 Elsevier Ltd. All rights reserved.
Keywords: Listeria spp.; Meat samples; Antibiotic resistance Listeria species are ubiquitous bacteria widely dis- tributed in the natural environment. The ubiquitous these foods have not been associated with documented character of the bacteria inevitably results in contam- outbreaks of human listeriosis. The detection of Listeria ination of numerous food products. Epidemiological spp. in meat is of particular concern in terms of studies performed in recently years have demonstrated consumer safety, as these organisms are capable of that Listeria monocytogenes is an important pathogen growing on both raw and cooked meat at refrigeration Although dairy products have been major source during further transformation processes of raw meat into meat products L. monocytogenes can be introduced, other raw or recontaminated products of animal where the amount depends on the extent of cross- or vegetable origin may serve as vehicles of transmission contamination, personal and general hygienic measures of this pathogen. To date, there have been almost no reports of outbreaks of foodborne listeriosis associated addition, assessing the prevalence of L. monocytogenes with meat consumption. However, Listeria spp. has in cooked meat is particularly important, since these been isolated from poultry, red meat and meat products products are often consumed after a brief heat in many countries around the world such as Yugoslavia treatment, which may not be sufficient to kill all viablecells ( Despite efficient antibiotic therapy, listeriosis repre- *Corresponding author. Tel.: +90-312-212-60-30; fax: +90-312- sents a public health problem since it is fatal in up to E-mail address: nyucel@gazi.edu.tr (N. Y .ucel).
30% of the cases. This threatening nature of listeriosis 0740-0020/$ - see front matter r 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.fm.2004.03.007 N. Y .ucel et al. / Food Microbiology 22 (2005) 241–245 Table 1Incidence of Listeria species from various meat products a Parenthesis indicate percentage of positive samples.
also prompted the World Health Organization (WHO) after 48 h of incubation at 37C. The suspect colonies to suggest that various food products must be frequently were subcultured to tryptone soy agar supplemented investigated for the presence of L. monocytogenes on a with 0.6% yeast extract (TSA-YE, LabM) for purity and incubated at 37C. Every colony was confirmed by Although occurrence of Listeria species in meat and biochemical reactions and morphology, including Gram meat products has been investigated in several countries, staining, catalase production, oxidase, motility and little has been reported about the incidence of the Voges Praskauer reaction. For further confirmation of organisms in meat products in Turkey. The purpose of Listeria spp., other biochemical reactions, b-haemolytic this study is to investigate the incidence of Listeria activity, and the CAMP tests were performed according species in raw and cooked meat products and to check to Bergey’s Manual of Systematic Bacteriology antibiotic resistance patterns of the isolated strains.
The isolates of L. monocytogenes andListeria spp. were identified using the API-Listeria(BioMerieux, Florence), along with the reference strains L. monocytogenes ATCC 19114 and L. innocua ATCC33090.
The samples were collected from approximately 200 g of meat obtained from the supermarkets, local butcher- All the isolates of Listeria were tested by the standart shops and restaurants located in Ankara from May 2001 to April 2002. The types and numbers samples collected from each of the sources are shown in All following antibiotics were spotted with a 3 cm interval samples were stored at 4C after sampling, until the ampicillin (10 mg), chloramphenicol (30 mg), cephalothin (30 mg), ciprofloxacin (5 mg), kanamycin (30 mg), tri-methoprim/sulfamethoxazole (SXT) (1.25/23.75 mg), na- 2.2. Isolation and identification of Listeria species lidixic acid (30 mg), tetracycline (30 mg), and tobramycin(10 mg). Isolates were cultured in trypticase-soy broth Meat samples were analysed for the presence of (TSB) supplemented with 0.6% yeast extract, and Listeria spp. using the enrichment and isolation transferred to Mueller–Hinton agar (Oxoid CM 337).
procedure, recommended by the USDA-FSIS Method The plates were incubated at 37C for 48 h.
Twenty-five grams of a samplewas aseptically taken, blended for 2 min in 225 ml ofUVM (University of Vermont) Listeria enrichment broth (UVM 1) (composition in g/l: tryptose 10; meatextract 5; yeast extract 5; NaCl 20; K2HPO4 1.35; esculin presented the types, numbers and sources of 1; nalidixic acid 0.02; acriflavine hydrochloride 0.012; the meat samples analysed in this study. Of a total of pH: 7.2), and incubated at 37C for 24 h. A portion of 146 samples examined, 79 (54.1%) were positive for 1 ml of primary enrichments were transferred to 9 ml of Listeria spp. The findings of our study are in agreement UVM 2 (UVM 1 with 0.025 g/l of acriflavine hydro- chloride in 10 ml of sterile distilled water, pH: 7.2) and incubated at 37C for 24 h. Secondary enrichments spp. in 56.6% of meat samples. Similarly, in a study in (0.1 ml) were streaked to modified Oxford agar (Oxoid) Switzerland, isolated the Listeria spp.
and plates were examined for typical Listeria colonies from 55.3% of raw chicken samples. In this study all the N. Y .ucel et al. / Food Microbiology 22 (2005) 241–245 Table 2Percentage and number of isolates of 79 Listeria resistant to 9 antimicrobial agents Trimethoprim-Sulfamethoxazole (1.25/23.75) various meat products, raw minced meat had the highest incidence of Listeria spp., with 37 (86.4%) of 42 samples According to these results, the existence of Listeria spp. in being positive. Incidence of Listeria spp. in raw meats meats would pose a threat only if the meat were could be attributed either to fecal contamination during insufficiently cooked or if there is cross-contamination. It was significantly important for public health to detect According to previous some reports, high incidences of Listeria spp., and particularly L. monocytogenes, in meat L. monocytogenes were found in raw meat. products sold in Ankara, since consumers are frequently isolated L. monocytogenes in 69% of minced meat exposed to these products. However, in Turkey raw meat is normally thoroughly cooked or grilled before consump- detected the bacteria in 24% of beef in Australia. tion, and L. monocytogenes is likely to be eliminated.
isolated it in 34% of raw meat in Japan.
It is interesting to note that L. innocua was isolated Some investigators have also found the incidence of L.
predominantly among Listeria species in our study monocytogenes to be moderate: 12.5% in New Zealand (). It was detected in 83.3% of the raw minced meat, 57.6% of the raw chicken meat, 63.1% of the raw beef, 9.6% of the cooked red meat and 10.7% of the cooked chicken samples. This finding is in agreement In the present study, we analysed raw meat samples with other studies where L. innocua was the most and the incidence of L. monocytogenes was found to be common species in raw and cooked meats, while other 4.7% in minced meat, 11.5% in chicken and 5.2% in beef. These results are in close agreement with the Until recently, the Listeria genus was thought to be , where the organism was recovered from 4.3% uniformly susceptible to antibiotics active against and 12.5% of meat samples, respectively. Also, in our Gram-positive bacteria including ampicillin or penicillin study, L. monocytogenes was isolated in cooked meat (combined with aminoglycosides), trimethoprim (alone products (red meat 3.5%, chicken meat 6.4%). The or combined with sulfamethoxazole), tetracyclines, incidence of L. monocytogenes in cooked meat was erythromycin, and gentamicin. Hence, these antibiotics similar to that reported by various authors: 7.9% in were used treatment of human listeriosis and veterinary first antibiotic-resistant L. monocytogenes was described 5 to 21 samples of cook-chill food, and all isolations resistant strains have been detected in food and sporadic were from poultry dishes. The thermal resistance of Listeria spp. and L. monocytogenes has been debated, but it is generally accepted that proper heating kills species is due to the acquisition of three type mobile viable Listeria cells. However, the occurrence of Listeria genetic elements: self-transferable and mobilizable plas- spp. in cooked meats may be as considered a conse- quence of inadequate heat treatment or post-heating In our study, L. monocytogenes, L. innocua and L.
recontamination. On the other hand, L. monocytogenes welshimeri were highly sensitive to chloramphenicol (88– has been strongly implicated particularly in the con- 100%) and to tetracycline (100%, except L. seeligeri), tamination of foods stored at low temperatures. Storage but resistant to ampicillin (66–100%). Similarly, of such products under such low temperature conditions indicated that L. monocytogenes, L. innocua may allow the growth of significant numbers of these isolated from meat products were high sensitivity to organisms leading to foodborne illnesses among con- N. Y .ucel et al. / Food Microbiology 22 (2005) 241–245 that L. monocytogenes were isolated; no strain was Beak, S.Y., Lim, Y.S., Lee, D.H., Min, K.H., Kim, C.M., 2000.
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