New Zealand Listener – August 03, 2019

16 LISTENER AUGUST 3 2019

K

ristin Dyet and Dr Michael

Addidle are responsible for MRSA

surveillance at the Institute of

Environmental Science and

Research (ESR). Labs around the

country used to send them every MRSA

isolate from human infections to record

and analyse. Now, however, there are

so many cases – the number doubled

between 2009 and 2017 – that they survey

all cases from one month only every few

years to get a picture of the rate of infec-

tion and which strains are involved. It

takes them up to a year to process just one

month’s worth.

Dr Pippa Scott, an infectious disease

epidemiologist at the University of

Otago, studies how the bacteria spread

among people in the community, with

a view to finding the best ways to limit

transmission. She says, “Infections with

Staphylococcus aureus can range from rela-

tively minor to potentially life-threatening

events. In the worst case, some people

with Staph aureus infection may develop

sepsis, where the immune system goes

into overdrive in response to a spread-

ing infection. The resulting widespread

inflammation can damage organs and

interfere with blood flow.”

MRSA appeared in New Zealand during

the 1970s, and since then some unique

strains have evolved here. As infections

continue to increase, periodic surveil-

lance is the only realistic way to monitor

them. However, surveillance techniques

have become more

sophisticated and all

the studied MRSA

samples will be

fully described

using “whole

genome sequenc-

ing” – which

gives a complete

blueprint of an

organism’s DNA.

Nigel French,

a professor of

food safety

and vet-

erinary

public health at Massey University, uses

whole genome sequencing to track the

evolution of, and relationship between,

pathogens isolated from different sources.

Staphylococcus aureus is one of about 40

species of staphylococcus, he says, and

has many different strains.

“Quite a few of the staph species can be

resistant. Examples are MRSA [Methicillin-

resistant Staphylococcus aureus] and one

that’s important in dogs, called MRSP

[Methicillin-resistant Staphylococcus pseud-

intermedius]. Countries with higher use

of antibiotics tend to have higher rates of

antibiotic resistance.

“A lot of us are probably colonised with

Staphylococcus aureus – on our skin, up

our noses and in our lower genital tracts

• and some of us with MRSA. It could
  be considered a normal part of our skin
  ‘microbiome’. It can be transmitted from
  person to person through direct contact
  and indirectly through things used by
  an infected person, such as towels and
  clothing, and in healthcare settings such
  as hospitals and nursing homes. Cows can
  get Staph aureus mastitis through the milk-
  ing machine.
  “Tracking the evolution of these
  diseases, and pinpointing the changes
  in their DNA that confer resistance, is
  now possible and precise, but finding
  new antibiotic medicines to kill resist-
  ant mutants can be hit and miss. The
  serendipitous discovery of penicillin was
  purely accidental. Researchers are testing
  hundreds, if not thousands, of natural
  and synthetic compounds in the hope
  that new, effective classes of antibiotic can
  be identified and trialled for both human
  and veterinary use.”

GE

TT

Y^ I
MA

GE

S

The urgent search for new

and effective antibiotics

ANTIBIOTICRESISTANT BUGS

A scientist

examines a

culture plate

of a deadly

bacterium.

ESR microbiologist Kristin

Dyet, Dr Pippa Scott, and

Massey University professor

Nigel French.