The characterization of Listeria spp. isolated from food products and the food-processing environment

Abstract

Aim: To enhance the information pertaining to the epidemiology of a collection of 378 Listeria spp. isolates obtained from several food‐processing plants in Ireland over a 3‐ year period (2004–2007). Methods and results: The collection was characterized by pulsed‐field gel electrophoresis (PFGE). The most prevalent pulse‐type was PFGE profile I (n = 14·5%) that consisted mainly of environmental Listeria spp. samples. Serotyping of 145 Listeria monocytogenes isolates was performed. The most common serovar was 1/2a and comprised 57·4% (n = 77) of the L. monocytogenes collection. The other serovars were as follows: 4b (14·1%, n = 19), 1/2b (9·7%, n = 13), 4c (4·4%, n = 6) and 1/2c (6·7%, n = 9), respectively. Eleven isolates were identified as non‐Listeria spp., the remaining ten L. monocytogenes isolates were nontypeable. The antimicrobial susceptibility testing revealed the antibiotic that isolates displayed the most resistance to was gentamicin (5%) followed by sulfamethoxazole‐trimethoprim (2%), tetracycline and ciprofloxacin (1·5%). Conclusions: The subtyping has indicated the diversity of the Listeria spp. The presence of serotype 1/2a, 1/2b and 4b in both raw and cooked ready‐to‐eat food products is a public health concern, as these serotypes are frequently associated with foodborne outbreaks and sporadic cases of human listeriosis. In addition, the emergence of antimicrobial‐resistant L. monocytogenes isolates could have serious therapeutic consequences. Significance and Impact of Study: The molecular subtyping and the further characterization of these isolates may be valuable particularly in the context of a suspected common source outbreak in the future.

Antimicrobial susceptibility and serotype distribution of Listeria monocytogenes isolates obtained from raw milk cheese samples sold in Nigde

“…One of the isolates obtained from cheese samples in this study belonged to serotype 1/2a which is in agreement with previous studies in several countries (10,17). The occurance of 1/2a serotype in local cheese samples that are commonly consumed in this region of Turkey is an important public health concern as this serotype is one of the the most frequently incriminated serotype associated with human listeriosis.…”

“…Similar MIC values for tetracycline were also reported by several authors (6,10,15). On the other hand tetracycline resistance among L. monocytogenes isolates has been recently observed by some researchers (1,10,17,26,27). High prevelance of tetracycline resistance in food isolates may be partly due to the frequent use of tetracycline in animal production (26).…”

“…Trimethoprim and sulphonamide resistant L. monocytogenes isolated from various food were reported in recent studies (17,26). This resistance is important as trimethoprimsulfamethoxazole treatment has been successfully used for listeriosis patients with beta-lactams allergy.…”

“…On the other hand MIC values for penicilin G was slightly higher than those reported by Zhang et al, (27) as 4 µg/ml. Penicillin G, ampicillin and gentamicin resistance of L. monocytogenes are mentioned in several studies (1,21,17,26).…”

Characterization of epidemic clones of Listeria monocytogenes serotype 4b isolated from humans and meat products in Brazil

“…Most human infections are caused by serotypes 1/2a, 1/2b and 4b, with predominance of 4b in the majority of the outbreaks and sporadic cases [7,8]. Furthermore, a small number of well-defined clonal groups, designated as epidemic clones (ECs), is involved in different temporally and geographically unrelated outbreaks [9].…”