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325 Journal ofFood Protection Vol. 40, No. 5. Pages 325-329 (May, 1977) Copyright 1977, International Association of Milk, Food, and Environmental Sanitarians Growth and Enterotoxin Production by Staphylococci in Genoa Salami 1 I. C. LEE2, L. G. HARMON, andJ. F. PRICE Department ofFood Science and Human Nutrition Michigan State University, East Lansing, Michigan 48824 Downloaded from http://meridian.allenpress.com/jfp/article-pdf/40/5/325/1649781/0362-028x-40_5_325.pdf by guest on 30 September 2021 (Received for publication August 30, 1976) ABSTRACT staphylococcal strains tested grew and produced Staphylococcus aureus strains 265 and 243 which produce enterotoxin aerobically at pH 5.t in broth media. Control enterotoxins A and B, respectively, were inoculated into meat beinJ of S. aureus in sausage by lactic cultures and chemical made into Genoa salami in the amount of lOl. lOS, and 107. cells/g. No acidulation was also reported by Daly et al. (4). Partial lactic starter culture was added. Samples were taken at different stages of processing to determine the microbial populations, percenta,e inhibition of staphylococcal cells was observed by using 8 moisture, tntal acidity, pH, and enterotoxin content. Staphylococcal the starter culture at t0 cells/g, or by chemical populations varying from about HY to 5 x 10'/g were detected during acidulation with 0.75% GDL and O.t% citric acid. They tempering of the salami. Enterotoxin A was detected in surfKe but not also suggested using a combination of chemical in core samples of salami inoculated with 105 and 107 S. aureus 265 acidulation and lactic culture. The effect of water activity cells/g. However, no enterotoxin B was detected in the salami inoculated with S. aureus 243, which requires a relatively high 9.w for (3w) on enterotoxin production and growth of S. aureus enterotoxin production. Staphylococcal counts were higher in surface was reported by Troller (JO, 11) who demonstrated the samples than in core samples, attributable to the difference in oxysen, production of enterotoxin B by S. aureus C-243 was but there was no significant difference in microaerophilic lactic Kid strongly inhibited by a reduction in aw from 0.99 to 0.98 bacteria in different portions of the salami. in broth despite the attainment of populations of 101 cells/mi. However, S. aureus t96E produced enterotoxin A at an 3w of0.90 and fmal cell counts were tO'/ml. Meat products such as ham, bacon, and fermented The purpose of this investigation was to evaluate sausage have been incriminated in staphylococcal food growth of staphylococci and production of enterotoxins poisoning, caused by careless manufacturing techniques in Genoa salami. which render these products vulnerable to staphvlococcal development. Use of cultures of lactic acid bacteria has YIATERIALS A:"<iD l\IETHODS facilitated inhibition of staphylococci during processing. Processing ofGelWCI salami However, "chance inoculation" and "back slopping" are Frozen pork was thawed, cut into strips and ground through a still used to some extent in industry (4). In 1971, several 1.2-cm plate. Spices and curing agents (fable 1) were miXJ:d in by outbreaks of gastroenteritis were traced to Genoa salami TABLE 1. Genoa salami ingredients containing up to to• coagulase positive staphylococci/a Quantity and type A enterotoxin was detected in some of these samples (12. 13). Niskanen and Nurmi (6) found Pork Sodium chloride J06.20g measurable amounts of enterotoxin A in a 200-g sample 11.34 g 1 White pepper of dry sausage containing per g 10 cells of Staphylococ· Whole pepper 2.84g cus aureus which produce type A toxin but enterotoxin B Sodium nitrite 0.71 g was not detected in corresponding samples containing Sodium nitrate 5.68g Garlic 1.89 g lQB cells per g of S. aureus which produce type B toxin. 68.10 g Barber and Deibel (2) studied the effect of pH and oxygen tension on staphylococcal growth and enterotoxin stirring. The meat was then inoculated with washed cells rA S. aureu.r formation in fermented sausage. They indicated growth 265 or 243 in the amount of about 10l, 10', and 107 cells/g. After could be controlled with l.So/o glucono-delta-lactone inoculation, meat was spread in layers and for 2days at4 C. (GDL), whereas a hig.h inoculum of Pediococcus It was re-ground and stuffed into pre-soaked, tied collaiFO CISings (9 x 56 em; Brechteen Co.). The casings of salami were refriaeratecl 1t cerevisiae failed to suppress aerobic growth. Most 4 C for 4 davs and then put in a tempering room at 20 to 25 C ano !!Oo/o relative- humidity (RH) for 2 days. FoUowinJ temperlna, the 1 MichiganAgriculturalExperiment Station Journal Article No. 7372. casings were heated in air at 38 C for 20 h, 43 C for 2 b, 49 C for 4 11: 1 Present address: Central Research Dept., Anheuser-Busch. Inc. 1101 and S4 C for J hat 80 to 90% RH. The salami was then dr1ed at 12 C Wyoming Street, St. Louis, Mo 63118 and 72%RH torabout60days. 326 LEE, HARMON, AND PRICE Sampling methods Samples from the outer 1 em of surface and sample~~ of the core were 7 taken from salami inoculated with S. aureus 265. Samples of the emire cross section were taken from salami inoculated with S. aureus 243. 6 The salami were examined at aifferent stages of processing as follows: (a) after inoculation, (b) before tempering, (c) after tempering, (d) after 5 heating, and (e) at various intervals during drying. 4 Enumeration ofmicrobial populations --- ..... -.... _~ Staphylococcal counts were made using spread plate technique 3 01 on Mannitol Salt Agar (MSA; Difco). Following incubation at 37 C for 2 48 h. coagulase tests were made on a representative number of typical '1/) S. aurous colonies. The aerobic counts were made in Plate Count Agar Q) () 8~ (PCA; Difco). Lactic acid bacteria were enumerated in plates of Lactobacillus Selective Agar (LBS: BBL). c 7~ 0 L-----------~~ Lactic acid and pH determination +- 6 /~ Downloaded from http://meridian.allenpress.com/jfp/article-pdf/40/5/325/1649781/0362-028x-40_5_325.pdf by guest on 30 September 2021 c I I Twenty grams of salami and 180 mi of de-ionized water were mixed ::1 in a Waring belnder for 2 min. The pH of the homogenate was a. 5 h.. __ ----------..c... measured on a Beckman pH meter. The homogenate was then filtered a..0 through Whatman #1 filter paper and portions of filtrate corresponding 01 to 5 g of sample were titrated with 0.1 N NaOH to pH 8.3. The total 0 ;[ _J titratable acid was calculated as percent lactic acid. 9 Moisture determination A 5-g sample of salami was spread in an aluminum moisture dish 5.5 em in diameter (Sargent and Co.} and dried in a convection oven at 100 C for 16 to 18 h and cooled. The weight loss was expressed as I percent moisture. I 6 I Determination ofwater activity --I ,I.. 5 b----------- ---.t>.- ---c. A moisture sensing element (No. 547535, Hygrodynamics. Inc.) was mounted in a rubber stopper on a 170-ml jar containing 20 g of salami 4L-------~------~--------~~~ and attached to a hygrometer indicator. Wate~ activity measurements 0 10 20 30 63 were carried out after the samples were equilibrated for 24 hat 22 C. Days Extraction and detection of enterotoxin Enterotoxin was enracted from 100-g samples of salami and determined by the serological procedure described by Casman and Figure 1. Populations of S. aureus strain '?65 determined on MSA Bennett (])with modifications described by Barber and Deibel (2). plates and enterotoxin A produced in salami inoculated with 10' (top), 105 (middle), and 107 (bottom) cells/fl. Legend: -o- surface sample;-/::,.­ core sample. Solid symbols indicate enterotoxin A was detected. RESULTS AND DISCUSSION Genoa salami inoculated with S. au reus 265 of the microbial populations was mainly due to the Samples of salami were obtained for analyses at 0 day difference in the oxygen tension. Total population trends (after inoculation), 6 days (after curing in the cooler), 8 for organisms enumerated by aerobic plate counts (Fig.2) days (after tempering), 9 days (after heating), 29 and 63 were similar to those of the staphylococci, except that days (during drying). Data in Fig. 1 illustrate the growth during the drying period the total populations decreased patterns of S. aureus 265 in the inoculated salami. The less than the staphylococcal populations. Data in Fig. 3 staphylococcal population remained the same or illustrate the population changes of the lactic acid decreased slightly during 6 days of curing in the cooler. bacteria in salami inoculated with S. aureus 265. The After tempering, counts of 1.5 x 107, 2.8 x 101, and original population of these organisms in the pork was 4.9 x 108 cells/g were obtained from the surfaces of the less than 150/g of meat, but the count was more than salami inoculated with 103 , 105 , and 107 staphylococci/ 105/g in samples taken after the salami was heated. The g, respectively. In the core samples, however, increases of anaerobic condition in core samples caused a decrease in 300-fold and 15-fold occurred in the salami inoculated the lactic acid bacteria, since they are microaerophilic. with 10 3 and 10 5 cells/g, respectively, while only a slight Samples taken from different locations ofthe salami did increase occurred in the salami inoculated with 10 7 not show any significant difference in the populations of cells/g. Heating caused a reduction of 10- to 100-fold in lactic acid bacteria. Also, there was no significant populations in both surface and core samples.

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