CITATION: Chikviladze D, Gabisonia T, Kereselidze T, Maruashvili I, Shubitidze A, Rekchviashvili N. 1990. APUA: Boston, MA, USA. <www.apua.org>.


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Antibiotic sensitivity of Acinetobacter strains isolated from patients in the intensive care unit of the Tbilisi Burn Center
D Chikviladze, T Gabisonia, T Kereselidze, I Maruashvili, A Shubitidze and N Rekchviashvili
Tbilisi State Medical University, Republic of Georgia


Over the last decade,
Acinetobacter, an aerobic nonfermenting Gram-negative bacterium has emerged as a clinically important, multiply resistant pathogen.1,2 It often causes inflammatory complications in burn, urologic and other patients.2,3 Thus, it is important not only to identify the organism when present, but also to determine isolated strains' susceptibility to antibiotics and the genetic nature of their antibiotic resistance, when present.

The purpose of this study was to review the biochemical features of clinical isolates and reference strains of Acinetobacter, their susceptibility to antibiotics and the presence of nonchromosomal genetic factors. One hundred strains of Acinetobacter were isolated from patients in Tbilisi Burn Center's intensive care unit between 1988 and 1989 and were compared with reference strains A. calcoaceticus (strain 5593) and A. lwoffi (strain 5581) from the Moscow State Institute of Standards and Control.
Mobility as well as growth under different conditions
Acinetobacter on simple and complex culture media were studied, as were the presence of cytochromoxidase and catalase and the production of indole and hydrogen sulfide. Additional tests assessed the ability of these organisms to reduce nitrates to nitrites, liquefy gelatin, produce urease and utilize citrate and sodium acetate.4 Carbohydrate fermentation was also studied. Antibiotic susceptibility was evaluated using agar diffusion and broth dilution tests.4

Conjugational transfer of R-plasmids was performed in accordance with the method of Sagai et al.5 Plasmids identified in clinical isolates of Acinetobacter were classified using test plasmids E. coli strains received from the Institute of Epidemiology and Microbiology of the Russian Academy of Sciences; these same E. coli strains were used to define plasmid incompatibility groups.

All Acinetobacter cultures grew at 42°C on MacConkey's agar, were catalase positive and did not produce indole or H2S. All cultures were oxidase negative and nonpigmentizing. Sugar fermentation varied by biochemical type: 100% (50 strains) of A. calcoaceticus cultures produced acid in response to glucose, lactose and galactose whereas no strains of A. lwoffi produced acid in response to any of the above substrates. Citrate was utilized by 100% of A. calcoaceticus strains and by 50% of A. lwoffi strains. Study results were less certain with respect to the ability of these organisms to reduce nitrates to nitrites and hydrolysis of urea and gelatine. Some strains of A. lwoffi demonstrated arginine dehydrolase activity when compared with the reference strains.

Results of antibiotic susceptibility testing are shown in Table 1. Some strains were multiply resistant to many antibiotics, including the aminoglycosides gentamicin, kanamycin and amikacin, as well as the beta-lactams carbenicillin, claforan and kefzol. The isolates demonstrated the greatest susceptibility to cefazolin, fortum and polymyxin.

Table 1. Antibiotic resistance in Acinetobacter strains isolated from patients in the Tiblisi Burn Center.

 

Resistant Acinetobacter Strains (%)

Antibioitic

A. calcoaceticus
(n=50 strains)

A. lwoffii
(n=50 strains)

Amikacin

42

36

Ampicillin

90

86

Carbenicillin

80

76

Cefazolin

0

0

Cefotaxime

20

10

Ceftazidim

0

0

Chloramphenicol

50

50

Erythromycin

100

100

Gentamicin

40

35

Kanamycin

48

58

Kefzol

38

20

Lincomycin

100

100

Methicillin

100

100

Monomycin

60

50

Neomycin

56

56

Oleandomycin

100

100

Oxacillin

100

100

Polymyxin B

5

5

Ristomycin (Ristocetin)

100

100

Streptomycin

68

68

Tetracycline

100

100

The ability of 25 clinical isolates with resistance markers to transfer resistance factors during conjugation with polyauxotropic strains I 53 was studied. Interaction between donor and recipient strains demonstrated that all strains of Acinetobacter conjugated R-plasmids that carried genes mediating resistance to tetracycline (80%), carbenicillin (72%), streptomycin (60%) and kanamycin (52%), chloramphenicol (44%) and gentamicin (32%).

Resistance to ampicillin, erythromycin, lincomycin, claforan, oxacillin and other antibiotics appeared to result from chromosomal genes or nonconjugated R-plasmids. Immobilization of these R-plasmids could not be achieved with conjugated R-plasmids.

The conjugated R-plasmids in the Acinetobacter strains from patients in the burn center had resistance determinants for streptomycin, kanamycin and tetracycline and belonged to the T, I, M and N incompatibility groups which are typical of the E. coli plasmid group (Table 2).

Table 2. Plasmids and incompatibility groups identified in Acinetobacter strains isolated from patients in the Tiblisi Burn Center.

Plasmid Plasmid Character Incompatibility Group Molecular Mass (mDa) Conjugational Transfer Frequency
pK221 Km Sm Tra+

I

44.0

10-3

pM211 Sm Tc Tra+

M

45.0

10-4

pK223 Sm Tc Km Tra+

N

30.0

10-4

pK203 Km Tra+

T

50.0

10-4

Isolates demonstrating Group I incompatibility carried type pK221 plasmids, whose molecular mass is 44.0 MD. These plasmids determine resistance to kanamycin and streptomycin. Plasmids pM211, pK223 and pK203 belong to incompatibility groups M, N and T, respectively, and have molecular masses of 45.0, 30.0 and 50.0 MD, respectively.

The results of this study demonstrate that the R-plasmids that determine antibiotic resistance are highly prevalent in clinical isolates of Acinetobacter from patients in the Tbilisi Burn Center intensive care unit. These plasmids belonged to incompatibility groups found in a wide range of other bacterial hosts, suggesting that these types of Acinetobacter R-plasmid may be useful as epidemiologic markers.

References

  1. Zubkov MN. 1988. Laboratornoe delo (Rus). 3: 15-18; Kalina GP. 1988. J Epidemiology, Microbiology & Immunology (Rus) 9:33-40; Broo KQ. 1986. Drugs AE Suppl (3): 97-102; Rubin SJ, Granato PA, Wasilauskas BL. 1980. Man Clin of Microbiol 301: 263-287.
  2. Martin RR, Riley PS, Hoblis DV. 1981. J Clin Microbiol (14): 39-47.
  3. Shenderov BA. 1988. J Antibiotics (Rus). 33(2): 141-145; Shenderov BA, Sarkova GP, Turin MV. 1985. J Antibiotics (Rus) 3: 191-195.
  4. Novashin SM, Fomina IP 1982. Rational Antioticotherapy (Rus) Medicine p. 494.
  5. Sagai H, Kremary V, Hasuda K et al. 1975. Jap J Microbiol 19(6): 427-432.
 

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