|Year : 1985 | Volume
| Issue : 1 | Page : 52-6
Typing of Pseudomonas aeruginosa on the basis of low and high molecular weight aeruginocins.
SR Pai, LM Joshi
S R Pai
|How to cite this article:|
Pai S R, Joshi L M. Typing of Pseudomonas aeruginosa on the basis of low and high molecular weight aeruginocins. J Postgrad Med 1985;31:52-6
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Pai S R, Joshi L M. Typing of Pseudomonas aeruginosa on the basis of low and high molecular weight aeruginocins. J Postgrad Med [serial online] 1985 [cited 2021 Jan 16 ];31:52-6
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The hospital environment usually harbours many different aeruginocin types of Pseudomonas aeruginosa. Without a suitable typing method of characterization, it would be impossible to monitor infections and investigate and control the outbreaks. Phage typing is less reproducible than aeruginocin typing and serotyping. The latter has good reproducibility but poor discrimination, and majority of strains can be allocated to only a few common types.
Various categories of aeruginocins are now recognised. They can be classified into two main groups. The high molecular weight aeruginocins have a molecular weight of approximately 10-10 daltons, and the low molecular weight aeruginocins have a molecular weight of approximately 10 daltons. The former can be sedimented by ultracentrifugation and show a close similarity to the phage tails. They are composed of two types of particles: (a) contractile and filamentous and (b) rod-shaped and flexuous., The low molecular weight aeruginocins cannot be sedimented by ultracentrifugation and have not been resolved even on electron microscopy. The diffusibility of low molecular weight aeruginocins is much more than that of the high molecular weight aeruginocins and the former can produce an inhibition extending far beyond the original growth area. This basic principle was made use of in the present study for aeruginocin typing to make the method more sensitive than the routinely used ones.
MATERIAL AND METHODS
Aeruginocin typing was carried out according to the method of Govan [Fig. 1] and [Fig. 2] using a total of 13 strains comprising 1 to 8 indicator strains and A to E sub-indicator strains. One hundred and five aeruginocin types based on inhibition patterns of indicator strains 1-8 have been described by Govan. Further differentiation of each aeruginocin type into subtypes "a" to "z" (there is no subtype "i") can be carried out based on inhibition patterns of subindicator strains A to E. Clinical isolates were labelled untypable (UT) if the indicator strains 1-8 were not inhibited at all. They were called unclassifiable (UC) if the inhibition pattern (with indicator- strains 1-8) were different from the standard patterns. The untypable and the unclassifiable strains, however, could be subtyped with the help of subindicator strains.
In addition to the designation of types based on inhibition of indicators 1-8 and subindicators A-E, the typing was made more sensitive by differentiating the type of aeruginocin on the basis of low or high molecular weight. Low molecular weight aeruginocins diffuse readily and create a wider zone of inhibition than the high molecular weight aeruginocins.
Four "standard producing strains" were used to check the reliability of the indicator strains from time to time. These standard strains are shown in [Table 1] below:
A total of 254 clinical isolates of Pseudomonas aeruginosa were studied. [Table 2] gives the sources of 210 predominant aeruginocin types. The rest of the types were relatively uncommon and hence are grouped as miscellaneous. The maximum number of isolates were from pus (82; 32.28%), urine (81; 31.89%) and stool (21; 8.27%). The incidence of type 1 in pus was significantly higher than that of other types.
Of the 254 clinical isolates, 232 (91.34%) were typable and the rest 22 were untypable. Of the 232 typable strains, 227 were classifiable3 whereas the rest 5 were unclassifiable. The classifiable strains belonged to types 1, 3, 4, 5, 8, 10, 12, 13, 22, 27, 31, 32, 34, 45, 56, 63, 64, 65, 83 and 97. A total of 193 strains belonged to types 1-37 and 34 belonged to types 38 to 105. In the original method of Govan and Gillies, only 37 types are described. In the present study, 105 inhibition patterns are described according to the modified method of Govan. Hence, the percentage of unclassifiable strains in the present study is smaller. Type 1 was the most common (29.92%), followed by type 10 (15.75%) and type 3 (9.45%).
Seventeen subtypes were isolated. They were a, b, c; f, g, h, k, l, m, n, o, r, s, u, v, w and x. Subtype 'f' was the most common followed by subtype "b" and subtype "a" respectively. Of the 22 untypable strains, 2 belonged to subtype "a" and 20 to subtype "f". This indicated that the latter 20 strains could not inhibit either the 8 indicator strains or the 5 subindicator strains.
Further division of the subtypes is possible by noting the pattern of inhibition produced by low and high molecular weight aeruginocins, making the method more sensitive [Fig. 1] and [Fig. 2]. [Table 3] gives the data of the types, subtypes and further subdivision on the basis of low or high molecular weight aeruginocins produced by various strains of Pseudomonas aeruginosa.
The amount of aeruginocins produced largely depends on the growth conditions. Slight variation in the composition of the media can affect aeruginocin production. However, this variation may affect only weak reactions and not strong ones.
Shriniwas opined that the high frequency of a particular type may be due to its resistance to disinfectants and antiseptics that are commonly used. A compromised host may be specially host receptive for a particular type and hence this type can cause infection. The prevalence of the type may be due to some inherent biological character or due to some environmental factors. Subindicator strains can reduce clustering of strains in aeruginocin types. They can also help in subdivision of untypable as well as unclassifiable strains. This has greatly improved the sensitivity of the technique.
Studies on the effect of low and high molecular weight aeruginocins show that they can be used to subdivide aeruginocin types to increase the sensitivity of the typing system., [Table 3] gives the detailed results of the low and high molecular weight aeruginocins of predominant aeruginocin types of Ps. aeruginosa.
One of the limitation of the present method is that the results are obtained on the third day. This can be eliminated by making use of mitomycin-C for rapid induction of aeruginocin.
We are thankful to Dr. J. R. W. Govan, Department of Bacteriology, University Medical School, Teviot Place, Edinburg, EH8, 9AG Scotland for the indicator and subindicator strains.
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