Abstract: The present study was carried out from 400 samples in different slaughterhouses to report the isolation along with the serotypes and antibiogram pattern of Salmonella among products in Tehran. Salmonella was isolated from samples of chicken, beef; veal, mutton, roast beef and sausage fermentive meat collected at slaughterhouses. The isolates were characterized by serotyping and antimicrobial-susceptibility testing. Eighty isolates of Salmonella enterica belonging to 19 serotypes- S. adelaide, S. agona S. abortus ovis, S. abortus bovis, S. derby, S. dublin, S. enteritidis, S. havana, S. heidelberg, S. indiana, S. infantis, S. kentucky, S. montevideo, S. newport, S. saint paul, S. senftenberg, S. typhimurium, S. thompson, S. worthington were obtained with an overall prevalence of 20%. The most strains of Salmonella enterica were isolated from roast beef. S. enterica serotype Thompson and S. enterica serotype typhimurium were isolated most frequently. All of the isolates were resistant to at least one antibiotic and 94% were resistant to at least three antibiotics. Six% were resistant to ceftriaxone, the drug of choice for treating salmonellosis in children. One isolates of S. enterica serotype infantis had resistance to 15 antibiotics and the one isolate of serotype Thompson and one isolate of Serotype havana were resistant to 14 antibiotics. Norfloxacin, cefteriaxone and cefotaxime were most effective, whereas, erythromycin, tetracycline, nalidixic acid, furazolidone and nitrofurantoin were relatively less effective. Resistant strains of Salmonella are common in meat products. These finding provide support for adoption of guidelines for the prudent use of antibiotics in food animals and for a reduction in the number of pathogens present on farms and slaughterhouses. Thus, it is imperative that salmonellosis control measures adopted for humans should give adequate importance to its control in animals particularly their products.
INTRODUCTION
Foodborne diseases caused by non-typhoid Salmonella represent an important public heath problem worldwide so nearly 1.4 million cases of salmonellosis occur each year in the United Stases (Angulo et al., 2000). Intestinal salmonellosis typically resolves in five to seven days and does not require treatment with antibiotics. However, bacteremia occurs in 3 to 10% of reported, cultured-confirmed cases and is particularly common among patient at the extremes of age and those who are immunocompromised. When infection spreads beyond the intestinal tract, appropriate antimicrobial therapy (e.g., ciprofloxacin in adults and ceftriaxone in children) can be lifesaving (Glynn et al., 1998; Hohmann, 2001). Non-typhoidal salmonellosis is an important enteric infection in humans, particularly in the neonates and younger children (Gupta and Vermo et al., 1993). Most salmonella infections in humans result from the ingestion of contaminated poultry, beef, pork, eggs and milk (Gomez et al., 1997). Lailler et al., (2002) isolated Salmonella serotypes from birds, pork and beef in France. Hidetake et al., (2002) isolated Salmonella serotypes from pork and beef in Japan. Nadine et al., 2004 isolated different Salmonella serotypes from pork and slaughterhouse in Belgium. The use of antimicrobial agents in any environment creates pressures that favor the survival of antibiotic-resistant pathogens. According to the infectious-disease report that was released by the World Health Organization (2000), such organisms have become increasingly prevalent worldwide. The routine practice of giving antimicrobial agents to domestic livestock as mean of preventing and treating disease, as well as promoting growth, is an important factor in the emergence of antibiotic-resistant bacteria that are subsequently transferred to humans through the food chain (Yu et al., 2004). Most infections with antimicrobial-resistant Salmonella are acquired by eating contaminated foods of animal origin (Anguloet al., 2000). Fey et al (2000) discovered a ceftriaxone-resistant Salmonella infection in a child that was acquired through exposure to cattle and the emergence of ceftriaxone-resistant salmonella infection are often unknown, but they most likely originate in contaminated food of animal origin.
Antibiotic resistance of Salmonella strains isolated from slaughtered and packed chicken meat in Tehran. All of isolates of Salmonella were resistant to streptomycin, penicillin and erythromycin.
We isolated and characterized salmonella strains from meat products obtained in slaughterhouses in Tehran with the use of methods described by Feingold and Baron (1990) and determined the antimicrobial- resistance phenotypes of the isolates with the use of disc method described by National Committee of Clinical Laboratory Standards (NCCLS) Sub Committee’s Recommendation (2001).
MATERIALS AND METHODS
Four hundred samples of meat (100 samples of chicken, 100 of beef, veal, mutton, 100 of roast beef and 100 of sausage fermentive meat) were collected at slaughterhouses in Tehran between September and August 2005: 06. Selenite F Broth (SFB) was used as a selective enrichment broth for primary isolation of Salmonella. Brilliant Green Agar (BGA) and Salmonella-Shigella Agar (SSA) were used as selective medium for primary isolation and MacConkey’s Lactose Agar (MLA) was used for purification of suspected colonies. Characterization and preliminary identification of suspected Salmonella cultures were made on the basis of morphology, characteristics and biochemical reactions (Glynn et al., 1998). The isolated strains of Salmonella were serotyped at Razi Vaccine and Serum Research Institute in Iran. In order to understanding of Antibiotic sensitivity, In vitro susceptibility of the organisms to various antimicrobial agents was determined by the disk diffusion technique. The antimicrobial agents (concentration in μg) used were:amikacin (AN, 30), ampicillin (AM, 10), cefalexin (CN, 30), cefotaxime (CTX, 30), ceftriaxone (CRO , 30), chloramphenicol (C, 30), ciprofloxacin (CP, 5), erythromycin (E, 15) furazolidone (FR, 100), gentamicin (GM, 10), kanamicin (K, 30) nalidixic acid (NA, 30), nitrofurantoin (FM, 300), norfloxacin (NOR, 10), streptomycin (S, 10)tetracycline (TE, 30), trimethoprim-sulfamethoxazole (SXT, 23.75, 1.25).
RESULTS
Serotypes: Salmonella were recovered from 80 of 400 samples of meat (20%). Salmonella was isolated more frequently from chicken (29%) than from roast beef (25%), from veal (19%), from beef (12%), from sausage fermentive meat (12%) or mutton (4%).
Ninetheen serotypes were identified among the 80 Salmonella isolated (Table 1). S. enterica serotype thompson (15%) and S. enterica serotype typhimurium (14%) were isolated most frequently. All of isolates of S. enterica serotype Thompson were recovered from chicken. In contrast, S. enterica serotype typhimurium was isolated from roast beef. Nine of the ten isolates of S. enterica serotype enteritidis were from chicken and one was from mutton. All four isolates of S. enterica serotype Heideleberg were recovered from sausage fermentive meat. Six of the eight isolates of S. enterica serotype Infantis were from veal and two were from roast beef. Two of the three isolates of S. enterica serotype adelaide were from veal and one was from beef. One of the two isolates of S. enterica serotype agona was from beef and another one was from veal. S. enterica serotype Abortus ovis was isolated from mutton and S. enterica serotype Abortus bovis was isolated from beef. S. enterica serotype Derby and S. enterica serotype Dublin were recovered from beef. Two of the four isolates of S. enterica serotype Havana were from veal and two were from roast beef. One of the two isolates of S. enterica serotype indiana was recovered from roast meat and one was from sausage fermentive meat. Two isolates of S. enterica serotype Kentucky were recovered from chicken and veal and two isolates of S. enterica serotype Montevideo were recovered from beef and roast beef.
| Table 1: | Number and percentage of Salmonella isolates from various
meat products |
| Table 2: | Isolation of Salmonella from meat products |
| Table 3: | Antibiotic resistance pattern of Salmonella isolates from various sources |
AN, amikacin; AM, ampicillin; CN, cefalexin; CTX, cefotaxime;
CRO, ceftriaxone; C, chloamphenicol; CP, ciprofloxacin; E, erythromycin;
FR, furazolidone; GM, gentamicin; K, kanamicin; NA, nalidixic acid; FM,
nitrofurantoin; NOR, norfloxacin; S, streptomycin; TE, tetracycline; SXT,
trimethoprim- sulfamethoxazole |
|
Two of the three isolates of S. enterica serotype newport were from beef and one was from veal. Two of the three isolates of S. enterica serotype saint paul were recovered from roast beef and one was from beef. S. enterica serotype Worthington was isolated from veal (Table 2).
Antimicrobial resistance: All the isolates (100%)were resistant to at least one of the 17 antibiotics tested and 96% (77 out of 80 samples) were resistant to at least three antibiotics. This could be due to the wide and varied use of different antibiotics with simultaneous evolution of newer antibiotics that have precipitated into pathogens of multiple drug resistance. Moreover, the presence of antibiotic residues in foods of animal origin may result in increased drug resistance amongst human isolates (2). Among multidrug- resistance isolates, resistance to erythromycin, tetracycline and nalidixic acid was most often observed. In the present study, isolates showed resistance against erythromycin (79%), tetracycline (67%), nalidixic acid (69.8%) furazolidone (68.8%), nitrofurantoin (67.8%), streptomycin (62.7%), trimethoprim-sulfamethoxazole (62.7%) ampicillin (48.6%), kanamicin (45.5%), chloramphenicol (30.3%), gentamicin (23.2%), ciprofloxacin (23.2%), amikacin (20.2%), cefalexin (11%), cefotaxime (7.9%), ceftriaxone (5.6%), norfloxacin (5.6%) (Table 3).
S. enterica serotype Worthington exhibited resistance to 12 antibiotics and one of the eight isolates of S. enterica serotype infantis exhibited resistance to 15 antibiotics.
All of the isolates of S. enterica serotypes agona, abortus ovis, abortus bovis, derby, dublin, havana, heidelberg, indiana, infantis, kentucky, montevideo, new port, senftenberg, thompson and Worthington were resistant to erythromycin and tetracycline. Thirteen isolates of S. enterica serotype typhimurium displayed resistance to at least five antibiotics, including nitrofurantoin, trimethoprim-sulfamethoxazole, nalidixic acid, erythromycin and tetracycline. Most of the strains of Salmonella were susceptible to norfloxacin, ceftriaxone and cefotaxime (Table 3).
The isolates were most likely to be resistant to erythromycin, tetracycline, nalidixic acid, furazolidone, nitrofurantoin and to a lesser extent, streptomycin.
DISCUSSION
Our observations show that the incidence of Salmonella serotypes isolated from meat products in Tehran during (2005-6) in contrast with other studies in this field, was a high rate (20%). Table 1 shows nineteen serotypes with their percentage and groups isolated from meat products. Resistance to two or more drugs was more commonly observed than resistance to a single drug.
Glynn MK studies of infections with S. enterica serotype typhimurium by the centers for disease control and prevention revealed that the percentage of isolates that were resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides and tetracycline increased from 0.6% during the period from 1979 to 1980 to 34% 1996 (Glynn et al., 1998). Resistance to some of the aminoglycosides such as kanamycin is of great concern since it has been a major drug of choice in the treatment of infections (Threlfull et al., 1986).
Lailler et al. (2002) announced that 48% of S. enterica serotype typhimurium isolated from birds, pork and beef in France displayed resistance to ampicillin, streptomycin, chloramphenicol, tetracycline and sulfonamids. Nanna et al. (2002) determined antimicrobial resistance pattern for S. enterica serotype agona from animals, food and human in Finland. All of the isolates displayed high resistance to tetracycline and streptomycin.
Nadine et al. (2004) determined antimicrobial resistance of Salmonella serotypes isolated from pork and slaughterhouses in Belgium. All the isolates displayed high resistance to tetracycline, sulphadiazine, ampicillin, chloramphenicol and streptomycin.
As observed in other studies and this study, isolated strains displayed a high multi-drug resistance. However, the contamination of meat products with resistant Salmonella mainly reflects carriage of the organism by the livestock; intervention strategies should therefore focus principally on reducing the number of pathogens present on farms and slaughterhouses. Although S. enterica serotype agona is less commonly associated with disease in human than is S. enterica serotype typhimurium. It has been the cause of several foodborne outbreaks in recent years (Synnott et al., 1998; Taylor et al., 1998).
Present study identified one isolate that was resistant to 15 antibiotics and was recovered from roast beef and 14 isolates that were resistant to twelve antibiotics and were recovered from different types of meat (except chicken). The dissemination of Salmonella that is resistant to multiple drugs, including cephalosporins, through food has important public health implications. The ability of bacteria to acquire antibiotic-resistance genes and subsequently spread them to many different bacterial species is well known (Hall, 1997). Although we have no corresponding culture data from humans, our data provide support for the theory that the food supply is a major source of antimicrobial-resistant Salmonella. The high prevalence of multidrug-resistant Salmonella in meat reflects a reservoir of resistance in animals that can be transmitted to humans. The prevalence of Salmonella resistant to multiple drugs is quite a serious problem from the standpoint of epidemiology and public health as resistance is transferred to pathogenic enteric organisms both directly and by way of non-pathogenic enteric bacteria such as E. coli and Klebsiella (MMWR Morb Mortal, 1998). Furthermore, the problem of multiple drug resistance is not limited to Salmonella and Shigella, but is also a problem with all Entrobacteriaceae (Quendnau et al., 1998). Apart from this medical importance, multidrug resistance offers interesting material for bacterial genetics. The resistance transfer factor is a new episome (extra chromosomal elements). Eighty strains of S. enterica isolated in Tehran were resistant to erythromycin, tetracycline and nalidixic acid (92%) and furazolidone (85%). This high percentage of resistance to antibiotics observed in our country may be related to the extensive usage of these drugs during the past decade as feed additives for growth promotion (Ranjbar et al., 2004). Such development of multiple antibiotic-resistance strains in poultry could be due to the use of antibiotics as feed additives for growth promotion and prevention of disease, as confirmed by the present study (Geomaras et al., 2001; Panigrahy and Ling, 1990, Rafiiei and Nasirian, 2004). Efforts are needed to reduce the prevalence of resistant Salmonella in food, including the adoption of guidelines for the prudent use of antimicrobial agents in animals used for food, the passage of new foodsafty regulations and a reduction in the number of pathogens present on farms and in slaughterhouses. In addition surveillance program focusing on the identification and molecular subtyping of zoonotic foodborne pathogens that are present in foods should be established.