Interna:;oual Journal of i ~ M Micr, d m d ~ ' , 15 (1992) 191-194 ~ 1992 Elsevier Science Publishers B.V All rights reserved 0168-1605/92/$05.00

191

FOOD 011459

Short Communication

Contamination of pig hindquarters with Staphylococcus aureus Heidi Schraft, Norbert Kleinlein and Friedrich Untermann lnstmd fiir tieriirztliche Lebensmittelhygiene,

Universit~t Ziirich, Ziirich, Switzerland

(Received 10 June 1991; revision received 11 October 1991; accepted 31 October 1991)

Swab specimens from 4357 pig hindquarters provided for production of cured raw ham were contaminated with Staphylococcus aureus in 22.7%. The bacterial counts for S. aurem on the rind surface of the raw. uncured ham were between 101 and 10 3 c f u / c m 2 in 89% of the p o s i t i v e samples, in the remaining i1% of contaminated ham counts of 10 3 tO 10 r' c f u / c m 2 were determined. There were major differences in the rate of contamination between pork from different suppliers. Questioning the suppliers revealed that pork highly contaminated with S. aureus could be traced back to certain abattoirs. This suggests that the technique of slaughter, concomitant hygiene precautions and the subsequent refrigeration of the carcasses affect the contamination of the meat with staphyk~cocci. Key words: Staphylococcus aureus; Pig hindquarters

Introduction

Fn~eroLoxin-producing Staphylococcus aureus plays an impnrtanl role as the causative organism of food intoxications. Statistics show that 41% of all staphylococcal infections in the U.S.A. from 1983-1987 occurred after consumption of meat and meat products. Pork was found to be the source of infection in 38.7% of these cases (Bean and Griffin, 1990). S. a u r e u s could be frequently identified both on the hands of the staff and on cutting boards and other equipment in meat-processing plants (Hadi-Khadem, 1978; Sp6rri, 1991). De Witt and Kampelmacher (1981) suspect that these S. a u r e u s strains are introduced into the plants with the raw meat and that they are spread in the meat-processing plants by cross-contaminations. The present investigations were intended to clarify how often and to what extent pig hindquarters provided for production of cured raw ham are contaminated with S. aureu_,', and thus contribute to ~;.ssemination of ¢.h~s p~thogen in meat-processing plants. Correspondence address: F. Untermann, lnstitut fiir tie#~irzlliche Lebensmittelhygiene, Universitiit Ziirich, Winterthurerstr. 272, Ctt-8057 Ziirich. Swilzerland.

192

Material and Methods

Swab specimens were taken from the surface of 4580 chilled pig hindquarters delivered !o a meat-processing plant and investigated quantitatively for S. a t t r e u s . The meat derived from a total of 18 different suppliers from the Federa! Republic of Germany and other EC countries. The samples were taken in accordance with the suggestion of a Commission of the European Community (1987). On the rind surface a sampling area of 40 cm z was swabbed with both a wet and a dry. sterile cotton swab. After the swab had been shaken up in 20 ml of sodium-chloride-peptone solution (0.85% NaCI, 0.1% peptone, pH 7.1)), the bacterial counts of S. a z t r e u s were determined with the spiral plater technique (Spiral Systems Inc., Cincinnati, Ohio) on Baird-Parker medium (Oxoid). Egg-yolk-po.~itive colonies and also typical colonies without egg-yolk-reaction were tested for thermostabie nuclease (TNase) production by the agar-diffusion method of Lachica et al. (1971). In addition the production of coagulase was determined by their action on coagulase-plasma-EDTA (Difco) in test tubes. Coagulasc- and TNase-positive colonies were identified as S. a t t r e u s . The lower limit of detection for S. a t t r e u s was 14 cfu/cm" (unpublished results).

Results and Discussion S. a t t r e u s could be identified in 33.6% of 223 pig hindquarters investigated during an initial period of two months from 18 different suppliers. Investigations of

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specimens from different supplicrs shows that there are major fluctuations in the percentage of positive hams between the individual suppliers (Fig. I ). On the basis of these results suppliers of pig hindquarters showing especially high rates of positive samples or high S. a u r e l t s counts were excluded from supply completely or for a time. During this time 988 (22.7%) of 4357 swab samples taken over 18 months from the same suppliers were still positive. This could indicate a slight reduction in the percentage of positive S. a u r e u s samples. The bacterial counts tot S a u r e u s on the rind surface of the ham were between l0 t and 103 cfu/cm-" in 89%. of the positive specimens, in lttC/c of the positive S~im L¢~S ¢ ~ O ~ ...*. .v. t. v t,~..~tlcvtk.,i,,.~ll l~kl di|~i l~l''~ c i u / c m - and some extreme values reached ll) ~' c f u / c m 2 (Fig. 2). The p~csent investigations show that pig hindquarters are frequently contaminated with S. attreus. Questioning the suppliers revealed that pork highly contaminated with S. a u r e u s could be traced back to certain abattoirs. Deliveries in which till: incidence of S. a t t r c u s was very low could likewise be attributed to certain abattoirs, it is to be suspected that the contamination of pork is related with the technique and hygiene of slaughter and the subsequent refrigeration. Rasch et al. (1978) observed that the slaughter technique can affect the S. a u r e u s counts on the skia of pig carcasses. Narucka (1979) showed that pig heads (of which up to 35% were contaminated with S. a u r e u s immediately after slaughter) displayed rates of contamination of 75% after cooling and deboning. In consequence, butchering and meat-processing plants are advised to carry out bacteriological controls on arrival of the meat. Moreover, these plants must observe strict hygiene measures, especially in dealing with pork, in order to keep the rate of cross-contamination as low as possible while processing the meat. These

t94

measures include above all regular changing as well as the cleaning a,aO disinfection of cutting boards and equipment during production.

R ~fe~nces Bean, N.H. and Griffin. P.M. (1990) Fo~ibor~te di.~a~ outbreaks in the United Stales. 1973-1987: pathogens, vehicles and trends, J. F ~ Pro*~eet. 53, ~kl-gl7. Commission of the European Communities ~!9'~7) Code of good hygienic practices. EG-Dokument: V!/5938/87 (PVET/2140). De Witt. J.C. and Kamp¢~macher. E.H. (1981) Some aspects of microbial contamination of hands of wockers in food industries. Zbi. Bakt. Hyg.. !. Abt. Orig. B 172. 390-400. Hadi-Khadem. S. (1978) Vorkommen yon antibiotikarcsistenten Staphylokokken bet Schlachttierkiirpern yon Schweinen und in der Vcrarbeitung unter I~-:ondcrer Beriicksichtigung der Flaw~mycin- und Virginiamyeinresistcnz. Vet. Med, Disserlation, Bet;in. Lachica. R.V.F., Genigeorgis, C. and Hoeprich, P,D. (1971) Metachronie agar-diffusion methods for detecting staphylococcal nuclease activity. Appl. Mierobiol. 21. 285-587. Narucka, U.J. (1979) Occurrence and health significance of Staphylococcus aureus in a pig slaughter line. A.A, Balkema, Rotterdam, Niederlande. Raseh, B,. Lie, O, und Yndestad. M. (1978)The bacterial flora in pork skin and the influence of various singeing methods on this flora, Nord. Vet, Med, 30, 274-281. Sp6rri. V. (lqgi) Vorkommen und Eigenschaften yon Staphylococcus aureus in fleischverarbeitenden Betrieben. Vet. Med. Di.~sertation. Ziirich,