Ants in a hospital environment and their potential as mechanical bacterial vectors

Wanda Ramos dos Santos Lima Sirlei Garcia Marques Fernanda Souto Rodrigues José Manuel Macário Rebêlo About the authors

Abstract

Introduction

We studied the richness and abundance of ant species, their bacteria and the bacteria isolated from patient clinical samples.

Methods

Ants were collected with baited traps at 64 sites in a public hospital in São Luis, State of Maranhão, Brazil.

Results

In total, 1,659 ants from 14 species were captured. The most frequent species were Crematogaster victima, Solenopsis saevissima, Tapinoma melanocephalum, Camponotus vittatus and Paratrechina fulva. Forty-one species of bacteria were isolated from the ants and 18 from patients.

Conclusions

Ants are potential vehicles for pathogenic and opportunistic bacteria, and they can represent a risk factor in nosocomial infections.

Urban ants; Vectors of nosocomial infection; Formicidae


Ants (Hymenoptera; Formicidae) represent a frequent and serious problem in Brazilian hospitals, where they are abundant and difficult to control11. Moreira DDO, Morais V, Vieira-da-Mota O, Campos-Farinha AE, Tonhasca Jr A. Ants as carriers of antibiotic-resistant bacteria in hospitals. Neotropl Entomol 2005; 34:999-1006.. Their presence in hospitals is favored by the structural characteristics of hospital buildings and their proximity to residential homes; the presence of packages of medicines, chemical products, food and water; and the large number of people circulating in the hospital with clothes and objects that could contain ant nests22. Bueno OC, Campos-Farinha AEC. Formigas urbanas - comportamento das espécies que invadem as cidades brasileiras. Vetores & Pragas 1998; 12:13-16.,33. Zarzuela MFM, Ribeiro MCC, Campos-Farinha AE. Distribuição de formigas urbanas em um hospital da região Sudeste do Brasil. Arq Inst Biol 2002; 69:85-87.. An association between ants and bacteria has been observed in various hospitals, leading to increased concern about the role of these insects as disease vectors44. Chadee DD, Lê Maitre A. Ants: Potential mechanical vectors of Institution Hospitalar infections in Trinidad. Trans R Soc Trop Med Hyg 1990; 84:297..

To our knowledge, this is the first such study performed in a hospital in the State of Maranhão (MA), Brazil. The aims were to study the richness, abundance and monthly and seasonal frequencies of ants; to identify any bacteria they carry; and to compare the bacteria with those isolated from patient clinical samples.

This study was performed in a medium-sized public hospital in São Luis, MA (02°32′S and 44°17′W) with four floors and an area of approximately 18,222m22. Bueno OC, Campos-Farinha AEC. Formigas urbanas - comportamento das espécies que invadem as cidades brasileiras. Vetores & Pragas 1998; 12:13-16.. The collection points were selected according to Beatson55. Beatson SH. Pharaoh's ants pathogen vectors in hospitais. The Lancet 1972; 1:425-427. and Fowler et al.66. Fowler HG, Bernardi OC, Sadatsube T, Montelli AC. Ants as potencial vectors of pathogens in Brazil hospitals in the State of São Paulo, Brazil. Insec Scie Applic 1993; 14:367-370., consisting of 64 points distributed over the first three floors ( Table 1). Ants were captured once a month between January and December 2008 with bait traps installed between 10-12am, 2-4pm and 6-8pm. The total number of traps used each collection day was 192, or 2,304 traps for all 12 collections throughout the year. Each trap was exposed for 2h every day, corresponding to a capture effort of 4,608h.

TABLE 1
- Numbers of ants and rates of bacterial contamination in a public hospital in São Luis, State of Maranhão, Brazil, between January and December 2008.

The ants were captured in aseptic conditions in traps assembled as follows. Plastic bottles (300ml) were cut in half at the middle of the bottle. Then, the upper half was turned upside down and placed in the bottom half to form a container with the funnel pointing inward. Each trap contained non-toxic sterile bait of a mixture of equal amounts of dried beef liver, fruit and honey-flavored cake33. Zarzuela MFM, Ribeiro MCC, Campos-Farinha AE. Distribuição de formigas urbanas em um hospital da região Sudeste do Brasil. Arq Inst Biol 2002; 69:85-87.. Between 1 and 3 ants were collected at random from each trap using a sterile swab and transferred to a flask containing brain-heart infusion broth (BHI) and incubated at 35.5 ± 1°C for 24 to 48h for microbiological analysis. Clinical samples collected from patients were seeded in conventional culture medium77. Koneman EW, Allen CD, Janda WM, Schreckenberger PC, Winn Jr WC. Diagnóstico Microbiológico. Texto e Atlas Colorido. 5th ed. Medsi: Rio de Janeiro; 2001..

This descriptive study with a 1-year collection period was approved by the Ethics Committee in Research from the University Hospital, Federal University of Maranhão, under registration n° 548/2007.

During the study, 1,659 ants (14 species, 10 genera and 5 subfamilies) were captured ( Table 1). The most abundant species were Crematogaster victima (42.4%), Solenopsis saevissima (20.7%), Pheidole sp.1 (19.4%), Tapinoma melanocephalum (5.5%) and Paratrechina fulva (3.7%). The ant frequencies were highest in the dry season (77.6%) ( Table 1).

Forty-one species of bacteria were isolated from patients and ants (18), only from ants (15) or only from patients (8). In total, 620 ants were analyzed, and bacterial growth was observed in 243 of the samples (39.2%) ( Table 1). The bacterial positivity rate was higher in the following ants: Atta sp., Camponotus sp., Camponotus vittatus, Pheidole sp.2, Pheidole sp.1, T. melanocephalum and P. fulva (44.1%) ( Table 1). The most frequent bacterial species isolated from the ants were Staphylococcus spp. (coagulase-negative), Acinetobacter baumannii, A. lwoffii and Staphylococcus aureus (69.6%) ( Table 2). The bacterial positivity frequencies for ant samples were highest in the dry season (62.9%) ( Table 2). The most frequent bacteria isolated from the patients were Staphylococcus spp. (coagulase-negative), Pseudomonas aeruginosa, A. baumannii and Klebsiella pneumoniae (68.9%) ( Table 2). The bacteria were isolated from 434 samples, and the frequency was higher in the dry season (63.1%).

TABLE 2
- Numbers of ant and clinical patient samples positive for bacteria in a public hospital in São Luis, State of Maranhão, Brazil, between January and December 2008.

The diversity of ant species observed was high, and the genera captured were the same as have been captured in hospitals in other states in Brazil22. Bueno OC, Campos-Farinha AEC. Formigas urbanas - comportamento das espécies que invadem as cidades brasileiras. Vetores & Pragas 1998; 12:13-16.,33. Zarzuela MFM, Ribeiro MCC, Campos-Farinha AE. Distribuição de formigas urbanas em um hospital da região Sudeste do Brasil. Arq Inst Biol 2002; 69:85-87.,66. Fowler HG, Bernardi OC, Sadatsube T, Montelli AC. Ants as potencial vectors of pathogens in Brazil hospitals in the State of São Paulo, Brazil. Insec Scie Applic 1993; 14:367-370.. However, Acromyrmex and Odontomachus, which were identified in this study, have not been reported from other states, showing the variation in the geographic distribution of ants associated with urban hospitals.

The abundance of ants during the dry season is of great ecological significance because it may represent a large potential vectorial mechanism. This hypothesis is supported by the seasonal pattern of patient samples positive for bacteria, which predominated in the dry season.

The ants were found on all floors and most areas of the hospital, as observed in other studies88. Tanaka JI, Viggiana AMFS, Person OC. Bactérias veiculadas por formigas em ambiente hospitalar. Arq Med 2007; 32:60-63.,99. Pereira R, Ueno M. Formigas como veiculadoras de microorganismos em ambiente hospitalar. Rev Soc Bras Med Trop 2008; 41:60-63., but were more abundant on the first floor ( Table 3). The presence of food and other stimuli, such as chemical substances diffused in the air, diluted in wastewater and impregnated in objects, can stimulate the movement of ants within the hospital environment irrespective of where they nest, making it important to keep the different areas of the hospital clean at all times. The presence of ants, particularly Camponotus, inside a hospital is indicative of structural defects in the building1010. Bueno OC, Fowler HG. Exotic ants and native ant fauna of Brazilian hospitals. In: Williams DF, editor. Exotic ants: Biology, impact and control of introduced species. Boulder: Westview Press; 1994. p. 191-198., especially when the ants search for food outside the building but their nests are found inside.

TABLE 3
- Numbers of ants captured in different areas of a public hospital in São Luis, State of Maranhão, Brazil, between January and December 2008.

The large number of bacterial species carried by ants is noteworthy. Some of the bacterial species are considered pathogenic because of the concomitant circulation of nosocomial infections, including Serratia marcescens, Citrobacter freundii, K. ozaenae, Enterobacter aerogenes, Proteus mirabilis and S. epidermidis 1111. Boursaux-Eude C, Gross R. New insights symbiotic associations between ants and bacteria. Res Microbiol 2000; 519:513-519.. Other species notable for high pathogenicity are S. aureus, P. aeruginosa and K. pneumoniae, all of which were isolated from ants in our study. Other species are considered opportunistic but can become pathogenic depending on the situation.

Nonetheless, it should be mentioned that Paratrechina longicornis is an important vector of pathogens that are considered risk factors for nosocomial infection66. Fowler HG, Bernardi OC, Sadatsube T, Montelli AC. Ants as potencial vectors of pathogens in Brazil hospitals in the State of São Paulo, Brazil. Insec Scie Applic 1993; 14:367-370.,1010. Bueno OC, Fowler HG. Exotic ants and native ant fauna of Brazilian hospitals. In: Williams DF, editor. Exotic ants: Biology, impact and control of introduced species. Boulder: Westview Press; 1994. p. 191-198.. The presence of these species puts patients at risk of nosocomial infection. Microbiological analysis of P. longicornis revealed their potential to act as mechanical vectors for genera such as Staphylococcus, Acinetobacter, Serratia, Klebsiella, Enterobacter and Enterococcus. Beatson55. Beatson SH. Pharaoh's ants pathogen vectors in hospitais. The Lancet 1972; 1:425-427., Edwards & Baker1212. Edwards JP, Baker LF. Distribution and importance of Tha Pharaoh's Monomorium pharaonis (L) in national Health Service Hospitals in England. J Hosp Infec 1981; 2:245-254. and Costa et al.1313. Costa SBD, Pelli A, Carvalho GP, Oliveira AG, Silva PR, Teixeira MM, et al. Formigas como vetores mecânicos de microorganismos no Hospital Escola da Universidade Federal do Triângulo Mineiro. Rev Soc Bras Med Trop 2006; 39:527-529. also observed these pathogens.

In summary, the ants were contaminated by pathogenic and opportunistic bacteria, representing a risk factor for nosocomial infection. However, additional studies are required to confirm their roles as mechanical vectors of nosocomial infections.

The authors would like to thank the University Hospital, Federal University of Maranhão (HUUFMA), and the Microbiology Department in particular for providing assistance in performing the research.

REFERENCES

  • 1
    Moreira DDO, Morais V, Vieira-da-Mota O, Campos-Farinha AE, Tonhasca Jr A. Ants as carriers of antibiotic-resistant bacteria in hospitals. Neotropl Entomol 2005; 34:999-1006.
  • 2
    Bueno OC, Campos-Farinha AEC. Formigas urbanas - comportamento das espécies que invadem as cidades brasileiras. Vetores & Pragas 1998; 12:13-16.
  • 3
    Zarzuela MFM, Ribeiro MCC, Campos-Farinha AE. Distribuição de formigas urbanas em um hospital da região Sudeste do Brasil. Arq Inst Biol 2002; 69:85-87.
  • 4
    Chadee DD, Lê Maitre A. Ants: Potential mechanical vectors of Institution Hospitalar infections in Trinidad. Trans R Soc Trop Med Hyg 1990; 84:297.
  • 5
    Beatson SH. Pharaoh's ants pathogen vectors in hospitais. The Lancet 1972; 1:425-427.
  • 6
    Fowler HG, Bernardi OC, Sadatsube T, Montelli AC. Ants as potencial vectors of pathogens in Brazil hospitals in the State of São Paulo, Brazil. Insec Scie Applic 1993; 14:367-370.
  • 7
    Koneman EW, Allen CD, Janda WM, Schreckenberger PC, Winn Jr WC. Diagnóstico Microbiológico. Texto e Atlas Colorido. 5th ed. Medsi: Rio de Janeiro; 2001.
  • 8
    Tanaka JI, Viggiana AMFS, Person OC. Bactérias veiculadas por formigas em ambiente hospitalar. Arq Med 2007; 32:60-63.
  • 9
    Pereira R, Ueno M. Formigas como veiculadoras de microorganismos em ambiente hospitalar. Rev Soc Bras Med Trop 2008; 41:60-63.
  • 10
    Bueno OC, Fowler HG. Exotic ants and native ant fauna of Brazilian hospitals. In: Williams DF, editor. Exotic ants: Biology, impact and control of introduced species. Boulder: Westview Press; 1994. p. 191-198.
  • 11
    Boursaux-Eude C, Gross R. New insights symbiotic associations between ants and bacteria. Res Microbiol 2000; 519:513-519.
  • 12
    Edwards JP, Baker LF. Distribution and importance of Tha Pharaoh's Monomorium pharaonis (L) in national Health Service Hospitals in England. J Hosp Infec 1981; 2:245-254.
  • 13
    Costa SBD, Pelli A, Carvalho GP, Oliveira AG, Silva PR, Teixeira MM, et al. Formigas como vetores mecânicos de microorganismos no Hospital Escola da Universidade Federal do Triângulo Mineiro. Rev Soc Bras Med Trop 2006; 39:527-529.

  • FINANCIAL SUPPORT: Research and Diagnostic Laboratory (RDL) at the Maranhão Medical Center Hospital.

Publication Dates

  • Publication in this collection
    Sept-Oct 2013

History

  • Received
    4 Sept 2012
  • Accepted
    17 Dec 2012
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