Salmonella Serotypes Analysed at the CODA-CERVA in 2009

Belgium's CODA-CERVA has published the results of the salmonella serotypes analysed in 2009, comparing the evolution of poultry, cattle and pig isolates between 1998 and 2009, as well as the results of antimicrobial resistance testing.
calendar icon 1 July 2010
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The Laboratory of General and Molecular Bacteriology of CODA–CERVA (Centrum voor Onderzoek in de Diergeneeskunde en Agrochemie – Centre d'Etude et de Recherches Vétérinaires et Agrochimiques) is the Belgian reference laboratory for Salmonella, animal health.

All Salmonella isolates obtained in the context of official sanitary programmes in the primary production are analysed at CODA-CERVA. In 2009, the Federal Agency for the Safety of the Food Chain organised programmes in poultry breeders, and in layers and broilers before slaughter. No European co-ordinated monitoring programme in animal production took place. In addition, most Salmonella that were isolated for diagnostic reasons from food producing animals, companion animals or other, or strains obtained during field research, were also sent to the reference laboratory for serotyping.

Laboratory Methodology

All requests to CODA-CERVA for isolation of Salmonella and for typing of Salmonella strains were routinely encoded in the Laboratory Management Information System (LIMS). Subsequently, the analytical results were introduced in the same database. The data on Salmonella isolation, serotyping and on antibiotic resistance as presented in this document were extracted from the LIMS files that were closed in 2009.

Isolation of Salmonella at CODA-CERVA was done based on ISO6579:2002. The Salmonella isolates were serotyped following the Kauffmann-White scheme.

In a number of cases, strains were sent to the Scientific Institute for Public Health in Brussels, which is the National Reference centre for Salmonella and Shigella for Public Health. Both isolation and serotyping at CODA-CERVA and the serotyping at IPH were done under Belac accreditation conditions (ISO 17025).

Susceptibility tests were performed by the disk diffusion test, using Neo-Sensitabs (Rosco). Tests and interpretation were done according to the manufacturers guidelines using the methodology as described by CLSI. Internal control was performed with quality control strain E. coli ATCC25922. Results were only accepted when results with the QC strain were within the limits as proposed by Rosco.

Results of Salmonella Isolation in 2009

Seventy-one Salmonella isolations were done in 2009; which is almost the same as in 2008 (n=74). Most samples were from sludge (n=27), from feed (n=15) or from cattle and poultry (both 13 samples).

Results of Salmonella Serotyping

In 2009, 2,132 Salmonella strains were typed, which is about 13 per cent fewer than in the previous year (n= 2 446). The isolates belonged to 58 distinct serotypes and to 6 serogoups (incomplete antigen expression; groups B, C1-C4, D1, D2, E1-E2-E3, E4). Seventy-five strains could not be typed due to autoagglutination.

Most Salmonella strains originated from poultry (53.6 per cent) and from pigs (25.1 per cent). Other isolates were from feed (6.1 per cent), cattle (3.8 per cent), all sorts of birds, including pigeons, pheasants and turkeys (3.0 per cent), fertilisers (nine strains) and from deposits from the purification of waste water (7 strains). From 132 isolates, the origin was not precise.

Serotypes Typhimurium (22.7 per cent) [62.7 per cent classic variant O5+ and 37.3 per cent Copenhagen variant O5-], Enteritidis (14.9 per cent) and Paratyphi B (11.4 per cent) [98.0 per cent was tartrate positive or var. Java] were most abundant among the isolates analysed. In contrast to poultry and pig S. Typhimurium isolates of which about 60 per cent to 70 per cent belong to classic variant O5+, S. Typhimurium from cattle equally belong to classic variant O5+ and Copenhagen variant O5-. Especially in pigs, but also in poultry monophasic Salmonella 4:i:- was found (17 and four isolates, respectively). In poultry, some Salmonella 4:-:2 were identified, as were some immobile O4:-:-.

Other prevalent serotypes included Mbandaka (4.5 per cent), Infantis (4.1 per cent), Group B Salmonella (3.7 per cent) and Derby (3.5 per cent). As compared to 2008, the proportion of serotypes Paratyphi B and Mbandaka have increased considerably (proportions in 2008: 3.6 per cent and 1.5 per cent, respectively), whereas that of Derby decreased (proportion of 6.9 per cent in 2008).

Poultry isolates

In total, 1,142 Salmonella strains from poultry origin were analysed in 2009, which is 20 per cent more than in 2008.

The proportions of serotypes Enteritidis (27.6 per cent; 36.0 per cent in 2008) and to a lesser extent Typhimurium (6.7 per cent; 9.3 per cent in 2008) decreased remarkably, whereas those of S. Paratyphi B (20.2 per cent and 8.8 per cent in 2009 and 2008, respectively) increased significantly. Also other serotypes were more readily typed, i.e. S. Mbandaka (2.4 per cent in 2008; 4.0 per cent in 2009), S. Agona (2.7 per cent in 2008, 3.9 per cent in 2009) and S. Livingstone (2.4 per cent in 2008, 3.9 per cent in 2009).

The origin of 631 Salmonella poultry isolates was known in more detail. Thirty-four strains were from breeders, of which 9, 7 and 5 isolates belonged to serotypes Senftenberg, Typhimurium and Hadar, respectively. The majority of layer isolates (n=122) were S. Enteritidis (59.0 per cent), but also serotypes Infantis (8.2 per cent), Typhimurium and Livingstone (both 4.1 per cent) were found. One S. Gallinarum strain was typed in 2009. The majority of broiler isolates (n=192) were S. Paratyphi B (32.3 per cent), but also Hadar (9.9 per cent), Agona (7.8 per cent), Minnesota (5.7 per cent) and Virchow (5.7 per cent) were frequently identified. Finally, isolates from spent hens (n=283) belonged often to S. Enteritidis (66.8 per cent) and to a minor extend to S. Paratyphi B (6.7 per cent).

Cattle isolates

The number of Salmonella isolates from cattle (n=81) has decreased as compared to 2008 (n=112 in 2008). Most frequently found serotype is Dublin (58.0 per cent), followed by serotype Typhimurium (33.3 per cent), which are exactly the same figures as in 2008.

Pig isolates

The number of pig strains tested in 2009 resembled that of 2007 (n=536, 1,017 and 481 in 2009, 2008 and 2007, respectively). More S. Typhimurium isolates were found (63.8 per cent; 48.5 per cent in 2008), but an equal proportion of S. Derby (13.4 per cent; 15.6 per cent in 2008). Nine per cent of pig strains were only partially typable, and belonged to group B Salmonella.

Bird isolates

The bird isolates were from pheasants, pigeons and turkeys. One S. Gallinarum from a pheasant was typed.

All pigeon strains analysed (n=12) were identified as S. Typhimurium var. Copenhagen, which is a common finding for these birds.

Other isolates

A limited number of food isolates (n=17) were analysed. Seven of these were S. Paratyphi B and for six of them, a link with poultry was evident.

As for feed, 50 strains were from animal origin; 16 per cent of Salmonella strains belonged S. Montevideo, 14 per cent to S. Livingstone and 10 per cent to S. Paratyphi B. Three S. Typhimurium isolates were typed, and one S. Enteritidis and S. Infantis each. The 26 isolates originating from vegetable sources (mainly soybean) mostly were S. Agona and S. Anatum. Neither S. Enteritidis nor S. Typhimurium was found.

Almost half of the strains originating from fertilisers (four out of nine isolates) were S. Senftenberg. The Salmonella from the deposits from the purification of waste water (n=7) belonged to several serotypes among, which also one S. Infantis and one S. Typhimurium.

Evolution in Salmonella Strains Analysed at the CODA-CERVA from 1997 to 2008

The evolution was studied of the most frequent poultry, cattle and pig serotypes during the past twelve years. For comparison, the Salmonella serotypes analysed during earlier years are presented in the addendum.

The number of poultry isolates yearly sent to the NRL varies between about 700 and almost 1,500. In 2009, almost one-third of poultry strains belonged to serotype Enteritidis, which is less than in 2008 and 2007. The proportion of Typhimurium strains is since 2001 less than 10 per cent and reached 6.7 per cent in 2009. The proportion of Salmonella Paratyphi B strains, after their peak in 2006, fell down in recent years but reached again 20 per cent in 2009. Serotypes Hadar, Infantis and Virchow represented about two to three per cent of poultry isolates in 2009.

In cattle, S. Dublin continues to be the principal serotype since 2002, and reaches a proportion of about 60 per cent among cattle strains. S. Typhimurium (about 30 per cent) is the second most important.

S. Typhimurium still is the most prevalent serotype among pig isolates, representing more than 60 per cent of pig Salmonella. Serotype Derby is the second most important serotype, and represents about 13 per cent of the strains.

Antibiotic Resistance in Selected Salmonella Serotypes

The susceptibility of 1,128 Salmonella isolates was tested in 2009. In order to reduce bias due to multiple strains from the same origin at the same sampling time and belonging to the same serotype, only one isolate per serotype and per origin was selected for susceptibility testing. Therefore, strains were likely to be independent from each other. The antimicrobials used were ampicillin (Ap), ceftiofur (Cef), streptomycin (Sm), neomycin (Ne), gentamicin (Gm), tetracycline (Tc), sulphonamides (Su), trimethoprim-sulphonamides (TSu), nalidixic acid (Nal), enrofloxacin (Enr), chloramphenicol (Cm) and florfenicol (Ff). The number of isolates, their serotype and their origin is presented.

A total of 613 Salmonella isolates (54.3 per cent) were fully susceptible to all antimicrobial drugs tested. In 2008, 62.6 per cent of strains were susceptible, which may be due to the lower proportion of S. Enteritidis strains tested in 2009. Resistance was mainly found against Ap (37.6 per cent), Su (32.1 per cent), Tc (28.2 per cent), St (23.9 per cent) but also against TSu (21.8 per cent). Noteworthy is the resistance against Nal (13.3 per cent) and against Cef (7.1 per cent), both considerably higher than in 2008 (8.7 per cent and 3.0 per cent, respectively). Resistance against Ne, Gm and Enr (all 0.4 per cent), and against Cm and Ff (7.6 per cent and 3.5 per cent, respectively) was similar to that of 2008.

Salmonella strains from poultry were found less resistant (34.0 per cent) than those from pigs and cattle (79.0 per cent and 71.5 per cent, respectively). Resistance against Ap, St, Tc, Su, TSu, Cm and Ff were all found higher in cattle and pig strains as compared to poultry isolates. On the other hand, 11.0 per cent of poultry isolates were resistant against Cef, whereas this was the case for 4.5 per cent and 1.8 per cent of cattle and pig strains, respectively. Twenty per cent of poultry Salmonella were found resistant against Nal, but hardly against Enr (0.3 per cent).

Most S. Agona isolates (n=48; 32 from poultry) were fully susceptible (81.3 per cent) for all antimicrobials tested. Most resistance was found against Ap and against Su (both 14.6 per cent).

Only seven S. Blockley isolates, all from poultry, were tested, and all had resistance profile Ap Tc Su Tsu Nal.

More than 60 per cent of S. Derby strains (n=26; most from pigs) were sensitive (61.5 per cent) although some resistance against Su (26.9 per cent), St and Tc (23.1 per cent) was noticed.

As for S. Dublin isolates (n=20; most from cattle), half of them were found completely susceptible. S. Enteritidis isolates (n=115) were mainly susceptible (96.5 per cent). One isolate from poultry showed the profile Ap St Tc.

Twenty-two S. Hadar strains were tested and only one (from poultry) was found sensitive. Resistance profiles Ap Tc Nal and Tc Nal were most often demonstrated (45.5 per cent and 40.9 per cent, respectively).

All 17 S. Indiana strains were multi-resistant of which 16 showed profile Ap St Su TSu.

Most of the S. Infantis strains (n=47) were susceptible (89.4 per cent). Two strains were Cef resistant. About 60 per cent of S. Mbandaka isolates (n=48) were susceptible to all antimicrobials tested. Ten strains showed profile Ap Su Tsu and 9 (all from poultry) were Cef resistant.

Sixteen from 21 S. Minnesota isolates were sensitive, but four (all from poultry) had profile Ap Cef Su Tsu.

Only 5.1 per cent of S. Paratyphi B (n=78) strains were fully sensitive. The most abundant profile was Ap Nal (69.2 per cent). Almost half of the strains were found Cef-resistant.

A limited number of S. Regent strains were tested (n=14), and all but one isolate were resistant against Ap and Nal. No sensitive isolates were identified.

Only 23.9 per cent of S. Typhimurium isolates (n=289) were found susceptible. Penta-resistance Ap St Tc Su Cm was encountered in 17.3 per cent of the isolates. Ff resistance was detected in 11.4 per cent of the strains, and Cef resistance in 2.4 per cent of S. Typhimurium.

About three-quarters of S. Virchow isolates (n=13) were resistant against all antimicrobials tested. As in former years, most resistance was found against Ap (69.2 per cent) and Nal (53.8 per cent). Cef resistance was remarkably high: 38.5 per cent.

Strains belonging to other serotypes were also tested, but to a lesser extent. Most of these isolates were fully sensitive for all the antimicrobials tested.

Further Reading

- You can view the full report by clicking here.

July 2010
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