Antimicrobial susceptibility of salmonella enteritidis isolated from pork and poultry

Marius Virgailis, Modestas Ruzauskas, Rita Siugzdiniene, Dainius Zienius
Veterinary institute of Lithuanian Veterinary Academy,
Instituto 2, 56115 Kaisiadorys, Lithuania.


Antimicrobial susceptibility of Salmonella enteritidis was tested. Salmonella isolates were
obtained from pork and poultry meat. Susceptibility was tested by agar diffusion method
according to NCCLS guidelines. Isolates from pork showed the highest resistance to
tetracycline 48.9 %, less to chloramphenicol 18.4 % and florfenicol 14.3 %. Isolates from
poultry showed the highest resistance to ampicillin 12.7 %, less to tetracycline 10.2 % and
sulphamethoxazole/trimethoprim 10.2 %. Isolates from pork showed a high resistance to
tetracycline was still frequent, while Salmonella susceptibility pattern from poultry was
Salmonella has been consistently associated with foodborne illnesses and an economic
burden in most countries of the world. More than seventy thousand notified cases of
salmonellosis occur each year in Germany, and most of them are attributed to food-borne
transmission. The main sources are foods of animal origin, such as poultry, eggs, milk, beef
and pork. In addition, fruit and vegetables have been implicated as vehicles in Salmonella
transmission. Contamination can occur at multiple steps along the food chain [7, 1]. Increased
application of antibiotics in both veterinary and human medicine is believed to be largely
responsible for the emergence of drug resistant bacteria. The emergence and spread of
antimicrobial resistant pathogens, among them Salmonella, has become a serious health
hazard worldwide. The routine practice of giving antimicrobial agents to domestic livestock
as means of preventing and treating diseases, as well as promoting growth, is an important
factor in the emergence of antibiotic resistant bacteria that are subsequently transferred to
humans by the food chain [10]. Diarrhea is an important problem to unhealthy sanitary
conditions. Furthermore, the development of antibiotic resistance in enteropathogens,
including Salmonella spp., has increased the problem. Resistance to some β-lactam
antibiotics, tetracycline, chloramphenicol, or trimethoprim is reported with increasing
frequency [6]. Being easily spread among the population, they can cause an epidemic
outbreak, especially if sanitary conditions are not optimum [5]. Another health concern is the
discovery that antibiotic resistance can be transferred through R-factor plasmid vectors, from
commensal to pathogenic bacteria.
The aim of this study was to determine the incidence of antimicrobial resistance in
Salmonella strains from pork and poultry.
Isolates from food (carcasses and products) were collected and identified by LVA
Veterinary institute and National veterinary laboratory during 12 month project (2006-2007).
Salmonella strains identification was performed using EnteroPluri Tests (Liofilchem, Italy)
and API20E strips (bioMerieux, France). Serotyping was performed according to the
Kaufman-White scheme with antisera from Sanofi (France). Only epidemiologically unrelated
strains were selected. Susceptibility was tested in LVA Veterinary institute. The agar
diffusion method according to NCCLS guidelines [8] was applied for antimicrobial
susceptibility testing of Salmonella isolates. Mueller Hinton Agar II (BBL, LAB39) was used
in order to perform this test. Discs were supplied by Oxoid (Besingstoke, UK). Results were
scored susceptible, intermediate or resistant according to NCCLS criteria [8]. Escherichia coli
(ATCC 25922) was used as a reference strain. The respective quantities (µg) of active
compounds were: ampicillin (AMP), 10; ceftiofur (EFT), 30; cephalotin (KF), 30;
ciprofloxacin (CIP), 5; chloramphenicol (C), 30; florfenicol (FFC), 10; gentamicin (CN), 10;
nalidixic acid (NA), 30; norfloxacin (NOR), 10; sulphamethoxazole/trimethoprim (SXT),
23,7/1,25; neomycin (N), 10; tetracycline (TE), 30.
Even though pork accounts for 50 % of the total meat consumption in Lithuania, reports of
outbreaks of salmonellosis in humans linked to pork consumption are rare. Information on the
potential role of commercial swine production in dissemination drug resistant strains in
Lithuania is very limited.
10% 20% 30% 40% 50% 60% 70% 80% 90% 100
Figure 1. Susceptibility of Salmonella strains isolated from pork, (n=49).
As shown in figure 1, isolated Salmonella was most resistante to tetracycline (48.9 %), chloramphenicol (18.4 %), and florfenicol (14.3 %). Salmonella strains resistant to flouroquinolones were not detected. Tetracycline has been widely used for the treatment purpose for many years in Lithuanian pig farms. High resistance to tetracycline was detected in previous studies during 1998-2003. Resistance to tetracycline was 55 %. Only Choleraesuis serotype was tested, but 92 % of isolated Salmonella from pigs depended on serovar S. Choleraesuis [9]. Salmonella resistance to tetracycline is high in other European Union countries: 36 % in Denmark, 38,3 % in Belgium, 84 % in Great Britain, and 83.3 % in Spain [4, 3, 2]. In spite of chloramphenicol prohibition for about 10 years, resistance to this antimicrobial agent still occurs. Some farming units are quite old, so some kind of persistence of resistant bacteria strains is possible. The frequency of resistance to individual antibiotics among isolates from poultry was different to that among pork isolates (Figure 2). The rates of resistance to sulphamethoxazole/trimethoprim, tetracycline, ampicilline and chloramphenicol were 10.9 %, 10.9 %, 12.7 % and 7.2 % respectively. None of the isolates was resistant to florfenicol, cephalotin, ciprofloxacin, norfloxacin and gentamicin. Resistance to nolidixic acid was low. Susceptibility trends of Salmonella isolates from poultry are changed. In 1998-2003 Salmonella were resistant to teracycline 20%, nalidixic acid 16 % and streptomycin 12 %. [8]. Sensitive
Figure 2. Susceptibility of Salmonella strains isolated from poultry, (n=55).
Salmonella resistance tendency is also similar to other EU countries. In Denmark 31 % of
Salmonella poultry isolates are resistant to tetracycline, 39 % to ampicillin. In Belgium 17.5
% resistant to taracycline, 25.2 % to ampicillin, 18.8 % to nolidixic acid. In Spain 33.9 %
Salmonella isolates showed resistance to tetracycline, 34.8 % to ampicillin, 44.6 % to
chloramphenicol. High resistance to ampicillin and tetracycline could be influenced by
intensive usage of these antimicrobials. They have a wide spectrum of action, with a low side
effect. But oral administration leaves posibility that concentration of antimicrobial could be at
low level, and this is one of most important factors for resistance development.
1. Salmonella isolates from pork showed the highest resistance to tetracycline 48.9 %, less to
chloramphenicol 18.4 % and florfenicol 14.3 %. High resistance to tetracycline is possible
due to a long time use of it and resistant bacteria persistent on farms.
2. Salmonella isolates from poultry was most resistant to ampicillin 12.7 %, less to
tetracycline 10.2 % and sulphamethoxazole/trimethoprim 10.2 %.
Lithuanian State Science and Study Foundation supported this work (programme
1. Angelika Miko, Karin Pries et al., Molecular mechanisms of resistence in multidrug-
resistant serovars of Salmonella enterica isolated from foods in Germany. Journal of Antimicrobial Chemoterapy, 2005. 56, 1025-1033. 2. Anon.: VAR (Veterinary and Agrochemical Research Centre). Salmonella serotypes analysed at the VAR in 2001. 2002. Brussels, Belgium. 3. Anon.: DANMAP. Consumption of Antimicrobial Agents and Occurrence of Antimicrobial Resistance in Bacteria from Food Animals, Foods and Humans in Denmark. Danish Veterinary Laboratory, Copenhagen, Denmark. 2000-2004. 4. Agustin A. I., Carraminana J. J., Rota C., Herrera A. Antimicrobial resistance of Salmonella spp. From pigs at slaughter in Spain in 1993-2001. Lett. Appl. Microbiol. 2005. 41:39-44. 5. Joaquim R, Liliana C, et al. Mechanisms of resistance to ampicilin, chloramphenicol and quinolones in multiresistant Salmonella Typhimurium strains isolated from fish. Journal of Antimicrobial Chemoterapy, 1999. 43, 699-702. 6. Gallardo F, Ruiz J, et al., Increase in incidence of resistance to ampicillin, chloramphenicol and trimethoprim in clinical isolates of Salmonella serotype Typhimurium with investigation of molecular epidemiology and machanisms of resistance. Journal of Medical Microbiology, 1999. 48, 367-374. 7. Gomez TM, Motarjemi Y, Miyagava S et al,. Fooodborne salmonellosis. World Health Stat 8. NCCLS. Performance standarts for antimicrobial disk and dilution susceptibility tests for bacteria isolated from animals. Villanova, USA. 2002. 9. Modestas Ruzauskas, Marius Virgailis, Vytautas Spakauskas. Serological diversity and antimicrobial resistance of Salmonella isolated from different sources in Lithuania. Veterinarski Arhiv 2005. 75 (3), 211-221, 10. Threlfall EJ., Antimicrobial drug resistance in Salmonella: problems and perspectives in food and water borne infections. FEMS Microbiol Rev., 2002. 26, 141-148.


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