Different O and K Serotype Distributions among Clinical and Environmental Strains of Serratia Marcescens

Abstract

Recent revision of the 0 serotyping scheme for Serratia marcescens has allowed the definitive serological identification of a collection of 51 1 epidemiologically distinct strains in terms of both lipopolysaccharide (0) antigens and capsular (K) antigens. High levels of typability were achieved, 88% and 91y0 respectively, with only 2% failing to type with either method. In most cases, non-typability was due to a lack of antigen, i.e., the strains produced only rough LPS or were acapsular, suggesting that typability would be little improved by the discovery of additional serotypes. The distribution of the 58 O:K serotypes was very uneven, with 014:K14 accounting for 30% of the 423 clinical strains in the collection, but only 5% of the 88 non-clinical, environmental strains. Thus, the prevalence of 014:K14 strains in hospitals is not reflected in the environment. Similar conclusions were valid for 027:K14, 021:K3 and 021:K14 strains, as well as those with rough lipopolysaccharide. Conversely, the proportions of 06:K3, 06:K14, 08:K14 or 028:K28 strains were significantly lower among the clinical collection than among their environmental counterparts (12% in total rather than 65%). This suggests that 014:K14 may have a selective advantage in colonising or infecting hospitalised patients and, therefore, that the 014 and K14 polysaccharides themselves may contribute towards the apparent pathogenicity of these serotypes.

Antibiotic Resistance and Putative Virulence Factors of Serratia Marcescens with Respect to O and K Serotypes

“…In addition, as 19% of the clinical strains were from urine, 16% from blood and 14% from the respiratory tract [3], the data from these strains were analysed with respect to clinical source. However, no significant associations were found and therefore these results are not presented.…”

“…Most schemes are based on either the 0 antigens of lipopolysaccharide (LPS) or the K antigens of capsular polysaccharide. Recently, new 0 and K typing schemes have been described for this species [2], and applied to a collection of both clinical and environmental S. rnarcescens isolates selected to represent distinct strains [3]. The latter study showed a marked difference in serotype distribution between the two populations.…”

“…Data were analysed for the collection of 469 strains as a whole and also with respect to those serotypes which have significantly different frequencies among clinical and environmental strains [3]. Rough and acapsular strains were also analysed separately in order to assess any involvement of LPS and capsular polysaccharide.…”

“…0 and K serotypes were identified by ELISA with adsorbed antisera [2] and the frequency distributions were reported in a separate study [3].…”

“…Tests for DNAase, lipase and gelatinase were performed as part of the initial identification for all strains [3], and, therefore, only qualitative and not quantitative results were obtained. Over 99% of the 469 strains were positive for all three enzymes, with four gelatinase-negative strains and two strains negative for either DNAase or lipase.…”