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Keywords:

  • Salmonella enteritidis;
  • enteric pathogens;
  • resistance;
  • Zimbabwe

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Summary The study was conducted to determine the prevalence of Salmonella enteritidis diarrhoea in an urban area in Zimbabwe. Stool specimens from people of all ages presenting at primary level health centres in Harare were investigated for S. enteritidis and other bacterial and parasitic enteric pathogens. The first 46 S. enteritidis isolates were phage-typed, and all isolates were tested for susceptibility to ampicillin (10 μg), chloramphenicol (30 μg), cotrimoxazole (25 μg), tetracycline (30 μg), gentamicin (10 μg), nalidixic acid (30 μg), ciprofloxacin (5 μg) and ceftriaxone (30 μg). S. enteritidis was isolated in 74 (1.8%) of 4155 stool specimens which represented 30.7% of all Salmonella species isolated. The most common S. enteritidis phage type was 4 (78.3%) followed by 7, 9 and 23 (8.7%, 2.2%, 2.2%, respectively) All S. enteritidis isolates were sensitive to gentamicin, ciprofloxacin and ceftriaxone. Less than 10% of the isolates were resistant to the other antimicrobials except ampicillin, to which 13.5% were resistant. One isolate was resistant to ampicillin, chloramphenicol, cotrimoxazole and nalidixic acid.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Human infections with Salmonella enteritidis have been increasing wordwide since 1980. S. enteritidis is an important serotype of Salmonella comprising 37% of Salmonella isolates in Maryland since 1990 ( Morris et al. 1992 ) and 28% in the north-eastern United States in 1986 ( St Louis et al. 1988 ). It is normally found in the intestinal tracts of humans and of animals such as chickens and domestic livestock and remains an important cause of gastroenteritis in humans worldwide. It is usually acquired by ingestion of contaminated water and food, mainly poultry, eggs and egg products ( Humphrey et al. 1988, 1989 ; St Louis et al. 1988 ; Cowden et al. 1989 ; Hedberg et al. 1993 ). Eggs are the most probable primary source of contamination in many outbreaks of S. enteritidis infection in developed countries ( St Louis et al. 1988 ).

Phage-typing of S. enteritidis in the United States showed that type 8 strains are the most common ( Hickman-Brenner et al. 1991 ; Usera et al. 1994 ). In Europe the most common phage type is 4 ( Ward et al. 1987 ; Cowden et al. 1989 ; Stanely et al. 1992 ; Schroeter et al. 1994 ). Data on the prevalence of S. enteritidis as a causative agent of diarrhoea in developing countries are scarce. We aimed to determine the prevalence of Salmonella enteritidis as a causative agent of diarrhoea in an urban area in Zimbabwe.

Materials and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The study was conducted over a period of 8 months during the hot and wet season (October – May), when diarrhoea caused by bacteria peaks in Zimbabwe ( Cruickshank & Zilberg 1976). We investigated stool specimens from all people with diarrhoea presenting as outpatients at primary level health centres in the city of Harare. Specimens were collected in sterile containers and processed within 5 h.

The specimens were cultured for Salmonella, Shigella and Campylobacter species, enteropathogenic Escherichia coli and Yersinia enterocolitica. We also looked for Giardia lamblia, Cryptosporidium and Entamoeba histolytica parasites. Xylose-Lysine-Desoxycholate agar medium was used for culturing Salmonella species. Inoculated agar plates were incubated at 37 °C for 24 h. Colonies which appeared pink-red with a black centre were presumptively identified as Salmonella species and biochemically tested ( Cheesbrough 1985). Isolates which gave positive reactions for Salmonella were serotyped using polyvalent and monovalent antisera (Wellcome Diagnostics, Dartford, UK). The first 46 S. enteritidis isolates were sent to the Instituto Superiore della Sanità in Italy for phage-typing. Other bacterial enteric pathogens were identified by standard procedures ( Cheesbrough 1985). The formol-ether concentration technique ( Allen & Ridley 1970) was used for parasites and staining with modified Ziehl Neelsen stain ( Cheesbrough 1987) for Cryptosporidium oocysts.

The Kirby–Bauer disc diffusion method was used to test for susceptibility to ampicillin (10 μg) chloramphenicol (30 μg), cotrimoxazole (25 μg), tetracycline (30 μg), gentamicin (10 μg), nalidixic acid (30 μg), ciprofloxacin (5 μg), and ceftriaxone (30 μg) using Mueller Hinton agar medium.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We processed 4155 stool specimens for the detection of enteric pathogens. Their distribution is shown in Table 1. Shigella species were the most common bacterial enteric pathogens, followed by Salmonella and then enteropathogenic Escherichia coli. S. enteritidis comprised 30.7% of the Salmonella isolates. Giardia lamblia was more common than Cryptosporidium. Multiple infections were observed in 23 specimens but only one specimen had S. enteritidis isolated together with another pathogen.

Table 1.  Incidence of bacterial and parasitic enteric pathogens in isolates from patients with diarrhoea Thumbnail image of

The distribution of S. enteritidis by age group is shown in Table 2. The highest incidence was observed in people > 50 years (3.8%), the lowest in children < 10 years (1.2%). The most common S. enteritidis phage type was 4 (78.3%) followed by types 7, 9 and 23 ( Table 3). All S. enteritidis isolates were sensitive to gentamicin, ciprofloxacin and ceftriaxone as shown in Table 4. Less than 10% of the isolates were resistant to chloramphenicol, nalidixic acid, cotrimoxazole and tetracycline. The highest resistance was observed against ampicillin with 13.5% of the isolates being resistant to this drug. About 19% of the S. enteritidis isolates were resistant to one or more drugs ( Table 5). One isolate showed multidrug resistance to ampicillin, chloramphenicol, cotrimoxazole and nalidixic acid.

Table 2.  Age distribution of patients with diarrhoea due to Salmonella enteritidisThumbnail image of
Table 3.  Distribution of phage types of Salmonella enteritidisThumbnail image of
Table 4.  Antimicrobial susceptibilities of Salmonella enteritidis isolates Thumbnail image of
Table 5.  Patterns of resistance in Salmonella enteritidisThumbnail image of

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Salmonella enteritidis infections are on the increase in many developed countries and have been associated with consumption of contaminated poultry, eggs and egg products. We found that S. enteritidis is the most common Salmonella serotype in diarrhoeal stool specimens, accounting for 30.7% and detected in 1.8% of all specimens cultured. Similar observations were noted by Morris et al. (1992) in the United States where S. enteritidis accounted for 37% in Maryland, and by St Louis et al. (1988) , who found that it comprised 28% of Salmonella isolates in the north-eastern United States.

We found S. enteritidis phage type 4 to be the most prevalent, which agrees with findings in Europe ( Ward et al. 1987 ; Cowden et al. 1989 ; Stanely et al. 1992 ; Schroeter et al. 1994 ) as well as Japan ( Suzuki et al. 1995 ) and Thailand ( Boonmar et al. 1998 ) since 1980. The predominance of this phage type in many countries suggests that S. enteritidis phage type 4 strains may possess unique characteristics and pose a great risk to public health in some regions of the world. Phage type 8, the most common in the United States ( Hickman-Brenner et al. 1991 ) and Canada ( Khakhria et al. 1991 ), was not found in our study. Phage type 7 was the second most common type among Zimbabwean isolates but was comparatively rare.

Some studies have implicated poultry and poultry products as the main source of human infection with S. enteritidis ( St Louis et al. 1988 ; Humphrey et al. 1988, 1989 ; Cowden et al. 1989 ; Hedberg et al. 1993 ). A study in Zimbabwe (unpublished data), which examined 113 S. enteritidis isolates in chickens and eggs from areas around Harare, identified phage type 4 as the most common (77.9%) followed by phage type 7 (14.2%), with a similar distribution pattern to that of human isolates observed in this study. The similarity of phage type distributions in humans and chickens suggests that chicken and egg consumption is an important cause of S. enteritidis, and that phage type 4 is the most important in humans and chickens in Zimbabwe. The other phage types were detected in comparatively low rates and appear to play a minor role in infections of both humans and chickens.

Although antimicrobial drugs are not recommended for the treatment of uncomplicated salmonellosis in humans, they are essential for the treatment of extraintestinal S. enteritidis infections such as septicaemia, endocarditis, empyema and meningitis. A few isolates of S. enteritidis in our study were resistant to one or more of the eight antimicrobial drugs tested, with one isolate displaying multidrug resistance to ampicillin, chloramphenicol, cotrimoxazole and nalidixic acid. Resistance to antimicrobial drugs in S. enteritidis isolated from humans has been shown to be low, as confirmed in our study. All S. enteritidis isolates were sensitive to ciprofloxacin, gentamicin and ceftriaxone; hence these are potentially useful in cases showing resistance to the antimicrobials. However, S. enteritidis resistance to some antibiotics is growing: a substantial increase in the incidence of resistance to ampicillin was observed in England and Wales ( Ward et al. 1990 ), and Tassios et al. (1997) found a high proportion of S. enteritidis to be resistant to ampicillin and doxycycline in Greece. The increase in resistance of S. enteritidis to ampicillin is due to a 34-MDa conjugative plasmid ( Vatopoulos et al. 1994 ) which is easily transferred to recipient cells ( Tassios et al. 1997 ). Multiple resistance has remained rare amongst human isolates of S. enteritidis, as was also observed in the present study, where only one isolate displayed resistance to four antimicrobial drugs.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We would like to thank the Istituto Superiore della Sanità in Italy for phage-typing the Salmonella enteritidis isolates and Dr Makaya of the Veterinary Laboratory Services in Zimbabwe, who made the necessary arrangements.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • Allen AVH & Ridley DS (1970) Further observations on the formol-ether concentration technique for faecal parasites. Journal of Clinical Pathology 23, 545 546.
  • Boonmar S, Bangtrakulnonth A, Pornrunangwong S et al. (1998) Epidemiological analysis of Salmonella enteritidis isolates from humans and broiler chickens in Thailand by phage typing and pulsed-field gel electrophoresis. Journal of Clinical Microbiology 36, 971 974.
  • Cheesbrough M (1985) Medical Laboratory Manual for Tropical Countries. Vol. 2. 1st edn. Butterworth, Cambridge, pp. 248 261.
  • Cheesbrough M (1987) Medical Laboratory Manual for Tropical Countries. Vol. 1. 2nd edn. Butterworth, Cambridge, pp. 216 218.
  • Cowden MJ, Lynch D, Joseph CA et al. (1989) Case-control study of infections with Salmonella enteritidis phage type 4 in England. British Medical Journal 299, 771 773.
  • Cruickshank JG & Zilberg B (1976) Winter diarrhoea and rotavirus in Rhodesia. South African Medical Journal 50, 1895 1896.
  • Hedberg CW, David MJ, White KE et al. (1993) Role of egg consumption in sporadic Salmonella enteritidis and Salmonella typhimurium infections in Minnesota. Journal of Infectious Diseases 167, 107 111.
  • Hickman-Brenner FW, Stubbs AD, Farmer JJ (1991) Phage typing of Salmonella enteritidis in the United States. Journal of Clinical Microbiology 29, 2817 2823.
  • Humphrey TJ, Mead GC, Rowe B (1988) Poultry meat as a source of salmonellosis in England and Wales. Epidemiology and Infection 100, 175 184.
  • Humphrey TJ, Cruickshank TJ, Rowe B (1989) Salmonella enteritidis phage type 4 and hens' eggs. Lancet i, 281 .
  • Khakhria R, Duck D, Lior H (1991) Distribution of Salmonella enteritidis phage types in Canada. Epidemiology and Infection 106, 25 32.
  • Morris JG, Dwyer DM, Hoge CW et al. (1992) Changing clonal patterns of Salmonella enteritidis in Maryland: Evaluation of strains isolated between 1985 and 1990. Journal of Clinical Microbiology 30, 1301 1303.
  • St Louis ME, Morse DL, Potter ME et al. (1988) The emergence of Grade A eggs as a major source of Salmonella enteritidis infections. New implications for the control of salmonellosis. Journal of the American Medical Association 259, 2103 2107.
  • Schroeter A, Ward LR, Rowe B et al. (1994) Salmonella enteritidis phage types in Germany. European Journal of Epidemiology 10, 645 648.
  • Stanely J, Burnens AP, Threlfall EJ et al. (1992) Genetic relationships among strains of Salmonella enteritidis in a national epidemic in Switzerland. Epidemiology and Infection 108, 213 220.
  • Suzuki Y, Ishihara M, Matsumoto M et al. (1995) Molecular epidemiology of Salmonella enteritidis. An outbreak and sporadic cases studied by means of pulsed-field gel electrophoresis. Journal of Infection 31, 211 217.
  • Tassios PT, Markogiannakis A, Vatopoulos AC et al. (1997) Molecular epidemiology of antibiotic resistance of Salmonella enteritidis during a 7-year period in Greece. Journal of Clinical Microbiology 35, 1316 1321.
  • Usera MA, Popovic T, Bopp CA, Strockbine NA (1994) Molecular subtyping of Salmonella enteritidis phage type 8 strains from the United States. Journal of Clinical Microbiology 32, 194 198.
  • Vatopoulos AC, Mainas E, Threlfall EJ, Kanelopoulou M (1994) Molecular epidemiology of ampicillin-resistant clinical isolates of Salmonella enteritidis. Journal of Clinical Microbiology 32, 1322 1325.
  • Ward LR, de Sa JD, Rowe B (1987) A phage typing scheme for Salmonella enteritidis. Epidemiology and Infection 99, 291 294.
  • Ward LR, Threlfall EI, Rowe B (1990) Multiple drug resistance in salmonellae in England and Wales: a comparison between 1981 and 1988. Journal of Clinical Pathology 43, 563 566.