MOLECULAR CHARACTERISTICS AND ANTIMICROBIAL RESISTANCE OF METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS ISOLATED FROM PIGS AND HUMANS IN KOGI STATE, NIGERIA
MOLECULAR CHARACTERISTICS AND ANTIMICROBIAL RESISTANCE OF METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS ISOLATED FROM PIGS AND HUMANS IN KOGI STATE, NIGERIA
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Date
2021-02
Authors
OTALU, Otalu Jnr
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Abstract
Staphylococcus aureus is a common cause of serious community and health care-associated
infections and limited antimicrobial treatment options for methicillin resistant Staphylococcus
aureus (MRSA) infections make their management challenging. This study was conducted to
determine the molecular characteristics and antimicrobial resistance of MRSA isolated from
pigs and humans in Kogi State, Nigeria. Using standard microbiological techniques, 680
nasal swab samples collected from 425 pigs, 55 „in-contact‟ and 200 „non-contact‟ humans
were analysed. Risk factors associated with MRSA carriage among humans was also
determined using a structured questionnaire. Staphylococcus aureuswas recovered from 20
(4.7%) of the 425 pigs screened and 19 (7.5%) from humans. Six (2.4%) of the human S.
aureus isolates were recovered from 55 „in-contact‟ while 13 (5.1%) were recovered from
200 „non-contact‟ humans. In addition 42 other isolates belonging to other Staphylococcus
species (S. hyicus, S. scuiri, S. intermedius, S. lentus, S. chromogens, S. warnari, S.
lugdunensis, S. saprophyticus, S. haemolyticus, S. xylosus) were recovered in the study. All of
the S. aureus isolates (39; 100%) irrespective of source were resistant to β-lactams only. Also
all of the S. aureusisolates had MIC values >4mg/ml for oxacillin and were termed
methicillin resistant. Five (6.2%) and 3 (3.7%) of the other Staphylococcus species isolates
from pigs and humans respectively showed multi-drug resistance patterns. Age and sex were
found to be factors associated with nasal carriage of S. aureuswithin the study population.
MRSA werecharacterized by a multiplex PCR to detect spa, mecA, lukF-PV(a marker of the
Panton-Valentine leucocidin, PVL), scn and aCC398 specific band. Direct sequencing ofthe
purified PCR reaction amplicon was used for spa typing. Four isolates (one pig, one pigcontact
human fromthe same pig farm, one non-pig-contact human from the samedistrict, and
one pig-contact human from a different district)were selected for further SCCmec, multilocus
sequence typing and whole genomesequencing (WGS).All 39 MRSA isolates belonged to spa
type t1603- sequence type (ST) 88, and mecA was associated with a SCCmecIVa element in
38/39 of the isolates. Core genome SNP analysis revealed high genetic similarity between
strains (3-11 SNP differences), despite the temporal (2 year gap) and geographic (165km)
differences between isolates. Furthermore, the MRSA isolates in this study form a distinct
clade when compared with other African MRSA ST88 isolates. Nineteen (95%) of the
porcine strains were positive for scnsuggesting a possible human origin and that pigs were
either transiently contaminated by humans or result of a very recent human-to-pig
transmission event.
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE
STUDIES, AHMADU BELLO UNIVERSITY IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD
OF DEGREE OF DOCTOR OF PHILOSOPHY IN VETERINARY
PUBLIC HEALTH AND PREVENTIVE MEDICINE
DEPARTMENT OF VETERINARY PUBLIC HEALTH AND
PREVENTIVE MEDICINE,
AHMADU BELLO UNIVERSITY,
ZARIA
Keywords
MOLECULAR CHARACTERISTICS,, ANTIMICROBIAL RESISTANCE,, METHICILLIN RESISTANT,, STAPHYLOCOCCUS AUREUS ISOLATED,, PIGS AND HUMANS,, KOGI STATE, NIGERIA