International Journal of Antimicrobial Agents 25 (2005) 38–43

Increasing prevalence of multidrug-resistant non-typhoidalsalmonellae, Kenya, 1994–2003

Samuel Kariukia,c,∗, Gunturu Revathib, Nyambura Kariukib, Jane Muyodia, Joyce Mwituriaa,Agnes Munyaloa, Dorothy Kagendoa, Lawrence Murungia, C. Anthony Hartc

a Centre for Microbiology Research, Kenya Medical Research Institute, PO Box 43640, Nairobi, Kenyab Department of Medical Microbiology, Kenyatta National Hospital, PO Box 20723, Nairobi, Kenya

c Department of Medical Microbiology and Genito-Urinary Medicine, University of Liverpool, Liverpool L693GA, UK

Received 4 June 2004; accepted 27 August 2004

Abstract

Over the last decade there has been a steady increase in the proportion of multidrug resistance among non-typhoidal salmonellae (NTS)i includinga omitantlyh ofS rnsf crease inM ection.©

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solated from adult patients with bacteraemia in Kenya. The prevalence of NTS multiply resistant to all commonly available drugsmpicillin, streptomycin, co-trimoxazole, chloramphenicol and tetracycline rose from 31% in 1994 to 42% at present, with concigher MICs of each drug. Resistance is encoded on large self-transferable 100–110 kb plasmids. Pulsed field gel electrophoresisXbaI andpeI digested chromosomal DNA revealed three main digest patterns forSalmonella entericaserotype Typhimurium and two main patte

or Salmonella entericaserotype Enteritidis. Although the genotypes of NTS remained fairly stable over the last decade, the large inICs of all commonly used drugs and increased MICs of ciprofloxacin, poses a major challenge for treatment of invasive NTS inf2004 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.

eywords:Non-typhoidal salmonellae; Bacteraemia; Multidrug resistant; Kenya

. Introduction

In developing countries non-typhoidal salmonellae (NTS)ccount for a steadily increasing proportion of human infec-

ions and represent about 20–30% of salmonella serotypes, inarticular multidrug-resistantSalmonella entericaserotypeyphimurium. which causes serious outbreaks. For exam-le in Zaire[1,2] and Rwanda[3] multidrug-resistantS. Ty-himurium were the predominant cause of bacteraemic ill-ess in children, while in Kenya, this serotype was the main

solate in adults with salmonellae bacteraemia[4,5]. In mosteveloped countries, outbreaks of NTS infection have beenaused mainly byS. Typhimurium andSalmonella enter-ca serotype Enteritidis[6–8] and predominantly present as

diarrhoeal disease acquired as a food poisoning. A vari-ty of foods have been implicated as vehicles transmitting

∗ Corresponding author. Tel.: +254 202 718247; fax: +254 202 711673.E-mail address:skariuki@wtnairobi.mimcom.net (S. Kariuki).

salmonellosis to humans, including poultry, beef, pork, emilk, cheese, fish, shell-fish, fresh fruits and juice and vegbles[9,10]. Contamination can occur at multiple steps althe food chain. The source and mode of transmission ofin the African context are unknown although it is thoughthuman-to-human transmission may play an important r

Infections caused by multidrug-resistant NTS are alscreasingly frequent in developing countries, including Keand frequently present as bacteraemia often withoutrhoeal disease[4,11]. The increasing rates of resistanof these isolates to readily available antimicrobial ag(i.e., ampicillin, chloramphenicol and co-trimoxazole) ato extended-spectrum cephalosporins, have made thement of invasive salmonellosis a clinical dilemma[12]. Forexample chloramphenicol is the drug of choice for invasalmonellosis in Malawian children; ciprofloxacin and ctriaxone are less available and much more expensive[13]. Inaddition infection with MDR NTS has been associatedan increased rate and duration of hospitalisation, a two

924-8579/$ – see front matter © 2004 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.

oi:10.1016/j.ijantimicag.2004.08.015

S. Kariuki et al. / International Journal of Antimicrobial Agents 25 (2005) 38–43 39

increased risk of death during a 2-year period after the in-fection, and an increased rate of invasive infection[14]. Alsoof particular concern is the emergence of fluoroquinolone re-sistance among NTS and the occurrence of outbreaks causedby such resistant clones[15], since this class of antimicrobialagents contain the drugs of choice for treating potentially life-threatening salmonella infections caused by the multidrug-resistant strains in adults. An additional recent concern is theincreased prevalence and widespread dissemination of penta-resistant (ACSSuT)S.Typhimurium Definitive Phage Type(DT)104 in many parts of the world[16–18].

In many developing countries bacteraemia due to invasiveNTS has been associated with an increased risk of death, par-ticularly in children with severe malaria[19,20]and amongimmunosuppressed adults, particularly with HIV/AIDS[5].NTS bacteraemia has also been reported as a complicationof the management of severe malarial anaemia causing clin-ical deterioration after blood transfusion. For instance bloodcultures were positive in 22% of Malawian children who be-came febrile after a blood transfusion and more than 80% ofisolates wereS. Typhimurium[20]. Here we have analysedthe trends in antimicrobial susceptibility of NTS from hospi-talised adult patients with bacteraemia over a 10-year period,in relation to the molecular characteristics of the bacterialstrains.

2

2

f 10y ns toh es oft aseso and1 latesb d bys ingS art-f tb UK)u tud-i

2.2. Antimicrobial susceptibility testing

Susceptibilities to various antimicrobials – ampi-cillin, tetracycline, co-trimoxazole, chloramphenicol, strep-tomycin, gentamicin, augmentin, ciprofloxacin, cefuroxime,ceftazidime and nalidixic acid – were determined both by diskdiffusion and measuring minimum inhibitory concentrations(MICs) using Etest strips (AB BIODISK, Solna, Sweden) ac-cording to the manufacturer’s instructions.Escherichia coliATCC 25922 (with known MICs) was used as a control forpotency of antibiotic disks and Etest strips. Disk diffusionsusceptibility tests and MICs were interpreted according tothe guidelines provided by the National Committee for Clin-ical Laboratory Standards[21].

2.3. Pulsed field gel electrophoresis of macrorestrictedchromosomal DNA

Chromosomal DNA from NTS isolates was prepared inagarose plugs as described previously[4]. DNA in agaroseplugs was digested using 25 units each ofXbaI or SpeI(Roche Diagnostics GmbH, Mannheim, Germany). PFGEof agarose plug inserts was then performed on a CHEF-DR III system (Bio-Rad Laboratories, Hercules, CA, USA)on a horizontal 1% agarose gel for 20 h at 120 V, with ap -s from5 NAs idea SanG areda en-o r-m s,a andn entp ly re-l uchp

2

midM ing

TD dy

N

SSSSSSSO

. Materials and methods

.1. Bacterial isolates

A total of 342 NTS isolates obtained over a period oears (1994–2003) from blood cultures of adult admissioospitals in Nairobi, Kenya, were analysed. For purpos

he analysis bacterial isolates were derived from three phf the study; 144 isolates were obtained between 1994996, 126 isolates between 1997 and 2000 and 72 isoetween 2001 and 2003. NTS isolates were identifieerotyping following the Kauffmann-White scheme utilizalmonellaagglutination antisera (Murex diagnostics, D

ord, UK). NTS isolates were stored at−70◦C on Proteceads (Technical Service Consultants Ltd., Heywood,ntil analysed. The distribution of the various serotypes s

ed over the 10-year period is shown inTable 1.

able 1istribution of NTS serotypes (number and %) during the 10-year stu

TS serotype 1994–1996 (n= 144)

. Typhimurium 108(75)

. Enteritidis 7(4.8)

. Newport 6(4.2)

. Choleraesuis 5(3.5)

. Saintpaul 7(4.8)

. Durban 3(2.1)

. Agona 0ther NTS 8(5.6)

ulse time of 1–40 s at 14◦C. A lambda DNA digest conisting of a ladder (ca. 22 fragments) of increasing size0 kb to approximately 1000 kb was included as a Dize standard. The gel was stained with ethidium bromnd photographed on a UV transilluminator (UVP Inc.,abriel, CA, USA). The RE digest patterns were compnd their similarities were scored by the method of Tver et al.[22] and using the Dice similarity coefficient foula, 2h/(a+b), whereh is the number of matching band+b is the total number of bands including matchingon-matching. Isolates that differed in their PFGE fragmatterns by one or two bands were regarded as close

ated, as minor mutational changes would result in satterns.

.4. Plasmid detection and sizing

Plasmid DNA extraction was performed using a Plasini Prep Kit (Qiagen Ltd., West Sussex, U.K.) accord

1997–2000 (n= 126) 2001–2003 (n= 72)

67 (53.2) 25 (34.7)48(38.1) 27(37.5)2(1.6) 3(4.2)0 0

1(0.8) 3(4.2)1(0.8) 2(2.7)1(0.8) 06(5.3) 12(16.7)

40 S. Kariuki et al. / International Journal of Antimicrobial Agents 25 (2005) 38–43

to manufacturer’s instructions. Plasmids were separated byelectrophoresis on horizontal agarose 0.8% gels at 100 V for2 h. Plasmid sizes were determined by co-electrophoresiswith plasmids of known sizes fromE. coli strains V517(NCTC 50193) (53.7, 7.2, 5.6, 3.9, 3.0, 2.7, 2.1 kb) and39R861 (NCTC 50192) (147, 63, 43.5, 6.9 kb). DNA bandswere visualized with an ultraviolet transilluminator (UVPInc.) after staining with ethidium bromide 0.05%.

3. Results

3.1. Bacterial isolates

From 1994 to 1996 the majority (108; 75%) of the NTSwereS. Typhimurium with smaller numbers ofS. Enteri-tidis, S.Newport,S.Choleraesuis,S. Saintpaul,S. Durbanand other untypable NTS. However, after 1997, the propor-tion ofS.Enteritidis increased steadily and by the year 2003,S.Typhimurium andS.Enteritidis occurred in almost equalproportions (Table 1).

3.2. Antimicrobial susceptibility

si-t tantt d 24( ycina ain-d bials( s toa lo-r ,3 ll ther de-v thel NTSf cina allt

For NTS from 1997 to 2000, and from 2001 to 2003,there were two main antibiotic susceptibility patterns; fullysusceptible isolates constituting 27 (21.4%) and 13 (18%)NTS isolates, respectively, and MDR (resistant to two ormore antibiotics) isolates making up 64.2 and 72%, respec-tively. For all commonly available antibiotics including ampi-cillin, co-trimoxazole, streptomycin, chloramphenicol, andtetracycline, MIC values were higher for the MDR isolates(Tables 3 and 4) than for previous NTS from 1994 to 1996.For instance, in 1994–1996 a total of 31% of NTS were mul-tiply resistant to ampicillin, co-trimoxazole, streptomycin,chloramphenicol and tetracycline (MIC90 in mg/l of >256,>32, >1024, >256 and >256, respectively) but the preva-lence of this phenotype rose steadily to 42% by 2003. Theprevalence of resistance for all the commonly used antimi-crobials has also risen steadily over the last 10 years of thestudy. Although no NTS from 1997 to 2000 were resistant tociprofloxacin, a number (4%) showed reduced susceptibility(MIC = 0.25 mg/l). There were no significant changes in lev-els of resistance between NTS from 1997 to 2000 and NTSfrom 2001 to 2003, except for a modest reduction in resis-tance to nalidixic acid from 11 to 4%. Of the 64.2 and 72%NTS showing MDR resistance phenotype during the period1997–2000 and 2001–2003, respectively, the prevalences forthe two most common serotypes,S.Typhimurium andS.En-t 6%.H com-p mbero

3

ofs tatives sters( en-d f sim-i gnif-i kbp)a or

TM om me

A (mg/l)

t

ACCCGSCCTNC

Only 23 (16%) of NTS from 1994 to 1997 were senive to all 11 antimicrobials tested, 28 (19.4%) were resiso one agent (usually streptomycin or tetracycline) an16.7%) were resistant to two agents (usually streptomnd tetracycline or tetracycline and ampicillin). The remer (47.9%) were resistant to three or more antimicroTable 2) and the most frequent resistance pattern wampicillin, cefuroxime, streptomycin, co-trimoxazole, champhenicol and tetracycline (MIC90 in mg/l of 64, 32, 1282, 32, and 128, respectively), which encompasses aeadily available antimicrobials in Kenya and most othereloping countries. There was no significant difference inevel of resistance between the different serotypes ofrom these patients. However, nalidixic acid, ciprofloxand ceftazidime were uniformly effective in vitro against

he NTS isolates.

able 2IC using the Etest of 11 antimicrobial agents for 144 NTS isolates fr

ntimicrobial agent Minimum inhibitory concentration

Range Mode

mpicillin 0.5–128 64o-amoxiclav 0.5–64 0.5efuroxime 2–128 8eftazidime 0.125–16 0.25entamicin 0.06–16 1treptomycin 2–128 8o-trimoxazole 0.25–64 0.5hloramphenicol 1–32 4etracycline 0.5–64 64alidixic acid 1–4 1iprofloxacin 0.015–0.25 0.03

eritidis, respectively, were 58 and 42%, and 54 and 4owever, these differences were not significant and noarisons were made for the period 1994–1996 as the nuf S.Enteritidis was too small (7; 4.8%).

.3. PFGE patterns of NTS isolates

Initially, dendrograms were constructed for groupstrains within each serotype, and from these, representrains were selected from each of the closely related clu100% similarity coefficient) to construct a composite drogram. Each of the NTS serotypes possessed a core o

lar fragments between 520 and 1000 kbp, but differed sicantly in RE patterns of the smaller fragments (40–500s shown inFig. 1. For all NTS, there was limited diversity f

dical wards at two Hospitals in Nairobi (1994–1996)

MIC50 MIC90 % Resistan

82 64 481 16 8

8 32 300.5 2 0

1 8 1616 128 498 32 46

4 32 2616 128 663 3 0

0.06 0.125 0

S. Kariuki et al. / International Journal of Antimicrobial Agents 25 (2005) 38–43 41

Table 3MIC using the Etest of 11 antimicrobial agents for 126 NTS isolates from medical wards at two Hospitals in Nairobi (1997–2000)

Antimicrobial agent Minimum inhibitory concentration (mg/l)

Range Mode MIC50 MIC90 % Resistant

Ampicillin 0.75 to >256 >256 >256 >256 65Co-amoxiclav 0.5–32 0.75 6 16 2Cefuroxime 2–128 3 8 12 28Ceftazidime 0.125–16 0.25 0.5 2 0Gentamicin 0.19–64 0.75 1 8 9Streptomycin 3 to >1024 32 >1024 >1024 70Co-trimoxazole 0.032 to >32 >32 >32 >32 60Chloramphenicol 1.5 to >256 >256 32 >256 40Tetracycline 0.75–192 1 16 64 48Nalidixic acid 1 to >256 3 3 >256 11Ciprofloxacin 0.006–0.25 0.023 0.023 0.125 0

Table 4MIC using the Etest of 11 antimicrobial agents for 72 NTS isolates from medical wards at two Hospitals in Nairobi (2001–2003)

Antimicrobial agent Minimum inhibitory concentration (mg/l)

Range Mode MIC50 MIC90 % Resistant

Ampicillin 1 to >256 >256 >256 >256 62Co-amoxiclav 0.5–16 3 4 8 6Cefuroxime 32 4 16 >32 52Ceftazidime 0.019 to >32 0.064 0.064 0.94 6Gentamicin 0.0125 to >256 0.38 0.38 8 11Streptomycin 4 to >1024 32 >1024 >1024 67Co-trimoxazole 0.032 to >32 >32 >32 >32 68Chloramphenicol 1.5 to >256 >256 >256 >256 50Tetracycline 2 to >256 2 8 >256 48Nalidixic acid 1.5 to >256 3 3 6 4Ciprofloxacin 0.006–0.25 0.016 0.09 0.25 0

PFGE genotypes of NTS strains within each year of isolation.In addition, over the last 10 years there has not been any majorchange in PFGE patterns. For instance over this periodXbaI-digested chromosomal DNA ofS. Typhimurium presentedthree main genotypes (over 78% of strains in these groups)and two minor variants (22% of the strains).S. Enteritidis pre-sented as two genotypes, one main one containing 60–65%

Fig. 1. Gel picture showing the three main digest patterns usingXbaI ofMDR S.Typhimurium from the three phases of study: panel A (lanes 1–6)isolates from 1994 to 1996; panel B (lanes 7–13) isolates from 1997 to 2000;and panel C (lanes 14–18) isolates from 2000 to 2003. Gels in panels A andB were run for 20 h each, gel in panel C was run for 24 h. Isolates representedin lanes 1, 2, 7, 8, 12, 14, 15, 16 and 17 are all in one closely related mostpredominant genotype 1; isolates represented in lanes 4, 5, 6, 9, 10, and 11are in genotype 2; isolates represented in lanes 3, 13 and 18 are in genotype3

of the isolates while a second genotype contained 35–40%of isolates. UsingSpeI digested chromosomal DNA, therewere a similar number of genotypes and with no significantvariability within each genotype. There was no apparent cor-relation between PFGE patterns and resistance phenotypesof eitherS. Typhimurium orS. Enteritidis.

3.4. Plasmids of NTS

In all cases of drug-resistant NTS ca. 100 kb plasmids inaddition to other smaller plasmids (15–45 kb) were detected.However, only the 100 kb plasmids were transferable by invitro conjugation toE. coli K12. In each case the 100 kbplasmids transferred resistance to ampicillin; in addition, re-sistance to co-trimoxazole, tetracycline and chloramphenicolwere transferred together in 32% ofS. Typhimurium and 29%of S. Enteritidis.

4. Discussion

Over the last 10 years the proportional distribution ofthe two most commonly isolated NTS serotypes –S. Ty-phimurium andS. Enteritidis – from adults with bacteraemiahas been changing. From 1994 to 1997 when we did thefi d

. M: 50 kb lambda molecular size ladder. rst phase of our surveillance,S. Typhimurium predominate

42 S. Kariuki et al. / International Journal of Antimicrobial Agents 25 (2005) 38–43

(prevalence of 75%) among cases of NTS bacteraemia andS. Enteritidis made up only 4.8%. However, after 1997, theproportion ofS. Enteritidis rose steadily and by 2003 the twocommonly isolated NTS serotypes were isolated in almostequal proportions. Although it is difficult to explain the rea-sons for the increased proportions of isolations ofS. Enteri-tidis it is possible that changes in lifestyles such as increasedcongestion, consumption of foods such as eggs and cookiesmade by food vendors among populations in the urban areasof Nairobi from where 75% of our patients come may con-tribute to this rise. It is noteworthy that in many other partsof the world these two serotypes contribute to over 75% ofall NTS infections[6–8].

Multidrug-resistant phenotypes have been increasinglydescribed among salmonella species worldwide according tothe infectious disease report released by the World HealthOrganization in 2000[23]. In our study over the last 10years there has been a marked increase in resistance – bothprevalence and MICs – of all NTS serotypes from adult pa-tients with bacteraemia. For instance the level of resistancefor some of the commonly available antimicrobials includingampicillin, streptomycin, co-trimoxazole and chlorampheni-col rose from 48, 49, 46 and 26%, respectively, in 1994, to62, 67, 68 and 50%, respectively, in 2003 (P< 0.01). The cor-responding MICs have also risen steadily over the 10-yearp lea g/l,r ond-i ec-t lineh ICsf Co theo llys las-m nsi-b aineds

mento hu-m ndry,a imalh treat-m owthp torsi bse-q ought icro-b atingcp nys ansa TSi andw thani man

transmission in tropical Africa is not known but is likely to beconsiderable. Cherubin et al.[28] found that an associationbetween salmonellosis and low-income areas of New YorkCity was particularly marked for childhood cases ofS. Ty-phimurium. The authors hypothesized thatS. Typhimuriummaintained itself by human-to-human transmission, whereasother serotypes were introduced into the community by foodvehicles. Further studies may be required to determine theimportance of human-to-human transmission of NTS in pop-ulations in Kenya and their likely reservoirs.

Studies from tropical Africa have consistently shown thatNTS bacteraemia is more common during the rainy season[13]. This may be the result of a seasonal increase of intesti-nal salmonellosis, which has been reported from other (non-malarious) tropical regions. It may also reflect the seasonalpattern of diseases such as malnutrition and malaria, whichmay confer an increased risk of bacteraemia per episode ofintestinal infection. The environment in many urban town-ships and rural villages may allow frequent exposure from avariety of sources. Possible sources of infection are animals,animal products, water and infected humans. The relative im-portance of each is likely to vary for different environmentalconditions and for different serovars.

UsingXbaI andSpeI digested chromosomal DNA digestanalysis, we observed that among the two most common NTSs di vert d in1m werea inorv ffer-e overt ationt he ex-c wasn ncep

NTSs . Fore -t in-c ively,f tot 980a 10t olef -c elyh y in-c ilablea nters sus-p se ina er-g vail-

eriod. MIC90 for ampicillin, streptomycin, co-trimoxazond chloramphenicol in 1994 were 64, 128, 32 and 32 mespectively, while between 1997 and 2003 the correspng MIC90 rose to >256, >1024, >32 and >256 mg/l, respively. Although the prevalence of resistance to tetracycas declined from 66% in 1994 to 48% in 2003, the M

or resistant isolates have remained very high with MI90f >256 mg/l. Over the 10-year period ciprofloxacin wasnly antimicrobial to which all NTS isolates remained fuusceptible. For all MDR NTS large self-transferable pids approximately 100–110 kb were found to be respole for multidrug-resistance and such plasmids have remtable in circulation over the 10-year study period.

A number of studies have suggested that the developf resistance stems from the use of antimicrobials inan medicine, veterinary medicine and animal husbas well as agricultural and aquaculture practices. In anusbandry practices, antimicrobial agents are used forent and prevention of animal diseases as well as for grromotion[24]. These routine practices are important fac

n the emergence of antibiotic resistant bacteria that suuently can be transferred from animals to humans thr

he food chain. In many developed countries most antimial resistant salmonella infections are acquired from eontaminated foods of animal origin[8,25,26]. However inrevious studies in Kenya[27], we were unable to show aignificant association between NTS isolates from humnd those from animals living in close contact. Indeed N

solates from animal sources were of different serotypesere more susceptible to commonly used antimicrobials

solates from humans. The importance of human-to-hu

erotypes –S. Typhimurium andS. Enteritidis – there existen circulation only a few gene types which persisted oime. For instance, for NTS analysed in 1994–1996 an997–2000 there were three mainS. Typhimurium and twoainS. Enteritidis PFGE strain types. These genotypeslso maintained in the period 2001–2003 with only mariants of the main digest fragment patterns (i.e. a dince of less than three fragments). It would appear that

he last 10 years, a major reservoir existed in the populhat enabled the persistence of these NTS genotypes to tlusion of emergence of new serotypes. However, thereo significant relationship between antimicrobial resistahenotypes and PFGE patterns.

The increased prevalence of resistance amongerotypes over a 10-year period is not unique to Kenyaxample, in the UK the prevalence ofS. Typhimurium resisant to ampicillin, chloramphenicol and co-trimoxazolereased from 1 to 25%, 1.5 to 25%, and 0 to 25%, respectrom 1986 to 1993[29]. In the United States, resistanceetracycline in NTS increased from 9 to 24% between 1nd 1990[30], resistance to ampicillin increased from

o 14%, chloramphenicol from 1 to 8%, and co-trimoxazrom 0 to 3%, between 1980 and 1995[30]. However, the inrease in MICs in NTS isolates from our study was extremigh over a 10-year period and this may be explained breased use and misuse of most of the commonly avantimicrobials. In Kenya the unregulated over-the-couale of these antimicrobials, mainly for self-treatment ofected infection in humans, and to a lesser extent for unimals without prescription, would inevitably lead to emence and rapid dissemination of resistance. In addition a

S. Kariuki et al. / International Journal of Antimicrobial Agents 25 (2005) 38–43 43

ability of cheaper generic drugs of variable quality in the mar-ket for treatment of bacterial infections may also contributeto the increased level of resistance. NTS infections in manydeveloping countries including Kenya cause high morbidityand mortality, particularly in the young and in immunosup-pressed individuals. It appears that more expensive and lessreadily available antimicrobials may be required in future totreat these infections.

Acknowledgement

We thank the Director, Kenya Medical Research Institutefor permission to publish this work. SK is supported by aWellcome Trust Training Fellowship.

References

[1] Green SD, Cheesbrough JS.Salmonellabacteraemia among youngchildren at a rural hospital in western Zaire. Ann Trop Paediatr1993;13:45–53.

[2] Cheesbrough JS, Taxman BC, Green SD, Mewa FI, Numbi. A clin-ical definition for invasiveSalmonellainfection in African children.Pediatr Infect Dis J 1997;16:277–83.

[3] Lepage P, Bogaerts J, Van Goethem C, Hitimana DG, Nsengumure-myi F. MultiresistantSalmonella typhimuriumsystemic infection in

timi-

A.-

i-

F.iencyring

is-

imi-andsist

intispi-

K.

[ p-trybial;53:

[ oped2.

[ rug-nt

to expanded-spectrum cephalosporins in the United States. J InfectDis 2003;188:1707–16.

[13] Graham SM, Molyneux EM, Walsh AL, Cheesbrough JS, MolyneuxME, Hart CA. Nontyphoidal Salmonella infections of children intropical Africa. Pediatr Infect Dis J 2000;19:1189–96.

[14] Helms M, Vastrup P, Gerner-Smidt P, Molbak K. Excess mortalityassociated with antimicrobial drug-resistantSalmonella typhimurium.Emerg Infect Dis 2002;8:490–5.

[15] Threlfall EJ, Frost JA, Rowe B. Fluoroquinolone resis-tance in salmonellas and campylobacters from humans. BMJ1999;318:943–4.

[16] Glynn MK, Bopp C, Dewitt MSW, Dabney P, Mokhtar M, AnguloFJ. Emergence of multidrug-resistantSalmonella entericaserotypeTyphimurium DT104 infections in the United States. New Engl JMed 1998;338:1333–8.

[17] Threlfall EJ. Epidemic Salmonella typhimuriumDT104 – atruly international multiresistant clone. J Antimicrob Chemother2000;44:2166–9.

[18] Horby PW, O’Brien SJ, Adak GK, et al. A national outbreak ofmulti-resistantSalmonella entericaserovar Typhimurium definitivephage type (DT) 104 associated with consumption of lettuce. Epi-demiol Infect 2003;130:169–78.

[19] Oundo JO, Muli F, Kariuki S, et al. Non-typhi salmonellae in chil-dren with severe malaria. East Afr Med J 2002;79:633–9.

[20] Walsh AL, Molyneux EM, Kabudula M, Phiri AJ, Molyneux ME,Graham SM. Bacteraemia following blood transfusion in Malawianchildren: predominance ofSalmonella. Trans Roy Soc Trop MedHyg 2002;96:276–7.

[21] National Committee for Clinical Laboratory Standards. Performancestandards for antimicrobial susceptibility testing; twelfth informa-

mit-

[ o-lec-iol

[ com-0.2,

[ ts ofuppl

[ nse-

rug

[ aimal4–6.

[ ck

tact.

[ r J.pi-

[ rumt

[ aseates,

Rwanda. Clinical features and treatment with cefotaxime. J Ancrob Chemother 1990;26(Suppl A):53–7.

[4] Kariuki S, Oundo JO, Muyodi J, Lowe B, Threlfall EJ, Hart CGenotypes of multidrug-resistantSalmonella entericaserotype Typhimurium from two regions of Kenya. FEMS Immunol Med Mcrobiol 2000;29:9–13.

[5] Arthur G, Nduba VN, Kariuki SM, Kimari J, Bhatt SM, Gilks CTrends in bloodstream infections among human immunodeficvirus-infected adults admitted to a hospital in Nairobi, Kenya, duthe last decade. Clin Infect Dis 2001;33:248–56.

[6] Ridley A, Threlfall EJ. Molecular epidemiology of antibiotic restance genes in multiresistant epidemicSalmonella typhimuriumDT104. Microb Drug Resist 1998;4:113–8.

[7] Threlfall EJ, Teale CJ, Davies RH, et al. A comparison of antcrobial susceptibilities in nontyphoidal salmonellas from humansfood animals in England and Wales in 2000. Microb Drug Re2003;9:183–9.

[8] Busani L, Graziani C, Battisti A, et al. Antibiotic resistanceSalmonella entericaserotypes Typhimurium, Enteritidis and Infanfrom human infections, foodstuffs and farm animals in Italy. Edemiol Infect 2004;132:245–51.

[9] Gomez TM, Motarjemi Y, Miyagawa S, Kaferstein FK, StohrFoodborne salmonellosis. World Health Stat Q 1997;50:81–9.

10] Esaki H, Morioka A, Ishihara K, et al. Antimicrobial suscetibility of Salmonella isolated from cattle, swine and poul(2001–2002): report from the Japanese Veterinary AntimicroResistance Monitoring Program. Antimicrob Chemother 2004266–70.

11] Graham S. Salmonellosis in children in developing and develcountries and populations. Curr Opin Infect Dis 2002;15:507–1

12] Gupta A, Fontana J, Crowe C, et al. Emergence of multidresistantSalmonella entericaserotype Newport infections resista

tional supplement. Approved standard M100-S12. National Comtee for Clinical Laboratory Standards, Wayne, PA, 2002.

22] Tenover FC, Arbeit RD, Goering RV, et al. Interpreting chromsomal DNA restriction patterns produced by pulsed-field gel etrophoresis: criteria for bacterial strain typing. J Clin Microb1995;33:2233–9.

23] World Health Organization Report on Infectious Diseases. Overing antimicrobial resistance. Publication Code: WHO/CDS/2002000.

24] Tollefson L, Fedorka-Cray PJ, Angulo FJ. Public health aspecantibiotic resistance monitoring in the USA. Acta Vet Scand S1999;92:67–75.

25] Angulo FJ, Johnson KR, Tauxe RV, Cohen ML. Origins and coquences of antimicrobial-resistant nontyphoidalSalmonella: implica-tions for the use of fluoroquinolones in food animals. Microb DResist 2000;6:77–83.

26] Gorman R, Adley CC. Characterization ofSalmonella entericserotype Typhimurium isolates from human, food, and ansources in the Republic of Ireland. J Clin Microbiol 2004;42:231

27] Kariuki S, Revathi G, Gakuya F, Yamo V, Muyodi J, Hart CA. Laof clonal relationship between non-typhiSalmonellastrain typesfrom humans and those isolated from animals living in close conFEMS Immunol Med Microbiol 2002;33:165–71.

28] Cherubin CE, Fodor T, Denmark L, Master C, Fuerst HT, WinteThe epidemiology of salmonellosis in New York City. Am J Edemiol 1969;90:112–25.

29] Threlfall EJ, Frost JA, Ward LR, Rowe B. Increasing spectof resistance in multiresistantSalmonella typhimurium. Lance1996;347:1053–4.

30] Lee LA, Puhr ND, Maloney EK, Bean NH, Tauxe RV. Increin antimicrobial-resistant Salmonella infections in the United St1980–1990. J Infect Dis 1994;170:128–34.