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Public Health

GARDEN FERTILISERS

AS A SOURCE OF SALMONELLÆ

MORAG C. TIMBURY*M.D., Ph.D. Glasg., M.C.Path.CONSULTANT BACTERIOLOGIST

WILLIAM C. FORSYTHF.I.M.L.T.

SENIOR TECHNICIAN

CITY LABORATORY, 23 MONTROSE STREET, GLASGOW C.1

JOHN S. STEVENSONM.D. Glasg., M.R.C.P.G., F.C.Path.

DIRECTOR, SALMONELLA REFERENCE LABORATORY, DEPARTMENT OF

BACTERIOLOGY, STOBHILL GENERAL HOSPITAL, GLASGOW N.1

ANIMAL products such as bone-meal, dried blood, andhoof-and-horn meal are in general use as garden fertilisers.Of these, bone-meal is by far the most widely used. Wewish to draw attention to the danger of bone-meal fertilisersas a source of salmonella:. Previous studies 1-3 have shownthat 27-70% of bone-meal fertilisers were contaminatedby salmonella;. In the investigation described here, sal-monella: were isolated from 94% of samples of bone-mealbought over the counter as fertiliser during the spring andsummer of 1966.

MATERIALS AND METHODS

90 samples of organic fertiliser were examined forsalmonella;. These included 50 samples of bone-meal, 25samples of dried blood, and 15 samples of hoof-and-hornmeal. These were bought from garden shops, pet shops,grocers, greengrocers, ironmongers, and grain stores,mainly in the West of Scotland. Sometimes a second

sample was bought from a shop after an interval of severalweeks.

21 of the 50 bone-meal samples were weighed out in theshop. The other 29 samples were prepacked in boxes or bagswhich bore 7 different trade-names. 16 of the 25 samples ofdried blood were prepacked, but only 4 of the 15 samples ofhoof-and-horn meal were made up in packets before purchase.

10 samples of " steamed " bone-flour were also examined.

Because this product has been taken off the market retail sampleswere difficult to obtain and, unlike the other fertilisers, couldnot be bought in a random manner. 3 of the samples wereobtained from one manufacturer, and 5 others were bought ona single occasion from the same shop.

Bacteriological ExaminationsBone-meal.-Approximately 10 g. of the sample under

investigation was added to each of 3 screw-capped jars contain-ing selenite F medium, Kauffman-Miiller tetrathionate broth,4and Rappaport’s medium respectively. After incubation at37°C overnight the cultures were plated on Wilson and Blair’smedium and on ’ Oxoid’ brilliant-green agar. Subcultureswere also made into containers with 10 ml. of the same enrich-ment media. The secondary enrichment cultures were platedin the same way after incubation for 8 hours. The plates wereexamined after incubation for 24 and 48 hours, and 18 colonies(usually 6 from each enrichment medium) were picked for"Present address: Institute of Virology, Church Street, Glasgow W.1.1. Walker, J. H. C. Lancet, 1957, ii, 283.2. Report of a Working Party of the Public Health Laboratory Service.

Mon. Bull. Min. Hlth, 1959, 18, 26.3. Galbraith, N. S., Taylor, C. E. D., Cavanagh, P., Hagan, J. G., Patton,

J. L. Lancet, 1962, i, 372.4. Cruickshank, R. Medical Microbiology; p. 762. Edinburgh, 1965.5. Rappaport, F., Konforti, N., Navon, B. J. clin. Path. 1956, 9, 261.6. de Louriero, J. A. J. Hyg., Camb. 1942, 42, 224.

investigation. This included subculture to Kohn’s compositemedium,’ followed by serological identification.

Dried blood, hoof-and-horn meal, and steamed bone-flour.-10 g. quantities of the samples were inoculated into 3 jars ofenrichment media, as described above; but incubation wascontinued for 48 hours and the cultures were plated at 24 and48 hours. No secondary cultures were set up.

RESULTS

The results of examination for salmonellse are shown intable i. Bone-meal fertilisers had a high rate of contamina-tion : salmonella; were isolated from 47 (94%) of the 50

TABLE I-EXAMINATION OF ORGANIC GARDEN FERTILISERS FOR

SALMONELLA

samples examined. Salmonellae were isolated from only1 (4%) of the 25 samples of dried blood and from 3 (20%)of the 15 samples of hoof-and-horn meal.Most of the bone-meal samples yielded more than one

serotype. The average was 4, some samples yielding upto 9 serotypes. These results are almost certainly anunderestimate, since only 18 colonies were picked forinvestigation from each specimen, regardless of how manycolonies appeared on the plates of selective media. 2 sero-types were isolated from 1 sample each of dried blood andhoof-and-horn meal: the 2 other samples of hoof-and-hornmeal yielded only 1 serotype.

66 different serotypes of salmonella; were isolated in the

7. Kohn, J. J. Path. Bact. 1954, 67, 286.

TABLE II-SEROTYPES OF SALMONELLA ISOLATED FROM GARDEN

FERTILISERS

Serotypes and no. of samples from I Serotypes isolated fromwhich serotype was isolated one sample only-

*S. senftenberg 29*S. anatum 22

*S. meleagridis 13S.cubana 11

’*’s. ,montevideo 11S. budapest 8

*S. typhimurium 8*S. worthington 6S. butantan 5

*S. minnesota 4*S. oranienberg 4S. adelaide 3

*S. bredeney 3*S. give 3*S. paratyphi B 3S. ruzizi 3 ’

S. san diego 3S. alachua 2S. congo 2S. edinburg 2

S. good 2S. hamilton 2S. london 2 I

*S. menston 2 IS. mlkawashima 2 ;

*S. newport 2

S. nyborg 2

S.panama 2S. poona 2

*S. reading 2

S. takoradi 2* S. tennessee 2S. virchow 2S. westhampton 2

S. bleadonS. blegdamS. blockleyS. bukavuS. carmel

’illS. chesterS. dugbeS. foulpointeS. friedenauS. hartfordS. hillbrowS. hvittingfoss

*S. infantisS. kentuckyS. kimbusiS. kingstonS. kotteS. magwe

*S. manhattanS. mgulaniS. newingtonS. nottinghamS. orion

! S. pretoriaS. quimelaS. roodepoort

*S. saintpaul*S. schwarzengrund*S. stanleyS. tshongweS. virginiaPreviously unrecognised

serotype

*= Strains isolated from more than 100 human sources during 1951-63.

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investigation (table 11). Many of the strains have beencommon causes of food-poisoning in Britain, and thoseisolated from more than 100 human sources from 1951 to1963 8 are indicated in table 11. Some strains are rarelyfound in human infections in Britain, and 1 proved to bea previously unknown serotype. The commonest sal-monella causing food-poisoning in Britain, Salmonella

typhimurium, was isolated from 8 samples of bone-meal.On the other hand, by far the commonest in bone-mealwas S. senftenberg, which is considerably less important asa cause of food-poisoning. These results probably reflectthe incidence of salmonella serotypes among the animal

populations from which the bones were derived. S. para-typhi B, however, was isolated from 3 samples of bone-meal, although this organism is not common in animals.None of the 10 samples of steamed bone-flour yielded

salmonellae.

DISCUSSION

These results confirm that most bone-meal fertilisersare contaminated with salmonella:. In fact, an average of4 serotypes was found in each of the samples examined.Most bone-meal imported into Britain comes from Asia,9 9and the high rate of contamination may be related to theincidence of salmonellosis in the cattle there. Bone-mealfrom the Far East usually contains sun-dried bones col-lected from animals dying in the open, and these may bemore heavily contaminated than bones from animals

slaughtered in abattoirs. Asian bones are ground but arenot exposed to heat before exportation. Smaller amountsof bone-meal are imported from Argentina and from someAfrican and European countries. Only a small proportionis home-produced. Bone-meal imported as fertiliser is notprocessed further after arrival in Britain but is merelypackaged for retail distribution. Dried blood, whichshowed a low rate of contamination, either comes fromBritish abattoirs or is imported from New Zealand, SouthAfrica, or Australia. Hoof-and-horn meal is obtained fromvarious sources, mostly foreign, but in the present surveyonly 20% of the samples yielded salmonellx.The rate of contamination of bone-meal found in this

investigation was higher than that reported by previousworkers. 94% of our samples yielded salmonella:, com-pared with 70% reported by Walker and 27% byGalbraith et awl. The working-party of the Public HealthLaboratory Service 2 found that 48% of bone productsused as fertilisers or as animal feeding-stuffs were con-taminated (77% for imported products, 43% for home-produced material). On the other hand, Harvey andPrice 10 found salmonellae in 98% of samples of crushedbone imported from India and Pakistan for the prepara-tion of animal feeding-stuffs. Their results are similar toours-perhaps because nearly all the bone-meal used asfertiliser now comes from the Far East.

It is difficult to assess the danger of fertiliser as a sourceof human salmonellosis. Since salmonellx do not survive

long when exposed to rain and sun,2 the risk when fertiliseris spread on growing foodstuff is probably very small.But packets of fertiliser may be stored in kitchens, wherethe dust from them could contaminate prepared food. Wefound that virtually every packet of bone-meal-even ifdoubly wrapped-leaked some dust; and opening a packet8. Taylor, J., Lapage, S. P., Brookes, M., King, G. J. G., Payne, D. J. H.,

Sandiford, B. R., Stevenson, J. S. Mon. Bull. Min. Hlth, 1965, 24,164, 236.

9. Report of the Committee of Inquiry on Anthrax; p. 47. London, 1959.10. Harvey, R. W. S., Price, T. H. Mon. Bull. Min. Hlth, 1962, 21, 54.

always released a cloud of dust. Fertiliser is commonlyspread by hand, and this too could easily lead to con-tamination of food. Storage of fertiliser in shops is alsoa considerable potential risk: several of the shops fromwhich we obtained samples also sold food. In one storeloose bone-meal (from which 5 serotypes were later

isolated) was weighed out close to open bags of grain,sugar, and dried fruits. In one country grocery a large bagof bone-meal was placed on the only weighing-machinein the shop. Judged from the way in which fertilisers laybeside other goods, including foodstuffs, the dangers ofthis are not widely recognised.

Although many of the serotypes found in fertilisers areuncommon in human infections, others have been majorcauses of food-poisoning in Britain in recent years. In theUnited States, cases of salmonella infection in a hospitalwere due to the same serotypes as strains isolated fromsludge used to fertilise the hospital lawn.ll Since thesource of infection of most incidents of food-poisoning inBritain is unknown, it may be that fertilisers are responsiblefor a proportion of the infections in this country also.Bone-meal can be rendered safe by heating-the samplesof steamed bone-flour we examined were notably freefrom contamination. Steamed bone-flour is a by-productof glue manufacture, during which the bones are subjectedto temperatures of 220-280°F. Unfortunately the costs ofthe heating process have made the production of steamedbone-flour uneconomical, and it is no longer on the market.Our results do not prove that bone-meal fertiliser has

caused infection. Nevertheless, the frequency of con-tamination by salmonella: suggests either that importationof contaminated material should be restricted or that bone-meal should be treated by heat before distribution asfertiliser.

SUMMARY

Salmonella: were isolated from 47 (94%) of 50 samplesof bone-meal fertiliser, compared with 1 (4%) of 25samples of dried blood and 3 (20%) of 15 samples ofhoof-and-horn meal. Ten samples of steamed bone-flourwere free from contamination.An average of 4 serotypes was isolated from the bone-

meal samples. A total of 66 serotypes were isolated, manyof which have been common causes of infection in Britain.The samples examined were bought in a variety of

shops, some of which also sold food. The potential dangerof bone-meal fertiliser as a source of salmonellx is

emphasised. It is suggested that either the importation ofcontaminated bone-meal should be restricted or that bone-meal should be treated by heat before distribution as

garden fertiliser.We thank Mr. Robert Kennedy, F.I.M.L.T., of the Salmonella

Reference Laboratory, Stobhill General Hospital, for technicalassistance.

Requests for reprints should be addressed to M. C. T., Instituteof Virology, Church Street, Glasgow W.1.

The Non-smoking TeenagerIN a letter to local authorities the Minister of Health presents

statistics which indicate a substantial rise in the proportion ofnon-smokers, especially in the 16-19 age-group. The figuresrelate to 1961-65. In this period the proportion of non-smokersrose from 38% to 49% for young men aged 16-19, and from55% to 61 % for young women. For the whole population theincrease is not so striking-the proportion of non-smokerswent up from 43% to 46%.

11. Edwards, P. R. Ann. N.Y. Acad. Sci, 1956, 66, 44.