Wanger A R, Morris S L, Ericsson C, Singh K V, LaRocco M T
Department of Pathology and Laboratory Medicine, University of Texas Medical School, Houston 77025.
J Clin Microbiol. 1992 Oct;30(10):2583-8. doi: 10.1128/jcm.30.10.2583-2588.1992.
An unusual strain of methicillin-resistant Staphylococcus aureus (MRSA) was repeatedly isolated from infants in a newborn special care unit (NBSC) and a newborn intensive care unit. Between January 1989 and March 1990, approximately 100 isolates from infected or colonized infants were recovered. Surveillance cultures taken during this time revealed a 20% colonization rate, which was defined as recovery of MRSA from the nares, umbilicus, or groin. Isolates were identified as S. aureus by tube coagulase reactivity and heat-stable nuclease production but were unreactive in a latex agglutination assay. Representative isolates that were collected during the outbreak and that were found to share the latex agglutination assay-negative phenotype were compared by antibiogram (12 isolates), bacteriophage typing (20 isolates), capsular polysaccharide typing (30 isolates), and plasmid as well as chromosomal DNA analyses (20 isolates). All isolates known to be associated with the outbreak had nearly identical antibiograms and were notably susceptible to clindamycin. Staphylococcal bacteriophage typing was not useful in determining the relatedness of the isolates, since the majority were nontypeable. Plasmid pattern analysis revealed one large plasmid (approximately 100 kb) of equivalent size among the isolates. Capsular polysaccharide typing revealed that 14 of 30 isolates tested were type 5. Isolates identified in children at two other hospitals in the city which were also unreactive by the latex agglutination assay and clindamycin susceptible had plasmid and antibiogram patterns identical to those of isolates from the NBSC. Pulsed-field gel electrophoresis of restriction enzyme-digested genomic DNAs from the outbreak isolates demonstrated identical patterns which could be clearly differentiated from those of other unrelated MRSA. The strain from the NBSC is, therefore, unique and underscores the need for caution in interpreting the latex agglutination reactivities of MRSA isolates.
在一家新生儿特别护理病房（NBSC）和一家新生儿重症监护病房中，反复从婴儿身上分离出一种不寻常的耐甲氧西林金黄色葡萄球菌（MRSA）菌株。在1989年1月至1990年3月期间，从受感染或定植的婴儿身上回收了约100株菌株。在此期间进行的监测培养显示定植率为20%，定植定义为从鼻腔、脐部或腹股沟处分离出MRSA。通过试管凝固酶反应性和热稳定核酸酶产生将分离株鉴定为金黄色葡萄球菌，但在乳胶凝集试验中无反应。对在疫情暴发期间收集的、具有乳胶凝集试验阴性表型的代表性分离株进行了抗菌谱分析（12株分离株）、噬菌体分型（20株分离株）、荚膜多糖分型（30株分离株）以及质粒和染色体DNA分析（20株分离株）。所有已知与疫情相关的分离株具有几乎相同的抗菌谱，并且对克林霉素显著敏感。葡萄球菌噬菌体分型在确定分离株的相关性方面无用，因为大多数分离株无法分型。质粒图谱分析显示分离株中有一个大小相当的大质粒（约100 kb）。荚膜多糖分型显示，在测试的30株分离株中有14株为5型。在该市另外两家医院的儿童中鉴定出的分离株，其乳胶凝集试验也无反应且对克林霉素敏感，其质粒和抗菌谱模式与NBSC的分离株相同。对疫情暴发分离株的限制性内切酶消化基因组DNA进行脉冲场凝胶电泳，显示出相同的图谱，可与其他无关MRSA的图谱明显区分开来。因此，NBSC的菌株是独特的，强调了在解释MRSA分离株的乳胶凝集反应性时需要谨慎。
