Effect of Low Temperature on Growth and Ultra-Structure of Staphylococcus spp

Abstract

The effect of temperature fluctuation is an important factor in bacterial growth especially for pathogens such as the staphylococci that have to remain viable during potentially harsh and prolonged transfer conditions between hosts. The aim of this study was to investigate the response of S. aureus, S. epidermidis, and S. lugdunensis when exposed to low temperature (4°C) for prolonged periods, and how this factor affected their subsequent growth, colony morphology, cellular ultra-structure, and amino acid composition in the non-cytoplasmic hydrolysate fraction. Clinical isolates were grown under optimal conditions and then subjected to 4°C conditions for a period of 8 wks. Cold-stressed and reference control samples were assessed under transmission electron microscopy (TEM) to identify potential ultra-structural changes. To determine changes in amino acid composition, cells were fractured to remove the lipid and cytoplasmic components and the remaining structural components were hydrolysed. Amino acid profiles for the hydrolysis fraction were then analysed for changes by using principal component analysis (PCA). Exposure of the three staphylococci to prolonged low temperature stress resulted in the formation of increasing proportions of small colony variant (SCV) phenotypes. TEM revealed that SCV cells had significantly thicker and more diffuse cell-walls than their corresponding WT samples for both S. aureus and S. epidermidis, but the changes were not significant for S. lugdunensis. Substantial species-specific alterations in the amino acid composition of the structural hydrolysate fraction were also observed in the cold-treated cells. The data indicated that the staphylococci responded over prolonged periods of cold-stress treatment by transforming into SCV populations. The observed ultra-structural and amino acid changes were proposed to represent response mechanisms for staphylococcal survival amidst hostile conditions, thus maintaining the viability of the species until favourable conditions arise again.

New insights in thermal resistance of staphylococcal strains belonging to the species Staphylococcus epidermidis, Staphylococcus lugdunensis and Staphylococcus aureus

“…This ability has been demonstrated in S. aureus, S. lugudensis and S. epidermidis, in which the thermal treatment caused a marked fluctuations in the morphology of survivors colonies. The data reported by Onyango et al (2012) and those presented in this study provided evidence that staphylococci can adapt to environmental stresses by altering their phenotypic characteristics. This can lead, in turn, to the formation of altered phenotypes to facilitate survival under harsh environmental conditions, which can also bring to the formation of colonies with different size and colors.…”

“…This adaptation process is clearly revealed during plate counting by the presence of colonies showing morphological differences, including variation in colony size, pigmentation and haemolytic irregularities (Kipp, Becker, Peters, & von Eiff, 2004;Onyango, Hugh Dunstan, Gottfries, Von Eiff, & Roberts, 2012). This ability has been demonstrated in S. aureus, S. lugudensis and S. epidermidis, in which the thermal treatment caused a marked fluctuations in the morphology of survivors colonies.…”

Genome-wide screen for genes involved in eDNA release during biofilm formation by Staphylococcus aureus

“…This sRNA has been found to show altered expression in a small colony variant of S. aureus isolated from a chronic osteomyelitis infection (32). Small colony variants of S. aureus have been found to have thick cell walls (44,45), and this sRNA could additionally contribute to the reduced lysis phenotype we observe in ΔxdrA.…”

Preliminary evaluation of good sampling locations on a pig carcass for livestock-associated MRSA isolation

“…S. aureus is able to bind strongly to corneocytes, which could imply that sponge swabbing might not be sufficient to collect all MRSA present and a more destructive method, such as cutting of slices is needed as was reported for Salmonella or E. coli (Ghafir and Daube, 2008;Martinez et al, 2010). Another possibility could be the reduced viability of MRSA after cooling of the carcasses, even though S. aureus is able to persist colder temperatures (Onyango et al, 2012).…”